Commercial Hydrophone Research Articles

Capacitive Low-Frequency Hydrophone Based on Micronanostructured Iontronic Hydrogel for Underwater Monitoring.

Hydrophones play a crucial role in underwater target detection within sonar systems. However, existing hydrophones often encounter challenges such as low sensitivity and poor signal-to-noise ratio (SNR) in the detection of low-frequency acoustic signals. This work introduces a capacitive hydrophone (CH) designed for highly sensitive detection of low-frequency underwater sound signals. Comprising a latex film/silver electrode and a structured hydrogel as the electrolyte layer, the CH is enclosed in a cylindrical casing. By strategically integrating a carbon nanotube (CNT) topology network within a pyramid microarray in the hydrogel, the sensor efficiently forms the electric double layer (EDL), enhancing sensitivity and precision. The CH showcases exceptional low-pressure sensitivity across a wide frequency spectrum (20 to 800 Hz), achieving a receiving sensitivity of up to -159.7 dB in the critical low-frequency band (20 to 125 Hz), surpassing the performance of the commercial hydrophone (RHC-14) by a substantial margin of 33.29 dB. Furthermore, the CH maintains a superior SNR, enabling the detection of sound waves as faint as 0.3 Pa. This study demonstrates the capabilities of the CH in detecting maritime vessels and underwater sounds, underscoring the potential of the CNT-enhanced EDL sensing mechanism for future low-frequency hydrophone design.

Development of a high sensitivity hydrophone at a spectrum range from 0.1 Hz to 100 kHz

This paper demonstrates the cost-effective development of a hydrophone that covers a spectrum range from 0.1 Hz to 100 kHz. The sensing element underwent characterization techniques, such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray (EDX) in order to examine the morphology, consistency, microstructure, and crystallography of traditional lead zirconate titanate (PZT) piezoelectric discs, which served as sensing components. Additionally, an electronic circuit with a microcontroller was designed for enhancing the hydrophone's performance and enabling further analysis on a personal computer. This circuit comprises stages for preamplification and filtering, Direct Current (DC) biasing, and Analog-to-Digital Conversion. The digitized signal is subsequently analyzed using specialized audio software. To calibrate the hydrophone, the substitution method was employed, comparing its acoustic response with that of a commercial hydrophone.

Multi-channel parallel ultrasound detection based on a photothermal tunable fiber optic sensor array.

A multi-channel parallel ultrasound detection system based on a photothermal tunable fiber optic sensor array is proposed. The resonant wavelength of the ultrasound sensor has a quadratic relationship with the power of a 980-nm heating laser. The maximum tuning range is larger than 15 nm. Through photothermal tuning, the inconsistent operating wavelengths of the Fabry-Perot (FP) sensor array can be solved, and then a multiplexing capacity of up to 53 can be theoretically realized, which could greatly reduce the time required for data acquisition. Then, a fixed wavelength laser with ultra-narrow linewidth is used to interrogate the sensor array. The interrogation system demonstrates a noise equivalent pressure (NEP) as low as 0.12 kPa, which is 5.5-times lower than the commercial hydrophone. Furthermore, a prototype of a four-channel ultrasound detection system is built to demonstrate the parallel detection capability. Compared with the independent detection, the SNR of parallel detection does not deteriorate, proving that the parallel detection system and the sensor array own very low cross talk characteristics. The parallel detection technique paves a way for real-time photoacoustic/ultrasound imaging.

Multielement Ring Array Based on Minute Size PMUTs for High Acoustic Pressure and Tunable Focus Depth.

This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities.

Metadata-Driven Universal Real-Time Ocean Sound Measurement Architecture

Underwater sound in the oceans has been significantly rising in the past decades due to an increase in human activities, adversely affecting the marine environment. In order to assess and limit the impact of underwater noise, the European Commission’s Marine Strategy Framework Directive (MSFD) included the long-term monitoring of low-frequency underwater sound as a relevant indicator to achieve a good environmental status. There is a wide range of commercial hydrophones and observing platforms able to perform such measurements. However, heterogeneity and lack of standardization in both hydrophones and observing platforms makes the integration and data management tasks time-consuming and error-prone. Moreover, their power and communications constraints need to be addressed to make them suitable for long-term ocean sound monitoring. Measured underwater sound levels are challenging to compare because different measurement methodologies are used, leading to a risk of misunderstandings and data misinterpretation. Furthermore, the exact methodology applied is not always public or accessible, significantly reducing ocean sound data re-usability. Within this work, a universal architecture for ocean sound measurement is presented, addressing hydrophone integration, real-time in situ processing and data management challenges. Emphasis is placed on generic and re-usable components, so it can be seamlessly replicated and deployed in new scenarios regardless of the underlying hardware and software constraints (hydrophone model, observing platform, operating system, etc.). Within the proposed architecture, a generic implementation of an underwater sound algorithm based on underwater noise measurement best practices is provided. Standardized and coherent metadata with emphasis on strong semantics is discussed, providing the building blocks for FAIR (Findable, Accessible, Interoperable, Reusable) ocean sound data management.

