Hydrophone Calibration Research Articles

Determination of ultrasound hydrophone phase from Fourier-Hilbert transformed 1 to 40 MHz time delay spectrometry amplitude

A Fourier-Hilbert transform (FHT) algorithm procedure was developed to obtain the complex characteristics of different hydrophones which included the most widely used membrane and capsule types. The theory presented was experimentally verified using magnitude response of the hydrophone probes determined with the time-delay-spectrometry (TDS) technique. The TDS setup implemented was similar to one used by Wear et al. in 2011, with the frequency range being extended to 1 to 40 MHz to ensure consistency with recently published international standards covering the properties, calibration, and performance evaluation of ultrasound hydrophones. The theoretical and experimental limitations of FHT were examined and revealed that extrapolations of the available logarithmic (volts per pascal magnitude) frequency response were needed to carry out acceptable FHT calculations of the phase response. The complex-valued analytic signal Hilbert transform (HT) algorithm was less practical in developing an efficient minimum phase calculation protocol than the equivalent real-valued discrete convolution HT algorithm. Examples of measured transfer function and FHT calculated phase response spectra of representative membrane and capsule ultrasound hydrophones are presented and are shown to obey the simple rule for minimum phase presented by Heyser in 1969.

Package Optimization of the Cilium-Type MEMS Bionic Vector Hydrophone

We optimize the package of the cilium-type MEMS bionic vector hydrophone introduced by Chenyang and Wendong in 2007, which has the disadvantages of a low receiving sensitivity, narrow frequency band, and fluctuating frequency response curve. Initially, a full parametric analysis of frequency response and sensitivity with different material sound transparent cap were made. Then, we propose and realize an umbrella-type packaged structure with high receiving sensitivity and wide frequency band. The theoretical analysis and simulation analysis are conducted by ANSYS software and LMS virtual. Lab acoustic software. Finally, to verify the practicability of the package, the umbrella-type packaged hydrophone calibration was carried out in the National Defense Underwater Acoustics Calibration Laboratory of China. The test results show that the performance of umbrella-type hydrophone has been greatly improved compared with the previous packaged hydrophone: exhibiting a receiving sensitivity of -178 dB (increasing by 20 dB, 0-dB reference 1 V/μPa), the frequency response ranging from 20 Hz to 2 kHz (broaden one times), the fluctuation of frequency response curve within ±2 dB, and a good dipole directivity.

Holography and numerical projection methods for characterizing the three-dimensional acoustic fields of arrays in continuous-wave and transient regimes

The use of projection methods is increasingly accepted as a standard way of characterizing the 3D fields generated by medical ultrasound sources. When combined with hydrophone measurements of pressure amplitude and phase over a surface transverse to the wave propagation, numerical projection can be used to reconstruct 3D fields that account for operational details and imperfections of the source. Here, we use holography measurements to characterize the fields generated by two array transducers with different geometries and modes of operation. First, a seven-element, high-power therapy transducer is characterized in the continuous-wave regime using holography measurements and nonlinear forward-projection calculations. Second, a C5-2 imaging probe (Philips Healthcare) with 128 elements is characterized in the transient regime using holography measurements and linear projection calculations. Results from the numerical projections for both sources are compared with independent hydrophone measurements of select waveforms, including shocked focal waveforms for the therapy transducer. Accurate 3D field representations have been confirmed, though a notable sensitivity to hydrophone calibrations is revealed. Uncertainties associated with this approach are discussed toward the development of holography measurements combined with numerical projections as a standard metrological tool. [Work supported by NIH EB007643, P01DK043881, R01DK092197 and T32DK007779, NSBRI through NASA NCC 9-58, and RFBR 13-02-00183.]

