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DESCRIPTION JPH07264697

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DESCRIPTION JPH07264697
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer for transmitting and receiving ultrasonic waves, and in particular, to a
configuration of an ultrasonic transducer that is compact, lightweight, excellent in efficiency and
sensitivity, and compatible with multiple frequencies. About.
[0002]
2. Description of the Related Art A conventional ultrasonic transducer used in water at a
frequency of several tens of kHz to several hundreds of kHz uses a piezoelectric vibrator, but in
order to miniaturize the portion used in water. Use a piezoelectric transducer with a small
ultrasonic radiation area (for example, a piezoelectric transducer having a square ultrasonic
radiation surface with a side of 1/2 the wavelength of the wavelength used in water) The
capacitance is small and the electrical impedance is high. For this reason, as a wave transmitter,
in order to obtain a large acoustic output, a voltage of about 200 to 500 V is required to drive
the piezoelectric vibrator, and the voltage is boosted using a transformer or the like.
[0003]
In addition, it is necessary for the receiver to have a high input impedance corresponding to the
electrical impedance of the piezoelectric vibrator as the receiver, and the loss of the receiving
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voltage sensitivity due to the wiring cable is It will also be necessary to compensate for this as it
grows. That is, the peripheral circuit of the piezoelectric vibrator that constitutes the ultrasonic
transducer has become large.
[0004]
In addition, in order to obtain a large acoustic output, the ultrasonic transducer generally uses
the basic mode of the piezoelectric transducer, and in an ultrasonic transducer that needs to use
a plurality of frequencies. In the above, a plurality of piezoelectric vibrators corresponding to
each used frequency are provided. Therefore, the entire ultrasonic transducer has become large,
and various restrictions have occurred in the use conditions of the ultrasonic transducer.
[0005]
As a technique for solving the above-mentioned problems, ultrasonic waves described in "Highsensitivity high-frequency ultrasonic wave transmitter applying piezoelectric actuator"
(Proceedings of the Meeting of the Acoustical Society of Japan, p. 49, 1991.5.17) A transducer is
known as a low impedance version of a piezoelectric vibrator, which utilizes a piezoelectric
actuator in which the piezoelectric vibrator is thinly laminated in multiple layers, and the
capacitance of the piezoelectric vibrator is determined. By increasing the impedance to lower the
impedance, it is possible to drive the piezoelectric vibrator at a low voltage, eliminating the need
for a transformer or the like.
[0006]
In addition, “Characteristic analysis of composite structure piezoelectric transducer for multifrequency ultrasonic waves” (Technical research report of the Institute of Electronics,
Information and Communication Engineers, US-91 (US) 91-47, P1, 1991.10.18) A sonic
transducer is known to transmit and receive multiple frequencies with the same piezoelectric
transducer, which partially drives stacked piezoelectric transducers and with the same
piezoelectric transducer This is to realize transmission and reception of frequency and to
miniaturize by reducing the number of piezoelectric transducers provided in the ultrasonic
transducer.
[0007]
The structure of the piezoelectric vibrator shown in the former paper is obtained by laminating a
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very thin vibrator (130 μm) in multiple layers (64 layers). Therefore, the impedance of the
piezoelectric vibrator is 0.5 Ω. However, it is too small as an actual ultrasonic transducer
(preferably about 50 Ω), and on the transmission side, the electrical signal is attenuated due to
the wiring loss.
That is, the electroacoustic conversion efficiency is deteriorated and the transmission voltage
sensitivity is lowered.
Further, on the receiving side, since the respective laminated piezoelectric vibrators are thin, the
receiving voltage sensitivity is reduced, and the minimum receiving sound pressure level
obtained by subtracting the receiving sensitivity from the amplification preamplifier noise is
increased. That is, it becomes difficult to receive a small sound, and it is not optimal as a
piezoelectric transducer of an actual ultrasonic transducer.
[0008]
The structure of the piezoelectric vibrator shown in the latter paper realizes multi-frequency
transmission and reception with the same piezoelectric vibrator element, but partially uses the
piezoelectric vibrator in a high-order resonance mode. It is a thing. That is, since only a part of
the multi-layered piezoelectric vibrator is used for low impedance, the effect of multi-layering
does not appear, the electrical impedance becomes large, and the transmission voltage sensitivity
It decreases similarly. Furthermore, in an actual ultrasonic transducer, in order to perform
acoustic matching between the medium transmitting the acoustic wave and the piezoelectric
vibrator, it is common to attach a matching layer or the like to the piezoelectric vibrator, and a
vibration mode Becomes complicated, making it difficult to increase the efficiency of the electromechanical conversion of the piezoelectric vibrator. That is, it is difficult to increase the
sensitivity of the piezoelectric vibrator, and again, it is not optimal as a piezoelectric vibrator of
an actual ultrasonic transducer.
[0009]
Accordingly, the object of the present invention is to solve the above-mentioned problems, and
the conversion efficiency of the electric signal and the ultrasonic wave is high, and the sensitivity
is high, even if it is small. An object of the present invention is to provide an ultrasonic
transducer capable of handling ultrasonic waves of a plurality of frequencies.
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[0010]
More specifically, on the transmission side, it is possible to set the transmission voltage
sensitivity to a desired value, and without using a transformer or the like, a piezoelectric vibrator
in which the impedance is matched to the impedance of the amplifier. This makes it possible to
drive this at a low voltage.
