Condenser Microphone Research Articles

О СРАВНЕНИИ КОНДЕНСАТОРНОГО И ЭЛЕКТРОКИНЕТИЧЕСКОГО МИКРОФОНОВ

Basing on the analysis of the physical features of the operation of the microphone on electrokinetic phenomena, it has been experimentally confirmed that this microphone works on a functional principle different from the principle of operation of a condenser microphone. It is shown that a microphone based on electrokinetic phenomena can increase its sensitivity by up to about 40 dB due to pumping. Comparison of two experimental studies shows that the sensitivity of an electrokinetic microphone can strongly depend on the size of the porosity of the dielectric placed between the electrodes of the microphone.

Electrotactile Feedback for the Discrimination of Different Surface Textures Using a Microphone.

Most commercial prosthetic hands lack closed-loop feedback, thus, a lot of research has been focusing on implementing sensory feedback systems to provide the user with sensory information during activities of daily living. This study evaluates the possibilities of using a microphone and electrotactile feedback to identify different textures. A condenser microphone was used as a sensor to detect the friction sound generated from the contact between different textures and the microphone. The generated signal was processed to provide a characteristic electrical stimulation presented to the participants. The main goal of the processing was to derive a continuous and intuitive transfer function between the microphone signal and stimulation frequency. Twelve able-bodied volunteers participated in the study, in which they were asked to identify the stroked texture (among four used in this study: Felt, sponge, silicone rubber, and string mesh) using only electrotactile feedback. The experiments were done in three phases: (1) Training, (2) with-feedback, (3) without-feedback. Each texture was stroked 20 times each during all three phases. The results show that the participants were able to differentiate between different textures, with a median accuracy of 85%, by using only electrotactile feedback with the stimulation frequency being the only variable parameter.

Development of highly sensitive fiber-optic acoustic sensor and its preliminary application for sound source localization

A metal diaphragm-based omnidirectional fiber-optic acoustic sensor with high sensitivity has been developed in this work. The acousto-optic transducer of the sensor is a single-wavelength extrinsic Fabry–Pérot interferometer (EFPI) that is highly sensitive to the displacement of the diaphragm’s center. The sensor can stably work in the linear response region of the EFPI in a wide range of temperature from −20 to 60 °C. The pressure sensitivity of the sensor is larger than 800 mV/Pa, and the sensitivity fluctuation in the frequency range from 100 Hz to 6 kHz is smaller than 3 dB. The noise-limited minimum detectable pressure obtained at 1 kHz of the sensor is 126 μPa/Hz1/2. In addition, the above-prepared fiber-optic acoustic sensors present excellent phase consistency with each other, which facilitates the formation of a sensor array for sound source localization. In this work, a cross-shaped fiber-optic sensor array was prepared and then used to detect and track a small drone flying in the field. The experimental results show that the sensor array can capture the acoustic fingerprint of the drone at a distance as far as 300 m. This detection distance is more than ten times longer than that of a conventional electret condenser microphone. The azimuth angle of the drone obtained with the fiber-optic acoustic sensor array has a deviation of smaller than 10° relative to the GPS data from the drone.

Vision and sound fusion-based material removal rate monitoring for abrasive belt grinding using improved LightGBM algorithm

Accurate material removal modeling is the basis for optimizing the surface quality and improving the performance of equipment components. In this study, a multi-sensor fusion method of vision and sound is used to monitor in-process grinding material removal rate (MRR). First, belt grinding experiments are conducted using different grinding parameters, and vision and sound signals are captured by industrial CCD cameras and an omnidirectional condenser microphone, respectively. Second, the features of the captured grinding spark images are extracted based on two aspects: color and texture, and those of the grinding sound are investigated in the time, frequency, and time–frequency domains. Moreover, the complementarity between the vision and sound signals and their sensitivity to different grinding parameters are discussed. Finally, based on feature-level fusion strategies, the Pearson correlation coefficient and the sequential backward selection algorithms are jointly used to select the optimal feature subsets. MRR prediction models are established using the selected feature subsets and an improved light gradient boosting machine (LightGBM) algorithm. The test results show that the error in the MRR prediction model of same-specification abrasive belts is less than 3 %, and the coefficient, R2, is as high as 99.2 %. The proposed method can be used to predict the MRR resulting from a single grinding parameter and multiple ones, using the same-specification abrasive belts. Compared to other prediction models, the improved LightGBM model is superior in terms of the time factor without reduction in the accuracy of the model.

