Electroacoustic Measurements Research Articles

The multichannel vibrotactile gloves: A transmodal technology to feel sound through touch

Development of devices for transmitting sounds through touch is motivated by needs coming from diverse disciplines. Hard-of-hearing individuals could benefit from vibrations to overcome the limitations of existing hearing technologies. Adding tactile cues can be useful for all in contexts where the acoustic information is limited due to sounds coming from multiple sources or noise. The potential sensory augmentation provided by the technology is also interesting in an entertainment context in order to offer immersive experiences. A transdisciplinary approach based on a framework recently developed in our laboratory was used to design this technology that enables the transmission of acoustic signals through touch. Validation experiments were carried out via electro-acoustic measurements as well as behavioral measurements in human subjects (n = 5). Electro-acoustic and behavioral measures support that the system provides uniform stimulation across hands and actuators. The frequency response curve as well as the summation effect measured via behavioral threshold measurements support that the tactile receptors are accurately stimulated by the devices. The multichannel vibrotactile gloves offer the flexibility to transmit diverse acoustic features to individual actuators, making them a valuable tool for research and a prospective technology capable of substituting, compensating, or extending sensory perception.

Structural characterization of LLDPE/MgO insulation composites in terms of space charge accumulation in an HVDC field

This study addresses the critical role of insulation materials in high-voltage direct current (HVDC) transmission systems, emphasizing the challenges associated with space charge accumulation and slow polarization effects. The primary objective of this study is to investigate the utilization of linear low-density polyethylene (LLDPE) in High Voltage Direct Current (HVDC) applications, with a focus on enhancing its performance through the incorporation of magnesium oxide (MgO) nanoparticles. The research employs various techniques, including X-ray diffraction, nuclear magnetic resonance, broadband dielectric spectroscopy, conductivity measurements and pulse electroacoustic measurements, to analyse the internal structure, crystallinity, and space charge dynamics of LLDPE/MgO nanocomposites. The results demonstrate that controlled MgO incorporation optimizes the internal electric field, improving the electrical properties without significantly altering the charge decay rate. The multidimensional approach of the study provides valuable insights into tailored modification of insulation materials for enhanced HVDC transmission performance, considering both electrical and structural aspects.

Effect of Li1.3Al0.3Ti1.7(PO4)3 on semiconductive composites: Positive temperature coefficient (PTC) performance and inhibition of space charge injection

The semiconductive layer located between the core and insulation layer of a high-voltage DC (HVDC) cable can inhibit the accumulation of space charge in the insulation layer. This helps increasing the electric field inside the cable, thus improving the stress distribution of the electric field on the inner and outer surfaces of the insulation layer and the electrical strength of the cable. An inevitable positive temperature coefficient effect (PTC) in the semiconductor layer leads to aging failure of the insulation layer. To improve this phenomenon, the semiconductive shielding layer was modified for suppressing its PTC effect and reducing the space charge injection into the insulation layer. Li1.3Al0.3Ti1.7(PO4)3(LATP) was prepared via a solid-phase reaction and added to a composite consisting of carbon black (CB), ethylene vinyl acetate copolymer (EVA), and low-density polyethylene (LDPE). Resistivity, thermally stimulated depolarization current (TSDC), and pulsed electroacoustic (PEA) measurements were performed on the modified sample. The results showed that when the LATP content was 4 wt%, the modification effect of the semiconductive shielding layer was most effective, the PTC effect was reduced by 11%, and the space charge injection into the insulating layer was improved significantly.

Measuring the effect of electronic hearing protection devices on behavioral detection thresholds

Electronic hearing protection devices can provide amplification for quiet ambient sounds, while still providing protection against loud sounds. These can be important in environments with sporadic and unpredictable hazardous noise, but also with a need for maintaining awareness of ambient sounds, or for conducting face-to-face communication. This study’s aim was to understand what impact electronic hearing protection devices have on auditory detection thresholds. Human subjects were used to measure thresholds for narrowband noise bursts without hearing protection, with electronic hearing protectors powered off, and with electronic hearing protectors powered on with several gain settings. In addition, electroacoustic measurements were made of the input/output functions and electronic noise floors of the hearing protectors at the same gain settings. The data showed that thresholds in quiet with electronic hearing protectors were higher than without, regardless of the device amplification. This could be attributed to the hearing protector electronic noise limiting performance. Thresholds measured with ambient masking noise were similar across open ear and device conditions, reflecting that the signal-to-noise ratio for ambient sounds does not change with amplification. Listeners with a simulated conductive hearing loss had lower thresholds with an electronic hearing protector than without, suggesting a benefit of the device amplification.

