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JP2001258879

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DESCRIPTION JP2001258879
[0001]
TECHNICAL FIELD The present invention relates to an ultrasonic transducer and an ultrasonic
transducer system used for harmonic imaging ultrasonic diagnosis.
[0002]
In recent years, harmonic imaging ultrasound has attracted attention. This diagnostic method is
roughly classified into contrast harmonic imaging using a contrast agent and tissue harmonic
imaging which detects and displays non-linearity of elastic properties of a living tissue. The
situation is described in detail in "Special topics on ultrasound in electronics-latest ultrasound-:
distributed text of the 1999 Japan Society of Ultrasonics Medical Society distributed text".
[0003]
In tissue-harmonic imaging, an ultrasonic pulse having a center frequency f0 is transmitted to a
living tissue without using an ultrasonic contrast agent, and a harmonic component nf0 (n is an
integer of 2 or more) contained in the echo signal returned. Are extracted, and the relationship
between the amplitude and the echo signal reception time is tomographically displayed to obtain
a diagnostic image. For extracorporeal use, diagnostic devices equipped with this function are
already commercially available. The tissue-harmonic imaging diagnostic method enables
relatively clear observation of heart structures such as the left ventricular wall even in obese
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cases where the echo image is often unclear due to the inclusion of noise, and in the elderly or
smokers.
[0004]
This diagnostic technique is currently only used for extracorporeal use, and only the second
harmonic (n = 2) is used. In order to efficiently receive this second harmonic, it is necessary to
transmit in the lower half of the band of the ultrasonic transducer and to receive in the upper
half. For this purpose, a broadband ultrasonic transducer has been used, and drive control has
been performed to widen the band.
[0005]
However, even under the current circumstances, the bandwidth and sensitivity are not sufficient.
Furthermore, when dealing with n ≧ 3 harmonics, a large relative bandwidth over the relative
bandwidth of the optimally designed current ultrasound transducer is realized. Is extremely
difficult with conventional ultrasonic transducer design and manufacturing techniques. As a
second best solution, it is possible to widen the bandwidth by devising the drive waveform, but
the widening causes a decrease in sensitivity.
[0006]
In general, it is said that the harmonics signal has lower sensitivity in the second order by 15 to
20 dB and in the third order by 15 to 20 dB as compared with the fundamental frequency signal.
Therefore, the decrease in sensitivity due to the wide band as described above causes the
deterioration of the diagnostic image, which is not preferable.
[0007]
Furthermore, when transmission and reception are performed by the same piezoelectric vibrator,
a fundamental wave signal is mixed with the harmonics signal, and a special device is required to
extract only a weak harmonics signal from this with high accuracy. The above problems can not
be avoided as long as f0 transmission and 2f0 reception are performed by the same piezoelectric
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vibrator.
[0008]
Japanese Patent Application Laid-Open No. 11-155863 discloses an ultrasonic transducer in
which a piezoelectric transducer for transmission and a piezoelectric transducer for reception are
accommodated in one case and a harmonic component is efficiently received, in order to improve
such problems. doing. The configuration of this ultrasonic transducer is shown in FIG.
[0009]
As shown in FIG. 14, the ultrasonic transducer 1000 has a transmitting piezoelectric ultrasonic
transducer 1002 and a receiving polymeric piezoelectric transducer 1004 disposed in front of
the transmitting ultrasonic ultrasonic transducer 1000. The molecular piezoelectric transducer
1004 and the piezoelectric ultrasonic transducer 1002 for transmission are arranged in layers
via an acoustic matching layer 1006.
[0010]
The transmitting ultrasonic ultrasonic transducer 1002 and the front electrode of the receiving
polymeric piezoelectric transducer 1004 are both connected to the grounding lead wire 1008
and kept at the ground potential.
The rear electrode of the transmitting piezoelectric ultrasonic transducer 1002 is connected to a
transmitting shield wire 1010, and a drive voltage is supplied via this. An electrode on the rear
side of the receiving polymeric piezoelectric vibrator 1004 is connected to a receiving shield wire
1012 through which a received signal is taken out.
[0011]
The piezoelectric ultrasonic transducer 1002 for transmission has a resonant frequency or an
antiresonant frequency that matches the frequency having a specific relationship with the
resonant frequency of the ultrasound contrast agent or the resonant frequency of the ultrasound
contrast agent. There is. On the other hand, the polymeric piezoelectric transducer 1004 for
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reception is a non-resonance type piezoelectric transducer, and can also receive harmonic
components generated based on the nonlinear behavior of the ultrasound contrast agent.
[0012]
In this ultrasonic transducer 1000, since the acoustic matching layer 1006 is provided between
the piezoelectric ultrasonic transducer 1002 for transmission and the polymeric piezoelectric
transducer 1004 for reception, capillaries in blood vessels and peripheral portions in the human
body are obtained. Only the site where the injected ultrasound contrast agent is present, such as
a concentrated cancer tissue, can be clearly seen from other sites.
[0013]
Since this ultrasonic transducer 1000 has separate transmitting piezoelectric transducers and
receiving piezoelectric transducers, it is a conventional single piezoelectric transducer which has
been generally used. Compared to ultrasonic transducers that perform transmission and
reception, it is expected that the band can be easily broadened and that they exhibit
characteristics suitable for harmonic imaging.
[0014]
However, since the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are
arranged in layers, residual vibration is superimposed on the transmitting ultrasonic wave when
transmitting the ultrasonic wave at the time of transmission. At the time of reception, when the
received ultrasonic waves reach the transmitting piezoelectric vibrator, residual vibration is
superimposed on the received ultrasonic waves.
Such superposition of residual vibration causes the resolution to be greatly degraded.
This fact has been confirmed by the present inventors experimentally and by simulation.
[0015]
As described above, the ultrasonic transducer 1000 disclosed in Japanese Patent Laid-Open No.
11-155863 includes the acoustic matching layer 1006 between the transmitting piezoelectric
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vibrator 1002 and the receiving piezoelectric vibrator 1004, so that the transmitting
piezoelectric can be used. Although the reflection at the boundary between the vibrator 1002
and the receiving piezoelectric vibrator 1004 can be eliminated, no countermeasure against the
residual vibration is taken. Moreover, the same document neither teaches nor suggests measures
for residual vibration.
[0016]
An object of the present invention is an ultrasonic wave that has a transmitting piezoelectric
vibrator and a receiving piezoelectric vibrator housed in the same case, but can detect harmonics
signals with high sensitivity without being adversely affected by resolution deterioration due to
residual vibration. It is to provide transducer technology.
[0017]
SUMMARY OF THE INVENTION The present invention, in one aspect, is an ultrasonic transducer
system, comprising a piezoelectric transducer for transmitting ultrasonic waves of a resonant
frequency ft and a resonant frequency nft (arranged in layers). n has an ultrasonic transducer
having a receiving piezoelectric transducer for receiving an ultrasonic wave of an integer of 2 or
more, and control means for controlling the ultrasonic transducer, and the control means
transmits only during time t1 The drive voltage is applied to the piezoelectric vibrator, and
between the electrodes of the reception piezoelectric vibrator is maintained in a low resistance
state including a short circuit for a predetermined time t2 (> t1) after the application of the drive
voltage, for a predetermined time It is an ultrasonic transducer system which holds between the
electrodes of the transmission piezoelectric transducer in a high resistance state including an
open state until the next drive voltage is applied to the transmission piezoelectric transducer
after the elapse of t2.
