Patent Description:
A SONAR (sound navigation and ranging) is a technique that utilizes sound propagation to navigate, measure distances, and communicate with or detect objects on or under the surface of the water, such as other vessels. The sonar contains a transmitter for transmitting ultrasonic waves underwater. Further, the transmitter drives a transducer based on a transmission signal to transmit the ultrasonic waves underwater. Since an impedance of the transducer is high, it is necessary to apply the transmission signal with a high voltage to the transducer at the time of transmission. Conventionally, a transformer has been used as a means for amplifying voltage. However, since a transformer is large in size, the sonar device becomes large.

Currently, a method has been implemented for amplifying a voltage without using a transformer, instead, uses a matching circuit. In this method, the impedance at a resonance frequency can be lowered by matching the resonance frequency of the transducer connected to the matching circuit with the resonance frequency of the transducer itself. Thus, the voltage can be effectively amplified in a vicinity of the resonance frequency, and a high voltage can be applied to the transducer. <CIT> discloses a drive circuit having the above-described configuration.

However, in the above configuration, since there is only one resonance frequency of the impedance, a band in which the transmission power of the transducer is stable is limited to a narrow band near the resonance frequency. On the other hand, the sonar should be able to transmit ultrasonic waves in as wide the band as possible. For example, when there is another ship in the vicinity of the own ship, it is preferable that the ultrasonic wave can be transmitted at a frequency different from a transmission frequency of the sonar installed in the other ship, in order to avoid interference. When the sonar transmits a wave based on a chirp signal, it is necessary to shift the transmission frequency of the ultrasonic wave by a shift amount.

However, in the above configuration, since the band in which the transmission power of the transducer is stable, is narrow, it is difficult to respond to these requests. Therefore, there is a need for an improved apparatus and method for the amplifier circuit to be used in the sonar.

An objective of the present disclosure is to provide an amplifier circuit capable of effectively expanding a band in which transmission power of a transducer is stable, and a sonar provided with the amplifier circuit.

<CIT> discloses an ultrasonic piezoelectric transducer is alternatingly operated in a transmitting mode and in a receiving mode. In the transmitting mode an electrical excitation signal is applied between one or more common electrodes and one or more transmission electrodes, and in the receiving mode an electrical reception signal is collected between the one or more common electrodes and one or more reception electrodes. Moreover, in the receiving mode one or more electrodes which are not used as reception electrodes are connected via a low impedance connection with the one or more common electrodes which has the effect that in the receiving mode the resonance frequencies of the piezoelectric transducer are shifted to lower values so that with the same operating frequency the piezoelectric transducer is in series resonance in the transmitting mode and in parallel resonance in the receiving mode. In this way, the piezoelectric transducer operates under optimum conditions with perfect frequency matching both for transmission and for reception.

<CIT> discloses an active SONAR system comprising a transmitter, a transducer and an impedance matching circuit for expanding bandwidth and increasing a power factor value in sound and ultrasonic wave bands by mutually matching resonant frequencies of the transducer and the impedance matching circuit or a resonant frequency between the transducer and the impedance matching circuit using an electrical equivalent model corresponding to actual impedance data of the transducer and controlling the positions and the intervals of the frequencies at which reactance components of the transducer including the impedance matching circuit become zero. This allows for efficient driving in a broadband between the transmitter and the transducer in the active SONAR system, contributing to output power performance and detection performance of the active SONAR system.

<CIT> discloses an ultrasonic device with a resonant circuit that is coupled to an ultrasonic transducer. An alignment unit is configured for tuning the resonant frequency of the resonant circuit. A control and reception unit is configured for controlling the switching resonant circuit for the transmission and reception of ultrasonic waves by the ultrasonic transducer. The alignment unit with a controllable switch is configured for electrically connecting the adjustment devices in the form of balancing resistors to the resonant circuit.

<CIT> discloses a transducer comprising a vibrator body for generating and/or receiving acoustic or ultrasonic waves, acoustically coupled to a second part for generating and/or receiving acoustic or ultrasonic waves and, a matching layer coupled to said vibrator body so as, in use, to acoustically match the vibrator body to a medium contacting said matching layer.

According to the present invention there is provided an amplifier circuit to be used in a sonar as defined in claim <NUM>.

Preferred features of the invention are recited in the dependent claims.

In accordance with an example embodiment, a first aspect of the present disclosure relates to the amplifier circuit to be used in the sonar. The amplifier circuit of the present aspect includes a transducer and a matching circuit. The transducer has an impedance characteristic having a resonance frequency and an anti-resonance frequency higher than the resonance frequency. The matching circuit is connected to the transducer. Further, the impedance characteristic of the transducer connected to the matching circuit includes a first resonance frequency and a second resonance frequency higher than the first resonance frequency.

Further, since the impedance characteristic of the transducer connected to the matching circuit includes the first resonance frequency and the second resonance frequency, the transmission power of the transducer can be stabilized in the vicinity of the band over these resonance frequencies. Thus, the band in which the transmission power of the transducer can be stabilized, can be effectively expanded.

In the amplifier circuit, according to the present aspect, the second resonance frequency of the transducer connected to the matching circuit may be adjusted higher than the anti-resonance frequency of the transducer. Further, since the second resonance frequency is higher than the anti-resonance frequency of the transducer, the band, in which the transmission power of the transducer is stabilized, is expanded to a high frequency side. In the amplifier circuit, according to the present aspect, the first resonance frequency of the transducer connected to the matching circuit may be adjusted lower than the resonance frequency of the transducer. Further, since the first resonance frequency is lower than the resonance frequency of the transducer, the band, in which the transmission power of the transducer is stabilized, is expanded to a low frequency side.

