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JPH07322395

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DESCRIPTION JPH07322395
[0001]
The present invention provides a piezoelectric thin plate provided with interdigital electrodes on
one surface F1 of a non-piezoelectric substrate, brings a liquid into contact with the other surface
F2 of the non-piezoelectric substrate, and uses phase shifting means More particularly, the
present invention relates to an ultrasonic microphone in which ultrasonic waves of a
predetermined frequency are irradiated into the liquid. 2. Description of the Related Art In the
case of irradiating an ultrasonic wave into a liquid, an ultrasonic transducer comprising an
interdigital electrode on a piezoelectric thin plate has conventionally been used. By using such an
ultrasonic transducer, it is possible to excite leaky Rayleigh waves, leaky Lamb waves and the like
in the liquid. Since the leaky Rayleigh wave shows a constant frequency with respect to the
velocity, the structure is simple but the degree of freedom in device design is small, and the plate
surface including the interdigital electrode is on the side that contacts the liquid. have. Further, in
order to promote high frequency, it is necessary to further reduce the thickness of the
piezoelectric thin plate, and the thinner the thickness, the more brittle the problem. As described
above, the conventional ultrasonic wave irradiating means in the liquid has a limitation in the
structure of the ultrasonic transducer itself, and therefore, the application area of such an
ultrasonic transducer is limited. SUMMARY OF THE INVENTION It is an object of the present
invention not only to be able to efficiently irradiate ultrasonic waves into a liquid with low power
consumption, but also to use an electric phase shift means to input an electric signal. To provide
an ultrasonic in-liquid microphone capable of irradiating an ultrasonic wave of a frequency
according to a voltage into the liquid and thus transmitting an electrical signal such as music into
the liquid in the form of an FM signal, for example. is there. Another object of the present
invention is to provide an ultrasonic liquid-in-liquid microphone which has a short response time,
good sensitivity, and excellent processability and mass productivity. The ultrasonic in-liquid
microphone according to claim 1 comprises a piezoelectric thin plate provided with an input
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electrode TX and an output electrode RX and an interdigital electrode group, a non-piezoelectric
substrate, and an amplifier. An ultrasonic in-liquid microphone comprising means for irradiating
ultrasonic waves into the liquid, wherein the interdigital transducer group comprises at least one
set of input interdigital transducer T0 and an output corresponding to the interdigital transducer
T0 The electrode TX and the interdigital electrodes T0 and R0 are provided on one plate surface
P1 of the piezoelectric thin plate, and the electrode RX is the electrode TX of the other plate
surface P2 of the piezoelectric thin plate. The piezoelectric thin plate is fixed to one plate surface
F1 of the non-piezoelectric substrate via the plate surface P2, and the ultrasonic wave irradiation
means includes phase shift means, and The phase shift means includes the electrodes TX and RX
and the piezoelectric thin plate, and the ultrasonic wave irradiation means inputs an electric
signal of a frequency according to the voltage of the electric signal input to the electrode TX to
the interdigital electrode T0 A surface acoustic wave of the frequency is excited at the interface
between the piezoelectric thin plate and the non-piezoelectric substrate, mode converting part of
the surface acoustic wave into the non-piezoelectric substrate as a bulk wave, and The bulk wave
is irradiated as a longitudinal wave into the liquid in contact with the other plate surface F2 of
the non-piezoelectric substrate, and the remaining part of the surface acoustic wave excited at
the interface is output as an electric signal from the interdigital electrode R0 , And the electrode
RX is disposed substantially at the center of the propagation path of the surface acoustic wave
between the interdigital electrodes T0 and R0.
The ultrasonic in-liquid microphone according to claim 2, wherein the interdigital electrode
group includes the interdigital electrodes T0 and R0 and at least two sets of input interdigital
electrodes T1 and T2, and the ultrasonic wave irradiating means includes An electrical signal of a
frequency according to the voltage of the electrical signal input to the electrode TX is input to
the interdigital electrodes T0, T1 and T2, and a surface acoustic wave of the frequency is
generated at the interface between the piezoelectric thin plate and the nonpiezoelectric substrate.
