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As promising candidates for widespread application, advanced ceramic fiber mats with robust mechanical properties are urgently needed. However, the brittleness, fatigue failure, and large density of ceramic fiber pose significant obstacles to its practical application. Herein, a novel SiO2 aerogel/ZrO2 composite nanofibrous membrane (SZCNFM) with excellent flexibility was prepared by introducing SiO2 aerogel nanoparticles into ZrO2 nanofiber via simple co‐electrospinning. The developed tetragonal zirconia phase without changing up to 1200°C endows SZCNFM material with excellent thermal stability. Furthermore, the as‐prepared membranes exhibit fatigue resistance ability which can maintain 98% of the original stress after 100 buckling cycle tests. The addition of mesoporous structure aerogel reduces the heat transfer of the nanofibrous membrane, giving its low thermal conductivity (30 mW/m/K) and low‐frequency sound absorption (noise reduction coefficient of 0.52). Combined with the high‐temperature resistance, low thermal conductivity and excellent sound‐absorption ability make it a promising material for heat insulation and acoustic absorption. [ABSTRACT FROM AUTHOR]

Porous materials with sound absorption and load‐bearing capabilities are in demand in engineering fields like aviation and rail transportation. However, achieving both properties simultaneously is challenging due to the trade‐off between interconnected pores for sound absorption and mechanical strength. Inspired by quilling art, a novel design using spiral material formed by rolling planar materials into helical structures is proposed. Experimental results show high structural strength through self‐locking mechanisms, while double porosities from interlayer spiral slits and aligned submillimeter pores provide excellent sound absorption. These spiral sheets surpass foam aluminum in specific strength (up to 5.1 MPa) and approach aerogels in sound absorption (average coefficient of 0.93 within 0–6400 Hz). With its adaptability to various planar materials, this spiral design allows for hybrid combinations of different materials for multi‐functionality, paving the way for designing advanced, lightweight porous materials for broad applications. [ABSTRACT FROM AUTHOR]

The reduction of noises, achieved through absorption, is of paramount importance to the well‐being of both humans and machines. Lattice structures, defined as architectured porous solids arranged in repeating patterns, are emerging as advanced sound‐absorbing materials. Their immense design freedom allows for customizable pore morphology and interconnectivity, enabling the design of specific absorption properties. Thus far, the sound absorption performance of various types of lattice structures are studied and they demonstrated favorable properties compared to conventional materials. Herein, this review gives a thorough overview on the current research status, and characterizations for lattice structures in terms of acoustics is proposed. Till date, there are four main sound absorption mechanisms associated with lattice structures. Despite their complexity, lattice structures can be accurately modelled using acoustical impedance models that focus on critical acoustical geometries. Four defining features: morphology, relative density, cell size, and number of cells, have significant influences on the acoustical geometries and hence sound wave dissipation within the lattice. Drawing upon their structural‐property relationships, a classification of lattice structures into three distinct types in terms of acoustics is proposed. It is proposed that future attentions can be placed on new design concepts, advanced materials selections, and multifunctionalities. [ABSTRACT FROM AUTHOR]

Under the condition of constant thickness, improving the low‐frequency sound absorption performance of conventional sound‐absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze‐drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as‐prepared porous structure showed significant enhancement in the low‐frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound‐absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices. [ABSTRACT FROM AUTHOR]

Highly porous silica ceramics with unidirectional pores were prepared using the freeze casting method. By adjusting the solid content and freezing temperature, the porosity of the ceramics was tailored in the range of 78.20%‐84.59% and pore size in the range of 8.4‐71.4 μm, respectively. Sound absorption properties of porous silica ceramics was studied and the effect of structural factors was systematically investigated. The results showed that higher porosity and smaller pores of the porous ceramics favored the sound absorption in the entire sound wave frequency. By backing the sample with small pore size porous ceramics, the sound absorption property was enhanced, particularly in the low and medium frequency range, thus the sound absorption peak shifted towards lower frequency. The presence of air gap in the back would also favor sound absorption in low and medium frequency range. The as‐fabricated porous silica ceramics owed excellent sound absorption properties due to their unidirectional pores and low flow resistances. [ABSTRACT FROM AUTHOR]

