A feedback control method for phase signal demodulation in fber-optic hydrophones

In the realm of acoustic signal detection,the identification of weak signals,particularly in the presence of negative signal-to-noise ratios,poses a significant challenge.This challenge is further heightened when signals are acquired through fiber-optic hydrophones,as these signals often lack physical significance and resist clear systematic modeling.Conventional processing methods,e.g.,low-pass filter(LPF),require a thorough understanding of the effective signal bandwidth for noise reduction,and may introduce undesirable time lags.This paper introduces an innovative feedback control method with dual Kalman filters for the demodulation of phase signals with noises in fiber-optic hydrophones.A mathematical model of the closed-loop system is established to guide the design of the feedback control,aiming to achieve a balance with the input phase signal.The dual Kalman filters are instrumental in mitigating the effects of signal noise,observation noise,and control execution noise,thereby enabling precise estimation for the input phase signals.The effectiveness of this feedback control method is demonstrated through examples,showcasing the restoration of low-noise signals,negative signal-to-noise ratio signals,and multi-frequency signals.This research contributes to the technical advancement of high-performance devices,including fiber-optic hydrophones and phase-locked amplifiers.

A Bionic Fish Cilia Median-Low Frequency Three-Dimensional Piezoresistive MEMS Vector Hydrophone

A bionic fish cilia median-low frequency three-dimensional MEMS vector hydrophone is reported in this paper. The piezoresistive reasonable position was obtained through finite element analysis by ANSYS and the structure was formed by MEMS processes including lithography, ion implantation, PECVD and etching,etc. The standing wave barrel results show that the lowest sensitivity of the hydrophone is-200 d B and reach up to-160 d B(in which the voltage amplification factor is 300). It has a good frequency response characteristics in 25 Hz ～ 1500 Hz band. Directivity tests displayed that the hydrophone has a good "8"-shaped directivity,in which the resolution is not less than 30 d B, and asymmetry of the maximum axial sensitivity value is less than 1.2 d B.

Low-radioactivity ultrasonic hydrophone used in positioning system for Jiangmen Underground Neutrino Observatory

To satisfy the accurate positioning requirement of the calibration source in the Jiangmen Underground Neutrino Observatory, a Tonpilz-type hydrophone with low radioactivity and high electroacoustics is developed.The radioactivity of the proposed hydrophone is strictly controlled by selecting pure raw materials, especially active piezoelectric ceramics. The electroacoustic performance of the hydrophone is improved by making structural optimization. High sensitivity and aimed directivity are achieved using 33-mode piezoelectric ceramic rings arranged in series and improvement in the radiating head of the Tonpilz hydrophone, respectively. All electroacoustic performances are studied through finite element analyses.The simulations indicate that the electroacoustic performances of the hydrophones in linear alkylbenzene-based liquid scintillator can be approximately predicted according to the results in water because their differences caused by two types of acoustic media, water and liquid scintillator, are known. The tests show that the hydrophone prototype can achieve a maximum sensitivity of-209.3dB and a beamwidth of 132.2° at a frequency of 143 kHz.In addition, eight hydrophones only contributed to a background radioactivity level of 26 ± 4 mHz in the neutrino analysis.

Design and Benchmark Tests of a Multi-Channel Hydrophone Array System for Dolphin Echolocation Recordings

This paper describes in depth the design and application considerations of a computer based measurement system enabling 1 MS/s simultaneous sampling of 47 hydrophones for cross sectional recordings of echolocation beams of toothed whales (Odontocetes). An earlier prototype version of the system has previously only been presented as a brief proof of principle that did not offer a complete description of the software and hardware solution. Crucial hardware and software design considerations of the further developed system include the re-arm times of the burst mode sampling and the dual-core distributed execution of the software components. The rearm time was measured to 283 μs, using a 550 μs long sample window around each click. This enables burst mode sampling of clicks with an inter-click interval as short as 833 μs. It is shown through both synthetic benchmark tests of the system and through field measurements of bottlenose dolphins (Tursiops truncatus) and a beluga whale (Delphinapterus leucas) that it is capable of acquiring, analyzing and visualizing data in run-time. It operates effectively also in highly reverberant surroundings like concrete pools and shallow waters. Burst mode sampling allows the system to block reflections with 0.3 - 0.5 m longer propagation paths than the direct path. It is suggested that the system’s compliance to reverberant recording sites makes it valuable in future dolphin echolocation studies.

