Sound attenuation using microelectromechanical systems fabricated acoustic metamaterials

Abstract

Unlike traditional rotational gyroscopes, microelectromechanical systems (MEMS) gyroscopes use a vibrating proof mass rather than a rotational mass to sense changes in angular rate. They are also smaller and less expensive than traditional gyroscopes. MEMS gyroscopes are known to be susceptible to the effects of acoustic noise, in particular high frequency and high power acoustic noise. Most notably, this has been proven true in aerospace applications where the noise can reach levels in excess of 120 dB and the noise frequency can exceed 20 kHz. The typical resonant frequency for the proof mass of a MEMS gyroscope is between 3 and 20 kHz. High power, high frequency acoustic noise can disrupt the output signal of the gyroscope to the point that the output becomes unreliable. In recent years, considerable research has focused on the fascinating properties found in metamaterials. A metamaterial is an artificially fabricated device or structure that is engineered to produce desired material responses that can either mimic known behaviors or produce responses that do not occur naturally in materials found in nature. Acoustic metamaterials, in particular, have shown great promise in the field of sound attenuation. This paper proposes a method to mitigate the performance degradation of the MEMS gyroscope in the presence of high power, high frequency acoustic noise by using a new acoustic metamaterial in the form of a two-dimensional array of micromachined Helmholtz resonators. The Helmholtz resonators are fabricated in a silicon wafer using standard MEMS manufacturing techniques and are designed to attenuate sound at the resonant frequency of the gyroscope proof mass. The resonator arrays were diced from the silicon wafer in one inch squares and assembled into a box open on one end in a manner to attenuate sound on all sides of the gyroscope, and to seal the gyroscope inside the box. The resulting acoustic metamaterial device was evaluated in an acoustic chamber and was found to successfully attenuate sound as much as 18 dB. This attenuation is in the form of a notch filter at and around 14.5 kHz, which was the target frequency of attenuation. The notch filter attenuation occurred over a 700 Hz frequency band with 18 dB being the largest attenuation in the band.

Enhancing the absorption properties of acoustic porous plates by periodically embedding Helmholtz resonators

“…This conclusion can be expected from those driven from the analysis of the effective parameters of infinite porous materials with weak concentration of HRs. 16 However, in the present article, the HR density is large so that the considered configurations do not fit homogenization requirements. When f r =f is larger than unity, the HRs resonance already leads to a quasi-total absorption peak.…”

“…10,11 Recently, membrane-type metamaterials that exhibit nearly total reflection at an anti-resonance frequency 12 or nearly total absorption due to the flapping motion of asymmetric rigid platelets added to the membrane 13 have been proposed, but their absorption properties are limited in the metamaterial resonance frequency range. The use of Helmholtz resonators as sound attenuators in ducts has already been proposed, [14][15][16] but not their use together with acoustic porous materials as common sound absorbing materials. Metamaterials have induced a revival of interest in Helmholtz resonators (HRs) to manufacture negative bulk modulus and mass density materials.…”

Effective rejection of acoustic and magnetic fields’ disturbances by single-mass differential vibratory gyroscope

“…The third sub-graph shows close to zero bias of differential channel, because (d yy -d xx )/2=-hcos2( * -  ), and h is close to zero. The fourth sub-graph represents z y +z x as a combination of differential CVG bias parameters (see (9)). It is mainly determined by the large enough term (d yy +d xx )/2=2/.…”

“…It is well known that resonant gyroscopes, including MEMS, degrade their performances when external disturbance is acting at a close to resonant frequency of the vibrating structure [9]. Acoustic signals can find way to CVG resonator through inducing mechanical vibrations of the gyro casing and anchors to which the resonator is attached.…”

“…shows output of differential channel under uniform intensity of 100 dB from all directions in the range of[1][2][3][4][5][6][7][8][9][10] kHz.…”