Acoustic Energy Loss Research Articles

Simulasi karakteristik mesin termoakustik pembangkit listrik dengan penambahan model kerugian minor dari dua segmen konis

Acoustic energy output level from regenerator segment of a thermoacoustic engine model is attenuated along it’s loop due to several conditions including minor losses. This article discusses the result of Delta EC simulation of a thermoacoustic engine model acting as simple electric power generator that inserted with two conical segments. The cone segments are capable to lower the energy loss which in turn improve the overall performance of the engine in term of nett heat to acoustic energy conversion efficiency. Combined acoustic energy loss induced by both cones is equivalent to 4.94 watts minor losses. At this condition, regenerator segment amplifies the incoming acoustic energy flow of 57.02 watt up to 93.57 watt, which is equals to 36.55 watts acoustic amplification. It leads to increasing of overall engines heat to acoustic efficiency into 14.05%, which is 1.29% higher than those at the case of without cones. This engine performance improvement addressed to smoother streamline of working fluid flow inside the loop.

Acoustic energy harvesting using phononic crystal fiber with conical input

In this paper, a novel phononic crystal fiber with conical input is introduced for coupling environmental acoustic waves to the fiber core. Environmental acoustic waves can be focused and coupled to the core through conical input. In the first step, a cone shape coupler has been considered for coupling the incident acoustic waves to the core region. This initial idea has a significant acoustic energy loss. This disadvantage encourages us to design a new phononic crystal fiber without it. Designed structure includes a phononic crystal fiber with conical input meaning solid rods have been shaped in conical way at the input section of fiber. By using this structure, environmental acoustic waves can be properly coupled to the core region of the fiber. Acoustic wave leakage to outside of the Phononic crystal fiber has been extremely decreased in comparison with initial coupler. Experimental results indicate that environmental acoustic waves can be focused and coupled to the core region by phononic crystal fiber with conical input.

Underwater Low-Frequency Acoustic Wave Detection Based on a High-Q CaF2 Resonator

Whispering gallery mode (WGM) resonators with an ultra-high quality (Q) factor provide a new idea for high-precision underwater acoustic sensing. However, acoustic energy loss due to watertight encapsulation has become an urgent problem for its underwater application. In order to solve this problem, this paper proposes a hollowed-out array structure. The finite element simulation shows that the acoustic wave transmission loss is improved by 30 dB compared with that of the flat plate encapsulation structure. Using a calcium fluoride (CaF2) resonator with a Q factor of 1.2 × 108 as an acoustic sensitive unit, the amplitude and frequency of the loaded acoustic wave are retrieved by means of the dispersion coupling response mechanism. The resonator’s underwater experimental test range is 100 Hz–1 kHz, its acoustic sensing sensitivity level reaches −176.3 dB re 1 V/µPa @ 300 Hz, and its minimum detectable pressure can be up to 0.87 mPa/Hz1/2, which corresponds to a noise-equivalent pressure (NEP) of up to 58 dB re 1 µPa/Hz1/2.

Conformable Shear Mode Transducers from Lead‐Free Piezoelectric Ceramic Coatings: An Innovative Ultrasonic Solution for Submerged Structural Health Monitoring

AbstractShear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.

Reconfigurable and Phase‐Engineered Acoustic Metasurfaces for Broadband Wavefront Manipulation

AbstractA novel type of phase‐engineered acoustic metasurfaces with reconfigurable properties is reported, enabling the flexible broadband manipulation of reflected wavefronts. The participants of the metasurface are elements conceived to possess even‐distributed reflected phases covering 2π span with linearity and small acoustic energy loss. The reconfigurable property of the metasurface is implemented by rearranging the fixed meta‐elements based on the phase profile, which is related to the characteristic of a specific wavefront shape. The metasurface's capability is successfully demonstrated to achieve acoustic focusing and bending within the frequency range of 2300–2800 Hz, showcasing its feasibility and adaptability. To enhance its practical applications, porous materials are incorporated, leveraging the robustness of phase differences among the meta‐elements to achieve high acoustic energy cancellation. Effective sound attenuation occurs within the frequency range of 1300–3100 Hz, even under wide‐angle incidences ranging from −80° to 80°. The work paves the way for further research on reconfigurable acoustic metasurfaces in broad frequency regions and exerts favorable implications for generally applicable structures applied in multi‐fields including biomedical acoustics, noise control, and so on.