A lightweight acoustic composite foams with unique sound absorption feature is reported, that is, the foam acoustic composite demonstrates surprisingly stable sound absorption performance in a wide bandwidth of frequency. The unique acoustic properties are attributed to the highly exfoliated nanolayered biocarbon nucleation, derived from the pyrolytic pinus resinosa, with tailoring the foam structure and properties. Polystyrene (PS) composite foams with porous graphitic biocarbon are obtained by sequestering recycled supercritical carbon dioxide assisted with torsion extrusion technology. Unique design concept is validated and implemented in the torsion‐induced extrusion process, with good mixing and thermal management, offering a suitable environment for the nucleation, uniform growth, and stability of the cells on the foam structures. The presence of porous graphitic nanolayered characteristics of biocarbon in the composition changes the sound insulation behavior from resonant absorber of pure PS closed cell foam to stable acoustic performance over a wide range in high frequency band (3.5–6.4 kHz), while preserving the closed cell structure. This allows the tailoring of cell structures and properties with varying renewable carbon content, so as to better adapt to a broadband sound absorption applications including absorbing panels, anechoic chamber with high accuracy and aircraft acoustic stealth technology. [ABSTRACT FROM AUTHOR]

Sound absorption coefficients (ACs) were determined in five solid woods (poplar, beech, walnut, mulberry, and fir) in the longitudinal and tangential directions at four different frequencies of 800, 1000, 2000, and 4000 Hz. The length of the longitudinal and tangential specimens was 50-mm and 10-mm, respectively. Separate sets of specimens were impregnated with either nanosilver suspension or water. The size range of nanoparticles was 30-80 nm. Results showed that sound ACs were lower in longitudinal specimens because sound waves could penetrate the open ends of vessels more easily, being trapped and damped there. Impregnation with both nanosilver suspension and water resulted in a significant decrease in the sound ACs. The decrease in the ACs was due to the collapsing and accumulation of perforation plates and cell parts, blocking the way through which waves could pass through the vessels. This caused higher damping due to a phenomenon called vibration decay. Correlation between gas permeability versus sound AC is significantly dependant on the porous structure of individual specimens. [ABSTRACT FROM AUTHOR]

Effects of impregnation with silver nano-suspension as well as heat-treatment on sound absorption coefficients (AC) were studied in tangential direction of five different solid woods based on their importance. AC was measured at two frequencies of 250 and 500 Hz. A 400 ppm nanosuspension was used for the impregnation; silver nanoparticles had a size range of 30-80 nm. Based on the obtained results, the species reacted significantly different in absorbing sound at the two frequencies. Impregnation with nano-suspension substantially decreased AC at the lower frequency of 250 Hz; it did not show any particular trend when AC was measured at the frequency of 500 Hz. Heat treatment significantly increased AC at the frequency of 250 Hz. ACs of mulberry tended to be similar at the two frequencies; in the other four species though, ACs were significantly different. High significant correlations were found in the hardwoods between the ACs measured at the two frequencies. [ABSTRACT FROM AUTHOR]

So far it is still a big challenge to construct the nanofibrous crosslinked composite aerogels with high compressive stress and excellent elastic resilience for pressure sensors. To solve this problem, a novel strategy of combining rigid inorganic nanofibers and flexible organic nanofibers is designed to obtain the crosslinked composite aerogels with outstanding compressive stress and stability. Surprisingly, the as‐prepared composite aerogels have an extremely low density of 11.27 mg cm−3, and the crosslinked composite aerogels with desire shapes can be easily controlled via changing the different molds on demand. More importantly, the composite aerogels can be compressed up to 80% with a quite high compressive stress of 41 kPa and it can recover to its original state well. It is worth mentioning that the as‐prepared aerogels can be encapsulated to construct ultrasensitive (0.53 kPa−1) and rapidly responsive (315 ms) pressure sensors for encrypted information transmission. Such excellent crosslinked composite aerogels will open up numerous application opportunities for pressure sensors, thermal insulation, and sound absorption. [ABSTRACT FROM AUTHOR]

