Condenser Microphone Research Articles

Fetal heart rate monitoring device using condenser microphone sensor: Validation and comparison to standard devices

Fetal heart rate (FHR) monitoring device is highly demanded to assess the fetus health condition in home environments. Conventional standard devices such as ultrasonography and cardiotocography are expensive, bulky and uncomfortable and consequently not suitable for long-term monitoring. Herein, we report a device that can be used to measure fetal heart rate in clinical and home environments. The proposed device measures and displays the FHR on a screen liquid crystal display (LCD). The device consists of hardware that comprises condenser microphone sensor, signal conditioning, microcontroller and LCD, and software that involves the algorithm used for processing the conditioned fetal heart signal prior to FHR display. The device's performance is validated based on analysis of variance (ANOVA) test. FHR data was recorded from 22pregnant women during the 17th to 37th week of gestation using the developed device and two standard devices; AngelSounds and Electronic Stethoscope. The results show that F-value (1.5) is less than F𝑐𝑟𝑖𝑡, (3.1) and p-value (p> 0.05). Accordingly, there is no significant difference between the mean readings of the developed and existing devices. Hence, the developed device can be used for monitoring FHR in clinical and home environments.

A Three-Dimensional Acoustic Boundary Element Method Formulation with Viscous and Thermal Losses Based on Shape Function Derivatives

Sound waves in fluids are subject to viscous and thermal losses, which are particularly relevant in the so-called viscous and thermal boundary layers at the boundaries, with thicknesses in the micrometer range at audible frequencies. Small devices such as acoustic transducers or hearing aids must then be modeled with numerical methods that include losses. In recent years, versions of both the Finite Element Method (FEM) and the Boundary Element Method (BEM) including viscous and thermal losses have been developed. This paper deals with an improved formulation in three dimensions of the BEM with losses which avoids the calculation of tangential derivatives on the surface by finite differences used in a previous BEM implementation. Instead, the tangential derivatives are obtained from the element shape functions. The improved implementation is demonstrated using an oscillating sphere, where an analytical solution exists, and a condenser microphone as test cases.

Using and selecting small condenser format microphones for impulsive noise measurement

The small format condenser microphone is the most often used transducer for impulsive measurements of firearms and suppressors. In this paper, the properties and characteristics of these microphones will be detailed and how the selection and use of these condenser microphones will affect the consistency and accuracy of measurements. The goal is to raise awareness and measurement consistency for developers, regulators, and user/hobbyists. The short wavelengths of sound at high frequencies are physically manipulated by the physical design of the transducers. A thorough testing of these products reveal these characteristics and their effect on the accuracy of the resulting measurement. The directivity, frequency response, impulse response, and damping characteristics will be compared. Results will be represented, along with anecdotal stories of real life implementation.

P071] The acoustic noise management in MRI

Purpose This work reports our experience on MRI acoustic noise as acoustic experts as well as advisors for the local authority. The aims are. • the protection of people health as a state of complete physical, mental and social well-being of any person in the magnetic resonance practice • reducing possible distortions of competition • avoiding expensive protection actions after installation. Materials and methods In order to correctly assess the risk, a procedure has been adopted in accordance to: • Italian law and 89/391/EEC Safety and Health of Workers at Work Directive, • European Standards, literature data and our experience. E.g. if RMI site is planned in civil contest, the noise levels are to be referred to WHO values and, in Italy, to values of municipal regulation for protection from noise. For the activity of medical reporting and control room we consider quality levels recommended in EN ISO 11690–1-1996. In this paper, are specified the necessary data and the roles involved as manufacturer, RM site project planner, and physician. When data are insufficient, the procedure describes experimental sets with reference points (isocenter bore&laser cross&..), phantoms, sequences, condenser and optic microphones and protocol to obtain information.. Results At isocenter ear position (1.5T) SPL shows more then 110 dBA&dBC for some sequences. In some cases a surrounding activity had to be moved. To neglect the noise could cause annoying problems as operator/patient interferences and health effects for patient, worker and surrounding inhabitants. It’s possible to manage the risk choosing adequate site, technology, HW, reducing noise at source and/or adopting collective protection and finally passive and active ear protectors and PPE. A suitable measurement protocol can be useful to assess noise and to plan adequate protections when RM is by now working. Conclusions Acoustic noise has to be considered and assessed as one of the first steps in the MR site planning and activity. It can be reduced to appropriate level. Acoustic noise would be evaluated mandatorily also by competent authorities for the control of compliance of the RM implants for a formal green light.