Cage-like structured flexible hybrid fiber/SiO2 aerogel composite for noise reduction

The fiber/aerogel material prepared by the traditional method of sol-gel has a serious powder shedding phenomenon, and has serious environmental pollution and health hazards. In this study, an environmentally friendly porous sound absorption material with a cage-like structure, which used flexible ultrafine glass/quartz hybrid fibers (HFs) as the carrier and SiO2 aerogel as the pore filler, was produced using the wet manufacturing process. The addition of aerogel enhanced the internal reflection of sound waves, reduced the propagation speed, increased the acoustic energy loss and improved the sound absorption coefficient (SAC). The noise reduction coefficient (NRC) reaches 0.49 in the range of 250–6300 Hz. The obtained composite presented a low density (73.5 mg/cm3) and heat resistance up to 500 °C.

Minor Losses Of Cone Segments Insertion Into Single Loop Thermoacoustic Engine Model

A thermoacoustic engine model has been built with Delta-EC simulation. This engine model is designed with a specific capability to utilize heat source from flue gas of low-grade biomass combustion. This engine model considered has a promising feature for low cost implementation according to the fact that the low-grade biomass abundantly available at rural area in the form of agricultural waste. This engine model is an improved version of a previous one, with the addition of two conical segments in two location at the engine’s loop. The cone segments lower the energy loss which in turn improve the overall performance of the engine, compared to the model installed with the straight segments. On a certain setting of the engine’s model parameters, their addition be able to slightly decreasing the acoustic energy loss occurred at loop ends and both cold and hot heat exchangers interface. The cone segments increase the engine performance by reducing the acoustic energy loss of 0.2 W, which is 0,3% lower than those with straight segment. In general, overall heat to acoustic conversion efficiency of the model is slightly increase from 6.97% to 7.01%.

A modified sonic black hole structure for improving and broadening sound absorption

In order to improve and broaden the absorption performance of Sonic Black Hole (SBH), we propose a modified SBH structure with micro-perforated panels which is embedded the multiple resonator cavities, and investigate the sound absorption effect of the structure. Characteristics of acoustic streaming effects are embodied in sound pressure and flow velocity distribution. Further, proposed SBH structure can achieve high sound absorption under 6.0 kHz. Based on the symmetry of the structure, the Two-dimensional axisymmetric Finite Element Method (FEM) model is proposed to study the sound absorption mechanism, which shows that the change of flow velocity gradient of acoustic medium leads to the loss of acoustic energy inside the structure. By discussion on acoustic streaming effects of different frequencies, the resonator cavity and micro-perforated panels contributes more to the sound absorption performance at low frequencies, and SBH produces a sound absorption advantage at high frequencies.The theoretical calculation and simulation result match and prove the correctness of the sound streaming effect. Sound absorption tests by acoustic impedance tube confirm that the proposed structure can maintain a sound absorption coefficient of over 0.5 in the range of 0.05–6.0 kHz. The combination of micro-perforated panels and SBH structure is widely applicable to muffler design and has good application prospects.

Simulasi pemasangan sebuah model kerugian minor perubahan penampang di konektor loop mesin termoakustik

A custom-designed thermoacoustic engine model has been created with the open source Delta EC simulation software. The specific design of the engine lies in the part of the heat exchanger, which allows it to receive heat from the hot gas stream resulting from the combustion of low grade biomass directly. The engine model can be coupled with a loudspeaker model that functions as a liner alternator, resulting in a simple power generator engine model. In this study, further simulations were carried out to increase the total efficiency of converting heat energy into electricity from the previous model. After that a model of minor loss of cross-sectional change was also added to the model. In a certain set of engine model parameter values without minor losses, the efficiency of converting heat energy to acoustic energy is 12.76%, equivalent to the amplification of acoustic energy by a regenerator of 33.26 W. The total efficiency of the engine model in converting heat energy into electrical energy is 10.53%. After the addition of a sub-program of minor losses due to the effect of one conical segment, there was an acoustic energy loss of 0.11 W. So that the efficiency of converting heat energy to acoustic energy was reduced by 0.01% to 12.75%. As a result, relatively small change occur in the total efficiency of the engine model.

