Design of driving and receiving circuit based on underwater acoustic transducer

Starting from the needs of military submarine communications and civil underwater communications, a single-directional planar underwater hydroacoustic transducerwith a resonance frequency of 150 kHz was fabricated, and the transmitter and receiver drive circuits of the transducer were designed based on the principle of point-to-point communication. The underwater acoustic transducer is placed in the water area and connected to the circuit to realize the long-distance underwater communication function. The circuit was tested on a self-designed experimental platform. The test results show that the fabricated transducer has higher emission voltage response and sensitivity, single directivity, and the underwater acoustic communication circuit has adjustable frequency, and the communication is clear and stable. The underwater acoustic communication circuit can be used for military and civilian communications, and is easy to move and carry, and easy to debug. Due to the absorption of electromagnetic waves, light waves and other energy forms by seawater and the existence of deep sea "convergence zones", sound waves are currently the only known energy form that can transmit signals wirelessly over long distances underwater. Sound waves with a vibration frequency above 20 kHz are called ultrasonic waves. Compared with ordinary sound waves, ultrasonic waves have better directivity, stronger penetrating power, and better reflection performance. Therefore, they are widely used in information transmission, damage detection, distance testing, and medical and health fields. But in the process of propagation, the energy loss of the sound wave in the water channel increases with the increase of the frequency, so that the available bandwidth of the water channel is narrow and the information capacity is small. Therefore, the performance of the transmitting and receiving drive circuit plays a vital role in the quality of underwater acoustic communication. In the last century, the US Harris Acoustic Products Company, France, and the United Kingdom developed hydroacoustic communicators suitable for underwater ship communications. They used single-sideband modulation and used large-volume hydrophones as the “window” for signal transmission and reception. , To achieve a certain distance of underwater communication, but the equipment is complex, the transducer is large and the directivity is not sharp enough, not suitable for civilian use; Assembled into an analog communication system based on Linux signal processing software, on the channel simulator Long-distance communication is realized, but the ideal design channel is different from the actual water channel; others have built an underwater communication system based on parallel combined mapping sequence spread spectrum, using DSP chip as the information processing module, thus realizing underwater Concealed, high-speed transmission of information between platforms. However, the 555 timer is traditionally used to generate a carrier wave with a specific vibration frequency to drive the drive circuit of the transducer, and the generated waveform frequency stability is relatively poor; and the recently emerging DSP chip processing technology has complex algorithms and needs to be carried out for different waters. The complicated calculation modification and compensation are not suitable for large-scale promotion in the civilian field. In addition, the probes used in the communication circuit signal transceiver devices that have been developed are not sharp enough, the power is not concentrated, and the bandwidth is relatively narrow, which is not conducive to signal transmission and reception. However, most ultrasonic transceivers are not suitable for water channel operation and cannot meet actual civilian and military needs.

1) Based on a small-volume unidirectional underwater acoustic transducer, this paper uses double-sideband modulation and coherent demodulation methods to develop a transmitting and receiving drive circuit suitable for underwater communication. The underwater acoustic communication circuit has high frequency band utilization and frequency adjustable, suitable for 0 kHz ~ 12. The 5 MHz frequency range transducer has a communication distance of up to 100 meters. The transmitting and driving circuit, the receiving and driving circuit, and the transmitting transducer and hydrophone in the circuit together form a set of hydroacoustic communication system. The system uses the transmitter and hydrophone as the "window" for signal exchange, uses STM32F103RCT6 and AD9833 as the carrier signal source, and combines the relevant modem components to finally achieve stable and clear communication.

1 Transducer production

The 1-3 piezoelectric composite material refers to a material formed by one-dimensional connected piezoelectric ceramic columns arranged in parallel in a three-dimensional connected polymer. Compared with pure ceramic piezoelectric materials 1-3 piezoelectric composite materials, it has better effects in damage detection and the production of transmitting and receiving transducers. Therefore, the acoustic wave transceiver module of this system adopts a planar ultrasonic transducer made of 1-3 piezoelectric composite materials developed in the laboratory, which is composed of a 1-3 piezoelectric composite planar sensitive element, a waterproof sound-permeable layer, an electrode lead, and a rigid Composed of high-quality foam and metal cover. Before making the transducer, it is necessary to use ANSYS finite element simulation software for model architecture and simulation calculation.