Fast demodulated white-light interferometry-based fiber-optic Fabry-Perot cantilever microphone.

We demonstrate a highly sensitive and stable fiber-optic Fabry-Perot cantilever microphone based on fast demodulated white-light interferometry. The cavity length of the low-finesse Fabry-Perot interferometry is absolutely measured by realizing a high-speed demodulation method utilizing a full spectrum, with the advantages of both high resolution and large dynamic range. An acoustic test demonstrates high sensitivities and linear responsivities at frequencies below 2kHz. The pressure responsivity and the noise-limited minimum detectable acoustic pressure level are measured to be 211.2nm/Pa and 5 μPa/Hz1/2, respectively, at the frequency of 1kHz. Comparative experimental results show that the signal-to-noise ratio is over 10 times higher than a reference condenser microphone.

Real-Time Hit Classification in a Smart Cajón

Smart musical instruments are a class of IoT devices for music making, which encompass embedded intelligence as well as wireless connectivity. In previous work, we established design requirements for a novel smart musical instrument, a smart cajon, following a user-centred approach. This paper describes the implementation and technical evaluation of the designed component of the smart cajon related to hit classification and repurposing. A conventional acoustic cajon was enhanced with sensors to classify position of the hit and the gesture that produced it. The instrument was equipped with five piezo pickups attached to the internal panels and a condenser microphone located inside. The developed sound engine leveraged digital signal processing, sensor fusion, and machine learning techniques to classify the position, dynamics, and timbre of each hit. The techniques were devised and implemented to achieve low latency between action and the electronically-generated sounds, as well as keep computational efficiency high. The system was tuned to classify two main cajon playing techniques at different locations and we conducted evaluations using over 2000 hits performed by two professional players. We first assessed the classification performance when training and testing data related to recordings from the same player. In this configuration, classification accuracies of 100% were obtained for hit detection and location. Accuracies of over 90% were obtained when classifying timbres produced by the two playing techniques. We then assessed the classifier in a cross-player configuration (training and testing were performed using recordings from different players). Results indicated that while hit location scales relatively well across different players, gesture identification requires that the involved classifiers are trained specifically for each musician.

Analysis of signal characteristics from rock drilling based on vibration and acoustic sensor approaches

Lithological recognition is of great significance in oil drilling fields. To investigate the relationship between rock properties and the vibro-acoustic signal characteristics generated by drilling, a rock drilling vibration measurement system has been developed, and a relative drilling test is conducted indoors. This paper illustrates the application of a vibration sensor and a special wideband acoustic sensor method to distinguish the specific time–frequency characteristics generated by drilling in different types of rock. Furthermore, an intuitive comparison of these two approaches is performed. In particular, an acoustic focusing device was designed to assist the wideband acoustic condenser microphone in detecting specific signals during the drilling process. In addition, time-domain and time–frequency analyses were proposed to reveal the differences in signal characteristics generated by different kinds of rock. The results indicate that both the vibration spectral characteristics and the acoustic spectral characteristics from 4 types of rock show significant differences, which may be promising for lithological recognition using the feature model. However, the acoustic sensor approach, benefiting from the specially designed acoustic focusing device, presents a better signal-to-noise ratio than the vibration sensor approach.

Fiber-Wrapped Mandrel Microphone for Low-Noise Acoustic Measurements

A low-noise fiber optic microphone has been developed using a fiber-wrapped mandrel as the acoustic transducer. The microphone has an average sensitivity of 0.206 rad/Pa between acoustic frequencies of 50 Hz and 16 kHz and a minimum detectable pressure as low as 3 μPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The noise floor of the microphone approaches the thermal limit set by the length of fiber used in the system. Performance of the microphone is comparable to a current state-of-the-art condenser microphone. The design is small, lightweight, and readily packaged into multiplexed systems, making it an ideal candidate for use in acoustic sensor array systems.

