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JP2011030046

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DESCRIPTION JP2011030046
An electro-acoustic transducer for headphones, which is basically a piezoelectric type and does
not require a step-up transformer or an electrical cable, and is particularly suitable for an MRI
apparatus. In an electro-acoustic transducer including a sound generation unit and a drive unit
for driving the sound generation unit, the sound generation unit comprises a PLZT element and a
composite piezoelectric body 12 connected in parallel to the PLZT element. The drive unit 20
mainly includes an ultraviolet light emitting diode 21 for emitting ultraviolet light of 365 nm,
and a drive amplifier 22 for driving the ultraviolet light emitting diode 21 by an audio signal, and
the PLZT element 11 and the ultraviolet light emitting diode 21 It is optically connected via the
optical fiber 30. [Selected figure] Figure 1
Electro-acoustic transducer
[0001]
The present invention relates to an electroacoustic transducer for converting an electrical signal
(sound signal) into a sound wave, and more specifically, used in the vicinity of a device for
detecting weak magnetism such as a magnetic resonance tomography imaging device (MRI
device) The present invention relates to an electroacoustic transducer suitable for headphones.
[0002]
In the imaging diagnosis of the MRI apparatus, the subject feels a great deal of anxiety because
the subject is passed through a narrow tunnel in an immobile condition in a noisy environment.
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Therefore, in order to reduce the anxiety of the subject, headphones are attached to the subject
so that they can listen to music and talk.
[0003]
However, since many of the existing headphones are equipped with an electroacoustic transducer
using magnetism, an MRI apparatus that obtains a tomographic image from micromagnetism
may cause a problem in examination.
[0004]
Therefore, in the MRI apparatus, for example, headphones in which an electroacoustic transducer
as described in Patent Document 1 is a piezoelectric type are being preferably adopted.
[0005]
JP 2008-53898 A
[0006]
However, relatively high signal levels (tens of volts to hundreds of volts) are required to drive the
piezoelectric speaker.
Usually, a boost transformer is used to boost the signal, but the use of a transformer in the
vicinity of the MRI apparatus is not preferable.
[0007]
In addition, since a high voltage voice signal is transmitted even to the current-carrying cable of
the headphone, sufficient insulation measures are required for covering the cable and the like in
order to prevent an electric shock.
[0008]
Therefore, an object of the present invention is to provide an electro-acoustic transducer for
headphones, which is basically a piezoelectric type and does not require a step-up transformer or
an electrical cable, and is particularly suitable for an MRI apparatus.
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2
[0009]
In order to solve the above problems, the present invention provides an electro-acoustic
transducer including a sound generation unit and a drive unit for driving the sound generation
unit, wherein the sound generation unit is connected in parallel to a PLZT element and the PLZT
element. The drive unit includes an ultraviolet light emitting diode mainly emitting ultraviolet
light of 365 nm and a drive amplifier for driving the ultraviolet light emitting diode by an audio
signal, and the PLZT element and the ultraviolet light emitting diode Is optically connected via an
optical fiber.
[0010]
In the present invention, it is preferable that a 1-bit digital amplifier be used as the drive
amplifier, and the sound generation unit be built in a headphone case.
[0011]
According to the present invention, the ultraviolet light emitting diode is driven by the audio
signal, and the ultraviolet light of 365 nm mainly emitted from the ultraviolet light emitting diode
is irradiated to the PLZT element through the optical fiber to thereby generate the photovoltaic
power generated in the PLZT element. An electric acoustic transducer for headphones
particularly suitable for an MRI apparatus, which is basically a piezoelectric type and does not
require a step-up transformer or an electric cable, is provided by generating a sound wave by
largely displacing the composite piezoelectric body. .
[0012]
Fig. 1 shows a schematic view of an electroacoustic transducer according to the invention.
The schematic diagram which shows the example of application to the headphone of the said
electroacoustic transducer.
[0013]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2,
but the present invention is not limited thereto.
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[0014]
As shown in FIG. 1, the electro-acoustic transducer of the present invention includes a sound
generation unit 10 and a drive unit 20 for driving the sound generation unit 10.
[0015]
The sound generation unit 10 includes a PLZT element 11 and a composite piezoelectric body 12
connected in parallel to the PLZT element 11.
[0016]
The PLZT element 11 is obtained by forming electrodes on both ends of PLZT (lead lanthanum
zirconate titanate) ceramic and performing polarization treatment, and when ultraviolet light of
365 nm is irradiated to the side of the element, a high voltage is generated by the photovoltaic
effect. Generate.
The generated voltage per electrode distance is 3.3 kV / cm, and the photovoltaic current is
proportional to the light intensity of the irradiation light.
[0017]
The composite piezoelectric body 12 is a piezoelectric body in which a piezoelectric body and a
polymer (organic matter) are combined, and by combining the piezoelectric effect of the
piezoelectric ceramic and the elasticity of the organic matter, a small size, light weight, thinness
and high sound quality can be obtained. .
[0018]
The PLZT element 11 is also a kind of piezoelectric body, but when the PLZT element 11 and the
composite piezoelectric body 12 are connected in parallel, the mechanical impedance of the
composite piezoelectric body 12 is lower, so the voltage generated in the PLZT element 11 The
composite piezoelectric body 12 is largely displaced, and this displacement excites the speaker
cone 12a to generate a sound wave.
[0019]
The driving unit 20 mainly includes an ultraviolet light emitting diode 21 which emits ultraviolet
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light of 365 nm, and a driving amplifier 22 which drives the ultraviolet light emitting diode 21
by an audio signal.
[0020]
As the said ultraviolet light emitting diode 21, Nichia Chemical Industry Co., Ltd. NSHU550B can
be illustrated.
The peak wavelength of this element is 365 nm.
[0021]
In the present invention, a 1-bit digital amplifier based on ΔΣ modulation is preferably adopted
as the drive amplifier 22.
[0022]
The ultraviolet light emitting diode 21 and the PLZT element 11 are optically connected via the
optical fiber 30.
[0023]
When the ultraviolet light emitting diode 21 is driven to emit ultraviolet light by an audio signal
(1-bit signal) output from the drive amplifier 22, the ultraviolet light is irradiated to the PLZT
element 11 through the optical fiber 30.
Thus, a voltage is generated in the PLZT element 11.
[0024]
The voltage generated in the PLZT element 11 is applied to the PLZT element 11 and the
composite piezoelectric body 12 respectively, but since the mechanical impedance of the
composite piezoelectric body 12 is low, the composite piezoelectric body 12 is largely displaced,
and thereby the speaker cone 12a Is excited and a sound wave is emitted.
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[0025]
As shown in FIG. 2, the sound generation unit 10 is preferably incorporated in a headphone case
2 provided in the headphone 1 and optically connected to the drive unit 20 via an optical fiber
30.
[0026]
In the example of FIG. 2, the sound generation unit 10 is housed in one headphone housing 2 of
the pair of headphone housings 2 and 2 included in the headphones 1, but may be housed for
each headphone housing 2 .
[0027]
According to the electro-acoustic transducer of the present invention, the ferromagnetic body is
not included, and the electrical conductor is wired only at the connection portion of the PLZT
element 11 and the composite piezoelectric body 12, and the PLZT element 11 and the
ultraviolet light emitting diode 21 are The optical connection with the optical fiber 30 makes it
possible to obtain headphones particularly suitable for an MRI apparatus.
[0028]
10 sound generation unit 11 PLZT element 12 composite piezoelectric body 20 drive unit 21
ultraviolet light emitting diode 22 drive amplifier (1 bit digital amplifier) 30 optical fiber
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