Simulation of 1-3 piezoelectric composite sensor

In the ANSYS finite element simulation software, first set the unit type, density, Poisson's ratio and Young's modulus of the epoxy resin, and set the density, stiffness matrix, dielectric constant matrix and piezoelectric matrix of the piezoelectric ceramic. Secondly, set the structure of the 1-3 piezoelectric composite material model: a plane with a length of 100 mm, a width of 100 mm, and a thickness of 10 mm, in which the width of the polymer phase is 0. 28 mm, the width of the piezoelectric ceramic column is 1. 44 mm, the height is 10 mm. In this way, the volume fraction of the PZT piezoelectric ceramic small column in the composite material is 51. 84%. Since the model of the 1-3 composite material contains two-phase materials, the calculation amount is large when the simulation calculation is performed. In order to reduce the calculation amount, one unit of the 1-3 piezoelectric composite material is selected for the simulation calculation. The structure diagram of the 1-3 piezoelectric composite material model and the three-dimensional diagram of the piezoelectric ceramic column are as follows:

1-3 type piezoelectric composite material elements are meshed, and symmetry boundary conditions are added to the boundary around the Z axis (length) of the element, and 1 V voltage is added to the upper surface of the piezoelectric ceramic in the positive direction of the Z axis, Z = 0 Add a voltage of 0 V to the bottom surface.Set the frequency analysis type and select the frequency analysis range (50 ~ 250 kHz) and the number of steps), and then solve and post-process, the obtained admittance diagram is shown in Figure 2. It can be seen from Figure 2 that the transducer meets the frequency requirements, and the sensitive components can be made according to the set parameters.

The 1-3 type piezoelectric composite sensor is made of piezoelectric ceramic blocks with a length of 100 mm, a width of 100 mm, and a thickness of 10 mm. Cut in the length and width directions according to the model design, and then inject epoxy resin 618. After standing for 24 hours, perform the same cutting on the reverse side to polish off the excess epoxy resin in the thickness direction to make a 1-3 type. Piezoelectric composite material. Use alcohol to clean the surface of the composite material, and apply silver paste to compensate the electrode destroyed by polishing the epoxy resin, and finally make the 1-3 piezoelectric composite material sensitive element. Use Agilent 4294A impedance analyzer to test the sensitive components. The test results show that the bandwidth of the 1-3 type piezoelectric composite material sensor is 1 when the resonant frequency is 151 kHz. 71 kHz, the acoustic impedance is 17. 47 Pa·s/m3, the conductivity value is 104. 6 mS, the electromechanical coupling coefficient is 0. 68. The mechanical quality factor is 88. 18. The test result of the sensitive material is good.

1.3 Fabrication of high-frequency unidirectional planar underwater hydro-acoustic transducer Add graphite to the polyurethane whose main component is epoxy resin and stir to make the required waterproof sound-permeable layer, and make the mold according to the size of the transducer for pouring and sealing , And finally made a high-frequency unidirectional planar underwater acoustic transducer.

1. 4 Transducer performance test

Testing the performance of the transducer mainly includes measuring its transmission voltage response, receiving sensitivity and directivity performance. Measuring the directivity of a transducer is usually used to draw its directivity pattern. During the measurement, the transducer under test is rotated to achieve the purpose of measuring the transducer's sending response or receiving sensitivity with the azimuth angle, and then the directional pattern of the transducer is obtained after conversion

2 Circuit design

Considering the point-to-point communication method and power utilization rate, this article adopts double-sideband (DSB) signal modulation and coherent demodulation. The modulation principle is shown in equation (1): uDSB = Kuc (t) uΩ (t) (1) The demodulation principle is shown in equation (2 ): uc (t) = uDSB (t) uΩ (t) ( 2) Where: uDSB is the modulated signal; uc (t) is the modulated signal; uΩ (t) is the carrier signal. The essential function of the DSB modulation circuit is a multiplier, which uses the carrier signal to transfer the information carried by the baseband signal. During demodulation, the modulated signal is multiplied by a carrier of the same frequency and phase, and then passed through a band-pass filter to obtain the original signal. The energy conversion device required for signal transmission adopts the planar ultrasonic transducer made in this article. The principle of the transmitting and receiving drive circuit system is shown .