An inexpensive sensor for noise

ABSTRACTNoise is a pervasive workplace hazard that varies spatially and temporally. The cost of direct-reading instruments for noise hampers their use in a network. The objectives for this work were to: (1) develop an inexpensive noise sensor (<$100) that measures A-weighted sound pressure levels within ±2 dBA of a Type 2 sound level meter (SLM; ∼$1,800); and (2) evaluate 50 noise sensors for use in an inexpensive sensor network. The inexpensive noise sensor consists of an electret condenser microphone, an amplifier circuit, and a microcontroller with a small form factor (28 mm by 47 mm by 9 mm) than can be operated as a stand-alone unit. Laboratory tests were conducted to evaluate 50 of the new sensors at 5 sound levels: (1) ambient sound in a quiet office; (2) 3 pink noise test signals from 65–85 dBA in 10 dBA increments; and (3) 94 dBA using a SLM calibrator. Ninety-four percent of the noise sensors (n = 46) were within ±2 dBA of the SLM for sound levels from 65–94 dBA. As sound level increased, bias decreased, ranging from 18.3% in the quiet office to 0.48% at 94 dBA. Overall bias of the sensors was 0.83% across the 75 dBA to 94 dBA range. These sensors are available for a variety of uses and can be customized for many applications, including incorporation into a stationary sensor network for continuous monitoring of noise in manufacturing environments.

Photoacoustic for Oral Soft Tissue Imaging based on Intensity Modulated Continuous-Wave Diode Laser

We built the photoacoustic imaging (PAI) systems to image oral soft tissue. To reduce the cost and size significantly, the PAI system used an intensity-modulated continuous-wave (CW) diode laser with a wavelength of 532nm and output peak power of 200mW as an excitation source, combined with a condenser microphone as photoacoustic signals detector. The Pulse Width Modulation technique was applied to form a square wave fluctuation of laser radiation by using certain duty cycle on single-frequency of 17.8 kHz. Sample of this study was Sprague Dawley rats tongue on plasticine media, irradiated by modulated CW diode laser. The result of this study showed that modulated laser exposure on one certain spot of the sample produced PA-signals in polynomial correlation with a duty cycle of laser modulation. Based on it, the photoacoustic imaging then was done by using gradual duty cycles, i.e., 20%, 30%, and 40%. This study also showed that using CW diode laser which is modulated with low duty cycle can produce most accurate PA image, as well as keeping the sample from the high energy of laser exposure that may cause biological changes. Furthermore, the maximum duty cycle to modulate laser for oral soft tissue imaging in this system was 30%.

Characterization of mechanical properties of battery electrode films from acoustic resonance measurements

Measurements of the mechanical properties of lithium-ion battery electrode films can be used to quantify and improve manufacturing processes and to predict the mechanical and electrochemical performance of the battery. This paper demonstrates the use of acoustic resonances to distinguish among commercial-grade battery films with different active electrode materials, thicknesses, and densities. Resonances are excited in a clamped circular area of the film using a pulsed infrared laser, and responses are measured using an electret condenser microphone. A numerical model is used to quantify the sensitivity of resonances to changes in mechanical properties. When the numerical model is compared to simple analytical models for thin plates and membranes, the battery films measured here trend more similarly to the membrane model. Resonance measurements are also used to monitor the drying process. Results from a scanning laser Doppler vibrometer verify the modes excited in the films, and a combination of experimental and simulated results is used to estimate the Young's modulus of the battery electrode coating layer.

Design and fabrication of high performance condenser microphone using C-slotted diaphragm

In this paper, we present a new design of MEMS condenser microphone using SOI wafer. To improve the performance of the microphone, a perforated diaphragm with C-shape slots has been designed. The aim is to achieve high sensitivity, low voltage and small size microphone with easy and low cost fabrication process. The structure has a diaphragm thickness of 5 µm, a diaphragm size of 0.38 mm × 0.38 mm. The novelty of this microphone relies on perforated diaphragm includes some C-shape slots to reduce the stiffness of diaphragm to decrease the bias voltage and increase the sensitivity. Moreover, the proposed microphone is fabricated on SOI wafer to minimize the number of masks, deposited layers and fabrication process. The new microphone can be fabricated using just one mask to pattern the proposed diaphragm. The deflection of the new diaphragm is increased 19.5 times rather than traditional clamped diaphragms under an equivalent acoustic pressure of 20 Pa. The results show that the pull-in voltage is 10.47 V, open circuit sensitivity of 3.16 mV/Pa and resonance frequency of 70 kHz. The new microphone has a better figure of merit rather than other MEMS condenser microphones.