In the amplifier circuit, according to the present aspect, the resonance frequency and the anti-resonance frequency of the transducer may be adjusted to be between the first resonance frequency and the second resonance frequency of the transducer connected to the matching circuit. Further, since the first resonance frequency and the second resonance frequency are outside the resonance frequency and the anti-resonance frequency of the transducer, respectively, the band in which the transmission power of the transducer is stabilized can be expanded to both the low frequency side and the high frequency side.

In the amplifier circuit, according to the present aspect, the impedance characteristic of the transducer connected to the matching circuit, includes a first anti-resonance frequency between the first resonance frequency and the second resonance frequency. The first anti-resonance frequency of the transducer connected to the matching circuit may be adjusted lower than the anti-resonance frequency of the transducer. Further, an impedance of the transducer connected to the matching circuit at the first anti-resonance frequency may be adjusted lower than the impedance characteristic of the transducer in a range between the first and second resonance frequencies.

Generally, the impedance at the first resonance frequency and the second resonance frequency is lower than the impedance at the first anti-resonance frequency. Therefore, as described above, by adjusting the impedance at the first anti-resonance frequency lower than the impedance of the transducer, the impedance of the transducer connected to the matching circuit is made lower than the impedance of the transducer itself in the vicinity of the band straddling the first resonance frequency and the second resonance frequency, and the transmission power of the transducer can be enhanced.

In the amplifier circuit, according to the present aspect, the impedance characteristic of the transducer may have one resonance frequency and one anti-resonance frequency. The impedance characteristic of the transducer connected to the matching circuit may have two resonance frequencies. Further, the impedance of the transducer connected to the matching circuit is lowered from the impedance of the transducer itself in the vicinity of the band across the two resonance frequencies, and the transmission power of the transducer can be enhanced.

In the amplifier circuit, according to the present aspect, the transducer may be fixed to a matching layer, and the impedance characteristic of the transducer fixed to the matching layer may have a plurality of anti-resonance frequencies. In this configuration, the second resonance frequency of the transducer fixed to the matching layer and connected to the matching circuit may be adjusted higher than an average of the plurality of anti-resonance frequencies of the transducer fixed to the matching layer. The impedance of the transducer fixed to the matching layer and connected to the matching circuit can be stabilized in the vicinity of the band across the first resonance frequency and the second resonance frequency, and the transmission power of the transducer is stabilized in the vicinity of this band. Thus, the band for stabilizing the transmission power of the transducer is effectively expanded.

In the amplifier circuit, according to the present aspect, the matching circuit includes a capacitive component and an inductor. The capacitive component is connected in parallel with the transducer, and the inductor is connected in series with the parallel connection. Further, the impedance characteristic of the transducer connected to the matching circuit is further adjusted to have the first anti-resonance frequency between the first resonance frequency and the second resonance frequency. The first anti-resonance frequency may be defined based at least in part on a capacitance of the capacitive component.

In the amplifier circuit, according to the present aspect, the first resonance frequency and the second resonance frequency of the transducer connected to the matching circuit may be defined based at least in part on the capacitance of the capacitive component or an inductance of the inductor. Therefore, by adjusting values of the inductor and the capacitive component constituting the matching circuit, the first resonance frequency and the second resonance frequency can be set to desired values, and the band in which the transmission power of the transducer is stabilized is set to a desired band.

In the amplifier circuit, according to the present aspect, the matching circuit may exclude a transformer. Further, since the amplifier circuit does not include the transformer, the amplifier circuit can be miniaturized.

In accordance with another example embodiment, the sonar for transmitting ultrasonic waves into water, generated from the transducer is described. The sonar includes the amplifier circuit according to the first aspect of the disclosure. Therefore, the band in which the transmission power of the transducer connected to the matching circuit is stable, can be expanded. Thus, the ultrasonic wave is transmitted from the transducer more stably in a wide band. Further, according to the present disclosure, it is possible to provide the amplifier circuit and the sonar capable of effectively expanding the band in which transmission power of the transducer is stable.

The effect or significance of the present disclosure will be further clarified by the following description of the embodiments. However, the embodiments shown below are only examples for implementing the present disclosure, and the present disclosure is not limited in any way to the embodiments described below.

Some embodiments of this disclosure, illustrating its features, will now be discussed in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to the listed item or items.

It should also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any apparatus and method similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the apparatus and methods are now described.

Embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings in which like numerals represent like elements throughout the several figures, and in which example embodiments are shown. Embodiments of the claims may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The examples set forth herein are non-limiting examples and are merely examples among other possible examples.

Embodiments of the present disclosure will be described below with reference to the drawings. For convenience, XYZ axes orthogonal to each other are appropriately appended to the drawings. An X-axis direction and a Y-axis direction are horizontal, and a Z-axis direction is vertical. The positive Y-axis direction is the direction in which a ship travels.

<FIG> is a diagram schematically illustrating a state in which a sonar <NUM> searches underwater, according to an embodiment of the present disclosure. In <FIG>, θ is an azimuth angle around a transducer assembly <NUM> installed on a bottom of a ship S1, and φ is a depression angle from a horizontal plane (X-Y plane). In one embodiment, the sonar <NUM> may include the transducer assembly <NUM> installed on the bottom of the ship S1. Further, ultrasonic waves may be transmitted from the transducer assembly <NUM> to a semi-spherical transmission space TS1 and resulting reflected waves may be received by the transducer assembly <NUM>. Further, the transducer assembly <NUM> may include a plurality of transducers for transmitting and receiving ultrasonic waves. The transducers may be arranged, for example, in a hemispherical or cylindrical shape. A reception signal corresponding to an intensity (echo intensity) of the reflected wave received by each transducer is generated for each transducer. It can be noted that the sonar <NUM> may form a plurality of reception beams RB1 distributed in the azimuth angle θ direction and the depression angle φ direction by beamforming the reception signals.