Challenges and Regulatory Considerations in the Acoustic Measurement of High‐Frequency (>20 MHz) Ultrasound

This article examines the challenges associated with making acoustic output measurements at high ultrasound frequencies (>20 MHz) in the context of regulatory considerations contained in the US Food and Drug Administration industry guidance document for diagnostic ultrasound devices. Error sources in the acoustic measurement, including hydrophone calibration and spatial averaging, nonlinear distortion, and mechanical alignment, are evaluated, and the limitations of currently available acoustic measurement instruments are discussed. An uncertainty analysis of acoustic intensity and power measurements is presented, and an example uncertainty calculation is done on a hypothetical 30-MHz high-frequency ultrasound system. This analysis concludes that the estimated measurement uncertainty of the acoustic intensity is +73%/-86%, and the uncertainty in the mechanical index is +37%/-43%. These values exceed the respective levels in the Food and Drug Administration guidance document of 30% and 15%, respectively, which are more representative of the measurement uncertainty associated with characterizing lower-frequency ultrasound systems. Recommendations made for minimizing the measurement uncertainty include implementing a mechanical positioning system that has sufficient repeatability and precision, reconstructing the time-pressure waveform via deconvolution using the hydrophone frequency response, and correcting for hydrophone spatial averaging.

Measurement of the sensitivity phase-frequency characteristics of hydrophones by the reciprocity method

Some new approaches for phase calibration of hydrophones by the reciprocity method are considered. Uses of this method for measuring the phase angle of the sensitivity for the geometric and acoustic centers of a hydrophone and for determining the position of the acoustic center from its shift relative to the geometric center of a hydrophone are described. Results from an experimental test of these techniques are presented.

Calibration of high-frequency hydrophone up to 40 MHz by heterodyne interferometer

A calibration technique for high-frequency hydrophone utilizing a heterodyne interferometer is presented in this article. The calibration system is mainly composed of optical and signal processing modules. In the displacement measurement, a pellicle is mounted at the surface of water to avoid acousto-optical interaction. The phase modulated carrier signal is digitized and transferred to the computer, then processed by digital phase demodulation. A phase unwrapping algorithm is employed to remove ambiguity of the arctangent function and has proven effective in large displacement measurements. Pellicle displacement and voltage output of the hydrophone in focused ultrasonic field are processed by DFT to determine the amplitudes of the fundamental and harmonic components. Experiments show that the heterodyne technique can provide hydrophone calibration up to 40MHz, with a slightly smaller sensitivity compared with the National Physical Laboratory (NPL) calibration results for most frequency ranges. Since the heterodyne technique is independent on assumptions about the geometry of the ultrasonic field and the performance of the transducer, it can be easily extended to high frequency and high power ultrasound measurement applications.

Calibration of Vector Hydrophones in Deep Water

To apply vector hydrophone to deep-sea detection, a calibration test of the vector hydrophone under different hydrostatic pressure was taken in the national defence underwater acoustics calibration laboratory. The effect of the relative sensitivity changes between channels on the vector hydrophones direction finding and zero-inhibition performance is explored, and the principle model for the influence of the directivity deviation on vector direction measuring is established. Meantime, the phase compensation between channels is found to be frequency-independent. The omnidirectional method is proposed to compensate the directional rotation. As a result, the influences of the hydrostatic pressure on direction finding are effectively reduced.

Improved hydrophone calibration by combining acoustic holography with the radiation force balance measurements

Ultrasound sources are frequently characterized by the radiation force (RF) balance method that is based on the relation between the total acoustic power and RF on absorbing or reflecting targets. This relation is usually taken from the plane-wave approximation or with a geometrical correction for focused sources. However, real sources emit inhomogeneous acoustic beams. Acoustic holography is a method of recording the true field by measuring both pressure magnitude and phase over a 2D surface (a hologram). The hologram makes it possible to accurately calculate the radiation stress tensor on the surface of the absorbing target. Such measurements allow the relation of hydrophone sensitivity with measured RF based on the known exact expression for RF as a function of the 2D pattern of acoustic pressure and particle velocity. This suggests an improved approach for single-frequency hydrophone calibration that benefits from the inherent accuracy of mass balances as well as the fact that pressure approximately scales with one half of the accuracy of the RF measurement. In the current study this approach was used to calibrate a hydrophone by characterizing a 1-MHz flat piezoceramic source in water using acoustic holography and a RF balance. [Work supported by RFBR and NIH EB007643.]

