Air Microphone Research Articles

Multidegree-of-Freedom State-Space Modeling of Nonlinear Pull-in Dynamics of an Electrostatic MEMS Microphone

Capacitive micromachined ultrasound transducers (CMUTs) are most frequently used to generate ultrasound by superimposing the stimulus waveform and a steady bias voltage. This results in the best signal linearity, but limits the maximum displacement to which the diaphragm can be driven. Operating in the collapse-snapback excitation mode involves applying a voltage larger than the electrostatic pull-in threshold, and allows the diaphragm to traverse the entire depth of the air gap. Modeling the dynamics of the pull-in process is complicated by the inherent nonlinearity of the electrostatic transduction, nonlinearity of viscous damping with respect to the diaphragm displacement, and coupling between the electrical, mechanical, and acoustical domains. We have developed a multi-degree-of-freedom numerical model, using lumped elements to discretize the mechanical diaphragm and acoustic components. Simple one-dimensional lumped element models fail to accurately account for the varying contact between diaphragm and backplate, and the change in effective diaphragm area over the course of the cycle. Our discretized model is in excellent agreement with LDV measurements made on a commercially-developed MEMS microphone in air, and shows promise for using collapse-snapback mode as a means of generating impulsive ultrasound signals in air. [2021-0216]

Acoustics of Drop Impact on Hydrophobic Surfaces and Liquid Pools

Drop impact on surfaces has been studied comprehensively as it has a wide range of fundamental and practical implications. The splash, spreading, and rebound have been investigated with respect to substrate interfaces with hydrophobic surfaces being of particular interest. However, impact on wetted substrates is less understood for the hydrophobic surfaces. Also the associated acoustics of the drop impact has not be explored in terms of air entrainment and substrate vibrations. We investigate the impact of water drops (∼2–10 mm diameter) from heights 100–400 cm upon hydrophilic– and hydrophobic–coated solid surfaces as well as free floating liquid pools (0.15–0.45 ml). A contact microphone coated with the Glaxco water repellant provides a hydrophobic surface upon which impact vibrations can be quantified. An air microphone is synchronized to a high-speed Phantom camera for sound recording and optical visualization of the impact and rebound phases. Cross-correlation of the two microphones reveals distinct differences between the two solid substrates. The initial rebound and subsequent jet break-up are found in an analysis of the signal’s amplitude and phase. These results are compared to those from gel spheres and discussed for applications of non-contact coating monitoring.

Fabrication of Glass Diaphragm Based Fiber-Optic Microphone for Sensitive Detection of Airborne and Waterborne Sounds.

A glass-diaphragm microphone was developed based on fiber-optic Fabry-Perot (FP) interferometry. The glass diaphragm was shaped into a wheel-like structure on a 150-μm-thick glass sheet by laser cutting, which consists of a glass disc connected to an outer glass ring by four identical glass beams. Such a structural diaphragm offers the microphone an open air chamber that reduces air damping and increases sensitivity and results in a cardioid direction pattern for the microphone response. The prepared microphone operates at 1550 nm wavelength, showing high stability in a range of temperature from 10 to 40 °C. The microphone has a resonance peak at 1152 Hz with a quality factor of 21, and its 3-dB cut-off frequency is 32 Hz. At normal incidence of 500 Hz sound, the pressure sensitivity of the microphone is 755 mV/Pa and the corresponding minimum detectable pressure is 251 μPa/Hz1/2. In addition to the above characteristics of the microphone in air, a preliminary investigation reveals that the microphone can also work stably under water for a long time due to the combination of the open-chamber and fiber-optic structures, and it has a large signal-to-noise ratio in response to waterborne sounds. The microphone prepared in this work is simple, inexpensive, and electromagnetically robust, showing great potential for low-frequency acoustic detection in air and under water.

The pressure wave induced by an asymmetrical Dielectric Barrier Discharge plasma actuator under the influence of residual charge

In order to improve the control effect of the plasma actuator at high Mach and Reynolds number, the pressure wave induced by an asymmetrical Alternating Current (AC) Dielectric Barrier Discharge (DBD) plasma actuator which is under the influence of residual charge on the dielectric surface is investigated by using a high accuracy phase-lock image Schlieren technique and a pressure-field microphone in quiescent air. It is of great significance that a single pressure wave created by the AC-DBD plasma actuator with the residual charge which co-exists with the starting vortex in the induced flow field is first observed. Based on the experimental results, a hypothesis is proposed on the formation mechanism of the induced pressure wave. This finding might inspire a new discussion on the control of the temporal and spatial distributions of the surface charge which might be helpful to flow separation at high Reynolds and Mach numbers.

