Experimental study on the insertion loss of multilayer panels featuring a periodic structure

This paper presents modeling and analysis methods for design of a acoustic metamaterial panel consisting of two isotropic plates and small membrane-mass subsystems for absorption of low frequencies transverse elastic waves. Two models of a unit cell are derived and used to demonstrate the existence of negative effective material properties. Moreover, the design of experiment sample confirms that the model and analysis methods are valid. (1) The frequency of the membrane-mass subsystems are uniform distribution in whole acoustic metamaterial panel have two vibration models. (2) The different distributions of membrane-mass subsystems and their resonance frequencies result in different vibration isolation characteristics. (3) PSV is used to test and the result show that a low frequency wave absorber does not require nano-manufacturing techniques. (4) If we design the frequency of the membrane-mass subsystems different it can change the character of the metamaterial panel.

Sonic crystals are the periodic arrangements of scatterers embedded in a homogeneous material. Their ability to prevent sound wave to propagate in a particular range of frequency demonstrates their use as potential noise barriers. The sonic crystal considered in this work is an array of PVC cylinders (5 × 5) in air bounded by acrylic sheets. This paper studies the sound transmission loss in the sonic crystal by changing the location of the sidewalls. The optimized location of sidewalls of the sonic crystal to get wide band gap and high sound transmission loss has been investigated. To increase the transmission loss, a periodic structure having bi-periodicity, i.e., periodicity in two perpendicular directions is introduced. Both computational (Finite Element simulation) and experimental work has been performed to study the sound transmission loss and the band gaps. To bridge the gap between the two results, an improved finite element model has been proposed with an aim to replicate the experimental situation more closely. Generally, in experiments, insertion loss is calculated while numerically transmission loss is computed, and the two are compared. In this paper, a comparison between insertion loss and transmission loss has also been made numerically, which is compared with the experimental results.

Commercially available sound absorbing materials attenuate sound over a broad frequency band. We are fabricating and characterizing geometrically compact composites called sonic crystals for shielding against noise generally limited to a particular frequency band. These sonic crystals have periodic arrays of macroscopic acoustic scatterers arranged in a pattern analogous to a single crystal lattice in a host matrix material. Most of the work done on sonic crystals so far has been using rod scatterers arranged in a 2-D lattice in air. Such sonic crystals have very little use as a noise reducing composites material for structures. Instead, we fabricated sonic crystals using solid metal spheres, or hollow metal beads arranged in a lattice pattern and embedded in an unsaturated polyester resin matrix. We demonstrate that in these composites, the sound transmission coefficient for certain frequencies drops abruptly, giving rise to frequency band gaps. In order to measure acoustic band gaps in these damping materials, an audio loudspeaker directs broadband sound at the specimen placed in a reflectionless acoustic enclosure. The transmitted sound is measured by a wide band microphone; fast Fourier transformed and normalized to obtain transmission coefficient spectra. Data was obtained, for example, on a sonic crystal made of 0.125-inch diameter metallic beads in a simple cubic lattice (13/spl times/13/spl times/13 array, with spacing of 0.16 inch between the beads) and cast in an unsaturated polyester resin matrix. We measured a band gap of /spl sim/3.8 kHz located at /spl sim/3.6 kHz where the drop in the transmission coefficient was /spl sim/11 dB. The reduction in transmission coefficient in the band gaps depends upon the material properties of scatterers and host, fill ratio and lattice configuration. We will present detailed results for acoustic band gaps in the propagation of sound waves through several macroscopic sonic crystal composites with various types of scatterers arranged in three dimensions and explore their industrial uses for noise reduction.

Environmental noise pollution (30-8000 Hz, 50-90 dB) has become a central health concern due to its impact on human psychology and physiology. Acoustically, aesthetic architecture has recently been explored for noise control, where sonic crystals (SCs) offer both effective sound attenuation and seamless architectural integration. However, conventional SCs with circular scatterers remain limited in suppressing low-frequency noise because Bragg scattering requires lattice constants comparable to the acoustic wavelength, making large structures impractical for subwavelength regimes. Herein, we propose a Hexa-resonator SC, optimized, simulated, and experimentally validated for its noise attenuation performance. With band structure calculations and eigenfrequency mode analysis, the insertion loss (IL) was investigated over 20-1000 Hz. In the sub-kilohertz region, the SC exhibited two first-order resonance peaks around 150 and 200 Hz and a first-order Bragg band (255-410 Hz). It showed a maximum IL of approximately 36 dB at 303 Hz (in the Bragg region), confirming its effectiveness for low-frequency noise attenuation. The influence of cavity geometry on phase pressure variations and IL was analyzed, revealing hybridization and mode coupling effects. Experiments qualitatively follow the simulated trends.