In one embodiment, the sonar <NUM> may generate the plurality of reception beams RB1 in fan-shaped reception spaces RS1 extending in the depression angle φ direction. Further, the plurality of reception beams RB1 may be formed in each reception space RS1 with a predetermined resolution in the depression angle φ direction. The reception spaces RS1 may be set at a predetermined pitch over the entire circumference in the azimuth angle θ direction. Further, an actual pitch of the reception spaces RS1 may be smaller than the pitch illustrated in <FIG>. It can be noted that a spread angle of the reception spaces RS1 in the depression angle φ direction is, for example, <NUM> degrees.

In one embodiment, the sonar <NUM> may acquire the echo intensity with a given distance resolution for each reception beam RB1 formed in the reception spaces RS1. Thus, the echo intensity is acquired at the given distance resolution for each depression angle of each reception beam RB1. The sonar <NUM> may integrate the echo intensity of each depression angle and each distance acquired for each reception space RS1 with respect to all the reception spaces RS1. It can be noted that, such use of the sonar <NUM> may facilitate acquiring an echo signal in which the echo intensity is three-dimensionally distributed in the transmission space TS1.

The sonar <NUM> may display an echo image showing a three-dimensional distribution of echo intensity on a display module by using the acquired echo signal. Each three-dimensional position on the echo image is coloured according to the echo intensity. For example, a position of a fish school F1 on the echo image is assigned a colour (for example, red) associated with a high echo intensity. Further, a user can grasp targets such as the fish school F1 by referring to the colour distribution on the echo image.

<FIG> is a block diagram illustrating a configuration of the sonar <NUM>, according to a present embodiment of the present disclosure. In one embodiment, the sonar <NUM> may include a control module <NUM>, a storage module <NUM>, the transducer assembly <NUM>, a transmission processing module <NUM>, a reception processing module <NUM>, a display module <NUM>, a display processing module <NUM>, an operation module <NUM>, and an operation processing module <NUM>. The transducer assembly <NUM> may be installed in the bottom of the ship S1 as described above, and other components such as the control module <NUM> may be installed in a wheelhouse of the ship S1.

Further, the control module <NUM> may be provided with an arithmetic processing circuit such as a CPU (Central Processing Unit) that executes control processing according to a program stored in the storage module <NUM>. The storage module <NUM> may include a storage medium such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk. The storage module <NUM> stores the program for the control module <NUM> to execute the control processing.

In one embodiment, the transducer assembly <NUM> may include one or more transducers <NUM>. Further, the one or more transducers <NUM> may be arranged in a hemispherical or cylindrical shape. Each transducer <NUM> may transmit ultrasonic waves to the transmission space TS1 in <FIG> for each processing step (ping) of transmitting and receiving waves and receive the reflected waves. The transducer assembly <NUM> may include an amplifier circuit <NUM> as a configuration for transmitting waves. The amplifier circuit <NUM> may amplify a voltage of a transmission signal and supply it to the transducer <NUM>.

In accordance with the control from the control module <NUM>, the transmission processing module <NUM> outputs the transmission signal to the transducer assembly <NUM> for transmitting ultrasonic waves. The reception processing module <NUM> may generate the reception signal by processing a signal outputted by each transducer of the transducer assembly <NUM> that receives the reflected wave, and outputs the generated reception signal to the control module <NUM>.

Further, the control module <NUM> may form the plurality of reception beams distributed in the azimuth angle θ direction and the depression angle φ direction by beamforming the reception signals acquired from the respective transducers. The control module <NUM> may acquire echo signals in the directions of the respective reception beams (the directions of the given azimuth angles θ and depression angles φ). The echo signal acquired for each reception beam is the signal indicating the echo intensity that changes according to the elapsed time from a transmission timing of the ultrasonic wave.

In one embodiment, the elapsed time from the transmission timing may correspond to a distance from the transducer assembly <NUM> in the direction of each reception beam. Further, the control module <NUM> may acquire the echo intensity of each distance position in the direction of each reception beam from the echo signal of each reception beam by associating the elapsed time from the transmission timing with the distance. The echo intensity may be acquired with a given distance resolution.

In one embodiment, the display module <NUM> includes a display device such as a liquid crystal display. The display processing module <NUM> may cause the display module <NUM> to display the echo image in response to the control from the control module <NUM>. The operation module <NUM> may be provided with an input means such as an operation key or a mouse. The operation processing module <NUM> may output a signal corresponding to an operation on the operation module <NUM> to the control module <NUM>. The user may, for example, change a viewpoint of the echo image by operating the operation module <NUM>. Further, the display module <NUM> and the operation module <NUM> may be constituted by a liquid crystal panel in which a touch panel is superimposed on the liquid crystal display.

<FIG> is a diagram illustrating a configuration of the amplifier circuit <NUM> in <FIG>, according to an embodiment of the present disclosure. In one embodiment, <FIG> illustrates a configuration for driving one transducer <NUM>. The same configuration in <FIG> may be provided for each of the one or more transducers <NUM>. The amplifier circuit <NUM> may include the transducer <NUM>, a matching circuit <NUM>, and a transmission amplifier <NUM>.

In one embodiment, the transducer <NUM> may include a piezoelectric element. Further, the transducer <NUM> may output ultrasonic waves when the voltage corresponding to the transmission signal is applied thereto. Further, the matching circuit <NUM> may include a capacitive component CL and an inductor LL. The capacitive component CL may be connected in parallel with the transducer <NUM>. Further, the inductor LL may be connected in series to the parallel connection of the capacitive component CL and the transducer <NUM>. The capacitive component CL may be a capacitor or other component (for example, cables, etc.) as long as it has the capacitance of a given value. The transmission amplifier <NUM> may amplify positively and negatively the voltage at a frequency corresponding to the transmission signal and output it at terminal T1. Terminal T2 is connected to the ground.

<FIG> is a diagram illustrating an equivalent circuit of the transducer <NUM>, according to an embodiment of the present disclosure. The equivalent circuit of the transducer <NUM> may be represented by a circuit in which a capacitor C1, an inductor L1, and a resistor R1 are connected in series, and a capacitor C0 is connected in parallel to the series connection. In the configuration illustrated in <FIG>, for example, by matching a resonance frequency of the transducer <NUM> connected to the matching circuit <NUM> with the resonance frequency of the equivalent circuit of the transducer <NUM> illustrated in <FIG>, an impedance at the resonance frequency can be effectively reduced. Thus, the voltage supplied to the transducer <NUM> can be increased, and transmission power can be effectively increased. It can be noted that, the configuration may be referred to as a "comparative example", hereinafter.

<FIG> is a graph illustrating impedance characteristics at transmission according to the comparative example. The upper graph of <FIG> illustrates an example of impedance characteristic of the equivalent circuit of the transducer <NUM> of <FIG>. The lower graph of <FIG> illustrates an example of impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM>.

Further, as illustrated in the upper graph of <FIG>, the impedance characteristic of the equivalent circuit of the transducer <NUM> has a resonance point P01 and an anti-resonance point P02. A resonance point is a local minimum in the impedance characteristic, whereas an anti-resonance point is a local maximum in the impedance characteristic. As there is a local minimum in the impedance at the resonance point, the transducer has a good ability of transmitting high power ultrasonic wave into water. On the other hand, at the anti-resonance point, as there is a local maximum in the impedance, the transducer has a low ability of transmitting ultrasonic wave. For example, with the same voltage applied to the transducer at the resonance point and at the anti-resonance point, ultrasonic waves with less power would be transmitted into the water at the anti-resonance point than at the resonance point. Moreover, the anti-resonance point is a characteristic of the transducer that indicates the frequency at which the transducer is optimum to receive ultrasonic wave at the best sensitivity. The frequency at the resonance point P01, that is, the resonance frequency is the frequency when the value obtained by multiplying a capacitance of the capacitor C1 and an inductance of the inductor L1 in the equivalent circuit of <FIG> is <NUM>. Therefore, the equivalent circuit of the transducer <NUM> at the resonance point is represented by the circuit of <FIG>.

In the comparative example, as illustrated in the lower part of <FIG>, values of the inductor LL and the capacitive component CL of the matching circuit <NUM> may be adjusted so that the resonance frequency (resonance point P11) of the transducer <NUM> connected to the matching circuit <NUM> matches the resonance frequency (resonance point P01) of the equivalent circuit of the transducer <NUM>. In one example embodiment, the value (i.e., capacitance) CL of component CL is set to about <NUM> times or more of value C<NUM> of the capacitor C0 in <FIG>, and value (i.e., inductance) LL of the inductor LL is set to satisfy ω<NUM> × LL × CL = <NUM> at the resonance frequency so that a circuit characteristic of the matching circuit <NUM> does not collapse due to interference with the transducer <NUM>.

It can be noted that, as shown in the lower part of <FIG>, the impedance of the transducer <NUM> connected to the matching circuit <NUM> at the resonance point P11 may be effectively lowered from the impedance of the transducer <NUM> in the upper part of <FIG>. Therefore, by setting the frequency of the transmission signal near the resonance point P11, the transmission power of the transducer <NUM> may be effectively increased.

Further, in the configuration of the comparative example, since only one resonance point P11 exists in the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM>, the band in which the transmission power of the transducer <NUM> is stable becomes considerably narrow as described later. Therefore, in the present embodiment, the values of the inductor LL and the capacitive component CL of the matching circuit <NUM> may be adjusted so that the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> has two resonance points (resonance frequencies).

<FIG> is a graph illustrating the impedance characteristics at transmission, according to an embodiment of the invention as claimed. In <FIG>, the impedance characteristics according to the embodiment is illustrated. In the upper and lower parts of <FIG>, the impedance characteristics of the transducer <NUM> and the comparative example illustrated in <FIG> are illustrated for comparison.

As illustrated in the middle of <FIG>, the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> has two resonance points P21 and P22, and one anti-resonance point P23. The resonance frequency at a resonance point P22 may be higher than the anti-resonance frequency at the anti-resonance point P02 of the transducer <NUM>. The resonance frequency at a resonance point P21 may be lower than the resonance frequency at the resonance point P01 of the transducer <NUM>. Therefore, the resonance point P01 (resonance frequency) and the anti-resonance point P02 (anti-resonance frequency) of the transducer <NUM> illustrated in the upper part are located between the resonance points P21 and P22 (resonance frequencies).

In the embodiment, the values of the inductor LL and the capacitive component CL of the matching circuit <NUM> are adjusted so that the two resonance points P21 and P22 satisfy the above conditions with respect to the resonance point P01 and the anti-resonance point P02 of the transducer <NUM>. The resonance frequencies and the anti-resonance frequency of the transducer <NUM> connected to the matching circuit <NUM> may be calculated from the following equations. <MAT> <MAT>.

In the equations (<NUM>) and (<NUM>), LL and CL are the values of the inductor LL and the capacitive component CL in the matching circuit <NUM> illustrated in <FIG>, respectively, and L<NUM>, C<NUM> and C<NUM> are the values of the inductor L1 and the capacitors C0 and C1 in the equivalent circuit illustrated in <FIG>, respectively. The resonance frequencies and the anti-resonance frequency are calculated as the value of f when expression ω=2πf is substituted into the above expressions (<NUM>) and (<NUM>).

It is to be noted that instead of using equations (<NUM>) and (<NUM>) above to calculate the values of the inductor LL and the capacitive component CL, the following calculation can also be performed. In equation (<NUM>), by setting CL to a value, the anti-resonance frequency ω of equation (<NUM>) can be calculated. Once ω is calculated, ω, the values R<NUM>, L<NUM>, C<NUM> and C<NUM> in the equivalent circuit, and the value CL of the capacitor CL can be substituted into the following equation to calculate the value LL of the inductor LL.

In an example embodiment, the value of the capacitive component CL is set to approximately twice the value of the capacitor C0 of <FIG>. The value of the inductor LL is calculated from the above equations (<NUM>) and (<NUM>) so that the two resonance points P21 and P22 (resonance frequencies) and the anti-resonance point P23 (anti-resonance frequency) satisfy the relationship illustrated in <FIG>.

In one embodiment, the values LL and CL of the inductor LL and the capacitive component CL in the matching circuit <NUM> may be adjusted so that the impedance of the transducer <NUM> connected to the matching circuit <NUM> becomes substantially the same value at the two resonance points P21 and P22. Thus, a fluctuation range of impedance between the resonance points P21 and P22 and the anti-resonance point P23 can be suppressed, and as described later, a frequency band at which the transmission power of the transducer <NUM> is stable can be widened.

As illustrated in <FIG>, in the configuration of the embodiment, when the matching circuit <NUM> is connected to the transducer <NUM>, the resonance point P01 of the transducer <NUM> before the connection shifts to the resonance point P21 on the low-frequency side after the connection, and in the vicinity of the frequency that was the resonance point P01 in the transducer <NUM> before the connection, not a resonance point but the anti-resonance point P23 appears. Further, an anti-resonance point may be unsuitable for transmitting high power because of its high impedance characteristic. However, since this anti-resonance point P23 is generated by the influence of the resonance points P21 and P22 generated by interference between the electrical resonance point originally possessed by the transducer <NUM> and the matching circuit <NUM>, the impedance of the anti-resonance point P23 becomes lower than the impedance of the transducer <NUM> itself. It is to be noted that when calculating the values CL and LL of the capacitive component CL and the inductor LL by solving the equations (<NUM>) and (<NUM>), or (<NUM>) and (<NUM>) above, the impedance at the resonance points P21, P22 is the same. However, having the same impedance at P21, P22 may not be a critical issue. If that is not an issue, it is possible to allow the values CL and LL to deviate from the calculated values. For example, the inventor has realized that even if the values CL and LL deviate +-<NUM>% from the calculated values, the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> (middle graph of <FIG>) still has the two resonance points P21, P22 and the anti-resonance point P23, but the impedance at P21 and P22 are different. Therefore, the values CL and LL of the capacitive component CL and the inductor LL of the present disclosure do not have to strictly respect above equations (<NUM>), (<NUM>) and (<NUM>). Furthermore, the skilled person will appreciate that the values CL and LL of the capacitive component CL and the inductor LL could be obtained in other ways, such as empirically or through trial and error.

In one embodiment, comparing the graphs in the middle and lower parts of <FIG>, compared to the matching circuit of the comparative example which is designed to have one resonance point, with the matching circuit <NUM> of the embodiment, the minimum impedance is higher. However, in the configuration of the embodiment, since the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> has two resonance points P21 and P22 (resonance frequencies), a bandwidth in which the transmission power of the transducer <NUM> is stable can be expanded compared with the case where there is only one resonance point P11 (resonance frequency) as in the comparative example, and a stable transmission of ultrasonic waves in a wide band is possible. This will be described below.

<FIG> is a graph illustrating the phase characteristics of the transducer <NUM> connected to the matching circuit <NUM> according to the embodiment and according to the comparative example. As illustrated in <FIG>, in the configuration of the comparative example, the phase of the transducer <NUM> connected to the matching circuit <NUM> rapidly inverts to a negative value in the vicinity of the resonance frequency (here, <NUM>) of the resonance point P11.

In one embodiment, in the configuration of the embodiment, the phase of the transducer <NUM> connected to the matching circuit <NUM> may have a small positive and negative amplitude around the anti-resonance frequency (in this case, a frequency slightly higher than <NUM>) of the anti-resonance point P23 and may then converge to a negative value. The frequencies of the positive and negative peak positions in this amplitude correspond to the resonance frequencies of the resonance points P21 and P22 in <FIG>.

Assuming that the phase of the transducer <NUM> connected to the matching circuit <NUM> is θ, the transmission power of the transducer <NUM> may be calculated by the following equation: <MAT> wherein V is a value of the voltage supplied from the terminal T1 of <FIG> to the matching circuit <NUM>, and Z is the impedance of the transducer <NUM> connected to the matching circuit <NUM>.

<FIG> is a graph illustrating the transmission power of the transducer <NUM> in the configuration of the embodiment and the comparative example. <FIG> is an enlarged view of a frequency band near the centre of <FIG> and <FIG> illustrate graphs illustrating the transmission power of the transducer <NUM> in the configuration of the embodiment and the comparative example, and a graph (dotted line) illustrating the impedance characteristic of the transducer <NUM> as in <FIG> and <FIG>.

As illustrated in <FIG>, in the comparative example, the transmission power of the transducer <NUM> rapidly increases in the vicinity of the resonance point P01 (resonance frequency) of the transducer <NUM>. In one embodiment, the change of the transmission power near the resonance point P01 may be gradual as compared with the comparative example. This is because, as illustrated in <FIG>, the phase change in the embodiment is smaller than that in the comparative example, and therefore the transmission power is more controlled with the phase parameter θ of equation (<NUM>), compared with the comparative example.

Referring to <FIG>, it can be seen that in the embodiment, the change of the transmission power when moving away from a centre frequency may be significantly suppressed compared to the comparative example. For example, using the definition of a general band-pass filter, when a bandwidth of the frequency in which the transmission power varies by <NUM> dB from the value of the centre frequency is compared, in the configuration of the comparative example, a <NUM> ~ <NUM> band W1 is in the variation range of <NUM> dB, while in the configuration of the embodiment, a <NUM> ~ <NUM> band W2 is in the variation range of <NUM> dB. Therefore, in the configuration of the embodiment, the band that can be stably transmitted can be remarkably expanded as compared with the configuration of the comparative example. Thus, in the configuration of the embodiment, ultrasonic waves can be transmitted more stably.

As illustrated in <FIG>, the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> has the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency) higher than the resonance point P21 (first resonance frequency). As a result, as illustrated in <FIG>, the transmission power of the transducer <NUM> can be stabilized in the vicinity of the band W2 across the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency). Thus, the band in which the transmission power of the transducer <NUM> can be stabilized can be effectively expanded.

Further, as illustrated in <FIG>, the resonance point P22 (second resonance frequency) of the transducer <NUM> connected to the matching circuit <NUM> may be higher than the anti-resonance point P02 (anti-resonance frequency) of the transducer <NUM>. Thus, as illustrated in <FIG>, the band in which the transmission power of the transducer <NUM> is stabilized can be expanded to the high-frequency side. It can be noted that, the resonance point P21 (first resonance frequency) of the transducer <NUM> connected to the matching circuit <NUM> may be lower than the resonance point P01 (resonance frequency) of the transducer <NUM>. Thus, as illustrated in <FIG>, the band in which the transmission power of the transducer <NUM> is stabilized can be expanded to the low-frequency side.

In one embodiment, as illustrated in <FIG>, the resonance point P01 (resonance frequency) and the anti-resonance point P02 (anti-resonance frequency) of the transducer <NUM> may be located between the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency) of the transducer <NUM> connected to the matching circuit <NUM>. In other words, the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency) may be located outside the resonance point P01 (resonance frequency) and the anti-resonance point P02 (anti-resonance frequency) of the transducer <NUM>, respectively. Further, as illustrated in <FIG>, the band in which the transmission power of the transducer <NUM> is stabilized can be expanded to both the low-frequency side and the high-frequency side.

In another embodiment, as illustrated in <FIG>, the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> may further have the anti-resonance point P23 (first anti-resonance frequency) between the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency), and the anti-resonance point P23 (first anti-resonance frequency) of the transducer <NUM> connected to the matching circuit <NUM> may be lower than the anti-resonance point P02 (anti-resonance frequency) of the transducer <NUM>.

In yet another embodiment, as illustrated in <FIG>, the impedance of the transducer <NUM> connected to the matching circuit <NUM> at the anti-resonance point P23 (first anti-resonance frequency) may be lower than the impedance characteristic of the transducer <NUM> in a range between the resonance points P21 and P22 (first and second resonance frequencies). Further, the impedance of the transducer <NUM> connected to the matching circuit <NUM> can be made lower than the impedance of the transducer <NUM> itself in the vicinity of the band W2 across the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency), and the transmission power of the transducer can be enhanced.

In yet another embodiment, as illustrated in <FIG>, the impedance characteristic of the transducer <NUM> may have exactly one resonance point P01 (resonance frequency) and exactly one anti-resonance point P02 (anti-resonance frequency), and the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> may have exactly two resonance points P21 and P22 (resonance frequencies). Further, the impedance of the transducer <NUM> connected to the matching circuit <NUM> can be lowered from the impedance of the transducer <NUM> itself in the vicinity of the band across the two resonance points P21 and P22 (resonance frequencies), and the transmission power of the transducer can be enhanced.

Further, as discussed above and illustrated in <FIG>, the matching circuit <NUM> may include the capacitive component CL and the inductor LL, the capacitive component CL may be connected in parallel with the transducer <NUM>, and the inductor LL may be connected in series with the parallel connection. In one embodiment, the impedance characteristic of the transducer <NUM> connected to the matching circuit <NUM> may be adjusted to further have the anti-resonance point P23 (first anti-resonance frequency) between the resonance point P21 (first resonance frequency) and the resonance point P22 (second resonance frequency), as illustrated in <FIG>. Here, the anti-resonance frequency (first anti-resonance frequency) at the anti-resonance point P23 may be determined by the above equation (<NUM>) based at least in part on the capacitance CL of the capacitive component CL.

Further, the resonance frequency (first resonance frequency) at the resonance point P21 and the resonance frequency (second resonance frequency) at the resonance point P22 of the transducer <NUM> connected to the matching circuit <NUM> may be determined by the above equation (<NUM>) based at least in part on the capacitance CL of the capacitive component CL or the inductance LL of the inductor LL.

Therefore, by adjusting the values of the inductor LL and the capacitive component CL constituting the matching circuit <NUM>, the first resonance frequency and the second resonance frequency can be set to desired values, and the band in which the transmission power of the transducer is stabilized can be set to the desired band.

It can be noted that as illustrated in <FIG>, the matching circuit <NUM> may not include a transformer. Thus, the amplifier circuit <NUM> can be miniaturized. Further, as illustrated in <FIG>, the sonar <NUM> may include the amplifier circuit <NUM> of <FIG>. Therefore, the amplifier circuit <NUM> can form a stable band with a small impedance change while reducing the impedance of the transducer <NUM> connected to the matching circuit <NUM> as described above. Thus, the ultrasonic wave can be transmitted from the transducer <NUM> more stably in a wide band.

In the above embodiment, as illustrated in <FIG>, the impedance characteristic of the transducer <NUM> has one resonance frequency (resonance point P01) and one anti-resonance frequency (anti-resonance point P02). On the other hand, in another embodiment, the transducer <NUM> is fixed to a matching layer, and the impedance characteristic of the transducer <NUM> fixed to the matching layer has a plurality of anti-resonance frequencies. That is, in another embodiment, a so-called transducer with a matching layer is used.

<FIG> is a diagram illustrating an example of a configuration of the transducer <NUM> with the matching layer. The transducer <NUM> may include a piezoelectric element 101a, an upper electrode 101b, and a lower electrode 101c. The piezoelectric element 101a may have a cuboid shape. The shape of the piezoelectric element 101a may not be limited to the cuboid, but may be any other shape such as a cube. A matching layer <NUM> may be fixed to one side surface of the piezoelectric element 101a by an adhesive or the like. A voltage inverting positive and negative at a given frequency may be applied to the upper electrode 101b via the terminal T1 of the transmission amplifier <NUM> illustrated in <FIG>, and the lower electrode 101c may be connected to the ground. Thus, ultrasonic waves are outputted from a side surface of the matching layer <NUM>.

Further, the configuration of the transducer <NUM> with the matching layer may not be limited to the configuration of <FIG>, but may be another configuration. The transducer <NUM> in one embodiment has the configuration in which the matching layer <NUM> is removed from the configuration in <FIG>.

<FIG> is a diagram illustrating an equivalent circuit of the transducer <NUM> with the matching layer illustrated in <FIG>. In the equivalent circuit of <FIG>, as compared with <FIG>, a capacitor C2, an inductor L2, and a resistor R2 corresponding to the matching layer <NUM> are further connected in parallel to the capacitor C0. When the matching layer <NUM> comprising a plurality of layers is fixed to the transducer <NUM>, the equivalent circuit has the configuration illustrated in <FIG>.

<FIG> is a graph illustrating impedance characteristics according to another embodiment. In <FIG>, an assumed size of the transducer <NUM> is different from that in <FIG>, and therefore frequency range of the horizontal axis is different from that in <FIG>. The impedance characteristic illustrated in <FIG> is an example and may vary depending on the size of the transducer <NUM>, the structure of the matching layer <NUM>, and the like.

The upper part of <FIG> may illustrate the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM>. As described above, in another embodiment, since the transducer <NUM> is fixed to the matching layer <NUM>, from the equivalent circuit illustrated in <FIG>, the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> has two resonance points P03 and P04 and two anti-resonance points P05 and P06. When the matching layer <NUM> to which the transducer <NUM> is fixed includes a plurality of layers, from the equivalent circuit of <FIG>, the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> may have more resonance points and more anti-resonance points.

The lower part of <FIG> may illustrate the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> and connected to the matching circuit <NUM>. Further, as illustrated in the lower part of <FIG>, the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> and connected to the matching circuit <NUM> has <NUM> resonance points P24, P25, P26 and <NUM> anti-resonance points P27, P28. Further, as illustrated in <FIG>, the resonance frequency at the resonance point P26 is higher than an average of the anti-resonance frequencies at the two anti-resonance points P05 and P06 of the transducer <NUM> fixed to the matching layer <NUM>.

As illustrated in the upper part of <FIG>, when the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> has two resonance points P03 and P04, the impedance of the transducer <NUM> fixed to the matching layer <NUM> and connected to the matching circuit <NUM> is expressed by the following equation.

In equation (<NUM>), LL and CL are respectively the values of the inductor LL and the capacitive component CL in the matching circuit <NUM> illustrated in <FIG>, and L<NUM>, L<NUM>, C<NUM>, C<NUM>, C<NUM>, R<NUM>, and R<NUM> are respectively the values of the inductors L1, L2, capacitors C0, C1, C2 and resistors R1, R2 in the equivalent circuit illustrated in <FIG>. Further, at the resonance points and the anti-resonance points, the value obtained by differentiating the above equation (<NUM>) becomes <NUM>, and the following relationship is satisfied.

Assuming that solutions satisfying the above equation (<NUM>) are ω1, ω2, ω3, ω4, and ω5 (ω1 < ω2 < ω3 < ω4 < ω5), ω1, ω3, and ω5 are resonance points, and ω2 and ω4 are anti-resonance points. Here, assuming that an impedance variation width in a target band across the three resonance points is ΔZ (for example, <NUM> decibels), by setting the values of the inductor LL and the capacitive component CL of the matching circuit <NUM> based on the values of inductors L1, L2, capacitors C0, C1, C2, and resistors R1, R2 in the equivalent circuit illustrated in <FIG> so that the following three equations are satisfied, maximum bandwidth having the impedance variation width ΔZ can be realized. <MAT> <MAT> <MAT>.

Further, by applying the expression ω=2πf to the values ω1, ω2, ω3, ω4, and ω5 thus obtained, the frequencies of the resonance points and the anti-resonance points are respectively calculated.

