Acoustic Amplifier Research Articles

Graphene-infused terracotta acoustic sound amplifiers

This work introduces a novel approach for enhancing mobile audio performance by incorporating graphene-infused terracotta as an acoustic amplifier. Leveraging the high thermal conductivity and mechanical strength of graphene, this study demonstrates the design, fabrication, and acoustic characterization of terracotta amplifiers. We demonstrate the significant impact of graphene-infused terracotta amplifiers on improving sound amplification in addition to mechanical strength. A graphene-based dispersion is prepared for incorporation in clay to make the amplifier. Testing is carried out on normal and graphene-dispersion-incorporated terracotta amplifiers. The experimental results illustrate a substantial improvement in audio quality with increased volume compared to conventional terracotta-based mobile speakers. The frequency-dependent variation of the output signal, SNR, and the influence of submerging in water have also been studied. This work contributes to the field of acoustic materials and offers new possibilities for augmenting the auditory experience of mobile device users while also presenting sustainable and aesthetically appealing acoustic accessories.

Transformation of the Acoustic Amplifier into a Modular Structure

Transformation of the Acoustic Amplifier into a Modular Structure

Graphene-based stand-alone nanomechanical membrane production and mass-acoustic hybrid-sensor application

In this article, experimental studies were carried out for the preparation, characterization, and nanomechanical membrane application of Graphene-based nanomechanical mass and acoustic hybrid sensors. The purpose of this study was to prepare facile and low-cost nanomechanical membrane-based mass-acoustic hybrid sensors by set-ups developed on the exfoliation and membrane transfer methods, and to examine their morphological, spectroscopical, and nanomechanical-vibrational properties, as well as the membrane characteristics like mass and acoustic sensitivities and durability over time. For the experiments, equipment and items such as optical, digital, atomic force and scanning electron microscopes, Raman spectroscope, acoustic signal source and amplifier, data-logger, sound pressure level meter, and laser Doppler vibrometer were used. Graphene-based nanomechanical membrane sensor chips with varying acoustic pressure levels and mass-loadings were tested. It was observed that the acoustic sensitivity of the produced 706.5 µm2 nanomechanical membranes increased with increasing sound pressure levels and decreased with increasing mass-loads. With 67.8 ± 5 nm/Pa, the unloaded nanomechanical membrane was the most sensitive sample. Experimental challenges and sensor development solutions were discussed. Existing application examples were examined and discussions were made on the current challenges and the future prospects of the nanomechanical membrane sensors.

Tunable unidirectional compact acoustic amplifier via space-time modulated membranes

Space-time modulation has recently attracted considerable attention as it enables new possibilities in wave manipulation and control. Here we propose a tunable unidirectional acoustic amplifier based on a space-time modulated membrane system. The transfer matrix method is applied to design this system and optimize the modulation parameters for the realization of unidirectional amplification. Efficient one-way amplification of acoustic waves is demonstrated theoretically and numerically within a frequency range from 2260 to 2520 Hz, with overall dimension being less than $1/3$ of the corresponding wavelength. Across this operation band, the amplification factor in the positive direction varies smoothly from 3.0 to 5.8, while the transmitted wave energy in the negative direction does not change significantly. Our work identifies a feasible approach to realize a tunable unidirectional acoustic amplifier via space-time modulated membranes, which offers a design platform for a number of applications in sensing, imaging, and communication.

Clinical aspects of otosclerotic ossicular chain fixations.

Otosclerosis is a human-specific ear disease characterised by complex bone-remodelling with multifactorial aetiology. It affects the bony labyrinth capsule and consequently fixates the stapes to the oval window rim. The fixation of the ossicular chain leads to a decrease in the middle ear's acoustic impedance-fitting and amplifier function that leads to conductive hearing loss. The process is progressive and when it involves the inner ear structures, it deteriorates the sensorineural function as well. The course of the illness can be prevented or delayed if hearing reconstructive surgery is performed on time. The development of stapes surgery spans the 20th century, and despite the major surgical steps - laid down by Shea and Marquet in the 1960s - are quite conservative, fine adjustments are still being made mainly due to technical progress. Several studies confirm that stapedotomy remained the first-to-offer therapeutic option in otosclerosis. With an adequate surgical technique, significant improvement can be achieved in the air conduction threshold, the air-bone gap may be minimalized or ceased over the speech frequencies, which significantly improves the quality of life of the patients. In this quest, we reviewed the Hungarian and the international literature as well in context with otosclerosis, with special attention to the newest methods in diagnostics and treatment management. Orv Hetil. 2020; 161(19): 780-788.

