Transmitter circuit and underwater detection apparatus

Abstract

The present disclosure provides a transmitter circuit (14) for supplying a transmission signal for performing impedance matching with an oscillator (13a), and an underwater detection apparatus (10) pr

Description

TRANSMITTER CIRCUIT AND UNDERWATER DETECTION APPARATUS

[0001] The present invention relates to underwater detection apparatuses, and specifically to transmitter circuits for supplying a transmission signal to a transducer and an underwater detection apparatus equipped with the transmitter circuit.

[0002] Conventionally, an underwater detection apparatus for detecting an object in water using ultrasonic waves has been known. This type of underwater detection apparatus includes a transmitter for transmitting ultrasonic waves into water. The transmitter drives the transducer based on the transmission signal to transmit ultrasonic waves into water. Since the impedance of the transducer is high, it is necessary to efficiently apply a transmission signal of a high voltage to the transducer during transmission in order to generate sufficient ultrasonic wave power.

[0003] A transmitter circuit using a matching circuit is known as a method for efficiently supplying a transmission signal to the transducer. In this transmitter circuit, the resonance frequency of the transducer connected to the matching circuit is matched with the resonance frequency of the transducer itself. This allows the impedance at the resonance frequency to be reduced. As a result, a high voltage transmission signal can be efficiently applied to the transducer in the vicinity of the resonance frequency. In certain cases, a drive circuit having the above configuration may be used within the transmitter circuit.

[0004] Generally, a transducer is installed at the bottom of a ship, and the transmitting circuit is arranged in a control unit installed in a cabin, a bridge, or the like of the ship. Therefore, an oscillator and a transmitting circuit are connected by a relatively long cable. A predetermined parasitic capacitance is generated between the cable and a nearby conductive member or the like. This parasitic capacitance changes according to a length of the cable. When the transducer includes a plurality of oscillators, each oscillator and its transmitting circuit are individually connected by a separate cable. In this case, each cable further generates a parasitic capacitance between other cables. This parasitic capacitance changes according to the length of the cable(s) as well as the distance between the cable(s).

[0005] In this way, the parasitic capacitance greatly affects a design of a matching circuit. In particular, the parasitic capacitance greatly affects the design of the matching circuit because the impedance of the transducer is large. Therefore, even if the matching circuit is designed by the above method, the impedance matching between the matching circuit and the transducer cannot be accurately obtained due to the variation of the capacitance value based on the parasitic capacitance of the cable.

[0006] In view of the above problem, it is an object of the present disclosure to provide a transmitter circuit for performing accurate impedance matching.

[0007] In view of the above problems, it is an object of the present invention to provide a transmitter circuit capable of more accurately performing impedance matching with an oscillator, and an underwater detection apparatus equipped with the transmitter circuit.

[0008] A first aspect of the present disclosure relates to a transmitter circuit for supplying a transmission signal to an oscillator. The transmitter circuit according to the present disclosure includes an L-type matching circuit. The L-type matching circuit may include a capacitance component connected in parallel to the oscillator to form a parallel connection, and an inductive component connected in series to the parallel connection. In an embodiment, a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator and the L-type matching circuit. Further, the transmitter circuit includes a parasitic capacitance (Ccable) of a cable connecting the transmitter circuit and the oscillator.

[0009] According to the transmitter circuit according to the present disclosure, since the parasitic capacitance, Ccable, of the cable is taken into account for impedance matching between the L-type matching circuit and the oscillator, impedance matching between the matching circuit and the oscillator may be obtained more accurately. Therefore, the transmission signal of a high voltage may be efficiently applied to the oscillator.

[0010] In the transmitter circuit according to the present disclosure, the impedance matching condition for the impedance matching is obtained at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD) and the resistor (RTD) itself. The impedance matching condition is obtained when an equivalent circuit of the oscillator is represented by the resistor (RTD), a capacitance (CTD), and an inductance (LTD) connected in series, and a capacitance (C0) connected in parallel to the series connection.

[0011] Thus, a design for impedance matching is performed in consideration of the parasitic capacitance of the cable and an inter-electrode capacitance of the oscillator as well as the matching circuit. Therefore, a higher transmission power may be supplied to the oscillator.

[0012] In the transmitter circuit according to the present disclosure, the circuit section may include a T-type circuit. In this regard, a first impedance jX3of the series connection between the capacitance (CTD) and the inductance (LTD) is connected in series with the resistor (RTD). Additionally, a second impedance (jX2) of a parallel connection between the capacitance (CLMT), the parasitic capacitance (Ccable) and the capacitance (C0) is connected in parallel with the first impedance (jX3) of the series connection. Furthermore, a third impedance (jX1) of the inductance (LLMT) is connected in series with the parallel connection of the first impedance (jX3), the resistor (RTD), and the second impedance (jX2).

[0013] According to this configuration, by converting a T-type circuit into a circuit in which two L-type matching circuits are connected, the design values (Capacitance (CLMT) and Inductance (LLMT)) of the capacitive component and the inductive component for obtaining the impedance matching at the ultrasonic transmission frequency may be smoothly obtained.

[0014] A second aspect of the present invention relates to a transmitter circuit for supplying a transmission signal to an oscillator. The transmitter circuit includes an L-type matching circuit including a capacitance component connected in parallel to the oscillator to form a parallel connection, and an inductive component connected in series to the parallel connection. Additionally, the L-type matching circuit includes a transformer arranged between the L-type matching circuit and the oscillator. In an embodiment, a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator and the L-type matching circuit. In an example, the transmitter circuit includes an inductance of the transformer, and a parasitic capacitance (Ccable) of a cable connecting the transmitter circuit and the oscillator via the transformer.

[0015] According to the transmitter circuit of the present disclosure, since the parasitic capacitance of the cable is taken into account for impedance matching between the L-type matching circuit and the oscillator, impedance matching between the matching circuit and the oscillator may be obtained more accurately. Therefore, a transmission signal of a high voltage may be efficiently applied to the oscillator.

