Incident Sound Pressure Level Research Articles

Transmission loss of a silencer using resonator arrays at high sound pressure level

Helmholtz resonator is generally used to reduce the low frequency noise. However, it has only high transmission loss in a narrow band at the resonance frequency. In order to obtain broad band transmission loss, studies of a silencer using various resonator arrays have been carried out. These previous studies have been limited to low incident sound pressure level conditions with no change of impedance with respect to pressure. In the case of high sound pressure, the resistance increases due to nonlinear behavior at the neck of a resonator. As a result, the desired noise reduction performance cannot be achieved due to the transmission loss decrease. To predict the transmission loss of a silencer using resonator arrays at high sound pressure level, impedance variation depending on the incident sound pressure level should be considered. Furthermore, resonator’s numbers and order of arrangement are significant design parameters for design of transmission loss shape.

Transparent Gradient-Index Lens for Underwater Sound Based on Phase Advance

Spatial gradients in refractive index have been used extensively in acoustic metamaterial applications to control wave propagation through phase delay. This study reports the design and experimental realization of an acoustic gradient index lens using a sonic crystal lattice that is impedance matched to water over a broad bandwidth. In contrast to previous designs, the underlying lattice features refractive indices that are lower than the water background, which facilitates propagation control based on a phase advance as opposed to a delay. The index gradient is achieved by varying the filling fraction of hollow, air-filled aluminum tubes that individually exhibit a higher sound speed than water and matched impedance. Acoustic focusing is observed over a broad bandwidth of frequencies in the homogenization limit of the lattice, with intensity magnifications in excess of 7 dB. An anisotropic lattice design facilitates a flat-faceted geometry with low backscattering at 18 dB below the incident sound pressure level. Three dimensional Rayleigh-Sommerfeld integration that accounts for the anisotropic refraction is used to accurately predict the experimentally measured focal patterns.

A Numerical Investigation on Sound Absorption Mechanism of Micro Resonator with Offset Slits

Acoustic liners are widely used in commercial aero-engine to suppress noise. In theoretical investigations, the liner geometry is often assumed as an array of symmetric micro resonator with orifice or slit at the center. However, in real application, orifices or slits distributed in micro resonator are offset. For better understanding of sound absorption mechanism of micro resonator with offset slits under high incident sound pressure level (SPL), direct numerical simulations (DNS) using high order low dispersion and low dissipation computational aeroacoustics (CAA) method are carried out. The simulations are first validated by experimental data, showing good agreement and establishing the relevance of the simulation methodology. Numerical simulations of resonators with single offset slit or two slits are then conducted. The two sound absorption mechanisms, namely viscous dissipation and vortex shedding, are discussed with detailed numerical data and analysis, which lead to quantitative parametric description of the energy partition between the two mechanisms as a function of both frequency and geometry. It is shown that offset slit can reduce vortex shedding and results in less sound absorption. The effects of more than one slit are, however, opposite; more vortex shedding occurs with more slits so that sound absorption is enhanced. This may potentially help guide liner design in practical applications.

Experimental study on self-powered synchronized switch harvesting on inductor circuits for multiple piezoelectric plates in acoustic energy harvesting

Self-powering mechanisms for synchronized switch harvesting on inductor circuits have been experimentally investigated to harvest low-frequency acoustic energy (∼200 Hz) using multiple lead zirconate titanate piezoelectric plates placed inside a quarter-wavelength straight-tube resonator. Unlike conventional synchronized switch harvesting on inductor circuits, the self-powered synchronized switch harvesting on inductor circuits can perform alternating current/direct current conversion without externally powered switch controllers, which is beneficial in real applications. In the acoustic energy harvester, the nonuniform driving force to piezoelectric plates generates the asynchronous charging effect in piezoelectric internal capacitances. Due to more energy dissipative components in the self-powered synchronized switch harvesting on inductor circuits, there exists a critical voltage above which the self-powered synchronized switch harvesting on inductor circuits outperform the standard circuit. With the incident sound pressure level of 112 dB at the frequency of 196 Hz, the output power of self-powered series-synchronized switch harvesting on inductor using three piezoelectric plates is measured as 0.796 mW. This is 13.2% higher than the standard circuit.

