Transmitting circuit and underwater detection device

Abstract

To provide a transmission circuit capable of more accurately matching impedance with an ultrasonic transducer, and an underwater detection device including the transmission circuit.SOLUTION: A transmission circuit 14 includes an L-type matching circuit 101 consisting of a capacitive component 101a connected in parallel to an ultrasonic transducer 13a and an inductive component 101b connected in series to the parallel connection. The capacitance CLMT of the capacitive component 101a and the inductance LLMT of the inductive component 101b are set as conditions for obtaining impedance matching at the transmission frequency of ultrasonic waves between the ultrasonic transducer 13a and a circuit including the L-type matching circuit 101 and the parasitic capacitance Ccable of a cable 20 that connects the transmission circuit 14 and the ultrasonic transducer 13a.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a transmission circuit for supplying a transmission signal to an ultrasonic transducer, and to an underwater detection device including the transmission circuit. [Background technology]

[0002] Conventionally, underwater detection devices that detect targets in water using ultrasonic waves are known. This type of underwater detection device is equipped with a transmitter for transmitting ultrasonic waves into water. The transmitter drives an ultrasonic transducer based on a transmission signal to transmit ultrasonic waves into water. Since the impedance of the ultrasonic transducer is high, it is necessary to efficiently apply a high-voltage transmission signal to the ultrasonic transducer during transmission.

[0003] A transmission circuit using a matching circuit is known as a transmission circuit for efficiently supplying a transmission signal to an ultrasonic transducer. In this transmission circuit, the impedance at the resonance frequency can be reduced by matching the resonance frequency of the ultrasonic transducer connected to the matching circuit with the resonance frequency of the transducer alone. This allows a high-voltage transmission signal to be efficiently applied to the transducer near the resonance frequency.

[0004] The following Patent Document 1 discloses a drive circuit having the above-mentioned configuration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5088924 Summary of the Invention [Problem to be solved by the invention]

[0006] Typically, the transducer is installed on the bottom of a ship, and the transmission circuit is placed in a control unit installed in the ship's wheelhouse or the like. For this reason, the ultrasonic transducer and the transmission circuit are connected by a relatively long cable. A certain amount of parasitic capacitance occurs between the cable and nearby conductive members, etc. This parasitic capacitance changes depending on the length of the cable. Furthermore, when the transducer includes multiple ultrasonic transducers, each ultrasonic transducer and its transmission circuit are individually connected by a cable. In this case, each cable further generates parasitic capacitance between the other cables. This parasitic capacitance changes depending on the length of the cable as well as the distance between the cables.

[0007] Such parasitic capacitance has a large effect on the design of the matching circuit. In particular, since the impedance of the ultrasonic transducer is large, the parasitic capacitance has a large effect on the design of the matching circuit. Therefore, even if the matching circuit is designed by the above method, the fluctuation of the capacitance value due to the parasitic capacitance of the cable makes it impossible to accurately match the impedance between the matching circuit and the ultrasonic transducer.

[0008] In view of the above problems, an object of the present invention is to provide a transmission circuit capable of more accurately achieving impedance matching with an ultrasonic transducer, and an underwater detection device including such a transmission circuit. [Means for solving the problem]

[0009] A first aspect of the present invention relates to a transmission circuit for supplying a transmission signal to an ultrasonic transducer. The transmission circuit according to this aspect includes an L-type matching circuit consisting of a capacitive component connected in parallel to the ultrasonic transducer and an inductive component connected in series to the parallel connection. The capacitance CLMT of the capacitive component and the inductive component LLMT of the inductive component are set under the condition of obtaining impedance matching at the transmission frequency of the ultrasonic wave between the ultrasonic transducer and a circuit including the L-type matching circuit and a parasitic capacitance Ccable of a cable connecting the transmission circuit and the ultrasonic transducer.

[0010] According to the transmission circuit of this embodiment, the parasitic capacitance Ccable of the cable is taken into consideration in impedance matching between the L-type matching circuit and the ultrasonic transducer, so that the impedance matching between the matching circuit and the ultrasonic transducer can be achieved more accurately. Therefore, a high-voltage transmission signal can be efficiently applied to the ultrasonic transducer.

[0011] In the transmission circuit according to the present embodiment, when the equivalent circuit of the ultrasonic transducer is represented by a series-connected resistance RTD, capacitance CTD, and inductance LTD, and a capacitance C0 connected in parallel to this series connection, the impedance matching can be set as a condition for the impedance matching to be obtained at the transmission frequency of the ultrasonic wave between the circuit portion upstream of the resistance RTD and the resistance RTD.

[0012] This allows a design to be made to achieve impedance matching, taking into consideration the parasitic capacitance of the cable and the inter-electrode capacitance of the ultrasonic transducer, as well as the matching circuit, making it possible to supply higher transmission power to the ultrasonic transducer.

[0013] In this case, the circuit unit may be composed of a T-type circuit in which an impedance jX3 of a series connection of the capacitance CTD and the inductance LTD is connected in series to the resistance RTD, an impedance jX2 of a parallel connection of the capacitance CLMT, the parasitic capacitance Ccable, and the capacitance C0 is connected in parallel to the series connection of the impedance jX3 and the resistance RTD, and an impedance jX1 of the inductance LLMT is connected in series to the impedance jX3 and the parallel connection of the resistance RTD and the impedance jX2.

