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JPS55121799

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DESCRIPTION JPS55121799
Description 1, title of the invention
Electro-acoustic transducer
3. Detailed Description of the Invention The present invention relates to an electro-acoustic
transducer using a polymeric piezoelectric film. More specifically, the practicality of the
ultrasonic transducer for generating and receiving ultrasonic waves formed by directly utilizing
the thickness vibration mode of the polymeric piezoelectric film disclosed in Japanese Patent
Publication No. 53-26799 is further enhanced. The invention relates to enhanced and improved
ultrasound transducers. An ultrasonic transducer that exerts an action and effect that can not be
expected from an inorganic piezoelectric material because a polymer piezoelectric material can
be easily obtained in a large area, has good processability, and is easy to bond to a curved
surface It can be used as The acoustic impedance of the polymeric piezoelectric material is a
fraction of the acoustic impedance of the inorganic piezoelectric material to 1710 and is close to
that of water, biological or organic materials. Therefore, it can be a convenient transmitterreceiver for the ultrasonic EndPage: 1 wave propagating to them. However, when using a
polymer piezoelectric film as an ultrasonic transducer, there are problems as described below.
That is, in a device using ultrasonic waves such as ultrasonic flaw detection or ultrasonic
diagnosis, a frequency of I MHz to 10 MHz is frequently used. As is well known, in ultrasonic
transducers, the ratio of acoustic output to electrical input (in order to increase the efficiency, it
is necessary to match the resonant frequency of the transducer to the operating frequency. For
this purpose, a piezoelectric film having a thickness predetermined by the target frequency is
required. In the case of polyvinylidene fluoride which is a typical example of a polymeric
piezoelectric material, the frequency constant f. Since to = 115 KH2-crn (fo: resonant frequency
of thickness free oscillator, to: thickness), for example, to efficiently transmit / receive, for
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example, 2.5 MHz ultrasonic waves commonly used for ultrasonic diagnosis Requires a thickness
of 230 μm even in the case of 460 μm 1 μ wavelength drive in the case of half wavelength
drive. However, the poling electric field required to impart the piezoelectricity of a polymer
requires about 10 'V / crn, and poling of a thick film as in the above example is accompanied by
various difficulties such as a gas discharge problem. It is difficult to obtain a thick film polymeric
piezoelectric film, and the range of easy production is usually 100 μm or less (first drawback).
Furthermore, it is difficult to control the thickness of the polymer piezoelectric film to a thickness
suitable for generating and receiving ultrasonic waves of a frequency according to the purpose.
This is because polymer piezoelectric films are often obtained by stretching after stretching an
unstretched film, and depending on processing conditions such as stretching, heat treatment, etc.,
the thickness of the final piezoelectric film obtained from the starting unstretched film is It is
because there are many different cases.
Unlike inorganic piezoelectric materials, the disadvantages of polymer 2). Furthermore, the
polymeric piezoelectric film does not have a high dielectric constant, as does a ferroelectric
inorganic piezoelectric material (eg, PZT). Therefore, when the film thickness becomes large, the
electric capacity decreases, and hence the electric impedance of the vibrator increases, and the
impedance matching with the power supply deteriorates, so that energy from the power supply
can not be injected into the vibrator Occurs (the third drawback). The present invention is an
ultrasonic transducer that efficiently (with a small loss) and receive longitudinal ultrasonic waves
of a frequency that loses the features such as flexibility, low acoustic impedance characteristics,
and ease of processing of a piezoelectric polymer. Intended to provide. The present invention for
achieving this object is as follows. An additional layer having an acoustic impedance (Z) having a
value close to or equal to the value of the acoustic impedance (Zo) of the polymer piezoelectric
film is located directly or indirectly on the surface on the acoustic operation side of the polymer
piezoelectric film. ) Electro-acoustic transducer. Examples of the polymeric piezoelectric film
according to the present invention include: Piezoelectricity is imparted by poling, and a polymer