[0016] In the transmitter circuit according to the present disclosure, when the inductance of the transformer is set to be small and the capacitance (CLMT) of the capacitive component is set to be large for performing the impedance matching, variations in the inductance (LT) of the transformer and variations in the parasitic capacitance of the cable and the inter-electrode capacitance of the (ultrasonic) oscillator may not interfere with or affect the impedance matching between the transmitter circuit and the oscillator. Therefore, impedance matching may be stably maintained by a simple design.

[0017] In the transmitter circuit according to the present disclosure, when a secondary side of the transformer is converted to a primary side, the impedance matching condition is associated with performing the impedance matching at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD') and the resistor (RTD') itself. In an embodiment, the impedance matching condition is obtained when an equivalent circuit of the oscillator is represented by the resistor (RTD'), a capacitance (CTD') and an inductance (LTD') connected in series to form a series connection, and a capacitance (C0') connected in parallel to the series connection.

[0018] Thus, a design for impedance matching is performed in consideration of the parasitic capacitance of the cable, the inductance (LT) of the transformer and the inter-electrode capacitance (C0) of the oscillator as well as the matching circuit. Thus, higher transmission power may be supplied to the oscillator.

[0019] In the transmitter circuit according to the present disclosure, when the secondary side of the transformer is converted to the primary side, the transmitter circuit comprises a first parasitic capacitance (Ccable1) of a first cable connecting the matching circuit and the primary side of the transformer, a second parasitic capacitance (Ccable2') of a second cable connecting the secondary side of the transformer and the oscillator, and the inductance (RT) of the transformer.

[0020] In the transmitter circuit according to the present disclosure, the circuit section may further include a T-type circuit. In this regard, a first impedance (jX3) of a series connection of the capacitance (CTD') and the inductance (LTD') is connected in series with the resistor (RTD'). Further, a second impedance (jX2) of a parallel connection of the capacitance (CLMT), the first parasitic capacitance (Ccable1), the second parasitic capacitance (Ccable2'), the capacitance (C0), and an inductance (LT) is connected in parallel with the series connection of the first impedance (jX3) and the resistor (RTD). In addition, a third impedance (jX1) of the inductance (LLMT) is connected in series with the parallel connection of the first impedance (jX3), the resistor (RTD) and the second impedance (jX2).

[0021] According to the above 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) and Inductance (LLMT)) of the capacitive component and the inductive component for obtaining impedance matching at the transmission frequency of ultrasonic waves.

[0022] A third aspect of the present invention relates to an underwater detection apparatus. The underwater detection apparatus according to this aspect includes a transmitter circuit for transmitting an ultrasonic wave to an oscillator in water. The transmitter circuit includes an L-type matching circuit. The L-type matching circuit includes a capacitance component connected in parallel to the oscillator to form a parallel connection, an inductive component connected in series to the parallel connection, and a transformer arranged between the L-type matching circuit and the oscillator. Further, a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator and the L-type matching circuit. The transmitter circuit includes an inductance of the transformer and a parasitic capacitance (Ccable) of a cable connecting the transmitter circuit and the oscillator via the transformer.

[0023] According to the underwater detection apparatus of the present disclosure, since the underwater detection apparatus includes the transmitter circuit according to the embodiments of the present disclosure, impedance matching may be accurately obtained between the transmitter circuit and the oscillator, and a high-voltage transmission signal may be efficiently supplied to the oscillator. Therefore, a target in water may be accurately detected.

[0024] In an embodiment, in the underwater detection apparatus when a secondary side of the transformer is converted to a primary side, the impedance matching condition is associated with performing the impedance matching at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD') and the resistor (RTD') itself. Further, the impedance matching condition is obtained when an equivalent circuit of the oscillator is represented by the resistor (RTD'), a capacitance (CTD') and an inductance (LTD') connected in series to form a series connection, and a capacitance (C0') connected in parallel to the series connection.

[0025] In an embodiment, when the secondary side of the transformer is converted to the primary side, the transmitter circuit includes a first parasitic capacitance (Ccable1) of a first cable connecting the matching circuit and the primary side of the transformer, a second parasitic capacitance (Ccable2') of a second cable connecting the secondary side of the transformer and the oscillator, and the inductance (RT) of the transformer.

[0026] As described above, according to the present invention, it is possible to provide a transmitter circuit capable of obtaining impedance matching with the oscillator more accurately, and an underwater detection apparatus equipped with the transmitter circuit.

[0027] The effect and significance of the present invention will become clearer from the following description of the embodiments. However, the embodiments shown below are merely examples of implementing the present invention, and the present invention is not limited to the embodiments described below.

[0028] FIG. 1 is a diagram schematically showing a manner in which an underwater search is performed by an underwater detection apparatus, in accordance with an embodiment of the present disclosure; FIG. 2 is a block diagram showing a configuration of the underwater detection apparatus, in accordance with an embodiment of the present disclosure; FIG. 3 is a diagram showing a configuration of a transmitter circuit, in accordance with an embodiment of the present disclosure; FIG. 4 is a diagram showing a configuration of the transmitter circuit when an oscillator is shown as an equivalent circuit, in accordance with an embodiment of the present disclosure; FIG. 5 is a diagram showing a configuration downstream from terminals in FIG. 4 grouped into a plurality of impedance elements, in accordance with an embodiment of the present disclosure; FIG. 6 is a diagram showing a state in which a circuit of FIG. 5 is converted into a configuration in which two L-shaped matching circuits are connected, in accordance with an embodiment of the present disclosure; FIG. 7 is a diagram showing a configuration of the transmitter circuit when the oscillator is shown as an equivalent circuit, in accordance with an embodiment of the present disclosure; and FIG. 8 is a diagram showing a circuit configuration when a secondary side of the transformer in FIG. 7 is converted into a primary side, in accordance with an embodiment of the present disclosure.

[0029] Embodiments of the present invention will be described below with reference to the drawings. For convenience, XYZ axes orthogonal to each other are appropriately indicated in the drawings. The X-axis direction and the Y-axis direction are horizontal, and the Z-axis direction is vertical. The positive Y-axis direction is the direction in which the ship travels.