[0014] According to this configuration, by converting the T-type circuit into a circuit in which two L-type matching circuits are connected, it is possible to smoothly determine the design values ​​(capacitance CLMT, inductance LLMT) of the capacitive and inductive components for impedance matching at the transmission frequency of the ultrasound.

[0015] A second aspect of the present invention relates to a transmission circuit for supplying a transmission signal to an ultrasonic transducer. The transmission circuit according to this aspect includes an L-type matching circuit consisting of a capacitive component connected in parallel to an ultrasonic transducer and an inductive component connected in series to the parallel connection, and a transformer disposed between the L-type matching circuit and the ultrasonic transducer. The capacitance CLMT of the capacitive component and the inductance LLMT of the inductive component are set under the condition of obtaining impedance matching at the transmission frequency of the ultrasonic wave between the ultrasonic transducer and a circuit including the L-type matching circuit, the parasitic capacitance of a cable connecting the transmission circuit and the ultrasonic transducer via the transformer, and the inductance of the transformer.

[0016] According to the transmission circuit of this embodiment, the parasitic capacitance of the cable is taken into consideration in impedance matching between the L-type matching circuit and the ultrasonic transducer, so that the impedance matching between the matching circuit and the ultrasonic transducer can be achieved more accurately. Therefore, a high-voltage transmission signal can be efficiently applied to the ultrasonic transducer.

[0017] In addition, according to the transmission circuit of this embodiment, in impedance matching, the inductance of the transformer is set small and the capacitance of the capacitive component is set large, so that the variation in the inductance LT of the transformer, the parasitic capacitance of the cable, and the inter-electrode capacitance of the ultrasonic transducer 13a are less likely to affect the impedance matching between the transmission circuit and the ultrasonic transducer. Therefore, the impedance matching can be stably maintained by a simple design.

[0018] In the transmission circuit according to the present embodiment, when the secondary circuit of the transformer is converted to the primary circuit, the equivalent circuit of the ultrasonic transducer is represented by a series-connected resistance RTD', capacitance CTD', and inductance LTD', and a capacitance C0' connected in parallel to this series connection. The impedance matching condition can be set to be that impedance matching is obtained at the transmission frequency of the ultrasonic wave between the circuit portion upstream of the resistance RTD' and the resistance RTD.

[0019] This allows the design to achieve impedance matching by taking into consideration the parasitic capacitance of the cable, the inductance LT of the transformer, and the inter-electrode capacitance of the ultrasonic transducer, along with the matching circuit. This allows a higher transmission power to be supplied to the ultrasonic transducer.

[0020] Here, in the circuit when the secondary side circuit of the transformer is converted to the primary side, the parasitic capacitance of the first cable connecting the matching circuit and the primary winding of the transformer is represented as parasitic capacitance Ccable1, the parasitic capacitance of the second cable connecting the secondary winding of the transformer and the ultrasonic transducer is represented as parasitic capacitance Ccable2', and the inductance of the transformer is represented as inductance RT. In this case, the circuit unit is configured as a T-type circuit in which the impedance jX3 of the series connection of the capacitance CTD' and the inductance LTD' is connected in series to the resistor RTD', the impedance jX2 of the parallel connection of the capacitance CLMT, the parasitic capacitances Ccable1, Ccable2', the capacitance C0 and the inductance LT is connected in parallel to the series connection of the impedance jX3 and the resistor RTD, and the impedance jX1 of the inductance LLMT is connected in series to the impedance jX3 and the parallel connection of the resistor RTD and the impedance jX2.

[0021] According to this configuration, by converting the T-type circuit into a circuit in which two L-type matching circuits are connected, it is possible to smoothly determine the design values ​​(capacitance CLMT, inductance LLMT) of the capacitive and inductive components for impedance matching at the transmission frequency of the ultrasound.

[0022] A third aspect of the present invention relates to an underwater detection device, the underwater detection device comprising the transmission circuit according to the first or second aspect, and the ultrasonic transducer transmits the ultrasonic waves into water.

[0023] According to the underwater detection device of this aspect, since it includes the transmission circuit of the first or second aspect, it is possible to accurately match impedance between the transmission circuit and the ultrasonic transducer, and it is possible to efficiently supply a high-voltage transmission signal to the ultrasonic transducer, thereby enabling it to accurately detect underwater targets. Effect of the Invention

[0024] As described above, according to the present invention, it is possible to provide a transmission circuit capable of more accurately matching impedance with an ultrasonic transducer, and an underwater detection device including the transmission circuit.

[0025] The effects and significance of the present invention will become clearer from the following description of the embodiment. However, the embodiment described below is merely an example of how the present invention can be put into practice, and the present invention is not limited to the embodiment described below. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram showing how underwater is searched by an underwater detection device according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing the configuration of the underwater detection device according to the first embodiment. [Diagram 3] FIG. 3 is a diagram illustrating a configuration of a transmission circuit according to the first embodiment. [Figure 4]FIG. 4 is a diagram showing a configuration of a transmission circuit when an ultrasonic transducer is represented by an equivalent circuit according to the first embodiment. [Diagram 5] FIG. 5 is a diagram showing the configuration downstream of the terminal in FIG. 4 according to the first embodiment, grouped into a plurality of impedance elements. [Figure 6] FIG. 6 is a diagram showing a state in which the circuit of FIG. 5 is converted into a configuration in which two L-type matching circuits are connected, according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing a configuration of a transmission circuit when an ultrasonic transducer is represented by an equivalent circuit according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing a circuit configuration when the secondary side circuit of the transformer in FIG. 7 is converted to the primary side according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For convenience, the drawings appropriately include X, Y, and Z axes that are perpendicular to each other. The X-axis and Y-axis directions are horizontal, and the Z-axis direction is vertical. The positive Y-axis direction is the direction in which the ship advances.