Non‐invasive sound‐based classifier of bearing faults in electric induction motors

Induction motors play a major role in the industry nowadays due to their simple construction, uncomplicated maintenance, and cost efficiency. As the motor operates for repeated hours, some faults may occur and, depending on the process sensitivity, can cause significant losses to the industrial production. In this context, an alternative method is proposed to detect and classify bearing faults using acoustic emission signals generated by the machines and simple features obtained from them. A pair of condenser microphones was used to acquire these signals and audio feature extraction is performed to obtain time and frequency patterns to characterize healthy and faulty machines. The major differences of the acoustic signals regarding the fault frequency signatures are discussed by analyzing specific peaks observed in their spectra. Several coupled load values and levels of power supply voltage unbalance were considered in the experimental tests, which emulate common situations encountered in industrial environments, obtaining accuracy rates over 97% of success. Finally, a comparison is presented of machine learning techniques for bearing faults classification under different load values and voltage unbalance levels.

Detection of Infrasonic Frequency Loudspeaker Using Microwave Motion Sensor Module

In the last few decades, research on loudspeakers, especially at low frequencies and infrasound, has made significant developments. Among them, the loudspeaker is used as a low-frequency mechanical signal generator to simulate human arterial pulses. An electret condenser microphone (ECM), one of the alternative sensors that will be used to measure the arterial pulse which is simulated by the loudspeaker. Interestingly, neither the mechanical signal generator nor the sensor that will be used has data on infrasonic frequencies or it can be concluded that both of them have not been calibrated. This paper proposes that the infrasonic signal generated by a moving coil loudspeaker can be observed using a calibrated sensor, a microwave motion sensor. The main contribution of this study is to find the infrasonic loudspeaker frequency response data used in previous studies so that it can be used as a compensator to calibrate ECM as an alternative arterial pulse sensor. Microwave motion sensors have basic concepts such as the Doppler effect principle, which reads an object based on its displacement. Microwave motion sensors can observe the movement of the diaphragm cone of the loudspeaker requires several supporting instruments, including a signal conditioning circuit and an undisturbed environment. In the end, the microwave motion sensor can observe infrasonic acoustic waves and get a compensator value for the ECM as an alternative arterial pulse sensor.

Analysis of wake velocities and pressure fluctuations in a bistable flow using Hilbert–Huang transform and wavelets

This article presents the experimental study of the wake velocity and pressure fluctuations in the bistable flow behind two cylinders side by side. Measurements were conducted in an aerodynamic channel with a pair of cylinders with 25.1 mm of diameter located in the test section, with a pitch-to-diameter ratio p/D of 1.26. The studied Reynolds numbers are Re = 1.61 × 104, Re = 2.16 × 104, and Re = 2.57 × 104, based on the cylinder diameter and the free stream velocity. Pressure fluctuations were measured using condenser microphones positioned in the wake region flush mounted with the upper channel wall. Wake velocity was measured employing hot wire anemometry. Data analysis was performed by Hilbert–Huang transform and by the continuous wavelet transforms, together with a PDF (probability density function) analysis to determine the tools that better represent the phenomena. The results show the presence of the bistable flow in the raw signal; the PDF emphasizes that there is no direct influence of the Reynolds number in the statistical moments, and the JPDFs (joint probability density function) present the bistable variations very clear in the time–frequency relations. The continuous wavelet has high energy under 150 Hz, which can be associated with the vortex shedding. Comparison of the techniques shows that the wavelet transform better represents the bistable signals, allowing the observation of the phenomena and corresponding main frequency ranges. Hilbert–Huang transform shows all the instantaneous frequency modulations present in the signal; the EEMD (Ensemble Empirical Mode Decomposition) represents the most important oscillations of the flow with the identification of the bistable phenomenon. The Hilbert spectra show the location of those oscillations on time and amplitude but cannot identify bistability.