film having piezoelectricity in the thickness direction of the film is used, and as a polymer
material for forming such a polymer film, polyvinylidene fluoride (hereinafter referred to as
PVDF may be described Or a copolymer thereof, a polyvinyl chloride, a polyacrylonitrile polymer,
or a polymer material mixed with a powder of a ferroelectric ceramic such as lead zirconate
titanate. The acoustically active side of the polymer piezoelectric film means the transmission of
a sound wave to a desired acoustic propagation medium or the desired one by utilizing the
thickness vibration mode of the polymer piezoelectric film of the two film surfaces of the
polymer piezoelectric film. In the reception of sound waves from an acoustic propagation
medium, the side facing the acoustic propagation medium is meant. Hereinafter, this surface may
be referred to as the front surface of the polymeric piezoelectric film. (6) EndPage: 2 or
indirectly, where the additional layer is located on the acoustically operating side of the
polymeric piezoelectric film means that the acoustically operating side of the polymeric
piezoelectric film and the additional layer The acoustically integrated form of direct liquid or the
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acoustically active side of the polymer piezoelectric film and the additional layer intervene with
other objects within the scope of the effects of the present invention. It means a form which is
indirectly located but acoustically integrated via an interposed layer (for example, an electrode
layer). This additional layer may be referred to hereinafter as the front additional layer. The
additional layer is an essential component for achieving the object of the present invention, and
the material whose acoustic impedance (Z) value is close to or equal to the value of the acoustic
impedance (Zo) of the polymer piezoelectric film is It is formed.
Regarding this Z and Zo, it is preferable that the relationship of 2 <Z / Zo (2 is satisfied, and 0.5
(Z / Zo <2, further 0, 5 (Z / Zo <2) is satisfied. More preferably, the relationship is satisfied. On
the other hand, when the acoustic propagation medium is water, the acoustic impedance (Zf) of
this water! It is preferable that the relationship of Z / Z f 05 05 is satisfied in the relationship of:,
and further, Z f <Z <Z. It is more preferable that the relationship of Examples of the substance
forming such an additional layer include a polymer material, and examples of the polymer
material include polyethylene terephthalate, polycarbonate, PMMA, polystyrene, ABS1
polyethylene, vinyl chloride, polyimide, aromatic polyamide, polyfluorocarbon, and the like.
Suitable examples include vinylidene fluoride or mixtures of these polymer materials with
inorganic powder. When shape retention is expected for this additional layer, a film molded by
interposing carbon fibers in these polymer materials can be used. Furthermore, a film may be
used in which thin metallic fibers (for example, stiff fiber) having a diameter sufficiently smaller
than the wavelength of the sound wave (e.g., stiff fiber) are mixed in the polymer material.
Furthermore, if it is desired to emphasize flexibility in a form in which the polymeric piezoelectric
film and the additional layer are integrated, for example, if it is desired to use a transducer
having a variable curvature in a desired direction, as an additional layer, For example, a sheet of
nylon, rubber, polyurethane, silicone rubber can be used. In order to acoustically integrate the
polymer piezoelectric film and the additional layer, or another intervening layer and the
additional layer, the material for forming the additional layer is formed in advance into a film,
and the film is adhered to the other. . Alternatively, it is appropriate to apply the material for
forming the additional layer directly to the partner to form the additional layer, and in the case of
the latter application, for example, dichlorobenzene solution of PMMA, chlorobenzene of
polyethylene terephthalate A solution may be used to evaporate the solvent after application.
After application, polymerization may be performed to form an additional layer, and in this case,
gas phase polymerization may be used. Next, before describing the present invention in more
detail using specific embodiments, definitions of various characteristic values used in each
embodiment and measurement methods thereof will be described. (9) When a tension T1 electric
field E acts in the thickness direction of the film-like piezoelectric substance, the relationship
between the strain S and the electrical displacement of the thickness oscillator and T and E is
given by the following basic equation.