[0028] <Embodiment 1> FIG. 1 is a diagram showing a schematic diagram of underwater searching by an underwater detection device 10. As shown in FIG.

[0029] In FIG. 1, θ is an azimuth angle centered on a transducer 13 installed on the bottom of a ship S1, and φ is a depression angle from the horizontal plane (XY plane).

[0030] The underwater detection device 10 includes a transducer 13 installed on the bottom of the ship S1. Ultrasonic waves are transmitted from the transducer 13 into a hemispherical transmission space TS1, and the reflected waves are received by the transducer 13. The transducer 13 includes a plurality of ultrasonic transducers for transmitting and receiving ultrasonic waves. The ultrasonic transducers are arranged, for example, in a hemispherical or cylindrical shape. A reception signal corresponding to the intensity (echo intensity) of the reflected wave received by each ultrasonic transducer is generated for each ultrasonic transducer. The underwater detection device 10 performs beamforming on these reception signals to form a plurality of reception beams RB1 distributed in the azimuth angle θ direction and the depression angle φ direction.

[0031] The underwater detection device 10 generates multiple reception beams RB1 in a sector-shaped reception space RS1 that spreads in the direction of the depression angle φ. In each reception space RS1, multiple reception beams RB1 are formed in the direction of the depression angle φ with a predetermined resolution. The reception spaces RS1 are set at a predetermined pitch over the entire circumference in the direction of the azimuth angle θ. The actual pitch of the reception space RS1 is several steps smaller than the pitch shown in FIG. 1. The spread angle of the reception space RS1 in the direction of the depression angle φ is, for example, 90 degrees.

[0032] The underwater detection device 10 acquires echo intensity at a predetermined distance resolution for each reception beam RB1 formed in the reception space RS1. This allows the echo intensity to be acquired at a predetermined distance resolution for each depression angle of each reception beam RB1. The underwater detection device 10 integrates the echo intensities for each depression angle and each distance acquired for each reception space RS1 for all reception spaces RS1, thereby acquiring an echo signal with echo intensity distributed three-dimensionally in the transmission space TS1.

[0033] The underwater detection device 10 uses the acquired echo signals to display an echo image showing a three-dimensional distribution of echo intensities on the display unit. Each three-dimensional position on the echo image is assigned a color according to the echo intensity. For example, the position of a school of fish F1 on the echo image is assigned a color (e.g., red) associated with high echo intensity. A user can identify targets such as the school of fish F1 by referring to the color distribution on the echo image.

[0034] FIG. 2 is a block diagram showing the configuration of the underwater detection device 10 according to this embodiment.

[0035] The underwater detection device 10 comprises a control circuit 11, a memory unit 12, a transducer 13, a transmission circuit 14, a reception circuit 15, a display unit 16, a display processing circuit 17, an operation unit 18, and an operation processing circuit 19. The transducer 13 is installed on the bottom of the ship S1 as described above, and the other components, such as the control circuit 11, are installed in the wheelhouse or the like of the ship S1.

[0036] The control circuit 11 includes an arithmetic processing circuit such as a CPU (Central Processing Unit), and executes control processing according to a program stored in a storage unit 12. The storage unit 12 includes storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The storage unit 12 stores programs for the control circuit 11 to execute the control processing.

[0037] The transducer 13 includes a plurality of ultrasonic transducers 13a. As described above, the ultrasonic transducers 13a are arranged in a hemispherical or cylindrical shape. Each ultrasonic transducer 13a transmits ultrasonic waves to the transmission space TS1 in FIG. 1 and receives the reflected waves for each processing step (ping) of transmitting and receiving waves.

[0038] The transmission circuit 14 outputs a transmission signal for transmitting ultrasonic waves to the transducer 13 in response to control from the control circuit 11. The reception circuit 15 processes the signals output by each ultrasonic transducer 13a of the transducer 13 upon receiving the reflected ultrasonic waves to generate reception signals, and outputs the generated reception signals to the control circuit 11.

[0039] The control circuit 11 performs beamforming on the reception signals acquired from each ultrasonic transducer 13a to form a plurality of reception beams distributed in the azimuth angle θ direction and the depression angle φ direction, and acquires an echo signal in the direction of each reception beam (the direction of a given azimuth angle θ and depression angle φ). The echo signal acquired for each reception beam is a signal indicating the echo intensity that changes according to the elapsed time from the transmission timing of the ultrasonic waves.

[0040] Here, the time elapsed from the transmission timing corresponds to the distance from the transducer 13 in the direction of each reception beam. The control circuit 11 obtains the echo intensity at each distance position in the direction of each reception beam from the echo signal of each reception beam by associating the time elapsed from the transmission timing with the distance. The echo intensity is obtained with a predetermined distance resolution.