Relevancy of Pulsed Electroacoustic Measurements for Investigating Spacecraft Charging

The magnitude and spatial distribution of charge embedded in dielectric materials and the evolution of the charge distributions with time are paramount for the understanding and mitigation of spacecraft charging. Spacecraft materials are charged primarily by incident fluxes of low-energy electrons, with electron fluxes in the 10–50 keV range often responsible for the most deleterious arcing effects. While the pulsed electroacoustic (PEA) method can provide sensitive nondestructive measurements of the internal charge distribution in insulating materials, it has often been limited for spacecraft charging applications by typical spatial resolutions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\le $</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> m, with a 10- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> m range of electrons in common spacecraft materials (e.g., polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), low-density polyethylene (LDPE), or SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{2})$</tex-math> </inline-formula> at incident energies from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 20 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 40 keV. A series of PEA tests over a range of incident electron energies were devised to investigate the relevance of the PEA method for typical spacecraft charging applications. Thin-film samples of vacuum-baked PEEK were irradiated with 10–80-keV monoenergetic electron beams. PEA measurements of deposited charge profiles determined the peak positions and magnitude of deposited charge. These were used to establish the minimum incident energies for which PEA measurements provided meaningful results and thus to characterize the merits of PEA measurements over energy ranges of relevancy to spacecraft charging issues.

A Simple Method for Determining Shallow Charge Distributions in Dielectrics via Pulsed Electroacoustic Measurements

The understanding of charge dynamics in dielectric materials is paramount in mitigating electrostatic discharge events for spacecraft. The most critical spacecraft charging events are found to result from incident electrons in the energy range of 10 keV to 50 keV. The charge embedded in dielectric materials in this energy range are deposited a distance into the material on the order of a few to tens of microns. One way to measure and understand the deposited charge is via pulsed electroacoustic measurements (PEA). However, the typical PEA spatial resolution of ~ 10 μm is not sufficient to resolve or discern charge deposited at the lower end of this incident electron energy range, where deposited charge distributions are obscured by the superposition of the signal originating from induced mirror charge on the electrode of the pulsed electroacoustic system. A simple method is proposed and demonstrated in which reference measurements from a pristine sample are used to separate the effect of the induced mirror charge from the measured embedded charge to obtain a more accurate determination of the deposited charge distribution.

PEA Signal Simulation Using Multiple Viscoelastic Relaxation Model for Determination of Acoustic Attenuation and Velocity Dispersion

Acoustic attenuation in polymer insulators prevents the accurate determination of space charge profiles measured by pulsed electroacoustic (PEA) measurements. A PEA signal simulation is developed on the basis of a multiple viscoelastic relaxation model, which can determine acoustic attenuation and sound velocity dispersion in polymer insulators. To implement the multiple relaxation model, we use an analogy between the viscoelastic and dielectric relaxations. The Kelvin–Voigt model is used as a single relaxation model, and the Cole–Cole model is used as a multiple relaxation model. The simulation based on the Cole–Cole model as a multiple relaxation model can accurately reproduce measured PEA signals. The distortion of a PEA measured space charge profile due to acoustic attenuation and velocity dispersion is also discussed. The charge profile calculated using the multiple relaxation model is in good agreement with the peak value, width, and tail shape obtained in experiments.

Effects of nanosecond impulse and step excitation in pulsed electro acoustic measurements on signals for space charge determination in high-voltage electrical insulation

The presence of space charges in high-voltage insulation can influence the operational stresses of the dielectric materials; the topic is present in various, even distant domains such as power grids or transportation segments that are represented by electromobility, rail, more-electric aircraft, and space systems. In this article, the effects of nanosecond impulse and step excitation in the pulsed electro-acoustic measurements (PEA) of space charges in high-voltage electrical insulation have been investigated. Various parameters of a pulser (such as impulse width, rise time, and sensor thickness) have been investigated by using a designed programable pulser. The investigations have been performed on a polyethylene sample in one- or double-layer configurations. In the latter, an interlayer sprinkled charge was analyzed. The experimental results have shown the main PEA effect during the transition phase of the applied voltage. It was observed that the pulse transition has a critical importance for stimulating space-charge vibrations and generating elastic waves. Hence, the slope’s rise and fall times are crucial in pulser design. The pulser width also has an impact on a signal’s magnitude as well as on its dispersion and attenuation. The correspondence between a pulse and step excitation was presented. Some advantages are attributed to the step-based excitation in terms of fewer wave reflections and interferences as well as the avoidance of the wavelet cancelation effect for a very narrow pulse width. Hence, step excitation can result in the easier postprocessing and interpretation of individual peaks in the acquired PEA signal. Another advantage may be recognizing the space-charge polarity instead of the net result. Important recommendations refer to the tuning of pulser timing settings with respect to signal attenuation (especially in thicker specimens) and the adequate adjustment of the sensor’s thickness. The presented analysis and experimental results extend the insight into PEA measurement – especially with a focus on diagnostic applications.

Comparison of Pulsed Electroacoustic Measurements and AF-NUMIT3 Modeling of Polymers Irradiated with Monoenergetic Electrons

Successful spacecraft design and charging mitigation techniques require precise and accurate knowledge of charge deposition profiles. This paper compares models of charge deposition and transport using a venerable deep dielectric charging code, AF-NUMIT3, with direct measurements of charge profiles via pulsed electroacoustic (PEA) measurements. Eight different simulations were performed for comparison to PEA experiments of samples irradiated by 50 or 80 keV monoenergetic electrons in vacuum and at room temperature. Two materials, polyether-ether ketone (PEEK) and polytetrafluoroethylene (PTFE), were chosen for their very low conductivities so that minimal charge migration would occur between irradiation and PEA measurements. PEEK was found to have low acoustic attenuation, while PTFE has high acoustic attenuation through the sample thicknesses of 125 and for each material. The measurements were directly compared to AF-NUMIT3 simulations to validate aspects of the code and to investigate the importance of various simulation options, as well as to characterize the PEA instrumentation, measurement methods, and signal processing used. The measurement and simulation values for magnitude of charge deposition, penetration depth, and charge deposition spatial profiles are largely in agreement, though spatial and temporal distributions in incident electron flux and effects of radiation-induced conductivity (RIC) and delayed RIC during the deposition process complicate the process. This work provides an experimental validation of the AF-NUMIT3 deep dielectric charging code and insight into the accuracy and precision of the PEA method.

Fundamental Concepts for Assessment and Interpretation of Wideband Acoustic Immittance Measurements.

Assessment of middle ear impedance using noninvasive electroacoustic measurements has undergone successive developments since its first clinical application in the 1940s, and gained widespread adoption since the 1970s in the form of 226-Hz tympanometry, and applications in multifrequency tympanometry. More recently, wideband acoustic immittance (WAI) is allowing unprecedented assessments of the middle ear acoustic mechanics thanks to the ability to record responses over a wide range of frequencies. The purpose of this article is to present fundamental concepts for the assessment and interpretation of wideband measures, including a review of acoustic impedance and its relation to the mass, stiffness, and resistance components of the middle ear. Additionally, an understanding of the middle ear transfer function reveals the relationship between impedance and middle-ear gain as a function of frequency. Wideband power absorbance, a WAI measure, quantifies the efficiency of sound conduction through the middle ear over a wide range of frequencies, and can serve as an analogous clinical measure to the transfer function. The interpretation of absorbance measures in ears with or without a conductive condition using absorbance measured at ambient pressure and pressurized conditions (wideband tympanometry) is described using clinical case examples. This article serves as an introduction to the fundamental principles of WAI measurements.

Effect of LiCoO 2 on the positive temperature coefficient effect (PTC) properties of semiconductive composites and its ability to inhibit space charge injection

The semiconductive shield layer is between the conductive core and the insulation layer of high voltage direct current transmission cables and plays an important role in suppressing the accumulation of space charge in the insulation layer. Since the prevalent positive temperature coefficient effect (PTC) of the semiconducting layer leads to cable ageing and failure, this paper proposes the use of lithium cobaltate to modify the semiconducting shield to suppress its PTC effect and improve its ability to inhibit space charge injection. The ionic conductor LiCoO2 was prepared by the sol–gel method. LiCoO2 particles with particle sizes ranging from tens to hundreds of nanometres were obtained by ball milling. The prepared LiCoO2 was used as a filler to modify the carbon black (CB)/ethylene vinyl acetate copolymer (EVA)/low density polyethylene (LDPE) composites. After melt blending and moulding cross-linking, LiCoO2/CB/EVA/LDPE semiconductive shielding specimens were successfully fabricated. Resistivity, Thermally Stimulated Depolarisation Currents (TSDC), and pulsed electro-acoustic measurements were conducted for the prepared specimens. The PTC effect, which is common in polymer composites, was successfully suppressed, and the PTC strength was reduced by 17%. The resistivity of the semiconductive shielding layer was significantly reduced. The ability of the semiconducting shield to inhibit space charge injection from the conductive core to the insulation layer was significantly improved. When LiCoO2 content is 0.5 wt%, the semiconductive shielding layer has the best performance, and the space charge in the insulation layer was reduced by 70% compared to the undoped semiconducting shield.