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Here, C and β have a relationship between the mechanical loss, the complex elastic modulus (aT
/ θS) D taking into account the dielectric loss, and the complex electric feeling. 0*=C! (1 +
jψ), β1 = β (1 thousand J () Further, h is a piezoelectric constant (real number). Loads (forces)
of F □ and F2 are applied to the front and back surfaces of the piezoelectric body of thickness t1
area A, density 、, and sound velocity V, respectively, and [Jl and L12 move (angular frequency
ω) The relationship of (10) EndPage: 3 is established between these, when a voltage of 3 and a
current of 3 flow between the electrodes (for example, Ikeda Fube "Sound wave physical
properties of solid" (Mitsuhisa Wada) p. 57 ( Kashiwa Shoten, 1967)). ここで、である。 For nonpiezoelectric films, it may be h-0 in (1). In general, the general configuration of the transducer is
as shown in FIG. Here, layers indicated by 0.1 + 2 + n + f are respectively a piezoelectric film, a
non-piezoelectric film in front, (1, 2, ... n), and a propagation medium (water, living body, etc.), 1 ',
The layers designated 2 ', ... m', b are rear non-piezoelectric films. These may be, if necessary, an
adhesive layer, an electrode, a protective film, a support plate, a reflector, or an additional layer
according to the present invention. exe 'is an electrode (ignoring thickness and mass). The
equivalent circuit in the case of driving the system of FIG. 1 is determined based on the equation
(1) that the force at the interface of each layer and the displacement are continuous and the real
charge inside the piezoelectric body is zero. Be The results are shown in FIG. In FIG. 2, ZAjBjanhYZO = -jBcosechrt, and ZAi, zoi, Z'A'Z'aj, etc. are also similar from Z-ρv, v, t, ψ in each
layer. It is expressed. Φ-hCo is a winding ratio of the secondary coil. When the circuit of FIG. 2 is
connected to a power supply having an internal impedance of Zs, the four-terminal network is
summarized as shown in FIG. The electrical impedance of the transducer viewed from the power
supply is 7 rL. At this time, energy Po from the power source is distributed and consumed as
follows (FIG. 4). Reflection Pr due to the mismatch between Z3 and Zin: Input energy PT (= POPr) to the lancer, acoustic radiation energy PAf forward, acoustic radiation energy PAb to the
back, and internal consumption (heat) energy Ptho of the transducer Here, Pth = PT (PAf + PAb).
ここでである。 Therefore, various losses are defined as follows. (13) Here, in order to enhance
the practicability of the transducer for nondestructive ultrasonic inspection, it is necessary to
design the TLf to be as wide as possible and to be as large as possible. Becomes clear.
In the present invention, the method of measuring and evaluating the characteristics of the
created transducer is as follows. The transducer CLflTLf created. ML was measured by the
following method. First, as shown in FIG. 5, in the measurement of OL'7, the transducer is excited
by a high frequency pulse power source having a known impedance (50 Ω), and the generated
ultrasonic pulse is emitted into water. This is reflected by the brass block and received by the
same transducer. Received message. The signal is amplified and detected, and the output is
displayed on the synchroscope. On the other hand, the excitation voltage is passed through an
attenuator, amplified and detected by the same amplifier, and displayed on a thin cross cord (14)
EndPage: 4 g. Determine the attenuation (dB) of the attenuator so that the two displays are the
same. Do this at each frequency. Assuming that the amount of attenuation is I'mes, CLf is as
follows. CLf (LmesLrefLw6)/2(dB)(6)である。 In the above
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equation, L, e, f are the reflection losses of brass, Lw is the loss due to the absorption of
ultrasonic waves by water and the spread of the wave front, which is associated with the 6 dB
pulse echo method. It is a loss due to parallel connection of transmission and reception
impedances (Kikuchi, Middle Needle Applied Physics, Vol. 36, No. 11, P 927 (1969)). Under the
conditions of the embodiment of the present invention, Lref + Lw is approximately 1 dB. In order
to determine the MLi, the transducer was placed in a water bath where the reflection of
ultrasonic waves can be ignored, and its impedance ZL was determined by measuring the
reflected voltage relative to the electrical input and its phase with the apparatus of FIG. In the
embodiment of the present invention, a piezoelectric film obtained by poling 1118512-217799
(5) -axially stretched polyvinylidene fluoride at 12.0 ° C. in an electric field of 106 v / crn for 1
hour as a polymer piezoelectric material is obtained. used. The electrical and acoustic properties,
such as the piezoelectric constant and the velocity of sound, were determined by one of the
inventors of the present invention, using the resonance method of a polymer piezoelectric film
free oscillator (Daido, J, Appl, Phys. 47.949(1975))。 Next, the present invention
will be described in more detail using specific examples and comparative examples as physical
property values of various substances in the theoretical evaluation of transducers in the present
example. FIG. 7 is a schematic view of a representative embodiment of the electro-acoustic
transducer according to the present invention, and in each of FIGS. 7 (a) to 7 (f), the lower side of
the figure is the side where the acoustic propagation medium is located. Therefore, the lower
surface of the polymeric piezoelectric film 11 corresponds to the surface on the acoustic
operation side of the polymeric piezoelectric film 11 in the figure.
