Electronic circuit for improving electromagnetic ultrasonic transmission power and reception efficiency, and control method

Abstract

Disclosed in the present invention are an electronic circuit for improving electromagnetic ultrasonic transmission power and reception efficiency, and a control method. An electromagnetic ultrasonic transducer uses N sub-coils as an integral main coil; during high voltage transmission, by means of an electronic circuit, the N sub-coils is connected in parallel into a high voltage power output network; and during signal reception, the electronic circuit connects the N sub-coils in series into a large coil for receiving an electromagnetic ultrasonic echo signal, so as to enhance an electromotive force signal received in the coil. The present invention is a control circuit that reduces the impedance of a transducer during high voltage transmission, improves the power supply power obtained by the transducer, increases ultrasonic echo signals output by the transducer during reception, achieves differential symmetrical output of transducer signals, suppresses common-mode noise of the transducer, and improves the signal-to-noise ratio of received signals. The present invention solves the problem of low signal-to-noise ratio of electromagnetic ultrasonic echo signals caused by difficulty in further improving the conversion efficiency of the same transducer on the basis of existing electromagnetic ultrasonic technology.

Description

Electronic circuit and control method for improving electromagnetic ultrasonic emission power and receiving efficiency TECHNICAL FIELD

[0001] The present application relates to the field of ultrasonic nondestructive testing, in particular to an electronic circuit and control method for improving electromagnetic ultrasonic emission power and receiving efficiency. BACKGROUND

[0002] Since the emergence of electromagnetic ultrasonic transducer technology, it has greatly enriched the application field of ultrasonic testing equipment, especially in recent years, it has been widely used in industrial production. The advantages of electromagnetic ultrasonic transducer technology include: no coupling agent is needed during detection, the detection process is fast, and the measured workpiece is not damaged. The application of electromagnetic ultrasonic transducer technology has a great contribution to the safety of industrial equipment, improves the safety of production and the yield of industrial products, and prolongs the service life of industrial equipment.

[0003] The electromagnetic ultrasonic transducer technology usually uses a high-power high-voltage power supply to excite the transducer on the surface of the measured workpiece in a constant magnetic field, so as to generate ultrasonic waves in the measured workpiece to detect the workpiece. Because the conversion efficiency of electromagnetic transducer is very low, in order to compensate for the low efficiency of the transducer, a passive matching network is generally added between the transducer and the transmission power supply to improve the active power of the transducer receiving the high-voltage transmission power supply, which improves the detection performance of the electromagnetic ultrasonic sensor instrument system to a certain extent. However, when the frequency of the high-power high-voltage power supply is fixed, the impedance of the power supply is fixed, and the obtained power is also fixed; in some more severe working conditions, the signal-to-noise ratio of the echo signal of the measured workpiece is very poor, and effective detection signal cannot be obtained. SUMMARY

[0004] In view of the problems existing in the prior art, the present application aims to provide an electronic circuit for improving electromagnetic ultrasonic emission power and receiving efficiency. A special electronic circuit is used to connect multiple sub-coils in parallel to the output end of an external high-power high-voltage power supply. Compared with connecting these sub-coils in series as a large coil connected to the high-voltage power supply, more energy of the high-voltage power supply output can be received. In addition, a special electronic circuit is used to connect the above-mentioned multiple sub-coils in series as a large coil to receive electromagnetic ultrasonic echo signals in a very short time, so as to achieve the purpose of enhancing the output signal amplitude of the transducer coil.

[0005] The present application solves two key technical difficulties:

[0006] (1) Isolation of high-voltage positive and negative voltages at the parallel common node of the transducer coil during parallel transmission.

[0007] (2) Circuit implementation method for converting the transducer from parallel to series.

[0008] The technical scheme of the present application is:

[0009] An electronic circuit for improving electromagnetic ultrasonic emission power and receiving efficiency, an electromagnetic ultrasonic transducer adopts N sub-coils as a whole parent coil, the N sub-coils are connected in parallel by using the electronic circuit and connected to a high-voltage power supply output network; when receiving a signal, the electronic circuit connects the N sub-coils in series as a large coil for receiving an electromagnetic ultrasonic wave echo signal, so as to enhance the received electromotive force signal in the coil.

[0010] Preferably, the electronic circuit comprises N current-filling diode bias current control circuits, N upper diode interconnection circuits, N lower diode interconnection circuits, N pull current diode bias current control circuits, and 2N high-voltage signal return circuits.

[0011] The N sub-coils of the electromagnetic ultrasonic transducer are numbered in sequence as 1, 2, …, n, …, N, each sub-coil contains two branch coils, numbered as Ln_1 and Ln_2; then:

[0012] The current-filling diode bias current control circuit n is connected with the upper diode interconnection circuit n.

[0013] One end of the upper diode interconnection circuit n is connected with the opposite name end of the branch coil L(n-1)_2 of the transducer sub-coil (n-1), the high-voltage signal return circuit (n-1)_1, and the other end is connected with the same name end of the branch coil Ln_1 of the transducer sub-coil n, the high-voltage power supply output network HVOUT-Ln_1.

[0014] The pull current diode bias current control circuit n is connected with the lower diode interconnection circuit n.

[0015] One end of the lower diode interconnection circuit n is connected with the opposite name end of the branch coil Ln_1 of the transducer sub-coil n, the high-voltage signal return circuit n_2, and the other end is connected with the same name end of the branch coil Ln_2 of the transducer sub-coil n, the high-voltage power supply output network HVOUT-Ln_2.

[0016] The above circuit function features are:

[0017] [1] The current-filling diode bias current control circuit; for controlling the presence or absence of bias current in the upper diode interconnection circuit connected with each transducer sub-coil.

[0018] [2] The upper diode interconnection circuit; for isolating or connecting two transducer sub-coils connected at the two ports of the upper diode interconnection circuit.

[0019] 【3】the lower end diode interconnection circuit; for isolating or connecting two transducer sub-coils connected at the two ports of the lower end diode interconnection circuit.

[0020] 【4】the N pull current diode bias current control circuits; for controlling the presence or absence of bias current in the lower end diode interconnection circuit connected to each transducer sub-coil;

[0021] 【5】the high voltage signal return circuit; for connecting the return path of high voltage signal to ground during high voltage transmission, or closing the path between the small signal return circuit and ground during small signal reception.