Model-based processing for the estimation of space-charge distribution from non-contact pulsed electro-acoustic measurements

Estimating the space-charge distribution using the pulsed electro-acoustic method requires a calibration procedure, in which a reference voltage signal is measured and used to divide the output voltage signal of the piezoelectric sensor. Such a procedure is time consuming and generally involves manually setting filter parameters whose values should be chosen to reduce ringing artifacts in the charge profile and, at the same time, preserve the bandwidth of the profile. This paper proposes a model-based estimation method called the matrix pencil that does not require a calibration procedure to retrieve the charge distribution, albeit with normalized amplitudes, and thus it paves the way for reducing data acquisition and processing times. Results on simulated and experimental data confirm the effectiveness of the proposed method in estimating the space-charge distribution in irradiated polymers.

Wideband and wide beam piezoelectric composite spherical cap transducer for underwater acoustics

A new class of piezoelectric composite spherical cap transducer that produces a wide beam and bandwidth was developed for underwater acoustics. A finite element analysis (FEA) simulation was used to design the transducer. Electroacoustic response measurements in water were made on a transducer to evaluate the performance characteristics and then compared with the FEA results. The measured results show the transducer can provide a 112° beamwidth and a usable frequency band from 215 kHz to 355 kHz. The maximum transmitting voltage response (TVR) of the transducer is 161.7 dB re 1µPa/V@1m at 255 kHz.

Influence of external electric fields and temperature on the behavior of water and acetophenone molecules in C120H242 chains: A molecular dynamics study

Polymers are widely used as electrical insulating materials, with polyethylene being one of the most commonly used materials. However, the presence of water and acetophenone (AP), which are byproducts of the cross-linking agents used to produce cross-linked polyethylene, can cause space charge formation and electrical degradation. In the present study, the effects of an external electric field and temperature (250–400 K) on the dynamic and structural properties of water molecules (1 wt%) with AP molecules (1 wt%) in C120H242 chains were evaluated by molecular dynamics simulations with the SPC/E water model and the general AMBER force field. The results showed that water molecules diffused into the C120H242 chains under the condition of E = 5 GV/m in the temperature range of 250–400 K. Moreover, the AP molecules diffused into the C120H242 chains under the condition of E = 1 and 5 GV/m in the temperature range of 350–400 K. These results support a previously proposed model for space charge formation in polyethylene, which was based on pulsed electro-acoustic measurements. Thus, we verified a molecular model for the space charge and a suppression mechanism for electrical degradation from the viewpoint of the diffusion of water and AP molecules.

Utilizing True Wireless Stereo Earbuds in Automated Pure-Tone Audiometry.

True wireless stereo (TWS) earbuds have become popular and widespread in recent years, and numerous automated pure-tone audiometer applications have been developed for portable devices. However, most of these applications require specifically designed earphones to which the public may not have access. Therefore, the present study investigates the accuracy of automated pure-tone audiometry based on TWS earbuds (Honor FlyPods). The procedure for developing an automated pure-tone audiometer is reported. Calibration of the TWS earbuds was accomplished by electroacoustic measurements and establishing corrected reference equivalent threshold sound pressure levels. The developed audiometer was then compared with a clinical audiometer using 20 hearing-impaired participants. The average signed and absolute deviations between hearing thresholds measured using the two audiometers were 3.1 dB and 6.7 dB, respectively. The overall accuracy rate in determining the presence/absence of hearing loss was 81%. The results show that the proposed procedure for an automated air-conduction audiometer based on TWS earbuds is feasible, and the system gives accurate hearing level estimation using the reported calibration framework.

Frequency Modulation System and Bone Conduction Hearing Aid: Electroacoustic Verification.

Introduction A protocol has not yet been developed to perform electroacoustic measurements and behavioral tests to fit the frequency modulation (FM) system in bone conduction hearing aid (BCHA) users. Electroacoustic verification, with “FM transparency” achieved, ensures user audibility of FM transmitter and hearing aid signals. Objective To propose and validate a protocol for electroacoustic verification of the FM system coupled to the BCHA. Method Twenty-four sets of FM system and BCHA were submitted to electroacoustic verification, using a receiver and a plastic adapter to connect the BCHA to a 2cc coupler in the hearing instrument analyzer. The measurements were performed in the acoustic box, at 65 dB sound pressure level (SPL), with International Speech Test Signal (ISTS), first to the BCHA microphone and then to the FM system microphone, to determine the transparency, in which equivalent inputs for both microphones result in equivalent outputs. The FM gain or volume has been adjusted to try to gain transparency for the outputs of the two input devices. Results Transparency was achieved for all sets evaluated, but in some combinations, adjustments to the FM receiver gain over the manufacturer's default setting were required. Conclusion The proposed protocol proved to be effective for the electroacoustic verification of the FM system coupled to the BCHA.