In addition, on the receiving side, an ultrasonic wave transmission / reception provided with a
piezoelectric vibrator of a thin film multilayer structure having a low input impedance amplifier
and an electrical impedance capable of realizing low noise Provide the Furthermore, in order to
handle ultrasonic waves of a plurality of frequencies with a small configuration, the conversion
efficiency between the electric signal and the ultrasonic wave is high even if the piezoelectric
vibrator of the thin film multilayer structure is vibrated in a high-order resonance mode. To
provide a highly sensitive ultrasonic transducer.
[0011]
SUMMARY OF THE INVENTION The object of the present invention described above is to use an
electrical impedance as a piezoelectric vibrator for converting an electric signal to an ultrasonic
wave by electro-mechanical conversion, which is used for an ultrasonic transducer. In the case of
using a thin film type piezoelectric vibrator and a piezoelectric vibrator in which the thin film
type piezoelectric vibrator is laminated in multiple layers, thermal noise of the piezoelectric
vibrator, thermal noise of an amplifier used for an ultrasonic transducer, and This can be
achieved by determining the thickness of the piezoelectric vibrators stacked in multiple layers
and the number of layers of thin film type piezoelectric vibrators to be stacked, with the lowest
received sound pressure level required for the acoustic transducer as a parameter.
[0012]
This is because when the thermal noise of the piezoelectric vibrator becomes larger than the
thermal noise of the amplifier, the thin film piezoelectric vibrator is stacked in multiple layers to
lower the impedance, and the noise of the amplifier is the thermal noise of the piezoelectric
vibrator In the case of larger size, the number of thin film type piezoelectric vibrators to be
stacked is reduced, and the thickness is increased, while the thin film type in a range satisfying
the minimum receiving sound pressure level required for the ultrasonic transducer. The
thickness of the piezoelectric vibrator and the number of layers to be stacked are determined so
that the piezoelectric vibrator is stacked in multiple layers to lower the impedance.
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[0013]
More specifically, this is achieved by using a multilayer piezoelectric vibrator in which the
thickness and the number of layers of the piezoelectric vibrator are determined by the following
formulas (1) to (3) having a predetermined relationship.
[0014]
AN = eE− {20 log (gh × t) −120} (1) where AN: amplifier noise pressure equivalent value (dB re
1 μPa) eE: amplifier noise (dB re 1 μPa) gh: piezoelectric constant (V) × m / N × 10 3) t:
Piezoelectric vibrator thickness (m) SN = −15 × 20 log F + 10 log {1 + QM / K 2 · FC / FS · Ω 2}
(2) where FC = t × 10 3 / (2π · R · n · ε · S) SN: Piezoelectric vibrator thermal noise sound
pressure converted value (dB re 1 μPa) F: Applicable frequency (kHz) QM: mechanical Q K:
electromechanical coupling coefficient R: amplifier input Impedance (Ω) n: Number of stacked
layers ε: Permittivity S: Piezoelectric vibrator area (m2) FS: Resonant frequency (kHz) Ω: − FS /
FAN <SN <NL (3) However, NL: System Required minimum received sound pressure (dB re 1
μPa) Here, as a piezoelectric vibrator, an ultrasonic wave of several tens of kHz to several
hundreds of kHz (for example, If the target to transmit and receive sound waves is a distance of
100 m or less and a size of 1 m or less, about 100 to 500 kHz, and if a distance of 1000 m or
more and a size of 10 m or more, 100 kHz or less) And piezoelectric ceramics such as lead
zirconate titanate and lead titanate based materials such as lead niobate and lead titanate. The
polymer (organic piezoelectric material) represented by PVDF etc. is mentioned.
[0015]
Moreover, in order to realize a high efficiency, multi-frequency, high sensitivity ultrasonic
transducer, the signal transmission cable is drawn from each thin film type piezoelectric
transducer of the piezoelectric transducer laminated in multiple layers, and the secondary or
higher Each thin film type of the portion where the phase of vibration displacement is reversed in
the high-order vibration mode by vibrating the piezoelectric vibrator in the next vibration mode
(for example, second-order or third-order high-order vibration mode) With respect to the
piezoelectric vibrator, an ultrasonic transducer is configured to perform the electro-mechanical
conversion by inverting the polarity of the electric signal transmitted and received by the signal
transmission cable.
[0016]
Furthermore, in order to obtain high efficiency and sensitivity, a predetermined delay is added to
each transmission and reception signal of each thin film piezoelectric vibrator for each thin film
piezoelectric vibrator, and the delay of electric signal according to the phase characteristic of
vibration displacement It is also possible to use an ultrasonic transducer which performs the
electro-mechanical conversion while adjusting the quantity.
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[0017]
In the case of an ultrasonic transducer equipped with a piezoelectric vibrator in which multiple
layers of materials having different acoustic impedances, such as epoxy resin, glass, etc., are
laminated in multiple layers, for example, a matching layer or the like for performing acoustic
matching, If it vibrates in the second or higher order vibration mode, it shows a complicated
vibration behavior. Therefore, using an equivalent circuit of piezoelectric vibrators equipped with
different substances, represented by Mason's equivalent circuit etc. In each vibration mode, the
positions of nodes and antinodes of vibration generated in the piezoelectric vibrator equipped
with different substances are calculated by calculation, and the signal transmission cable is used
for each laminated thin film type piezoelectric vibrator. The ultrasonic transducer is configured
to perform the electro-mechanical conversion while determining the polarity and the delay
amount of the electric signal to be transmitted and received, and adjusting the delay amount of
the electric signal according to the phase characteristic of the vibration displacement.
[0018]
In addition, in a piezoelectric vibrator laminated in multiple layers to which a matching layer or
the like is attached, the matching layer is made of the same material as the piezoelectric vibrator,
and is converted and converted back into an electrical signal including vibration energy
generated in the matching layer. Thus, the configuration may be such that high efficiency and
high sensitivity can be obtained.
[0019]
Here, the matching layer is a piezoelectric vibrator in which a medium for transmitting an
ultrasonic wave and acoustic impedance are matched, and is represented by the abovementioned lead titanate based materials such as lead zirconate titanate and lead titanate.
Piezoelectric ceramics include those having pores for adjusting acoustic impedance, and
polymers represented by polyvinylidene fluoride (PVDF) and the like.
[0020]
In general, the minimum received sound pressure level of an ultrasonic transducer using a
piezoelectric vibrator can be determined by the under-water electro-acoustic transducer, bus
universality press and acoustics (1991). As shown in [Under Water Electro-acoustic Transducers,
Bath University Press and Acoustics, (1991)], it is determined by the noise level of the noise of
the amplifier and the thermal noise of the piezoelectric vibrator minus the receiving voltage
sensitivity.
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[0021]
The equation (1) shows the sound pressure converted level AN of amplifier thermal noise, the
equation (2) shows the sound pressure converted level SN of the thermal noise of the
piezoelectric vibrator, and when used as a receiver, the equation (1) (2) so that the value of
Equation (2) is as close as possible, and the inequality of Equation (3) is satisfied, that is, the
receiver is an optimal value that allows the smallest sound to be received. By selecting the
thickness t of the piezoelectric vibrators stacked in multiple layers using equation (1) and
equation (2) and the number n of the thin film type piezoelectric vibrators stacked, an ultrasonic
wave receiver with high receiving sensitivity can be obtained. .
[0022]
However, in the case of using the piezoelectric vibrator as a transmitter-receiver for the purpose
of miniaturizing the ultrasonic transducer, it is desirable that the piezoelectric vibrator has low
impedance, and the thickness of the thin-film piezoelectric vibrator should be as low as possible.
To reduce the receiving sensitivity and to lower the impedance within the range satisfying the
required minimum receiving sound pressure level NL.
[0023]
Thus, by selecting the thickness t of the piezoelectric vibrator and the number n of laminated thin
film piezoelectric vibrators, the electrical impedance of the piezoelectric vibrator can be
optimized, which is generally high impedance. .
That is, the impedance can be lowered to match the input impedance of the amplifier, and a
small, low noise amplifier can be used.
[0024]
In addition, since the electrical impedance of the piezoelectric vibrator is small, for example, the
piezoelectric vibrator can be driven at a low voltage, so that the reduction in size and weight of
the ultrasonic transducer peripheral circuit can be realized.
Therefore, by optimizing the electrical impedance of the piezoelectric vibrator, it is possible to
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apply a small-sized, light-weight, small-scale, general-purpose electronic device, and realize a
reduction in size and weight.
[0025]
Furthermore, in order to miniaturize and economically realize an ultrasonic transducer capable of
dealing with a plurality of frequencies, a piezoelectric vibrator in which one multilayer is stacked
is vibrated in a plurality of vibration modes, and the piezoelectric vibrator is Needs to be shared.
Hereinafter, it demonstrates still more concretely using FIGS. 5-7.
[0026]
FIG. 5 is a model diagram showing the vibration state of the piezoelectric vibrators stacked in
multiple layers, showing how the piezoelectric vibrators stacked in multiple layers vibrate in each
vibration mode.
The broken line in the figure shows the velocity distribution of the piezoelectric vibrator, and the
broken line in the upper half of the center line shows the velocity component in the left direction,
and the broken line in the lower half shows the velocity component in the right direction.
The point at which the center line and the broken line intersect is a node at which the vibration is
minimized, and the point at which the solid line and the broken line at the outer periphery are in
contact is an antinode at which the vibration is maximal.
[0027]
Here, FIG. 5 (A) shows the vibration of the basic vibration mode, and the six stacked piezoelectric
vibrators a, b, c, d, e, f are piezoelectric vibrators a, b and c vibrate in the left direction, and the
piezoelectric vibrators d, e and f vibrate in the right direction, all extending around a node.
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That is, it vibrates in the state which has nothing which presses the vibration of each
piezoelectric vibrator.
[0028]
FIG. 5 (B) shows the vibration of the second vibration mode, and the six stacked piezoelectric
vibrators a, b, c, d, e, f are piezoelectric vibrators a, f. Is vibrating in the left direction, in the right
direction of the piezoelectric vibrators c and d, and around the nodes in the piezoelectric
vibrators b and e.
That is, the left piezoelectric vibrators a, b and c vibrate in the extending direction and the right
piezoelectric vibrators d, e and f contract (the contracted portions are indicated by oblique lines).
[0029]
FIG. 5C shows the vibration of the third vibration mode, in which the piezoelectric vibrators a, b
and e, f on both sides extend in the direction in which the middle piezoelectric vibrators c and d
contract. It vibrates in the direction, and like the secondary vibration mode, the piezoelectric
vibrators vibrate so as to cancel the vibration.
As described above, in the piezoelectric vibrators laminated in multiple layers, since the
extending direction and the contracting direction of each piezoelectric vibrator occur, in the
cable for transmitting and receiving the electric signal wired in the polarization direction of each
piezoelectric vibrator, electricity The phase of the signal will be inverted.
That is, if the polarity and signal delay amount of each cable are not adjusted, the electrical
signals from the respective piezoelectric vibrators are output so as to cancel the signals, or large
vibrations do not occur even if the electrical signals are input. .
[0030]
FIG. 6 is a diagram showing the relationship between the wiring of the signal cable provided in
the piezoelectric vibrator laminated in multiple layers and each vibration mode, and the wiring of
the signal cable makes it possible to use the electric-mechanical system in each vibration mode. It
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shows the state of conversion.
[0031]
That is, FIG. 6A shows the case where the wiring directions of the respective piezoelectric
vibrators are connected in parallel with the same polarization direction of the respective
piezoelectric vibrators (in the same figure, ⇒ indicates the polarization direction of the
piezoelectric vibrators). The received electrical signal is canceled at the secondary resonance and
the sensitivity is improved at an odd multiple of the fundamental wave.
Conversely, when the wiring of the right half and the left half of the piezoelectric vibrator is
reversed, the received electrical signal is canceled at the fundamental resonance, and the
sensitivity is most improved at the secondary resonance.
Therefore, the reception voltage sensitivity is improved by delaying and adding the electric
signals from the respective piezoelectric vibrators so as to be in phase with each other even in
the high-order resonance.
[0032]
In the case of transmitting waves, if the polarity of the cable wired in the polarization direction of
the piezoelectric vibrator is the same for each piezoelectric vibrator as shown in FIG. 6A, the
characteristic curve of FIG. As indicated by ●, at the fundamental frequency, each piezoelectric
vibrator vibrates in phase, but at the secondary resonance frequency, an electrical signal is
applied to vibrate half of the piezoelectric vibrator in the opposite direction to the vibration
mode. Therefore, the transmission voltage sensitivity decreases.
Therefore, the transmission voltage sensitivity is improved by delaying the electric signal
supplied to each piezoelectric vibrator in the same manner as in the case of wave reception, or by
changing the polarity and supplying the same to the piezoelectric vibrator as in the case of wave
reception. Do.
[0033]
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That is, as shown in FIG. 6 (A), as shown by the characteristic curve (● mark) in FIG. 6 (D), when
each piezoelectric vibrator is made the same, high sensitivity is exhibited at the fundamental
resonance and the third resonance. The transmission voltage sensitivity decreases at the
secondary resonance frequency.
Therefore, in the case of transmitting the secondary resonance frequency, a method using only a
part of the piezoelectric vibrator in the wiring shown in FIG. 6B has been conventionally adopted.
Also in this method, as shown by the characteristic curve (.DELTA. Marks) in FIG. 4D, the
sensitivity at the fundamental resonance decreases but the sensitivity at the secondary resonance
improves.
[0034]
Furthermore, according to the method of the present invention, all the piezoelectric vibrators are
used in the wiring shown in FIG. 6C, and according to the method of changing the polarity of the
signal, the characteristic curve (o) in FIG. Thus, as compared with other wiring methods, it is
possible to utilize an all piezoelectric transducer having the highest sensitivity in secondary
resonance, and to realize an ultrasonic transducer with high efficiency and high sensitivity. Of
course, instead of changing the polarity of the signal, a method of delaying the signal may be
used. When the matching layer or the like is attached to the piezoelectric vibrator as described
above, the velocity distribution of the piezoelectric vibrator and the matching layer becomes
complicated.
[0035]
FIG. 7 is a model diagram showing the vibration state of the piezoelectric vibrator on which the
matching layer is mounted, showing that the multilayer piezoelectric vibrator vibrates in each
vibration mode. As shown in the figure, in each vibration mode, the velocity distribution of the
piezoelectric vibrator and the matching layer becomes complicated and the position of the node
moves, so the polarity of each piezoelectric vibrator is simply changed as described above. Only
by doing this, it is not possible to obtain a highly efficient and highly sensitive ultrasonic
transducer. Therefore, by the analysis method represented by the analysis method of Mason's
equivalent circuit and the extension part and the contraction part, the operation of the
piezoelectric vibrator equipped with different substances is calculated from the equivalent circuit,
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and the delay optimum for each piezoelectric vibrator It realizes high-efficiency, high-sensitivity
ultrasonic transducer, which gives the amount and utilizes all piezoelectric transducers.
[0036]
In addition, when the vibrator is made of piezoelectric ceramic, matching can be achieved and
vibration energy of the matching layer can be utilized by using a ceramic containing air bubbles
as the matching layer, etc. A sensitive ultrasonic transducer can be obtained.
[0037]
As described above, by adjusting the signal polarity of each piezoelectric transducer
corresponding to each vibration mode, or providing an optimal delay amount according to each
frequency, highly efficient, multi-frequency, highly sensitive ultrasonic waves A transducer can
be realized.
[0038]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, the
present invention comprises piezoelectric vibrators stacked in multiple layers and signal lines for
transmitting and receiving electrical signals attached to each piezoelectric vibrator, wherein the
signal lines An embodiment of an ultrasonic transducer in which highly efficient electromechanical conversion is performed by adjusting the amount of delay and the equipment such as
an amplifier and the impedance are optimized will be described in detail.
[0039]
<Example 1> In this example, highly efficient electro-mechanical conversion is performed by
adjusting the polarity of the electric signal of the signal line for transmitting and receiving the
electric signal attached to each piezoelectric vibrator of the multilayer laminated piezoelectric
vibrator. And a configuration of an ultrasonic transducer in which the equipment such as the
amplifier and the impedance are optimized.
[0040]
(1) Configuration of Ultrasonic Transducer FIG. 1 is a cross-sectional view of an essential part of
an ultrasonic transducer according to the present invention.
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The ultrasonic transducer 1 performs conversion between vibration energy and electric energy,
piezoelectric vibrators 1a to 1f (details will be described later) laminated in six layers, and a
backing 3 for the purpose of sound reflection. A frame 2 for positioning the respective
piezoelectric vibrators 1a to 1f, an acoustic window 4 for transmitting an acoustic signal, and a
signal line 5 connected to the respective piezoelectric vibrators 1a to 1f for transmitting a
transmitted / received electrical signal; A matching circuit 6 for converting the wiring of the
signal line 5 of each of the piezoelectric transducers 1a to 1f to adjust the polarity or amplifying
the transmitted / received electric signal according to the frequency used as the ultrasonic
transducer 1, power supply, control signal , And an attachment bracket 8 for coupling and
holding the matching circuit section 6, the frame 2, and the cable 7 with a cable 7 for
transmitting / receiving an electrical signal such as an FM, PCW, etc. to / from an external device
(not shown). Configured.
It is also possible to control the directivity of ultrasonic transmission and reception by arranging
a plurality of piezoelectric vibrators 1a to 1f stacked in six layers in parallel.
Further, as shown in Example 2 described later, instead of converting the wiring of the signal line
5 in the matching circuit unit 6, a predetermined delay can be given to the signal line 5.
[0041]
(2) Configuration of Piezoelectric Vibrator The configuration of the laminated piezoelectric
vibrator used in the ultrasonic transducer 1 of this embodiment is shown below.
FIG. 7 shows the structure of the laminated piezoelectric vibrator and its characteristics (the
number of layers of the piezoelectric vibrator, the frequency used, and the lowest received sound
pressure level) determined by the aforementioned equations (1) to (3). (Relationship) is a
characteristic diagram of the piezoelectric vibrator showing one example. In the present
embodiment, PZT ceramic is used as the material of each piezoelectric vibrator, and the area
emitting sound is a square of 10 mm × 10 mm, and the thickness of the laminated piezoelectric
vibrator is 22 mm. A laminated piezoelectric vibrator was used.
[0042]
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More specifically, FIG. 7 shows the calculated values of the minimum received sound pressure
level when the number of stacked piezoelectric vibrators is changed, and the thin solid line in the
graph is an expression of preamplifier noise. The broken line indicates the value of SN of the
equation (2) which is the piezoelectric vibrator thermal noise, which is the value of AN of (1).
According to the calculation results, if the ultrasonic transducer 1 of this embodiment is used
only as a wave receiver, the optimum number of sheets satisfying the relationship of the equation
(3) is obtained when n = 3 (three laminated sheets). . However, in general, the minimum received
sound pressure level NL is determined systemically according to the purpose of use of the
ultrasonic transducer 1 and the environment. For example, as in the present embodiment, if the
ultrasonic transducer 1 is used at 100 kHz or less, the required minimum receiving sound
pressure level is 30 dB or less, because the noise is smaller than underwater noise. The purpose
of use of the transducer 1 can be achieved.
[0043]
That is, since there is a margin of about 6 dB for the noise margin when n = 3 (three laminated
sheets), the electric impedance can be lowered by further laminating in multiple layers.
Therefore, based on the calculation results, the optimum number was selected to be n = 6 (six
layers). As described above, if the environment (size, frequency band, sound pressure level) in
which the ultrasonic transducer is used is determined, it has the optimum impedance as a
communication system according to the above-mentioned relational expression, and Since a
laminated piezoelectric vibrator having desired electro-mechanical conversion efficiency can be
easily selected, a compact ultrasonic transducer with excellent characteristics can be realized.
[0044]
(3) Transmission / reception operation The transmission / reception operation of the ultrasonic
transducer 1 of this embodiment shown in FIG. 1 will be described in detail with reference to the
drawings. FIG. 2 is a block diagram showing the detailed configuration of the ultrasonic
transducer 1 of the present embodiment. The ultrasonic transducer 1 includes a piezoelectric
vibrator 1A in which piezoelectric vibrators 1a to 1f and electrodes 51a to 51g are alternately
stacked and laminated in six layers, and electrodes 51a to 51g in contact with the piezoelectric
vibrators 1a to 1f. Signal lines 5a to 5g connected to each of the piezoelectric vibrators 1a to 1f
and transmitting / receiving electric signals, and further, according to the frequency used as the
ultrasonic transducer 1, the signal lines 5a of the piezoelectric vibrators 1a to 1f , A switching
circuit 11 consisting of contacts 11a to 11g and contacts 111 to 118, and a matching circuit unit
6 having at least a transmission amplifier 12 and a reception amplifier 13 for amplifying
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transmitted / received electric signals; A control signal and a cable 7 for transmitting and
receiving electrical signals such as FM and PCW to and from an external device (not shown). In
the same figure, the backing 3 is in contact with the electrode 51g to reflect the sound wave, and
the sound wave is transmitted / received from the electrode 51a through the acoustic window 4
shown in FIG. It is.
[0045]
In the case of transmission, first, transmission electric signals such as FM and PCW are
transmitted to the matching circuit section 6 through the cable 7. The transmitted electric signal
is amplified by the power amplifier 12, passes through the switching circuit 11 which changes
according to the frequency, and is transmitted to the respective piezoelectric vibrators 1a to 1f
such as piezoelectric ceramic. Each of the piezoelectric vibrators 1a to 1f performs electromechanical conversion, transmits the vibration after mechanical conversion to the electrode 51a,
and transmits an ultrasonic wave from the acoustic window. In addition, the backing 3 reflects
the vibration transmitted to the back to the front, and enables highly efficient transmission. More
specifically, the switching circuit 11 connects the electrical polarities of the piezoelectric
vibrators 1a to 1f so as to be reversed between the extended portion and the contracted portion
in each vibration mode. For example, in the case of the basic vibration mode, as shown in FIG. 5A,
since the piezoelectric vibrators 1a to 1f are extended portions, as shown in FIG. 6A, they have
the same polarity. The respective contacts are preferably the contacts 11a and 112, the contacts
11b and 113, the contacts 11c and 114, the contacts 11d and 115, the contacts 11e and 116,
the contacts 11f and 117, and the contacts 11g and Connect with the contact point 118. Further,
in the case of the secondary vibration mode, as shown in FIG. 5B, since each of the piezoelectric
vibrators 1a to 1f has an extended portion and a contracted portion, as shown in FIG. 6C. The
respective contacts connect the contacts 11a and 112, the contacts 11b and 113, and the
contacts 11c and 114 such that the extension and the contraction are reversed, and further, the
contacts 11d and 114 and the contacts 11e and 11e It is connected to the contact point 115, the
contact point 11f and the contact point 116, and the contact point 11g and the contact point
117. In the present embodiment, the amplifier 12 and the amplifier 13 are provided between the
switching circuit 11 and the cable 7. However, the piezoelectric vibrators 1a to 4 are provided
between the switching circuit 11 and the piezoelectric vibrator 1A stacked. You may arrange for
every 1f. Furthermore, a switch switching mechanism may be provided in the matching circuit
unit 6, and a vibration mode notification signal may be added to the control signal transmitted
from the cable 7 to thereby switch from an external device.
[0046]
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In the case of receiving waves, the operation is the reverse of the case of transmitting waves, and
the sound that has passed through the acoustic window 4 passes through the electrodes 51a and
is transmitted to the piezoelectric vibrators 1a to 1f. Each of the piezoelectric vibrators 1a to 1f
mechanically-electrically converts an acoustic signal, and transmits the acoustic signal to the
switching circuit 11 as an electrical signal. The electrical polarity of the piezoelectric vibrators 1a
to 1f in each vibration mode, that is, the connection of the respective contacts is the same as in
the case of transmission. The electric signal of reception is amplified by the amplifier 13 and
transmitted as a reception signal by the cable 7. Here, the backing 3 performs the same function
as transmission.
[0047]
As described above, according to the ultrasonic transducer of the present invention, it is basically
possible to provide one multi-layered piezoelectric vibrator simply by switching the polarity of
each electrical signal input to and output from the multi-layered piezoelectric vibrator. An
ultrasonic transducer capable of transmitting and receiving ultrasonic waves of a plurality of
frequencies from the vibration mode to the high-order vibration mode can be realized, and
moreover, the electro-mechanical conversion operation of all the piezoelectric vibrators can be
utilized. An efficient ultrasonic transducer can be realized. That is, according to the present
invention, it is possible to realize a small-sized, highly efficient ultrasonic transducer capable of
coping with a plurality of frequencies. Furthermore, since the configuration of the laminated
piezoelectric vibrator having an impedance matching the input / output impedance of a general
communication device such as an amplifier, which is suitable for performing transmission and
reception of electrical signals, can be determined from a simple calculation formula. The design
of ultrasonic transducers such as piezoelectric vibrators is easy, general-purpose communication
devices can be used for switches and amplifiers that process electrical signals, and a compact and
economical ultrasonic transducer can be realized. .
[0048]
Example 2 In this example, highly efficient electro-mechanical conversion is performed by
adjusting the delay amount of signal lines for transmitting and receiving electric signals attached
to each piezoelectric vibrator of a multilayer laminated piezoelectric vibrator. And an example of
another configuration of an ultrasonic transducer in which the equipment such as an amplifier
and the like are optimized.
[0049]
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FIG. 3 is a block diagram showing the detailed configuration of the ultrasonic transducer 1.
In the present embodiment, the ultrasonic transducer 1 shown in the first embodiment is the one
in which the polarity of each electric signal is adjusted by the switching circuit 11, but in place of
the switching circuit 11, the ultrasonic transducer 1 is used. By providing a plurality of different
delay elements and passing each electric signal through these delay elements, the amount of
delay of each electric signal is adjusted to implement high-efficiency electro-mechanical
conversion. Specifically, in the present embodiment, four types of delay elements of 0 ° (no
delay), 90 ° (1/4 phase delay), 180 ° (antiphase delay), 270 ° (3/4 phase delay) 14 a, 14 b,
14 c and 14 d are provided in the matching circuit unit 6. Of course, the 0 ° delay element 14a
is through, and may be an unnecessary configuration. The delay elements 14a to 14d are
terminals 14a1 to 14a7 and 14b1 to 14b7 for connection to the contacts 11a to 11g, which are
terminals of the signal lines 5a to 5g on the matching circuit unit 6 side, 14c1 to 14c7 and 14d1
to 14d7 are provided, and according to each vibration mode, the contacts 11a to 11g are
connected to these terminals to transmit and receive electric signals with each piezoelectric
vibrator. And
[0050]
Of course, the number of these terminals can be increased or decreased in accordance with the
number of layers of the piezoelectric transducer and the situation in which the ultrasonic
transducer is used. The configurations of the piezoelectric vibrator, the electrodes, the amplifier,
and the like of the present embodiment are the same as those of the ultrasonic transducer shown
in the first embodiment.
[0051]
In the present embodiment, in the case of the basic vibration mode, as shown in FIG. 5A, since
the piezoelectric vibrators 1a to 1f are extended portions, as shown in FIG. 6A, Since it is
desirable that they have the same polarity, that is, it is not necessary to adjust the delay amount
for each signal, the respective contacts are the contacts 11a and 14a1, the contacts 11b and
14a2, the contacts 11c and 14a3, and the contacts 11d. The terminal 14a4, the contact 11e and
the terminal 14a5, the contact 11f and the terminal 14a6, and the contact 11g and the terminal
14a7 are connected, and all signals are connected to the delay element 14a without delay.
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[0052]
Further, in the case of the secondary vibration mode, as shown in FIG. 5B, since each of the
piezoelectric vibrators 1a to 1f has an extended portion and a contracted portion, as shown in
FIG. 6C. The respective contacts are the contacts 11a, the contacts 11b, the contacts 11c, and the
contacts 11d as the terminals 14a1 to 14a7 of the delay element 14a so that the signals at the
portions where the extension portion and the contraction portion are reversed are in phase by
delay. Further, the contact 11e, the contact 11f and the contact 11g are connected to the
terminals 14c1 to 14c7 of the delay element 14c for delaying the signal by 180 °.
[0053]
Also in the present embodiment, the amplifiers 12 and 13 are provided between the delay
elements 14a to 14d and the cable 7. However, between the delay elements 14a to 14d and the
piezoelectric vibrator 1A as in the first embodiment. It may be arranged for each piezoelectric
vibrator.
Furthermore, the matching circuit section 6 is provided with a switching mechanism for
connection between the contact of the signal line and the terminal of the delay element, and a
vibration mode notification signal is added to the control signal transmitted from the cable 7. It
can also be configured to switch from the device of.
As each delay element, since the impedance of the laminated piezoelectric vibrator 1A is adjusted
to match the impedance of the general-purpose communication device, a delay element
composed of a commercially available coil or the like was used similarly.
[0054]
FIG. 4 is also a block diagram showing a detailed configuration of another embodiment of the
ultrasonic transducer according to the present invention. In this embodiment, the ultrasonic
transducer described above selects a plurality of delay elements having fixed delays, and adjusts
the delay amount of the electric signal in the signal line connected to each piezoelectric
transducer. On the other hand, a delay element capable of setting a variable delay amount to
each signal line is provided, and the delay amount of the electric signal input / output to each
piezoelectric vibrator of the laminated piezoelectric vibrator is finely made according to each
vibration mode. It is adjusted to further improve the electromechanical conversion efficiency.
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More specifically, the amount of delay can be varied for each of the signal lines 5a to 5g instead
of the four types of delay elements 14a, 14b, 14c, and 14d in the above-described embodiment
in the matching circuit unit 6, or The variable delay elements 141 to 147 having a plurality of
input / output terminals with different delay amounts are provided, and the input / output delay
amounts are selected according to each vibration mode. Also in this embodiment, the delay
amount can be set and switched from the outside, or a commercially available variable delay
element is used as in the above-described embodiment.
[0055]
According to the ultrasonic transducer of this embodiment, the phases of the electric signals can
be adjusted more finely than in the case of switching the polarity of each electric signal in the
embodiment 1. It is possible to realize an ultrasonic transducer capable of transmitting and
receiving ultrasonic waves of a plurality of frequencies from the basic vibration mode to the highorder vibration mode with higher efficiency. In particular, an ultrasonic transducer using a
variable delay element is capable of precise phase adjustment, and is provided with a matching
layer for acoustic matching as shown in the following embodiments to produce complex
vibrations. It is effective for an ultrasonic transducer.
[0056]
Embodiment 3 In this embodiment, matching for acoustic matching is performed to facilitate the
transmission of sound waves between a transmission medium such as water or air that actually
transmits ultrasonic waves and a piezoelectric vibrator. The structure of the ultrasonic
transducer which added the layer is shown. Here, the matching layer performs acoustic matching
between the piezoelectric vibrator and the medium, and in the case of the configuration of the
ultrasonic transducer shown in FIG. 1, it is mounted between the acoustic window 4 and the
piezoelectric vibrator 1a. It is As a material of the matching layer, generally, an epoxy resin or the
like mixed with glass, a metal having a heavy specific gravity, or the like is used to change the
acoustic impedance. If such a matching layer is used, the wiring of the electrical signal becomes
only each piezoelectric vibrator portion as shown in FIG.
[0057]
Also, as in the present invention, for example, if a piezoelectric ceramic is used as a piezoelectric
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vibrator and the matching layer is made of a material in which pores are inserted in this
piezoelectric ceramic to adjust the acoustic impedance, signals from the matching layer are also
transmitted. You can wire the lines. In any case, the attachment of the matching layer
complicates the vibration state depending on the vibration mode, so the configuration of the
ultrasonic transducer according to the present invention shown in the first embodiment and the
second embodiment is the present embodiment. Become more effective.