Excitation and mode conversion of a part of the surface acoustic wave as bulk wave in the nonpiezoelectric substrate, the bulk wave in the non-piezoelectric substrate is irradiated as the
longitudinal wave into the liquid, and the interdigital electrodes T0 and T1 , T2 and R0 have
electrode cycle lengths substantially equal to the wavelength of the surface acoustic wave, and
the velocity of the bulk wave propagating through the non-piezoelectric substrate alone is
smaller than the velocity of the surface acoustic wave propagating through the piezoelectric thin
plate alone. To. The ultrasonic in-liquid-solution microphone according to claim 3 has a line
which makes the interdigital electrodes T0 and R0 axisymmetric with each other on the surface
P1 and the interdigital electrodes T1 and T2 on the surface P1. Are made to be line symmetrical
with each other, and the intersections thereof intersect the center point of the electrode TX. In
the ultrasonic in-liquid microphone according to claim 4, an output end of the interdigital
transducer R0 is connected to an input terminal of the amplifier, and an output of the amplifier is
included in the interdigital transducer group. An oscillator is constructed, which is connected to
the input end of the L-shaped electrode and whose propagation path of the surface acoustic wave
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in the non-piezoelectric substrate from the inter-shaped electrode T0 to the inter-shaped
electrode R0 is a delay element. The signal loop of the oscillator is characterized by comprising
the interdigital electrode T0, the propagation path of the surface acoustic wave in the nonpiezoelectric substrate, the interdigital electrode R0, and the amplifier. The ultrasonic in-liquid
microphone according to claim 5 is characterized in that an interdigital electrode included in the
interdigital electrode group has an arc shape. The ultrasonic in-liquid microphone according to
claim 6 is characterized in that a thickness of the piezoelectric thin plate is equal to or less than
an electrode cycle length of an interdigital electrode included in the interdigital electrode group.
In the ultrasonic in-liquid microphone according to claim 7, the non-piezoelectric substrate is
made of an acrylic plate, the piezoelectric thin plate is made of a piezoelectric ceramic, and the
direction of the polarization axis of the piezoelectric ceramic has an interdigital electrode in the
piezoelectric ceramic. It is characterized by being perpendicular to the plate surface. The
ultrasonic in-liquid microphone according to claim 8 is characterized in that the non-piezoelectric
substrate is made of an acrylic plate, and the piezoelectric thin plate is made of LiNbO3 or
another single crystal.
The ultrasonic in-liquid microphone according to claim 9 is characterized in that the piezoelectric
thin plate is made of PVDF or other piezoelectric polymer film. The ultrasonic liquid-in-liquid
microphone according to the present invention irradiates ultrasonic waves into a liquid, a
piezoelectric thin plate provided with an input electrode TX, an output electrode RX and an
interdigital electrode group, a non-piezoelectric substrate, an amplifier and And a simple
structure with means. The ultrasonic wave irradiating means includes phase shifting means, and
the phase shifting means is composed of the electrodes TX and RX and the piezoelectric thin
plate, and has a function of changing the oscillation frequency according to the voltage of the
electric signal inputted to the electrode TX. Have. The electrode TX and the interdigital
transducer group are provided on one plate surface P1 of the piezoelectric thin plate, and the
electrode TX has a structure disposed substantially at the center of the plate surface P1. On the
other hand, the electrode RX is provided at a portion corresponding to the electrode TX of the
substantially central portion of the other plate surface P2 in the piezoelectric thin plate. The
piezoelectric thin plate is fixed to one plate surface F1 of the non-piezoelectric substrate via the
plate surface P2. In the ultrasonic liquid-in-liquid microphone of the present invention, by
making full use of the phase shift means, when the liquid is brought into contact with the other
plate surface F2 of the non-piezoelectric substrate, the ultrasonic wave whose frequency is
modulated with the passage of time is It can be irradiated inside. At this time, the electrodes TX,
RX and the piezoelectric thin plate function as phase shifters. That is, it becomes possible to
irradiate the ultrasonic wave of the frequency according to the voltage of the electrical signal
input to the electrode TX into the liquid. Therefore, the ultrasonic in-liquid microphone of the
present invention has a function as an in-liquid microphone which transmits the music in the
form of an FM signal into the liquid by inputting an electric signal such as music to the electrode
TX. In this way, it is possible to apply ultrasonic waves of a predetermined frequency to the
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liquid according to the type of fish, for example, when cultivating fish, training dolphins, or
breeding tropical fish in a water tank, so It is possible to promote growth. Moreover, since it
becomes possible to irradiate the ultrasonic wave of a predetermined | prescribed frequency in a
liquid according to the kind of the plant in the water culture culture of a plant, it is also possible
to promote the growth of a plant. In the ultrasonic in-liquid microphone of the present invention,
it is possible to employ a structure in which the interdigital electrode group includes at least one
set of input interdigital electrodes T0 and an output interdigital electrode R0 corresponding to
the interdigital electrodes T0. In this case, an electric signal of a frequency according to the
voltage of the electric signal input to the electrode TX is input to the interdigital electrode T0,
and the surface acoustic wave of the velocity VS having the frequency at the interface between
the piezoelectric thin plate and the nonpiezoelectric substrate Is excited.
By adopting a structure in which the piezoelectric thin plate is fixed to the non-piezoelectric
substrate, it is possible to perform mode conversion in a form in which the surface acoustic wave
leaks to the non-piezoelectric substrate as a bulk wave. The phase velocity of the surface acoustic
wave leaked at this time is larger than the velocity VAT of the shear wave in the non-piezoelectric
substrate alone. That is, among the surface acoustic waves excited in the piezoelectric thin plate,
one satisfying the relation that VS is larger than VAT is leaked to the non-piezoelectric substrate.