Acoustic Multifunctional Logic Gates and Amplifier Based on Passive Parity-Time Symmetry

Acoustic analogue computation and signal processing are of great significance; however, it is challenging to realize acoustic computing devices because of their limitations of single function and complex structure. Here, an acoustic multifunctional device, which can gate or amplify acoustic waves without resorting to altering the frequency and structure using a passive acoustic parity-time (PT)-symmetric metamaterial, is realized theoretically and experimentally. The metamaterial is constructed by five lossless-loss periodically distributed media, which are modulated to achieve passive PT symmetry. At the coherent perfect absorber emitter point in the broken PT-symmetric phase, the logic gates (and, or, xor, and not) and small signal amplifier are realized in a single system by adjusting the phase and amplitude differences between two incoming beams, respectively. This work provides a route for the connection between PT symmetry and the acoustic metamaterial, which has potential applications in acoustic modulation and acoustic multifunctional devices.

Comparison of amplification via the acousto-electric effect of Rayleigh and Leaky-SAW modes in a monolithic surface InP:InGaAs/lithium niobate heterostructure

This paper demonstrates a monolithic surface acoustic wave amplifier fabricated by state-of-the-art heterogenous integration of a III-V InGaAs-based epitaxial material stack and LiNbO3. We compare amplification of Raleigh-SAW and leaky-SAW modes on a on Y-cut, X-propagating delay line amplifier. Due to the superior properties of the materials employed, we observe a net terminal gain of 3dB for an LSAW overtone mode This platform enables further advances in active and non-reciprocal piezoelectric acoustic devices.

High-gain leaky surface acoustic wave amplifier in epitaxial InGaAs on lithium niobate heterostructure

Active surface acoustic wave components have the potential to transform RF front ends by consolidating functionalities that currently occur across multiple chip technologies, leading to reduced insertion loss from converting back and forth between acoustic and electronic domains in addition to improved size and power efficiency. This letter demonstrates a significant advance in these active devices with a compact, high-gain, and low-power leaky surface acoustic wave amplifier based on the acoustoelectric effect. Devices use an acoustically thin semi-insulating InGaAs surface film on a YX lithium niobate substrate to achieve exceptionally high acoustoelectric interaction strength via an epitaxial In0.53Ga0.47As(P)/InP quaternary layer structure and wafer-scale bonding. We demonstrate 1.9 dB of gain per acoustic wavelength and power consumption of 90 mW for 30 dB of electronic gain. Despite the strong intrinsic leaky propagation loss, 5 dB of terminal gain is obtained for a semiconductor that is only 338 μm long due to state-of-the-art heterogenous integration and an improved material platform.

Multiple Quantum Wells for PT-Symmetric Phononic Crystals.

We demonstrate that the parity-time symmetry for sound is realized in laser-pumped multiple-quantum-well structures. Breaking of the parity-time symmetry for the phonons with wave vectors corresponding to the Bragg condition makes the structure a highly selective acoustic wave amplifier. Single-mode distributed feedback phonon lasing is predicted for structures with realistic parameters.

On the estimation of actual space charge using pulsed electro-acoustic system

Pulsed electro-acoustic measurement system is one of the versatile systems for measurement of charges accumulated in dielectric materials. The charge is measured as a voltage signal observed at an amplifier output which gets input from an acoustic sensor. Because of limited frequency bandwidth of the acoustic sensor and amplifier, all experimentally acquired signals require processing technique like deconvolution to estimate original signal (charge). Due to presence of noise in all experimental signals, deconvolution turns out to be an optimization problem. The optimum deconvolution involves estimation of optimum value of a deconvolution parameter, also known as regularization parameter. This parameter controls the tradeoff between signal distortion and noise minimization. In literature, several methods were suggested for estimation of optimum value of regularization parameter. However, each method yields a different estimate for the parameter. In this paper, the suitability of these conventional methods is investigated for estimation of space charge. Also a simple, yet, better estimation method, specific to space charge estimation, is presented. Interesting results and discussion on efficacy of these methods against, simple spectral division followed by Gaussian filtering, is also presented.