Multidomain modeling of acoustic transducers using SimScape

Finite element modeling of acoustic transducers can capture many complex behaviors that are neglected in simpler analyses. However, the complexity that requires finite element modeling is often confined to a small region of the total device. In that case it is possible to combine the finite element model of the subsection that requires this complexity with dynamic system modeling methods for the balance of the design. Dynamic system modeling includes earlier methods of analog circuit modeling and generalizes those methods appropriately tor acoustic transducer analysis. This paper will describe SimScape modeling of transducer structures in a way that allows combined modeling with FEA where needed. Simple examples will be selected from among moving coil speakers, balanced armature transducers, condenser microphones, and piezoelectric devices.Finite element modeling of acoustic transducers can capture many complex behaviors that are neglected in simpler analyses. However, the complexity that requires finite element modeling is often confined to a small region of the total device. In that case it is possible to combine the finite element model of the subsection that requires this complexity with dynamic system modeling methods for the balance of the design. Dynamic system modeling includes earlier methods of analog circuit modeling and generalizes those methods appropriately tor acoustic transducer analysis. This paper will describe SimScape modeling of transducer structures in a way that allows combined modeling with FEA where needed. Simple examples will be selected from among moving coil speakers, balanced armature transducers, condenser microphones, and piezoelectric devices.

Detection System of Sound Noise Level (SNL) Based on Condenser Microphone Sensor

The research aims to know the noise level by using the Arduino Uno as data processing input from sensors and called as Sound Noise Level (SNL). The working principle of the instrument is as noise detector with the show notifications the noise level on the LCD indicator and in the audiovisual form. Noise detection using the sensor is a condenser microphone and LM 567 as IC op-amps, which are assembled so that it can detect the noise, which sounds are captured by the sensor will turn the tide of sinusoida voice became sine wave energy electricity (altering sinusoida electric current) that is able to responded to complaints by the Arduino Uno. The tool is equipped with a detector consists of a set indicator LED and sound well as the notification from the text on LCD 16*2. Work setting indicators on the condition that, if the measured noise > 75 dB then sound will beep, the red LED will light up indicating the status of the danger. If the measured value on the LCD is higher than 56 dB, sound indicator will be beep and yellow LED will be on indicating noisy. If the noise measured value <55 dB, sound indicator will be quiet indicating peaceful from noisy. From the result of the research can be explained that the SNL is capable to detecting and displaying noise level with a measuring range 50-100 dB and capable to delivering the notification noise in audiovisual.

A MEMS condenser microphone based acoustic receiver for totally implantable cochlear implants

The goal of the present project is to develop intracochlear acoustic receivers (ICAR’s) for measurement of the sound pressure in the inner ear of human temporal bones and in acute large animal experiments. In addition, the ICAR is designed to be used as an implantable microphone for totally implantable cochlear implant (TICI) systems. The presented ICAR concept is based on a commercially available MEMS condenser microphone customized with a protective diaphragm providing sealing properties and optimized sensor head geometry for accessing the tiny fluid-filled cavities of the human inner ear. The first ICAR prototypes (PT I) have been used for numerous intracochlear sound pressure measurements in human and sheep temporal bones. The data thus obtained are in good agreement with the literature. The second ICAR prototype (PT II) was further adapted for surgical insertion in the scala tympani in acute large animal experiments. First experiments have been successfully performed and further revealed that the presented ICAR concept is a suitable receiver technology for TICI systems. Currently, the development of a fully biocompatible ICAR (PT III) is ongoing. This sensor must fulfill all important requirements of a TICI device such as high performance, low power consumption and good system integration.

Determination of the critical bending speeds of a multy-rotor shaft from the vibration signal analysis

The purpose of this paper is the development and validation of an impulse excitation technique to determine flexural critical speeds of a single rotor shaft and multy-rotor shaft. The experimental measurement of the vibroacoustic response is carried out by using a condenser microphone as a transducer. By the means of Modal Analysis using Finite Element Method (FEM), the natural frequencies and shape modes of one rotor and three rotor specimens are determined. The vibration responses of the specimens, in simple supported conditions, are carried out using algorithms based on Fast Fourier Transform (FFT). To validate the results of the modal parameters estimated using Finite Element Analysis (FEA) these are compared with experimental ones.