[0022] Preferably, the N pull current diode bias current control circuits, wherein the pull current diode bias current control circuit n includes a transistor Qsrc_n, bias resistors Rsrc-t_n and Rsrc-b_n, a negative feedback resistor Rsrc-f_n, and a load resistor Rsrc_n; wherein the bias resistors Rsrc-t_n and Rsrc-b_n are connected in series, with the common end connected to the base of Qsrc_n, the other end of Rsrc-b_n connected to ground, and the other end of Rsrc-t_n connected to +12V; the emitter of Qsrc_n is connected to one end of Rsrc-f_n, and the other end of Rsrc-f_n is connected to VCC controlled by the system processor, with VCC outputting 0V or +12V; the collector of Qsrc_n is connected to one end of Rsrc_n, and the other end of Rsrc_n is connected to the control terminal of the upper end diode interconnection circuit n.

[0023] Preferably, the N upper end diode interconnection circuits, wherein the upper end diode interconnection circuit n includes diodes D-t1_n and D-t2_n; the anode of D-t1_n is connected to the anode of D-t2_n, and both are connected to Rsrc_n at the output terminal of the pull current diode bias current control circuit n; the other end of D-t1_n is connected to the non-same name terminal of the L(n-1)_2 branch coil of the transducer sub-coil (n-1) and the high voltage signal return circuit (n-1)_1; the other end of D-t2_n is connected to the same name terminal of the Ln_1 branch coil of the transducer sub-coil n and the high voltage power supply output network HVOUT-Ln_1.

[0024] Preferably, the N current-source diode bias current control circuits, wherein the current-source diode bias current control circuit n includes a transistor Qsk_n, bias resistors Rsk-t_n and Rsk-b_n, a negative feedback resistor Rsk-f_n, and a load resistor Rsk_n; wherein the bias resistors Rsk-t_n and Rsk-b_n are connected in series, their common terminal is connected to the base of Qsk_n, the other end of Rsk-t_n is grounded, and the other end of Rsk-b_n is connected to a negative voltage of -12V; the emitter of the transistor Qsk_n is connected to one end of the resistor Rsk-f_n, and the other end of Rsk-f_n is connected to the VEE controlled by the system processor, with the VEE outputting 0V or -12V; the collector of the transistor Qsk_n is connected to one end of the load resistor Rsk_n, and the other end of Rsk_n is connected to the control terminal of the lower diode interconnect circuit n;

[0025] Preferably, the N lower diode interconnection circuits, wherein the lower diode interconnection circuit n includes diodes D-b1_n and D-b2_n; the cathodes of diodes D-b1_n and D-b2_n are connected and together connected to the output terminal Rsk_n of the current-pull-type diode bias current control circuit n; the other end of D-b1_n is connected to the opposite-name terminal of the high-voltage signal return circuit n_2 and the Ln_1 branch coil of the transducer sub-coil n, and the other end of D-b2_n is connected to the same-name terminal of the high-voltage power supply output network HVOUT-Ln_2 and the Ln_2 branch coil of the transducer sub-coil n.

[0026] Preferably, the 2N high-voltage signal return circuits include: high-voltage signal return circuit n_1 comprising D-hv-t1_n and D-hv-t2_n; and high-voltage signal return circuit n_2 comprising D-hv-b1_n and D-hv-b2_n.

[0027] A control method for an electronic circuit to improve electromagnetic ultrasonic transmission power and reception efficiency, comprising:

[0028] Step S1: Before the high-voltage power supply is transmitted, the system controls VCC to output 0V and VEE to output 0V. All transistors in the current-sinking diode bias current control circuit are cut off, and simultaneously, all transistors in the current-source diode bias current control circuit are cut off. Therefore, the upper diode interconnect circuit connected to the current-sinking diode bias current control circuit has no bias current and is in a cut-off state. Similarly, the lower diode interconnect circuit connected to the current-source diode bias current control circuit has no bias current and is in a cut-off state. At this time, the two transducer branch coils connected to the upper diode interconnect circuit port are isolated from each other; the two transducer branch coils connected to the lower diode interconnect circuit port are also isolated from each other.

[0029] At this time, the high voltage power supply outputs a high voltage pulse that can be applied to each sub-coil of the transducer. Under the magnetic field, the transducer coils are excited by the high voltage pulse voltage to generate ultrasonic waves in the test block, thus completing one ultrasonic emission.

[0030] Step S2: The high-voltage power supply stops outputting high-voltage pulses. The system controls VCC to output +12V and VEE to output -12V. All transistors in the current-sinking diode bias current control circuit are turned on, and their collectors output a constant current. At the same time, all transistors in the current-pull diode bias current control circuit are also turned on, and their collectors absorb a constant current. As a result, the upper diode interconnect circuit connected to the current-sinking diode bias current control circuit generates a bias current, and the lower diode interconnect circuit connected to the current-pull diode bias current control circuit also generates a bias current. Therefore, both the upper and lower diode interconnect circuits are in a conducting state. At this time, the two transducer branch coils connected to the port of the upper diode interconnect circuit achieve low-impedance connection; the two transducer branch coils connected to the port of the lower diode interconnect circuit also achieve low-impedance connection. All branch coils are connected in series and connected to the ultrasonic signal receiving circuit to complete the reception of one ultrasonic small signal.

[0031] Preferably, step S1 specifically includes:

[0032] When both VCC and VEE are 0V under system control, transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N in the N current-sinking diode bias current control circuits are all in the off state, with no static current at their collectors; transistors Qsk_1, Qsk_2, Qsk_n…Qsk_N in the N current-source diode bias current control circuits are also in the off state, with no static current at their collectors; therefore, the N upper diode interconnect circuits connected to the N current-sinking diode bias current control circuits and the N lower diode interconnect circuits connected to the N current-source diode bias current control circuits also have no bias current; therefore, all diodes in the upper diode interconnect circuits are in the off state, and all diodes in the lower diode interconnect circuits are in the off state; at this time, when the system controls high-voltage transmission, the high-voltage pulse is input from the same-name terminals of the 2N branch coils of the N transducer sub-coils, passes through the high-voltage return circuit connected to the opposite-name terminals of the 2N branch coils, and is connected to ground, forming a loop.