[0018]
The present invention, in another aspect, is an ultrasonic transducer, which transmits an
ultrasonic wave having a resonance frequency ft, and receives an ultrasonic wave having a
resonance frequency nft (n is an integer of 2 or more). A transmitting piezoelectric vibrator and
one of the receiving piezoelectric vibrators have a ring shape, and the other of the transmitting
piezoelectric vibrator and the receiving piezoelectric vibrators has a disc shape, and has a disc
shape. The piezoelectric vibrator in the form of an arrow is an ultrasonic transducer disposed
inside a ring-shaped piezoelectric vibrator.
[0019]
The present invention, in still another aspect, is an ultrasonic transducer, which comprises a
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plurality of transmitting piezoelectric transducers for transmitting ultrasonic waves at a
resonance frequency ft, and ultrasonic waves at a resonance frequency nft (n is an integer of 2 or
more). An ultrasonic transducer having a plurality of receiving piezoelectric vibrators for
receiving, and the transmitting piezoelectric vibrators and the receiving piezoelectric vibrators
are alternately arranged radially.
[0020]
DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The present embodiment
is an ultrasonic transducer system suitable for harmonic imaging ultrasonic diagnosis, which
includes an ultrasonic transducer and its control system, In the following, the ultrasound
transducer will be described first, followed by a description of its control system.
[0021]
[Configuration] As shown in FIG. 1, the ultrasonic transducer comprises a transmitting
piezoelectric transducer 102, a receiving piezoelectric transducer 104, a housing 106 for
accommodating the piezoelectric transducers 102 and 104, and a concave shape. And an
acoustic lens 108.
[0022]
The transmission piezoelectric vibrator 102 is, for example, a piezoelectric element made of
piezoelectric ceramic such as lead zirconate titanate PZT or bismuth layered structure or a single
crystal such as quartz crystal, lithium niobate, or PZT.
The receiving piezoelectric vibrator 104 is, for example, a polymer piezoelectric element made of
a polymer resin such as polyvinylidene fluoride or vinylidene cyanide, or a composite
piezoelectric element in which columnar piezoelectric ceramics are distributed in an epoxy resin
or the like.
[0023]
The transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104 are
stacked with the acoustic matching layer 110 interposed therebetween, and a damping layer 112
is provided on the back of the transmitting piezoelectric vibrator 102.
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The laminated structure is fixed in the housing 106 by an insulating layer 114 lined with the
inner wall of the housing 106.
The insulating layer 114 insulates the housing 106 from the electrodes of the piezoelectric
vibrators 102 and 104.
The acoustic lens 108 is disposed on the front surface of the receiving piezoelectric vibrator 104.
[0024]
The electrode on the ultrasonic wave emitting side of the transmitting piezoelectric vibrator 102
and the electrode on the opposite side of the ultrasonic wave emitting side of the receiving
piezoelectric vibrator 104 are electrically connected to the housing 106 by the wiring 116, and
have the same potential as the housing 106. Be kept
In the twin-core coaxial cable 118, the lead wire 122 is electrically connected to the electrode on
the opposite side of the ultrasonic wave emitting side of the transmitting piezoelectric vibrator
102, and the lead wire 124 is an ultrasonic wave emitting of the receiving piezoelectric vibrator
104. The shield wire 120 is electrically connected to the side electrode, and the shield wire 120
is electrically connected to the housing 106.
[0025]
The transmitting piezoelectric vibrator 102 has a resonant frequency ft, and the receiving
piezoelectric vibrator 104 has a resonant frequency nft (n is an integer of 2 or more).
For example, the transmitting piezoelectric vibrator 102 has a resonance frequency of 5 MHz,
and the receiving piezoelectric vibrator 104 has a resonance frequency of 10 MHz. The resonant
frequency of the piezoelectric vibrators 102 and 104 is adjusted by controlling its thickness.
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[0026]
There is also a method of bonding the piezoelectric polymer film in a polarized state in advance
by adhesion, but the piezoelectric vibrator for transmission is influenced by the pressure at the
time of bonding, the influence of air bubble entrapment, and the influence of the adhesive layer.
In some cases, the structure or characteristics as designed can not be stably obtained due to the
damage caused by cracking or the uneven thickness of the adhesive layer. In such a case, it is
desirable to form a surface energy poling piezoelectric polymer layer. This method is described in
the literature "Junya IDE et al: Jpn J. Appl. Phys. Vol. 38 (1999) pp 2049-2052 ", and a polymer
material such as polycyanophenyl sulfide is formed on the electrode formed on the surface of the
acoustic matching layer 110, and the upper electrode is formed after curing. It is possible to
realize a polarization state spontaneously after film formation by the effect of surface energy
even without polarization treatment in particular. Since it can be formed by spin coating or the
like, it is easier to realize a target structure than a method of bonding a piezoelectric polymer
film in a polarized state by adhesion. The polymer material is dropped onto an electrode (not
shown) formed on the surface of the acoustic matching layer 110, spin-coated at an appropriate
number of rotations, and then an upper electrode is formed, and the receiving piezoelectric
vibrator 104 It is formed.
[0027]
Next, setting of the radius of curvature of the spherical surface of the acoustic lens 108 will be
described with reference to FIG. FIG. 5A shows the relationship between the radius of curvature R
of the acoustic lens disposed on the front surface of the disk piezoelectric vibrator and the focal
length F of the ultrasonic wave propagation medium of water along the horizontal axis D (= a2 /
λR ′, a: aperture radius, λ: wavelength of ultrasonic wave propagation material, R ′: apparent
curvature radius of lens R ′ = 2.25R, R: radius of curvature of acoustic lens), vertical axis F / R
′ The relationship is derived from the well-known Rayleigh equation. FIG. 5B shows the
relationship between the focal point and the actual processing radius of curvature of the acoustic
lens for the cases of 5 MHz and 10 MHz. From FIG. 5B, in order to focus on the same position, for
example, 30 mm at any frequency, it is necessary to set different radius of curvature, for
example, 16 mm for 10 MHz and 40 mm for 5 MHz. Is desirable. However, the aperture surface
for transmitting and receiving ultrasonic waves is shared. For this reason, the acoustic lens 108
is set to an intermediate value of both the curvature radiuses, for example, 25 mm, to realize the
optimum focus imaging state in this structure.
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[0028]
Although the average value is used in the above description, the radius of curvature may be
partially changed (or vice versa) so that the center is optimal for reception and the periphery is
optimal for transmission.
[0029]
The above is the case where the harmonics signal of 10 MHz is generated from the time of
transmission, but in fact the harmonics signal is gradually generated due to the nonlinearity of
the elasticity of the living body along with the propagation distance of ultrasonic waves. It does
not mean to be far away.
However, as the order of the harmonics signal moves away from the focal point at the
fundamental frequency, the defocusing between the two becomes large, which cancels out the
improvement of the ultrasonic image resolution by the harmonics imaging.
[0030]
Next, a control system for controlling transmission and reception of the above-described
ultrasonic transducer will be described with reference to FIG.
[0031]
FIG. 6A schematically shows the configuration of the control system.
As shown in FIG. 6A, the control system includes an on / off control device 150 for controlling
the transmitting piezoelectric vibrator 102 and a selector 160 for controlling the flow of signals
of the receiving piezoelectric vibrator 104. There is. The on-off control device 150 supplies the
high voltage Vd supplied from the terminal 152 to the transmission piezoelectric vibrator 102 in
accordance with the control signal Vt input from the terminal 154. The selector 160 guides the
reception signal of the reception piezoelectric vibrator 104 to one of the branch 164 connected
to the amplifier and the ground 166 in accordance with the control signal Vr input from the
terminal 162.
