Insulating against low-frequency sound (below 500 Hz) remains challenging despite the progress that has been achieved in insulation and absorption. In this work, an acoustic metamaterial based on membrane-coated perforated plates is presented for achieving a range, even covering lower audio frequency limit, 20 Hz. Theoretical analysis finite element simulations demonstrate can effectively block waves over wide band regardless of incident angles. Two mechanisms, non-resonance monopolar...

Abstract With the advance of research on acoustic metamaterials, limits passive metamaterials have been observed, which prompts studies concerning actively tunable with adjustable characteristic frequency bands. In this work, we present a metamaterial double-negativity composed periodical membranes and side holes, in pass band can be controlled by an external direct-current voltage. The tension stiffness periodically arranged are electromagnets producing additional stresses, thus,...

We report a high-efficiency cw Raman conversion with BaWO4 crystal in diode-end-pumped Nd:YVO4 laser. The threshold is as low 3.6 W of diode power at 808 nm. highest output obtained the 1180 nm first-order Stokes line 3.36 under 25.5 W, corresponding to slope efficiency 15.3% and diode-to-Stokes optical 13.2%. intracavity 21.5% respect available 1064 fundamental.

Physical phenomena induced by nonlinear effects in an acoustic metamaterial with double-negativity based on two types of scatterers, side holes and membrane, located along a pipe are theoretically experimentally studied. We find that the pass forbidden bands related to single-negativity vary input intensities because nonlinearities both scatterers. The can disrupt unique features associated these characteristic frequency metamaterial; however, may also lead applications as automatically...

Zak phases in two types of acoustic metamaterials with negative density or modulus are studied. Different from phononic crystals based on Bragg scattering, extraordinary performance originates local resonance. We find that the determined by resonances scatterers, side pipes, membranes. Additionally, it is observed topological transition points, symmetrical properties edge states, input impedances, and reflection forbidden bands all related to relationship can be used create surface states at...

Hydrogen, as a potential replacement for fossil fuels, exhibits promising application prospects and, meanwhile, demands hydrogen sensors with high performance due to flammability and explosivity. Currently, most of work based on sorption hydrogen-sensitive materials. Thus, the sensitivities decrease operating temperature because reaction between sensitive materials weakens. Here, we create sensor basis an acoustic topological material, in which can be detected by measuring shift interface...

The advancement of acoustic metamaterials enables the highly efficient absorption low-frequency noise with a subwavelength structure thickness, but complexity these structures often hinders their large-scale practical applications. Here, we propose straightforward and compact metamaterial composed Helmholtz resonators side slits (HRSS) for absorption. introduction not only simplifies overall also allows easy adjustment characteristics. By adjusting depth resonator within slit across 25...

A hydrogen sensor is created on the basis of an acoustic topological material with a coiled structure. Compared to traditional sensors, does not possess sensitive layer and works shift interface state induced by hydrogen. The composed two phononic crystals distinct characteristics, achieved at both crystals. When introduced into sensor, density sound velocity gas in change, which shifts frequency state. Thus, concentration can be obtained measuring Due absence layer, operates without...

To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent flow air. In this research, an acoustic metamaterial adopting side structures, loops, labyrinths, arranged along a main tube, is presented. By combining accurately designed extremely wide forbidden band with low cut-off frequency 80 Hz produced, which demonstrates powerful low-frequency wide-band sound insulation ability. Moreover, by virtue bypass arrangement, open structure, thus air...

Nonlinear acoustic fields in transmission-line metamaterials based on a cylindrical pipe with periodically arranged side holes are studied, which the dispersions and characteristic parameters of nonlinear waves obtained Bloch theory, meanwhile distributions fundamental wave (FW) second harmonic (SHW) metamaterial simulated. Three frequency bands defined according to relations between frequencies FW, SHW, low-frequency forbidden band (LFB) metamaterial. Especially, when FW is LFB while SHW...

Ultrasonic treatment was applied during solidification forming of 6016 aluminium alloys. The effects ultrasonic vibration on the microstructure and mechanical properties alloy ingot were studied. Compared with conventional casting, prepared ultrasound to molten metal had a fully refined greater material homogeneity. reduced amount porosity developed by embedded gas also resulted in an obvious decrease defects, like shrinkage. In addition, component segregation minimised enhanced.