This paper reports a natural ventilation silencer for an animal cage having considerable sound insertion loss. Many veterinary hospitals face a serious problem that hospitalized animals are stressed from the barks of other dogs in the hospital. To address this problem, a solution that barely affects caged dogs’ health is required. First, we estimated aperture ratio of the silencer device which was considered by physiological sustainability of dog. Next, we attempted to use a silencer with sound insertion loss by attaching it to an opening side of the cage. We constructed the tested prototype silencers by using the resonance of a rectangular room and a nonwoven fabric. We measured the acoustic characteristics of the silencers that were attached to the real scale model of the animal cage. We also measured their insertion loss by considering the estimated frequency characteristics of the dogs’ barking sound. The result shows that proposed silencers have more than 10 dB insertion loss; therefore, they can maintain respiratory environment of a caged dogs along with good visibility.

Novel plenum window with sonic crystals for indoor noise control

Acoustic metamaterials (AMMs) have emerged as a promising strategy for low-frequency noise control in ventilation ducts, offering subwavelength, tunable solutions that overcome key limitations of conventional silencers, such as high pressure drop and reduced long-term performance. This review presents a structured analysis of 54 studies on AMMs for duct acoustics, with civil, mechanical, aerospace, and biomedical engineering applications. AMM unit designs are categorized by physical mechanism, including resonant cavities, acoustic membranes, Herschel-Quincke tubes, Fano-like interference structures, duct shape modifications, micro-perforated panels, and porous materials. The associated acoustic and flow-related performance parameters, such as insertion loss, transmission loss, absorption coefficient, flow velocity, temperature, pressure drop, Reynolds number, and Mach number, are systematically examined. Analytical, numerical, and experimental approaches are reviewed with attention to their respective merits and limitations, particularly in capturing multi-physical interactions between acoustics, fluid flow, and structural dynamics. Of the studies surveyed, 35 employed monophysical models, 8 used loosely coupled (monophysical parallel) methods, and only 11 adopted fully coupled multi-physical frameworks. This review highlights the need for integrated design methodologies and standardized evaluation under realistic flow conditions to advance the effective implementation of AMMs in ducted acoustic systems.

In this paper, a three-component cladding acoustic metamaterial panel with good sound insulation effect in the low-frequency range is proposed. The sound transmission loss of metamaterial panels under different structural configurations and different material parameters is investigated by combining finite element simulation calculations with experimental research. The results show that the closer the center of gravity of the scatterer is to the substrate, the better the stability of the resonance unit, the wider the range of effective sound isolation frequencies, and the higher the degree of normalization. The filling rate of the scatterer is maintained at about 0.5 to obtain a better sound insulation effect. At the same time, choosing lower density materials for the substrate and metal materials with high density and high modulus of elasticity for the scatterer can maximally widen the bandgap and allows for low-frequency sound insulation below 600 Hz. This approach improves the low-frequency sound insulation efficiency of acoustic metamaterials. The results provide important explanations and references for a deeper understanding of the sound insulation mechanism and the effects of different parameters on sound insulation.

A highly sensitive temperature sensor is proposed and demonstrated based on a UV-curable polymer-infiltrated Mach-Zehnder interferometer (MZI) created in a graded index fiber (GIF). The device was constructed by splicing a half-pitch GIF between two single-mode fibers and creating an inner air cavity in one lateral side of the GIF core by means of femtosecond laser micromachining. The air cavity and the residual GIF core functioned as two interference arms of the MZI. Moreover, the GIF was used as a miniature in-fiber collimator to reduce insertion loss of the air cavity. Experimental results show such an MZI device has a high refractive index (RI) sensitivity of 24611.54nm/RIU (RI=1.545-1.565). Subsequently, thermo-sensitive polymer liquid was infiltrated into the air cavity, then cured with UV illumination, and annealed at 50°C for 12h. The infiltrated MZI exhibits a high temperature sensitivity of -13.27 nm/°C. In addition, this MZI also has excellent thermal stability and repeatability, compact structure, low insertion loss, and high fringe visibility. As such, the proposed MZI could be developed for high-accuracy temperature measurements in many areas such as biomedical or oceanographic applications.