Electret condenser microphone as a traditional Chinese medicine arterial pulse sensor

Arterial pulse signal reading by a therapist in Traditional Chinese Medicine (TCM) requires considerable experience and thoroughness. The interpretation resulted by the therapist is very subjective. The objectivity of the device can be achieved by increasing the accuracy and the consistency of the reading in the range of 1-2 Hz. An electret condenser microphone (ECM) can be used as a pulse sensor in such device. This study reveals that ECM performs a number of advantages such as small-sized and inexpensive. Unfortunately, this ECM also picks up mechanical noises during direct contact with the subject. This study proposed soft silicon rubber as a medium between subjects and ECM. The technique was designed to enhance the mechanical coupling between the ECM and the source signal without affecting the signal source. The results show that the ECM could measure the signal of 0.5-10 Hz with the average accuracy of 99,47%.

A sensitivity-enhanced flexible acoustic sensor using side-polished fiber Bragg grating

A miniature flexible fiber Bragg grating (FBG) acoustic sensor with enhanced pressure sensitivity was fabricated by using a side-polished configuration of ∼54 μm depth and ∼15 mm length. The photoelectromechanical response of the sensor suspended as a dual-end-fixed beam was characterized based on the acoustic-induced strain interaction with fiber gratings. The opto-mechanical response of the sensor to bending strain was firstly investigated and exhibited about 11 times larger in wavelength shift, in comparison with a conventional bare FBG. Then acoustic testing demonstrated an acoustic pressure-induced wavelength shift of 0.041 nm/Pa and a noise equivalent acoustic signal level of ∼1.66 mPa/Hz1/2 in the frequency region around 2.5 kHz. Also, a relative flat frequency response with a fluctuation of less than 12.9 dB was achieved in the measurement between 400 Hz and 20 kHz, which is in well agreement with the result obtained by a reference condenser microphone. Along with strain-sensitive nanomaterials, the use of the side-polished FBG could be further extended for highly sensitive acousto-ultrasonic sensors in structural health monitoring and wearable applications.

DESIGN AND DEVELOPMENT SYSTEM OF ELECTRONIC CANDLE BASED ON MICROCONTROLLER

In this paper is described how the assembly process of designing and developing a series of inflatable candles microkontroller. The series based on electronics is a simple circuit that utilizes condenser microphone as a sensor. The use of these components are suitable for use in an application circuit electronic candles where the workings of this series starts from LEDs that analogous to wax and then lit using a pushbutton that analogy as lighters, and a flame from the LED can be extinguished by blowing. The concept of this series is simple but could be developed into a series of more innovative and interesting. One development is to add the output of the LED running that made candles burn more lively and interesting. Running LED of this circuit works by using a transistor as a switch that controls power of Az IC 368 and IC Az 418 M J. To simplify the development process, combination of a series of electronic candles with LED running can be simulated using the software Livewire and Proteus. Results of designing and developing a tool is not a new thing or that have not been found but the result of this achievement can be a source of inspiring in the world of electronics that can later be developed further so that it becomes a result of more recent example, lights out with once pat.

Relationship between voice function and skeletal effects of rapid maxillary expansion.

To evaluate the effects of rapid maxillary expansion (RME) on the vocal quality, maxillary central incisors, midpalatal suture, and nasal cavity in patients with maxillary crossbite. Coronal CT scans of 30 subjects (14 boys, 16 girls; mean age, 12.01 ± 0.75) were taken before RME (T0), and at the end of the expansion phase (T1). Voice samples of all patients were recorded with a high-quality condenser microphone (RODE NT2-A) on a desktop computer at T0 and T1. Statistical analyses were performed using a paired-sample t-test. The degree of association between the changes in the voice parameters and nasal width was assessed with Pearson's correlation. RME treatment produced a significant increase in the transverse dimensions of the midpalatal suture and nasal cavity between T0 and T1 ( P < .05). The maximum F0 and jitter (%) results were shown to decrease statistically significantly from T0 to T1 ( P < .001 and P = .042, respectively). Between T0 and T1, shimmer (%) and shimmer (dB) exhibited statistically significant increases ( P = .037 and P = .019, respectively). After RME therapy, voice quality differences were found to be associated with increases in nasal width.