Microphone Detection Research Articles

Two-layer hybrid sol-gel system's thermal parameters investigated with the optical nondestructive photoacoustic method in the frequency domain

This work presents results of studies of thermal parameters such as thermal diffusivity, thermal conductivity, thermal effusivity and volumetric heat capacity of thin hybrid sol-gel corrosion protective layers deposited on the aluminum substrate. In the studies two groups of samples were investigated. The first group was: TMZ.1, TMZ.2 and TMZ.3 (TMZ- Si/Zr-based hybrid sol-gel coatings), with different amount of zirconium, and the second group was: TMZ.1/Ce, TMZ.2/Ce and TMZ.3/Ce (TMZ/Ce - Ce-doped Si/Zr-based hybrid sol-gel coatings) with the same amount of zirconium and an addition of cerium. This work presents the influence of the content of zirconium and cerium on their thermal parameters. The possibility of using the nondestructive photoacoustic method (PA), with the microphone detection, to characterize this type of layers was analyzed theoretically and experimentally too.

Frequency-tunable sound insulation via a reconfigurable and ventilated acoustic metamaterial

In acoustic engineering, sound-proofing ventilation barriers find wide applications in diverse situations. However, most of the structures only have responses with fixed frequencies and a very narrow frequency range, especially for low frequency acoustics. Here we show a subwavelength acoustic metamaterial based on labyrinthine structures, which possesses tunable sound insulation and ventilation properties. The Fano-like asymmetric transmission dips is formed by the interference between the resonant scattering of discrete states and the background scattering of continuous states. By adjusting the spacing between these two half zigzag molds, the sound insulation dip frequency can shift from 360 Hz to 575 Hz while the free ventilation area ratio is kept to over 36.3% and the total thickness is only about 0.06λ. Moreover, the noise peak frequency can be detected by a microphone detection and adaptive adjustment of the spacing with a small stepping motor is demonstrated, the results agree well with numerical simulations. We anticipate our design may find potential applications in acoustic air vents, soundproofing window and duct noise control.

All-optical laser ultrasonic technique for imaging of subsurface defects in carbon fiber reinforced polymer (CFRP) using an optical microphone

Defects, such as delamination and debonding, are critical to the performance of carbon fiber-reinforced polymer (CFRP) composites. In recent years, non-destructive testing techniques have been improved for the inspection of these defects among CFRPs. In this study, an all-optical and non-destructive laser ultrasonic technique with an optical microphone detection module has been presented to detect the artificial subsurface defects among the CFRP composites. A finite element simulation based on the thermo-mechanical coupling model was used to study the process of nanosecond pulsed laser excitation of the CFRP laminate to produce ultrasound and the propagation behavior of ultrasound among the CFRP laminate. A series of non-contact laser ultrasonic testing experiments were carried out to study the flat bottom holes of different sizes via a laser ultrasonic detection system. The artificial subsurface defects were reliably identified by the presented all-optical laser ultrasonic system imbedded in the optical microphone using four feature images.

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.

Resonant Photoacoustic Spectroscopy of NO₂ with a UV-LED Based Sensor.

Nitrogen dioxide (NO2) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO2 with a photoacoustic sensor using a T-shaped resonance cell. An inexpensive UV-LED with a peak wavelength of 405 nm as radiation source as well as a commercial MEMS microphone for acoustic detection were used. In this work, a cell has been developed that enables a “non-contact” feedthrough of the divergent LED beam. Thus, unwanted background noise due to absorption on the inside walls is minimized. As part of the development, an acoustic simulation has been carried out to find the resonance frequencies and to visualize the resulting standing wave patterns in various geometries. The pressure amplitude was calculated for different shapes and sizes. A model iteratively optimized in this way forms the basis of a construction that was built for gas measurement by rapid prototyping methods. The real resonance frequencies were compared to the ones found in simulation. The limit of detection was determined in a nitrogen dioxide measurement to be 200 ppb (6 σ) for a cell made of aluminum.