[0033] Preferably, step S2 specifically includes:

[0034] After high-voltage transmission is completed, when the system controls VCC to output +12V and VEE to output -12V, the transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N in the N current-sinking diode bias circuits are in the conducting state. The negative feedback resistors Rsrc-f_1, Rsrc-f_2, Rsrc-f_n…Rsrc-f_N stabilize the static operating current of the transistors connected to them. At this time, the collector of each transistor outputs a constant static current. Simultaneously, the transistors Qsk_1, Qsk_2, Qsk_n…Qsk_N in the N current-pull diode bias current control circuits are in the conducting state. The negative feedback resistors Rsk-f_1, Rsk-f_2, Rsk-f_n…Rsk-f_N stabilize the static operating current of the transistors connected to them. The collector of each transistor absorbs a constant static current. Therefore, the N sub-lines of the transducer… In the transmitting and receiving circuit connected to the Ln_1 branch coil in the coil, the current output from the collector of transistor Qsrc_n in the current-sinking diode bias current control circuit n passes through D-t1_n of the upper diode interconnect circuit n to the opposite-name terminal of the L(n-1)_2 branch coil of the (n-1)th sub-coil, forming a low-impedance AC signal path 2(n-1)+1; the current output from the collector of transistor Qsrc_n in the current-sinking diode bias current control circuit n flows through diode D-t2_n in the upper diode interconnect circuit n, the Ln_1 branch coil of the transducer sub-coil n, D-b1_n in the lower diode interconnect circuit n, and Rsk_n of the current-pull diode bias current control circuit, and finally converges into the collector of transistor Qsk_n. At this time, the collector of transistor Qsk_n in the current-pull diode bias current control circuit absorbs a constant current, thereby forming a low-impedance AC signal path 2n;

[0035] Simultaneously, the current flowing into the collector of transistor Qsk_n in the current-pull diode bias current control circuit n also passes through Rsk_n, D-b2_n in the lower diode interconnect circuit n, Ln_2 branch coil of the transducer sub-coil n, D-t1_(n+1) in the upper diode interconnect circuit n+1, Rsrc_(n+1) in the current-sinking diode bias current control circuit n+1, and finally connects to the collector of transistor Qsrc_(n+1). At this time, the collector of Qsrc_(n+1) outputs a constant current, thus forming a low-impedance AC signal path 2n+1; the current output from the collector of transistor Qsrc_(n+1) in the current-sinking diode bias current control circuit n+1 flows through diode D-t2_(n+1) in the upper diode interconnect circuit n+1, and the transducer sub-coil... The L(n+1)_1 branch coil of coil n+1, D-b1_(n+1) in the lower diode interconnection circuit n+1, and Rsk_(n+1) of the current-pull diode bias current control circuit finally converge into the collector of transistor Qsk_(n+1) to form AC signal low impedance path 2(n+1); the Ln_1 branch coil of transducer sub-coil n is connected to the L(n-1)_2 branch coil of the previous sub-coil (n-1) through the above-mentioned low impedance path 2(n-1)+1 and low impedance path 2n, and the Ln_2 branch coil of transducer sub-coil n and the L(n+1)_1 branch coil of sub-coil n+1 are connected together through low impedance path 2n+1 and low impedance path 2(n+1), realizing the series connection of sub-coil n with the previous sub-coil n-1 and the next sub-coil n+1;

[0036] Similarly, from the nth sub-coil forward to the first sub-coil connected to the transmitting and receiving circuit, low-impedance path 1 is the path formed by the collector of transistor Qsrc_1 in the current-sinking diode bias current control circuit 1, the load resistor Rsrc_1, the diode D-t2_1 in the upper diode interconnection circuit 1, and the positive terminal of the signal input of the ultrasonic signal receiving circuit; low-impedance path 2 is the path formed by the collector of transistor Qsrc_1 in the current-sinking diode bias current control circuit 1, Rsrc_1, D-t1_1 in the upper diode interconnection circuit 1, Ln_1 of the first sub-coil of the transducer, and the collectors of D-b1_1, Rsk_1, and Qsk_1 in the lower diode interconnection circuit 1.

[0037] Analogous from the nth sub-coil to the Nth sub-coil connected in the transmitting and receiving circuit, the low-impedance path 2N+1 is formed by the collector of transistor Qsk_N in the current-pull diode bias current control circuit N, the load resistor Rsk_N, the diode D-b2_N in the lower diode interconnection circuit N, the LN_2 branch coil of sub-coil N, and the negative terminal of the signal input of the ultrasonic signal receiving circuit; the low-impedance path 2N is formed by the collector of transistor Qsrc_N in the current-sinking diode bias current control circuit N, Rsrc_N, and the D-t2_N in the upper diode interconnection circuit 1. The path formed by the collectors of the lower diode interconnect circuit N (D-b1_N, Rsk_N, Qsk_N) of the Nth sub-coil of the transducer (LN_1) is thus connected in series through low-impedance loops 1, 2, ... 2n, 2n+1 ... 2N, 2N+1 to form a single coil. One end of the coil is connected to the positive input terminal of the ultrasonic signal receiving circuit, and the other end is connected to the negative input terminal of the ultrasonic signal receiving circuit. This realizes that the 2N branch coils of the N sub-coils are connected in series and then connected to the ultrasonic signal receiving circuit to complete the output of small signals.

[0038] Compared with the prior art, the advantages of the present invention are:

[0039] 1. This invention manufactures an even number of 2N identical coils as a single main coil within an electromagnetic ultrasonic transducer. A circuit is used to connect all the sub-coils of the transducer in parallel to the transmitting high-voltage power supply circuit, reducing the transducer's input impedance, increasing the output power of the high-voltage power supply, and thus enhancing the active power received by the transducer. During reception, the circuit of this invention connects all the sub-coils within the transducer in series within a very short time to the ultrasonic signal receiving circuit; this enhances the amplitude of the ultrasonic echo signal. The signal amplitude is increased to 4N compared to the amplitude of a single sub-coil. 2 2N is the total number of branch coils.