A CNN based Speaker Recognition System using an Alternate Bone Microphone

State-of-art speaker recognition system uses acoustic microphone speech to identify/verify a speaker. The multimodal speaker recognition system includes modality of input data recorded using sources like acoustics mic,array mic ,throat mic, bone mic and video recorder. In this paper we implemented a multi-modal speaker identification system with three modality of speech as input, recorded from different microphones like air mic, throat mic and bone mic . we propose and claim an alternate way of recording the bone speech using a throat microphone and the results of a implemented speaker recognition using CNN and spectrogram is presented. The obtained results supports our claim to use the throat microphone as suitable mic to record the bone conducted speech and the accuracy of the speaker recognition system with signal speech recorded from air microphone get improved about 10% after including the other modality of speech like throat and bone speech along with the air conducted speech.

Impact of viscoelastic spheres on to hydrophobic and hydrophilic substrates with liquid pools

The study of the sound of impact has an extensive history with seminal studies done by Rayleigh. Rayleigh studied the subsequent vibrations of an impacting elastic sphere on a solid surface formulating a preliminary, analytical theory for rigid body radiation based on energy considerations. For a spherical particle incident on a non-wetted substrate, the sound pressure level can be related to the particle’s impulsive acceleration. Impact onto wetted substrates is less understood for the cases of hydrophobic surfaces. We investigate the impact of visco-elastic water beads (12.5 mm, 17.5 mm diameter) from heights 35–400 cm upon hydrophilic and hydrophobic liquid pools (0.15–0.45 ml). A hydrophobic surface is obtained by coating the metallic surface of a contact microphone with Soft99 Glaco Mirror Coat Zero water repellant. Sound production is measured using both contact and air microphones, which are synchronized with a high-speed camera (Phantom V2512) for visualization. In the hydrophobic case at low heights, the rebound of the water bead results in the attachment and lift-off of the liquid. The collapse of entrained gas cavities corresponds to an oscillatory acoustic signature upon lift-off. At higher impact heights, the liquid pool is atomized with signatures of drop break-up.

Acoustics of water entry of hydrophobic spheres

Hydrophobic spheres form different cavities depending on the sphere size and the impact parameters. Cavities types have been investigated with respect to their interface characteristic, and regimes denoted as deep seal, surface seal, shallow seal, quasi-static seal, and rebound have been previously reported. The acoustic characteristics of these cavities have relatively unexplored compared with that of impacting liquid drops. A previously developed experimental setup for water entry visualization is extended for acoustic measurements. Simultaneous acoustic and optical measurements are done with the synchronization of a condenser air microphone and hydrophone with two high speed video cameras. Spheres of diameter 8–40 mm are investigated for corresponding impact velocities of 1.4–6.0 m/s. Room temperature metal spheres sprayed with Cytonix WX-2100 coated are compared with those heated up to the inverse Leiden temperature (120–440°C). In both cases, acoustic signature is found to be directly related to sealing phenomena. Upon impact, the heat spheres have a specific vaporization sound compared to the coated case. The transition and values of the Leiden frost temperature are investigated with respect to spectral acoustics signal features.

