http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications. By Christophe Caloz and Tatsuo Itoh.

Phononic crystals (PCs) and metamaterials (MMs) can exhibit abnormal properties, even far beyond those found in nature, through artificial design of the topology or ordered structure of unit cells. This emerging class of materials has diverse application potentials in many fields. Recently, the concept of tunable PCs or MMs has been proposed to manipulate a variety of wave functions on demand. In this review, we survey recent developments in tunable and active PCs and MMs, including bandgap and bandgap engineering, anomalous behaviors of wave propagation, as well as tunable manipulation of waves based on different regulation mechanisms: tunable mechanical reconfiguration and materials with multifield coupling. We conclude by outlining future directions in the emerging field.

Tunable and Active Phononic Crystals and Metamaterials

A hybrid acoustic metamaterial is proposed as a new class of sound absorber, which exhibits superior broadband low-frequency sound absorption as well as excellent mechanical stiffness/strength. Based on the honeycomb-corrugation hybrid core (H-C hybrid core), we introduce perforations on both top facesheet and corrugation, forming perforated honeycomb-corrugation hybrid (PHCH) to gain super broadband low-frequency sound absorption. Applying the theory of micro-perforated panel (MPP), we establish a theoretical method to calculate the sound absorption coefficient of this new kind of metamaterial. Perfect sound absorption is found at just a few hundreds hertz with two-octave 0.5 absorption bandwidth. To verify this model, a finite element model is developed to calculate the absorption coefficient and analyze the viscous-thermal energy dissipation. It is found that viscous energy dissipation at perforation regions dominates the total energy consumed. This new kind of acoustic metamaterials show promising engineering applications, which can serve as multiple functional materials with extraordinary low-frequency sound absorption, excellent stiffness/strength and impact energy absorption.

/pdf/hybrid-acoustic-metamaterial-as-super-absorber-for-broadband-3nur6wullx.pdf

Hybrid acoustic metamaterial as super absorber for broadband low-frequency sound

Over the past decade there has been a great amount of research effort devoted to the topic of acoustic metamaterials (AMMs). The recent development of AMMs has enlightened the way of manipulating sound waves. Several potential applications such as low-frequency noise reduction, cloaking, angular filtering, subwavelength imaging, and energy tunneling have been proposed and implemented by the so-called membrane- or plate-type AMMs. This paper aims to offer a thorough overview on the recent development of membrane- or plate-type AMMs. The underlying mechanism of these types of AMMs for tuning the effective density will be examined first. Four different groups of membrane- or plate-type AMMs (membranes with masses attached, plates with masses attached, membranes or plates without masses attached, and active AMMs) will be reviewed. The opportunities, limitations, and challenges of membrane- or plate-type AMMs will be also discussed.

Membrane- and plate-type acoustic metamaterials

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

An acoustic metamaterial composed of multi-layer membrane-coated perforated plates for low-frequency sound insulation

With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with double-negativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.

/pdf/a-tunable-acoustic-metamaterial-with-double-negativity-5cm07fryet.pdf

A tunable acoustic metamaterial with double-negativity driven by electromagnets.

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 and experimentally studied. We find that the pass and forbidden bands related to double-negativity and single-negativity effects in the metamaterial vary with the input acoustic intensities because of the nonlinearities of both types of scatterers. The nonlinearities can disrupt the unique features associated with these characteristic frequency bands of the metamaterial; however, the nonlinear effects may also lead to applications as automatically triggered acoustic isolators, tunable acoustic metamaterials, and so on.

Nonlinear effects in a metamaterial with double negativity

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

https://iopscience.iop.org/article/10.7567/APEX.8.107301/pdf

An open-structure sound insulator against low-frequency and wide-band acoustic waves

In an ultrasonic sensor, the electromechanical coupling coefficient, sensitivities related to the mass load and conductivity variation, insert loss and minimum detectable mass are important parameters determining the performance of the sensor, while it is challenging to optimize the abovementioned five parameters simultaneously. In this paper, we show that the multi-mode characteristic of Lamb wave provides possibilities to improve the performance of ultrasonic sensors by simultaneously considering the five parameters. According to the simulated results, piezoelectric films, relative thicknesses of films and substrates, structures of interdigital transducers, operating wavelengths and frequencies are optimized based on properly selected operating modes of Lamb wave. Then, high performance of Lamb wave sensors can be realized, in which high electromechanical coupling coefficients, mass sensitivities and conductivity sensitivities in addition to low insert losses and minimum detectable masses are simultaneously achieved.

Zhe Chen

Papers

An acoustic metamaterial composed of multi-layer membrane-coated perforated plates for low-frequency sound insulation

A tunable acoustic metamaterial with double-negativity driven by electromagnets.

Nonlinear effects in a metamaterial with double negativity

An open-structure sound insulator against low-frequency and wide-band acoustic waves

Theoretical research on ultrasonic sensors based on high-order Lamb waves