2. 1 Circuit module

The STM32F103RC single-chip microcomputer uses the Cortex-M3 core, and its maximum CPU speed is 72 MHz. Compared with the 51 and 52 model single-chip microcomputers, the instruction execution speed is faster, the volume is smaller, and the integration is easy. AD9833 is a low power consumption,

programmable signal generation module, which can be programmed to generate sine, square and triangle waves in a certain frequency range. The FSYNC port on it is the input level trigger port, which serves as the frame synchronization and enable signal. When FSYNC is low, data can be transferred. In addition, AD9833 has a 16-bit control register. By programming the control register, AD9833 can work in the state required by the user. Using STM32F103RC model single-chip microcomputer to control AD9833 signal generation module produces less sine wave distortion. The circuit is powered by the TPS5430 switching power supply module, which can provide stable 5 V and 12 V voltages, avoiding the distortion and delay of signal transmission.

When the external audio signal enters the drive circuit, it is multiplied with the 150 kHz sine wave generated by the carrier generation module in the multiplier AD835 module (double-sideband modulation step), and then the band-pass filter filters out part of the noise of the multiplier output signal. The generated signal is amplified by the power amplifier and then connected to the transmitting transducer, and finally the transmitting transducer transmits the signal into the water. Double-sideband modulation can move the baseband signal to the carrier frequency to achieve multiplexing and improve channel utilization; secondly, it expands the signal bandwidth, improves the anti-interference ability of the system, and improves the signal-to-noise ratio. In this driving circuit, the power amplifier amplifies the signal to drive the transducer to work. The external audio signal can be music conducted by the earphone jack of an electronic device, such as a mobile phone, or a signal converted and conducted by external sound through a microphone module.

2. 3 Receiving and driving circuit

After the transmitting transducer transmits the sound wave signal to the water channel, a corresponding receiving drive circuit is required to receive the signal in the water channel and restore the original modulated signal. The working principle of the receiving drive circuit designed in this article. After the receiving drive circuit receives the signal in the channel, it is passed to the high-pass filter through the high-frequency wire, and the noise generated by the circuit and mixed in the channel is removed. Then this signal and 150 kHz sine wave are multiplied in the multiplier AD835 module. The output of the multiplier operation is transmitted to the band-pass filter through the coaxial high-frequency cable, and the signal in the required frequency range is selected (coherent demodulation step). Finally, the power amplifier module TDA2030A is used to drive the speaker module, and the demodulated signal is played in the form of audio. In this system, both the transmitting drive circuit and the receiving drive circuit need to use the voltage stabilizing module TPS5430 to ensure the stable and stable operation of the voltage of each module, and the filters are all 4th-order active filters. The carrier waves used in the modulation and demodulation process are all of the same frequency, which is generated by the active AD9833 module after being programmed by the STM32F103RC microcontroller.

3 Experimental verification

3. 1 Hydroacoustic communication verification

In order to verify the function of this system, an underwater acoustic communication test was carried out in a lake with a radius of about 100 m. Transmit the transmitter transducer and the receiver transducer

The receivers are respectively placed on the two sides of the lake in the diameter direction, respectively connected to the transmitting drive circuit and the receiving drive circuit. Since the frequency of human voice is generally in the range of 8-10 kHz, including many overtone components, the audio signal of a song is randomly selected as the modulation signal. The signal is displayed by an oscilloscope, the original audio modulation signal is shown in Figure 7(a), and the 150 kHz carrier signal output by AD9833 is shown in Figure 7(b)

The carrier signal and audio modulation signal are input to the multiplier to perform preliminary modulation. After being measured by an oscilloscope, the output signal of the multiplier is shown in Figure 8.