The SPLENDID Eating Detection Sensor: Development and Feasibility Study

BackgroundThe available methods for monitoring food intake—which for a great part rely on self-report—often provide biased and incomplete data. Currently, no good technological solutions are available. Hence, the SPLENDID eating detection sensor (an ear-worn device with an air microphone and a photoplethysmogram [PPG] sensor) was developed to enable complete and objective measurements of eating events. The technical performance of this device has been described before. To date, literature is lacking a description of how such a device is perceived and experienced by potential users.ObjectiveThe objective of our study was to explore how potential users perceive and experience the SPLENDID eating detection sensor.MethodsPotential users evaluated the eating detection sensor at different stages of its development: (1) At the start, 12 health professionals (eg, dieticians, personal trainers) were interviewed and a focus group was held with 5 potential end users to find out their thoughts on the concept of the eating detection sensor. (2) Then, preliminary prototypes of the eating detection sensor were tested in a laboratory setting where 23 young adults reported their experiences. (3) Next, the first wearable version of the eating detection sensor was tested in a semicontrolled study where 22 young, overweight adults used the sensor on 2 separate days (from lunch till dinner) and reported their experiences. (4) The final version of the sensor was tested in a 4-week feasibility study by 20 young, overweight adults who reported their experiences.ResultsThroughout all the development stages, most individuals were enthusiastic about the eating detection sensor. However, it was stressed multiple times that it was critical that the device be discreet and comfortable to wear for a longer period. In the final study, the eating detection sensor received an average grade of 3.7 for wearer comfort on a scale of 1 to 10. Moreover, experienced discomfort was the main reason for wearing the eating detection sensor <2 hours a day. The participants reported having used the eating detection sensor on 19/28 instructed days on average.ConclusionsThe SPLENDID eating detection sensor, which uses an air microphone and a PPG sensor, is a promising new device that can facilitate the collection of reliable food intake data, as shown by its technical potential. Potential users are enthusiastic, but to be successful wearer comfort and discreetness of the device need to be improved.

Discriminating Pathological Voice From Healthy Voice Using Cepstral Peak Prominence Smoothed Distribution in Sustained Vowel

This paper deals with cepstral peak prominence smoothed (CPPS) distribution and its descriptive statistics as possible indicators of vocal health status. A total of 41 voluntary patients and 35 control subjects participated in the experiment: all of them followed the same protocol, which includes three repetitions of the sustained vowel /a/ simultaneously acquired with a microphone in air and a contact sensor, the perceptual assessment of voice quality, and the videolaringoscopy examination. The fifth percentile and the standard deviation of CPPS distribution were the parameters included in the best logistic regression models for the microphone in air and the contact sensor, respectively. The selected CPPS parameters had a strong to good discrimination power: an area under curve of 0.95 and 0.87 has been found for the microphone in air and for the contact sensor, respectively. For each CPPS parameter, the repeatability has been also estimated and the Monte Carlo method has been implemented for the uncertainty evaluation of the discrimination threshold. Furthermore, preliminary recommendations for better accuracy and repeatability of future studies are provided: analyses on the main CPPS influence quantities and on the effect of the frequency content of the signal spectrum on the CPPS parameters have been provided.

Novel Methods for Sensing Acoustical Emissions From the Knee for Wearable Joint Health Assessment.

We present the framework for wearable joint rehabilitation assessment following musculoskeletal injury. We propose a multimodal sensing (i.e., contact based and airborne measurement of joint acoustic emission) system for at-home monitoring. We used three types of microphones-electret, MEMS, and piezoelectric film microphones-to obtain joint sounds in healthy collegiate athletes during unloaded flexion/extension, and we evaluated the robustness of each microphone's measurements via: 1) signal quality and 2) within-day consistency. First, air microphones acquired higher quality signals than contact microphones (signal-to-noise-and-interference ratio of 11.7 and 12.4dB for electret and MEMS, respectively, versus 8.4dB for piezoelectric). Furthermore, air microphones measured similar acoustic signatures on the skin and 5cm off the skin (∼4.5× smaller amplitude). Second, the main acoustic event during repetitive motions occurred at consistent joint angles (intra-class correlation coefficient ICC(1, 1) = 0.94 and ICC(1, k) = 0.99). Additionally, we found that this angular location was similar between right and left legs, with asymmetry observed in only a few individuals. We recommend using air microphones for wearable joint sound sensing; for practical implementation of contact microphones in a wearable device, interface noise must be reduced. Importantly, we show that airborne signals can be measured consistently and that healthy left and right knees often produce a similar pattern in acoustic emissions. These proposed methods have the potential for enabling knee joint acoustics measurement outside the clinic/lab and permitting long-term monitoring of knee health for patients rehabilitating an acute knee joint injury.