An Improved Cymbal Hydrophone Made of Lanthanum-Modified Lead Zirconate Titanite

Lanthanum-modified lead zirconate titanite （PLZT） piezoelectric ceramics has higher piezoelectric and dielectric properties compared with the common lead zirconate titanite （PZT） ceramics. These properties endue the cymbal hydrophones made of PLZT usually with stable performance but lower receiving sensitivity. In order to improve the sensitivity, through a static analysis on hydrophone we did some changes for the PLZT hydrophone by reducing the radius of the piezoelectric ceramics and sealing its boundary. Furthermore, ANSYS simulations were made, and the experiments for the improved PLZT hydrophone and the original one were carried out in water pool. The results show that the receiving sensitivity of the improved cymbal hydrophone made of PLZT is 3 -4 dB higher than that of the original, and that the frequency response still keeps flat within 18 kHz band.

FBG Hydrophone: Theory and Experiment

A fiber Bragg grating （FBG） hydrophone with enhanced sensitivity is demonstrated. A novel piston-like diaphragm with a hard core fixed at the center is used as the sensing element. Theoretical analysis shows that the Young＇s modulus of the diaphragm and the radius of the hard core have significant effect on the pressure sensitivity. Experiments are carried out to test this effect and the performance of the hydrophone. The static measure- ment result is in good agreement with the theoretical result and an acoustic sensitivity of 7 nm/MPa has been achieved.

Recent Progress in Fiber-Optic Hydrophones

Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.

Underwater hybrid near-field acoustical holography based on the measurement of vector hydrophone array

Hybrid near-field acoustical holography(NAH) is developed for reconstructing acoustic radiation from a cylindrical source in a complex underwater environment. In hybrid NAH,we combine statistically optimized near-field acoustical holography(SONAH) and broadband acoustical holography from intensity measurements(BAHIM) to reconstruct the underwater cylindrical source field. First,the BAHIM is utilized to regenerate as much acoustic pressures on the hologram surface as necessary,and then the acoustic pressures are taken as input to the formulation implemented numerically by SONAH. The main advantages of this technology are that the complex pressure on the hologram surface can be reconstructed without reference signal,and the measurement array can be smaller than the source,thus the practicability and efficiency of this technology are greatly enhanced. Numerical examples of a cylindrical source are demonstrated. Test results show that hybrid NAH can yield a more accurate reconstruction than conventional NAH. Then,an experiment has been carried out with a vector hydrophone array. The experimental results show the advantage of hybrid NAH in the reconstruction of an acoustic field and the feasibility of using a vector hydrophone array in an underwater NAH measurement,as well as the identification and localization of noise sources.

Comparison of optical detection system,PVDF detection system,and PVDF needle hydrophone for optoacoustic tomography

Optoacoustic tomography （PAT） is a two-dimensional medical imaging method that has the advantage of optical contrast and resolution of ultrasonic waves. The detection systems with a high sensitivity can be used for detecting small tumors, located deeply in human tissues, such as the breast. In this study, the sensitivity of existing ultrasonic detection systems has been compared experimentally with that by using thermoelastic waves as a broadband ultrasonic source. For the comparison, an optical stress transducer （OST）, a polyvinylidene difluoride （PVDF） sheet and a calibrated PVDF needle hydrophone were used. To ensure all of the detection systems interrogated by the same ultrasonic field, a small optical instrument that fixed the generating laser head was constructed. The sensitivity was evaluated by measuring signalto-noise ratios （SNRs） and noise equivalent pressures （NEPs）. The PVDF system, with a 4-kPa NEP has a 22 dB better performance than the OST. The OST showed nearly the same sensitivity as the hydrophone for detecting ultrasound waves at a 1-cm distance in water. PVDF detection system provides a useful tool for imaging of soft tissues because of its high sensitivity and broad detection range.

Fiber Bragg grating hydrophone with high sensitivity

A fiber Bragg grating （FBG） hydrophone with high sensitivity was demonstrated. This hydrophone used a rubber diaphragm and a copper hard core as the sensing element. To compensate the hydrostatic pressure, a capillary tube was fixed at the end of the hydrophone. Theoretical analysis of the acoustic pressure sensitivity was given in this letter. Experiments were carried out to test the frequency response of the hydrophone. The result shows that when the Young＇s modulus of the diaphragm is higher, a flatter frequency response will be obtained.