59 The effects of audio exposure to goat kids’ relative intensity ratios of harmonics from birth to weaning

Abstract This study evaluated the effects of exposure to sound stimuli on goat kids’ relative intensity ratios (RIR) of harmonics one through five from d 0 to d 49 of growth. RIR are the ratio between a harmonic and the first harmonic. Day zero boer kids were randomly assigned to three treatment groups: treatment 1 (n=5) was only exposed to a single human voice recording, treatment 2 (n=4) was exposed to their boer dams, and treatment 3 (n=4) was exposed to no vocalizations. Each group was housed in pens (2.44 x 3.05 m) and received the same diets, which met or exceeded NRC requirements. The kids were isolated in their respective pens 1x/wk for 7 wk for 120 to 1000 s to obtain vocalization recordings. The kid’s vocalizations were collected via a Blue Snowball iCE condenser microphone and laptop. VoceVista Video software was utilized to analyze the relative intensities (dB) of the first five harmonics. Results indicate there is no difference in average RIR between the human and treatment 1 of the second, third, and the fifth harmonics. Kids raised next to the dams had significantly lower average (P < 0.05) RIR for all of the harmonics. No significant difference was noted between the average RIR of harmonics three, four, and five of treatment 3 and the human recording. No difference in the RIR of second, third, and fifth harmonics suggest that a goat kid exposed to only human vocalization exhibits a human-like tone in relation to these harmonics within the first 7 wks. A difference in treatment two from the average RIR of the dams and no difference between treatments one and three compared to the human recording indicate that exposure to vocalizations during growth does have an effect on seven-week-old kid harmonic intensities.

Millimeter-sized few-layer suspended graphene membranes

In this work, suspended 4-mm-wide graphene membranes are obtained through a sublimation-assisted transfer process, using few-layer films grown by microwave plasma chemical vapor deposition. This result is achieved by a new approach involving the removal of the graphene-transfer supporting layer in vacuum. The membranes produced by this procedure show the largest area-to-thickness ratio described in the literature with a 2-fold improvement when compared to the best results using the conventional PMMA-assisted transfer, and a five orders of magnitude increase when compared to previous sublimation-assisted processes. This breakthrough allows the implementation of a wide variety of technological applications where 2D materials with atomic thickness and large areas are required. As large-area free-standing membranes are difficult to obtain, a new figure of merit is defined to benchmark the various methods of suspending graphene. A high transfer yield is achieved, and the mechanical and optical properties of the 3.7 nm thick membranes are evaluated. Finally, a prototype condenser microphone is built and tested, and found to exhibit an enhanced specific response.

The use of optical methods for measuring weak acoustic shock waves in homogeneous air and close to reflecting boundaries

Measuring blast waves in laboratory-scale experiments using acoustical methods is a challenge. Optical methods provide an attractive possibility for recording pressure signatures of weak acoustic shocks. In this presentation, recent experiments for reconstructing pressure waveforms of spark-generated spherically divergent blast waves (1.8 kPa amplitude and 50 μs duration at 15 cm distance from the source) both in homogeneous air and close to reflecting surfaces are overviewed. Three methods were employed: shadowgraphy, schlieren, and interferometry. It was shown that shadowgraphy method allowed for measuring shock thickness and its amplitude. Schlieren technique provided reconstruction of the pressure waveforms in homogeneous air. In the reconstruction process the front geometry was assumed to be spherical or cylindrical. The exposure time of the high-speed camera was a limiting factor for the time resolution. Mach-Zehnder interferometer method was the most relevant for laboratory-scale measurements. The method reached 0.4 μs of time resolution, which was more than 6 times higher than that of 1/8-in condenser microphones. Moreover, the Mach-Zehnder interferometry allowed quantitative reconstruction of the pressure waveform without additional calibrations. The method was successfully applied for measuring waveforms in homogeneous air and reflected waves from rigid smooth and rough surfaces. [Work supported by ANR-10-LABX-0060/ANR-16-IDEX-0005.]