Time-Frequency Analysis of Clinical Percussion Signals Using Matrix Pencil Method

This paper discusses time-frequency analysis of clinical percussion signals produced by tapping over human chest or abdomen with a neurological hammer and recorded with an air microphone. The analysis of short, highly damped percussion signals using conventional time-frequency distributions (TFDs) meets certain difficulties, such as poor time-frequency localization, cross terms, and masking of the lower energy features by the higher energy ones. The above shortcomings lead to inaccurate and ambiguous representation of the signal behavior in the time-frequency plane. This work describes an attempt to construct a TF representation specifically tailored to clinical percussion signals to achieve better resolution of individual components corresponding to physical oscillation modes. Matrix Pencil Method (MPM) is used to decompose the signal into a set of exponentially damped sinusoids, which are then plotted in the time-frequency plane. Such representation provides better visualization of the signal structure than the commonly used frequency-amplitude plots and facilitates tracking subtle changes in the signal for diagnostic purposes. The performance of our approach has been verified on both ideal and real percussion signals. The MPM-based time-frequency analysis appears to be a better choice for clinical percussion signals than conventional TFDs, while its ability to visualize damping has immediate practical applications.

Experimental verification of enhanced sound transmission from water to air at low frequencies

Laboratory-tank measurement of enhanced sound transmission from water to air at low frequencies is presented. Findings are consistent with the theory of anomalous transparency of the water-air interface in which almost all of the acoustic energy emitted by a shallow submerged source is emitted into the air [Godin, Phys. Rev. Lett. 97 (2006)]. The classical picture in the water remains very much the same: the monopole source suffers a radiation efficiency decrease due to interference with the strong surface reflection [McDonald and Calvo, J. Acoust. Soc. Am. 122 (2007)]. For source depths progressively less than a fraction of an acoustic wavelength in water, the measured radiation pattern in the air becomes progressively omnidirectional. The wider radiation pattern owes itself to the conversion of inhomogeneous (evanescent waves) into propagating waves that fill the angular space outside the usual 13-degree cone. On-axis point measurements using a microphone in air and a hydrophone in water, along with the measured directivities, are consistent with previously published power transmission ratios from water to air. Asymptotic expressions for the radiated field in the air are also presented. [Work sponsored by the Office of Naval Research.]

Application of Reproducing the Kernel Particle Method on the Simulation of the Membrane of a Capacitive Micromachined Microphone in Viscothermal Air

Simulation of the microphone membrane determines whether highest sensitivity is attainable when it comes to the field of microelectromechanical system (MEMS) microphone design. The reproducing kernel particle method is introduced to simulate a MEMS microphone membrane in viscothermal fluid. The result from a numerical axisymmetry model of 1 mm radius and 10 μm thickness membrane with a fixed boundary condition upon 1 mm thickness viscothermal air is identical to that from the theoretical model. Finally, a MEMS axisymmetry model of a 180 μm radius and 10 μm thickness membrane upon 10 μm thickness viscothermal air is simulated here.

Application of reproducing kernel particle method and element-free Galerkin method on the simulation of the membrane of capacitive micromachined microphone in viscothermal air

Simulation of the microphone membrane determines whether highest yield and sensitivity is attainable when it comes to the field of microelectromechanical system (MEMS) capacitive microphone design. Consequently, it is significantly critical to predict and understand the behavior of the membrane in the air. The reproducing kernel particle method and element-free Galerkin, RKPM and EFG respectively, are introduced to differentiate from the traditional finite element method (FEM) since RKPM and EFG models are meshless to greatly improve the problems of FEM with large size aspect ratio. The result from a numerical axisymmetry model of 1 mm radius and 10 μm thickness membrane with fixed boundary condition upon 1 mm thickness viscothermal air is identical to that from the theoretical model. Finally, a MEMS axisymmetry model of a 180 μm radius and 10 μm thickness membrane upon 10 μm thickness viscothermal air is simulated in this paper.

Sensor models and localization algorithms for sensor networks based on received signal strength

Received signal strength (RSS) can be used in sensor networks as a ranging measurement for positioning and localization applications. This contribution studies the realistic situation where neither the emitted power nor the power law decay exponent be assumed to be known. The application in mind is a rapidly deployed network consisting of a number of sensor nodes with low-bandwidth communication, each node measuring RSS of signals traveled through air (microphones) and ground (geophones). The first contribution concerns validation of a model in logarithmic scale, that is, linear in the unknown nuisance parameters (emitted power and power loss constant). The parameter variation is studied over time and space. The second contribution is a localization algorithm based on this model, where the separable least squares principle is applied to the non-linear least squares (NLS) cost function, after which a cost function of only the unknown position is obtained. Results from field trials are presented to illustrate the method, together with fundamental performance bounds. The ambition is to pave the way for sensor configuration design and more thorough performance evaluations as well as filtering and target tracking aspects.