Abstract We report a composite waveguide fabricated by attaching coupling aperture to waveguide. The acoustic impedance of the can be regulated merely controlling its vibrations, depending on structure size. By changing size adjust at an impedance-mismatched fluidic interface, tunable sound transmission desired frequencies is achieved. reported provides new method for regulation mismatched interface and has extensive frequency hopping agility applications in air-water communication.

An acoustic metamaterial is designed based on a simple and compact structure of one string side pipes arranged along waveguide, in which diverse group velocities are achieved. Owing to Fabry-Perot resonance the pipes, negative phase time achieved, thus, waves transmitting with produced near resonant frequency. In addition, both fast slow also observed vicinity The extraordinary can be explained spectral rephasing induced by anomalous dispersion analogy Lorentz electromagnetic waves.

Defect inspection of small-diameter thin-walled pipes is a difficult problem in the field nondestructive testing. In this paper, new detection method based on laser ultrasonics and guided circumferential wave technology proposed used to inspect defects pipes. First, theoretical model theory acoustic propagation solids for The dispersion characteristics waves are obtained by numerical simulation. Second, ultrasonic system constructed detect flaws Finally, analyze welding quality stainless...

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To promote the use of solid waste in concrete production and solve problem secondary pollution caused by a large amount waste, four-factor four-level orthogonal test method was used to investigate different replacement rates coal gangue (CG) ceramics (15%, 20%, 25%, 30%), ceramic sand (CGS) (10%, 15%, 25%), fly ash (FA) steel fiber (SF) content (0.30%, 0.60%, 0.90%, 1.2). By using range analysis, variance matrix regression prediction models primary factors, optimal dosage, strength under...

Tunable ferroelectric film capacitors play an important role in tunable microwave devices and filter systems due to their high dielectric constant, low loss, tunability. However, there is a trade-off between loss tunability, which limits further enhancement of performance. Here, we propose ultra-tunable capacitor by designing Ba0.7Sr0.3TiO3 (BST)–semiconductor heterostructure. In the capacitor, BST fabricated directly on p-type silicon substrates magnetron sputtering, heterostructure layer...

An acoustic metamaterial based on a fractal structure, the Koch curve, is designed to simultaneously realize slow and fast waves. Owing multiple transmitting paths in structure resembling waves travelling along different interfere with each other. Therefore, are created basis of resonance Koch-curve-shaped loop, meanwhile, even negative group velocities obtained due destructive interference two opposite phases. Thus, transmission wave can be freely manipulated Koch-curve shaped structure.

Two new species of Tuber are described and illustrated. microverrucosum is recognized by its brown verrucose ascomata, blackish gleba, broadly ellipsoid to subglobose ascospores with a large-meshed regular reticulum. huizeanum diagnosed glabrous Molecular phylogenetic analysis supports the erection two species.

We report a coupling structure to realize tunable sound transmission in various frequency ranges. The structure, consisting of flexible Helmholtz resonator and waveguide, excites three main modes that generate bandpass bandstop filter effects. Importantly, the are controlled by membrane tension or device structure. These properties show can be realized simply regulating vibration states changing with different electromagnetic forces. In applications, operating at its multiple resonances...

In order to miniaturize thermoacoustic refrigerators, piezoelectric loudspeakers are used as acoustic sources for operating at high resonance frequencies. An integrated equivalent circuit model of a pipe driven by loudspeaker is presented investigate the coupling conditions between and pipe. Using optimized can be obtained, with which highest electroacoustic transfer efficiency largest output power source achieved. The theoretical simulations taken optimize structures frequencies systems.

Hollow boxes with their faces made up of elastic membranes are used to block acoustic waves. It is demonstrated that placing a cuboid membrane-type box inside pipe can effectively insulate waves even if the smaller than cross-section pipe. The sound insulation achieved within multiple frequency-bands below 500 Hz based on different mechanisms, which originate from coaction cavity, faces, and intervals between walls. Furthermore, by adjusting structural parameters establishing an array boxes,...