[0040] 2. This invention relates to a control circuit that reduces transducer impedance and increases the power received by the transducer during high-voltage transmission, increases the ultrasonic echo signal output by the transducer during reception, and achieves differential symmetrical output of the transducer signal, thereby improving the signal-to-noise ratio of the received signal. Multiple identical sub-coils are manufactured within an electromagnetic ultrasonic sensor. A programmable impedance transformation circuit connects the same-name terminals of the multiple sub-coils within the transducer to the positive terminal of the high-voltage power supply during high-voltage transmission, and connects the opposite-name terminals of the multiple sub-coils to the negative terminal of the high-voltage power supply. This reduces the transducer impedance and increases the active power received by the transducer. When the high-voltage power supply stops transmitting and a single transducer is needed to receive a small ultrasonic signal, under the electronic circuit control of this invention, the same-name terminals of each sub-coil within the transducer are connected to the opposite-name terminals of adjacent sub-coils, and the opposite-name terminals of each sub-coil are connected to the same-name terminals of adjacent sub-coils, forming a main coil connected to the positive and negative input terminals of the ultrasonic signal receiving circuit. This solves the problem that, based on existing electromagnetic ultrasonic technology, it is difficult to further improve the conversion efficiency of a single transducer, resulting in a low signal-to-noise ratio of the electromagnetic ultrasonic echo signal. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0042] Figure 1 is a circuit block diagram of an electronic circuit for improving electromagnetic ultrasonic transmission power and reception efficiency according to the present invention.

[0043] Figure 2 is a schematic diagram of circuit part A in Figure 1;

[0044] Figure 3 is the schematic diagram of circuit part B in Figure 1;

[0045] Figure 4 is the schematic diagram of circuit part C in Figure 1;

[0046] Figure 5 is an equivalent circuit diagram of the present invention for controlling multiple coils of an electromagnetic ultrasonic transducer to achieve parallel transmission and series reception.

[0047] Figure 6 is an equivalent circuit of a typical one or two coils connected to an electromagnetic ultrasonic transducer electronic device prior to the disclosure of this invention.

[0048] Figure 7 shows a comparison of the electronic circuit scheme of the present invention with the electronic circuit scheme of a typical electromagnetic ultrasonic transducer under the same transmit voltage and receive gain. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0050] The following specific embodiments will be used for further explanation and verification.

[0051] Example 1

[0052] As shown in Figure 1, the electronic circuit of the present invention for improving electromagnetic ultrasonic transmission power and reception efficiency includes circuit parts A, B, and C. Wherein:

[0053] Circuit section A: This is the circuit diagram of the first two branch coils in a parallel-connected series-connected transmitting and receiving circuit with N branch coils, as shown in Figure 2.

[0054] Circuit section B: This is the circuit diagram of the nth branch coil in a parallel-connected series-connected transmitting and receiving circuit with N branch coils, as shown in Figure 3.

[0055] Circuit section C: This is the circuit diagram of the Nth branch coil in a parallel-connected series-connected transmitting and receiving circuit, as shown in Figure 4.

[0056] The circuit section marked with an ellipsis between circuit section A and circuit section B is an omitted circuit diagram of parallel transmission and series reception from the 3rd branch coil to the (n-1)th branch coil.

[0057] The circuit section marked with an ellipsis between circuit section B and circuit section C is an omitted circuit diagram of parallel transmission and series reception from the (n+1)th branch coil to the (N-1)th branch coil.

[0058] The aforementioned branch coil is also called a sub-coil, and the parallel transmitter-series receiver circuit is the same as the parallel transmitter-series receiver circuit.

[0059] This embodiment presents a novel electronic circuit for controlling multiple coils of an electromagnetic ultrasonic transducer to achieve parallel transmission and series reception; it includes a current-sinking diode bias current control circuit, an upper diode interconnection circuit, a lower diode interconnection circuit, a current-pull diode bias current control circuit, and a high-voltage signal return circuit.

[0060] [1] The current-sinking diode bias current control circuit includes a PNP transistor, two resistors in the PNP transistor base bias circuit, a negative feedback resistor in the PNP transistor emitter, and a load resistor in the PNP transistor collector. Specifically, the first current-sinking diode bias current control circuit consists of: a PNP transistor Qsrc_1, resistors Rsrc-t_1 and Rsrc-b_1 in the transistor base bias circuit, one end of Rsrc-t_1 and Rsrc-b_1 being connected to the base of Qsrc_1, the other end of Rsrc-t_1 being connected to +12V, and the other end of Rsrc-b_1 being grounded; the emitter of Qsrc_1 is connected to the negative feedback resistor Rsrc-f_1, the other end of Rsrc-f_1 being connected to the system control VCC, and VCC output... 0V or +12V; the collector of Qsrc_1 is connected to the load resistor Rsrc_1, and the other end of Rsrc_1 is connected to the upper diode interconnection circuit, from which a constant current is output; and so on, the nth current sinking diode bias current control circuit n includes: transistor Qsrc_n, resistors Rsrc-t_n and Rsrc-b_n, one end of Rsrc-t_n and Rsrc-b_n are connected to the base of Qsrc_n, the other end of Rsrc-t_n is connected to +12V, and the other end of Rsrc-b_n is grounded; the emitter of Qsrc_n is connected to the feedback resistor Rsrc-f_n, and the other end of Rsrc-f_n is connected to VCC; the collector of Qsrc_n is connected to Rsrc_n, and the other end of Rsrc_n is connected to the upper diode interconnection circuit n.

[0061] [2] The upper diode interconnection circuit includes two diodes, whose anodes are connected in series and simultaneously connected to the output load resistor of the current-sinking diode bias current control circuit; specifically, the first two upper diode interconnection circuits are as follows: the first upper diode interconnection circuit consists of D-t1_1 and D-t2_1, the anodes of D-t1_1 and D-t2_1 are connected together and connected to the output load resistor Rsrc_1 of the current-sinking diode bias current control circuit 1, and the cathode of D-t1_1 is connected to the same-name terminal of the transducer sub-coil L1_1, which is simultaneously connected to the high-voltage power supply. The positive terminal HVOUT-L1_1 and the cathode of D-t2_1 are connected to the positive input terminal of the ultrasonic signal receiving circuit. The second upper diode interconnection circuit consists of D-t1_2 and D-t2_2. The anodes of D-t1_2 and D-t2_2 are connected together and connected to the output load resistor Rsrc_2 of the current sinking diode bias current control circuit 2. The cathode of D-t1_2 is connected to the opposite terminal of the transducer sub-coil L1_2, which is also connected to the high-voltage signal return circuit 1_1. The cathode of D-t2_2 is connected to the same terminal of the adjacent sub-coil L2_1, which is also connected to the same terminal of L2_1. Connect to the positive terminal HVOUT-L2_1 of the high-voltage power supply; the nth upper diode interconnection circuit consists of D-t1_n and D-t2_n. The anodes of D-t1_n and D-t2_n are connected together and connected to the output load resistor Rsrc_n of the current sinking diode bias current control circuit n. The cathode of D-t1_n is connected to the opposite terminal of the transducer sub-coil L(n-1)_2, which is also connected to the high-voltage signal return circuit (n-1)_1. The cathode of D-t2_n is connected to the same terminal of the next adjacent sub-coil Ln_1, which is also connected to the positive terminal of the high-voltage power supply. HVOUT-Ln_1; and so on up to the Nth upper diode interconnection circuit N: including diodes D-t1_N and D-t2_N; the anodes of D-t1_N and D-t2_N are connected to the output load Rsrc_N of the current sinking diode bias current control circuit N, the cathode of D-t1_N is connected to the opposite terminal of the (N-1)th sub-coil L(N-1)_2, which is also connected to the high voltage return circuit (N-1)_1, and the cathode of D-t2_N is connected to the same terminal of the Nth sub-coil LN_1, which is also connected to the positive terminal of the high voltage power supply HVOUT-LN_1.