[0030] It is to be understood that not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0031] All of the processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may be embodied in specialized computer hardware.

[0032] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0033] The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processor. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0034] Conditional language such as, among others, "can", "could", "might" or "may" unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps. Thus, such conditional language is not generally intended to imply that features, elements and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and / or steps are included or are to be performed in any particular embodiment.

[0035] Disjunctive language such as the phrase "at least one of X, Y, or Z" unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.

[0036] Any process descriptions, elements or blocks in the flow diagrams described herein and / or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or elements in the process. Alternate implementations are included within the scope of the embodiments described herein in which elements or functions may be deleted, executed out of order from that shown, or discussed, including substantially concurrently or in reverse order, depending on the functionality involved as would be understood by those skilled in the art.

[0037] Unless otherwise explicitly stated, articles such as "a" or "an" should generally be interpreted to include one or more described items. Accordingly, phrases such as "a device configured to" are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, "a processor configured to carry out recitations A, B and C" can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. The same holds true for the use of definite articles used to introduce embodiment recitations. In addition, even if a specific number of an introduced embodiment recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations" without other modifiers, typically means at least two recitations, or two or more recitations).

[0038] It may be understood by those within the art that, in general, terms used herein, are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to" the term "having" should be interpreted as "having at least" the term "includes" should be interpreted as "includes but is not limited to" etc.). For expository purposes, the term "horizontal" as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the system being described is used or the method being described is performed, regardless of its orientation. The term "floor" can be interchanged with the term "ground" or "water surface." The term "vertical" refers to a direction perpendicular to the horizontal as just defined. Terms such as "above", "below", "bottom", "top", "side", "higher", "lower", "upper", "over" and "under" are defined with respect to the horizontal plane.

[0039] As used herein, the terms "attached", "connected", "mated" and other such relational terms should be construed, unless otherwise noted, to include removable, moveable, fixed, adjustable, and / or releasable connections or attachments. The connections / attachments can include direct connections and / or connections having intermediate structure between the two components discussed.

[0040] Numbers preceded by a term such as "approximately", "about" and "substantially" as used herein include the recited numbers, and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms "approximately", "about" and "substantially" may refer to an amount that is less than 10% of the stated amount. Features of embodiments disclosed herein preceded by a term such as "approximately", "about" and "substantially" as used herein represent the feature with some variability that still performs a desired function or achieves a desired result for that feature.

[0041] It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

[0042] FIG. 1 is a diagram schematically showing a manner in which an underwater search is performed by an underwater detection apparatus 10, in accordance with an embodiment of the present disclosure.

[0043] The underwater detection apparatus 10 includes a transducer 13 installed at a bottom of a ship S1. Ultrasonic waves are transmitted from the transducer 13 to a hemispherical transmission space TS1, and the reflected waves are received by the transducer 13. The transducer 13 includes a plurality of oscillators for transmitting and receiving ultrasonic waves. The oscillators are arranged, for example, in a hemispherical or cylindrical shape. A reception signal corresponding to an intensity (echo intensity) of the reflected waves received by each oscillator is generated for each oscillator.

[0044] In FIG. 1, θ is an azimuth angle about the transducer 13 installed at the bottom of the ship, S1, and φ is a depression angle from a horizontal plane (X-Y plane). The underwater detection apparatus 10 performs beam forming on these received signals to form a plurality of reception beams, RB1, distributed in the azimuth angle θ direction and the depression angle φ direction.

[0045] The underwater detection apparatus 10 generates a plurality of reception beams, RB1, in a sector-shaped reception space, RS1, extending in the depression angle, φ, direction. In each reception space, RS1, a plurality of reception beams, RB1, are formed with a predetermined resolution in the depression angle, φ, direction. The reception space, RS1, is set with a predetermined pitch over the entire circumference in the azimuth angle, θ, direction. 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 depression angle, φ, direction is, for example, 90 degrees.

[0046] The underwater detection apparatus 10 acquires the echo intensity at a predetermined distance resolution for each reception beam, RB1, formed in the reception space, RS1. Thus, an echo intensity is acquired at a predetermined distance resolution for each depression angle of each reception beam, RB1. The underwater detection apparatus 10 acquires an echo signal in which the echo intensity is distributed three-dimensionally in the transmission space, TS1, by integrating the echo intensity at each depression angle and each distance acquired for each reception space, RS1, for all reception spaces, RS1.

[0047] The underwater detection apparatus 10 uses the acquired echo signal to display an echo image showing the three-dimensional distribution of the echo intensity on a display section. Each three-dimensional position on the echo image is assigned a color corresponding to the echo intensity. For example, the position of a fish school, F1, on the echo image is assigned a color (e.g., red) corresponding to a high echo intensity. By referring to the color distribution on the echo image, the user can identify and understand the target such as a fish school, F1.

[0048] FIG. 2 is a block diagram showing a configuration of the underwater detection apparatus 10, in accordance with an embodiment of the present disclosure.

[0049] The underwater detection apparatus 10 includes a control circuit (processing circuitry) 11, a storage module 12, a transducer 13, a transmitter circuit 14, a reception circuit 15, a display module 16, a display processing circuitry 17, an operation module (interface) 18, and an operation processing circuitry 19. The transducer 13 may be installed on the bottom of the ship, S1, as described above, and the other components such as the control circuit 11 are installed in a cabin, a bridge, or the like of the ship, S1.

[0050] The control circuit 11 includes an arithmetic processing circuitry such as a CPU (Central Processing Unit) and executes control processing according to a program stored in the storage module 12. The storage module 12 includes a storage medium such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk. The storage module 12 stores a program for the control circuit 11 to execute control processing.

[0051] The transducer 13 includes a plurality of oscillators (depicted as an ultrasonic oscillator 13a, referred to as an oscillator 13a hereinafter). As described above, the oscillators 13a are arranged in a hemispherical or cylindrical shape. Each oscillator 13a transmits an ultrasonic wave to the transmission space, TS1, in FIG. 1 and receives the reflected wave at each processing step (ping) of the transmitted and received wave.