Low frequency acoustic energy harvesting using PZT piezoelectric plates in a straight tube resonator

A novel and practical acoustic energy harvesting mechanism to harvest traveling sound at low audible frequency is introduced and studied both experimentally and numerically. The acoustic energy harvester in this study contains a quarter-wavelength straight tube resonator with lead zirconate titanate (PZT) piezoelectric cantilever plates placed inside the tube. When the tube resonator is excited by an incident sound at its acoustic resonance frequency, the amplified acoustic pressure inside the tube drives the vibration motions of piezoelectric plates, resulting in the generation of electricity. To increase the total voltage and power, multiple PZT plates were placed inside the tube. The number of PZT plates to maximize the voltage and power is limited due to the interruption of air particle motion by the plates. It has been found to be more beneficial to place the piezoelectric plates in the first half of the tube rather than along the entire tube. With an incident sound pressure level of 100 dB, an output voltage of 5.089 V was measured. The output voltage increases linearly with the incident sound pressure. With an incident sound pressure of 110 dB, an output voltage of 15.689 V and a power of 12.697 mW were obtained. The corresponding areal and volume power densities are 0.635 mW cm−2 and 15.115 μW cm−3, respectively.

Discrete vortex model of a Helmholtz resonator subjected to high-intensity sound and grazing flow

In this paper, a theoretical model is developed to study the acoustical response of a Helmholtz resonator as a duct-branched acoustic absorber subjected to both high-intensity sound and grazing flow. The present model is comprised of a discrete vortex model in combination with a one-dimensional duct sound propagation model. The present work is to study the overall effect of incident sound interacting with grazing flow but putting emphasis on the nonlinear or intermediate regime where the sound intensity has a marked or non-negligible influence on the acoustic behavior of the Helmholtz resonator. The numerical results reveal that the flow field around the orifice is dominated by the evolution of the vortex sheet and the flow pattern is influenced by the ratio of the orifice flow velocity to the grazing flow velocity. When the incident sound pressure is high or the resonance occurs, the resonator shows nonlinearity, i.e., the acoustic impedance and absorption coefficient vary not only with duct flow Mach number buy also with incident frequency and incident sound pressure level.

높은 입사 음압 및 설계 인자의 변화에 따른 미세 천공판 흡음 기구의 흡음 특성

The micro-perforated panel absorber(MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high(around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

높은 입사 음압에서의 미세 천공판을 이용한 흡음 기구의 설계

Reduction of acoustic loads of space launch vehicles can be achieved by acoustic absorbers satisfying strict cleanness requirements. This limited the use of general porous materials and requires non-porous sound absorbers. Micro-perforated panel absorbers(MPPA) is one of promising sound absorbers satisfying the cleanness requirement for launch vehicles. However, its applicability was limited to low sound pressure levels according to the acoustic impedance model of micro-perforated panels. In this paper the applicability of micro-perforated panel absorbers at high incident sound pressure was investigated in experimental ways. The absorption characteristics of a micro-perforated panel absorber was simulated according to its design variables, e.g., minute hole diameters and aperture ratios. It was shown that optimal design can be readily done by using proposed design charts. Experiments were conducted to measure acoustic properties of the designed micro-perforated panel absorbers. The results showed that acoustic resistance increases rapidly as incident sound pressure level does but change of acoustic reactance can be neglected in a practical point of view. This caused the decrease of peak value of absorption coefficient at high incident sound pressure level, but the amount of reduction can be accepted in practice. The major advantage of the micro-perforated panel absorber(wide absorption bandwidth) was still kept at high sound pressure level.

Acoustic energy harvesting using an electromechancal Helmholtz resonator.

This talk presents the development of an acoustic energy harvester using an electromechanical Helmholtz resonator (EMHR). The EMHR consists of an orifice, cavity, and a piezoelectric diaphragm. When the acoustic wave is incident on the EMHR, a portion of acoustic energy is converted to electrical energy via piezoelectric transduction in the diaphragm of the EMHR. Moreover, the diaphragm is coupled with energy reclamation circuitry to increase the efficiency of the energy conversion. Two power converter topologies are adopted to demonstrate the feasibility of acoustic energy reclamation using an EMHR. The first is comprised of only a rectifier, and the second uses a rectifier connected to a flyback converter to improve load matching. Experimental results indicate that approximately 30 mW of output power is harvested for an incident sound pressure level of 160 dB with a flyback converter. Such power level is sufficient to power a variety of low power electronic devices.