High-resolution azimuth estimation algorithm based on data fusion method for the vector hydrophone vertical array

To aim at the problem that the horizontal directivity index of the vector hy- drophone vertical array is not higher than that of a vector hydrophone, the high-resolution azimuth estimation algorithm based on the data fusion method was presented. The proposed algorithnl first employs MUSIC algorithm to estimate the azimuth of each divided sub-band signal, and then the estimated azimuths of multiple hydrophones are processed by using the data fusion technique. The high-resolution estimated result is achieved finally by adopting the weighted histogram statistics method. The results of the simulation and sea trials indicated that the proposed algorithm has better azimuth estimation performance than MUSIC algorithm of a single vector hydrophone and the data fusion technique based on the acoustic energy flux method. The better performance is reflected in the aspects of the estimation precision, the probability of correct estimation, the capability to distinguish multi-objects and the inhibition of the noise sub-bands.

Utilizing vector hydrophones to achieve an active anechoic terminal in an acoustic tube

A new integrated active sound absorptive terminal using vector hydrophones is developed for the anechoic terminal of impedance tube,with which the reflected and the incident waves can be separated.The method overcomes the limitations imposed by the sensor spacing and measuring frequency range in the traditional two-hydrophone method,and can effectively expand low-frequency sound absorption band of the terminal.The effect of hydrophone sensitivity on the sound absorptive performance of the terminal is evaluated,a correction method is also provided for the reflection and transmission coefficient.The experimental results show that the absorption coefficient in the frequency band of 0.1-2 kHz is over 0.98,which agrees well with the theoretical results.

The characteristics of frequency-time azimuth spectrum estimation by a vector hydrophone in shallow water

The mechanism of interaction between the energy flows of the far-field ship noise and the near-field platform is studied, and the characteristics of frequency-time azimuth spec- trum is discussed. Based on normal modes theory in acoustic vector fields, the model of the near-field platform is established, and the simulated result is similar to the investigation in shallow water. The frequency-time aziinuth spectrum of the energy flow is investigated by the vector hydrophone changes with frequency. The energy flow of the far-field ship noise interacts with the near-field platform, so four kinds of stripes are shown in the frequency4ime azimuth spectrum, which is the same with the investigation of sea trial. The estimation of direction of arrival appears inaccuracy, and varies with frequency. The main factor that affects the charac- teristics of frequency-time azimuth spectrum of resultant energy flow is the difference of sound pressure level. The estimation of the direction of arrival benefits from this when a number of sources exist in shallow water.

A novel optical multilayer hydrophone with a triangular pyramid substrate

A novel concept for an optical multilayer ultrasonic hydrophone with the sensing film deposited on a triangular pyramid glass substrate is proposed. Using the calculation model for the spectral coefficients＇ derivatives of a dielectric multilayer optical coating, the acousto-optic sensitivity characteristic of the hy- drophone is analyzed with different measurement laser polarizations and incident angles. We present a reasonable method and adjusting strategy for the optimum working point selection of the ultrasound mea- surement. Analytic results show that the novel hydrophone possesses all the other merits of a plate glass substrate optical multilayer hydrophone but with improved detection sensitivity. A longer measurement time without distortion decreases the difficulty of high frequency signal circuits. Spatial split of the ultra- sound signal caused by the substrate＇s triangular pyramid roof simplifies the spatial spot area correction, which contributes to the accurate calibration of the hydrophone＇s wideband frequency response.