[0052] The transmitter circuit 14 outputs a transmission signal for transmitting an ultrasonic wave to the transducer 13 in accordance with the control from the control circuit 11. The reception circuit 15 processes the signal that the oscillators 13a of the transducer 13 receive and output the reflected wave of the ultrasonic wave, generates a reception signal, and outputs the generated reception signal to the control circuit 11.

[0053] The control circuit 11 performs beam forming on the received signal acquired from each oscillator 13a to form a plurality of received beams distributed in the direction of the azimuth angle, θ, and the direction of the depression angle, φ, and acquires echo signals in the direction of each received beam (the direction of the predetermined azimuth angle, θ, and the direction of the depression angle, φ). The echo signals acquired for each received beam are signals indicating echo intensities that vary according to the elapsed time from the transmission timing of the ultrasonic wave.

[0054] Here, the elapsed time from the transmission timing corresponds to a distance from the transducer 13 in a direction of each received beam, RB1. The control circuit 11 acquires echo intensities at respective distance positions in the direction of each received beam from the echo signals of each received beam by associating the elapsed time from the transmission timing with the distance. The echo intensities are acquired with a predetermined distance resolution.

[0055] The display module 16 includes a display such as a liquid crystal display (LCD). The display processing circuitry 17 causes the display module 16 to display an echo image in accordance with the control from the control circuit 11. The operation module 18 includes input means such as operation keys and a mouse. The operation processing circuitry 19 outputs a signal corresponding to an operation performed on the operation module 18 to the control circuit 11, in accordance with the control from the control circuit 11. The user may change the viewpoint of the echo image, for example, by operating the operation module 18. The display module 16 and the operation module 18 may be composed of a liquid crystal panel in which a touch panel is superposed on a liquid crystal display.

[0056] FIG. 3 is a diagram showing a configuration of the transmitter circuit 14 when an oscillator is shown as an equivalent circuit, in accordance with an embodiment of the present disclosure. For convenience, FIG. 3 shows a configuration for driving one oscillator 13a. The same configuration, as that shown in FIG. 3, may be performed or provided for a plurality of oscillators 13a.

[0057] The transmitter circuit 14 includes a matching circuit 101 and a transmission amplifier 102. The matching circuit 101 is connected to the oscillator 13a via a cable 20. The cable 20 includes a cable 20a for supplying a transmission signal and a cable 20b connected to the ground. The oscillator 13a is, for example, a piezoelectric element, and outputs ultrasonic waves when a voltage corresponding to a transmission signal is applied.

[0058] In an embodiment, 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 with the oscillator 13a, and the inductive component 101b is connected in series with this parallel connection.

[0059] A filter may be arranged between the inductive component 101b and a terminal, T1. However, since this filter is not involved in the calculation related to impedance matching described later, this filter is not specifically mentioned below for the sake of brevity.

[0060] The transmission amplifier 102 outputs to the terminal, T1, a transmission signal obtained by amplifying a control signal input from the control circuit 11. A terminal, T2, is connected to ground in the transmission amplifier 102. The control signal is a pulse signal having a frequency corresponding to the transmission signal and a predetermined duty. The transmission amplifier 102 outputs to the terminal, T1, a transmission signal (pulse signal) obtained by increasing the control signal (pulse signal) to a predetermined voltage. 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 that of the control signal. By controlling the duty of the transmission signal, the transmission power of the oscillator 13a is controlled.

[0061] FIG. 4 is a diagram showing a configuration of the transmitter circuit 14 when the oscillator 13a is shown as an equivalent circuit, in accordance with an embodiment of the present disclosure.

[0062] The equivalent circuit of the oscillator 13a is represented by a circuit in which a capacitance, CTD, an inductance, LTD, and a resistor, RTD, are connected in series, and a capacitance C0is connected in parallel to this series connection. In addition, the circuit of FIG. 4 includes a parasitic capacitance, Ccable, of a cable 20 of FIG. 3.

[0063] As described above, the oscillator 13a and the transmitter circuit 14 are connected by a relatively long cable 20 because the transducer 13 is installed at the bottom of a ship and the transmitter circuit 14 is installed in a cabin, a bridge, or the like of a ship. Normally, a predetermined parasitic capacitance is generated between the cable 20 and a nearby conductive member or the like. This parasitic capacitance varies according to the length of the cable 20.

[0064] As described above, when the transducer 13 includes a plurality of oscillators 13a, each oscillator 13a and its transmitter circuit 14 are individually connected by a cable 20. In this case, parasitic capacitance is generated between each cable 20 and another cable. This parasitic capacitance varies depending on the length of the cable 20 and the distance between the cable 20 and another cable.

[0065] Therefore, if the matching circuit 101 is designed without considering the parasitic capacitance of the cable 20, matching between the matching circuit 101 and the oscillator 13a cannot be obtained. In particular, in the above configuration, since the resistance, RTD, of the oscillator 13a is large, the parasitic capacitance of the cable 20 greatly affects the design of the matching circuit 101.

[0066] Therefore, in the present embodiment, as shown in FIG. 4, the matching circuit 101 is designed in consideration of the parasitic capacitance, Ccable, of the cable 20. In other words, between the circuit including the L-type matching circuit 101 and the parasitic capacitance, Ccable, of the cable 20 and the oscillator 13a, the capacitance, CLMT, of the capacitance component 101a and the inductance, LLMT, of the inductive component 101b are set so as to obtain impedance matching at the ultrasonic transmission frequency.

[0067] Here, a value of the parasitic capacitance, Ccable, of the cable 20 is measured in advance and obtained for each type and length of the cable 20. The type of the cable 20 means a type of multi-axis cable (Number of conductors, distance between conductors, etc.) in which a plurality of cables 20 are integrated as core wires.

[0068] Hereinafter, a method of designing the matching circuit 101, that is, a method of setting the values of the capacitance component 101a and the inductive component 101b constituting the matching circuit 101 will be described.

