Acoustic Calibration Research Articles

Calibration and assessment of noise monitoring instrumentation used by the Mine Safety and Health Administration

The use of noise dosimeters is the standard method for noise exposure monitoring and assessment in the United States mining industry. The Mine Safety and Health Administration (MSHA) calibrates and maintains a fleet of various noise dosimeters and acoustical calibrators for the purpose of conducting enforcement activities and providing technical support to mine operators. The dosimeter fleet is comprised of both corded- and badge-type instruments. MSHA studies have conclusively revealed evidence in support of both types as to performing acceptably both in practice and when tested against standardized criteria, ANSI S1.25-1991. MSHA operates an acoustical calibration laboratory which maintains National Institute of Standards and Technology (NIST) traceable calibration records for all noise dosimeters and calibrators used for enforcement and support functions. The laboratory is currently in the process of modernization. Replacement test systems will provide increased reliability, reduced turn-around time, and improved accuracy through the implementation of modern computer-based components. Improvements provided by the laboratory modernization project will greatly improve quality assurance and provide the ability to pursue accredited compliance with ISO/IEC 17025:2005, through the American Association for Laboratory Accreditation (A2LA).

Research on double T-shape MEMS bionic vector hydrophone and its application in obstacle avoidance sonar

Purpose – The purpose of this paper is to develop a novel MEMS vector hydrophone with the key features of smaller size, better consistency, higher sensitivity and directional reception, and to develop a highly effective and economical obstacle avoidance sonar system. Currently, the typical vector hydrophones are resonant vector hydrophones based on the accelerometer, which greatly increases the volume and constrains the detection sensitivity. Also, because the system is composed of a number of devices, its size is difficult to be reduced. Design/methodology/approach – A novel double T-shape MEMS vector hydrophone is proposed with a fish’s lateral line organs as prototypes. The structure size and layout location of the piezoresistors were determined by simulation analysis, and the double T-shape microstructure was fabricated integrally by MEMS manufacturing technology, after which, the acoustic package of the microstructure was completed and the prototype was produced. Finally, the packaged hydrophone was calibrated in a standing wave field in the first-class national-defense underwater acoustic calibration station of China. Also, the design and test of an obstacle avoidance sonar system based on the vector hydrophone were completed. Findings – The calibration data show that the double T-shape vector hydrophone has a flat frequency response curve, exhibits a sensitivity of −180 dB (1 kHz, 0 dB reference 1 V/uPa) and shows a good directivity pattern in the form of an “8” shape. The test results of the obstacle avoidance sonar system further verify the feasibility of detecting underwater acoustic signals. Research limitations/implications – The next work is to increase the sensitivity by optimizing the microstructure and to realize orientation by organizing array. Practical implications – The hydrophone has the advantages of smaller size, lower cost and directional reception. It can be used to develop highly effective and economical obstacle avoidance sonar system, thus solving the problems of water transport efficiency and traffic safety. The hydrophone has broad application prospects and a huge market potential in the civilian fields. Originality/value – The MEMS technology and innovative bionic microstructure enable the miniaturization and low cost of the hydrophone. The hydrophone is easy to form array and can narrow the array aperture greatly. So, the hydrophone can be widely used in civil sonar systems.

Open-source, high-throughput ultrasound treatment chamber.

Studying the effects of ultrasound on biological cells requires extensive knowledge of both the physical ultrasound and cellular biology. Translating knowledge between these fields can be complicated and time consuming. With the vast range of ultrasonic equipment available, nearly every research group uses different or unique devices. Hence, recreating the experimental conditions and results may be expensive or difficult. For this reason, we have developed devices to combat the common problems seen in state-of-the-art biomedical ultrasound research. In this paper, we present the design, fabrication, and characterisation of an open-source device that is easy to manufacture, allows for parallel sample sonication, and is highly reproducible, with complete acoustic calibration. This device is designed to act as a template for sample sonication experiments. We demonstrate the fabrication technique for devices designed to sonicate 24-well plates and OptiCell™ using three-dimensional (3D) printing and low-cost consumables. We increased the pressure output by electrical impedance matching of the transducers using transmission line transformers, resulting in an increase by a factor of 3.15. The devices cost approximately €220 in consumables, with a major portion attributed to the 3D printing, and can be fabricated in approximately 8 working hours. Our results show that, if our protocol is followed, the mean acoustic output between devices has a variance of <1%. We openly provide the 3D files and operation software allowing any laboratory to fabricate and use these devices at minimal cost and without substantial prior know-how.