[0041] The display unit 16 includes a display such as a liquid crystal display. The display processing circuit 17 causes the display unit 16 to display an echo image in response to control from the control circuit 11. The operation unit 18 includes input means such as an operation key and a mouse. The operation processing circuit 19 outputs a signal corresponding to an operation on the operation unit 18 to the control circuit 11 in response to control from the control circuit 11. The user can operate the operation unit 18 to change the viewpoint of the echo image, for example. The display unit 16 and the operation unit 18 may be configured by a liquid crystal panel in which a touch panel is superimposed on a liquid crystal display.

[0042] Fig. 3 is a diagram showing the configuration of the transmission circuit 14 in Fig. 2. For convenience, Fig. 3 shows a configuration for driving one ultrasonic transducer 13a. A configuration similar to that in Fig. 3 is provided for each of the multiple ultrasonic transducers 13a.

[0043] The transmission circuit 14 includes a matching circuit 101 and a transmission amplifier 102. The matching circuit 101 is connected to the ultrasonic transducer 13a via a cable 20. The cable 20 is made up of a cable 20a for supplying a transmission signal and a cable 20b connected to the ground. The ultrasonic transducer 13a is, for example, a piezoelectric element, and outputs an ultrasonic wave when a voltage corresponding to the transmission signal is applied thereto.

[0044] The matching circuit 101 is an L-type matching circuit having a capacitive component 101a having a capacitance CLMT and an inductive component 101b having an inductance LLMT. The capacitive component 101a is connected in parallel to the ultrasonic transducer 13a, and the inductive component 101b is connected in series to this parallel connection.

[0045] A filter may be disposed between the inductive component 101b and the terminal T1. However, since this filter is not involved in the calculation related to impedance matching described later, the following description will not specifically mention this filter.

[0046] The transmission amplifier 102 outputs a transmission signal obtained by amplifying a control signal input from the control circuit 11 to a terminal T1. The terminal T2 is connected to the ground within the transmission amplifier 102. The control signal has a frequency corresponding to the transmission signal and is a pulse signal with a predetermined duty. The transmission amplifier 102 outputs a transmission signal (pulse signal) obtained by increasing the control signal (pulse signal) to a predetermined voltage to the terminal T1. The voltage value of the transmission signal is maintained at the voltage value of the power supply voltage VB supplied to the transmission amplifier 102. The duty of the transmission signal is the same as the duty of the control signal. The transmission power of the ultrasonic transducer 13a is controlled by controlling the duty of the transmission signal.

[0047] FIG. 4 is a diagram showing the configuration of the transmission circuit 14 when the ultrasonic transducer 13a in the configuration of FIG. 3 is shown as an equivalent circuit.

[0048] The equivalent circuit of the ultrasonic transducer 13a is represented by a circuit in which a capacitance CTD, an inductance LTD, and a resistance RTD are connected in series, and a capacitance C0 is connected in parallel to the series connection. In addition, the circuit in FIG. 4 includes the parasitic capacitance Ccable of the cable 20 in FIG. 3.

[0049] As described above, the transducer 13 is installed on the bottom of the ship, and the transmission circuit 14 is installed in the wheelhouse or the like of the ship, so the ultrasonic transducer 13a and the transmission circuit 14 are connected by a relatively long cable 20. Normally, a certain amount of parasitic capacitance occurs between the cable 20 and nearby conductive members, etc. This parasitic capacitance changes depending on the length of the cable 20.

[0050] Furthermore, as described above, when the transmitter / receiver 13 includes a plurality of ultrasonic transducers 13a, each ultrasonic transducer 13a and its transmission circuit 14 are individually connected by a cable 20. In this case, a parasitic capacitance is generated between each cable 20 and other cables 20. This parasitic capacitance varies depending on the length of the cable 20 and the distance between the cable 20 and other cables.

[0051] Therefore, if the matching circuit 101 is designed without considering the parasitic capacitance of the cable 20, matching cannot be achieved between the matching circuit 101 and the ultrasonic transducer 13a. In particular, in the above configuration, since the resistance RTD of the ultrasonic transducer 13a is large, the parasitic capacitance of the cable 20 has a large effect on the design of the matching circuit 101.

[0052] 4, the matching circuit 101 is designed in consideration of the parasitic capacitance Ccable of the cable 20. That is, the capacitance CLMT of the capacitive component 101a and the inductance LLMT of the inductive component 101b are set so that impedance matching is obtained at the transmission frequency of the ultrasonic waves between the circuit including the L-type matching circuit 101 and the parasitic capacitance Ccable of the cable 20, and the ultrasonic transducer 13a.

[0053] Here, the value of the parasitic capacitance Ccable of the cable 20 is measured and obtained in advance for each type and length of the cable 20. The type of cable 20 refers to the type (number of cores, distance between cores, etc.) of a multiaxial cable in which multiple cables 20 are integrated as cores.

[0054] A method for designing matching circuit 101, that is, a method for setting the values ​​of capacitive component 101a and inductive component 101b that constitute matching circuit 101, will be described below.

[0055] FIG. 5 is a diagram showing the configuration downstream of terminals T1 and T2 in FIG. 4, grouped into a plurality of impedance elements.