Low‐grade nonmetal ore, mainly magmatic soil and tuff, was used to prepare porous sound‐absorbing ceramics. A new processing method that combines the foaming and templating methods was used to produce open‐cell porous ceramics. Silicon carbide and carbon powders were used as the foaming agent and template agent, respectively, and their effects on open‐cell preparation and sound‐absorption properties were also investigated. The results showed that sound‐absorption performance was closely related to the apparent porosity (H). Compared with either foaming or template methods, the new method incorporating both processes increased the sound‐absorption coefficient (α) and H by 51%‐258% and 69%‐728%, respectively. Optimum sound absorption of the ceramics, that is, α = 0.68, noise reduction coefficient (NRC) = 0.48, and H = 50.22%, were obtained at foaming agent contents (FACs) of 1.5 wt% and template agent contents (TACs) of 4 wt%. The Delany‐Bazley and Voronina models were selected to simulate the sound‐absorption coefficients and the latter one fitted well with our experimental results. [ABSTRACT FROM AUTHOR]

This letter proposes a new statistical model of thunder. The tortuous geometry of the emitting return stroke is randomly generated to fit observations of negative cloud‐to‐ground discharges. Pressure waves are initialized by radiation‐hydrodynamics simulations and linearly propagated into an isothermal atmosphere incorporating standardized sound absorption. The thunder pressure frequency signal is defined as the product of the input pressure governed by a deposited energy with the stochastic frequency response of the elongated discharge. We find the low‐frequency content of thunder is mostly due to stroke elongation originating from tortuosity. Acoustic energy per stroke length and spectrum slope are statistically compared to measurements, with good agreement found. We show both a near‐ and far‐field regime of the acoustical energy over distance described by two different power laws. The correlation found between the lightning energy and the acoustic energy paves the way for using thunder measurement to estimate deposited energy. Plain Language Summary: Thunder is the remote acoustic signature of lightning. It covers a wide range of frequencies, from infrasound below 20 Hz to higher audible sounds. To what extent the recording of thunder can provide useful information about lightning? As an attempt to answer this question, a new thunder model is proposed and compared with measurements made in Southern France in Fall 2012. The model relies on three key ingredients. The first one is the geometry of the lightning channel from cloud to ground, modeled as a random process whose parameters are chosen to fit well‐known optical observations. The second component is the acoustical pressure wave near the discharge that originates from the hot air expanding from the lightning discharge, obtained from radiation‐hydrodynamic simulations. The third aspect is propagation, assuming simply a homogeneous but sound absorbing atmosphere. Acoustic model predictions are compared at different distances with measured data with good agreements. Comparison shows, for the first time to our knowledge, that the easily measured overall acoustic energy at one distant microphone can inform us about the order of magnitude of deposited energy within the lightning channel. Key Points: Novel statistical model of thunder with tortuous channel and radiation‐hydrodynamics simulated source is presentedGood agreement found between modeled and measured acoustic energy over a distance range is shownMeasurement of acoustic energy paves the way to estimate lightning deposited energy [ABSTRACT FROM AUTHOR]

A radio frequency (RF)-based medical device implanted deep inside a human body can be wirelessly powered using RF energy. However, this method experiences loss in the form of attenuation and absorption, which is caused by the lossy human body. The need for a path loss (PL) model is, therefore, necessary to characterise these losses. This study presents a novel PL method, which is based on the |S21| measurements, obtained from a series of experiments on two different Dorset breed ovine models. Also, the uncertainty analysis of the equipment has been performed and the available RF power inside the body at a proposed implant location has been computed. The results are then used to develop and propose an equivalent model for PL in an anechoic chamber. Overall, an approximate PL of 3.5 dB/cm in the ovine body was measured at 1.2 GHz. Moreover, it was concluded that with the inevitable errors in the equipment, the total PL for 6 cm deep implant location was ∼21 dB with an uncertainty of 2.034 dB. The PL model presented is novel and has a great potential for applications in the design and development of RF-based implantable devices, especially leadless pacemakers. [ABSTRACT FROM AUTHOR]