Ambiguity in phoneme recognition when using a bone conduction microphone

Bone conduction microphones are often promoted as good means for recoding voice signals in very noisy and/or harsh environments. However, it is reported in the literature that the speech intelligibility when using contact microphones is, in all noise conditions, worse than when using a boom microphone. Therefore, long term spectra of speech signals simultaneously recorded with bone and air microphones have been analyzed. This analysis shows, for all measured subjects, that the module of the transfer function between the signal recorded at the air-microphone and, because of this, at the contact microphone increases toward higher frequencies. The results also show large interindividual differences. In order to get more perception related information, a corpus of French vowels has been recorded simultaneously with air and contact microphone. This corpus has been used for a listening test aiming to show confusion between different vowels. The main confusions are for vowels having the same frequency of the first formant (e.g., [i][y][u]) which then are perceived as the central vowel. These confusions could explain the systematically lower intelligibility reported for speech when recorded with contact microphones. Planned experiments using plosive and fricative consonants should give more information about transfer mechanisms of bone conducted voice.

Speech intelligibility of air conducted and bone conducted speech over radio transmission.

Personal radio-communication devices are traditionally used with built-in or external air conduction microphones. Recently, there have been some efforts to use bone conduction microphones mounted on the operator’s head as a replacement for external air microphones. The goal of this study was to compare the intelligibility of speech transmitted through a boom-type noise-cancelling air microphone and a bone microphone using Thales multiband inter-intra-team radios. Eight participants were divided into four pairs with each participant serving as both a talker and a listener. The Callsign Acquisition Test was used to collect speech intelligibility data with the talker in quiet and in 100 dB(A) noise. The listener was always located in a quiet environment. Both types of microphones resulted in speech intelligibility scores ranging from 100% to 94% in quiet and from 100% to 90% in noise condition. There was no statistically significant difference in speech intelligibility between the two types of microphones. The advantages and disadvantages of using bone microphones under various civilian and military conditions are discussed.

Multisensory processing for speech enhancement and magnitude-normalized spectra for speech modeling

In this paper, we tackle the problem of speech enhancement from two fronts: speech modeling and multisensory input. We present a new speech model based on statistics of magnitude-normalized complex spectra of speech signals. By performing magnitude normalization, we are able to get rid of huge intra- and inter-speaker variation in speech energy and to build a better speech model with a smaller number of Gaussian components. To deal with real-world problems with multiple noise sources, we propose to use multiple heterogeneous sensors, and in particular, we have developed microphone headsets that combine a conventional air microphone and a bone sensor. The bone sensor makes direct contact with the speaker’s temple (area behind the ear), and captures the vibrations of the bones and skin during the process of vocalization. The signals captured by the bone microphone, though distorted, contain useful audio information, especially in the low frequency range, and more importantly, they are very robust to external noise sources (stationary or not). By fusing the bone channel signals with the air microphone signals, much improved speech signals have been obtained.

Modular active noise air filter speaker and microphone assembly

An air induction system comprises an air induction body and air filter to provide filtered air to a vehicle engine. A microphone is disposed within the air filter. A control unit may receive signals from the microphone. The control unit may further control a speaker, which produces a noise canceling sound to thereby reduce engine noise associated with the air induction system.

The perception of speech sounds recorded within the uterus of a pregnant sheep

The intelligibility of speech stimuli recorded within the uterus of a pregnant sheep was determined perceptually using a group of untrained judges. The intrauterine sound environment of the ewe was intended to simulate that of a pregnant woman. Two separate lists, one of meaningful and one of nonmeaningful speech stimuli, were delivered through a loudspeaker to the side of the ewe and were simultaneously recorded with an air microphone located 15 cm from the flank and with a hydrophone previously sutured to the neck of the fetus. Perceptual test tapes generated from these recordings were played to 102 judges. The intelligibility of the phonemes recorded in the air was significantly greater than the intelligibility of phonemes recorded from the uterus. A male talker's voice was more intelligible than a female talker's voice when recorded from within the uterus, but not so when recorded in the air. An analysis of the feature information transmission from recordings inside and outside the uterus revealed that voicing information is better transmitted in utero than place or manner information.