Estimation of population density of stored grain pests via bioacoustic detection

The potential of bioacoustics in estimating the population density of insect pests inside the stored grain mass was evaluated in the laboratory. We used a piezoelectric sensor and a portable acoustic emission amplifier connected to a computer for recording acoustic emissions of insects. The software analyses the vibration recordings of the piezoelectric sensor, performs signal parameterization and eventually classification of the infestation severity inside the grain mass in four classes, namely: Class A (densities ≤1 adult/kgr), Class B (densities 1–2 adults/kgr), Class C (densities 2–10 adults/kgr) and Class D (densities >10 adults/kgr). Adults of the most important beetle pests of stored cereals and pulses, in various population densities (1, 2, 10, 20, 50, 100, 200 & 500 beetle adults/kgr grain) were used during the present study. The linear model was very effective in describing the relationship between population density and number of sounds. Multiple classifiers were used to evaluate the accuracy of bioacoustics on predicting the pest density given per minute counts of vibration pulses. Based on our results, our system's performance was very satisfactory in most cases (∼68%) given that probabilities for successful prediction typically exceeding 70%. Our study suggests that automatic monitoring of infestations in bulk grain is feasible in small containers. This kind of service can assist with reliable decision making if it can be transferred to larger storage establishments (e.g. silos). Our results are discussed on the basis of enhancing the use of acoustic sensors as a decision support system in stored product IPM.

다중채널 능동소음제어기법을 이용한 KTX 실내소음의 구간별 저감성능 비교

Since the eco-era is getting closer, the importance of noise reducing in the passenger cars of high-speed train is very important. The active noise control is best choice to reduce low frequency noise because the passive one is too heavy for high speed trains where weight is so critical. Also ANC is able to reduce the ambient noise when the environmental-factor changes. To reduce a three-dimensional closed-space sound field like a car of a high-speed rail is hard to do using single channel ANC control system. We used multi-channel FXLMS algorithm which calculation speed is fast and the secondary path estimation is possible in order to take into account the physical delay in electro acoustic hardware control loudspeaker and power amplifier. Firstly, we have measured interior noise of KTX and estimated noise path in KTX test-bed. However there was some problem related to algorithm divergence and increasing the filter order. We have made a simulation of interior environment of KTX car by using three frequency bands of 120Hz, 280Hz, 360Hz as the most important for KTX ANC system. During this research the interior noise reduction of KTX car was made by using the multi-channel FXLMS algorithm. Reduction performance was evaluated and compared each other for open space section and tunnel section. in-situ experiment for the KTX noise reduction by proposed ANC was performed based on data obtained in simulation and they were compared for open space section and tunnel section as well.

Hearing and morphological specializations of the mojarra (Eucinostomus argenteus)

The air-filled swimbladder acts as an acoustic amplifier for some fish by converting sound pressure into particle motion, which is transmitted to the inner ear. Here, we describe in detail the specialized connection between the swimbladder and ear in the mojarra, as well as a modified cone on the anal fin in which the posterior end of the swimbladder sits. Hearing tests show the mojarra has better hearing sensitivity than other species of fish without a connection. However, mojarras do not seem to use this adaptation for communication. Furthermore, the inclined position of the swimbladder may help the fish to catch their prey more easily, as the swimbladder will be horizontal when they are picking up benthic prey.

A GaAs/AlAs superlattice as an electrically pumped THz acoustic phonon amplifier

In a semiconductor superlattice (SL), phonon-assisted electron transitions can occur under a quasi-population inversion, brought about by electrical biasing. This paper demonstrates the amplification of an optically excited quasi-monochromatic phonon beam by stimulated emission of phonons. Coherent phonons are generated by ultrafast optical excitation of a generator SL and passed once through a dc biased, GaAs/AlAs gain SL. A 20% increase in the phonon flux is detected when pumping is applied to the gain superlattice, which corresponds to an acoustic gain coefficient of 3600 cm−1. A theoretical model of the phonon amplification is presented that also includes the effects of disorder in the SL. It is found that the amplification process is robust in the presence of disorder and good agreement is obtained with the main features of the experimental observations.