Estimation of suspended sediment concentration by acoustic scattering: an experimental and theoretical analysis for spherical particles

This study deals with an alternate acoustic calibration method to determine suspended sediment concentration (SSC). Calculations of backscattering from a suspension of spherical particles were compared with a series of experimental measurements neglecting attenuation. Backscattering predictions were obtained using the “form function” description of spherical scattering from modal theory and by fitting according to Beer’s law, which was originally used to measure the transmitted light scattered by a collection of particles, to calculate the acoustic backscattering intensity. Measurements were undertaken in a laboratory using a simple experimental apparatus; an acoustic Doppler velocimeter (ADV) operating at a central frequency of 6 MHz was immersed in a 50-l acrylic tank in which known concentrations of glass microspheres (63- to 90-μm size range) were mixed in freshwater to obtain a homogeneous solution. Measurements expressed in terms of signal to noise ratio (SNR) were taken with different acoustic equipment settings and compared to theoretical predictions. Modal theory form function for elastic glass spheres was used taking into consideration the contributions due to natural vibrations induced by acoustic insonification and because the principal constituent of non-cohesive sediments is quartz. Traditional calibrating procedures were performed; the power of the equipment had an important effect on the results. The preliminary theoretical backscattering predictions were qualitatively satisfactory and suggested that the model can be used to generate the calibration curves for different particle properties. It is feasible to use the proposed model to calibrate the ADV from a reduced number of water samples. From this, it is possible to obtain the characteristics of the particles (shape, density, and size distribution) and so estimate the SSC using the modeled backscattering intensity as a function of appropriate form functions and the number of particles in the ADV sampling volume.

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.

Reaffirmation of measurement uncertainty in pressure sensitivity determination of LS2P microphones by reciprocity method

Abstract The paper presents the accuracy and precision associated with realization of primary standard of sound using the reciprocity method. An experimental determination of the front cavity volume on Universal Measuring Machine has lead to reaffirmation of measurement uncertainty in pressure sensitivity determination to 0.04–0.15 dB in frequency range 31.5 Hz to 25 kHz. The reduced measurement uncertainty has also been validated from the results of the recent APMP Key comparison and also by comparison to the manufacturer’s value for LS2P microphones. The use of optical method for measuring the front cavity volume has refined the measurement methodology followed with adaptation of a self reliant, traceable and systematic measurement procedure in comparison to the earlier use of nominal values for sensitivity fitting exercise conducted on MP.EXE program. Consequently, the measurement uncertainty associated with the calibration of working standard microphones, multifunction acoustic calibrator and A-weighted sound pressure level measurements is also reduced.

First look: Acoustic calibration of carbon nanotube transducers

Material researchers at the University of Texas at Dallas (UT-D) have recently been reporting on the development of underwater acoustic carbon nanotube (CNT) yarn sheets capable of high acoustic output at low frequencies with broad bandwidth. The principle transduction mechanism for their approach is through thermal acoustic means as opposed to conventional underwater transducers that utilize electromechanical vibrations. This presentation will begin with an overview of the CNTs including the design of a first generation packaging technique that was incorporated for the fabrication of three prototypes. The prototypes were acoustically calibrated in April 2013 at the US Navy acoustic calibration facility in Okahumpka, Florida. The presentation will include measured unbiased and biased transmitting voltage responses (TVRs) and directivity patterns over a two and a half decade band. Final discussions will include on-going research directions for further development. [Work supported by NAVSEA Division Newport.]

First investigation on the applicability of an active noise control system on a tracked tractor without cab

In last years, several research teams pointed their attention on the application of active noise control systems (ANC) inside the cabs of agricultural tractor, with the purpose of reducing the driver exposition to noise, that is only partially controlled by the frame of the cab. This paper reports the results of a first experience that aimed at verifying the applicability of an ANC on a medium-high power, tracked tractor without cab. The tested tractor was a Fiat Allis 150 A, equipped with rear power take off, used in the execution of deep primary tillage in compact soils. It is a tracked tractor without cab, with maximum power of 108.8 kW at 1840 min–1 of the engine. The ANC consists of a control unit box based on a digital signal processor (DPS), two microphones, two speakers and a power amplifier. The instrumentation used in noise data collecting and processing consisted of a multichannel signal analyzer (Sinus - Soundbook), a ½” microphone capsule and an acoustic calibrator, both Bruel &amp;amp; Kjaer. The study aimed at evaluating the behaviour of the ANC by means of tests carried out under repeatable conditions, characterized by pre-defined engine speed values. Three replications have been made for each engine speed. The sampling time was 30 s. Two series of tests were performed in order to compare the results observed with the ANC on and off. The engine speed adopted in the study ranged from 600 min– 1, up to 2000 min–1 (maximum speed) with steps of 100 min–1. The ANC proved to be effective in the interval of speed between 1400 and 1700 min–1, where the samplings have been intensified, adopting steps of 50 min–1. In such an interval, the attenuation observed with the ANC system on appeared evident both as weighed A sound pressure level (from 1.29 up to 2.46 dB(A)) and linear (from 4.54 up to 8.53 dB). The best performance has been observed at the engine speed of 1550 min–1, with attenuations, respectively of 2.46 dB(A) and 7.67 dB. Outside of the engine speed interval 1400 - 1700 min–1, the attenuations always resulted lower than 1 dB(A) for the weighed A sound pressure level and between 0.66 and 7.72 dB.