[0069] FIG. 5 is a diagram showing a configuration downstream from the terminals, T1 and T2, in FIG. 4 grouped into a plurality of impedance elements, in accordance with an embodiment of the present disclosure.

[0070] In FIG. 5, two boundaries, namely, a boundary, B1, and a boundary, B2, on a right side and left side, respectively, are shown by broken lines. An impedance upstream of the boundary, B1, on the left side is shown as an impedance, R1, and an impedance downstream of the boundary, B1, is shown as an impedance, RA. An impedance upstream of the boundary, B2, on the right side is shown as an impedance, RB, and an impedance downstream of the boundary, B2 is shown as an impedance, RTD'. The impedance, RTD', is an impedance of the resistor, RTD, shown in FIG. 4, which constitutes the equivalent circuit of the oscillator 13a.

[0071] In order to efficiently apply a transmission signal having a high voltage at the frequency of the transmission signal to the oscillator 13a, it is necessary to match an impedance, RB, and the impedance, RTD', as condition 1. Further, it is necessary to convert the impedance from the impedance, RB, to an impedance, RA, so as to realize the desired impedance, RA, as condition 2. It may not be necessary to match the impedance, R1, and the impedance, RA.

[0072] First, the following equation is established from the above condition 1.Math 01

[0073] ... (1)

[0074] Next, assuming that an active power is to be supplied to the resistor, RTD, is, WL. Further, a power supply voltage is supplied to the transmission amplifier 102, as shown in FIG. 4. A voltage of the transmission signal (pulse signal) output to the terminal, T1, for example, VB, and a duty of the transmission signal is D, and a circuit efficiency of the circuit shown in FIG. 5 is η. The impedance, RA, is expressed by the following equation.Math 02

[0075] ... (2)

[0076] In the configuration of FIG. 5, the capacitances, C0and CTD, the inductance, LTD, and the resistance, RTD, are known because they are elements of the equivalent circuit of the oscillator 13a. Therefore, from the above equation (1), the impedance, RA, is also known. The value of the parasitic capacitance, Ccable, of the cable 20 is known because it is measured and obtained in advance as described above.

[0077] Therefore, in the configuration of FIG. 5, the inductance, LLMT, and the capacitance, CLMT, are set so that the above condition 2 is satisfied at the frequency of the transmission signal. Hereinafter, the derivation process of the inductance, LLMT, and the capacitance, CLMT, based on the above condition 2 is further described.

[0078] When the impedances, jX1, jX2, and jX3, are set in the circuit shown in FIG. 5. A circuit section sandwiched between the right boundary, B1, and the left boundary, B2, becomes a T-type circuit in which the impedance, jX3, is connected in series to the resistance, RTD; the impedance, jX2, is connected in parallel to the series connection of the impedance, jX3, and the resistance, RTD. Moreover, the impedance, jX1, is connected in series to the impedance, jX3, and a parallel connection of the resistance, RTD, and the impedance, jX2.

[0079] Here, the impedance, jX1, the inductance, jωLLMT, of the inductive component 101b are considered. The impedance, jX2, is an impedance of a parallel connection of the capacitance, C0, the parasitic capacitance, Ccable, of the cable 20, and the capacitance, CLMT, of the capacitive component 101a. The impedance, jX3, is an impedance of a series connection of the capacitance, CTD, and the inductance, LTD.

[0080] If the impedance, jX2, shown in FIG. 5 is divided into two impedances, i.e., jXBand jXD, the circuit shown in FIG. 5 is transformed into a form in which two L-shaped matching circuits, i.e., LM1 and LM2, are connected, as shown in FIG. 6. In FIG. 6, jX3in FIG. 5 are replaced with jXAand jXC, respectively. In FIG. 6, a boundary, B3, is newly set, and an impedance upstream of the boundary, B3, is shown as an impedance, RC, and an impedance downstream of the boundary, B3, is shown as an impedance, RD. In this configuration, an impedance matching (RC=RD) is performed between the impedances, RCand RD.

[0081] Of these two L-types matching circuits, LM1 and LM2, the matching circuit, LM2 on the right side is first examined. In this matching circuit, LM2, QRis defined by the following equation.Math 03

[0082] ... (3)

[0083] Thus, the impedances, jXCand jXD, are expressed by the following equation using QRin Equation (3).Math 04

[0084] ... (4)Math 05

[0085] ... (5)

[0086] Here, the impedance, jXC, is a combined impedance of the inductive component, jωLTD, and the capacitive component, 1 / (jωCTD), as shown in FIG. 5. Therefore, the impedance, jXC, becomes known from ω=2πf depending on a frequency, i.e., a frequency of the transmission signal, f, to be matched. The impedance, RB, is known from the above equation (1). Thus, since the impedances, jXCand RB, are known, QRis obtained from the above equation (4), and the impedances, RDand jXD, are obtained from the above equations (3) and (5).

[0087] Similarly, QLin a left-side matching circuit LM1 is defined by the following equation:Math 06

[0088] ... (6)

[0089] Thus, the impedances, jXAand jXBare expressed by the following equation using QLin the equation (6):Math 07

[0090] ... (7)Math 08

[0091] ... (8)

[0092] Here, the impedance, RA, is a known number from the above equation (2), and the impedance, RC, is equal to an impedance RD, obtained from the above equations (3) to (5) because impedance matching is performed between the impedances, RCand RD. Therefore, the impedance, RC, is a known number. Therefore, QLis obtained by applying these known numbers to Equation (6), and the impedances, jXAand jXB, are obtained by applying known numbers of impedances, RAand RC, together with QLto Equations (7) and (8).

[0093] As shown in FIG. 5 and FIG. 6, the following relationship exists between X1, XAand LLMT.Math 09

[0094] ... (9)

[0095] The inductance, LLMT, of the inductive component 101b is obtained from the Equation (9) and the impedance, jXA, is obtained from the Equation (7).