[0058]
FIG. 8 is a main part explanatory view showing the relationship between the structure of the
laminated piezoelectric vibrator having a configuration in which the matching layer is mounted
on the piezoelectric vibrator and the vibration mode. In this example, using the same six layers
1a to 1f as the above-described example as the piezoelectric vibrator, the acoustic impedance is
adjusted by inserting pores in the same PZT ceramic as the piezoelectric vibrator, and having a
thickness of about 3 mm The matching layers M1 and M2 are mounted between the piezoelectric
vibrator 1a and the acoustic window 4. The matching layers M1 and M2 can also be used as
piezoelectric vibrators, and thus are not shown in this figure, but the matching layers M1 and M2
are similar to the ultrasonic transducer shown in FIGS. 1 to 3. The electrodes are also connected,
the signal lines connect between the electrodes and the matching circuit section, input and
output electric signals, and by electro-mechanical conversion, the matching layers M1 and M2
also transmit and receive sound waves. Configuration. The vibration states of the piezoelectric
vibrator and the matching layer in each vibration mode shown in the same figure are the results
obtained from the equivalent circuit of the Mason using the analysis method of the equivalent
circuit.
[0059]
In the case of the present embodiment, in the basic vibration mode shown in FIG. 8A, since the
matching layers and the piezoelectric vibrator vibrate in phase, the polarities of the electric
signals are wired in phase, or the same delay is applied. Just set the amount.
[0060]
Further, in the secondary vibration mode shown in FIG. 8B, although there are two nodes (●
marks) of vibration, the case of only the piezoelectric vibrator and the state of vibration as in the
above-described embodiment , And the portions of the matching layers M1 and M2 and the other
portions of the piezoelectric vibrator vibrate in opposite phases.
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Therefore, the polarity of the electric signal may be reversed in the portions of the matching
layers M1 and M2 and the portion of the piezoelectric vibrator, or any signal may be delayed by
180 °. Furthermore, by adjusting the delay amount of the variable delay elements provided in
each signal line by the amount of the position shift of the node and in the case of only the
piezoelectric vibrator and adjusting the phase of each signal, higher efficiency can be achieved.
Electro-mechanical conversion can be implemented.
[0061]
In the third vibration mode shown in FIG. 8C, there are three vibration nodes (●), and the
matching layer M2, the portions 1a and 1b of the piezoelectric vibrator, and the other portions,
the matching layer M1. The piezoelectric vibrators 1c to 1f vibrate in opposite phases. Therefore,
the polarities of the electric signals of the matching layer M2 and the portions 1a and 1b of the
piezoelectric vibrator and the electric signals of the matching layer M1 and the piezoelectric
vibrators 1c to 1f are wired in opposite directions, or any signal is delayed by 180 °. You should
do it. Furthermore, as in the secondary vibration mode, the phase of each signal is adjusted by
adjusting the delay amount of the variable delay element provided for each signal line by the
amount of deviation of the node position and in the case of only the piezoelectric vibrator. To
achieve more efficient electro-mechanical conversion.
[0062]
As in the present invention, for example, a piezoelectric material made of a piezoelectric ceramic
such as lead zirconate titanate is used as a piezoelectric vibrator, and an acoustic impedance in
which pores are inserted in such a piezoelectric ceramic as a matching layer is adjusted. If
materials are used, signal lines can also be wired from the matching layer, and furthermore, by
mounting the matching layer, the polarity and delay amount of the electrical signal can be
adjusted even if the vibration state becomes complicated. Therefore, an ultrasonic transducer
with high efficiency of electro-mechanical conversion can be realized.
[0063]
<Embodiment 4> In the above-described embodiments, although the configuration in which
rectangular piezoelectric vibrators are stacked in multiple layers is used as the piezoelectric
vibrator, the polarity of the electric signal transmitted / received to / from each piezoelectric
vibrator according to the present invention is used. In a compact ultrasonic transducer that
transmits and receives ultrasonic waves of multiple frequencies from basic vibration mode to
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high-order vibration mode with high efficiency, the configuration of the piezoelectric vibrator is
The invention is not limited to the rectangular piezoelectric vibrator.
[0064]
FIG. 9 is a block diagram showing the configuration of another embodiment of the ultrasonic
transducer according to the present invention.
In the present embodiment, cylindrical piezoelectric vibrators 15 are stacked in multiple layers,
and signal lines are output from each vibrator.
In the case of the cylindrical piezoelectric vibrator 15, since vibration modes in the cylinder and
height direction are also generated, as shown in the figure, the piezoelectric vibrator can be used
so that only the vibration mode in the thickness direction can be used. An ultrasonic transducer
was configured by inserting fine slits 15 a into 15.
[0065]
As described above, the present invention has achieved the intended purpose. That is, it is
possible to easily configure a multilayer laminated piezoelectric vibrator having an impedance
matching the input / output impedance of a general-purpose communication device, switch the
polarity of each electrical signal input / output to this piezoelectric vibrator, or Only by
adjustment, if one multi-layer piezoelectric vibrator is provided, high ultrasonic transmission and
reception with high electro-mechanical conversion can transmit and receive ultrasonic waves of
multiple frequencies from basic vibration mode to high-order vibration mode. A wave can be
realized. Furthermore, a general-purpose communication device can be used for a switch, an
amplifier, etc. which processes an electric signal, and a small and economical ultrasonic
transducer can be realized.
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