Decreasing the free-field calibration error of hydrophones in a reverberating water tank

Questions related to free-field calibration of hydrophones in continuous radiation of a bandpass signal in a reverberating water tank with the use of the cumulative moving weighted average method are considered. A broadening of the frequency range and a decrease in the calibration error are achieved by incorporating additional information on the behavior of the desired frequency dependence of the transfer impedance of the reflector-detector pair and with the use of multi-step averaging.

A comparison of two methods for phase response calibration of hydrophones in the frequency range 10–400 kHz

A comparison is made of two methods for determining the phase response of hydrophones in the kilohertz frequency range: The three-transducer spherical-wave reciprocity method and the method of optical interferometry. The implementation of the methods and the corresponding experimental systems are described. To facilitate a comparison, the methods are used to determine the phase response of three commercially available measuring hydrophones over the frequency range from 10 to 400 kHz. The results are compared, showing agreement within the estimated uncertainties of the methods. An investigation is conducted into the sources of uncertainties in the methods which increase with frequency. The major sources of uncertainty are residual positioning errors giving rise to phase uncertainties; a significant problem for the reciprocity method is that it requires one hydrophone to be rotated during the measurement procedure. An additional source of uncertainty at higher frequencies may be present if the position of the sensing element is not central within the outer hydrophone boot.

3J5-7 Primary calibration of hydrophones up to 40 MHz in ultrasonic far-field using optical interferometry(Biomedical Ultrasound 2)

3J5-7 Primary calibration of hydrophones up to 40 MHz in ultrasonic far-field using optical interferometry(Biomedical Ultrasound 2)

Comparison of Hydrophone Calibration by Reciprocity and Heterodyne Interferometer in the Frequency Range 500 kHz to 15 MHz

This paper presents a comparison of high-frequency hydrophone calibration by a heterodyne interferometer and two-transducer reciprocity method respectively. For the calibration using the heterodyne interferometer, a vertical arrangement is applied to avoid the acousto-optical interaction which is a major uncertainty source in previous studies. For the demodulation of the acoustic displacement, a PC-based digital demodulation using arctangent algorithm is applied which has overcome the drawback of analog demodulation and achieved a higher demodulation accuracy. The demodulation is independent of the intensity of the carrier signal and thus can avoid the correction for the frequency response of the photodiode which is another uncertainty source. Comparison results between these two methods showed a good agreement. Owing to the optical measurement is independent of the acoustic field generating by the transducer, it has wider usage compared to the reciprocity method and can be easily extended to higher frequency and higher acoustic power application.

Hydrophone calibration using ambient noise

Hydrophone calibration typically requires a good signal-to-noise (SNR) ratio in order to calculate the free-field voltage sensitivity (FFVS). However, the SNR requirements can limit the calibration of hydrophones with low sensitivity, particularly in the low frequency range. Calibration methods using ambient noise in lieu of a generated signal will be explored at the Underwater Sound Reference Division (USRD) Leesburg Facility in Okahumpka, FL. The USRD Leesburg Facility is at a natural spring in rural central Florida and is one of the Navy’s quietest open water facilities with no boating noise, limited biological noise, an isolated location, low reverberation and an isothermal water temperature profile below 5 meters. Comparison calibrations will be made with two similar hydrophones using the ambient noise in the natural spring and the results will be compared to calibrations made with the same hydrophones using a generated signal.

MEMS Bionic Vector Hydrophone

A novel MEMS vector hydrophone with bionics structure was introduced in 2007. As the acoustic-electric transducer infrastructure has been optimized, the performance of the hydrophone has been greatly improved compared with the previous. This hydrophone calibration was finished in National Defense Underwater Acoustics Calibration Laboratory of China. According to test results, the sensitivity of the hydrophone is -165dB（including pre-amplification 20 dB）,The frequency response ranges from 20Hz to 2kHz (±5dB). And this hydrophone has a good directional pattern in form of "8"-shape.