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[0032]
FIG. 6B shows a timing chart of control signals Vt and Vr input to the on / off control device 150
and the selector 160. As can be seen from this timing chart, a pulse with a pulse width t1 is input
to the terminal 154 of the on / off control device 150 at a period of t3, and a pulse with a pulse
width t2 (> t1) is input to the terminal 162 of the selector 160. Ru. Although a control waveform
of a single rectangular wave is shown in the timing chart, the control waveform is more
preferably a bipolar double pulse voltage waveform according to the method disclosed by the
present inventors in Japanese Patent Application No. 10-178861. .
[0033]
[Function] A bipolar double pulse voltage is applied to the transmitting piezoelectric vibrator in
accordance with the method disclosed by the present inventors in Japanese Patent Application
No. 10-178861, for example. Since the transmission piezoelectric vibrator has a relatively large
Qm, this voltage application method can generate an ultrasonic pulse having a large sound
pressure amplitude and a wide band. Since the actual Qm largely depends not only on the Qm of
the piezoelectric vibrator but also on the damping degree of the damping layer 112, for example,
even with a piezoelectric vibrator with several tens of Qm, it is possible to weaken the damping
degree and obtain an equivalent effect. It is.
[0034]
When this transmission ultrasonic wave passes through the receiving ultrasonic transducer
disposed on the front surface, the ultrasonic compression wave generates a surface charge of a
polarity that periodically restrains deformation in the receiving ultrasonic transducer. This
charge generates an electric field in a direction that constrains the change of polarization state in
the piezoelectric vibrator, and induces a state in which mechanical displacement hardly occurs
due to the reverse piezoelectric effect, that is, a hard state. On the other hand, when the surface
charge is discharged by an external circuit, an electric field in a direction that constrains the
change in polarization state is not generated, and as a result, a hard state is not induced. That is,
a difference appears in the hardness of the piezoelectric vibrator depending on how the charge
generated between the electrodes of the piezoelectric vibrator is treated. This phenomenon is a
unique phenomenon that occurs in a piezoelectric vibrator. Generally, the stiffness of the
piezoelectric vibrator is represented by cE (electric field 0) and cD (electric displacement 0), cE =
(1-K2) cD (K: Electromechanical coupling constant) is a well-known phenomenon. When the
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thickness of the piezoelectric vibrator through which the ultrasonic wave is transmitted is
sufficiently thick compared to the wavelength of the ultrasonic wave, the generation of the
surface charge is hardly affected, but the thickness of the piezoelectric vibrator is the same as in
this embodiment. In the case of about 1⁄4 λ, a large influence is exerted.
[0035]
FIG. 8 shows a simulation result in which the influence is calculated. In FIG. 8, when the vertical
column changes the relationship between the charge processing state between the electrodes of
the reception piezoelectric vibrator 104 at the time of transmission and the charge processing
state between the electrodes of the transmission piezoelectric vibrator 102 at the time of
reception. That is, in (a), (b) and (c), the state of charge processing between the electrodes of the
receiving piezoelectric vibrator 104 during transmission / the state of charge processing
between the electrodes of the transmitting piezoelectric vibrator 102 during reception is short
Short, (d), (e), (f) short / open, (g), (h), (i) open / open, (j), (k), (l) open / short The figure shows
ultrasonic pulses only for transmission (left row), ultrasonic pulses only for reception (middle
row), and ultrasonic pulses for total transmission and reception (right row). From (b) and (k) in
the case of short / short and open / short, respectively, it is apparent from FIG. 8 that residual
vibration appears, and it can not be said that it is a preferable charge processing method between
electrodes. The short circuit state is a low resistance state including a short circuit, and the open
state is a high resistance state including an open circuit.
[0037]
Also, Table 1 summarizes the characteristic values of these pulse waveforms, that is, Vpp:
maximum pulse amplitude, CF: center frequency, PW: -20 dB pulse width. From the table, we can
see from the chart that the short / open interelectrode charge processing method, that is, for
reception when transmitting a fundamental ultrasonic wave, in the general view that large Vpp
and small PW lead to wide band and high sensitivity. It can be seen that it is most preferable that
the ultrasonic transducer 104 is controlled so that the electrodes are short-circuited, and that the
transmitting ultrasonic transducer 102 is controlled in the open state during reception. Basically,
this phenomenon is fundamentally different from the effect obtained by providing the acoustic
matching layer 112 at the boundary between the transmitting ultrasonic transducer 102 and the
receiving ultrasonic transducer 104, and an essential control is necessary. It can be said that it is
a method.
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[0038]
Next, an operation according to the present embodiment will be described with reference to FIG.
[0039]
In the on-off control device 150, a DC voltage Vd is applied to a terminal 152, and a control
signal Vt whose pulse width or the like is controlled is input to a terminal 154.
The control signal Vt is a rectangular wave, an impulse wave, a bipolar double pulse wave or the
like, for example, as shown in FIG. 6B, it is a rectangular wave having a period of t3 and a pulse
width of t1. The transmitting piezoelectric vibrator 102 generates an ultrasonic pulse 174
according to the pulse waveform of the control signal Vt to be input.
[0040]
The transmitted ultrasonic pulse 174 has a center frequency ft, which is reflected by the acoustic
discontinuous boundary surface 172 of the living tissue 170, and the nonlinearity of the elastic
property of the living body causes the frequency nft (n is 2 or more). The received signal is
received by the receiving piezoelectric vibrator 104 as an echo signal 176 containing a relatively
large number of harmonics signals. The receiving piezoelectric vibrator 104 has a resonant
frequency having a center frequency at a frequency nft (n is an integer of 2 or more), and
therefore, selectively receives this harmonics signal and converts it into an electric signal.
[0041]
The selector 160 guides the reception signal of the reception piezoelectric vibrator 104 to one of
the branch 164 and the branch 166 in accordance with the control signal Vr input to the
terminal 162. The control signal Vr is a rectangular wave having a pulse width of t2 having the
same cycle as the cycle t3 of the control signal Vt, and is synchronized with the control signal Vt.
The selector 160 guides the received signal to the grounded branch 166 for the time t2
corresponding to "H", and the subsequent signal processing unit such as an amplifier for the time
t4 = t3-t2 corresponding to "L". Lead to branch 164 connected to
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[0042]
The pulse width t2 of the control signal Vr is set longer than the pulse width t1 of the control
signal Vt, which means that at least the ultrasonic wave generated by the transmitting
piezoelectric vibrator 102 is completely transmitted through the receiving piezoelectric vibrator
104. It corresponds to the time to do it.
[0043]
The control signal Vr input to the terminal 162 is switched to "L" at the timing when the echo
signal 176 is received by the receiving piezoelectric vibrator 104. Therefore, the received signal
Vout from the receiving piezoelectric vibrator 104 is It is led to a subsequent signal processing
unit such as an amplifier.
[0044]
As described above, it is preferable to control the gap between the electrodes of the transmitting
piezoelectric vibrator 102 at the time of reception to an open state or a state close thereto.
Since the control signal Vr is "L" while the echo signal 176 is received by the receiving
piezoelectric vibrator 104, the electrodes of the transmitting piezoelectric vibrator 102 are
substantially kept in an open state.
[0045]
In this control, it is preferable that the final stage of the transmission drive circuit is not a
transformer coupling, but a control device in which the output resistance is small when ON, large
when OFF, and large in output voltage.
For such control devices, for example, high-speed power MOSFETs with large output voltages are
suitable.