Off-axis frequency response in a dual diaphragm, uniphase moving coil microphone

When the rear port in a uniphase, unidirectional condenser microphone is modified to include a series compliance element (dual diaphragm) the low frequency performance can be improved. The benefit is most notable in the off-axis response as it relates to source/receiverproximity (proximity effect). Due to the significant operational differences between uniphase moving coil and condenser microphones, incorporating a dual diaphragm element into the rear port of a moving coil microphone requires careful attention to the design. Simplified network models of the uniphase system, proximity effect, and dual diaphragm moving coil design are presented. Measured results of a dual diaphragm, uniphase moving coil microphone are presented with off-axis response comparisons to a single diaphragm, uniphase moving coil microphone.

Weird science microphones are coming

Electret condenser microphone elements ruled for decades, are being displaced, at first in the late 1990s, and more rapidly in the last decade, by capacitive MEMs. Breaking the signal to noise ceiling at 70 dB in small consumer electronics microphone formats has been a tenacious barrier for far field voice control and sound pickup. Some existing conventional solutions and those just below the radar are more than promising. The advances in materials science in the last few years have been remarkable. Product demand in all categories, especially mobile electronics and voice command, are driving this rapid advancement. Some of these developments in materials and their application to existing microphones and for the next generation microphone products will be revealed. “Weird microphone science projects” that are jelling toward commercial productization, such as graphene electrostatic and ribbon mics, optical microphones, piezo MEMs, insect eye mics, and more will be explored.

Interferometric measurements of supersonic projectile acoustic signatures

Supersonic projectiles cause disturbances in the air that propagate and coalesce to form acoustic signatures. In the far-field, these signatures approach ideal N-waves. However, near the projectile these signatures are closely related to the projectile's shape. To study the generation and formation of acoustic signatures from supersonic projectiles, an experiment was conducted using optical methods. A z-type schlieren imaging system and laser interferometer were used in conjunction with acoustic sensors to measure the pressure field surrounding supersonic projectiles of various sizes and shapes. The rate of change of the phase difference recorded by the interferometer is inverted to obtain the ballistic pressure field by assuming cylindrical symmetry and using an inverse Abel transform. The accuracy of these reconstructed time series is evaluated by comparing N-wave parameters, such as period and peak pressure, with analytical results derived from the Whitham F-function. Improved rise time resolution obtained from the interferometric measurement is demonstrated by comparison with recordings from standard condenser microphones. Advantages of measuring acoustic signatures near the projectile by interferometric methods are discussed.

Photoacoustic tomography system based on Diode Laser to Imaging of some types of materials

<p>Photoacoustic tomography imaging research has been conducted to distinguish several types of materials. The photoacoustic tomography imaging system used in this study uses a diode laser as a source of radiation and a condenser microphone as a detection tool. The sample is a combination of two types of materials, namely plasticine + iron wire, plasticine + cardboard, plasticine + mica plastic, and mica plastic + cardboard. Optimum setting of laser modulation frequency and duty cycle system to distinguish images from plasticine samples + iron wire and plasticine + cardboard, i.e., 19 kHz and 50%, while to recognize images from plasticine samples + mica plastic and mica plastic + cardboard, which is 19.5 kHz and 50%. The photoacoustic tomography image system used can detect and image the sample clearly, the striking color difference between one material, and another shows the difference in sound intensity.</p>

Experimental evaluation of rock disintegration detection in drilling by a new acoustic sensor method