Improvement of the MEMS bionic vector hydrophone

A kind of MEMS vector hydrophone with bionics structure was introduced in 2007. As the acoustic–electric transducer structure and the acoustic package of hydrophone have been optimized, the performance of the hydrophone has been greatly improved compared with the previous. This hydrophone calibration was completed in the National Defense Underwater Acoustics Calibration Laboratory of China. According to the test results, the sensitivity of the hydrophone is −165dB (including pre-amplification 20dB), the frequency response ranges from 20Hz to 2kHz (±5dB), and this hydrophone has a good directional pattern in the form of “8”-shape.

Improvement of a Novel MEMS Bionic Vector Hydrophone

A novel MEMS vector hydrophone with bionics structure was introduced in 2007. As the acoustic-electric transducer infrastructure and the acoustic package of hydrophone have been optimized, the performance of the hydrophone has been greatly improved compared with the previous. This hydrophone calibration was finished in National Defense Underwater Acoustics Calibration Laboratory of China. According to the test results, the sensitivity of the hydrophone is -165dB（including pre-amplification 20 dB）, the frequency response ranges from 20Hz to 2kHz (±5dB). And this hydrophone has a good directional pattern in the form of "8"-shape.

Nonlinear acoustics determination of phase characteristics of PVDF membrane hydrophones

When an ultrasonic pressure wave propagates through a nonlinear medium, the relative phasing of the generated harmonics causes a distinct asymmetry between the positive and negative pressure levels and between the rise and fall time of examined waveforms. A faithful quantitative reproduction of the source transducer's pressure field requires amplitude and phase measurements by calibrated hydrophone probes. Nonlinear hydrophone calibration provides amplitude and phase information at discrete multiples of an acoustic source's fundamental frequency. Two PVDF bilaminar membrane hydrophones were first calibrated in terms of their amplitude sensitivity to the pressure levels generated by two different HIFU (High Intensity Focused Ultrasound) circular source transducers operating at 5 MHz and 10 MHz, enabling phase studies up to 105 and 100 MHz, respectively. Introducing two newly-developed phase-dispersion representations, the phase responses of the two membrane hydrophones were determined with respect to the phase of the complex frequency response extracted from the nonlinear field simulated by a semi-empirical computer model which predicts the near and the far field pressure distributions. These phase differences compared favorably with the results obtained from the commercially available PiezoCAD simulation model. The protocol for specifying the complex pressure field of source transducers through measurements using the calibrated hydrophones is described. The results obtained indicate that the membranes exhibit close to linear decay of phase against the frequency.

Hydrophone calibration based on microcontrollers for acoustic detection of UHE neutrinos

This paper discusses hydrophone calibration for generation of artificial Ultra High Energy (UHE) neutrino-induced pulses. Signal processing techniques are applied to hydrophone modelling. A bipolar acoustic generation module is built using PIC microcontrollers for processing and control. The NI-USB6211 commercial module is used for comparison. The modelling is compared to experimental data generated in a laboratory water tank. The result from simulation and experiment are compared, showing excellent agreement. This opens the way to excite steerable hydrophone arrays, which was not possible with previous hardware.

一种新型半球形基片光学薄膜水听器

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 hydrophone 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 measurement. 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 ultrasound 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.

COOMET pilot comparison 473/RU-a/09: Comparison of hydrophone calibrations in the frequency range 250 Hz to 200 kHz

A description is given of the COOMET project 473/RU-a/09: a pilot comparison of hydrophone calibrations at frequencies from 250 Hz to 200 kHz between Hangzhou Applied Acoustics Research Institute (HAARI, China)—pilot laboratory—and Russian National Research Institute for Physicotechnical and Radio Engineering Measurements (VNIIFTRI, Designated Institute of Russia of the CIPM MRA). Two standard hydrophones, B&K 8104 and TC 4033, were calibrated and compared to assess the current state of hydrophone calibration of HAARI (China) and Russia. Three different calibration methods were applied: a vibrating column method, a free-field reciprocity method and a comparison method. The standard facilities of each laboratory were used, and three different sound fields were applied: pressure field, free-field and reverberant field. The maximum deviation of the sensitivities of two hydrophones between the participants' results was 0.36 dB.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCAUV-KCWG.