[0056] In Fig. 5, two boundaries B1 and B2 arranged side by side are indicated by dashed lines. The impedance upstream of the boundary B1 on the left side is indicated as impedance R1, and the impedance downstream of the boundary B1 is indicated as impedance RA. The impedance upstream of the boundary B2 on the right side is indicated as impedance RB, and the impedance downstream of the boundary B2 is indicated as impedance RTD. The impedance RTD is the impedance of the resistor RTD in Fig. 4 that constitutes the equivalent circuit of the ultrasonic transducer 13a.

[0057] In order to efficiently apply a high-voltage transmission signal at the frequency of the transmission signal to the ultrasonic transducer 13a, it is necessary to match the impedance RB with the impedance RTD (condition 1), and it is necessary to convert the impedance RB to the impedance RA so as to realize the desired impedance RA (condition 2). It is not necessary to match the impedance R1 with the impedance RA.

[0058] First, from the above condition 1, the following formula is established.

[0059]

number

[0060] Next, assuming that the active power to be input to the resistor RTD is WL, the power supply voltage supplied to the transmission amplifier 102 in FIG. 4, i.e., the voltage of the transmission signal (pulse signal) output to the terminal T1 is VB, the duty of the transmission signal is D, and the circuit efficiency of the circuit in FIG. 5 is η, then the impedance RA is expressed by the following equation.

[0061]

number

[0062] In the configuration of Fig. 5, the capacitance C0, CTD, inductance LTD, and resistance RTD are elements of the equivalent circuit of the ultrasonic transducer 13a and are therefore known. Therefore, the impedance RB is also known from the above formula (1). In addition, the value of the parasitic capacitance Ccable of the cable 20 is known because it is measured and obtained in advance as described above.

[0063] 5, the inductance LLMT and the capacitance CLMT are set so that the frequency of the transmission signal satisfies the above condition 2. The process of deriving the inductance LLMT and the capacitance CLMT based on the above condition 2 will be described below.

[0064] When impedances jX1, jX2, and jX3 are set in the circuit shown in FIG. 5, the circuit portion sandwiched between the two left and right boundaries B1, B2 becomes a T-shaped circuit in which impedance jX3 is connected in series to the resistor RTD, impedance jX2 is connected in parallel to the series connection of impedance jX3 and the resistor RTD, and impedance jX1 is connected in series to the impedance jX3 and the parallel connection of the resistor RTD and impedance jX2.

[0065] Here, impedance jX1 is the inductance LLMT of the inductive component 101b. Impedance jX2 is the impedance of the parallel connection of capacitance C0, the parasitic capacitance Ccable of the cable 20, and the capacitance CLMT of the capacitive component 101a. Impedance jX3 is the impedance of the series connection of capacitance CTD and inductance LTD.

[0066] If the impedance jX2 in Fig. 5 is divided into two impedances jXB and jXD, the circuit in Fig. 5 is transformed into a form in which two L-type matching circuits LM1 and LM2 are connected, as shown in Fig. 6. In Fig. 6, jX1 and jX3 in Fig. 5 are replaced with jXA and jXC, respectively. In Fig. 6, a new boundary B3 is set, and the impedance upstream of this boundary B3 is shown as impedance RC, and the impedance downstream of this boundary B3 is shown as impedance RD. In this configuration, impedance matching (RC=RD) is achieved between impedance RC and impedance RD.

[0067] Of these two L-type matching circuits LM1 and LM2, the right matching circuit LM2 will be considered first. In this matching circuit LM2, QR is defined by the following equation.

[0068]

number

[0069] As a result, the impedances jXC and jXD are expressed by the following equation using QR in equation (3).

[0070]

number

[0071]

number

[0072] Here, impedance jXC is a composite impedance of inductive component jωLTD and capacitive component 1 / (jωCTD) as shown in Fig. 5. Therefore, impedance jXC is known from ω=2πf depending on the frequency f at which matching is desired (frequency of the transmission signal). Furthermore, impedance RB is known from equation (1) above. Thus, since impedances jXC and RB are known, QR can be found from equation (4) above, and impedances RD and XD can be found from equations (3) and (5).

[0073] Similarly, in the left matching circuit LM2, QL is defined by the following equation:

[0074]

number

[0075] As a result, the impedances jXA and XB are expressed by the following equation using QL in equation (6).

[0076]

number

[0077]

number

[0078] Here, the impedance RA is a known quantity from the above formula (2), and the impedance RC is equal to the impedance RD calculated from the above formulas (3) to (5) because impedance matching is performed between the impedances RC and RD. Therefore, the impedance RC is a known quantity. Therefore, QL is calculated by substituting these known quantities into formula (6), and further, the impedances jXA and jXB are calculated by substituting the impedances RA and RC, which are known quantities, into formulas (7) and (8) together with this QL.

[0079] Furthermore, as shown in FIG. 5 and FIG. 6, the following relationship exists between X1, XA, and LLMT.

[0080]

number

[0081] The inductance LLMT of the inductive component 101b can be calculated from equation (9) and the impedance jXA calculated from equation (7).

[0082] Further, the following equation holds based on the relationship between the impedance jX2 and the impedances jXB and XD in FIG.

[0083]

number

[0084]

number

[0085] In equations (10) and (11), the impedances jXB and XD are known quantities from equations (8) and (5), and the capacitance C0 and the parasitic capacitance Ccable are also known quantities, so the capacitance CLMT of the capacitive component 101a can be found from equations (10) and (11).