A simple and reliable method for monitoring the rock properties in drilling is recognized as a global challenge, especially for cluster and infill development well drilling in oil and gas production. To improve the existing limitations in the detection of formation lithology in drilling systems, an acoustic sensor approach for rock disintegration in the drilling using a polycrystalline diamond compact (PDC) drill bit is developed and evaluated. In this paper, we report the application of a special acoustic sensor device to qualitatively survey rock disintegration by rotary drilling. In this work, an acoustic focusing component is designed to assist a condenser microphone in detecting signals emerging in the process of drilling as an integrating information resource. A time-frequency with zoom fast-Fourier-transform analysis method is presented to recognize the acoustic signal features in breaking different rocks. Additionally, principal component analysis and Support Vector Machine method are used to check the qualitative analysis results for the monitored rock information. An experimental investigation considered four types of rock broken by a PDC drill bit with drilling weights ranging from 5 to 12.5 kN and drilling rates ranging from 64 to 128 r/min. To verify the reliability and accuracy of our acoustic rock detection method, two sensors installed in the orthogonal direction are examined. Furthermore, the coherent analysis was used to reveal the correlation of the output auto-correlation spectrum for each measurement. The results show that there is a good average percentage of lithology calculated by the time-frequency analysis results between the acoustic signal features and different types of rock. Accordingly, the acoustic sensor approach can help enhance the detection of rock properties in drilling systems, laying the foundation for quantitative lithology identification in more complex drilling.

ELECTRET CONDENSER MICROPHONE AS SENSOR IN ARTERIAL PULSE RECORDING DEVICE

One of the human pulses could be detected on an arterial radial that represents the human health condition. Several sensors could capture the pulse signal. However, it still needed a sensor with a small dimension and lightweight. One of the sensors that comply with those specifications is an electret condenser microphone (ECM). The ECM was designed to pick up the signal from the human radial arterial pulse. The ECM pick up system was equipped with an instrumentation amplifier and a signal processing system. The characteristic of the ECM was analyzed using a sixth-order polynomial equation. The equation was used to reconstruct the signal, which flattened the frequency response at the range of 0.5-4.5 Hz. The signal processing consists of an FFT, peak detection and a sixth-order anti-polynomial computational unit which is implemented in a computer. The minimum error was found at 1.5 Hz, which is closed to the designated frequency of the arterial pulse normal frequency.

Determination of frequency response of MEMS microphone from sound field measurements using optical phase-shifting interferometry method

Accurate determination of microphone sensitivity is important to build reliable acoustical instruments. The sensitivity is usually determined by calibration. However, because available microphone calibration methods determine the sensitivity from a mathematical model derived from the geometry of a conventional condenser microphone, they cannot be applied to the calibration of microelectromechanical systems (MEMS) microphone straightforwardly. To compromise this geometry difference with the available calibration methods, some authors have proposed the development of adapters that fits the conventional calibration apparatus and modified the calibration procedure. In this paper, we propose a different approach to calibrate the MEMS microphone. The sensitivity is calculated directly from the measurement of the sound field applied to the MEMS microphone and its output voltage. The projection of the sound field is measured by parallel phase-shifting interferometry (PPSI), and sound pressure on the MEMS microphone is obtained by tomographic reconstruction. Experimental calibration of a MEMS microphone was performed and validated using a microphone substitution method to evaluate the discrepancies of the sensitivity result. It is shown that the proposed method can be used to determine the frequency response of the MEMS microphone in the frequency range of 1000 Hz to 12000 Hz.

Evaluation of the voice onset time in Turkish-Speaking schoolchildren

ObjectivesTo determine the voice onset time (VOT) values of Turkish speaking schoolchildren and to evaluate the effect of gender, age and vowel height on VOT values in this age group. MethodsOne hundred and twenty native Turkish children between the ages of 7–11 years were included in the study. All children were divided into 4 age groups: Group I 7.0 to 7 years, 11 months; Group II 8.0 to 8 years, 11 months; Group III 9.0 to 9 years, 11 months; and Group IV 10.0 to 10 years, 11 months. The six Turkish plosive sounds (/p/,/b/,/t/,/d/,/k/,/g/) and the eight Turkish vowel sounds (/a/,/e/,/ɯ/,/i/,/o/,/oe/,/u/,/y/) were compiled into 48 different syllables, such as/pa/,/be/,/ti/, and/ko/. The syllables were repeated three times and were recorded by Behringer C-1 studio condenser microphone. Records were analysed by Praat software. The VOT values was established by measuring the time between temporary plosion of the pause and the onset of vocal fold vibration. ResultsThe mean voice onset time values of the voiced and voiceless plosive sounds of the groups were analysed with One Way ANOVA test. There was no statistically significant difference between the groups (p > 0.05). The VOT values of voiceless plosive sounds in all groups were established as positive, and VOT values of voiced plosive sounds were found to be negative. Mean VOT values according to gender was analysed by Independent Samples t-test. A significant difference was found between genders in voiced (/b/,/d/,/g/) plosive sounds and in the/t/sound among the voiceless plosive sounds (p < 0.05). The difference between the heights of vowels and VOT were analysed by one-way ANOVA test. A significant difference was observed between the height of the following vowel and the voiceless plosives/p/,/t/,/k/and voiced plosive/b/(p < 0.05). ConclusionsThe VOT values of voiceless plosive sounds in Turkishspeaking schoolchildren were positive and the VOT values of their voiced plosive sounds were found negative. It was established that the height of the following vowel increases the VOT values of voiceless plosive sounds and has a variable effect on voiced plosive sounds.