Acoustic and aerodynamic dissipations induced by a sound wave‐impacted Helmholtz resonator

The purpose of the work introduced herein is to study the dissipation of the acoustic energy carried by sound waves, by a Helmholtz resonator. Two‐dimensional direct numerical simulations (DNS) are performed with the CEDRE code, a Navier‐Stokes equations solver developed by Onera, for a resonator with a 0.8 × 0.8 mm square opening. The incident sound pressure level (SPL) varies between 100 dB and 150 dB: it is checked that when the SPL is low, the acoustic energy is dissipated in the resonator opening by viscous wall friction, whereas when the SPL is high, the acoustic energy is converted in kinetic energy carried by micro‐vortices induced at the opening mouths. However, when the SPL takes intermediate values, both mechanisms coexist. Thus, for each case, we aim at splitting the aeraoacoustic field into respective acoustic and aerodynamic contributions, and at evaluating the ratio between these two distinct mechanisms in order to quantify their relative weight on the global dissipation. Our results are compared with those obtained by Tam et al. for the same geometry. A three‐dimensional study for a Helmholtz resonator with a cubic opening is eventually considered.

Acoustic energy harvesting using an electromechanical Helmholtz resonator

This paper presents the development of an acoustic energy harvester using an electromechanical Helmholtz resonator (EMHR). The EMHR consists of an orifice, cavity, and a piezoelectric diaphragm. Acoustic energy is converted to mechanical energy when sound incident on the orifice generates an oscillatory pressure in the cavity, which in turns causes the vibration of the diaphragm. The conversion of acoustic energy to electrical energy is achieved via piezoelectric transduction in the diaphragm of the EMHR. Moreover, the diaphragm is coupled with energy reclamation circuitry to increase the efficiency of the energy conversion. Lumped element modeling of the EMHR is used to provide physical insight into the coupled energy domain dynamics governing the energy reclamation process. The feasibility of acoustic energy reclamation using an EMHR is demonstrated in a plane wave tube for two power converter topologies. The first is comprised of only a rectifier, and the second uses a rectifier connected to a flyback converter to improve load matching. Experimental results indicate that approximately 30 mW of output power is harvested for an incident sound pressure level of 160 dB with a flyback converter. Such power level is sufficient to power a variety of low power electronic devices.

Development of an acoustical energy harvester

This paper presents the development of one component of a miniature acoustical energy harvesting system that is designed to convert acoustical energy into electrical energy. This component consists of a composite circular membrane containing a circular piezoelectric ring near the clamped boundary. An acoustic pressure fluctuation leads to a deflection of the membrane. This deflection generates a strain concentrated near the clamped boundary. The piezoelectric material, strategically placed in this region of high strain, converts the strain into an electrical voltage that can then be utilized in an electrical circuit or stored in a battery. The energy harvester was designed by combining a linear piezoelectric composite plate model with a lumped-element, electroacoustic model. Characterization was performed via acoustic excitation in a plane-wave tube. Preliminary results indicate a maximum generated output voltage of 18.2 mV across a 78.3−kΩ resistive load, resulting in 4.2 μW of generated power for an incident sound pressure level of 153.4 dB.

Remote ultrasonic classification of fluids in cylindrical containers by analyzing the response of circumferential guided waves

A novel technique for classifying fluids in sealed, metal containers at large stand-off distances has been developed. It utilizes a recently constructed air-coupled acoustic array made from inexpensive, commercial-off-the-shelf components to excite the resonance vibrations of fluid-filled vessels. The sound field from the array is constructed by transmitting a high-frequency modulated carrier wave which utilizes the nonlinearity in the air medium to demodulate the carrier frequency along its propagation path in air. The array has a narrow beamwidth and an operating bandwidth of greater than 25 kHz. The vibrations are detected using a laser vibrometer in a monostatic configuration with the acoustic source. It is shown that the propagation characteristics of the ao Lamb wave are highly affected by different interior loading conditions on the interior wall of a cylindrical container. Classification of the interior fluid is obtained by analyzing the change of this response as a function of frequency. Experiments demonstrate that classification of the fluid-filler inside closed, steel vessels is possible with incident sound pressure levels of the demodulated wave as low as 80 dB at the container location. Preliminary experiments demonstrate that stand-off distances greater than 3 m are achievable for classification purposes.