[0086] To summarize the above, the inductance LLMT of the inductive component 101b and the capacitance CLMT of the capacitive component 101a are expressed by the following equations.

[0087]

number

[0088]

number

[0089] Since the overall impedance can be found by the above calculations, the transmission power can be automatically found once the applied voltage is determined.

[0090] <Effects of the First Embodiment> According to the above embodiment, the following effects can be achieved.

[0091] 4 to 6, the parasitic capacitance Ccable of the cable 20 is taken into consideration in impedance matching between the L-type matching circuit 101 and the ultrasonic transducer 13a, so that impedance matching between the matching circuit 101 and the ultrasonic transducer 13a can be achieved more accurately. Therefore, a high-voltage transmission signal can be efficiently applied to the ultrasonic transducer 13a.

[0092] As described with reference to Figures 4 and 5, when the equivalent circuit of the ultrasonic transducer 13a is represented by a series-connected resistance RTD, capacitance CTD, and inductance LTD, and a capacitance C0 connected in parallel to this series connection, the condition for impedance matching is set to be that impedance matching is obtained at the transmission frequency of the ultrasonic wave between the circuit portion upstream of the resistance RTD and the resistance RTD.

[0093] As a result, a design for impedance matching is performed taking into consideration the parasitic capacitance Ccable of the cable 20 and the inter-electrode capacitance C0 of the ultrasonic transducer 13a in addition to the matching circuit 101. Therefore, higher transmission power can be supplied to the ultrasonic transducer.

[0094] As shown in FIG. 5, the circuit section in which impedance matching is achieved with the resistance RTD of the ultrasonic transducer 13a is configured as a T-shaped circuit in which an impedance jX3 of a series connection of a capacitance CTD and an inductance LTD is connected in series to the resistance RTD, an impedance jX2 of a parallel connection of a capacitance CLMT, a parasitic capacitance Ccable, and a capacitance C0 is connected in parallel to the series connection of the impedance jX3 and the resistance RTD, and an impedance jX1 of an inductance LLMT is connected in series to the parallel connection of the impedance jX3 and the resistance RTD and the impedance jX2.

[0095] As a result, by converting the T-type circuit into a circuit in which two L-type matching circuits LM1 and LM2 are connected, as shown in Figure 6, it is possible to smoothly determine the design values ​​(capacitance CLMT, inductance LLMT) of the capacitive component 101a and the inductive component 101b for impedance matching at the transmission frequency of the ultrasonic wave, as described above.

[0096] As shown in FIG. 2, the underwater detection device 10 includes the transmission circuit 14 configured as described above, and the ultrasonic transducer 13a transmits ultrasonic waves into water.

[0097] According to this configuration, since the underwater detection device 10 includes the transmission circuit 14 configured as above, it is possible to accurately match impedance between the transmission circuit 14 and the ultrasonic transducer 13a, and a high-voltage transmission signal can be efficiently supplied to the ultrasonic transducer 13a. Therefore, it is possible to accurately detect underwater targets.

[0098] <Embodiment 2> FIG. 7 is a diagram showing a configuration of a transmission circuit 14 when an ultrasonic transducer 13a is represented by an equivalent circuit according to the second embodiment.

[0099] 7, in the second embodiment, a transformer 103 is further disposed between the L-shaped matching circuit 101 and the ultrasonic transducer 13a. The matching circuit 101 is connected to the primary winding of the transformer 103 by a first cable 21, and the ultrasonic transducer 13a is connected to the secondary winding of the transformer 103 by a second cable 22.

[0100] In this configuration, the capacitance CLMT of the capacitive component 101a and the inductance LLMT of the inductive component 101b are set so that impedance matching is obtained at the transmission frequency of the ultrasonic waves between the matching circuit 101, which includes the parasitic capacitance Ccable1 of the first cable 21 and the parasitic capacitance Ccable2 of the second cable 22, and the inductance of the transformer 103, and the ultrasonic transducer 13a.

[0101] The turns ratio N of the transformer 103 is expressed as follows by the number of turns N1 of the primary winding and the number of turns N2 of the secondary winding.

[0102]

number

[0103] When the secondary side circuit of the transformer 103 is converted to the primary side, the circuit in Fig. 7 is expressed as shown in Fig. 8. In the circuit in Fig. 8, parameters that change due to the above conversion are expressed as follows.

[0104]

number

[0105] LT in the circuit of FIG. 8 is the inductance of the transformer 103 when the circuit of FIG. 7 is converted into the circuit of FIG.

[0106] In the circuit of Fig. 8, when the impedances jX1, jX2, and jX3 are set as shown in Fig. 8, the circuit of Fig. 8 becomes a T-type circuit, similar to Fig. 5. Therefore, similar to the circuit of Fig. 6, the circuit of Fig. 8 is transformed into a circuit in which two L-type matching circuits LM1 and LM2 are connected by dividing the impedance jX2 into two impedances jXB and XD. In this case, too, the impedance jX1 is replaced with the impedance jXA, and the impedance jX3 is replaced with the impedance jXC.

[0107] After rearranging the circuit in this way, the impedances jXA, XB, XC, and XD can be found by applying the same calculations as in the case of Fig. 6. Then, from the way in which the impedance jX1 is placed, the inductance LLMT of the inductive component 101b can be found from the above formula (9).