Acoustical power amplification and damping by temperature gradients

Ceperley proposed a concept of a traveling wave heat engine ["A pistonless Stirling engine-The traveling wave heat engine," J. Acoust. Soc. Am. 66, 1508-1513 (1979).] that provided a starting point of thermoacoustics today. This paper verifies experimentally his idea through observation of amplification and strong damping of a plane acoustic traveling wave as it passes through axial temperature gradients. The acoustic power gain is shown to obey a universal curve specified by a dimensionless parameter ωτα; ω is the angular frequency and τα is the relaxation time for the gas to thermally equilibrate with channel walls. As an application of his idea, a three-stage acoustic power amplifier is developed, which attains the gain up to 10 with a moderate temperature ratio of 2.3.

Influence of acoustic pressure amplifier tube on a 300 Hz thermoacoustically driven pulse tube cooler

High frequency thermoacoustically driven pulse tube coolers (PTCs) have the advantages of high energy density, compact structure, and high reliability. Through a series of improvements, the 300 Hz thermoacoustically driven PTC in this paper achieved a fourfold increase in the cooling power compared with that in our last report. A cooling power of 1.04 W at 80 K and a no-load temperature of 63 K are obtained with 500 W heating power. In the system, the acoustic pressure amplifier tube (APAT) plays an important role in coupling the thermoacoustic engine and the PTC. The effects of APAT on the system performance are investigated here through both numeric simulations and experiments. The simulation indicates that length of the APAT is limited due to impedance match requirement between the PTC and the engine, which is partly evidenced by experiments. Calculation also gives a good agreement between calculated pressure wave amplification ratio and experimental values. APAT with different lengths and diameters are investigated through experiments which indicate that there is an optimum diameter for the system performance.

A passive network model for large diameter thermoacoustic tube systems and its experimental verification

Linear thermoacoustic theory is currently well accepted for simulating thermoacoustic systems, and correction is used to reduce the discrepancy between calculations and experimental results for turbulent flow. In order to calculate passive tube systems and make linear thermoacoustic theory coincide closely with experiments, a passive network model based on fluid network theory is derived. An amendment method is proposed to further correct for turbulence by amending thermal and viscous penetration depths when the ratio of the tube radius to the viscous penetration depth R/ δ v is large. The experiments have been done to verify the model in the acoustic amplifier, Helmholtz resonator, and inertance tube. In addition, the mechanisms of such tubes are further analyzed based on the model.

Advances in a 300 Hz thermoacoustic cooler system working within liquid nitrogen temperature range

With the combined advantages of high reliability, compact size and low electromagnetic interference, a high frequency operating thermoacoustic cooler system, i.e. a pulse tube cooler driven by a thermoacoustic heat engine, is quite promising for space applications. This article introduced a high frequency standing-wave thermoacoustic heat engine-driven pulse tube cooler system working around 300 Hz with axial length being 1.2 m. To improve the thermal efficiency of such system, an optimization has been carried out, both analytically and experimentally, by observing the influence of the dimensions of the stack, the hot buffer length and the acoustic pressure amplifier tube length. So far, a no-load temperature of 68.3 K has been obtained with 4.0 MPa helium and 750 W heating power. With 500 W heating power, a no-load temperature of 76.9 K and 0.2 W cooling power at 80 K have been achieved. Compared with former reports, the performance has been improved.

Experimental study of whistle noise generated by insert edge and oil separator model of refrigeration cycle

The compressed air experiments are conducted to investigate the whistle noise radiated from the oil separator component of refrigerant cycle system. Two types of insert edge and a height-adjustable oil separator model are adopted. The acoustic characteristic of flow through plain top insert edge is more likely to be broadband. Flow through ramp top insert edge would induce whistle peaks at Mach number higher than 0.1197 and the oil separator model works like an acoustic amplifier. Moreover, the Strouhal number jumps are captured inside oil separator model and two mechanisms are presented to clarify the phenomena. First, the whistle noise at Modes A1, A3, B1 and B3 is regarded as coupling of shear layer instability with resonance acoustic modes of oil separator model. Second, the whistle noise at Modes A2 and B2 is regarded to be the feedback loop of flow–acoustic interaction in fluctuated shear layer and defined as jet–cavity interaction tones.

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting