Design and Algorithm Integration of High-Precision Adaptive Underwater Detection System Based on MEMS Vector Hydrophone
Yan LiuBoyuan JingGuojun ZhangJiayu PeiLi JiaYanan GengZhengyu BaiJie ZhangZimeng GuoJiangjiang WangYuhao HuangLele XuGuochang LiuWendong Zhang
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Abstract:
Real-time DOA (direction of arrival) estimation of surface or underwater targets is of great significance to the research of marine environment and national security protection. When conducting real-time DOA estimation of underwater targets, it can be difficult to extract the prior characteristics of noise due to the complexity and variability of the marine environment. Therefore, the accuracy of target orientation in the absence of a known noise is significantly reduced, thereby presenting an additional challenge for the DOA estimation of the marine targets in real-time. Aiming at the problem of real-time DOA estimation of acoustic targets in complex environments, this paper applies the MEMS vector hydrophone with a small size and high sensitivity to sense the conditions of the ocean environment and change the structural parameters in the adaptive adjustments system itself to obtain the desired target signal, proposes a signal processing method when the prior characteristics of noise are unknown. Theoretical analysis and experimental verification show that the method can achieve accurate real-time DOA estimation of the target, achieve an error within 3.1° under the SNR (signal-to-noise ratio) of the X channel of −17 dB, and maintain a stable value when the SNR continues to decrease. The results show that this method has a very broad application prospect in the field of ocean monitoring.Keywords:
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Simulation and Measurement of an Acceleration Sensitivity for a Fiber-optic Vector Hydrophone System
Promoting acceleration sensitivity of three-dimensional fiber-optic inertial vector hydrophone is an important requirement in underwater acoustic sensing. Firstly, numerical calculating and finite element simulating technologies are both used to study the acceleration sensitivity. By simulation, it gets the relationship curve between acceleration sensitivity and sensing frequency, with the work frequency 20Hz-2000Hz and acceleration sensitivity 28.7dB in designing parameters. Secondly, the hydrophone is fabricated with using the designing parameters of the simulation. Finally, a fiber-optic vector hydrophone acceleration sensitivity measurement setup is built, and its acceleration sensitivity is tested. In the measurement, vibration signals can successfully be detected and demodulated, when it shows that work frequency of the hydrophone is 20Hz-2000Hz and its acceleration sensitivity is 30dB, whose deviation is 1.3dB from simulation. Comparing and analyzing the simulation and the measurement on acceleration sensitivity, the structure of the hydrophone is proved to be correct and applicable. It is reference significance for its practical application of a fiber-optic vector hydrophone.
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This article introduces the design and experimental verification of a fiber-optic hydrophone. This kind of optical fiber hydrophone is composed of a Michelson interferometer, and the sensitivity enhancement structure is optimized through finite element analysis to improve sensitivity. The developed hydrophone has the characteristics of small size and high sensitivity. In the case of reduced diameter, high sound pressure sensitivity can still be ensured. In the frequency band below 2 kHz, the sensitivity of the hydrophone sample is -140 dB, and the sensitivity fluctuation does not exceed 4 dB.
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Calibration of ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz is required to sufficiently assess the peak rarefactional pressure (pr) and the Mechanical Index (MI) of medical ultrasound imaging devices. However, the ultrasonic hydrophone calibration in this low frequency is barely conducted. Therefore, the objective of this research was to develop a calibration technique for ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz. Two ultrasonic hydrophone probes, one membrane hydrophone and one needle hydrophone, were calibrated using a substitution method combined with time-delay spectrometry (TDS). The calibration results are presented in term of end-of-cable voltage sensitivity as a function of frequency. The calibration data show that the membrane hydrophone exhibit a very flat frequency response, to within ±1 dB for the entire investigated frequency range, whereas the needle hydrophone demonstrates a relative large variations in sensitivity of about 5 dB. These results are in good agreement with the limited data previously reported. Therefore, the substitution calibration technique with Time Delay Spectrometry (TDS) is capable of calibrating the ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz.
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The directivity model of hydrophone describes the frequency response of the hydrophone at different incident angles, which can be used for estimation of the effective diameter of the hydrophone. This parameter is very important because of the correction of the spatial average effect and the accurate measurement of the sound field parameters. At present, the nominal diameter of most commercial hydrophones is difficult to meet the requirement that the effective radius of hydrophone should be less than or equal to 1 / 4 of the acoustic wave wavelength, which may result in large errors because of spatial averaging. To solve this problem, this paper studies an effective diameter measurement method based on three kinds of hydrophone directivity models. In this method, the received signals of the hydrophone at different angles are measured, and the directional response model of hydrophone is established by least square method according to rigid baffle (RB), un-baffled (UB) and soft baffle (SB) model. The influence of directional models on effective diameter measurement is evaluated at different frequencies. The experimental results show that the directivity response data of hydrophone are not only matched with one model at different frequencies, but the directivity model closest to the data points should be selected to estimate the effective diameter of hydrophone.
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A substitution calibration technique for piezoelectric ultrasonic hydrophones is presented that uses an optical multilayer hydrophone as the reference receiver. Broadband nonlinearly distorted focused pulses are first measured with the reference hydrophone and then with the hydrophone to be calibrated. By Fourier transformation of the time wave forms and division of the frequency spectra, the complex-valued frequency response of the hydrophone under test is obtained in a broad frequency range in a very fast and efficient way and with high frequency resolution. The results obtained for a membrane hydrophone and a needle-type hydrophone are compared with those obtained by independent calibration techniques such as primary calibration using optical interferometry and secondary calibration using time-delay spectrometry, and good agreement is found. The calibration data obtained are apt to improve the results of ultrasound exposure measurements using broadband voltage-to-pressure conversion. This is demonstrated for standard pulse parameter determination from exemplar exposure measurements on a commercial diagnostic ultrasound machine. For the membrane hydrophone, the evaluation method commonly used leads to an overestimation of the positive peak pressure by up to 50%, an underestimation of the rarefactional peak pressure by up to 11%, and an overestimation of the pulse intensity integral by up to 28%.
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The principle of simple ultrasonic hydrophone is briefly introduced.The structural design and fabrication method are discussed in detail as well.The experiment results show that the ultrasonic hydrophone has the characteristic of high sensitivity,simple and practical.It has strong anti-jamming ability while the cost is merely 3 % of hydrophone.The sensitivity of simple subaqueous ultrasonic transducer is 95 % of hydrophone in 40 kHz.The working frequency range is 10~100 kHz.It is calibrated by the CS—3 hydrophone.Ultrasonic hydrophone could be widely used as subaqueous ultrasonic pressure sensor in simple measurement.
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A hydrophone away is used to measure spatial distribution in underwater sound field and to detect incoming direction of sound waves in the ocean. It is not usually convenient to handle the hydrophone away because of its extensive scale. And it is not easy to purchase the hydrophone away because of expensive price. A hydrophone logger combined with a hydrophone and data logger was developed to consist conveniently of a hydrophone away for use to receive underwater sound waves. And a hydrophone array system with the hydrophone loggers was developed. Main configurations of the hydrophone 1o99er and the hydrophone array system are introduced in this paper. Also we present some measurement results by the hydrophone logger in a water tank and measurement examples on ambient noise in the sea by the hydrophone away system. And we discuss some advantages in use of the hydrophone array system.
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Most commercially available ultrasonic transducers exhibit finite amplitude distortion in water during hydrophone measurements needed to comply with regulatory requirements. The frequencies observed due to finite amplitude distortion can easily exceed ten times the transducer center frequency and 100 MHz. Typically, hydrophone calibrations are supplied only up to 15 or 20 MHz and do not exhibit a flat response. The frequency response above 15 MHz should be known to accurately represent the acoustic information, especially for high-frequency transducers ranging between 7.5 and 15 MHz. A new hydrophone calibration technique has successfully predicted the frequency response of hydrophones up to 100 MHz. A circular source transducer was first characterized and then modeled using the KZK wave propagation model. This model accounts for diffraction, absorption, and nonlinearity. The transducer frequency response was measured with a hydrophone and compared to the simulation. This difference characterized the frequency response of the hydrophone and was used to estimate the hydrophone calibration. The estimated calibration at 20 MHz was checked and provided good agreement with the manufacturer calibration supplied. Acoustic measurement accuracy will be improved if the hydrophone frequency response is deconvolved from the actual acoustic transducer response.
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A fibre-optic hydrophone consisting of a polarisation-maintaining fibre carrying light from a laser source has been used to measure the acoustic output parameters of a single focused hyperthermia transducer and a six-transducer assembly. Beam profiles of the transducers were measured using the fibre-optic hydrophone and the results compared with those obtained using a PVDF hydrophone. The acoustic power output from the hyperthermia transducer was measured using a radiation force balance. It was observed that the root mean square voltage of the fibre-optic hydrophone output is proportional to the square root of the acoustic power up to more than 80 W. It was also observed that, under continuous-wave operation, the fibre optic hydrophone can stand up to very high power (more than 200 W) without being damaged. As its sensing element is the fibre itself, whose diameter is considerably narrower than the width of the ultrasonic beam, it can provide resolution of about 80 microm in beam profile measurement. The fibre is a line sensor and a computer tomographic technique is used to recover the pressure profile from the hydrophone output voltage. In typical clinical operations, the six-transducer assembly is driven with less than 150 W of electrical power input. In such cases, each individual transducer receives less than 25 W of input power and non-linearity and generation of high frequency harmonics at the focus is not a significant problem.
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Calibration of medical shock wave sources is critical and challenging. Aside from the fiber optic probe hydrophone, there are few if any commercially available hydrophones designed for measuring medical shock waves. We have developed a new PVDF membrane hydrophone and compared it to measurements with a fiber optic probe hydrophone (FOPH) in several lithotripters. One part of the hydrophone held the 5 cm times 5 cm times 25 mum PVDF film with geometrical element size 0.5 mm. The other part housed the preamplifier. By substitution comparison to FOPH and an NTR hydrophone, the sensitivity was found to be 0.035 MPa/mV at 2 MHz. Initial spot frequency comparisons showed the response to be fairly flat from 1-20 MHz but showed an elevated sensitivity at 15-20 MHz, and lithotripsy waveforms indicated some high-pass filtering. The impulse response of a 25 mum membrane was calculated and used to de-convolve the signal after which agreement with waveforms from the other hydrophones was excellent. The hydrophone is sufficiently robust to measure 1000 s of lithotripter shock waves. It is inexpensive, sensitive, and has a lower signal to noise ratio than the FOPH
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