[0062] [3] The lower diode interconnection circuit includes two diodes, the cathodes of which are connected in series and simultaneously connected to the output load resistor of the current-carrying diode bias current control circuit; specifically, the first two and the nth lower diode interconnection circuits are: the lower diode interconnection circuit 1 is composed of D-b1_1 and D-b2_1, the cathodes of D-b1_1 and D-b2_1 are connected together and simultaneously connected to the output load resistor Rsk_1 of the current-carrying diode bias current control circuit 1, the anode of D-b1_1 is connected to the opposite terminal of the transducer sub-coil L1_1, and this opposite terminal is simultaneously connected to the high voltage signal return circuit 1_2; the anode of D-b2_1 is connected to the same terminal of the transducer sub-coil L1_2, and this same terminal is simultaneously connected to the positive terminal HVOUT-L1_2 of the high voltage power supply. The lower diode interconnect circuit 2 consists of D-b1_2 and D-b2_2. The cathodes of D-b1_2 and D-b2_2 are connected together and simultaneously connected to the output load resistor Rsk_2 of the current-source diode bias current control circuit 2. The anode of D-b1_2 is connected to the opposite terminal of the transducer sub-coil L2_1, which is also connected to the high-voltage signal return circuit 2_2. The anode of D-b2_2 is connected to the same terminal of the transducer sub-coil L2_2, which is also connected to the positive terminal HVOUT-L2_2 of the high-voltage power supply. The lower diode interconnect circuit n consists of D-b1_n and D-b2_n. The cathodes of D-b1_n and D-b2_n are connected together and simultaneously connected to the output load resistor Rsk_n of the current-source diode bias current control circuit n. The anode of D-b1_n is connected to the opposite terminal of the transducer sub-coil Ln_1, which is also connected to the high-voltage signal return circuit 2_2. In the current circuit n_2, the anode of D-b2_n is connected to the same-name terminal of the transducer sub-coil Ln_2, which is also connected to the positive terminal HVOUT-Ln_2 of the high-voltage power supply; and so on to the Nth lower diode interconnect circuit N: including diodes D-b1_N and D-b2_N; the cathodes of D-b1_N and D-b2_N are connected to the output load resistor Rsk_N of the current-source diode bias current control circuit N; that is, the cathodes of D-b1_N and D-b2_N are connected together and connected to the output load resistor Rsk_N of the current-source diode bias current control circuit N; the anode of D-b1_N is connected to the opposite-name terminal of the Nth sub-coil LN_1, which is also connected to the high-voltage return circuit N_2, and the anode of D-b2_N is connected to the same-name terminal of the Nth sub-coil LN_2, which is also connected to the positive terminal HVOUT-LN_2 of the high-voltage power supply.

[0063] [4] The current-pull diode bias current control circuit includes one NPN transistor, two resistors in the NPN transistor base bias circuit, an NPN transistor emitter negative feedback resistor, and a load resistor in the NPN transistor collector; specifically, the current-pull diode bias current control circuit 1 consists of: an NPN transistor Qsk_1, resistors Rsk-t_1 and Rsk-b_1 in the transistor base bias circuit, one end of Rsk-t_1 and Rsk-b_1 being connected to the base of Qsk_1, the other end of Rsk-t_1 being grounded, and the other end of Rsk-b_1 being connected to -12V; the emitter of Qsk_1 is connected to the negative feedback resistor Rsk-f_1, the other end of Rsk-f_1 being connected to the system-controlled VEE, and the VEE output... Output 0V or -12V; the collector of Qsk_1 is connected to the load resistor Rsk_1, and the other end of Rsk_1 is connected to the lower diode interconnect circuit 1, drawing a constant current from Rsk_1; and so on, the nth current-source diode bias current control circuit n includes: transistor Qsk_n, resistor Rsk-t_n, Rsk-b_n, one end of Rsk-t_n and Rsk-b_n are connected to the base of Qsk_n, the other end of Rsk-t_n is grounded, and the other end of Rsk-b_n is connected to -12V; the emitter of Qsk_n is connected to the feedback resistor Rsk-f_n, and the other end of Rsk-f_n is connected to VEE; the collector of Qsk_n is connected to Rsk_n, and the other end of Rsk_n is connected to the lower diode interconnect circuit n.

[0064] [5] The high-voltage signal return circuit includes two diodes, one of which has its anode and the other has its cathode connected together and connected to the opposite ends of each sub-coil of the transducer. The other ends of the two diodes are connected together and connected to ground.