Thus, among surface acoustic waves excited in the piezoelectric thin plate, waves having a phase
velocity larger than the velocity VAT of the shear wave in the non-piezoelectric substrate alone
and smaller than the velocity VAL of the longitudinal wave have a velocity substantially equal to
the velocity VAT. It is efficiently converted into waves and leaked to the non-piezoelectric
substrate. Further, among surface acoustic waves excited in the piezoelectric thin plate, waves
having a phase velocity greater than the velocity VAL of the longitudinal wave in the nonpiezoelectric substrate alone are efficiently converted into waves having a velocity substantially
equal to the velocity VAT or the velocity VAL. And leak to the non-piezoelectric substrate.
Furthermore, a part of the bulk wave leaked in this way is efficiently emitted as a longitudinal
wave of velocity VW into the liquid in contact with the surface F2 of the non-piezoelectric
substrate. Among surface acoustic waves excited at the interface between the piezoelectric thin
plate and the non-piezoelectric substrate, those whose phase velocity is smaller than the velocity
VAT of the longitudinal wave in the single non-piezoelectric substrate are not leaked to the nonpiezoelectric substrate and propagate through the piezoelectric thin plate Thus, the surface
acoustic wave (where VS is smaller than VAT) can be output as an electrical signal from the
interdigital transducer R0. In the ultrasonic in-liquid microphone of the present invention, a
structure is employed in which the electrode RX is disposed substantially at the center of the
surface acoustic wave propagation path between the interdigital electrodes T0 and R0. This is
because the propagation path length of the surface acoustic wave between the interdigital
electrodes T0 and R0 can be efficiently expanded or contracted by inputting an electrical signal
to the electrode RX. That is, the change of the propagation path length brings about the change
of the oscillation frequency. The degree of change of the oscillation frequency is correlated with
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the voltage of the electrical signal input to the electrode RX. In this way, it is possible to obtain a
predetermined oscillation frequency by controlling the voltage of the electrical signal input to the
electrode RX. A structure including at least two sets of input interdigital electrodes T1 and T2 in
addition to interdigital electrodes T0 and R0 can be employed as the interdigital electrode group.
In this case, a line in which the interdigital electrodes T0 and R0 are in line symmetry with each
other on the plate surface P1 of the piezoelectric thin plate and a line in which the interdigital
electrodes T1 and T2 are in line symmetry with each other are substantially parallel to each
other. The structure can be adopted.
Further, a line in which the interdigital electrodes T0 and R0 are in line symmetry with each
other and a line in which the interdigital electrodes T1 and T2 are in line symmetry with each
other cross each other, and the intersection point is substantially coincident with the center point
of the electrode TX. The structure which arrange | positions the electrode TX in such a position
can be employ | adopted. In the ultrasonic microphone, which has a structure including at least
two sets of input interdigital electrodes T1 and T2 in addition to interdigital electrodes T0 and
R0, an electric of a frequency corresponding to the voltage of the electrical signal input to the
electrode TX A signal is input to the interdigital electrodes T0, T1 and T2, and a surface acoustic
wave of velocity VS having the above-mentioned frequency is excited at the interface between the
piezoelectric thin plate and the non-piezoelectric substrate. A portion of this surface acoustic
wave (where VS is greater than VAT) is mode-converted in such a manner that it leaks to the nonpiezoelectric substrate as a bulk wave, and the bulk wave is irradiated as a longitudinal wave into
the liquid that contacts plate surface F2. Be done. The remainder of the surface acoustic wave
(where VS is smaller than VAT) is output as an electrical signal from the interdigital transducer
R0. The output end of the interdigital transducer R0 for output is connected to the input end of
the amplifier, and the output terminal of the amplifier is the input interdigital transducer
included in the interdigital transducer, that is, the input of interdigital transducers T0, T1 and T2
Connected to the end. Therefore, the electric signal output from the interdigital transducer R0 is
amplified by the amplifier and applied again to the input interdigital transducer. In this manner,
an oscillator is formed in which the propagation path of the surface acoustic wave in the nonpiezoelectric substrate from the interdigital electrode T0 to the interdigital electrode R0 is a
delay element. The signal loop of this oscillator comprises an interdigital electrode T0, the
aforementioned propagation path of surface acoustic waves on a non-piezoelectric substrate, an
interdigital electrode R0, and an amplifier. Therefore, in the ultrasonic liquid-in-liquid
microphone of the present invention, the circuit configuration is simplified and a device with a
built-in oscillator is formed, thereby facilitating reduction in size and weight of the device,
facilitating portability and consuming low voltage and low power. Power drive is possible. In the
ultrasonic liquid microphone according to the present invention, not only regular ones but also
circular ones are possible as interdigital electrodes. By adopting a structure in which the
thickness of the piezoelectric thin plate is made equal to or less than the electrode period length
of the interdigital electrode and the electrode period length of the interdigital electrode is
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substantially equal to the wavelength of the surface acoustic wave excited on the piezoelectric
thin plate Not only can the degree of conversion of the applied electrical energy into surface
acoustic waves be increased, but it is also possible to suppress reflections and the like caused by
acoustic impedance mismatch at the interface between the piezoelectric thin plate and the nonpiezoelectric substrate. .