Auditory evoked potentials in children with auditory neuropathy spectrum disorder

The objective of the present study was to estimate peculiarities of the auditory brainstem evoked potentials (ABR), auditory steady-state responses (ASSR) and cortical auditory evoked potentials (CAEP) in the children presenting with bilateral auditory neuropathy spectrum disorder (ANSD). The study included 100 patients with bilateral ANSD diagnosed based on the positive response of otoacoustic emissions (OAEs) and/or cochlear microphonic (CM) detection, while no synchronous neural activity was detected in the ABR test. Cochlear microphonic was the main clue for the ANSD diagnosing, because OAE was absent in both ears of 49 children. ABR testing revealed no response bilaterally in 72 cases (out of 100). In contrast to ABR, the ASSR thresholds were detectable at all the four main frequencies in both ears in 73 % of the cases (47 out of the 64 tested ones). Both ABR and ASSR in most cases were incomparable with the behavioral audiometric thresholds. 28 children underwent CAEP testing. In 7 cases out of 8 with mild hearing loss detectable CAEP were recorded. CAEP registration in l7 children making use of the hearing aids and in 3 children after cochlear implantation revealed, in the majority of the cases, the concordance between CAEP detectability with behavioral thresholds and rehabilitation outcomes with fairly good speech intelligibility. It is concluded that the ABR registration with CM evaluation is the most informative test for ANSD diagnosis. However, ABR as well as ASSR is useless for the estimation of the behavioral thresholds. The results of this study suggest that the presence or absence of CAEPs can provide some indication of the audibility of a speech sound in the children with ANSD; however this method requires further investigation.

Comparison of Theoretical Basics of Microphone and Piezoelectric Photothermal Spectroscopy of Semiconductors

Photothermal spectroscopy has found a wide range of applications as a method of monitoring thermal, optical and recombination parameters of semiconductors. We consider microphone detection, widely used in photoacoustic spectroscopy, and piezoelectric detection. Both methods require knowledge of the temperature distribution in the sample and in its surroundings, the support surface and gas. For the microphone signal, we simulated the temperature at one of the sample surfaces; for the piezoelectric signal, we simulated the spatial temperature distribution orthogonal to the sample surface. We modeled an idealized semiconducting sample and one with surface defects. We found that the amplitude and phase spectra vary between the methods, enabling determination of optical and thermal parameters.

A Mobile Enterprise Solution (True Monitor)

In a gradually idealized, homogeneous and sanitized world, Security and confidentiality of organization’s policies, practices, rules and procedure is becoming a major issue for any enterprise or association and there are also such a variety of criminal cases. So to maintain the security of organization’s future projects and secret missions, to help to avoid criminal cases like child kidnapping, mobile snatching and etc. by monitoring geographical location and to monitor the children by their parents after tracking their daily activities along with its date and time, we proposed a mobile and web based monitoring system “A Mobile, Enterprise Solution (True Monitor)” which “ll run invisibly on target device to track all the activities including device information (Inc. Id, Name, Model, OS, OS Version, IMEI No., Carrier, Carrier No., IMSI No., Battery, Wi-Fi/GPRS/3G, Location Tracker Status, Microphone Detection, Status (Lock/Unlock), Last Login, IP Address, Primary Email ID), Contact Logs, Call logs (Incoming, Outgoing, Missed), Call Recordings, Call Duration, Text Message Logs (Inbox, Sent) with its source and destination mobile number, GPS Location, Instant Messages (Facebook, Whatsapp, Skype, Viber & etc.), Mailbox, Browser History, Multimedia files and Blocked Websites along with its date and time. This information would have sent to the server (monitored by administrator) with an alert notification to the administrator in the result of any activity which does from the user mobile with detailed information.

A Low-Complexity Multistage Polyphase Filter Bank For Wireless Microphone Detection in CR

In this paper, we propose a low-complexity multistage polyphase filter bank for the detection and estimation of center frequency of wireless microphone (WM) in television channels for cognitive radios. The detection precision is directly related to the number of subbands (granularity) in the filter bank. This implies that the computational complexity becomes high if the number of stages and granularity of the filter bank structure are increased. The novelty of the proposed method is the estimation of center frequency with higher precision and reduced computational complexity using the centroid method. The merit of the centroid method is that the presence of WM can be detected along with estimation of center frequency in the first stage, if the WM lies partly in one subband and partly in the adjacent subband. This single-stage detection and estimation of WM significantly reduces computational and hardware complexities as well as latency. However, if the WM appears anywhere exclusively within a single subband, the detection process can be completed in the second stage without ambiguity. A mathematical expression for calculating the center frequency of WM from the subband energy (power) using centroid method is also derived and presented. The proposed scheme is analyzed and validated through extensive simulations for the detection of WM. The error in estimation of center frequency in most of the cases is less than 4 % for SNR variations from 0 to ź20 dB.