[0065] Example 2

[0066] In this embodiment, the circuit operation process for controlling multiple sub-coils of an electromagnetic ultrasonic transducer to achieve parallel transmission and series reception is as follows:

[0067] Before high-power, high-voltage transmission, the system controls VCC to output 0V and VEE to output 0V. At this time, the emitter junctions of the PNP transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsk_N in the N current-sinking diode bias current control circuit are all reverse-biased, and their collector junctions are also reverse-biased. Therefore, Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N are all in the off state. Simultaneously, the 0V output of VEE causes the emitter junctions and collector junctions of the NPN transistors Qsk_1, Qsk_2, Qsk_n…Qsk_N in the N current-source diode bias current control circuit to be reverse-biased, and their output voltages are also reverse-biased. k_N is also in the off state; the N upper diode interconnect circuits connected to the N current-sinking diode bias current control circuits and the N lower diode interconnect circuits connected to the N current-pulling diode bias current control circuits have no forward bias current; therefore, all upper and lower diode interconnect circuits are in the off state, and each branch coil connected to them is isolated from each other; at this time, the high voltage output of the high voltage power supply is input from the same-name terminal of each transducer branch coil, passes through the opposite-name terminal of each transducer branch coil, passes through each high voltage signal return circuit, and finally returns to ground, forming a transmission circuit of 2N high voltage signals, completing one transmission of 2N transducer branch coils connected in parallel to the high voltage power supply;

[0068] After the high-voltage power supply stops outputting, the system controls VCC to output +12V and VEE to output -12V. The emitter junctions of the PNP transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N in the N sinking diode bias current control circuit are all forward-biased, while their collector junctions are reverse-biased. Therefore, Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N are all in amplification mode, and each PNP transistor outputs a constant DC current from its collector. Simultaneously, the -12V output from VEE causes the NPN transistors Qs… The emitter junctions of k_1, Qsk_2, Qsk_n…Qsk_N are forward biased, and the collector junctions are reverse biased. Qsk_1, Qsk_2, Qsk_n…Qsk_N are also in an amplification state, and the collectors of each NPN transistor absorb a constant DC current. The N upper-end diode interconnect circuits connected to the N sink-type diode bias current control circuits and the N lower-end diode interconnect circuits connected to the N source-type diode bias current control circuits generate a constant forward bias current. Therefore, all upper-end and lower-end diode interconnect circuits are in a conducting state, and the connected branch coils… The coils are interconnected by connecting the same-name terminal of one coil to the opposite-name terminal of another adjacent coil. Therefore, the 2N coils are connected in series to form a single coil, which is then connected to the ultrasonic signal receiving circuit to receive a small signal. Specifically, the receiving circuit for each coil is as follows: the same-name terminal of coil L1_1 is connected to the positive input terminal of the ultrasonic signal receiving circuit via the upper diode interconnection circuit 1; the opposite-name terminal of L1_1 is connected to the same-name terminal of coil L1_2 via the lower diode interconnection circuit 1; simultaneously, the opposite-name terminal of coil L1_2 is connected to the next coil via the upper diode interconnection circuit 2. The same-name terminal of L2_1 and the opposite-name terminal of L2_1 are connected to the same-name terminal of branch coil L2_2 through the lower diode interconnection circuit 2; the opposite-name terminal of L2_2 is connected to branch coil L3_1 through the upper diode interconnection circuit 3, and the opposite-name terminal of L3_1 is connected to branch coil L3_2 through the lower diode interconnection circuit 3; each subsequent branch coil is connected to the upper diode interconnection circuit in the same way, and the lower diode interconnection circuit is finally connected to the last 2Nth branch coil. The opposite-name terminal of branch coil LN_2 is finally connected to the negative terminal of the signal input of the ultrasonic signal receiving circuit, completing the output of the signal after the series connection of 2N branch coils.

[0069] Example 3

[0070] In this embodiment, we compare the effect of the circuit disclosed in this invention, which controls multiple branch coils of an electromagnetic ultrasonic transducer to achieve parallel transmission and series reception, with that of the commonly used electromagnetic ultrasonic transducer electronic circuit. The biggest feature of the electronic circuit disclosed in this invention is that it can dynamically adjust the impedance of the electromagnetic ultrasonic transducer coils. The characteristic of the commonly used electromagnetic ultrasonic transducer electronic circuit is that once the transmission frequency is fixed, the impedance of the coil is fixed. To simplify the explanation, we can draw the equivalent transmission and reception circuits. Figure 6(a) is an equivalent transmission and reception circuit diagram of an electromagnetic ultrasonic transducer coil connected in a commonly used electronic circuit; Figure 6(b) is an equivalent transmission and reception circuit diagram of two coils connected in series in a commonly used electromagnetic ultrasonic transducer electronic circuit; Figure 6(c) is an equivalent transmission and reception circuit diagram of two coils connected in parallel in a commonly used electromagnetic ultrasonic transducer electronic circuit.

[0071] Figure 7(a) shows the test results of Figure 6(a). More specific parameters for the test are: coil outer diameter 18mm, inner diameter 6mm, electromagnetic ultrasonic transducer 2mm away from the workpiece surface, transmission frequency 4.3MHz, gain 73.3dB, and the test sample is 10mm thick low-carbon steel. The test results of Figures 6(b) and 6(c) are almost identical. Taking one equivalent circuit structure as an example, Figure 7(b) shows the test results of using two coils identical to those in Figure 6(a) in Figure 6(c). We can see that compared to the single coil in Figure 7(a), the signal amplitude obtained by the parallel transmitting and receiving dual coils in Figure 7(b) is twice that of the single coil. Figure 7(c) shows the test results of the electronic circuit of the present invention on two identical coils in Figure 6(a). The equivalent circuit diagram of the coil is shown in Figure 5. We can see that its signal amplitude is 4 times that of a single coil and 2 times that of a parallel transmitting and receiving coil. Figure 7(d) shows the test results of the circuit of the present invention on four identical coils in Figure 6(a). The equivalent circuit diagram of the coil is shown in Figure 5. We can see that its signal amplitude is 16 times that of a single coil and 4 times that of a parallel transmitting and receiving coil, that is, 4 times that of a parallel transmitting and receiving coil.

Claims

1. An electronic circuit for improving electromagnetic ultrasonic transmission power and reception efficiency, characterized in that: The electromagnetic ultrasonic transducer uses N sub-coils as a single main coil. When transmitting high voltage, the N sub-coils are connected in parallel to the high voltage power supply output network using electronic circuitry. When receiving signals, the electronic circuitry connects the N sub-coils in series to form a large coil to receive electromagnetic ultrasonic echo signals, thereby enhancing the electromotive force signal received in the coil.

2. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 1, characterized in that: The electronic circuit includes N current-sinking diode bias current control circuits, N upper diode interconnection circuits, N lower diode interconnection circuits, N current-source diode bias current control circuits, and 2N high-voltage signal return circuits. The electromagnetic ultrasonic transducer has N sub-coils numbered 1, 2, ..., n, ..., N in sequence. Each sub-coil contains two branch coils, numbered Ln_1 and Ln_2. Then: The current-sinking diode bias current control circuit n is connected to the upper diode interconnection circuit n. One end of the upper diode interconnection circuit n is connected to the opposite-name terminal of the branch coil L(n-1)_2 of the transducer sub-coil (n-1) and the high-voltage signal return circuit (n-1)_1, and the other end is connected to the same-name terminal of the branch coil Ln_1 of the transducer sub-coil n and the high-voltage power output network HVOUT-Ln_1. The current-pull-type diode bias current control circuit n is connected to the lower diode interconnection circuit n; One end of the lower diode interconnect circuit n is connected to the opposite-name terminal of the branch coil Ln_1 of the transducer sub-coil n and the high-voltage signal return circuit n_2, and the other end is connected to the same-name terminal of the branch coil Ln_2 of the transducer sub-coil n and the high-voltage power supply output network HVOUT-Ln_2.

3. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 2, characterized in that, The N current-sinking diode bias current control circuits include a transistor Qsrc_n, bias resistors Rsrc-t_n and Rsrc-b_n, a negative feedback resistor Rsrc-f_n, and a load resistor Rsrc_n. The bias resistors Rsrc-t_n and Rsrc-b_n are connected in series, with their common terminal connected to the base of Qsrc_n. The other end of Rsrc-b_n is grounded, and the other end of Rsrc-t_n is connected to +12V. The emitter of transistor Qsrc_n is connected to one end of resistor Rsrc-f_n, and the other end of Rsrc-f_n is connected to VCC controlled by the system processor. VCC outputs 0V or +12V. The collector of transistor Qsrc_n is connected to one end of the load resistor Rsrc_n, and the other end of Rsrc_n is connected to the control terminal of the upper diode interconnect circuit n.

4. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 2, characterized in that, The N upper diode interconnection circuits, wherein the upper diode interconnection circuit n includes diodes D-t1_n and D-t2_n; the positive terminals of diodes D-t1_n and D-t2_n are connected and connected together to the Rsrc_n of the output terminal of the current sinking diode bias current control circuit n; the other end of D-t1_n is connected to the opposite-name terminal of the high-voltage signal return circuit (n-1)_1 and the L(n-1)_2 branch coil of the transducer sub-coil (n-1); the other end of D-t2_n is connected to the same-name terminal of the high-voltage power supply output network HVOUT-Ln_1 and the Ln_1 branch coil of the transducer sub-coil n.

5. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 2, characterized in that, The N current-source diode bias current control circuits include a transistor Qsk_n, bias resistors Rsk-t_n and Rsk-b_n, a negative feedback resistor Rsk-f_n, and a load resistor Rsk_n. The bias resistors Rsk-t_n and Rsk-b_n are connected in series, with their common terminal connected to the base of Qsk_n. The other end of Rsk-t_n is grounded, and the other end of Rsk-b_n is connected to a negative voltage of -12V. The emitter of transistor Qsk_n is connected to one end of resistor Rsk-f_n, and the other end of Rsk-f_n is connected to VEE controlled by the system processor. VEE outputs 0V or -12V. The collector of transistor Qsk_n is connected to one end of the load resistor Rsk_n, and the other end of Rsk_n is connected to the control terminal of the lower diode interconnect circuit n.

6. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 2, characterized in that, The N lower diode interconnection circuits, wherein the lower diode interconnection circuit n includes diodes D-b1_n and D-b2_n; the cathodes of diodes D-b1_n and D-b2_n are connected and connected together to the Rsk_n of the output terminal of the current-pull-type diode bias current control circuit n; the other end of D-b1_n is connected to the opposite-name terminal of the high-voltage signal return circuit n_2 and the Ln_1 branch coil of the transducer sub-coil n, and the other end of D-b2_n is connected to the same-name terminal of the high-voltage power supply output network HVOUT-Ln_2 and the Ln_2 branch coil of the transducer sub-coil n.

7. The electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 2, characterized in that, The 2N high-voltage signal return circuits; wherein high-voltage signal return circuit n_1 includes D-hv-t1_n and D-hv-t2_n; high-voltage signal return circuit n_2 includes D-hv-b1_n and D-hv-b2_n.

8. A control method for an electronic circuit to improve electromagnetic ultrasonic transmission power and reception efficiency, characterized in that, include: Step S1: Before the high-voltage power supply is transmitted, the system controls VCC to output 0V and VEE to output 0V. All transistors in the current-sinking diode bias current control circuit are cut off, and simultaneously, all transistors in the current-source diode bias current control circuit are cut off. Therefore, the upper diode interconnect circuit connected to the current-sinking diode bias current control circuit has no bias current and is in a cut-off state. Similarly, the lower diode interconnect circuit connected to the current-source diode bias current control circuit has no bias current and is in a cut-off state. At this time, the two transducer branch coils connected to the upper diode interconnect circuit port are isolated from each other; the two transducer branch coils connected to the lower diode interconnect circuit port are also isolated from each other. At this time, the high voltage power supply outputs a high voltage pulse that can be applied to each sub-coil of the transducer. Under the magnetic field, the transducer coils are excited by the high voltage pulse voltage to generate ultrasonic waves in the test block, thus completing one ultrasonic emission. Step S2: The high-voltage power supply stops outputting high-voltage pulses. The system controls VCC to output +12V and VEE to output -12V. All transistors in the current-sinking diode bias current control circuit are turned on, and their collectors output a constant current. At the same time, all transistors in the current-pull diode bias current control circuit are also turned on, and their collectors absorb a constant current. As a result, the upper diode interconnect circuit connected to the current-sinking diode bias current control circuit generates a bias current, and the lower diode interconnect circuit connected to the current-pull diode bias current control circuit also generates a bias current. Therefore, both the upper and lower diode interconnect circuits are in a conducting state. At this time, the two transducer branch coils connected to the port of the upper diode interconnect circuit achieve low-impedance connection; the two transducer branch coils connected to the port of the lower diode interconnect circuit also achieve low-impedance connection. All branch coils are connected in series and connected to the ultrasonic signal receiving circuit to complete the reception of one ultrasonic small signal.