Slotted piezoelectric ring deep ocean hydrophone

Based on the energy method,the underwater resonance frequency equation and electrical admittance curve of the slotted piezoelectric ring are derived.By establishing the equivalent circuit of slotted piezoelectric ring in low-frequency receiving condition,the lowfrequency open circuit voltage sensitivity of slotted piezoelectric ring is deduced.Compared the low-frequency receiving sensitivity of the slotted piezoelectric ring and the complete ring,the thought to design the deep ocean hydrophone is presented,which combines the slotted piezoelectric ring and the free flooded structure.By establishing finite element simulation model of free flooded slotted piezoelectric ring,the relationship between ring structure parameters and low-frequency open circuit voltage sensitivity are discussed.Through the simulation and optimization,the deep-sea slotted piezoelectric ring hydrophone with the resonance frequency of 600 Hz is fabricated.The acoustic and pressure tests results indicated that the low-frequency open circuit voltage sensitivity of free flooded slotted piezoelectric ring hydrophone in work bandwidth 100-300 Hz is-193.2 dB and the least value is-197.9 dB with the-4.7 dB fluctuation.Hydrostatic pressure resistance of 30 Mpa is obtained.Compared with the same structure size free flooded piezoelectric ring hydrophone,the low-frequency open circuit voltage sensitivity of slotted piezoelectric ring hydrophone raised 20 dB.The results verify the practicability of deep ocean hydrophone presented here with free flooded slotted piezoelectric ring structure.

Research on the relaxor ferroelectric single crystal flexural beam vector hydrophone

A two-dimensional vector hydrophone was developed utilizing the PMN-PT relaxor ferroelectric single crystal,which is composed of a dual-axis piezoelectric composite flexural beam accelerometer and PZT-5 piezoelectric ceramic rings.Based on the principle of elastic mechanics and underwater particle velocity measurement,the receiving voltage sensitivity of the flexural beam vector hydrophone is derived.The influence of stress distribution in the flexural beam on the performance of hydrophones is analyzed,and the match between PMNPT single crystal cells and the structure of flexural beam is studied.The tested results indicate that the PMN-PT hydrophone presents an 11 dB increase in sensitivity and a 3 dB decrease in self-noise than the PZT-5 one.

Research on fiber-optic interferometric hydrophone array using frequency division multiplying technique

From the point of view of system design, a configuration of fiber-optic interferomet- ric hydrophone array and its modulation and demodulation approach using frequncy division multiplexing technique based on Phase Generated Carrier (PGC) is introduced. And the em- phasis on demonstrating the relationship among the number of units N, the detectable signal amplitude D and the detectable frequency ws through analyzing the frequency spectrum of the output signal of the J × K array and the key factor which restricts N, D, Ws for increasing are presented. The maximum phare shift and the law of its variation according to frequency are specially analyzed. The results induced from some relative theory were verified by experiments.

Spectrum of turbulent-boundary-layer fluctuation pressure and response of a polyvinylidence fluoride hydrophone

The point power spectrum density and the wavenumber frequency spectrum density of turbulent - boundary- layer fluctuation pressure were measured in water-tunnel by use of a 8 mm hydrophone and a 20-element array, respectively. The non-dimensional representation of measured point power spectrum coincides with the measured results by Bull M. K. et. al. in wind tunnel. The convection peak can be seen clearly in the measured wavenumber frequency spectrum and the convection velocity can be calculated from the location of the convection peak. The response spectrum of a polyvinylidence fluoride (PVDF) hydrophone, which receiving area is 100 mm× 60 nun, was also measured. By comparing it with the response spectrtum of the 8 mm hydrophone, it is shown that the PVDF hyrdophone has a strong wavenumber filtering effect on turbulent - boundary-layer pressure fluctuation.

Behavior of single mode optic-fiber ring resonant hydrophone

The behavior of a single mode optic-fiber interferometric hydrophone with ring resonator is discribed in this paper. The optic-fiber ring resonant hydrophone has rery high optical finesse, and receiving sensitivity level about -130 dB (re 1 V/μPa).

Interior noise field of a viscoelastic cylindrical shell excited by TBL pressure fluctuations:Ⅱ. finite hydrophone and array

Finite hydrophone and hydrophone array are the wave vector filter and can re-duce the flow noise. In this paper the responses of the cylindrical area hydrophone and two-circular area hydrophone within viscoelastic cylindrical shell to the TBL (turbulent boundary layer) pressure fluctuations are investigated. Applying the method based on the wavenumber frequency spectrum analysis, the expressions of 1) the noise power spectrum of a single hy-drophone; 2) the space correlation of two hydrophones; 3) the noise power spectrum of array are derived. The dependencies of the noise reduction on hydrophone shape, dimension, element amount and separation of hydrophones of array are calculated by numerical integration. The wide-band and narrow-band correlation for two hydrophones is also calculated. The numerical results show that hydrophone array can effectively reduce the interior noise.