Low-Cost, High-Sensitivity Hydrophone Based on Resonant Air Cavity

Underwater acoustic ranging and detection usually require hydrophones to have high sensitivity at narrowband operating frequencies. Different from traditional sensitization methods with the help of new materials and solid/liquid resonance structure, this paper proposes a low-cost, high-sensitivity hydrophone based on a resonant air cavity containing an affordable MEMS microphone inside to sense the focused acoustic waves transmitted from the external water across the solid shell into the air cavity. Both finite element simulations and experiments are carried out to test its acoustic sensing performances. Resonance frequency and directivity of the proposed hydrophone are determined by the air cavity size and the acoustic mode, but is independent of the solid shell, which facilitates the precise designability. The sensitivity of the developed hydrophone at the resonance frequency is up to −157 dB re 1V/ $\mu $ Pa calibrated by commercial standard hydrophone TC4013. Finally, several further considerations, improvements and applications on the proposed hydrophone are discussed.

Spectral Analysis of Ultrasonic and Photo Acoustic Signals Generated by a Prototypal Fiber Microprobe for Media Characterization

Combination of photoacoustics and ultrasound can provide complemental features and mutual benefits, useful for a complete tissue characterization and consequently for early diagnosis or therapy monitoring. Furthermore, minimally invasive techniques are required both to reach organs or tissue not accessible and to reduce patient discomfort and costs. This work has tested a prototypal microprobe for media characterization analysing their optical and mechanical features. Two different transmitters compose the miniaturized probe: one for large bandwidth ultrasonic signals generation and one for guiding the laser light into tissue to photogenerate ultrasound. The aim is to evaluate the possibility of employing in the future this new type of microprobe to characterize internal tissue, combining ultrasound and photoacoustic investigations. A calibrated commercial hydrophone has been used to detect generated signals, with the aim to provide repeatable and reliable results. Dedicated test objects have been realized by using solutions of corn starch flour and of Chinese ink with different and calibrated dilutions. The spectral algorithm HyperSPACE (Hyper SPectral Analysis for Characterization in Echography), applied on ultrasonic and photoacoustic signals has allowed differentiating scatterers’ concentration and distribution.

Suppression of reverberations at fiber tips for optical ultrasound sensing

Fabry-Perot-based ultrasound sensors at fiber tips have performed high sensitivity and immunity of electromagnetic interference with a relatively compact size. Nevertheless, the reverberation at fiber tips causes a strong noise that degrades the sensing capability. Here we propose a fiber optical-based ultrasound sensor with three design approaches to reduce the reverberation, including designs with an eccentric core, absorptive shield, and arc edge. The effect was experimentally validated with a photoacoustic signal excitation. Compared with bare single-mode fibers in simulation, the low-reverberation design increased the signal-to-noise ratio by 32.1 dB with identical excitation. The experimental results demonstrated the "clean" response with almost invisible reverberations, which was validated by a commercial hydrophone. This research solved the reverberation problems and provided a low-noise design for fiber optic ultrasound sensing.

A Piezoceramic Sensor for Detection of Focused Ultrasound-Induced Cavitation

Acoustic cavitation plays a key role in blood-brain-barrier opening. Stable cavitation is required for safely transient barrier disruption when inertial cavitation may cause potentially undesirable damage to brain. To ensure the safety, an appropriate passive cavitation detector is needed to monitor cavitation activity during focused ultrasound treatment. The purpose of this study was to develop a passive cavitation detector with high sensitivity at the specific frequency used in blood-brain-barrier opening. The detector was designed with the assistance of pulse-echo response simulations, using the software PiezoCAD. The active transducer of the detector was constructed of two matching layers, a PZT-5A ceramic disk and the titanium backing. The detector was characterized via the pulse-echo measurements and a commercial hydrophone was used to determine the sensitivity of the developed detector. Cavitation experiments were also performed to validate the detector. The experimental results showed that the detector had the center frequency of 1.16 MHz with the bandwidth of 44.8% and its sensitivity was 2.87 V/MPa at 1.0 MHz. In cavitation experiments, 2-MHz focused ultrasound with the focal intensity of 58 W/cm2 and 1461 W/cm2 induced stable cavitation and inertial cavitation in free field, separately. The spectra of the ultrasound signals detected by the detector indicated the occurrence of peak voltages at the subharmonic frequency of 1 MHz and the increase in the level of wideband signals, reflecting stable cavitation and inertial cavitation, respectively. Based on the design guideline of this study, the passive cavitation detector can be developed dedicated for blood-brain-barrier opening.

Calibration of an ultrasonic transducer in a standing wave field

Acoustofluidics is one of the emerging technologies for cell sorting. Most of the acoustofluidics platforms use an acoustic standing wave field for the separation. The calibration of the standing wave field is a challenging task. In the past, there have been few studies to quantify the standing wave indirectly using particle tracing in the field. In the present work, we attempt to calibrate the standing wave field using acoustic techniques. Hydrophones are used to find the pressure in an acoustic field. They are designed and constructed in a way that they do not alter the field. Most of the commercial hydrophone in market is made of PVDF (polyvinylidene fluoride): an acoustically transparent material. When a hydrophone is inserted in a standing wave field, the field in front of the tip is no longer a standing wave field as PVDF is acoustically transparent. This was observed in our acoustic chamber also. Here, we propose to use the receiving characteristics of a transducer to quantify the standing wave field. In brief, two identical PZT transducers are used to generate the standing wave field: one as a transmitter and other as a receiver (reflector). The receiving characteristics of the transducer used as a reflector are calibrated using a needle hydrophone. Using the signal recorded by the receiving PZT transducer in the standing wave field and the calibration value, the pressure at the surface of reflecting transducer can be found. For the sake of comparison, the field will be quantified also by the particle tracing method.

Development of disposable membrane hydrophones for a frequency range from 1 MHz to 10 MHz

A method for fabricating disposable membrane hydrophones is presented. The disposable hydrophones are intended for onetime use in such damaging environments as chemically contaminating fluids and high-amplitude (peak amplitude ∼100MPa) shock wave fields, where the use of commercial membrane hydrophones is not recommended. Fabrication of a hydrophone is done using only off-the-shelf components and hand tools, which translates into ease of fabrication and orders-of-magnitude reduction in unit cost. In particular, poling and sputtering, the two processes that are chiefly responsible for the cost and difficulty associated with the conventional fabrication method, are replaced with the use of pre-poled polyvinylidene fluoride (PVDF) films and polyethylene terephthalate (PET)-coated aluminum foils, respectively. Despite the seemingly crude construction, these disposable hydrophones can exhibit voltage sensitivity response that compares favorably with that of commercial hydrophones. For example, one prototype having a 2mm×2mm active element shows the end-of-cable voltage sensitivity of −270 (±1.9) dB re 1V/μPa over the frequency range of 1–10MHz.

광음향 영상화를 위한 PMN-PZT 바늘형 수중청음기 제작

수 MHz의 초음파를 이용하는 저주파 광음향 영상장치에 적용하는 것을 목적으로 압전단결정 PMN-PZT를 사용한 바늘형 수중청음기를 설계 제작하고, 그 특성을 수신감도가 알려져 있는 상용 PVDF(Polyvinylidene Fluoride) 수중청음기와 비교하여 평가하였다. 설계한 수중청음기의 임펄스응답을 KLM 모델에 의해 시뮬레이션한 결과, <TEX>$50{\Omega}$</TEX>의 종단 임피던스에 걸리는 최대 전압을 기준으로 한 수신감도는 -261.6 dB re <TEX>$1V/{\mu}Pa$</TEX>이며, 2 ~ 12 MHz 대역에서 5 dB 이내의 비교적 평탄한 특성을 가지는 것으로 예측되었다. 제작한 수중청음기의 수신감도를 순음 펄스를 사용하여 측정한 결과, 측정 가능한 2 ~ 8 MHz 대역에서 상용의 수중청음기에 비해 평균 10.9 dB 높게 나타났으며, 그 값은 <TEX>$-255.8{\pm}2.8$</TEX> dB re <TEX>$1V/{\mu}Pa$</TEX>이었다. 나아가, 제작한 수중청음기를 기계주사형 광음향 영상장치에 적용하여 머리카락에 대한 영상을 획득하였는바, 수신된 광음향 신호가 상용의 것보다 크고, 영상 또한 우수함을 알았다. For application to several MHz photoacoustic imaging systems, a needle hydrophone was designed and fabricated by using PMN-PZT piezoelectric single crystal, and its characteristics were evaluated through comparison with a commercial PVDF(Polybinylidene Fluoride) hydrophone of which receiving sensitivity is known. The simulation using the KLM model results show that the peak receiving impulse response for <TEX>$50{\Omega}$</TEX> terminating impedance of the fabricated hydrophone is -261.6 dB re <TEX>$1V/{\mu}Pa$</TEX> and the frequency response is relatively flat over 2 ~ 12 MHz with fluctuation less than 5 dB. The measurement results using tone burst signals also show that it has higher (ave. 10.9 dB) sensitivity than the commercial hydrophone in 2 ~ 8 MHz, and the receiving sensitivity of <TEX>$-255.8{\pm}2.8$</TEX> dB re <TEX>$1V/{\mu}Pa$</TEX> was measured for the fabricated hydrophone. In addition, it is known that the photoacoustic signals and the image of a hair obtained by a mechanical scanned photoacoustic imaging system with the fabricated hydrophone were bigger and better than those obtained with the commercial hydrophone.