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.

Acoustic calibration of the signal propagation path in the shallow water

The propagation of low-frequency pulsed frequency-modulated signals in the shallow water (80m deep) is analyzed. The characteristics of the first five modes in the frequency range from 25 to 155 Hz are found by the correlation analysis of signal spectra. The group velocities and mode attenuation coefficients are used to reconstruct the acoustic characteristics of the sea bottom. A model of the sea bottom is developed, which allows one to formulate the model of transfer function along the signal propagation path.

First investigation on the applicability of an active noise control system on a tracked tractor without cab

In last years, several research teams pointed their attention on the application of active noise control systems (ANC) inside the cabs of agricultural tractor, with the purpose of reducing the driver exposition to noise, that is only partially controlled by the frame of the cab. This paper reports the results of a first experience that aimed at verifying the applicability of an ANC on a medium-high power, tracked tractor without cab. The tested tractor was a Fiat Allis 150 A, equipped with rear power take off, used in the execution of deep primary tillage in compact soils. It is a tracked tractor without cab, with maximum power of 108.8 kW at 1840 min–1 of the engine. The ANC consists of a control unit box based on a digital signal processor (DPS), two microphones, two speakers and a power amplifier. The instrumentation used in noise data collecting and processing consisted of a multichannel signal analyzer (Sinus - Soundbook), a ½” microphone capsule and an acoustic calibrator, both Bruel &amp; Kjaer. The study aimed at evaluating the behaviour of the ANC by means of tests carried out under repeatable conditions, characterized by pre-defined engine speed values. Three replications have been made for each engine speed. The sampling time was 30 s. Two series of tests were performed in order to compare the results observed with the ANC on and off. The engine speed adopted in the study ranged from 600 min– 1, up to 2000 min–1 (maximum speed) with steps of 100 min–1. The ANC proved to be effective in the interval of speed between 1400 and 1700 min–1, where the samplings have been intensified, adopting steps of 50 min–1. In such an interval, the attenuation observed with the ANC system on appeared evident both as weighed A sound pressure level (from 1.29 up to 2.46 dB(A)) and linear (from 4.54 up to 8.53 dB). The best performance has been observed at the engine speed of 1550 min–1, with attenuations, respectively of 2.46 dB(A) and 7.67 dB. Outside of the engine speed interval 1400 - 1700 min–1, the attenuations always resulted lower than 1 dB(A) for the weighed A sound pressure level and between 0.66 and 7.72 dB.

Acoustic metrology – an overview of calibration methods and their uncertainties

The paper gives a brief description of the principles and the uncertainty of the acoustic calibration methods that today are applied by National Metrology Institutes and calibration service centers. Even if some of the calibration principles have been applied over more than half a century, the methods and the instrumentation are still being refined in order to minimize their uncertainty, to extend their frequency ranges, to include extra parameters and to speed up slow processes. In addition to the traditional methods for microphone sensitivity and frequency response calibration, new development areas, like for example wind power, has created needs for low-frequency and infra-sound calibration, down to 0.1 Hz. Other high-tech areas have lead to the development of methods for phase response comparison calibration of microphones for large arrays, for sound intensity measurement and for verification of dynamic linearity of microphones at very high sound pressure levels, up to about 174 dB that corresponds to 10 kPa.

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.

Low peak-power laser ultrasonics

Techniques for the successful excitation of guided ultrasonic waves using a low peak-power laser ultrasonic source are discussed and compared with more conventional Q-switched laser sources. The paper considers acoustic propagation in thin plates, in which the frequencies used, typically only the fundamental guided wave modes, are considered. Aspects of excitation and detection geometry are considered along with the physical mechanisms of photo-acoustic generation and the practical issues surrounding available source wavelengths and power outputs. Understanding of the effects of these constraints is critical for the successful application of the technique. Continuous wave excitation and fully arbitrary modulation schemes are compared, and a technique to control the bandwidth of Golay code modulation is introduced. It is shown that earlier work by the authors was capable of guided wave detection at peak-power densities of 104 W cm− 2. Later work has focussed on the use of erbium-doped fibre amplifiers combined with Golay code modulation to improve the recovered signal-to-noise ratio. Two key applications of the techniques are considered: material properties measurements (using inversion of dispersion curve data) and acoustic emission system calibration.