According to the frequency display in Figure 8, it conforms to the double-sideband modulation law. The output signal of the multiplier is input into the power amplifier through the coaxial cable, and the power of the signal is increased in a smaller distortion range to drive the transducer to output the signal. Transmit transducer input displayed by oscilloscope.The signal is shown in Figure 9.

It can be observed in Figure 9 that the burr has disappeared, that is, the noise generated by the circuit has been filtered out. The receiving transducer, that is, the hydrophone, receives the signal from the channel as shown in Figure 10.

The signal received by the hydrophone contains audio signals, noise, and part of the superimposed signal caused by the multipath effect in the channel, resulting in glitches and overlaps in some signal waveforms. After the received signal is filtered by a high-pass filter to remove low-frequency noise and superimposed signals, it is demodulated with a 150 kHz sine wave in a system composed of a multiplier and a band-pass filter to restore the original baseband signal, and the speaker is driven by the power amplifier module TDA2030A. The original audio signal is broadcast without distortion. The broadcast audio signal is the original music signal. The audio signal restored by the receiving drive circuit is shown in the bottom waveform of Figure 11.

Figure 11 shows a comparison of the two waveforms. The upper part shows the signal received by the hydrophone, and the lower part is the restored audio signal waveform. The audio restoration effect is good. The waveforms of the original audio signal and the restored audio signal are compared and compared with the original audio and the actual audio sound quality. The result shows that the system can drive a 150 kHz high-frequency unidirectional planar hydro-acoustic transducer. The audio signal can be transmitted with high quality, and the audio at the broadcast end is clear and stable.

3. 2 Frequency Adjustability Verification

After verifying that the system and the matched transducer are working and functioning normally, a second experiment is carried out to verify the adjustability of the frequency of the system. Program the signal generation module to modify it to match the 300 kHz transducer made in the laboratory. Test the signal transmission effect. The audio modulation signal is shown in Figure 12(a), and the newly restored audio signal is shown in Figure 12(b).

The signal waveform detected by the oscilloscope represents the transmitted audio signal. In Figure 12(b), the upper part is the signal received by the hydrophone, and the lower part is the restored audio signal waveform. By comparing and analyzing the input and output audio signals of the system, it can be seen that the system can transmit audio signals with high quality, that is, the system can adapt to signals of different resonance frequencies within a certain frequency range.

3. Performance index analysis

First of all, under the condition of high-frequency accurate transmission of information, the propagation distance of this system is more than 100 m at 150 kHz, which far exceeds the underwater acoustic communication distance of less than 100 meters achieved by many underwater communication systems at the expense of signal transmission quality. Secondly, in terms of the performance of the transmission information bandwidth, compared with many underwater acoustic communication systems with a bandwidth of about 200 Hz on the market, the transmission bandwidth of this system can reach 1. 71 kHz, which largely avoids the distortion of audio signals during communication. Finally, in terms of the quality of voice communication, the clarity of the voice broadcast by the last receiving end is used as the measurement standard. Compared with many civil water voice communication equipment with large noise and unclear signals, the system is tested under the same lake conditions. The audio is clear and stable.

4 Conclusion

This article designs a set of underwater acoustic communication circuit based on the practical application of point-to-point communication and underwater acoustic communication. First of all, based on the relevant theories of transducer design and the results of the laboratory, the structure of the transducer is simulated by ANSYS finite element simulation software, and the method of cutting and filling is performed by using the high-performance sensitive material PZT5-A as the piezoelectric Ceramic functional material phase, epoxy resin 618 is polymer phase, filling the gap of piezoelectric column to make unidirectional 1-3 type piezoelectric composite hydro-acoustic planar transducer. Then, the manufactured transducer was used in the communication system, and an underwater acoustic communication circuit with stable structure and clear communication was developed. This circuit can realize effective underwater communication, and because of the design of the modulation and demodulation circuit and the adjustable frequency of the carrier signal, the circuit can also be matched with the ultrasonic probe to realize the functions of long-distance flaw detection and distance measurement.