High‐performance cellular foams with superior mechanical properties and heat resistance are urgently needed to fulfill the applications in extreme environments. However, they are difficult to be prepared because of low gas diffusion rate in high‐performance polymers. In this work, a facile solution‐foaming strategy to prepare multifunctional foams based on poly(m‐phenylene isophthalamide) (PMIA) is reported. The achieved PMIA foams show a hierarchically cellular structure containing macropores and mesopores. Due to their high porosity, the PMIA foams exhibit low thermal conductivity (0.0447–0.0498 W m−1 K−1) and high sound absorption coefficient at different frequency. A bimodal distribution on acoustic absorption is observed. With a bulk density range of 0.089–0.122 g cm−3, PMIA foams possess compressive moduli of 3.2–14.2 MPa and bending strength of 1.1–2.1 MPa, respectively. Moreover, they exhibit a recoverable deformation of 55.4% after 10 cycling 10% strain compressions and maintain a dimensional stability under harsh environment (–196 to 250 °C). Despite generated byproducts like polyurea, they still show a limiting oxygen index (25.2–26.3%) and relatively low heat release rate (178.3 kW m−2). This work provides a facile strategy to efficiently prepare high‐performance PMIA foams for broad application prospects. [ABSTRACT FROM AUTHOR]

High‐damping acoustic composites with unique sound insulation feature is reported, demonstrating surprisingly stable soundproof properties over a wide bandwidth of frequency (63–6300 Hz) with good mechanical properties. The extraordinary acoustic properties are attributed to the multiscale synergy of lamellar and hollow structures by multifillers adding. The acoustic composites are designed and fabricated through a low‐temperature one‐time rubber mixing process using nitrile butadiene rubber(NBR), chloroprene rubber (CR) as matrix and mica powder (MP), hollow glass beads (HGB), and montmorillonite (MMT) as multifillers. The soundproof mechanism is discussed in detail. Results indicate that the synergism of damping and sound absorption behaviors in the composition has a considerable impact on the acoustic characteristics, which can be controlled by the blending ratio of NBR/CR matrixes and the multiscale structures of MP/HGB/MMT multifillers. The designed multifillers acoustic composites can adapt to broadband engineering noise control including walls in express train constructions, panels of vessel or aircraft cabins, and large transportation pipelines. [ABSTRACT FROM AUTHOR]

This paper studies the equivalent transmission line model of the pulsed electro‐acoustic (PEA) method with its applications. Based on the consistency of acoustic wave behaviour inside lossy acoustic materials and voltage wave propagation in transmission line, an equivalent simulation model of the PEA system is developed, whose reliability is verified by the output from the transducer and amplifier models and the comparison with measured waveforms. For the problem of acoustic impedance mismatch between different modules, simulation indicates that the unequal impedances of semiconducting electrode and sample can affect the amplitude of the measured signal at the upper electrode side, and the reflected acoustic waves caused by the transducer can affect the charge waveform. Further simulation for multi‐layer materials finds that the reflected acoustic waves of different samples and sound absorbing module can superimpose on the charge signal. Accordingly, a selection criterion is proposed to avoid the effect of the reflected waves at the interface. As for the acoustic reflection caused by internal charge, it needs to be dealt with sequentially in calibration process, starting from the result inside the sample near ground electrode. The research can provide a foundation for analyzing the acoustic properties of the PEA method. [ABSTRACT FROM AUTHOR]

Antenna characterisation is usually performed by antenna pattern measurements in an anechoic chamber. Subsequently, a conducted test, the radiated two-stage or the wireless-cable method can be used for an overall system evaluation considering the measured patterns. In this study, the authors present a method to perform device tests for antenna arrays/smart antennas with and without the need of radiation pattern measurements, and they validate it experimentally. By using over-the-air tests in a virtual electromagnetic environment and wave-field synthesis, the propagation environment can be realistically recreated in the region around a device-under-test. This allows for reproducible performance comparisons of different antennas or systems under identical propagation environment conditions. As a special application, they consider the controlled reception pattern antenna in a global navigation satellite systems environment in the presence of interferer signals. [ABSTRACT FROM AUTHOR]