[0096] The following equation can be obtained from the relationship between the impedance jX2and the impedances, jXBand jXD, in FIGs. 5 and 6.Math 10

[0097] ... (10)Math 11

[0098] ... (11)

[0099] In Equations (10) and (11), since the impedances, jXBand jXD, are known numbers from Equations (8) and (5), and the capacitance, C0, and the parasitic capacitance, Ccable, are also known numbers, the capacitance, CLMT, of the capacitor component 101a may be obtained from Equations (10) and (11).

[0100] In summary, the inductance, LLMT, of the inductive component 101b and the capacitance, CLMT, of the capacitor component 101a can be expressed by the following equation:Math 12

[0101] ... (12)Math 13

[0102] ... (13)

[0103] Since the overall impedance is obtained by the above calculation, the transmission power can be automatically obtained when the applied voltage is determined.

[0104] According to the above embodiment, the following effects may be obtained.

[0105] As described with reference to FIGs. 4 to 6, since the parasitic capacitance, Ccable, of the cable 20 is taken into account for impedance matching between the L-type matching circuit 101 and the oscillator 13a, impedance matching between the matching circuit 101 and the oscillator 13a may be obtained more accurately. Therefore, a transmission signal of a high voltage may be efficiently applied to the oscillator 13a.

[0106] As described with reference to FIGs. 4 and 5, when the equivalent circuit of the oscillator 13a is represented by a resistor, RTD, a capacitance, CTD, and an inductance, LTD, connected in series, and a capacitance, C0, connected in parallel to the series connection, it is set as a condition of impedance matching that impedance matching is obtained at the ultrasonic transmission frequency between the circuit section upstream of the resistor, RTD, and the resistor. RTD.

[0107] Thus, a design for impedance matching is performed in consideration of the parasitic capacitance, Ccable, of the cable 20 and the inter-electrode capacitance, C0, of the oscillator 13a as well as the matching circuit 101. Therefore, a higher transmission power may be supplied to the oscillator.

[0108] As shown in FIG. 5, the circuit section of the oscillator 13a which is impedance matched with the resistor, RTD, comprises a T-type circuit in which a first impedance, jX3, of the series connection of the capacitance, CTD, and the inductance, LTD, is connected in series with the resistor, RTD. Further, a second impedance, jX2, of a parallel connection of the capacitance, CLMT, the parasitic capacitance, Ccable, and the capacitance, C0, is connected in parallel with the first impedance, jX3, of the series connection. In addition, the resistor, RTD, and a third impedance, jX1, of the inductance, LLMT, is connected in series with the first impedance, jX3, and the parallel connection of the resistor, RTD, and the second impedance, jX2.

[0109] Thus, by converting the T-type circuit into a circuit in which two L-type matching circuits LM1 and LM2 are connected as shown in FIG. 6, the design values (Capacitance, CLMT, and Inductance, LLMT) of the capacitance component 101a and the inductive component 101b for impedance matching at the ultrasonic transmission frequency may be smoothly obtained as described above.

[0110] As shown in FIG. 2, the underwater detection apparatus 10 includes the transmitter circuit 14 having the above configuration, and the oscillator 13a transmits ultrasonic waves into the water.

[0111] According to this configuration, since the underwater detection apparatus 10 includes the transmitter circuit 14 having the above configuration, impedance matching may be accurately obtained between the transmitter circuit 14 and the oscillator 13a, and a high-voltage transmission signal may be efficiently supplied to the oscillator 13a. Therefore, a target in the water may be accurately detected.

[0112] FIG. 7 is a diagram showing a configuration of the transmitter circuit 14 when the oscillator 13a is an equivalent circuit, in accordance with an example embodiment of the present disclosure.

[0113] As shown in FIG. 7, a transformer 103 is further arranged between the L-shaped matching circuit 101 and the oscillator 13a. The matching circuit 101 is connected to a primary side or a primary winding of the transformer 103 by a first cable 21, and the oscillator 13a is connected to a secondary side or a secondary winding of the transformer 103 by a second cable 22.

[0114] In this configuration, the capacitance, CLMT, of the capacitance component 101a and the inductance, LLMT, of the inductive component 101b are set in the matching circuit 101 so as to obtain impedance matching at the ultrasonic transmission frequency between the transmitter circuit including a first parasitic capacitance, Ccable1, of the first cable 21, a second parasitic capacitance, Ccable2, of the second cable 22, and the inductance of the transformer 103, and the oscillator 13a.

[0115] The winding ratio, N, of the transformer 103 is expressed as follows: a winding number, N1, of the primary side or the primary winding and a winding number, N2, of the secondary side or the secondary winding.Math 14

[0116] ... (14)

[0117] When a circuit on the secondary side of the transformer 103 is converted to the primary side, the circuit shown in FIG. 7 is expressed as shown in FIG. 8. In the circuit of FIG. 8, the parameters changed by the conversion are expressed as follows.Math 15

[0118] ... (15)Math 16

[0119] ... (16)Math 17

[0120] ... (17)Math 18

[0121] ... (18)Math 19

[0122] ... (19)

[0123] In an embodiment, LTin 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. 8.

[0124] 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 as shown in FIG. 5. Therefore, like the circuit of FIG. 6, the circuit of FIG. 8 is transformed into a form in which two L-type matching circuits, i.e., LM1 and LM2, are connected by dividing the second impedance, jX2, into two impedances, jXBand jXD. Also in this case, the third impedance, jX1, is replaced with the impedance, jXA; and the first impedance, jX3, is replaced with the impedance, jXC.

[0125] After rearranging the circuits in this way, the impedances, jXA, jXB, jXC, and jXD, are obtained by applying the same calculation as in FIG. 6. From the arrangement of the third impedance, jX1, the inductance, LLMT, of the inductive component 101b is obtained from the above equation (9).

[0126] From the arrangement of the second impedance, jX2, the following two equations are established.Math 20

[0127] ... (20)Math 21

[0128] ... (21)

[0129] Equation (20) is the same as equation (10). Therefore, the capacitance, CLMT, of the capacitive component 101a and the inductance, LT, of the transformer 103 must be set to satisfy the following equation.Math 22

[0130] ... (22)

[0131] In this case, the inductance, LT, of the transformer 103 is preferably as small as possible because the variation is generally large. On the other hand, when the inductance, LT, is made small, the capacitance, CLMT, of the capacitive component 101a must be made large from the above equation (22). When the capacitance, CLMT, is made large, the capacitance, CLMT, becomes dominant over the parasitic capacitances, Ccable1and Ccable2', and capacitance C0' in the above equation (22). Therefore, in relation to the equation (22), an influence of the parasitic capacitances, Ccable1and Ccable2' of the first cable 21 and the second cable 22, respectively, and the inter-electrode capacitance, C0', of the oscillator 13a having large variation is suppressed.

[0132] Therefore, when adjusting the capacitance, CLMT, of the capacitive component 101a and the inductance, LT, of the transformer 103 so as to satisfy the above equation (22), it is preferable to set the inductance, LT, to be small and the capacitance, CLMT, to be large. Thus, the influence of the variation of the inductance, LT, of the transformer 103 and the variation of the parasitic capacitances, Ccable1and Ccable2', and the inter-electrode capacitance, C0', of the oscillator 13a on the impedance matching between the transmitter circuit 14 and the oscillator 13a can be suppressed, and the impedance matching can be stably maintained by a simple design.

[0133] Although the circuit of FIG. 7 includes the parasitic capacitances of the first cable 21 and the second cable 22, the parasitic capacitance of any cable may be omitted if either one of the cables 21 and 22 is short and the parasitic capacitance of the cable does not significantly affect the design related to the impedance matching. In this case, 0 is applied to the value of the parameter of the parasitic capacitance of this cable in the above equation (22).

[0134] As shown in FIGs. 7 and 8, since the parasitic capacitances, Ccable1and Ccable2, of the first cable 21 and the second cable 22, respectively, are taken into account for impedance matching between the L-type matching circuit 101 and the oscillator 13a, impedance matching between the matching circuit 101 and the oscillator 13a can be obtained more accurately. Therefore, a transmission signal of a high voltage can be efficiently applied to the oscillator.

[0135] In addition, in the above equation (22) for impedance matching, the inductance, LT, of the transformer 103 is set to be small and the capacitance, CLMT, of the capacitance component 101a is set to be large, so that variations in the inductance, LT, of the transformer 103 and variations in the parasitic capacitances Ccable1and Ccable2, of the first cable 21 and the second cable 22 and the capacitance between electrodes of the oscillator 13a can be suppressed from affecting impedance matching between the transmitter circuit 14 and the oscillator 13a. Therefore, impedance matching can be stably maintained by a simple design.

[0136] As shown in FIG. 8, in a circuit obtained by converting the circuit on the secondary side of the transformer 103 to the primary side when the equivalent circuit of the oscillator 13a is represented by the resistor, RTD', the capacitance, CTD', and the inductance, LTD', connected in series, and the capacitance, C0', connected in parallel to the series connection. In an example, the impedance matching condition is set to obtain impedance matching at the ultrasonic transmission frequency between the circuit section upstream of the resistor RTD' and the resistor RTD.

[0137] Thus, in consideration of the parasitic capacitances, Ccable1and Ccable2', of the first cable 21 and the second cable 22, the inductance, LT, of the transformer, and the inter-electrode capacitance of the oscillator 13a, as well as the matching circuit 101, a design for impedance matching is performed. Therefore, a higher transmission power can be supplied to the oscillator 13a.

[0138] As shown in FIG. 8, the circuit section for impedance matching with the resistor, RTD, of the oscillator 13a comprises a T-type circuit in which the first impedance, jX3, of the series connection of the capacitance, CTD', and the inductance, LTD', is connected in series to the resistor, RTD'. Further, the second impedance, jX2, of the parallel connection of the capacitance, CLMT, the first parasitic capacitance, Ccable1, the second parasitic capacitance, Ccable2', the capacitance, C0, and the inductance, LT, is connected in parallel to the series connection of the first impedance, jX3, and the resistance, RTD.

[0139] Thus, by converting this T-type circuit into a circuit in which the two L-type matching circuits, L1 and L2, are connected as shown in FIG. 6, the design values (Capacitance CLMT, Inductance LLMT) of the capacitance component 101a and the inductive component 101b for impedance matching at the transmission frequency of the ultrasonic wave can be smoothly obtained.

[0140] Further, although a plurality of oscillators 13a are arranged in the transducer 13 or transceiver and the transmitter circuit 14 is prepared for each oscillator 13a, the oscillators 13a and the transmitter circuit 14 arranged in the transducer 13 need not be plural. For example, only one oscillator 13a may be arranged in the transducer 13, and only one transmitter circuit 14 may be assigned to this oscillator 13a.

[0141] Further, the oscillator 13a may be shared between a transmitting wave and a receiving wave, but the oscillator for transmitting a wave and the oscillator for receiving a wave may be arranged separately. In this case, the above configuration is applied to the transmitter circuit that supplies the transmission signal to the oscillator for transmitting the wave.

[0142] In an example, a spread angle of the receiving space, RS1, in the depression angle, φ, direction is 90 degrees, but it is not limited to this. For example, the spread angle of the receiving space, RS1, in the depression angle, φ, direction may be smaller than 90 degrees. For example, the underwater detection apparatus 10 may be a two-dimensional (2D) sonar using an umbrella type transmission beam.

[0143] It is not necessary to use an all-round type of sonar for detecting a target over the entire circumference in the azimuth angle, θ, direction, but for example, a half-round-type sonar or a sonar for forward detection may be used.

[0144] In addition, the embodiments of the present invention may be suitably modified in various ways within the scope of claims. Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and it is of course possible for those skilled in the art to make various modifications.

[0145] 10: Underwater Detection Apparatus, 13: Transducer, 13a: Ultrasonic Oscillator, 14: Transmitter Circuit, 20: Cable, 21: First Cable, 22: Second Cable, 101: Matching Circuit, 101a: Capacitance Component, 101b: Inductive Component, 103: Transformer, C0, CTD, CLMT: Capacitance, Ccable, Ccable1, Ccable2: Parasitic Capacitance, RTD: Resistance

[0146] Patent Literature 1: Japanese Patent No. 5088924

Claims

1. A transmitter circuit (14) for supplying a transmission signal to an oscillator (13a), comprising: 　　an L-type matching circuit (101) comprising: 　　a capacitance component (101a) connected in parallel to the oscillator (13a) to form a parallel connection; and 　　an inductive component (101b) connected in series to the parallel connection, 　　wherein a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator (13a) and the L-type matching circuit (101), wherein the transmitter circuit comprises a parasitic capacitance (Ccable) of a cable (20) connecting the transmitter circuit (14) and the oscillator (13a).

2. The transmitter circuit (14) as claimed in claim 1, wherein 　　the impedance matching condition for the impedance matching is obtained at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD) and the resistor (RTD) itself, and 　　the impedance matching condition is obtained when an equivalent circuit of oscillator is represented by the resistor (RTD), a capacitance (CTD), and an inductance (LTD) connected in series, and a capacitance (C0) connected in parallel to the series connection.

3. The transmitter circuit (14) as claimed in claim 2, wherein the circuit section further comprises a T-type circuit, and wherein: 　　a first impedance (jX3) of the series connection between the capacitance (CTD) and the inductance (LTD) is connected in series with the resistor (RTD), 　　a second impedance (jX2) of a parallel connection between the capacitance (CLMT), the parasitic capacitance (Ccable) and the capacitance (C0) is connected in parallel with the first impedance (jX3) of the series connection, and 　　a third impedance (jX1) of the inductance (LLMT) is connected in series with the parallel connection of the first impedance (jX3), the resistor (RTD), and the second impedance (jX2).

4. A transmitter circuit for supplying a transmission signal to an oscillator (13a), comprising: 　　an L-type matching circuit (101) comprising: 　　a capacitance component (101a) connected in parallel to the oscillator (13a) to form a parallel connection; and 　　an inductive component (101b) connected in series to the parallel connection; and 　　a transformer arranged between the L-type matching circuit (101) and the oscillator (13a), wherein: 　　a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator (13a) and the L-type matching circuit (101), and 　　the transmitter circuit comprises an inductance (22) of the transformer (103) and a parasitic capacitance (Ccable) of a cable (20) connecting the transmitter circuit (14) and the oscillator (13a) via the transformer (103).

5. The transmitter circuit (14) as claimed in claim 4, wherein: 　　when a secondary side of the transformer (103) is converted to a primary side, the impedance matching condition is associated with performing the impedance matching at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD') and the resistor (RTD') itself, and 　　the impedance matching condition is obtained when an equivalent circuit of the oscillator (13a) is represented by the resistor (RTD'), a capacitance (CTD') and an inductance (LTD') connected in series to form a series connection, and a capacitance (C0') connected in parallel to the series connection.

6. The transmitter circuit (14) as claimed in claim 5, wherein when the secondary side of the transformer (103) is converted to the primary side, the transmitter circuit comprises: 　　a first parasitic capacitance (Ccable1) of a first cable (21) connecting the matching circuit and the primary side of the transformer, 　　a second parasitic capacitance (Ccable2') of a second cable (22) connecting the secondary side of the transformer and the oscillator, and 　　the inductance (RT) of the transformer (103).

7. The transmitter circuit (14) as claimed in claim 6, wherein the circuit section further comprises a T-type circuit, wherein 　　a first impedance (jX3) of a series connection of the capacitance (CTD') and the inductance (LTD') is connected in series with the resistor (RTD'), 　　a second impedance (jX2) of a parallel connection of the capacitance (CLMT), the first parasitic capacitance (Ccable1), the second parasitic capacitance (Ccable2'), the capacitance (C0), and an inductance (LT) is connected in parallel with the series connection of the first impedance (jX3) and the resistor (RTD), and 　　a third impedance (jX1) of the inductance (LLMT) is connected in series with the parallel connection of the first impedance (jX3), the resistor (RTD) and the second impedance (jX2).

8. An underwater detection apparatus (10), comprising: 　　a transmitter circuit (14) for transmitting an ultrasonic wave to an oscillator (13a) in water, the transmitter circuit comprising an L-type matching circuit (101), the L-type matching circuit comprising: 　　a capacitance component (101a) connected in parallel to the oscillator (13a) to form a parallel connection; and 　　an inductive component (101b) connected in series to the parallel connection; and 　　a transformer arranged between the L-type matching circuit (101) and the oscillator (13a), wherein: 　　a capacitance (CLMT) of the capacitance component and an inductance (LLMT) of the inductive component are set as an impedance matching condition for performing an impedance matching at an ultrasonic transmission frequency between the oscillator (13a) and the L-type matching circuit (101), and 　　the transmitter circuit comprises an inductance (22) of the transformer (103) and a parasitic capacitance (Ccable) of a cable (20) connecting the transmitter circuit (14) and the oscillator (13a) via the transformer (103).

9. The underwater detection apparatus (10) as claimed in claim 8, wherein: 　　when a secondary side of the transformer (103) is converted to a primary side, the impedance matching condition is associated with performing the impedance matching at the ultrasonic transmission frequency between a circuit section upstream of a resistor (RTD') and the resistor (RTD') itself, and 　　the impedance matching condition is obtained when an equivalent circuit of the oscillator (13a) is represented by the resistor (RTD'), a capacitance (CTD') and an inductance (LTD') connected in series to form a series connection, and a capacitance (C0') connected in parallel to the series connection.

10. The underwater detection apparatus (10) as claimed in claim 9, wherein when the secondary side of the transformer (103) is converted to the primary side, the transmitter circuit comprises: 　　a first parasitic capacitance (Ccable1) of a first cable (21) connecting the matching circuit and the primary side of the transformer, 　　a second parasitic capacitance (Ccable2') of a second cable (22) connecting the secondary side of the transformer and the oscillator, and 　　the inductance (RT) of the transformer (103).

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