Forchheimer-type nonlinearities for high-intensity propagation of pure tones in air-saturated porous media

A linear rigid frame, cylindrical capillary theory of sound propagation in porous media is extended to include nonlinear effects of the Forchheimer type, by making a particle velocity-dependent correction to the complex density. This type of nonlinearity becomes important at incident sound-pressure levels above approximately 120 dB re: 20 μPa for highly porous fibrous materials. Data from three experiments on air-saturated porous media and foams, at levels up to 170 dB, are compared to the rigid frame theory with Forchheimer-type extension. One of the experiments measured a low-frequency approximation for the complex density directly; the others measured internal attenuation and surface admittance (inverse impedance). The generally good agreement found between predictions based on the Forchheimer-type nonlinear theory and each of the experiments suggests that this type of nonlinearity is the dominant one for propagation in many types of air-saturated fibrous porous media. Some interesting surface absorption characteristics are predicted at incident sound-pressure levels above 140 dB, especially at lower frequencies.

The acoustic impendance of perforates at medium and high sound pressure levels

A study has been carried out of the behaviour of the acoustic impedance of a range of perforates at medium and high incident sound pressure levels. It included a detailed experimental programme together with a theoretical analysis of the problem. The theoretical work yields, for the linear impedance range, an improved formula for the impedance of perforates which is based on that for a single isolated orifice modified for interaction effects. This prediction technique is substantiated by the results of the experimental programme. Theoretical modelling of the non-linear impedance is based on a quasi-steady approximation to the acoustic flow through the orifice; this approach yields a formula for the non-linear acoustic resistance based on steady flow data for the perforate, which is readily obtainable. Further, the analysis yields a method of predicting when the non-linear mass reactance attains its asymptotic minimum. The correlation between experimental and theoretical results is good. Other associated aspects of the work are discussed in some detail. These include (i) the coupling of the mechanical and acoustic impedance of the perforated plate, (ii) the effects of honeycomb in the backing cavity and (iii) the two-microphone method of impedance measurement. Finally, some consideration is given both to modifying the non-linear behaviour of perforates and to applications of the prediction formula where the pressure rather than the velocity field is specified.

The Correlation of Non-Linear Resistance, Flow Resistance, and Differential Resistance for Sharp-Edged Circular Orifices

According to Sivian's analysis of the acoustic resistance of small orifices a close correlation should exist between three kinds of measurable resistance in small orifices. If the losses are mainly due to the kinetic energy acquired by the air in the orifice the non-linear acoustic resistance RN, the analogous flow resistance RF, and the analogous differential resistance RD, are related thus: RN = 12RF, RD = 2RF. The non-linear acoustic resistance RN of orifices of 0.375 cm and 0.50 cm diameter has been obtained from plane wave transmission loss measurements made in a three-inch tube equipped with a ρc termination. Orifice thicknesses were varied from 0.05 to 1.25 cm. In this manner RN was measurable at incident pressures greater than that required to cause a deviation from constancy in the transmission loss. It was found that, in the non-linear region, the sound pressure of the wave transmitted by the orifice depends on the square of the incident sound pressure. This relation has been verified for incident sound pressure levels ranging from 115 to 160 decibels, and for frequencies from 238 to 800 c.p.s. (All levels considered were well into Region 4 of Ingaard's “phase diagrams.”) Analogous flow resistance measurements have been made on the same orifices for average particle velocities from 100 to 1,600 cm/sec. The analogous flow resistance was found to be given, within ± 30 percent, by a formula derived by Sivian from kinetic energy considerations. In most cases RN was found to be 25 percent greater than RF/2, and essentially independent of frequency over the range considered. For this comparison RN is taken at a peak orifice particle velocity equal to the orifice average velocity at which RF is measured. The differential resistance RD is the small signal acoustic resistance measured with a superimposed unidirectional flow. RD has been found to be approximately equal 2RF.