Analysis of an automobile door closure vibroacoustic response

The acoustic response of a car door latch has been shown to directly impact the customers’ perceived quality and value evaluation of the automobile. This work introduces an experimentally validated computational model of three door latch components. The transient sound pressure level response of the three door latch components during door closure was collected in a semianechoic chamber using a three-element condenser microphone array. Postprocessing methodologies such as sound pressure level versus 1/3 octave band and continuous wavelet transform analysis were performed. This provided an in-depth analysis on the overall acoustic response and identification of dominant frequencies corresponding to four specific impact events during latch operation. Computational finite element analysis of the closure system using a rigid body, and explicit dynamic and transient structural acoustic analyses provided additional insights into the latch component interactions and the acoustic response generated empirically. Recorded average sound pressure level, frequency decomposition, and impact reaction forces are presented in addition to a comparison between the acoustic response for two different door closure speeds. It was found that an increased door closure speed increased the response sound pressure level, decreased damping of the primary impact, and decreased the frequency bandwidth of the response, thereby generating an acoustic response that would be perceived as noisier, less safe, and less secure by customers. These findings provide additional insights into the primary impact acoustic response of an automotive door latch during closure. The methodology introduced in this work allows automotive engineers to perform future work with modified latch components to further improve the psychoacoustic response of the automotive car door latch, further increasing the value evaluation of the automobile.

Abdominal Palpation Does Not Modify the Number of Bowel Sounds in Healthy Volunteers and Gastrointestinal Outpatients

The effect of abdominal palpation on bowel sounds is controversial. The authors developed an auscultation apparatus to count bowel sounds and determined whether abdominal palpation modifies the number of bowel sounds in healthy volunteers and gastrointestinal outpatients. Four medical students developed an auscultation apparatus by attaching a Littmann stethoscope to an electret condenser microphone. The students examined 20 healthy volunteers and 20 gastrointestinal outpatients between March and June 2018. Abdominal auscultation lasting 4 minutes (1-minute each quadrant) was performed before and after abdominal palpation with registration of sound tracings. The software Audacity was used to count the bowel sounds. The effect of palpation on bowel sounds was analyzed using Generalized Estimating Equations. The volunteers were predominantly young (mean ± SD, 21 ± 2 years) and men (70%), whereas the outpatients were older (60 ± 11 years) and women (80%). The apparatus was able to generate sound tracings with good quality from all participants. In the comparison before/after palpation, the number of bowel sounds did not differ either in volunteers (mean ± SD, 12.6 ± 4.7 and 11.6 ± 3.5; P=0.482) or in patients (15.6 ± 7.5 and 15.8 ± 7.9; P=0.714). In the analysis of all participants, the difference before-after palpation was not statistically significant (mean ± SD, 14.1 ± 6.3 and 13.7 ± 6.4, respectively; P=0.550; mean difference=0.4; 95% CI -1.2 to 2.0) and did not depend on the group studied. Using an apparatus devised by medical students, the authors found that abdominal palpation did not modify the number of bowel sounds in healthy volunteers and gastrointestinal outpatients.