[0108] Additionally, the following two equations hold based on the way impedance jX2 is placed.

[0109]

number

[0110] Equation (20) is similar to equation (10). Therefore, the capacitance CLMT of the capacitive component 101a and the inductance LT of the transformer 103 need to be set so as to satisfy the following equation.

[0111]

number

[0112] In this case, since the inductance LT of the transformer 103 generally varies widely, it is preferable that it is as small as possible. On the other hand, if the inductance LT is reduced, it is necessary to increase the capacitance CLMT of the capacitive component 101a according to the above formula (22). Here, if the capacitance CLMT is increased, the capacitance CLMT becomes dominant over the parasitic capacitances Ccable1, Ccable2' and capacitance C0' in formula (22). Therefore, in relation to formula (22), the influence of the parasitic capacitances Ccable1, Ccable2' of the first cable 21 and the second cable 22, which vary widely, and the inter-electrode capacitance (capacitance C0') of the ultrasonic transducer 13a is suppressed.

[0113] Therefore, when adjusting the capacitance CLMT of the capacitive component 101a and the inductance LT of the transformer 103 to satisfy the above formula (22), it is preferable to set the inductance LT small and the capacitance CLMT large. This makes it possible to suppress the influence of the variation in the inductance LT of the transformer 103 and the variation in the parasitic capacitances Ccable1, Ccable2' and the inter-electrode capacitance (capacitance C0') of the ultrasonic transducer 13a on the impedance matching between the transmission circuit 14 and the ultrasonic transducer 13a, and to stably maintain the impedance matching with a simple design.

[0114] 7 includes the parasitic capacitances of the first cable 21 and the second cable 22, but if one of the cables is short and the parasitic capacitance of this cable does not significantly affect the design related to impedance matching, the parasitic capacitance of this cable may be omitted. In this case, zero is applied to the parameter value of the parasitic capacitance of this cable in the above equation (22).

[0115] <Effects of the second embodiment> 7 and 8, the parasitic capacitances Ccable1 and Ccable2 of the first cable 21 and the second cable 22 are taken into consideration in impedance matching between the L-type matching circuit 101 and the ultrasonic transducer 13a, so that impedance matching between the matching circuit 101 and the ultrasonic transducer 13a can be achieved more accurately. Therefore, a high-voltage transmission signal can be efficiently applied to the ultrasonic transducer.

[0116] In addition, in the above equation (22) for impedance matching, by setting the inductance LT of the transformer 103 small and the capacitance CLMT of the capacitive component 101a large, it is possible to suppress the influence of the variation in the inductance LT of the transformer 103 and the variation in the parasitic capacitances Ccable1 and Ccable2 of the first cable 21 and the second cable 22 and the inter-electrode capacitance of the ultrasonic transducer 13a on the impedance matching between the transmission circuit 14 and the ultrasonic transducer 13a. Therefore, it is possible to stably maintain impedance matching with a simple design.

[0117] As shown in FIG. 8, in a circuit in which the secondary circuit of the transformer 103 is converted to the primary circuit, when the equivalent circuit of the ultrasonic transducer 13a is represented by a series-connected resistance RTD', capacitance CTD', and inductance LTD', and a capacitance C0' connected in parallel to this series connection, the condition for impedance matching is set to be that impedance matching is obtained at the transmission frequency of the ultrasonic wave between the circuit part upstream of the resistance RTD' and the resistance RTD.

[0118] As a result, a design for impedance matching is performed taking into consideration the parasitic capacitances Ccable1 and Ccable2' of the first cable 21 and the second cable 22, the inductance LT of the transformer, and the inter-electrode capacitance of the ultrasonic transducer 13a, along with the matching circuit 101. Therefore, higher transmission power can be supplied to the ultrasonic transducer 13a.

[0119] As shown in FIG. 8, the circuit section in which impedance matching is achieved with the resistance RTD of the ultrasonic transducer 13a is configured as a T-shaped circuit in which an impedance jX3 of a series connection of a capacitance CTD' and an inductance LTD' is connected in series to the resistance RTD', an impedance jX2 of a parallel connection of a capacitance CLMT, parasitic capacitances Ccable1, Ccable2', capacitance C0 and inductance LT is connected in parallel to the series connection of the impedance jX3 and the resistance RTD, and an impedance jX1 of an inductance LLMT is connected in series to the parallel connection of the impedance jX3 and the resistance RTD and impedance jX2.

[0120] As a result, by converting this T-shaped circuit into a circuit in which two L-shaped matching circuits L1 and L2 similar to those in Figure 6 are connected, it is possible to smoothly determine the design values ​​(capacitance CLMT, inductance LLMT) of the capacitive component 101a and the inductive component 101b for impedance matching at the transmission frequency of the ultrasonic wave.

[0121] <Example of change> In the above-mentioned first and second embodiments, a plurality of ultrasonic transducers 13a are arranged in the transducer 13, and a transmission circuit 14 is prepared for each ultrasonic transducer 13a, but the number of ultrasonic transducers 13a and transmission circuits 14 arranged in the transducer 13 may not be multiple. For example, only one ultrasonic transducer 13a may be arranged in the transducer 13, and only one transmission circuit 14 may be assigned to this ultrasonic transducer 13a.