LoCHAid: An ultra-low-cost hearing aid for age-related hearing loss.

Hearing aids are the primary tool in non-medical rehabilitation for individuals with hearing loss. While the costs of the electronic components have reduced substantially, the cost of a hearing aid has risen steadily to the point that it has become unaffordable for the majority of the population with Age-Related Hearing Loss (ARHL) especially for those residing in low- and middle-income countries. Here, we present an ultra-low-cost, affordable and accessible hearing aid device ('LoCHAid'), specifically targeted towards treating ARHL in elderly patients. The LoCHAid components cost 98 cents (< $1) when purchased in bulk for 10,000 units and can be personalized for each user through a 3D-printable case. It is designed to be an over-the-counter (OTC) self-serviceable solution for elderly individuals with ARHL. Electroacoustic measurements show that the device meets most of the targets set out by the WHO Preferred Product Profile and Consumer Technology Association for hearing aids. The frequency response of the hearing aid shows selectable gain in the range of 4-8 kHz, and mild to moderate gain between 200-1000 Hz, and shows very limited total distortion (1%). Simulated gain measurements show that the LoCHAid is well fitted to a range of ARHL profiles for males and females between the ages of 60-79 years. Overall, the measurements show that the device offers the potential to benefit individuals with ARHL. Thus, our proposed design has the potential to address the challenge of affordable and accessible hearing technology for hearing impaired elderly individuals especially in low- and middle-income countries.

On the Hamaker constant of the metallic iron, the retardation effect and their relevance in DLVO theory applied to oil-based magnetorheological fluid with 1-octylamine

To explain the redispersibility results of a poly(alpha-olefine) oil-based magnetorheological fluid with carbonyl iron powder (80 vol%) and 1-octylamine (0.5 wt% on iron powder), as a dispersant, we apply the DLVO theory. We reviewed and discussed values of the Hamaker constant for the iron metal and adopted AFe ∼ 460 ± 100 zJ. For the MRF studied, therefore, the Hamaker constant Fe / PAO oil / Fe can be estimated as A131 ∼ 2.4 ± 0.5 × 10–19 J. We have analysed the equations for the retardation factor and as such factor changes the total potential curves in the DLVO approach. We conclude that the equation proposed by Ho and Higuchi can be applied to correct the van der Waals attractive potential curve. The electrokinetic potential (or zeta potential) of MR fluid was estimated from electroacoustic measurements, resulting ζ = 158 ± 15 mV. For A131 = 288 zJ, with ζ = 60 mV and including the retardation factor, the total potential curve resulted in a barrier height of 11 kT, without presenting a secondary minimum. The results of redispersibility of the MR fluid after one year at rest showed a normal force peak of 0.15 N and work of 1.12 mJ at 80 mm depth penetration.

Experimental demonstration of deep traps in silica-based polyethylene nanocomposites by combined isothermal surface potential decay and pulsed electro-acoustic measurements

The ability to suppress space charge accumulation at high electric fields makes nanocomposites attract significant research interest as potential insulation materials in high-voltage direct current cable development. At present, the deep trap introduced by nanoparticles is frequently applied to be responsible for the observed space charge suppression in nanocomposites. However, the experimental results that support deep-trap formation have not been rigorously examined. We therefore propose herein a simple and more direct approach based on isothermal surface potential decay combined with pulsed electro-acoustic measurements to verify the presence of deep traps in silica-based blend polyethylene nanocomposites. The results indicate that the deep traps are indeed introduced by filling nanosilica and the space charge suppression observed in the nanocomposite with a low loading ratio is caused by deeply trapped charges in the sub-surface region of specimens.

Lifetime of electret microphones by thermal degradation analysis via electroacoustic measurements

Electronic equipment frequently utilises low cost electret microphones. In this paper, a complete accelerated life-test on commercial electret microphones is presented using thermal chamber testing. The test was conducted on the microphones under study at three different temperatures. After each thermal probe, the electroacoustic characteristics of each transducer was analysed for obtaining the degradation model. In the literature such tests have been performed through charge losses on the electret materials. Life models were obtained for the degradation failures revealed from the tests and a complete temperature model was then developed, which can calculate the useful life of the microphones under any of these conditions.