Aluminum Nitride Based Film Bulk Acoustic Resonator With Anchor Column Structure

In order to reduce the lateral acoustic energy loss of thin film bulk acoustic resonators (FBARs), the trench structure for FBAR is generally designed to block the leakage of acoustic wave and help improving the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor. One method the designers often used is etching the piezoelectric material around the active area of the FBAR to form the air-wall structure as a perfect reflection boundary condition. In this paper, the FBAR with trench structure is fabricated. The multilayer films in the FBAR with trench structure are easily warped due to excessive compressive stress. The numerical analysis and finite element simulation are used to verify the effects of different stresses on the devices. In order to avoid the degradation of FBAR performance caused by film warpage, the FBAR with anchor columns is proposed. The anchor columns are located on both sides of the FBAR, and they are designed to reduce film bending and the compressive stress of active area of the resonator. The measured results show that the Qs and Qp of the FBAR with anchor columns are increased by 55.8% and 21.1%, respectively, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k_{eff}{}^{2}$ </tex-math></inline-formula> improved from 5.6% to 6.7% compared with the FBAR without the anchor columns. [2022-0179]

Shear Mode Ultrasonic Transducers from Flexible Piezoelectric PLLA Fibers for Structural Health Monitoring

AbstractShear mode guided waves are highly demanded for underwater structural health monitoring (SHM) applications due to their simplified non‐dispersive feature and minimal acoustic energy loss in the presence of liquid. Excitation and detection of pure shear wave are challenging using conventional piezoelectric materials used in the current ultrasonic transducers because they have complex piezoelectric responses mixed with multiple longitudinal, transverse, and shear modes. They also suffer from aging issue due to depoling. Here, conformable shear mode ultrasonic transducers are designed and made of flexible piezoelectric poly (L‐lactic acid) (PLLA) fibers on both flat and tubular structures. The electromechanical responses over a macroscopic area of the transducers are evaluated in a wide frequency range up to 500 kHz. The PLLA fiber‐based shear mode ultrasonic transducers exhibit a consistent sensitivity of detecting defects in liquid and air. In addition, the only shear mode in PLLA fibers originates from crystal structure without requiring electrical poling to render piezoelectricity, thus does not depole due to aging. The theoretical analyses including ab initio calculations and experimental results on both flat and tubular structures show the great potential of PLLA material and significant advantage of PLLA fiber‐based shear mode ultrasonic transducers for underwater SHM applications.

ACOUSTIC TOMOGRAPHY ALGORITHM FOR DETERMINING THE SPATIAL ISOTROPICITY OF THE HYDROACOUSTIC FIELD

One of the primary characteristics of the marine environment is the speed of sound, which very sensitively reflects its smallest changes. Moreover, this characteristic is integral, integral. It inseparably characterizes the state of the system, which is formed by a whole complex of influences and reactions to them. By separating the effects and reactions on the so-called temperature, salinity, pressure, known to us at this stage of the development of the physics, we supposedly simplify the system and its understanding, but in fact we get confused, giving one of the factors very great or very little importance (the possibilities of influence on system). Acoustic tomography is based, among other things, on the sound irradiation of the marine environment and the analysis of the received signal for the purpose of evaluating changes in its characteristics after passing through the water space. Changes in the characteristics of the acoustic signal can occur for annual reasons, one of which is spatial changes in the vertical distribution of sound speed. As a result of theoretical research in the direction of passive acoustic tomography, using the methods of modeling the refraction of acoustic waves, a new type of quantitative characteristics of the acoustic field was determined for the first time. The principle of determining the appropriate reference characteristic of the acoustic field is proposed, on the basis of which the basis for creating algorithms for restoring the vertical distribution of sound speed is developed. The algorithm for determining the reference characteristic, including, includes the calculation of acoustic energy losses, which is translated into the frequency domain to determine the positive extremum of the amplitude spectrum and the calculation of the reference characteristic of the regional acoustic field in the time domain. One of a number of algorithms for determining the spatial isotropy of the vertical sound speed distribution has been adapted. The implementation of the specified algorithm of passive acoustic tomography will provide ship sonar with input data for depth determination, which will increase the safety of navigation.