In FIG. 7 (I) to (H), the surface of the polymer piezoelectric film 11 on the acoustic operation side
is directly or indirectly close to or equal to the value of the acoustic impedance (Zo) of the
polymer piezoelectric film 11 An additional layer 12 with an acoustic impedance (Z) of value is
located. In the embodiment of FIG. 7e to (f), the surface on the opposite side to the surface on the
acoustic operation side of the polymer piezoelectric film 11 (this surface may be called the rear
surface of the polymer piezoelectric film in the following) may also be used. An electro-acoustic
transducer is shown in which the additional layer 13 is located directly or indirectly, which is
also meant to be included in the category of the electro-acoustic transducer according to the
present invention. The pair of electrodes (17) 14.14 may be, for example, the additional layer 12
or the additional layer via another intervening layer directly on the both sides of the polymeric
piezoelectric film 11 or in a range where the effect as an electrode is exerted. Located through
13th. In the following description, the additional layer 13 may be referred to as a back additional
layer with respect to the additional layer 12 which is an essential component of the present
invention, that is, the front additional layer. FIG. 8 is a cross-sectional view of an example of the
structure when the electro-acoustic transducer according to the present invention is incorporated
into a specific transducer device. The back acoustic reflection plate 16 serving as an electrode is
attached to the front surface of the cylindrical support 15, and the periphery thereof is covered
with a thickness (step) adjusting material 17 with an adhesive or the like, and the front surface of
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the reflection plate 16 is The polymer piezoelectric film 11 made of PVDF is attached, the
electrode layer 14 is provided on the front surface of the polymer piezoelectric film 11, and the
additional layer 12 made of PVDF is stuck on the front surface of the electrode layer 14 The
periphery is hardened by the adhesive layer 19 through a conductive thin plate 18 electrically
connected to the electrode layer 14 (18 ° EndPage: 5). One lead wire 2G is led out from the
reflection plate 16 and the other lead wire 21 is led out from the electrode layer 14. The
transducer contacts the acoustic propagation medium 22 in front of the additional layer 12. The
support 15 is formed of a material having a small acoustic impedance, for example, a polymer
material, and as this polymer material, for example, PMMA, PSIABS, Bakelite, epoxy resin is
suitable, and flexibility is required. For the purpose of the present invention, a rigid film, a
rubbery material such as rubber, silicone rubber is used. The reflecting plate 16 is formed of a
material having a sufficiently large acoustic impedance than the polymeric piezoelectric film 11
and the support 15, generally, metals such as Au, Cu, W. When the electrode on the back surface
of the polymeric piezoelectric film 11 is formed on the polymeric piezoelectric film 11 in
advance, a ceramic plate made of an insulating material such as PZT can also be used for the
reflecting plate 16.
