Review of Recent Development of MEMS Speakers

Abstract

Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive attention for potential applications in hearing instruments, portable electronics, and the Internet of Things (IoT). MEMS speakers based on different transduction mechanisms, including piezoelectric, electrodynamic, electrostatic, and thermoacoustic actuation, have been developed and significant progresses have been made in commercialization in the last few years. In this article, the principle and modeling of each MEMS speaker type is briefly introduced first. Then, the development of MEMS speakers is reviewed with key specifications of state-of-the-art MEMS speakers summarized. The advantages and challenges of all four types of MEMS speakers are compared and discussed. New approaches to improve sound pressure levels (SPLs) of MEMS speakers are also proposed. Finally, the remaining challenges and outlook of MEMS speakers are given.

Review of Piezoelectric Micromachined Ultrasonic Transducers for Rangefinders

“…The signal is spread spherically, reflected by the target, and received by the pMUT. For far-field radiation, when acoustic absorption is neglected, the on-axis acoustic pressure function at a distance from a circular-membrane pMUT and a time, , is given by [ 4 , 40 , 41 ] where is the imaginary unit, is the mass density of the medium, is the average velocity of the membrane, is the Rayleigh distance, is the angular frequency, and is the wave number. In Equation (3), the amplitude of the term “ ” is equal to [ 41 ].…”

“…In Equation (3), the amplitude of the term “ ” is equal to [ 41 ]. Equation (3) is usually used to calculate the sound pressure level [ 4 ] or the transmitting sensitivity [ 42 ] of a pMUT in its transmit mode since in Equation (2) is not directly measurable and must be derived using Equation (3). For the cases in which acoustic absorption is not neglectable (e.g., in-air range-finding) and the acoustic gain , which is related to the target geometry [ 31 ], must be considered, Equation (3) is changed to: where is the absorption coefficient, which is used to evaluate the energy losses along the acoustic propagation path in the medium.…”

“…Piezoelectric micromachined ultrasonic transducers, or pMUTs, are microelectromechanical system (MEMS) devices that convert electrical energy to mechanical energy or vice versa through the flexural vibration (or deflection) of a membrane composed of a thin piezoelectric film based on piezoelectric effects [ 1 , 2 , 3 ]. A system with a single or several pMUTs can be used to transmit [ 4 ], to receive [ 5 ], or to both transmit and receive ultrasound signals (e.g., a pMUT imager [ 6 , 7 ], flowmeter [ 8 ], or rangefinder [ 9 , 10 ]), as illustrated in Figure 1 . This article is focused on pMUT rangefinders.…”

FEM‐Modeling of thermal and viscous effects in piezoelectric MEMS loudspeakers

“…The acoustic behavior of the MEMS loudspeakers depends on the solid structure, its material behavior and acoustic design [7]. To design and characterize PMEMS, various methods such as FEM and lumped element modeling are often applied [8,9].…”

The push-pull principle: an electrostatic actuator concept for low distortion acoustic transducers

“…MEMS μSpeaker approaches rely on the piezoelectric transduction mechanism [1][2][3][4][5][6][7][8] , the electrostatic transduction mechanism [9][10][11][12][13][14][15] , the magnetic transduction mechanism [16][17][18][19][20] and the thermoacoustic transduction mechanism 21,22 . A thorough review paper about micro speakers was recently published by Wang et al 23 . A few publications shall be highlighted in the following.…”