Frequency characteristics of receiving sensitivity and waveform of an anti-acoustic cavitation hydrophone

Novel anti-cavitation hydrophones were fabricated by depositing a hydrothermally synthesized lead zirconate titanate polycrystalline film on the back of a titanium plate. These hydrophones were not damaged by the measurement of the acoustic field formed by a high-intensity focused ultrasound (HIFU) device. The hydrophones were designed using Mason’s equivalent circuit and by numerical simulation to improve their receiving characteristics for the measurement of the HIFU device. High receiving sensitivity with flat frequency characteristics was obtained by using a backing material with a specific acoustic impedance of about 20 × 106 kg/(m2 s) [Rayl]. We developed a new type of hydrophone using a tin and titanium rods as backing materials, which have specific acoustic impedances of 24 × 106 and 27 × 106 kg/(m2 s), respectively. The fabricated anti-cavitation hydrophone showed wide frequency characteristics of the receiving sensitivity. Furthermore, we observed the output waveform with distortion due to nonlinear propagation using the fabricated anti-cavitation hydrophone. This hydrophone was not damaged by exposure to a high-intensity acoustic field of an ultrasound cleaner under acoustic cavitation for duration of about ten times longer than the conventional commercial hydrophone.

Spectral response analysis of PVDF capacitive sensors

We investigate the spectral response to ultrasound waves in water of low-noise capacitive sensors based on PVDF polymer piezoelectric films. First, we analyze theoretically the mechanical-to-electrical transduction as a function of the frequency of ultrasonic signals and derive an analytic expression of the sensor's transfer function. Then we present experimental results of the frequency response of a home-made PDVF in water to test signals from 1 to 20 MHz induced by a commercial hydrophone powered by a signal generator and compare with our theoretical model.

The South Pole Acoustic Test Setup: calibrations and lake test

In order to detect the small neutrino fluxes expected at ultra-high energies, large volumes of materials have to be instrumented with inexpensive but sensitive acoustic sensors. The South Pole Acoustic Test Setup (SPATS) will be installed in the Antarctic ice during the polar season 2006/2007 after which the collected data will be used to reveal the acoustic properties of the South Polar ice cap. The developed piezoceramic based ultrasound sensors and transmitters that are part of this system have been extensively studied during calibration measurements in water, using a commercial hydrophone as reference. Also, a SPATS system test was accomplished in Lake Torneträsk, Abisko (Sweden). This allowed verification of the DAQ system, transmitter range and sensor performance. Here the results of the calibrations and the Abisko lake measurements are reported.

DEVELOPEMENT OF GLACIOPHONES AND ACOUSTIC TRANSMITTERS FOR ICE

For the detection of the feeble fluxes of neutrinos in the EeV range, recently acoustic detection is again discussed as a promising method. With the signal amplitude determined by the Greeneisen parameter, ice seems to be preferable as compared to water. However, neither suitable sensors nor transmitters existed two years ago. We present results on acoustic sensors and transmitters specially developed for that purpose. A new calibration method has been used to measure sensitivities in water, already showing some improvement with respect to commercial hydrophones.

Characterization of high-frequency, single-element focused transducers with wire target and hydrophone

In this paper, a wire-target technique was used for lateral beam profile measurements for a single-element, focused transducers in the very high-frequency range (35-60 MHz). Two wire targets made from 9-cm long tungsten wires with diameters of 8 microm and 20 microm were used as the pulse-echo targets to measure the lateral beam profiles at the focal plane of two single-element, focused transducers, a spherically focused 40 MHz transducer and a lens-focused in-house lithium niobate (LiNbO3) 60 MHz transducer. For comparison, measurements on the same transducers were performed by three small-aperture hydrophones with geometrical diameters varying from 37 microm to 150 microm. Tomographic reconstruction of the acoustic field from the spherically focused transducer also was conducted. Results obtained with the wire-target technique are comparable to those obtained with small-aperture hydrophones in characterizing lateral radiation patterns of a single-element, focused transducer in the high-frequency range (35-60 MHz). However, the wire-target method may overestimate pulse length because of the additional attenuation caused by the return path. Compared to small-aperture hydrophones, the wire-target technique is simpler and more cost effective. Its major advantage, however, is in the frequency range above 100 MHz in which commercial hydrophones are not yet available.