In FIG. 8, the electro-acoustic transducer according to the present invention of the type shown in
FIG. 7 (A) is shown on the front surface of the back acoustic reflection plate 16, but this electroacoustic conversion is shown. Instead of the element, the electro-acoustic transducer according
to the present invention shown in FIGS. 7 (b) to 7 (c) may be provided on the front face of the
back acoustic reflection plate 16, in which case one electrode 14 , And may be concurrently used
by the reflector 16. Example 1 and Comparative Example 1 FIG. 9 is a schematic structural view
of an example of the electro-acoustic transducer according to the present invention and a graph
showing the effect of the element. Thickness 30 μm 1 area 0.92 c! The front additional layer 12
made of 25 μm, 50 pm, 60 pm PVDF (non-piezoelectric or piezoelectric) may be adhered to the
front surface of the piezoelectric material provided with the PVDF piezoelectric film 11 and
double-sided Kt poles 14 and 14 respectively. The loss OL (= ML + TLf frequency characteristic is
measured for the 0 μm thick conversion element of the front additional layer 12 with no electroacoustic conversion element according to the present invention and the front additional layer 12
provided. Is shown in FIG. On the other hand, FIG. 10 is a graph showing the structure of the
transducer in the comparative example f11 attempted by the present inventors for the purpose
of confirming the effect of the present invention and the effect thereof. The transducer of this
comparative example is made of a high-polymer piezoelectric Cu plate 25 having a thickness of
665 μm, which deviates significantly from the condition of the front additional layer according
to the present invention, instead of the front additional layer according to the present invention
in FIG. It is provided on the front surface of the film 11 via the electrode 14. As apparent from
the graph of FIG. 10, the electro-acoustic transducer of this comparison implementation fll has a
specific frequency, for example, in the case of a wedge wavelength plate, it is not. The loss is
small at / 2 and fO13 fO / 2, but at an external frequency, the loss rapidly increases, and it is a
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power that has narrow band filter characteristics; FIG. 10 shows the case where there is no
mechanical loss and dielectric loss of PVDF (ψ = 0.ψ−〇) and the case (ψ = 0 · 1 · ψ−0, 25). In
both cases, the mechanical loss (21) of the Ou plate is neglected (ψ−0). Here, comparing the
case of the present invention of FIG. 9 with the case of the comparative example of FIG. 10, the
frequency characteristic of loss, that is, OLf ′ = TL1 + ML is extremely wide in the case of the
present invention. In addition, it is clear that the loss is hardly increased. Further, in the case of
the present invention, in accordance with the thickness of the front additional layer 12, the
resonance frequency (the frequency at which T ′ ′ Lf exhibits a local minimum) shifts to the
low frequency side.
Therefore, by controlling the thickness of the front additional layer 12, it becomes possible to
create a transducer having a resonance point at a target frequency without changing the
thickness of the polymer piezoelectric film 11, and It can eliminate the difficulty in production.
Furthermore, in this embodiment, since the additional layer 12 is provided through the electrode
of the polymer piezoelectric film, the additional layer 12 becomes a protective layer of the
electrode, and the durability of the transducer is improved and the electricity to the outside is
obtained. (22) EndPage: 6 effects are also effective in terms of preventing the leakage of and
enhancing the safety. Embodiment 2 FIG. 11 is a cross-sectional view showing the structure of
another transducer device using the electro-acoustic transducer according to the present
invention. Inside the metal housing 24 having a flange portion on the lower surface, electrodes
14.14 are provided on both surfaces on the inner surface of the flange portion and the polymeric
piezoelectric film 11 is mounted, and on the front surface thereof is located in the flange portion
space The front additional layer 12 is formed, and the fixing adhesive 25 is interposed between
the periphery thereof and the periphery of the flange portion, while the rear additional layer 13
is formed on the back surface of the piezoelectric polymer film 11 via the electrode 14. The
metal plate ring 26 for electrode-to-wire connection is placed around the upper surface of the
electrode 14, and the back surface additional layer 13, the metal plate ring 26, the electrode 14,
the polymer piezoelectric film 11 and the housing 24 are formed. A gap between the inner
surface and the inner surface is filled with a fixing adhesive 27. Furthermore, the lead wire 20 is
taken out from the metal plate ring 26 and the housing 24 is grounded. The front surface of the
front additional layer 12 is immersed in water which is the acoustic propagation medium 22. FIG.