[0046]
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The polymeric piezoelectric material constituting the receiving piezoelectric vibrator 104 has a
large piezoelectric g constant and a large receiving sensitivity but a small Qm, and hence a small
selectivity to a receiving frequency. Therefore, it may be effective to connect an inductance in
parallel to the receiving piezoelectric vibrator 104 in order to improve this selectivity. In
addition, Qm of the composite piezoelectric material is larger than Qm of the polymeric
piezoelectric material, and the selectivity is relatively large, which is more preferable.
[0047]
Hereinafter, modifications of the present embodiment will be described with reference to the
drawings. In the drawings, members equivalent to the members described above are denoted by
the same reference numerals, and the detailed description thereof will be omitted in the following
description in order to avoid duplication.
[0048]
FIG. 2 shows a first variant of the ultrasound transducer. The ultrasonic transducer of the present
modification has a convex acoustic lens 132 and a buffer layer 134 provided between the
acoustic lens 132 and the receiving piezoelectric vibrator 104. The convex acoustic lens 132
corresponds to the case where the speed of sound of the lens material is smaller than the speed
of sound 1500 m / sec of the living tissue. The buffer layer 134 improves the bonding between
the acoustic lens 132 and the receiving piezoelectric vibrator 104.
[0049]
In this modification, although the acoustic matching layer 110 in FIG. 1 is not provided between
the transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104, the
transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104 are not
provided. More preferably, there is an acoustic matching layer in between. The silicone resin
used as the material of the convex acoustic lens 132 generally has poor adhesion to other resin
materials, so a polyimide resin film is previously heated and joined as a buffer layer, and then the
acoustic lens 132 and the piezoelectric vibrator 104 for reception are used. Join the two.
[0050]
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FIG. 3 shows a second variant of the ultrasound transducer. The ultrasonic transducer of this
modification does not have an acoustic lens, and only the insulating layer 136 is formed on the
front surface of the receiving piezoelectric vibrator 104. This ultrasonic transducer does not have
much problem with the lateral resolution, and can be provided inexpensively for the purpose of
detecting biological information which has not been conventionally obtained by the harmonics
signal. Also in this modification, it is more preferable to have an acoustic matching layer between
the transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104.
[0051]
FIG. 4 shows a third variant of the ultrasound transducer. In the ultrasonic transducer of this
modification, the transmitting piezoelectric vibrator 138, the receiving piezoelectric vibrator 140,
and the insulating layer 142 are all concave. This structural feature allows the ultrasound
transducer to focus ultrasound without an acoustic lens. Also in this modification, it is more
preferable to have an acoustic matching layer between the transmitting piezoelectric vibrator
138 and the receiving piezoelectric vibrator 140.
[0052]
FIG. 7A schematically shows the configuration of a modification of the control system, and FIG.
7B shows a timing chart of the control signal Vt.
[0053]
In this control system, the control unit of the receiving piezoelectric vibrator 104 does not
include the selector 160, but instead has a transformer 180 connected in parallel and a capacitor
182 connected to the secondary side of the transformer 180. ing.
The other configuration is the same as that of the control system shown in FIG.
[0054]
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The transformer 180 has a small inductance on the primary side, and at the time of transmission,
the impedance ωL (L is the inductance on the primary side of the transformer 180) with respect
to the frequency ft is set to an inductance value that can be regarded as substantially short. In
addition, the capacitor 182 has a capacitance tuned to the frequency nft (n is an integer of 2 or
more).
[0055]
In this control system, only the component of nft (n is an integer of 2 or more) of the received
signal from the receiving piezoelectric vibrator 104, that is, only the harmonics signal is
selectively selected by the secondary side tuning circuit (transformer 180 and capacitor 182). It
is boosted and sent as an output Vout to a subsequent signal processing unit such as an
amplifier.
[0056]
[Effect] The ultrasonic transducer has the piezoelectric transducer for transmission and the
piezoelectric transducer for reception arranged in layers, and the control system shorts or
approximates the electrodes of the piezoelectric transducer for reception during ultrasonic
transmission. The noise component due to residual vibration is eliminated by performing control
for holding for a specific time in the state and holding between the electrodes of the transmission
piezoelectric transducer for a specific time during ultrasonic reception when there is no noise
component and the aperture structure Since the ultrasonic waves are identical and transmit and
receive ultrasonic waves over the entire aperture, it is possible to receive harmonics signals with
a large output.
[0057]
Although the present embodiment describes the configuration of the single type ultrasonic
transducer for mechanical sector scanning, the technology described in the present embodiment
can also be applied to an array type ultrasonic transducer for electronic scanning, The present
invention is not limited to application to a single type ultrasonic transducer for mechanical sector
scanning.
In addition, various combinations of the basic form and the structure of the modification in the
present embodiment can be made, and various configurations of ultrasonic transducers for
harmonic imaging can be made according to the diagnosis target site and diagnostic accuracy,
and these can also be used in the present embodiment. As another variation of.
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[0058]
Second Embodiment The present embodiment is an ultrasonic transducer suitable for harmonic
imaging ultrasonic diagnosis.
[0059]
[Configuration] As shown in FIG. 9, the ultrasonic transducer comprises a transmitting
piezoelectric transducer 202, a receiving piezoelectric transducer 204, a housing 206 for
housing these piezoelectric transducers 202 and 204, and a concave shape. And an acoustic lens
208.
[0060]
The transmitting piezoelectric vibrator 202 is a piezoelectric element made of, for example, lead
zirconate titanate (PZT) ceramic, which has electrodes on both sides and is polarized.
The receiving piezoelectric vibrator 204 is made of, for example, a lead zirconate titanate (PZT)
ceramic of the same material or other composition, a single crystal, or a piezoelectric material
having a larger piezoelectric g constant than a transmitting piezoelectric vibrator such as a
composite piezoelectric body. It is a piezoelectric element.
[0061]
The transmitting piezoelectric vibrator 202 has a ring shape, the receiving piezoelectric vibrator
204 has a disc shape, and the receiving piezoelectric vibrator 204 is located inside the
transmitting piezoelectric vibrator 202.
[0062]
A damping layer 210 is provided on the back of the transmitting piezoelectric vibrator 202, and
a damping layer 212 is provided on the back of the receiving piezoelectric vibrator 204.
[0063]
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Since the receiving ultrasonic wave has a frequency that is an integral multiple of the
transmitting ultrasonic wave, the degree of damping of the damping layer 212 on the back
surface of the receiving piezoelectric transducer 204 is set weaker than that of the damping layer
210 on the back surface of the transmitting piezoelectric transducer 202 For example, the
thickness of the layer may be set relatively thin, or a damping material with relatively small
ultrasonic attenuation may be used.
This makes it possible to use an insulating damping layer in which alumina is dispersed in epoxy
resin as a material of the damping layer 212, and can also avoid the influence of electrical
crosstalk through the damping layer.
[0064]
The acoustic lens 208 is disposed in front of the piezoelectric vibrators 202 and 204, and is
made of, for example, an epoxy resin or the like.
The acoustic lens 208 has a radius of curvature rT at the lens portion located in front of the
transmitting piezoelectric vibrator 202 and a radius of curvature rR at the lens portion located in
front of the receiving piezoelectric vibrator 204. Both lens parts are concave.
The transmitting ultrasonic wave is connected to the focal point F2 by the opening of the
transmitting piezoelectric transducer 202 and the wavelength λT corresponding to the radius of
curvature rT and the frequency fT, and the receiving ultrasonic wave also has the opening of the
receiving piezoelectric transducer 204 and the radius of curvature rR and the frequency nfT It is
designed to be connected to a focal point F2 determined by the wavelength λT / n
corresponding to (n is an integer of 2 or more).
[0065]
Furthermore, in order to give the acoustic lens the function of acoustic matching, the lens portion
of the curvature radius rT of the acoustic lens and the lens portion of the curvature radius rR
each have an average thickness of 1/4 λ corresponding to the frequency. It is desirable to have
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Assuming that the frequency of the target harmonics signal is 2 fT, the average thickness tR of
the lens portion on the front surface of the receiving piezoelectric vibrator 204 is desirably the
average thickness tT of the lens portion on the front surface of the transmitting piezoelectric
vibrator 202. It is 1/2. When this condition and the condition that the focal point coincide with
each other are met, a step may be generated at the boundary between two lens portions having
different radii of curvature. In order to correct this deviation, the surface position of the receiving
piezoelectric vibrator 204 protrudes from the surface position of the transmitting piezoelectric
vibrator 202 by the length td. Here, as shown in FIG. 9B, the average thickness tR is from the
surface of the receiving piezoelectric vibrator 204 to the middle of the concave bottom of the
curvature radius rR and the upper end of the concave of the curvature radius rR. Distance. Also,
the average thickness tT is from the surface of the transmitting piezoelectric vibrator 202 to the
virtual bottom of the radius of curvature rT and the upper end of the concave of the radius of
curvature rT (however, up to the lens effective end for the transmitting piezoelectric vibrator)
And the distance to the middle.
[0066]
The structure including the transmitting piezoelectric vibrator 202, the receiving piezoelectric
vibrator 204, and the acoustic lens 208 is fixed to the inside of the housing 206 via the
insulating layer 214. The front electrode of the receiving piezoelectric vibrator 204 is connected
to the front electrode of the transmitting piezoelectric vibrator 202 by a wiring 216, and the
front electrode of the transmitting piezoelectric vibrator 202 is connected to the housing 206 by
a wiring 218. There is. In the twin-core coaxial cable 220, the lead wire 222 is connected to the
electrode on the rear side of the transmission piezoelectric vibrator 202, the lead wire 224 is
connected to the electrode on the rear side of the reception piezoelectric vibrator 204, and the
shield wire 226 is a housing Connected to 206.
[0067]
[Operation] The ultrasonic wave of the center frequency fT transmitted from the transmitting
piezoelectric vibrator 202 is converged by the acoustic lens 208 and focused on the position F2.
An echo signal that propagates a large biological tissue with a large nonlinear effect and contains
a harmonics signal enters a receiving piezoelectric vibrator 204 having a resonant frequency at
nfT (n is an integer of 2 or more) via an acoustic lens 208. , Converted to electrical signals.
[0068]
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19
When the receiving piezoelectric vibrator 204 is a material having the same sound velocity as the
transmitting piezoelectric vibrator, the thickness of the receiving piezoelectric vibrator 204 is set
to approximately 1 / n of the thickness of the transmitting piezoelectric vibrator 202. Thus, the
receiving piezoelectric vibrator 204 selectively receives nfT (n is an integer of 2 or more)
frequency components.
[0069]
The acoustic lens also determines the radius of curvature rT and rR so that the focal point with
respect to the transmission frequency of the central frequency fT and the focal point with respect
to the reception frequency of the central frequency nfT (n is an integer of 2 or more) coincide
with each other. Be Furthermore, since the average thickness of the acoustic lens is set to a
thickness of 1⁄4 λ for each frequency, wide band, high sensitivity transmission and reception
can be performed.
[0070]
In the present embodiment, since the transmitting piezoelectric vibrator 202 and the receiving
piezoelectric vibrator 204 are arranged almost in the same plane, the ultrasonic waves generated
by the transmitting piezoelectric vibrator 202 can be received piezoelectric It does not pass
through the transducer 204 or be reflected there. Therefore, there is no need to control the state
between the respective electrodes, such as open / short, and the control is extremely easy.
[0071]
In the present embodiment, the harmonic g signal is further received by making the piezoelectric
g constant of the receiving piezoelectric vibrator 204 larger than the piezoelectric g constant of
the transmitting piezoelectric vibrator 202 and using a piezoelectric material having a large
mechanical quality factor Qm. The selectivity of will increase.
[0072]
By making the signal to be applied a bipolar double pulse, it is possible to obtain a transmission
03-05-2019
20
ultrasonic wave with a large amplitude, and it is possible to proportionately increase the
amplitude of the harmonics signal.
This leads to the improvement of the S / N of the harmonics signal, which makes it possible to
obtain good harmonic imaging.
[0073]
Hereinafter, modifications of the present embodiment will be described with reference to the
drawings. In the drawings, members equivalent to the members described above are denoted by
the same reference numerals, and the detailed description thereof will be omitted in the following
description in order to avoid duplication.
[0074]
FIG. 10 shows a first modification of the ultrasonic transducer. In the ultrasonic transducer of
this modification, the acoustic lens 230 has the same radius of curvature over the entire
aperture. The acoustic lens 230 is a circle connecting a point at which the average thickness tT
of the front surface of the transmitting piezoelectric vibrator 202 is 1⁄4 of the wavelength λ of
the ultrasonic wave of the fundamental frequency fT along a donut shape. A sphere
circumscribing both the front surface 204 so that the average thickness tR of the front surface
204 is a circle connecting points of 1⁄4 of the wavelength λ of the ultrasonic wave of the
fundamental frequency nfT (n is an integer of 2 or more) Has a curvature surface with the radius
of curvature as the radius of curvature. Here, as shown in FIG. 10, the average thickness tR is
from the surface of the receiving piezoelectric element 204 to the bottom of the concave surface
of the acoustic lens 230 and its upper end (however, up to the effective end for the receiving
piezoelectric element 204). The average thickness t T is the distance between the surface of the
transmitting piezoelectric element 202 and the bottom of the acoustic lens 230 and the upper
end thereof (but up to the lens effective end with respect to the transmitting piezoelectric
element 202). It is the distance to
[0075]
As a result, although the spatial resolution is somewhat reduced, the acoustic matching condition
03-05-2019
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is approximately satisfied, and high sensitivity reception can be performed for the harmonics
signal. In addition, since the radius of curvature of the acoustic lens 230 is the same over the
entire aperture, it is easy to process, thus providing an inexpensive ultrasonic transducer for
harmonic imaging ultrasound diagnosis.
[0076]
FIG. 11 shows a second modification of the ultrasonic transducer. The ultrasonic transducer
according to this modification has a ring-shaped receiving piezoelectric vibrator 232 and a discshaped transmitting piezoelectric vibrator 234. The transmitting piezoelectric vibrator 234 is
disposed inside the receiving piezoelectric vibrator 232. positioned. In the acoustic lens 236, the
lens portion located on the front surface of the transmitting piezoelectric vibrator 234 has a
spherical curvature radius rT, and the lens portion located on the front surface of the reception
piezoelectric vibrator 232 has a spherical curvature radius rR. These lens parts are both convex.
[0077]
The purpose of the acoustic lens 232 is to focus ultrasonic waves, but it is more preferable that
the acoustic lens 232 doubles as a function of an acoustic matching layer. The thickness of the
acoustic matching layer for the harmonics signal is thin compared to the thickness of the
acoustic matching layer for the fundamental frequency. The acoustic lens 232 has a thick lens
portion near the center and a thin lens portion at the periphery. For this reason, the transmitting
piezoelectric vibrator 234 is disposed at the central portion, and the receiving piezoelectric
vibrator 232 is disposed at the peripheral portion.
[0078]
FIG. 12 shows the main part of a third modification of the ultrasonic transducer. The main part of
the ultrasonic transducer of this modification is a part accommodated in the housing, and has a
circular transmitting portion 248 and a ring-shaped receiving portion 250 surrounding this, and
the transmitting portion 248 is piezoelectric The receiving unit 250 is constituted by the central
portion of the vibrator 242, and the peripheral portion of the piezoelectric vibrator 242 and the
damping layer 252 provided on the back surface thereof.
03-05-2019
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[0079]
The piezoelectric vibrator 242 has a disk shape, and has an electrode 244 common to the
transmitting unit 248 and the receiving unit 250 on its front surface, and a circular electrode
246 of the transmitting unit 248 and an annular shape of the receiving unit 250 on its back
surface. And the electrode 256 of FIG. The receiving unit 250 of the piezoelectric vibrator 242
has a thickness 1 / n of the thickness of the transmitting unit 248, and nft (n is 2 or more) with
respect to the fundamental transmission ultrasonic wave ft transmitted from the transmitting
unit 248 Can selectively receive an n-th harmonic having a frequency component of
[0080]
The damping layer 252 has a concave depression at a central portion corresponding to the
transmitting portion 248 of the piezoelectric vibrator 242, and the ring zone outside thereof is
joined to the receiving portion 250 of the piezoelectric vibrator 242, and the concave portion is
concave The bottom of the depressed portion is not in contact with the transmission portion 248
of the piezoelectric vibrator 242, and a gap portion 254 is formed on the back surface of the
transmission portion 248.
[0081]
In this structure, the transmission unit 248 has a large mechanical quality factor Qm, and can
emit wide-band transmission ultrasonic waves with large amplitude by performing the abovedescribed bipolar double pulse drive control.
In the present modification, the damping layer 252 has a concave depression at a central portion
corresponding to the transmitting portion 248, but may have a through hole.
[0082]
FIG. 13 shows the main part of a fourth modification of the ultrasonic transducer. The main part
of the ultrasonic transducer of this modification is a part accommodated in a housing, and has
four transmitting parts 260 and four receiving parts 270. The transmitting unit 260 and the
receiving unit 270 both have the same sector, and they are alternately arranged in a radial
manner. That is, the fan-shaped transmission units 260 and the reception units 270 are
03-05-2019
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alternately arranged along the angular direction.
[0083]
The transmitting unit 260 includes a transmitting piezoelectric vibrator 262 for transmitting a
fundamental ultrasonic wave having a frequency ft, a transmitting acoustic lens 264 disposed on
the front surface thereof, and a damping layer provided on the back surface of the transmitting
piezoelectric transducer 262 And H.266. The acoustic lens for transmission 264 has a surface
radius of curvature rT centered on the point F2, and the ultrasonic wave of the fundamental
frequency ft transmitted from the piezoelectric transducer for transmission 262 is focused on the
point F2 at the sound ray 268. tie.
[0084]
The receiving unit 270 selectively receives a harmonic ultrasonic wave of frequency nft (n is an
integer of 2 or more), a receiving acoustic lens 274 disposed on the front surface, and a receiving
piezoelectric vibration. And a damping layer 276 provided on the back of the child 272. The
receiving acoustic lens 274 has a surface radius of curvature rR centered at the point F1 and
focuses on the point 2 at the acoustic ray 278 for harmonic ultrasonic waves of frequency nft.
[0085]
In this structure, the aperture areas of the transmitting unit 260 and the receiving unit 270 are
the same for transmission and reception, and the focal point can be matched only with the lens
surface shape.
[0086]
[Effect] In the ultrasonic transducer according to the present embodiment, since the transmitting
unit and the receiving unit are separated in the plane, the efficiency of transmission and
reception is improved by optimizing the shape of the acoustic lens disposed on the front surface
of the piezoelectric transducer. In addition to the above, it is possible to receive a large
harmonics signal with a good spatial resolution in which the fundamental and harmonics
ultrasounds are in focus.
[0087]
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24
Although this embodiment has described the configuration of the single type ultrasonic
transducer for mechanical sector scanning, the contents described in this embodiment are the
array type ultrasonic for electronic scanning, except for the fourth modification. The present
invention is also applicable to a transducer, and is not limited to a single type ultrasonic
transducer for mechanical sector scanning.
In addition, the configurations of the present embodiment and the modifications thereof can be
combined in various ways, and various configurations of ultrasonic transducers for harmonic
imaging can be implemented according to the diagnostic target site and diagnostic accuracy, and
these can also be implemented in the present embodiment. It shall be included as another
modification of the form.
[0088]
Although several embodiments have been specifically described above with reference to the
drawings, the present invention is not limited to the above-described embodiments, and all the
embodiments can be performed without departing from the scope of the invention. Includes
implementation.
[0089]
Therefore, the following can be said about the ultrasonic transducer of the present invention.
[0090]
1.
An ultrasonic transducer having a structure in which a transmitting piezoelectric vibrator at a
resonance frequency ft and a receiving piezoelectric vibrator at a resonance frequency nft (n is
an integer of 2 or more) are arranged in layers in the same structure.
[0091]
03-05-2019
25
[Operation and effect] When ultrasonic pulses of approximately ft are transmitted to living tissue
from a transmitting ultrasonic transducer having a resonance frequency ft, the nonlinearity of
the elastic property of the living tissue is transmitted by propagating in the living tissue. An
ultrasonic echo signal in which ft and harmonics signals of almost integral multiples of ft are
mixed is received.
Since the resonant frequency of the receiving piezoelectric vibrator is approximately an integral
multiple of the resonant frequency ft of the transmitting ultrasonic transducer, it is possible to
selectively detect only the harmonics signal of approximately integral multiple of ft. .
Further, since the transmission and reception apertures of the ultrasonic waves coincide with
each other and the aperture of the ultrasonic transducer is fully utilized, ultrasonic pulses with
large sound pressure can be transmitted. This means that the sound pressure of the reception
harmonics signal increases, and it becomes possible to process the harmonics signal which is a
weak signal compared to the reference frequency with a relatively high S / N. In addition, since
the beam axes of the transmitting and receiving ultrasonic beams coincide with each other, the
lateral resolution is improved.
[0092]
2. It is connected to the ultrasonic transducer described in item 1, and between the electrodes
of the receiving piezoelectric vibrator is kept in a low resistance state including a short circuit for
a specific time after applying the drive voltage to the transmitting piezoelectric vibrator. Control
means for the ultrasonic transducer, characterized in that
[0093]
[Function and effect] When ultrasonic waves pass through the piezoelectric vibrator in the
electrically restrained state, the electrical restraint state changes periodically depending on the
relationship between the wavelength of the transmitted ultrasonic wave and the thickness of the
vibrator, As a result, the speed of sound of the piezoelectric vibrator may change periodically and
residual vibration may appear. By short-circuiting the electrodes of the receiving piezoelectric
vibrator, it becomes an unconstrained state at all times, and residual vibration does not occur at
the time of transmission ultrasonic wave transmission. As a result, ultrasonic diagnosis with good
S / N and excellent spatial resolution is possible. It will be.
03-05-2019
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[0094]
The term "low resistance state" as used herein refers to several 10 kΩ or less between both
electrodes, and the high resistance state refers to several 100 kΩ or more between both
electrodes.
[0095]
3.
It is controlled that the control means of the ultrasonic transducer described in item 2 hold the
electrode of the transmitting piezoelectric vibrator in a high resistance state including an open
until the next transmission is performed after the specific time has elapsed. Control means of the
ultrasonic transducer characterized.
[0096]
[Operation and Effect] After the control unit of the ultrasonic transducer holds the electrode of
the transmission piezoelectric vibrator in a high resistance state including opening until the next
transmission is performed after the specific time has elapsed, the transmission piezoelectric
vibrator As a result, residual vibration does not occur during reception, and as a result,
ultrasound diagnosis with good S / N and excellent spatial resolution can be performed.
[0097]
4.
In the control means of the ultrasonic transducer described in the second item, it is an
inductance circuit that is controlled to maintain the low resistance state including a short circuit
for a specific time between the electrodes of the receiving piezoelectric vibrator for a specific
time. Control means of an acoustic transducer.
[0098]
03-05-2019
27
[Operation and Effect] When connected to the receiving circuit through the inductance circuit, a
resonance system is constituted by the inductance circuit and the capacitance of the receiving
piezoelectric vibrator, so that an optimum reception band characteristic can be obtained. As a
result, the fundamental wave is cut off, and only the harmonics signal can be detected with high
selectivity. At the same time, the inductance circuit can be connected to the receiving
piezoelectric vibrator to maintain the resistance between the electrodes low.
[0099]
5. In the control means of the ultrasonic transducer described in the third aspect, an on / off
control device which combines the final stage of the circuit for applying a drive voltage to the
transmission piezoelectric vibrator to control to hold in the high resistance state including the
opening. A control means of an ultrasonic transducer characterized by being.
[0100]
[Operation and Effect] Since the final stage of the circuit for applying the drive voltage to the
transmission piezoelectric vibrator is composed of the on / off control device, the device remains
in the reception signal by controlling the device to be off when receiving and on when
transmitting. It is possible to prevent the vibration from being superimposed, and as a result, it is
possible to perform ultrasonic diagnosis with good S / N and excellent spatial resolution.
[0101]
6.
The ultrasonic transducer according to claim 1, wherein the receiving piezoelectric transducer is
either a polymer piezoelectric material or a composite piezoelectric material.
[0102]
[Operation and Effect] By using either a polymeric piezoelectric material or a composite
piezoelectric material as the piezoelectric transducer for reception, the reception sensitivity can
be enhanced, and the harmonics signal can be detected with high sensitivity.
03-05-2019
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[0103]
7.
The ultrasonic transducer described in item 6, wherein the polymeric piezoelectric material is
disposed on the surface of the ultrasonic wave emitting side of the transmitting piezoelectric
vibrator directly or through an acoustic matching layer. Transducer.
[0104]
[Function and Effect] In general, in the piezoelectric polymer, the acoustic impedance is close to
the acoustic impedance of the living body. Therefore, by using this as a piezoelectric transducer
for reception and arranged on the side in contact with a living tissue, the occurrence of multiple
reflection in the vicinity of the surface can be suppressed and high contrast resolution in the
vicinity of the body surface can be realized.
[0105]
8. The ultrasonic transducer according to claim 7, wherein said polymeric piezoelectric body is
made of a polymer film in which piezoelectricity is spontaneously generated by surface energy
polarization.
[0106]
[Operation and Effect] Since no adhesive layer intervenes, stable transmission and reception
characteristics can be obtained. Furthermore, immediately after the formation of the polymer
piezoelectric layer, the polarization state is spontaneously reached by the action of surface
energy, and the polarization state can be expressed without the application of an external electric
field. In addition, since there is no bonding step, air bubbles are involved during bonding, and
there is no deterioration in sensitivity or zone. In addition, since adhesive pressure does not act
on the transmitting piezoelectric vibrator present on the back surface, the manufacturing process
03-05-2019
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can be simplified without causing harm to the transmitting piezoelectric vibrator and the like,
and for harmonic imaging with low cost and good reproducibility. Ultrasonic transducers will be
obtained.
[0107]
9. The ultrasonic transducer according to claim 1, wherein a damping layer is disposed on the
back surface of the transmitting piezoelectric transducer, and an acoustic lens having an acoustic
matching function is disposed on the front surface of the receiving piezoelectric transducer.
Transducer.
[0108]
[Operation and Effect] By providing a damping layer on the back surface of the transmission
piezoelectric vibrator, the pulse width of the transmission ultrasonic pulse is shortened, spatial
resolution in the depth direction is enhanced, and an acoustic lens having an acoustic matching
function is formed. It is possible to obtain an ultrasonic transducer with high sensitivity and good
focusing and to obtain good lateral spatial resolution.
[0109]
10.
In the ultrasonic transducer described in item 9, the surface of the acoustic lens is a concave or
convex spherical surface with a radius of curvature R, where R is an acoustic focus at ft and an
acoustic focus at nft (n is an integer of 2 or more). An ultrasonic transducer characterized in that
it is set to a value indicating an acoustic focus which is an average value.
[0110]
[Function and effect] When the transmission ultrasonic wave is ft, the reception frequency is nft
(n is an integer of 2 or more), and the curvature radius of the spherical surface of the acoustic
lens is the same, the transmission focal point and the reception focal point will be different
positions. . This leads to deterioration of the uniformity of the ultrasound image. It is impossible
03-05-2019
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to integrally form in the same position a lens structure having a radius of curvature
corresponding to each layer in a layered structure. Therefore, the radius of curvature of the lens
is the average value of the acoustic focus at ft and the acoustic focus at nft (n is an integer
greater than or equal to 2) where R is a spherical surface with a concave or convex curvature
radius R on the surface of the insulating layer Good ultrasound image uniformity is obtained by
setting it to a value that indicates a certain acoustic focus.
[0111]
11. The ultrasonic transducer according to claim 9, characterized in that the surface of the
acoustic lens has a partially different radius of curvature.
[0112]
[Operation and Effect] Since the surface of the acoustic lens has different curvature radii at
different positions, the acoustic focus connecting at the frequency f t of the transmission
ultrasound and the acoustic focus connecting at the reception ultrasound n ft (n is an integer of 2
or more) It is possible to match. This improves the lateral resolution.
[0113]
12. In the ultrasonic transducer having the transmitting piezoelectric vibrator of the
resonance frequency ft and the receiving piezoelectric vibrator of the resonance frequency nft (n
is an integer of 2 or more) in the same structure, the relative arrangement thereof is as follows:
An ultrasonic transducer characterized by being in the relation of a disc disposed within an inner
diameter.
[0114]
[Operation and Effect] Since the relative positions of the transmitting piezoelectric vibrator and
the receiving piezoelectric vibrator are in the relationship between the annular plate and the disc
disposed within the inner diameter thereof, the transmitting ultrasonic wave and the receiving
ultrasonic wave also have another piezoelectric vibrator It is not necessary to take measures for
03-05-2019
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residual vibration because it does not transmit or reflect light. Further, the acoustic matching
layer between the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator is
also unnecessary, the structure is simplified, and transmission of the fundamental wave and
reception of the harmonics signal can be performed with high reliability.
[0115]
13. The ultrasonic transducer according to claim 12, further comprising an acoustic lens
having an acoustic matching function on the upper surfaces of the transmitting and receiving
piezoelectric vibrators.
[0116]
[Function and Effect] The acoustic lens function restricts the ultrasonic beam to improve lateral
resolution, and the acoustic matching function enables high sensitivity transmission / reception.
[0117]
14.
The ultrasonic transducer according to claim 13, wherein the annular plate is a transmitting
piezoelectric transducer, and the disk disposed in the inner diameter is a receiving piezoelectric
transducer.
[0118]
[Function / Effect] The resonant frequency of the transmitting piezoelectric vibrator is ft, and the
receiving frequency of the receiving piezoelectric vibrator is nf (n is 2 or more, where t is the
average thickness of the acoustic lens disposed on the front surface). Since it is an integer, the
average thickness of the acoustic lens disposed on the front surface is t / n. Since the
transmitting piezoelectric vibrator which is an annular plate is disposed outside and the receiving
piezoelectric vibrator which is a disc is disposed inside, the thickness relationship is applied
when the acoustic velocity of the acoustic lens material is larger than the acoustic velocity of the
living tissue. The acoustic lens structure is thick at the periphery and thin at the center. This
03-05-2019
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means that the surface shape of the acoustic lens can be made concave, and it becomes possible
to add an acoustic matching function to the acoustic lens.
[0119]
15. The ultrasonic transducer according to claim 12, further comprising: damping layers
having different thicknesses or different damping characteristics on the back surface of the two
piezoelectric transducers.
[0120]
[Function and effect] Since the frequency of the reception harmonics signal is nft (n is an integer
of 2 or more) and is higher than the frequency of the transmission ultrasonic wave, the same
material should be thinner than the thickness of the damping layer on the back of the
transmission piezoelectric vibrator. It is possible. Or, an insulating damping layer with low
damping capacity can be used. As a result, it is possible to reduce the electrical crosstalk in which
the damping layer between the transmitting piezoelectric vibrator and the receiving piezoelectric
vibrator is met, and it becomes possible to make it difficult for the fundamental signal to be
applied to the harmonics signal.
[0121]
16. In the ultrasonic transducer described in item 13, the surface of the acoustic lens has a
partially different radius of curvature, and the focal point by the acoustic lens of the transmitting
ultrasonic wave and the focal point by the acoustic lens of the receiving ultrasonic wave coincide
with each other An ultrasonic transducer characterized in that the radius of curvature of both
acoustic lenses is set.
[0122]
[Function / Effect] The frequency of the transmitted ultrasonic pulse is ft, and when the
curvature radius Rt of the acoustic lens is set so that the focal point of the transmitted ultrasonic
wave is at the specific position A, the focal point of the received ultrasonic wave coincides with
03-05-2019
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the position A In order to do this, it is necessary to set the curvature radius Rr of the acoustic
lens to a value different from Rt. Therefore, as in this section, the focal point of the transmission
fundamental wave and that of the harmonics reception signal coincide by making the spherical
portion on the transmitting piezoelectric vibrator and the spherical portion on the receiving
piezoelectric vibrator have different radii of curvature. Good spatial resolution and ultrasound
image uniformity.
[0123]
17. 14. The ultrasonic transducer according to claim 13, wherein the surface of the receiving
piezoelectric transducer protrudes to the ultrasonic transmission side more than the surface of
the transmitting piezoelectric transducer.
[0124]
[Operation and Effect] According to the acoustic lens structure of the sixteenth term, if the
aperture size and the inner diameter of the annular piezoelectric transducer are determined, the
focal position is uniquely determined. When diagnosing living tissue at different deep positions, it
is desirable that design changes be made to have focal positions corresponding thereto. By
making the surface of the receiving piezoelectric vibrator project toward the ultrasonic wave
transmission side more than the surface of the transmitting piezoelectric vibrator as in this
paragraph, nf (n is 2 or more without changing the curvature radius of the concave surface The
acoustic matching condition at the time of reception corresponding to the integer number of
[0125]
18. In the ultrasonic transducer described in item 16, the radius of curvature rR of the
concave or convex surface of the acoustic lens on the receiving piezoelectric transducer is
smaller than the radius of curvature rT of the concave or convex surface of the acoustic lens on
the transmitting piezoelectric transducer An ultrasonic transducer characterized by
[0126]
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[Function / Effect] The frequency of the transmitted ultrasonic pulse is ft, and the focal point of
the received ultrasonic wave coincides with the position A when setting the curvature radius rT
of the concave shape so that the focal point of the transmitted ultrasonic wave is at the specific
position A. To do this, the concave radius of curvature rR> rT must be satisfied. Therefore, as in
this section, the focal point of the transmitting ultrasonic wave matches the focal point of the
receiving ultrasonic wave by making rR> rT in the spherical part on the transmitting piezoelectric
vibrator and the spherical part on the receiving piezoelectric vibrator. It is possible to obtain
harmonics imaging ultrasound diagnostic images with good lateral resolution and ultrasound
image uniformity.
[0127]
19. In the ultrasonic transducer having the transmitting piezoelectric vibrator of the
resonance frequency ft and the receiving piezoelectric vibrator of the resonance frequency nft (n
is an integer of 2 or more) in the same structure, the relative arrangement thereof is alternately
arranged radially. An ultrasonic transducer characterized by having a relationship of
[0128]
[Operation and Effect] Since the plurality of transmitting piezoelectric vibrators and the plurality
of receiving piezoelectric vibrators are alternately arranged radially, the average aperture
diameter of the transmitting ultrasonic waves matches the average aperture diameter of the
receiving ultrasonic waves. The degree of freedom in design of the acoustic lens in front of each
piezoelectric transducer is increased, and it becomes possible to realize various ultrasonic
imaging ultrasound transducers having different focal regions.
[0129]
20.
The ultrasonic transducer described in item 19, wherein the ultrasonic transducer has a
curvature radius rT on the front surface of the transmitting piezoelectric transducer, and an
acoustic lens having the relationship of rR <rT with the radius of curvature rR on the front
surface of the receiving piezoelectric transducer. The ultrasonic transducer characterized by
having each.
03-05-2019
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[0130]
[Operation and Effect] Since the plurality of transmitting piezoelectric vibrators and the plurality
of receiving piezoelectric vibrators are alternately arranged radially, the average aperture
diameter of the transmitting ultrasonic waves matches the average aperture diameter of the
receiving ultrasonic waves. Since the acoustic lens having the relationship of rR <rT with the
radius of curvature rT at the front of the transmitting piezoelectric transducer and the radius of
curvature of rR at the front of the receiving piezoelectric transducer is provided, the focal point
of the transmitting ultrasonic wave is received It will be possible to match the focus of the sound
waves and obtain harmonic imaging ultrasound diagnostic images with good lateral resolution.
[0131]
21.
In the same structure, a transmission piezoelectric vibrator having a resonance frequency ft and
a reception piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more)
are provided, and an acoustic lens is disposed on the front surface of the ultrasonic wave
emission side. An ultrasonic transducer, wherein a damping layer electrically isolated from each
other is disposed on the back surface of each of the transmitting piezoelectric transducer and the
receiving piezoelectric transducer.
[0132]
[Operation and Effect] Electrical crosstalk does not occur between the transmitting and receiving
piezoelectric vibrators, and it is possible to prevent the mixing of the fundamental frequency into
the nft (n is an integer of 2 or more) harmonics reception signal.
[0133]
22.
A control unit connected to an ultrasonic transducer having a transmitting piezoelectric vibrator
at a resonance frequency ft and a receiving piezoelectric vibrator at a resonance frequency nft (n
is an integer of 2 or more) in the same structure; The control means is characterized in that the
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voltage waveform applied to is a trapezoidal wave or a double pulse.
[0134]
[Function and effect] A transmission ultrasonic signal with a large amplitude and a wide band can
be obtained, and the amplitude of a weak harmonics signal can be increased, and a high
sensitivity and S / N good harmonics imaging ultrasonic diagnostic image can be obtained. It will
be.
[0135]
According to the present invention, ultrasonic waves which have the transmitting piezoelectric
vibrator and the receiving piezoelectric vibrator contained in the same case but are not adversely
affected by the resolution deterioration due to the residual vibration Transducer technology is
provided.
According to the ultrasonic transducer and the ultrasonic transducer system, the harmonics
signal can be detected with higher sensitivity than ever.
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