Design of low-frequency and broadband acoustic metamaterials with I-shaped antichiral units

Recently, a significant attention has been directed toward so called ‘acoustic metamaterials’ which have large similarity with already-known ‘electromagnetic metamaterials’ which are applied for elimination of the electromagnetic waves. The stop of electromagnetic waves is realized with the negative refractive index, negative permittivity and negative permeability. Motivated by the mathematical analogy between acoustic and electromagnetic waves, the acoustic metamaterials are introduced. It was asked the material to have negative effective mass. To obtain the negative effective mass, the artificial material, usually composite, has to be designed. The basic unit is a vibration absorber which consists of a lumped mass attached with a spring to the basic mechanical system. The purpose of the unit is to give a band gap where some frequencies of acoustic wave are stopped. We investigated the nonlinear mass-in-mass unit excited with any periodic force. Mathematical model of the motion is a system of two coupled strongly nonlinear and nonhomogeneous second-order differential equations. The solution of equations is assumed in the form of the Ateb (inverse beta) periodic function. The frequency of vibration is obtained as the function of the parameters of the excitation force. The effective mass of the system is also determined. Regions of negative effective mass are calculated. For these values the motion of the forced mass stops. It is concluded that the stop frequency gaps are much wider for the nonlinear than for the linear system. Based on the obtained parameter values, the acoustic metamaterial could be designed.

Sound transmission loss of a novel acoustic metamaterial sandwich panel: Theory and experiment

Two high‐gain broadband 60GHz integrated planar patch array antennas, without and with air cavity, are designed and implemented on Rogers 5880 substrate. The differential antenna structure is used to improve the signal integrity at millimetre‐wave frequencies. The antennas are co‐designed with bonding wires of which the parasitic effect is compensated using a passive network. The proposed antennas have the advantages of symmetrical radiation pattern, wide bandwidth and low insertion loss. In the measurement, a differential transmission line based de‐embedding structure is developed on silicon, mimicking the real chip packaging environment and providing reliable terminations for antennas. The measured fractional bandwidths (|S11| < −10dB) are 13.8 and 26.2%, respectively, for the two structures without and with air cavity, including the effect of a waveguide‐to‐microstrip line transition and a branch‐line balun. Both antennas have measured gain of about 12 dBi. After de‐embedding the return loss, the measured insertion loss of the bond wire compensation network is only 0.07dB at 61GHz.

The trunking communication system operating on 300-400 MHz requires an antenna duplexer with low insertion loss, sharp-cutoff frequency characteristics, reactive characteristic in the mutual frequency bands and small size, which is not commercially available. We have proposed a SAW antenna duplexer to fulfill the requirements mentioned above. To satisfy the demand of reactive characteristic in the mutual frequency bands to reduce disturbing between the Rx and the Tx, we add a /spl pi/-type high pass LC filter between the antenna and the Rx as phase shifter. In order to both get good stopband rejection and enhance the power endurance, we divide the Tx filter into two parts, one part before the power amplifier and the other coupling with antenna. The part before the power amplifier is composed of a ladder-type SAW filter coupled with SAW bandstop filter with insertion loss about 2.1 dB and attenuation about 60 dB in receiving frequency band (382-386 MHz). The part coupling with the antenna is composed of a ladder-type SAW filter with insertion loss about 0.6 dB and attenuation about 15 dB in receiving frequency band. The Rx filter is composed of a ladder-type SAW filter coupled with a longitudinally coupled resonator filter in the receiver with insertion loss about 3.8 dB and high attenuation of about 60 dB in the transmitting frequency band (372-376 MHz).

In recent years study acoustic metamaterials have found great attention due to its enormous ability to guide and manipulate elastic wave in a medium. Frequency bandgap is a great feature that can be achieved by acoustic metamaterials. The bandgap is the frequency range at which the elastic wave doesn't propagate through the medium. In another word, the frequency band gap offers wave isolation ability for a structure. An acoustic metamaterial usually consists of resonators and a host media. The frequency bandgap is mainly the result of brag scattering in the structure. The orientation and geometry of resonators in a unit cell possess a great influence on brag scattering. This study is dedicated to understanding the influence of resonators volume percentage in the frequency bandgap. Several resonator geometries of two different combinations are studied. Finally, comparing the outcome from both the combinations, a claim is made regarding the effect of volume fraction on frequency band gaps.