12 shows a transducer of the structure shown in FIG. Using an aca PVDF piezoelectric film, as a
front additional layer 12, a 1 () 25 μm J-5 T μm polyester film (East 11 mirror 11) is adhered to
the polymer piezoelectric film 11 via the electrode 14, Thick tb as the additional layer 13; The
effect of the present invention is applied to four types of transducers in which cam and 5 opmo
polyester film (made by Toshi 11) mirror polymer piezoelectric film 11 adhered via electrode 14
and without back surface addition layer 13 FIG. As in the case of the first embodiment, the
second embodiment also has wide band characteristics, and the resonance frequency can be
easily adjusted to the desired one by changing the thickness of the front additional layer 12 or
the back additional layer 13. It is clear that it can be adjusted.
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Example 3 FIG. 15 is a cutaway view of another transducer device using the electro-acoustic
transducer according to the present invention. Put a temporary lid on the lower end of the metal
cylinder 28, position the back reflector 16 made of stainless steel with a thickness of 100μm1
and a diameter of 21.0m inside and position it, pour the low polymerization degree PMMA from
the niga, and further polymerize The advanced support 15 was formed. The temporary lid is
removed, a 56 μm thick uniaxially stretched PVDF piezoelectric film 11 is adhered to the front
surface of the back reflection plate 16, and A / 4-evaporated to the front surface of this
piezoelectric film 11, and an electrode 14 of 03 μm thickness It formed. A front additional layer
12 made of a 25 μm thick polyester film (East 11 L mirror) was attached to the front of the
electrode 14. From the outside, the metal tip cylindrical body 29 was fixed to the cylinder 28 by
welding with the front surface of the front additional layer 12 looking outward. The lead wire 20
is derived in advance from the reflection plate 16 which also serves as an electrode, and is
embedded therein according to the flow of the PMMA. (25) The ultrasonic transducer was
immersed in water, and a high frequency pulse having a time width of several μs was emitted
from the power supply (50 Ω) into the water, and the sound wave reflected by the brass plate
was received by the same transducer. . FIG. 14 shows the frequency characteristics of this
transducer loss TLf. On the other hand, the theoretical value of the loss of this transducer was
calculated by the above m- (5) equation, which is also shown in FIG. As apparent from FIG. 14,
the TLf agrees within 2 to 3 dB, the peak value of the frequency agrees within 0.5 MHz, and the
agreement between the theoretical value and the measured value is satisfactory. For comparison,
the measured and calculated values of TLf of the transducer from which the front additional
layer 12 has been removed and the 'f: shown in FIG. Also in this case, the agreement between the
measured value and the calculated value is good as in the case of FIG. The difference in
frequency characteristics of TLf between FIG. 14 and FIG. 15 is due to the presence or absence of
the front additional layer 12. That is, in the presence of the front additional layer 12 made of
polyester film of 25 μm thickness, (26) EndPage: 7, the frequency giving the minimum value of
loss decreases from about 10 MHz to 8 MHz, and there is no decrease in bandwidth. This makes
it possible to manufacture a transducer having resonance at a low frequency even with a thin
polymer piezoelectric film which is easy to manufacture, and also to protect the electrode 14.
The main cause of the discrepancy between the measured value and the calculated value is
considered to be that the adhesive (epoxy resin) layer has a finite thickness.
Example 4 In the case of an ultrasonic transducer having the same structure as in Example 5, a
front additional layer 12 made of a polyethylene terephthalate (PET) film having a thickness of 5
μm 125 μm and 50/7 m is provided on the front surface of the PVDF piezoelectric film 11 A
comparison of the frequency characteristics of the untuned conversion loss OLf and the
electroacoustic conversion loss TLf with OLf and TL (when the front additional layer 12 is not
provided) is shown in FIG. In this case, a PVDF film formed by poling a uniaxially stretched film
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with a thickness of 76 μm is used for the polymer piezoelectric film 11, and an A-wave plate
(thickness 168 μm) is used for the back reflection plate 16. A copper plate was used. In addition,
a 50 μm thick addition layer is formed by bonding a 50 μm thick 11 mm mirror 1 ′ gold
bond, and a 25 μm thick and 5 μm addition layer is coated with a chlorophenol solution of
polyethylene terephthalate and dried. It formed firmly. Loss of these ultrasound transducers CLf.