Closed/Open-Cell Photoacoustic Imaging for Spectroscopic Measurements

Photoacoustic imaging using a closed photoacoustic cell and an open photoacoustic cell with gas- microphone detection scheme was described. R/G/B LED light sources were used for the closed photoacoustic (PA) cell configuration. The colored specimen enclosed in a PA cell was imaged with R/G/B color light sources, and an image restored from the inverted PA images was compared with the original image. For open cell configuration, an open PA cell using a spheroidal acoustic resonator was applied to measure the amount of large-sized colored specimens. A calibration curve for a food red dye was obtained that apparently showed the ability of the present scheme to measure as a spectroscopic measurement tool.

Next-generation psychiatric assessment: Using smartphone sensors to monitor behavior and mental health.

Optimal mental health care is dependent upon sensitive and early detection of mental health problems. We have introduced a state-of-the-art method for the current study for remote behavioral monitoring that transports assessment out of the clinic and into the environments in which individuals negotiate their daily lives. The objective of this study was to examine whether the information captured with multimodal smartphone sensors can serve as behavioral markers for one's mental health. We hypothesized that (a) unobtrusively collected smartphone sensor data would be associated with individuals' daily levels of stress, and (b) sensor data would be associated with changes in depression, stress, and subjective loneliness over time. A total of 47 young adults (age range: 19-30 years) were recruited for the study. Individuals were enrolled as a single cohort and participated in the study over a 10-week period. Participants were provided with smartphones embedded with a range of sensors and software that enabled continuous tracking of their geospatial activity (using the Global Positioning System and wireless fidelity), kinesthetic activity (using multiaxial accelerometers), sleep duration (modeled using device-usage data, accelerometer inferences, ambient sound features, and ambient light levels), and time spent proximal to human speech (i.e., speech duration using microphone and speech detection algorithms). Participants completed daily ratings of stress, as well as pre- and postmeasures of depression (Patient Health Questionnaire-9; Spitzer, Kroenke, & Williams, 1999), stress (Perceived Stress Scale; Cohen et al., 1983), and loneliness (Revised UCLA Loneliness Scale; Russell, Peplau, & Cutrona, 1980). Mixed-effects linear modeling showed that sensor-derived geospatial activity (p < .05), sleep duration (p < .05), and variability in geospatial activity (p < .05), were associated with daily stress levels. Penalized functional regression showed associations between changes in depression and sensor-derived speech duration (p < .05), geospatial activity (p < .05), and sleep duration (p < .05). Changes in loneliness were associated with sensor-derived kinesthetic activity (p < .01). Smartphones can be harnessed as instruments for unobtrusive monitoring of several behavioral indicators of mental health. Creative leveraging of smartphone sensing could provide novel opportunities for close-to-invisible psychiatric assessment at a scale and efficiency that far exceeds what is currently feasible with existing assessment technologies.

Analog Front-End Circuitry in Piezoelectric and Microphone Detection of Photoacoustic Signals

This paper is a review of analog front-end circuitry used in photoacoustic equipment with microphone or piezoelectric detection. A block structure of the front end as well as detailed circuit diagrams of preamplifiers dedicated for piezoelectric sensors and measurement condenser and electret microphones are described. The presented circuits are optimized toward low-noise operation. Practical remarks regarding the design of the remaining analog blocks are also given. The analysis shows that it is possible to design an analog front end for which specifications will be comparable with the best commercial solutions.

The thermoacoustic method of determination of the air-tightness of metal transistors׳ packagings

The paper presents a new method of determination of the air-tightness of metal packagings of transistors. This method is based on the thermoacoustic approach with a microphone detection. The thermoacoustic approach means that the periodical overpressure is generated by the periodical temperature of the transistor caused by the periodical electric power dissipation in it. In the paper both the experimental thermoacoustic frequency characteristics and theoretical approach applied for numerical interpretations of experimental data are presented and discussed. The paper presents the experimental thermoacoustic set-up used in experiments, mathematical models, procedures applied and experimental results obtained for TO-3, TO-39 and TO-18 packagings. General predictions of the thermoacoustic theory concerning the sensitivity of this method for different types of packagings are also presented and discussed.