Characterization of very high frequency transducers withwire target and hydrophone

In this paper, the wire-target technique will be shown to be a useful alternative for beamprofile measurements in very high frequency range (30–60 MHz). A 9 cm long tungsten wire with adiameter of 8 µm was used as the pulse-echo target to measure the lateral beam profiles at the focalpoints of two transducers, a spherically focused 40 MHz Panametrics transducer with an aperturesize of 6.35 mm and a geometrical focal length of 12.7 mm and a lense-focused in-house lithiumniobate (LiNbO3) 60 MHz transducer with an aperture size of 2 mm and a geometrical focal lengtharound 6.5 mm. For comparison, measurements on the same transducers were performed by threesmall-aperture hydrophones. The first one is a polyvinylidene fluoride trifluoroethylene (PVDF-TrFE)membrane hydrophone developed by Hewlett-Packard, which has a geometric diameter of 37µm, a measured effective diameter of less than 100 µm and a –3 dB bandwidth of more than 150MHz. The second one is a needle-type PVDF hydrophone from Precision Acoustics, which has a 9µm-thick PVDF element, a 40 µm geometrical aperture and a measured effective diameter of lessthan 100 µm. The third one is a needle-type PVDF hydrophone from Onda, which has a 150 µmgeometrical aperture and an effective diameter of about 180 µm. Experimental results show that the–6 dB two-way beam widths measured by this 8 µm wire-target are in agreement with –3 dBtransmitted beam widths measured by small-aperture hydrophones. Compared to small-aperturehydrophones, the wire-target technique is simpler and more cost-effective. Its major advantagehowever is in the frequency range above 100 MHz in which commercial hydrophones are not yetavailable.

Interlaboratory evaluation of hydrophone sensitivity calibration from 0.1 to 2 MHz via time delay spectrometry

Knowing the low-frequency response of hydrophones, down to 100 kHz at least, is important for accurate biomedical ultrasound measurements. However, current international standards do not extend below 500 kHz. Furthermore, commercial hydrophone sources typically do not supply sensitivity data below 1–2 MHz. Therefore, to help identify and validate practical calibration methods below 2 MHz, the authors have extended their previous individual efforts in an interlaboratory evaluation of sensitivity calibration using the swept-frequency technique, time delay spectrometry (TDS). Calibrations were performed for needle and membrane PVDF hydrophones using each laboratory's TDS system. Each site employed the same purpose-built broadband source transducers, comprising both plano-concave and biconcave 1–3 piezocomposite elements 4 cm in diameter, with maximum and minimum thicknesses of approximately 1.5 and 0.1 cm. Agreement between laboratories was within the estimated measurement precision of ±0.6 dB. The results demonstrated that a TDS system employing such transducers constitutes a viable method for hydrophone calibrations in this frequency range.

Are current hydrophone low frequency response standards acceptable for measuring mechanical/cavitation indices?

The purpose of this paper is to determine the error introduced by ultrasonic hydrophones used to measure current or proposed Mechanical (MI) and Cavitation (CI) Indices, assuming that the hydrophones meet bandwidth specifications contained in US and IEC measurement standards. These indices are based on the peak rarefactional pressure, pr. Since the portion of the pressure waveform where pr occurs is dominated by low frequency components, attention was placed on the low frequency hydrophone response specifications. Both simulated and actual diagnostic pressure pulses (with center frequency fc) were subjected to single-pole high-pass filtering for a range of -3 dB cut-off frequencies (fa). The error in the indices introduced by this filtration was evaluated. At both fa = 0.5fc (the US requirement) and fa = 0.86fc (calculated from the IEC -6dB bandwidth specification at 0.5fc), results showed that errors exceeding -30% could be expected. Furthermore, to reduce errors to less than 5%, the low frequency hydrophone response should extend at least an order of magnitude below the center frequency of the pressure wave. For example, for a 3.5 MHz transducer, the hydrophone should have a lower cut-off frequency of less than 350 kHz, which at present constitutes a challenge because of the lack of commercial hydrophones calibrated below 1 MHz.