The calculation result of the frequency characteristic of TLf is a graph of FIG. The measured
results agree with the calculated results shown in FIG. 16 within 0.5 MHz at the resonance
frequency and within 3 dB of loss. The resonant frequency shifts to a low frequency with the
thickness of the additional layer 12, and the relative bandwidth (frequency range Δf at the
increase of loss 3 dB and the resonant frequency frO ratio Δf / fr), the thickness of the additional
layer 12 is 0. For 5.25.50 μm, Δf / fr increases with increasing thickness of the additional layer
12 at 0, 52.054. 0.57.063, respectively. Embodiment 5 FIG. 17 is a cross-sectional view showing
the structure of still another transducer using the electro-acoustic transducer of the present
invention. The outer diameter is 20. A horn-shaped copper support 31 with a diameter of 16
cylinders is inserted into the polycarbonate vibro 0, and embedded with an epoxy resin 52 from
above, while the 76 μm-thick PVDF piezoelectric film 11 is used as an adhesive. The pressure
was applied to the front curved concave sphere of the radius 30 of the support 51 to bond. In the
PVDF piezoelectric film 11, in advance, AA is vapor-deposited on a part of the back surface and
the entire front surface to form an electrode 14.14. Further, after bonding a thin plate ring 33 of
phosphor bronze to the peripheral portion of the electrode 14 with a conductive adhesive, a front
surface comprising a PVDF unstretched film with a thickness of 19.38.57 and 76 / Jm molded by
hot pressing. The additional layer 12 was bonded to the front surface of the PVDF piezoelectric
film 11 via the electrode 14. Furthermore, five types of transducers (including one having lead
wire 20 from support body 31 and lead wire 21 from electrode 14 on the front surface, the
whole housed in metal case 34 and not having front additional layer 12 ( 29) was created.
FIG. 18 shows calculated values of the TLf frequency characteristics when ultrasonic waves are
emitted into water by the ultrasonic transducer configured as described above or when sound
waves from the water are received. As in the case of the fourth embodiment, by providing the
front additional layer 12, the frequency giving the minimum TLf (resonance frequency) is shifted
to the low frequency side, and a living body or the like is produced using a thin polymer
piezoelectric film which is easy to manufacture. Not only is it possible to generate sound waves
of controlled frequency that can be used for ultrasound diagnosis, but an excellent ultrasound
transducer is provided which increases the fractional bandwidth and which does not have a drop
in capacitance. The measured values of the TLf frequency characteristics obtained by measuring
the intensity of the echo signal from the brass plate placed at the pyroelectric position (50 °) of
this transducer coincided with the calculated values. In this embodiment, a transducer with a
thickness of 38 μm of the front additional layer 12 is used, and high side (30) EndPage: 8-wave
coil LfL main 5 μH is coupled in series in order to obtain impedance matching with the power
supply. And housed in the case. This transducer is scanned in a lateral direction, and a
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tomographic image (head, side) of a fish placed in water by ultrasonic tomography similar to that
performed using a conventional inorganic piezoelectric material by pulse echo method. Was
obtained using a frequency of 5 MH2, and the azimuth and depth resolutions were extremely
satisfactory. Example 6 As shown in the basic configuration of FIG. 19, a PMMA support
substrate 15, a back reflector 16 of Ou, PVDF (-axially stretched piezoelectric film) 11 having a
thickness of 76 μm on which both surfaces have been kt deposited, and PVDF (- The front
additional layer 12 of the axially stretched non-piezoelectric film was sequentially laminated. The
thickness of the PVDF front additional layer was 19 μm, 38 μm, 76 μm, 152 μm, and the back
reflector was correspondingly set to a thickness of 210 μm, 245 μm, 1320 μm, 500 μm. The
thickness of the reflector is such as to operate as a waveplate near the lowest loss resonant
frequency. FIG. 20 shows the loss TLfi when these transducers are operated in water. With a 152
μm front additional layer, a transducer without a front additional layer with maximum efficiency
at 2.5 MHz, but with resonance at the same frequency, requires a 230 μm PVDF piezoelectric
film, Creation is not easy. Also, in this case, the capacitance decreases with an increase in the
thickness of the piezoelectric film, and ML increases. However, in the case of the present
invention, the capacitance does not decrease, so that the matching with the power supply is not
deteriorated. Can.