Temperature Distributions in Piezoelectric Photothermal Spectroscopy

Piezoelectric photothermal spectroscopy is a method in which the stress and strain of a sample due to the absorption of electromagnetic radiation is detected by a piezoelectric transducer. The temperature distribution in the sample is the basis to obtain the theoretical amplitude and phase of photothermal piezoelectric spectra. In contrast to microphone detection, which needs only the temperature at one of the sample surfaces, in the piezoelectric one, it is necessary to know the spatial temperature distribution. The distributions given by Blonskij and by the modified interferential model of Malinski are applied. The influence of defect states in a volume and at the surfaces on the character of the amplitude and phase piezoelectric spectra is analyzed. The comparison of these approximate models and the two-layer one of Fernelius is presented.

Optodynamics: dynamic aspects of laser beam–surface interaction

This paper presents a synthesis of the results of our original research in the area of laser–material interaction and pulsed laser material processing with a special emphasis on the dynamic aspects of laser beam–surface interaction, which include the links between the laser material removal and the resulting material motion. In view of laser material processing, a laser beam is not only considered as a tool but also as a generator of information about the material transformation. The information is retained and conveyed by different kinds of optically induced mechanical waves. Several generation/detection schemes have been developed to extract this information, especially in the field of non-destructive material evaluation. Blast and acoustic waves, which propagate in the air surrounding the work-piece, have been studied using microphone detection as well as various setups of the laser beam deflection probe. Stress waves propagating through the work-piece have been studied using piezoelectric transducers and laser interferometers.

Hammer impact test applied for fouling detection in pipelines

The fouling detection in duct systems is a persistent problem and remains a relevant demand for the chemical, oil, food and pharmaceutical industries. The fouling is a deposition process of heavy organic and other dissolved solid materials in the transported fluids or suspensions onto inner wall surfaces in fluid transport systems. This work presents research results of hammer test for vibration analysis using non-invasive tests to fouling detection in pipelines. Data were taken from the vibration in presence of an inner pipe fouling layer using an accelerometer and a microphone for detection. With the analysis of the obtained results is possible to detect the fouling process, in the monitored pipelines, with and without load conditions, using a microphone and an accelerometer as sensors.

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.

車上測定データによる軌道の異常検出 : 第2報,プローブシステムの開発と検証(機械力学,計測,自動制御)

Conditions of railway track have conventionally been maintained with exclusive inspection vehicle. If the conditions of the track can be inspected by using service vehicles with condition monitoring system, more efficient maintenance would be possible. This paper describes the development and the verification of the "probe system" which estimates the track conditions without sensors on bogie. To detect the track conditions from the data which can be observed in the interior of a service vehicle, two methods have been proposed: the method to detect track irregularities using RMS of the lateral/vertical accelerations and the rolling of the vehicle body, and the method to detect rail corrugations from the interior noise using the windowed Furrier transform. The probe system including two proposed methods has been developed which is composed by an accelerometer, a rate gyroscope and a microphone for detection of track conditions; a GPS for the localization; and notebook PC for the analysis. The developed system has been installed onto the cab of a service vehicle to carry out a field test for the validation of the system. The results of comparison with the ground data show that the probe system can estimate effectively the amplitude of track irregularities, the grade of rail corrugations and its location.

Non-Invasive Fast Detection of Internal Fouling Layers in Tubes and Ducts by Acoustic Vibration Analysis

The easy detection of fouling in duct systems is a persistent problem and remains a relevant demand for the chemical, oil, food, and pharmaceutical industries. The fouling process is the slow unwanted layer deposition of heavy organic and other dissolved solid materials out of transported fluids onto inner wall surfaces over an extended period of time. This work presents preliminary research results of vibrational hammer excitation for easy-to-use external non-invasive nondestructive fouling detection in pipelines and other large-scale duct systems. The main goal is the localization of inner pipe-layer formation and thickness estimation of the adsorbed material. Data were taken from the vibration variation in the presence of an inner pipe fouling layer using acoustic microphone detection. The experimental setup, achievable sensitivities, and limitations of the method are outlined.

Determination of a quantum efficiency of AII–BVIcompounds on the basis of photoacoustic spectra

The method of determination of the quantum efficiency η of irradiative relaxation processes in semiconductors is introduced and discussed. The correlation of the amplitude photoacoustic spectra in the high absorption region with the annealing process is used to estimate the values of η. The values of η, both for as grown and annealed crystals were determined and have been discussed. The results are presented for microphone and piezoelectric detection methods.