Changes to mixed layer acoustic energy from spice and isopycnal tilt

Mixed layer acoustic propagation is predicted for fields that approximate two dynamically separate sources of sound speed variation: the tilting of isopycnals and “spice,” density compensated temperature and salinity changes. These fields are decomposed from a transect measurement over approximately 1000 km of the northeast Pacific Ocean. At a frequency with only one mixed layer mode, both fields contain blocking features, defined as sound speed structures less than 5 km wide that create significant acoustic energy loss. The transect shows two distinct regions where blocking features are caused by tilt or spice, indicating the acoustic importance of these dynamic processes depends on location. Statistics of mixed layer acoustic energy are investigated at two frequencies, averaging one or three mixed layer modes, both with and without blocking features. The spice field was found to produce higher loss than the tilt field. Both fields create more loss at lower frequencies when locations with blocking features were included, and more loss at higher frequencies without blocking features. Mixed layer mode amplitudes demonstrate more mixed layer modes at the higher frequency increases mode coupling, both preventing large scale acoustic energy loss and creating a more consistent loss mechanism.

Figure of Merit Enhancement of Laterally Vibrating RF-MEMS Resonators via Energy-Preserving Addendum Frame.

This paper examines a new technique to improve the figure of merit of laterally vibrating RF-MEMS resonators through an energy-preserving suspended addendum frame structure using finite element analysis. The proposed suspended addendum frame on the sides of the resonant plate helps as a mechanical vibration isolator from the supporting substrate. This enables the resonator to have a low acoustic energy loss, resulting in a higher quality factor. The simulated attenuation characteristics of the suspended addendum frame are up to an order of magnitude larger than those achieved with the conventional structure. Even though the deployed technique does not have a significant impact on increasing the effective electromechanical coupling coefficient, due to a gigantic improvement in the unloaded quality factor, from 4106 to 51,136, the resonator with the suspended frame achieved an 11-folds improvement in the figure of merit compared to that of the conventional resonator. Moreover, the insertion loss was improved from 5 dB down to a value as low as 0.7 dB. Furthermore, a method of suppressing spurious mode is demonstrated to remove the one incurred by the reflected waves due to the proposed energy-preserving structure.

Periodic Tubular Structures and Phononic Crystals towards High-Q Liquid Ultrasonic Inline Sensors for Pipes

The article focuses on a high-resolution ultrasound sensor for real-time monitoring of liquid analytes in cylindrical pipes, tubes, or capillaries. The development of such a sensor faces the challenges of acoustic energy losses, including dissipation at liquid/solid interface and acoustic wave radiation along the pipe. Furthermore, we consider acoustic resonant mode coupling and mode conversion. We show how the concept of phononic crystals can be applied to solve these problems and achieve the maximum theoretically possible Q-factor for resonant ultrasonic sensors. We propose an approach for excitation and measurement of an isolated radial resonant mode with minimal internal losses. The acoustic energy is effectively localized in a narrow probing area due to the introduction of periodically arranged sectioned rings around the tube. We present a sensor design concept, which optimizes the coupling between the tubular resonator and external piezoelectric transducers. We introduce a 2D-phononic crystal in the probing region for this purpose. The Q-factor of the proposed structures show the high prospects for phononic crystal pipe sensors.

Investigation of long acoustic waveguides for the very low frequency characterization of monolayer and stratified air-saturated poroelastic materials

When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms which are switched on or off as the excitation frequency varies. The classical way of measuring acoustic energy loss in porous materials uses the Kundt impedance tube. However, due to its short length, measurements are made in the steady state harmonic regimes. Its lower cutoff frequency is often limited to a few hundreds of Hertz. Two long acoustic waveguides were assembled from water pipes and mounted to create test-rigs for the low-frequency acoustic characterization of monolayer and stratified air-saturated poroelastic materials. The first waveguide was straight and had a length of 120 m, while the second was coiled to gain space and was 135 m long. The long waveguides appeal to very low frequency measurements using impulsive acoustic waves (with rich spectral content) because the incident waves can be separated in time from echoes off the extremities of the guides. The transmission coefficient of porous materials recovered using the two waveguides compared well with those from the transfer matrix method (TMM) used here in combination with Biot’s 1962 theory to describe propagation in porous dissipative media. This wave-material interaction model permitted the recovery of the properties of poroelastic materials from transmitted acoustic waves propagating in air. The parameters involved are the Young’s moduli, Poisson ratio and microstructural properties such as tortuosity and permeability. Being able to descend to lower frequencies guarantees the correct verification of the magnitude of the measured transmission coefficient which approaches unity towards the static frequency. The coiled and straight waveguides were found to be equivalent and provided data down to frequencies of the order of ≈12 Hz.