9. The control method for the electronic circuit for improving electromagnetic ultrasonic transmission power and reception efficiency according to claim 8, characterized in that, Step S1 specifically includes: When both VCC and VEE are 0V under system control, transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N in the N current-sinking diode bias current control circuits are all in the off state, with no static current at their collectors; transistors Qsk_1, Qsk_2, Qsk_n…Qsk_N in the N current-source diode bias current control circuits are also in the off state, with no static current at their collectors; therefore, the N upper diode interconnect circuits connected to the N current-sinking diode bias current control circuits and the N lower diode interconnect circuits connected to the N current-source diode bias current control circuits also have no bias current; therefore, all diodes in the upper diode interconnect circuits are in the off state, and all diodes in the lower diode interconnect circuits are in the off state; at this time, when the system controls high-voltage transmission, the high-voltage pulse is input from the same-name terminals of the 2N branch coils of the N transducer sub-coils, passes through the high-voltage return circuit connected to the opposite-name terminals of the 2N branch coils, and is connected to ground, forming a loop.

10. The control method for the electronic circuit for improving electromagnetic ultrasonic transmission power and receiving efficiency according to claim 8, characterized in that, Step S2 specifically includes: After high-voltage transmission is completed, when the system controls VCC to output +12V and VEE to output -12V, the transistors Qsrc_1, Qsrc_2, Qsrc_n…Qsrc_N in the N current-sinking diode bias current control circuit are in the conducting state. The negative feedback resistors Rsrc-f_1, Rsrc-f_2, Rsrc-f_n,…, Rsrc-f_N stabilize the static operating current of the transistors connected to them. At this time, the collector of each transistor outputs a constant static current. Simultaneously, the transistors Qsk_1, Qsk_2, Qsk_n,…, Qsk_N in the N current-pull diode bias current control circuit are in the conducting state. The negative feedback resistors Rsk-f_1, Rsk-f_2, Rsk-f_n…Rsk-f_N stabilize the static operating current of the transistors connected to them. The collector of each transistor absorbs a constant static current. Therefore, the transducer… In the transmitting and receiving circuit connected to the Ln_1 branch coil of the N sub-coils, the current output from the collector of transistor Qsrc_n in the current-sinking diode bias current control circuit n passes through D-t1_n of the upper diode interconnection circuit n to the opposite-name terminal of the L(n-1)_2 branch coil of the (n-1)th sub-coil, forming a low-impedance AC signal path 2(n-1)+1; the current output from the collector of transistor Qsrc_n in the current-sinking diode bias current control circuit n flows through diode D-t2_n in the upper diode interconnection circuit n, the Ln_1 branch coil of the transducer sub-coil n, D-b1_n in the lower diode interconnection circuit n, and Rsk_n of the current-pull diode bias current control circuit, and finally converges into the collector of transistor Qsk_n. At this time, the collector of transistor Qsk_n in the current-pull diode bias current control circuit absorbs a constant current, thereby forming a low-impedance AC signal path 2n; Simultaneously, the current flowing into the collector of transistor Qsk_n in the current-pull diode bias current control circuit n also passes through Rsk_n, D-b2_n in the lower diode interconnect circuit n, Ln_2 branch coil of the transducer sub-coil n, D-t1_(n+1) in the upper diode interconnect circuit n+1, Rsrc_(n+1) in the current-sinking diode bias current control circuit n+1, and finally connects to the collector of transistor Qsrc_(n+1). At this time, the collector of Qsrc_(n+1) outputs a constant current, thus forming a low-impedance AC signal path 2n+1; the current output from the collector of transistor Qsrc_(n+1) in the current-sinking diode bias current control circuit n+1 flows through diode D-t2_(n+1) in the upper diode interconnect circuit n+1, and the transducer sub-coil... The L(n+1)_1 branch coil of coil n+1, D-b1_(n+1) in the lower diode interconnection circuit n+1, and Rsk_(n+1) of the current-pull diode bias current control circuit finally converge into the collector of transistor Qsk_(n+1) to form AC signal low impedance path 2(n+1); the Ln_1 branch coil of transducer sub-coil n is connected to the L(n-1)_2 branch coil of the previous sub-coil (n-1) through the above-mentioned low impedance path 2(n-1)+1 and low impedance path 2n, and the Ln_2 branch coil of transducer sub-coil n and the L(n+1)_1 branch coil of sub-coil n+1 are connected together through low impedance path 2n+1 and low impedance path 2(n+1), realizing the series connection of sub-coil n with the previous sub-coil n-1 and the next sub-coil n+1; Similarly, from the nth sub-coil forward to the first sub-coil connected to the transmitting and receiving circuit, low-impedance path 1 is the path formed by the collector of transistor Qsrc_1 in the current-sinking diode bias current control circuit 1, the load resistor Rsrc_1, the diode D-t2_1 in the upper diode interconnection circuit 1, and the positive terminal of the signal input of the ultrasonic signal receiving circuit; low-impedance path 2 is the path formed by the collector of transistor Qsrc_1 in the current-sinking diode bias current control circuit 1, Rsrc_1, D-t1_1 in the upper diode interconnection circuit 1, L1_1 of the first sub-coil of the transducer, and the collectors of D-b1_1, Rsk_1, and Qsk_1 in the lower diode interconnection circuit 1. Analogous from the nth sub-coil to the Nth sub-coil connected in the transmitting and receiving circuit, the low-impedance path 2N+1 is formed by the collector of transistor Qsk_N in the current-pull diode bias current control circuit N, the load resistor Rsk_N, the diode D-b2_N in the lower diode interconnect circuit N, the LN_2 branch coil of sub-coil N, and the negative terminal of the signal input of the ultrasonic signal receiving circuit; the low-impedance path 2N is formed by the collector of transistor Qsrc_N in the current-sinking diode bias current control circuit N, Rsrc_N, and the diode D-t2_N in the upper diode interconnect circuit N. The path formed by the collectors of the lower diode interconnect circuit N (D-b1_N, Rsk_N, Qsk_N) of the Nth sub-coil of the transducer (LN_1) is thus connected in series through low-impedance loops 1, 2, ... 2n, 2n+1 ... 2N, 2N+1 to form a single coil. One end of the coil is connected to the positive input terminal of the ultrasonic signal receiving circuit, and the other end is connected to the negative input terminal of the ultrasonic signal receiving circuit. This realizes that the 2N branch coils of the N sub-coils are connected in series and then connected to the ultrasonic signal receiving circuit to complete the output of small signals.

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