[0122] In the above-mentioned first and second embodiments, the ultrasonic transducer 13a is used for both transmitting and receiving, but the ultrasonic transducer for transmitting and the ultrasonic transducer for receiving may be arranged separately. In this case, the above-mentioned configuration is applied to the transmission circuit that supplies a transmission signal to the ultrasonic transducer for transmitting.

[0123] In the above first and second embodiments, the spread angle of the reception space RS1 in the direction of the depression angle φ is 90 degrees, but this is not limited to this. For example, the spread of the reception space RS1 in the direction of the depression angle φ may be narrower than 90 degrees. For example, the underwater detection device 10 may be a two-dimensional sonar that uses an umbrella-shaped transmission beam.

[0124] Furthermore, the sonar does not have to be an all-around type that detects targets over the entire circumference in the azimuth angle θ direction, and may be, for example, a half-circle type sonar or a sonar for forward detection.

[0125] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the claims. [Explanation of symbols]

[0126] 10 Underwater detection equipment 13 Transmitter / Receiver 13a Ultrasonic transducer 14 Transmitting circuit 20 Cable 21 First Cable 22 Second Cable 101 Matching circuit 101a Capacitive parts 101b Inductive components 103 Trans C0, CTD, CLMT capacitance Ccable, Ccable1, Ccable2 parasitic capacitance RTD resistance

Claims

1. A transmission circuit for supplying a transmission signal to an ultrasonic transducer, The ultrasonic transducer includes an L-type matching circuit including a capacitive component connected in parallel to the ultrasonic transducer and an inductive component connected in series to the parallel connection, A capacitance CLMT of the capacitive component and an inductance LLMT of the inductive component are set as a condition for obtaining impedance matching at a transmission frequency of the ultrasonic wave between the ultrasonic transducer and a circuit including the L-type matching circuit and a parasitic capacitance Ccable of a cable connecting the transmission circuit and the ultrasonic transducer. A transmission circuit comprising:

2. 2. The transmission circuit according to claim 1, When the equivalent circuit of the ultrasonic transducer is represented by a resistance RTD, a capacitance CTD, and an inductance LTD connected in series, and a capacitance C0 connected in parallel to this series connection, The condition for the impedance matching is set such that impedance matching is obtained at a transmission frequency of the ultrasonic wave between the circuit portion upstream of the resistor RTD and the resistor RTD. A transmission circuit comprising:

3. 3. The transmission circuit according to claim 2, The circuit unit includes: A T-type circuit is formed in which an impedance jX3 of a series connection of the capacitance CTD and the inductance LTD is connected in series to the resistance RTD, an impedance jX2 of a parallel connection of the capacitance CLMT, the parasitic capacitance Ccable, and the capacitance C0 is connected in parallel to the series connection of the impedance jX3 and the resistance RTD, and an impedance jX1 of the inductance LLMT is connected in series to the impedance jX3 and the parallel connection of the resistance RTD and the impedance jX2. A transmission circuit comprising:

4. A transmission circuit for supplying a transmission signal to an ultrasonic transducer, an L-type matching circuit including a capacitive component connected in parallel to the ultrasonic transducer and an inductive component connected in series to the parallel connection; A transformer disposed between the L-type matching circuit and the ultrasonic transducer, A capacitance CLMT of the capacitive component and an inductance LLMT of the inductive component are set as conditions for obtaining impedance matching at a transmission frequency of the ultrasonic wave between the ultrasonic transducer and a circuit including the L-type matching circuit, the parasitic capacitance of a cable connecting the transmission circuit and the ultrasonic transducer via the transformer, and the inductance of the transformer, A transmission circuit comprising:

5. 5. The transmission circuit according to claim 4, In a circuit obtained by converting the secondary circuit of the transformer into the primary circuit, when an equivalent circuit of the ultrasonic transducer is represented by a resistance RTD', a capacitance CTD', and an inductance LTD' connected in series, and a capacitance C0' connected in parallel to this series connection, The condition for the impedance matching is set such that impedance matching is obtained at a transmission frequency of the ultrasonic wave between the circuit portion upstream of the resistor RTD′ and the resistor RTD′. A transmission circuit comprising:

6. 6. The transmission circuit according to claim 5, In the circuit when the secondary side circuit of the transformer is converted to the primary side, the parasitic capacitance of a first cable connecting the matching circuit and the primary winding of the transformer is represented as parasitic capacitance Ccable1, the parasitic capacitance of a second cable connecting the secondary winding of the transformer and the ultrasonic transducer is represented as parasitic capacitance Ccable2', and the inductance of the transformer is represented as inductance RT, The circuit unit includes: a T-type circuit in which an impedance jX3 of a series connection of the capacitance CTD' and the inductance LTD' is connected in series to the resistance RTD', an impedance jX2 of a parallel connection of the capacitance CLMT, the parasitic capacitances Ccable1, Ccable2', the capacitance C0 and the inductance LT is connected in parallel to the series connection of the impedance jX3 and the resistance RTD, and an impedance jX1 of the inductance LLMT is connected in series to the impedance jX3 and the parallel connection of the resistance RTD and the impedance jX2, A transmission circuit comprising:

7. A transmitter circuit according to any one of claims 1 to 6, The ultrasonic transducer transmits the ultrasonic waves into water. An underwater detection device characterized by:

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