The three-measurement two-calibration method for measuring the transfer matrix

Extensive use of transfer matrices (TMs) is made in determining the acoustic properties of a duct and in in-duct acoustic propagation models in the automotive industry and for musical acoustics purposes. The experimental apparatuses of classical TM measurement methods feature two measurement heads. Two microphones are flush with the walls of each head. The pressure signals are processed following the transfer function method constructed on an analytical model of acoustic propagation in measurement heads. The present paper aims at presenting a measurement method based on a three-microphone experimental apparatus and on its acoustic calibration through two reference measurements: the three-measurement two-calibration method for measuring the TM (3M2C-TM). Two microphones are flush with the measurement head walls and one is in the cap closing one side of the measured duct. 3M2C-TM proved essential for an accurate measurement of the four TM elements of two different ducts: a cylindrical duct and an expansion chamber.

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.

Construction, calibration, and field test of a home‐made low‐cost hydrophone system for cetacean acoustic research.

Marine mammals are reliable bioindicators of aquatic ecosystems health. Since cetacean highly rely on the use of sound for conspecifics interaction, feeding, and navigation, research in bioacoustics becomes fundamental to unravel the influence of anthropogenic activities on their environment and vocal behavior. Unfortunately, the widespread studies in this area are often limited due to lack of affordable equipment. This paper first describes how to build a low‐cost hydrophone‐amplifier system suitable for cetacean acoustic research and then shows how to perform hydrostatic pressure tests and acoustic calibrations using easily available tools. Finally, field recordings of individuals of two dolphin species: common dolphin (Delphinus spp.) and bottlenose dolphins (Tursiops truncatus) in La Paz Bay, Baja California Sur, Mexico using the proposed system and a professional hydrophone system [AQ‐1s and ITC‐1042 transducers (10 Hz–100 kHz)] are compared.

PC 기반 순음청력검사기를 위한 자동보정시스템 개발

순음청력검사기는 정확한 주파수와 음압을 갖는 순음과 차폐 음을 생성하여 출력할 수 있어야 한다. 이를 위해 일정한 기간마다 보정을 하는 것이 불가피하다. 그러나 수동 보정을 사용하는 일반 순음청력검사기의 음향 보정은 집중력이 필요할 뿐 아니라 시간이 많이 걸리는 단점이 있다. 반면, PC 기반 순음청력검사기의 경우 소프트웨어를 이용하여 자동으로 보정을 수행하는 것이 가능하다. 본 논문에서는 PC 기반 순음청력검사기의 자동 보정을 지원하기 위해 PC 사운드카드를 이용하여 구현한 음압측정기와 이를 이용한 순음청력검사기의 자동보정모듈을 기술한다. 자동 보정모듈을 이용하여 보정한 PC 기반 순음청력검사기를 국제표준기구가 제공하는 기준등가역치음압수준과의 적합 여부를 검증한다. A pure tone audiometer should be able to produce both pure tone and masking noise with exact sound pressure level and frequency. For such purpose, it is unavoidable to periodically calibrates pure tone audiometer. However, manual acoustic calibration requires not only attention but also long time. It is possible to execute automatically calibration using software if it is PC-based pure tone audiometer. In this paper, we describe auto-calibration software for PC-based pure tone audiometer and dedicated sound level meter which has been implemented upon PC by us. To verify auto-calibration module, we examine whether output of PC-based audiometer calibrated through auto-calibration of this paper satisfies RETSPL of IEC or not.

Acoustic calibration of the exterior effects room at the NASA Langley Research Center.

The exterior effects room (EER) at the NASA Langley Research Center is a 39-seat auditorium built for psychoacoustic studies of aircraft community noise. The original reproduction system employed monaural playback and hence lacked sound localization capability. In an effort to more closely recreate field test conditions, a significant upgrade was undertaken to allow simulation of a three-dimensional (3-D) audio and visual environment. The 3-D audio system consists of 27 full-range satellite speakers and four subwoofers, driven by a real-time audio server running a derivation of vector base amplitude panning. The audio server is part of a larger simulation system, which controls the audio and visual presentation of recorded and synthesized aircraft flyovers. The focus of this work is on the calibration of the 3-D audio system, including gains used in the amplitude panning algorithm, speaker equalization, and absolute gain control. Because the speakers are installed in an irregularly shaped room, the speaker equalization includes time delay and gain compensation due to different mounting distances from the focal point, filtering for color compensation due to different installations (half space, corner, and baffled/unbaffled), and crossover filtering.