Therefore, effective leakage of the surface acoustic wave to the non-piezoelectric substrate can
be promoted. The smaller the ratio (d / λ) of the thickness d of the piezoelectric thin plate to the
electrode period length of the interdigital transducer, that is, the wavelength λ of the surface
acoustic wave, the larger the effect. The ultrasonic in-liquid microphone of the present invention
overcomes the fragility associated with reducing the thickness d of the piezoelectric thin plate by
fixing the piezoelectric thin plate to the non-piezoelectric substrate. That is, the non-piezoelectric
substrate plays an important role in overcoming the fragility of the piezoelectric thin plate.
Further, the interdigital electrode is provided on the plate surface P1 of the piezoelectric thin
plate, and the plate surface P2 of the piezoelectric thin plate is fixed to one plate surface F1 of
the non-piezoelectric substrate. That is, by adopting a structure in which the piezoelectric thin
plate is fixed to the non-piezoelectric substrate via the plate surface having no interdigital
electrode, the electrical energy applied to the interdigital electrode is efficiently converted to
surface acoustic waves. Can. By adopting an acrylic plate as the non-piezoelectric substrate,
adopting a piezoelectric ceramic as a piezoelectric thin plate, and adopting a structure in which
the direction of the polarization axis of the piezoelectric ceramic is perpendicular to the plate
surface having an interdigital electrode in the piezoelectric ceramic. The surface acoustic wave
can be efficiently excited on the piezoelectric thin plate, and the surface acoustic wave can be
efficiently leaked to the non-piezoelectric substrate. By employing an acrylic plate as the nonpiezoelectric substrate and employing LiNbO3 or other single crystals as the piezoelectric thin
plate, surface acoustic waves can be efficiently excited on the piezoelectric thin plate, and the
surface acoustic waves can be further applied to the non-piezoelectric substrate. It can leak
efficiently. By employing PVDF or other piezoelectric polymer film as the piezoelectric thin plate,
surface acoustic waves can be efficiently excited on the piezoelectric thin plate in a form capable
of higher frequency response, and the surface acoustic waves can be further efficiently applied to
the non-piezoelectric substrate. It can leak well. DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT FIG. 1 is a cross-sectional view showing an embodiment of the ultrasonic
microphone in accordance with the present invention. The present embodiment comprises an
input electrode TX, an output electrode RX, an input interdigital transducer T0, T1, T2, an output
interdigital transducer R0, a piezoelectric ceramic thin plate 1, an acrylic plate 2 and an amplifier
3. The electrodes TX and RX are made of an aluminum thin film. Each interdigital transducer has
an arc shape and is made of an aluminum thin film. However, the interdigital electrodes T1 and
T2 are not drawn in FIG. The piezoelectric ceramic thin plate 1 is made of a disc-shaped TDK
101A material (product name) having a diameter of 15 mm and a thickness (d) of 200 μm. The
acrylic plate 2 is a disc having a diameter of 16 mm and a thickness (TA) of 1 mm.
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The electrode TX and each interdigital electrode are provided on one plate surface of the
piezoelectric ceramic thin plate 1, and the electrode RX is provided on a portion corresponding to
the electrode TX on the other plate surface of the piezoelectric ceramic thin plate 1. The
piezoelectric ceramic thin plate 1 is fixed on the acrylic plate 2 by epoxy resin. The output of the
interdigital transducer R0 is connected to the input of the interdigital transducers T0, T1 and T2
via the amplifier 3. However, in FIG. 1, the connection circuit to the input ends of the interdigital
electrodes T1 and T2 is omitted. Further, the electrode RX is grounded to the ground, but is
omitted in FIG. FIG. 2 is a plan view of the ultrasonic in-liquid microphone of FIG. However, in
FIG. 2, the connection circuit to the input ends of the interdigital electrodes T1 and T2 and the
amplifier 3 are omitted. Each interdigital electrode forms an arc having an electrode cycle length
(2P) of 430 μm, and has five pairs of electrode fingers. The inter-electrode distance between the
interdigital electrodes T0 and R0 and the inter-electrode distance between the interdigital
electrodes T1 and T2 are both 6.88 mm. The electrode TX is provided substantially at the center
of the piezoelectric ceramic thin plate 1. FIG. 3 is a perspective view of the ultrasonic in-liquid
microphone of FIG. However, in FIG. 3, the connection circuit to each interdigital electrode and
the amplifier 3 are omitted. When an electric signal is input to the interdigital transducer T0 at
the time of driving the ultrasonic microphone in FIG. 1, only the electric signal of the center
frequency corresponding to the interdigital transducer T0 and its neighboring frequency among
the frequencies of the electric signal is elastic surface It is converted into waves and propagates
at a velocity VS at the piezoelectric ceramic thin plate 1. If the velocity VS of the surface acoustic
wave is larger than the velocity VAT of the transverse wave in the acrylic plate 2 alone and
smaller than the velocity VAL of the longitudinal wave, the surface acoustic wave is converted to
the transverse wave of the velocity VAT and is converted to the acrylic plate 2 It is leaked. When
the velocity VS of the surface acoustic wave is larger than the velocity VAL of the longitudinal
wave in the acrylic plate 2 alone, this surface acoustic wave is converted into the transverse wave
of the velocity VAT and the longitudinal wave of the velocity VAL and leaked to the acrylic plate
2 Be done. The bulk wave leaked to the acrylic plate 2 is converted into a longitudinal wave of
velocity VW at the interface between the acrylic plate 2 and the liquid and emitted into the liquid.
If the velocity VS of the surface acoustic wave is smaller than the velocity VAT of the shear wave
in the acrylic plate 2 alone, this surface acoustic wave is output as an electrical signal from the
interdigital transducer R0. At this time, when an electric signal whose voltage changes with time,
for example, an electric signal such as music, is input to the electrode TX, the propagation path
length of the surface acoustic wave between the interdigital electrodes T0 and R0 is expanded
and contracted.
The change of the propagation path length corresponds to the increase or decrease of the wave
number of the surface acoustic wave. Therefore, a change in propagation path length results in a
change in oscillation frequency. Since the degree of change of the oscillation frequency is
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correlated with the voltage of the electrical signal input to the electrode RX, it is possible to
obtain a predetermined oscillation frequency by controlling the voltage of the electrical signal
input to the electrode RX. In this way, an electrical signal of a frequency according to the voltage
of the electrical signal input to the electrode TX is input to the interdigital electrodes T0, T1 and
T2, and as a result, the frequency is modulated with the passage of time It is possible to irradiate
an ultrasonic wave into the liquid. In the ultrasonic in-liquid microphone of FIG. 1, the electric
signal output from interdigital transducer R0 is amplified by amplifier 3 and input to interdigital
transducers T0, T1 and T2 again. An oscillator can be configured in which the propagation path
of the surface acoustic wave in the acrylic plate 2 between the electrodes R0 is used as a delay
element. The signal loop of this oscillator comprises interdigital electrodes T0, the
aforementioned propagation path, interdigital electrodes R0 and an amplifier 3. By configuring
such an oscillator, the circuit configuration is simplified, the reduction in size and weight of the
device is promoted, and driving with low power consumption and low power consumption
becomes possible. FIG. 4 is a view showing a propagation form until a surface acoustic wave
propagating through the piezoelectric ceramic thin plate 1 is propagated through the acrylic
plate 2 into the liquid as a longitudinal wave. However, in FIG. 4, the interdigital electrode T0, the
piezoelectric ceramic thin plate 1 and the acrylic plate 2 are shown. When an electrical signal is
input to the interdigital transducer T0, a surface acoustic wave of velocity VS propagates through
the piezoelectric ceramic thin plate 1. When the velocity VS of the surface acoustic wave is larger
than the velocity VAT of the transverse wave in the acrylic plate 2 alone and smaller than the
velocity VAL of the longitudinal wave (VAT <VS <VAL), the surface acoustic wave is converted
into the transverse wave of the velocity VAT. And leaked to the acrylic plate 2. The leakage angle
θAT when the bulk wave leaks from the piezoelectric ceramic thin plate 1 correlates to the ratio
of VAT to VS (VAT / VS). The bulk wave propagating through the acrylic plate 2 is converted into
a longitudinal wave of velocity VW at the interface between the acrylic plate 2 and the liquid and
emitted into the liquid. The radiation angle θW at this time is correlated with the ratio of the
velocity VW to the VAT (VW / VAT). FIG. 5 is a view showing an ultrasonic wave propagation
mode in the case where the velocity VS of the surface acoustic wave propagating to the
piezoelectric ceramic thin plate 1 is larger than the velocity VAL of the longitudinal wave in the
acrylic plate 2 alone. In this case (VAL <VS), the surface acoustic wave is converted to the
transverse wave of the velocity VAT and the longitudinal wave of the velocity VAL and leaked to
the acrylic plate 2.
The leak angle θAT when the transverse wave is leaked as a bulk wave from the piezoelectric
ceramic thin plate 1 is correlated with the ratio of VAT to VS (VAT / VS), and the leak angle θAL
in the case of longitudinal wave is the ratio of VAL to VS ( Correlates to VAL / VS). The bulk wave
that excites the acrylic plate 2 is converted into a longitudinal wave of velocity VW at the
interface between the acrylic plate 2 and the liquid and emitted into the liquid. The radiation
angle θW at this time is correlated with the ratio of the velocity VW to the VAT (VW / VAT) or
the ratio of the velocity VW to the VAL (VW / VAL). FIG. 6 is a view showing an ultrasonic wave
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propagation form in the vicinity of the interface between the acrylic plate 2 and the liquid in
contact with the acrylic plate 2. However, this is when the velocity VS satisfies the condition of
FIG. 4 (VAT <VS <VAL). When the bulk transverse wave propagating through the acrylic plate 2
reaches the interface, three components of a transverse wave reflectance RT indicating a
reflection angle θAT, a longitudinal wave reflectance RL indicating a reflection angle θAL, and a
longitudinal wave transmittance TL are generated. Thus, the bulk transverse wave propagating
through the acrylic plate 2 is partially reflected at the interface as the transverse wave
reflectance RT and the longitudinal wave reflectance RL, and the remaining part is radiated into
the liquid at the radiation angle θ W as the longitudinal wave transmittance TL Be done. FIG. 7 is
a characteristic diagram showing the velocity dispersion curve of the surface acoustic wave
propagating in the layered medium consisting of the piezoelectric ceramic thin plate 1 and the
acrylic plate 2 in the ultrasonic liquid microphone of FIG. 1, and the frequency f of the surface
acoustic wave and the piezoelectric ceramic It is a figure which shows the phase velocity of each
mode with respect to the product with thickness d of the thin plate 2. FIG. However, in the
piezoelectric ceramic thin plate 1, both the plate surface (acrylic side plate surface) in contact
with the acrylic plate 2 of the piezoelectric ceramic thin plate 1 and the plate surface (air side
plate surface) in contact with the other air are electrically Used in the open state. In the figure,
"open" indicates the open state. Moreover, (circle) mark shows actual value. The surface acoustic
wave has a plurality of modes. When the fd value is approximately 0.4 MHz · mm or less, the
wave speed of the A0 mode is smaller than the shear wave speed VAT of the acrylic plate 2. Such
a wave is a surface wave in which the energy of the wave is localized and propagated near the
surface and is not leaked to the acrylic plate 2. An imaginary component of the velocity exists in
waves of the A0 mode and other modes whose velocity is greater than VAT, and part of the
energy of the wave leaks into the acrylic plate 2 as a bulk wave. Among the surface acoustic
waves of each mode, waves in a region where the velocity is larger than VAT and smaller than
VAL are effectively leaked into the acrylic plate 2 as bulk transverse waves. Waves in the region
where the velocity is greater than VAL are leaked into the acrylic plate 2 as bulk longitudinal
waves and bulk transverse waves.
FIG. 8 is a characteristic diagram showing the relationship between the mode conversion
efficiency C and the fd value in the microphone in ultrasonic liquid in FIG. However, as the
piezoelectric ceramic thin plate 1, one in which both the acrylic side plate surface of the
piezoelectric ceramic thin plate 1 and the other air side plate surface were electrically open was
used. It can be seen that the surface acoustic wave propagating to the piezoelectric ceramic thin
plate 1 is efficiently leaked to the acrylic plate 2 as a bulk wave in any mode except the A0 mode.
FIG. 9 is a characteristic diagram showing the relationship between the effective
electromechanical coupling coefficient k2 calculated from the phase velocity difference under
two different electrical boundary conditions of the piezoelectric ceramic thin plate 1 and the fd
value. However, as the piezoelectric ceramic thin plate 1, one in which each interdigital electrode
(IDT) is provided on the air side plate surface of the piezoelectric ceramic thin plate 1 and the
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acrylic side plate surface is electrically opened is used. K2 of the A0 mode shows a substantially
constant value (k2 = 4%) from around fd = 2.8 MHz.mm. In the S0 mode, one peak (k2 = 17.5%)
is present around fd = 1.4 MHz.mm. This peak is considered to correspond to the surface wave
leaked from the piezoelectric ceramic thin plate 1 to the acrylic plate 2. The A1 and A2 modes
also show good values efficiently. In this manner, the surface acoustic wave can be efficiently
leaked from the piezoelectric ceramic thin plate 1 to the acrylic plate 2 in any mode except the
A0 mode, and the most efficient to the acrylic plate 2 can be achieved by adjusting the fd value. It
is possible to realize leakage. In addition, the structure in which the interdigital electrodes are
provided on the air side plate surface of the piezoelectric ceramic thin plate 1 has an advantage
of being able to be easily manufactured. FIG. 10 is a characteristic diagram showing the
relationship between the effective electromechanical coupling coefficient k2 calculated from the
phase velocity difference under two different electrical boundary conditions of the piezoelectric
ceramic thin plate 1 and the fd value. However, as the piezoelectric ceramic thin plate 1, one in
which interdigital electrodes are provided on the air side plate surface of the piezoelectric
ceramic thin plate 1 and the acrylic side plate surface is electrically short-circuited is used. In the
present embodiment, the plate surface of the piezoelectric ceramic thin plate 1 is covered with a
metal thin film to electrically short the plate surface. In the figure, "short" indicates a short circuit
condition. Also in FIG. 10, as in FIG. 9, the surface acoustic wave can be efficiently leaked from
the piezoelectric ceramic thin plate 1 to the acrylic plate 2 in any mode except the A0 mode, and
the acrylic plate 2 can be obtained by adjusting the fd value. The most efficient leakage of In
addition, the structure in which the interdigital electrodes are provided on the air side plate
surface of the piezoelectric ceramic thin plate 1 has an advantage of being able to be easily
manufactured.
FIG. 11 is a characteristic diagram showing the relationship between the energy distribution ratio
and the angle with respect to the phase velocity of the shear wave reflectance RT, the
longitudinal wave reflectance RL and the longitudinal wave transmittance TL shown in FIG. That
is, it is a characteristic view regarding bulk transverse waves. However, the angle at this time
indicates the reflection angle θAT for the shear wave reflectance RT, the reflection angle θAL
for the longitudinal wave reflectance RL, and the radiation angle θW for the longitudinal wave
transmittance TL. The value of the longitudinal wave transmittance TL is the largest in the region
around the phase velocity of about 1800 m / s to about 2400 m / s, and it can be seen that the
radiation angle θ W at this time is about 60 to about 40 degrees. FIG. 12 is a characteristic
diagram showing the relationship between the energy distribution ratio and the angle with
respect to the phase velocity of the shear wave reflectance RT, the longitudinal wave reflectance
RL and the longitudinal wave transmittance TL regarding bulk longitudinal waves. The
transmittance of the longitudinal wave transmittance TL is the largest in the region where the
phase velocity is larger than approximately 2800 m / s, and it can be seen that the radiation
angle θ W at this time is about 40 degrees or less. FIG. 13 is a characteristic diagram showing
an example of the relationship between the insertion loss and the frequency in the ultrasonic
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liquid microphone of FIG. 1, wherein the thickness d of the piezoelectric ceramic thin plate 1 is
200 μm, and the electrode period of the interdigital electrodes T0 and R0. This is the result
when the length 2P is 460 μm. In the drawing, the solid line shows the case where the liquid is
not in contact with the acrylic plate 2, and the dotted line shows the case where the liquid is in
contact with the acrylic plate 2. The larger the difference between the solid line and the dotted
line at each frequency, the greater the extent to which the liquid is radiated as a longitudinal
wave in the liquid, so surface waves in any mode except the A0 mode are efficiently radiated as a
longitudinal wave in the liquid I understand. In particular, it can be seen that surface waves of
the S0 mode having a center frequency of about 6 MHz and the S2 mode having a center
frequency of about 13 MHz have a large degree of being emitted as a longitudinal wave into the
liquid. According to the ultrasonic in-liquid microphone of the present invention, the piezoelectric
thin plate provided with the input electrode TX, the output electrode RX and the interdigital
electrode group is fixed to one plate surface F1 of the non-piezoelectric substrate By adopting the
above, it is possible to irradiate an ultrasonic wave whose frequency is modulated with the
passage of time into the liquid in contact with the other plate surface F2 of the non-piezoelectric
substrate. That is, by making full use of the phase shift means, it is possible to irradiate the
ultrasonic wave of the frequency according to the voltage of the electric signal inputted to the
electrode TX into the liquid. Therefore, the ultrasonic in-liquid microphone of the present
invention has a function as an in-liquid microphone which transmits the music in the form of an
FM signal into the liquid by inputting an electric signal such as music to the electrode TX.
In this way, it is possible to apply ultrasonic waves of a predetermined frequency to the liquid
according to the type of fish, for example, when cultivating fish, training dolphins, or breeding
tropical fish in a water tank, so It is possible to promote growth. Moreover, since it becomes
possible to irradiate the ultrasonic wave of a predetermined | prescribed frequency in a liquid
according to the kind of the plant in the water culture culture of a plant, it is also possible to
promote the growth of a plant. The interdigital transducer group needs to include at least one set
of normal or arc-shaped input interdigital transducer T0 and an output interdigital transducer R0
corresponding to the interdigital transducer T0. A structure in which only input interdigital
electrodes are added to such a basic structure as the interdigital electrode group, for example, a
structure in which interdigital electrodes T1 and T2 are added can be adopted. In this case, an
electrical signal of a frequency according to the voltage of the electrical signal input to the
electrode TX is input to the interdigital electrodes T0, T1 and T2, and the velocity VS having the
frequency is generated at the interface between the piezoelectric thin plate and the
nonpiezoelectric substrate. Surface acoustic waves are excited. A portion of this surface acoustic
wave (where VS is larger than the velocity VAT of the shear wave in the non-piezoelectric
substrate alone) is mode-converted in such a manner that it leaks to the non-piezoelectric
substrate as a bulk wave, and Is emitted efficiently as a longitudinal wave of velocity VW in the
liquid in contact with the. The remainder of the surface acoustic wave (where VS is smaller than
VAT) is output as an electrical signal from the interdigital transducer R0. At this time, by
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adopting a structure in which an electrical signal is input to the electrode RX disposed
substantially at the center of the propagation path of the surface acoustic wave between the
interdigital electrodes T0 and R0, between the interdigital electrodes T0 and R0. The propagation
path length of the surface acoustic wave can be efficiently extended and contracted. Since the
change in propagation path length causes a change in oscillation frequency, and the degree of
change in oscillation frequency is correlated with the voltage of the electrical signal input to
electrode RX, the voltage of the electrical signal input to electrode RX is A predetermined
oscillation frequency can be obtained by control. Also, by adopting a structure in which the
output end of interdigital transducer R0 is connected to the input of the amplifier and the output
of amplifier is connected to the input of interdigital transducers T0, T1 and T2, the output from
interdigital transducer R0 is obtained The amplified electrical signal is amplified by the amplifier
and input again to the interdigital electrodes T0, T1 and T2. In this manner, an oscillator is
formed in which the propagation path of the surface acoustic wave in the non-piezoelectric
substrate from the interdigital electrode T0 to the interdigital electrode R0 is a delay element.
The signal loop of this oscillator comprises an interdigital electrode T0, the aforementioned
propagation path of surface acoustic waves on a non-piezoelectric substrate, an interdigital
electrode R0, and an amplifier. Therefore, in the ultrasonic liquid-in-liquid microphone of the
present invention, the circuit configuration is simplified and a device with a built-in oscillator is
formed, thereby facilitating reduction in size and weight of the device, facilitating portability and
consuming low voltage and low power. Power drive is possible. By adopting a structure in which
the thickness of the piezoelectric thin plate is made equal to or less than the electrode period
length of the interdigital electrode and the electrode period length of the interdigital electrode is
substantially equal to the wavelength of the surface acoustic wave excited on the piezoelectric
thin plate Not only can the degree of conversion of the applied electrical energy into surface
acoustic waves be increased, but it is also possible to suppress reflections and the like caused by
acoustic impedance mismatch at the interface between the piezoelectric thin plate and the nonpiezoelectric substrate. . Therefore, effective leakage of the surface acoustic wave to the nonpiezoelectric substrate can be promoted. The smaller the ratio (d / λ) of the thickness d of the
piezoelectric thin plate to the electrode period length of the interdigital transducer, that is, the
wavelength λ of the surface acoustic wave, the larger the effect. The ultrasonic in-liquid
microphone of the present invention overcomes the fragility associated with reducing the
thickness d of the piezoelectric thin plate by fixing the piezoelectric thin plate to the nonpiezoelectric substrate. That is, the non-piezoelectric substrate plays an important role in
overcoming the fragility of the piezoelectric thin plate. Further, the interdigital electrode is
provided on the plate surface P1 of the piezoelectric thin plate, and the plate surface P2 of the
piezoelectric thin plate is fixed to one plate surface F1 of the non-piezoelectric substrate. That is,
by adopting a structure in which the piezoelectric thin plate is fixed to the non-piezoelectric
substrate via the plate surface having no interdigital electrode, the electrical energy applied to
the interdigital electrode is efficiently converted to surface acoustic waves. Can. By adopting an
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acrylic plate as the non-piezoelectric substrate, adopting a piezoelectric ceramic as a piezoelectric
thin plate, and adopting a structure in which the direction of the polarization axis of the
piezoelectric ceramic is perpendicular to the plate surface having an interdigital electrode in the
piezoelectric ceramic. The surface acoustic wave can be efficiently excited on the piezoelectric
thin plate, and the surface acoustic wave can be efficiently leaked to the non-piezoelectric
substrate. Further, by adopting LiNbO3 or other single crystal as the piezoelectric thin plate, it is
possible to excite the surface acoustic wave efficiently on the piezoelectric thin plate, and it is
possible to efficiently leak the surface acoustic wave to the non-piezoelectric substrate.
Furthermore, by adopting PVDF or other piezoelectric polymer film as the piezoelectric thin
plate, the surface acoustic wave can be efficiently excited on the piezoelectric thin plate in a form
capable of higher frequency response, and further, the surface acoustic wave can be used as a
non-piezoelectric substrate Can leak efficiently.
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