Design for high-quality factor of piezoelectric-on-silicon MEMS resonators using resonant plate shape and phononic crystals

Piezoelectric-on-silicon MEMS resonator is very well known for its compatibility with CMOS integrated circuit technology. However, its quality factor (Q) is highly affected by acoustic energy loss through the supporting structures. In this study, a resonator with butterfly-like round edge resonating plate structure and deploying properly designed PnC arrays on the tether and the anchoring boundaries are proposed to scale up the quality factor by effectively reducing the energy loss. The finite element analysis simulation results reveal that the proposed topologies can efficiently change the displacement field in the resonating plate and reduce the anchor loss. Consequently, an unloaded quality factor of the conventional resonator is raised from 29 899 to 51 503 (butterfly-like round edge resonating structure), 83 349 (Phononic crystal on the tether) and 83 899 (Phononic crystal on the anchor), representing 1.7 folds, 2.78 folds and 2.8 folds improvement respectively.

A Low-Cost Optoacoustic Sensor for Environmental Monitoring.

Attention to Black Carbon (BC) has been rising due to its effects on human health as well its contribution to climate change. Measurements of BC are challenging, as currently used devices are either expensive or impractical for continuous monitoring. Here, we propose an optoacoustic sensor to address this problem. The sensor utilizes a novel ellipsoidal design for refocusing the optoacoustic signal with minimal acoustic energy losses. To reduce the cost of the system, without sacrificing accuracy, an overdriven laser diode and a Quartz Tuning Fork are used as the light source and the sound detector, respectively. The prototype was able to detect BC particles and to accurately monitor changes in concentration in real time and with very good agreement with a reference instrument. The response of the sensor was linearly dependent on the BC particles concentration with a normalized noise equivalent absorption coefficient (NNEA) for soot equal to 7.39 × 10−9 W cm−1 Hz−1/2. Finally, the prototype was able to perform NO2 measurements, demonstrating its ability to accurately monitor both particulate and gaseous pollutants. The proposed sensor has the potential to offer a significant economic impact for BC environmental measurements and source appointment technologies.

Hybrid composite meta-porous structure for improving and broadening sound absorption

In order to improve and broaden the sound absorption performance of porous materials with low flow resistance, this study proposes the composite meta-porous structure embedded multiple lateral plates of different lengths, and investigates the corresponding sound absorption coefficients with the fixed and periodic boundary. Characteristics of spatial fluctuation and slow wave effect are embodied in acoustic pressure distributions. Further, the hybrid composite meta-porous structure with periodic boundary could achieve high sound absorption in range of 0–6.4 kHz. The Theoretical model using transfer matrix method suitable for these models is proposed, and verify the FEM results. Normalized surface impedance, phase and trajectory of the complex reflective coefficient illustrates the loss of acoustic energy inside the structure and leakage to the outside. By detailed discussion on the relationship between the geometric parameters and the corresponding sound absorption coefficients, the three boundaries would have different effects on sound absorption performance. Sound absorption test results by acoustic impedance tube confirm the rationality of the composite meta-porous structure with fixed boundary in range of 0.2–5.716 kHz and its practical application in the noise reduction.

Analysis of volume attenuation of hydro-acoustic signal propagation in the Romanian Black Sea Coast

The Romanian coastal area of the Black Sea has particularities related to the marine environment, namely a low average salinity and seasonal winter/summer temperature variations that influence the attenuation in volume for the propagation of acoustic signals. In this paper, the influence of the marine environment on the volume attenuation of the acoustic signals was analyzed using different calculation formulas for the attenuation coefficient. For this purpose, the Hydro-acoustic Forcast Modules application developed within the Research Center for Navy was used to simulate the acoustic energy losses.