Example 7 As shown in FIG. 21, the supporting base 15 is a bakelite plate (Z = 4.84 × 10′kf /
m ′ ′s), and the reflecting plate 16 is a copper plate (thickness 50 μm, area i, OcrA).
Ultrasonic transducer (A) in which the molecular piezoelectric film 11 is made of piezoelectric
PvDF (70 μm thick), the front additional layer 12 is made of PET (100 μm thick), and these are
laminated (50 μm), PVDF piezoelectric film 11 (140 μm), transducer (B) on which PET film 12
(25 μm) is laminated, and PMMA support substrate 15, Cu foil 16 (40 μm), PVDF piezoelectric
film 11 (comparatively) The TLf was determined for three types of transducers (0), 76 μm),
without a front additional layer. The results are shown in FIG. The resonant frequencies of (A)
and (B) both shift to lower frequencies compared to (C), but in (A), in addition to that, the
frequency is nearly doubled (˜10 MHz), There is a small loss resonance. For this reason, it
becomes possible to have extremely wide band characteristics, and also possible to perform short
pulse drive. As described above using the various embodiments, the electro-acoustic transducer
according to the present invention not only exhibits remarkable effects in reducing the resonant
frequency, broadening the bandwidth, and reducing the electrical capacity, but also the seventh
embodiment. As shown in the figure, by appropriately selecting the material of the support base,
the back reflector, and the front additional layer, and their thickness, it is possible to perform a
low loss operation at a high frequency (63). . Furthermore, it is also possible to use other
polymer films having low mechanical loss as an additional layer without increasing the thickness
of the polymer piezoelectric film having relatively large mechanical loss, in order to form a low
loss transducer. It will be an advantage. Furthermore, the additional layer has a machine that is
resistant to water, chemicals, and wear, and also functions to prevent electrical leakage.
Therefore, it can be said that the electro-acoustic transducer according to the present invention
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makes the utility of the polymeric piezoelectric film, which is conventionally known per se,
extremely high for ultrasonic transducers.
4. Brief description of the drawings. FIG. 1 is a diagram for explaining the general construction of
a transformer, FIG. 2 is an equivalent circuit diagram for driving the system of FIG. 1, and FIG. 5
is FIG. 4 is a circuit diagram of the case of connecting the circuit of the present invention to a
power supply having an internal impedance, and FIG. 4 is a diagram for explaining distribution
and consumption of energy PO from the power supply in FIG. (34) EndPage: an explanatory view
of the method apparatus of 9 reservoirs, FIG. 6 is an explanatory view of the method apparatus of
the embodiments for measuring the loss ML, and FIG. 7 is an electro-acoustic transducer
according to the present invention Fig. 8.11.13.17.19 and Fig. 21 illustrate various embodiments
of an ultrasonic transducer device using the electro-acoustic transducer according to the present
invention. Figure 9.10.12.14.15.16.18.2. And FIG. 22 is a graph showing comparison with a
comparative example the effect of the present invention. Brief Description of the Drawings: 11 ···
Polymer piezoelectric film 12 ··· · · · Additive layer or front additional layer 13 · · · Additive layer
or rear additional layer 14 · · · · · · Electrode 15 · · · ----- support 16 ...... reflected sales applicant E
and Co. (35); + 1 Zusai 21 Zuo 3 FIG ti Roh (b) th FIG. 51 Reflecta (O 61 Cause EndPage: 10 Fang
1 圓 (/ Li (0) C Phone (-·, Noo 8 (! 1 year old 11 Figure □-4 j 8 End EndPage: 11 14 1417
exhibition number (Ml-1 牙 15 困 CMHy) End Page: 12 fye double Figure 21 End Page: 13
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