The graph at the bottom of <FIG> illustrates an example. In this example, the impedance values at the resonance points P24, P25, and P26 do not exactly coincide with each other due to effect such as the size of the transducer <NUM>, but are substantially the same, thus satisfying the equation (<NUM>) above. Similarly, the impedance values at the anti-resonance points P27 and P28 do not exactly coincide with each other, but are substantially the same, thus satisfying the equation (<NUM>) above. Thus, the bandwidth in which the impedance variation width ΔZ becomes <NUM> dB can be expanded to about <NUM> (in <FIG>, approximately <NUM> ~ <NUM>). Therefore, based on the equation (<NUM>), the bandwidth in which the transmission power of the transducer <NUM> is stabilized can be expanded to about <NUM>. Therefore, the ultrasonic wave can be stably transmitted over a wider band while lowering the impedance at the time of transmission.

In one embodiment, when the equivalent circuit of the transducer <NUM> fixed to the matching layer <NUM> is represented in <FIG> by increasing the number of layers of the matching layer <NUM>, the resonance points and the anti-resonance points may be adjusted by the same method. In this case, the equation (<NUM>) above is modified to the following equation.

In this case as well, ω is acquired as resonance point or anti-resonance point when a differential of equation (<NUM>) is <NUM>.

Further, the values of the inductor LL and the capacitive component CL of the matching circuit <NUM> are set so as to satisfy the conditions that the impedance values at the plurality of acquired resonance points are substantially the same, the impedance values at the plurality of acquired anti-resonance points are substantially the same, and a relationship between the resonance points and the anti-resonance points satisfies the equation (<NUM>) above. Thus, the maximum bandwidth having the impedance variation width ΔZ (for example, <NUM> dB) can be realized.

As illustrated in <FIG>, the transducer <NUM> may be fixed to the matching layer <NUM>, and the impedance characteristic of the transducer <NUM> fixed to the matching layer <NUM> may have a plurality of anti-resonance points P05 and P06 (anti-resonance frequencies), as illustrated in <FIG>. The frequency (second resonance frequency) of the resonance point P26 of the transducer <NUM> fixed to the matching layer <NUM> and connected to the matching circuit <NUM> may be adjusted higher than an average of the frequencies (anti-resonance frequencies) of the plurality of anti-resonance points P05 and P06 of the transducer <NUM> fixed to the matching layer <NUM>. Further, the impedance of the transducer <NUM> fixed to the matching layer <NUM> and connected to the matching circuit <NUM> can be stabilized in a vicinity of a band across the resonance point P24 (first resonance frequency) and the resonance point P26 (second resonance frequency), and the transmission power of the transducer <NUM> can be stabilized in the vicinity of this band. Therefore, the band for stabilizing the transmission power of the transducer can be effectively expanded, and the ultrasonic wave can be transmitted stably in a wider band.

In the above embodiments, as illustrated in <FIG>, the values CL and LL of the capacitive component CL and the inductor LL of the matching circuit <NUM> are adjusted so that the impedances at the two resonance points P21 and P22 substantially coincide with each other. As a result, as illustrated in <FIG>, a characteristic of the transmission power is substantially flattened in the band W2, and variation of the transmission power when moving away from the centre frequency is substantially suppressed.

Further, the matching circuit <NUM> may be designed to change the transmission power for each frequency by inclining a characteristic of the transmission power in a given band. In this case, according to this inclination, the values CL and LL of the capacitive component CL and the inductor LL of the matching circuit <NUM> may be adjusted so that the impedance at the resonance points P21 and P22 are different from each other.

Similarly, in another embodiment, the matching circuit <NUM> may be designed to incline the transmission power characteristic in a given band. In this case, it is sufficient to add aω (a is a coefficient corresponding to the desired inclination of the transmission power characteristic) to the right side of the f(ω) equation in the equations (<NUM>) or (<NUM>) above to perform a design based on the same conditions as in the equations (<NUM>) to (<NUM>).

Further, in each of the above embodiments, the spread angle of the reception spaces RS1 in the depression angle φ direction is <NUM> degrees, but the present disclosure is not limited thereto. For example, the spread of the reception spaces RS1 in the depression angle φ direction may be made smaller than <NUM> degrees. For example, a two-dimensional sonar using an umbrella-shaped transmission beam may be used.

Claim 1:
An amplifier circuit (<NUM>) to be used in a sonar (<NUM>), the amplifier circuit (<NUM>) comprising:
a transducer (<NUM>) having an impedance characteristic, the impedance characteristic comprising a resonance frequency (P01), and an anti-resonance frequency (P02) higher than the resonance frequency; and
a matching circuit (<NUM>) connected to the transducer (<NUM>), the matching circuit (<NUM>) comprising a capacitive component (CL) and an inductor (LL),
characterised in that:
the capacitive component (CL) is connected in parallel with the transducer (<NUM>) and the inductor (LL) is connected in series with the parallel connection of the capacitive component (CL) and the transducer (<NUM>); and
the capacitance of the capacitive component (CL) and the inductance of the inductor (LL) are selected such that:
the impedance characteristic of the transducer (<NUM>) connected to the matching circuit (<NUM>) has a first resonance frequency (P21) and a second resonance frequency (P22) higher than the first resonance frequency, wherein the first resonance frequency (P21) is a first local minimum in the impedance characteristic of the transducer (<NUM>) connected to the matching circuit (<NUM>) and the second resonance frequency is a second local minimum in the impedance characteristic of the transducer (<NUM>) connected to the matching circuit (<NUM>); and
the impedance characteristic of the transducer (<NUM>) connected to the matching circuit (<NUM>) further has an anti-resonance frequency (P23) between the first resonance frequency (P21) and the second resonance frequency (P22), the anti-resonance frequency (P23) being a local maximum in the impedance characteristic.