Wearable multifunctional piezoelectric MEMS device for motion monitoring, health warning, and earphone

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 Recent Development of MEMS Speakers.

Among the main problems affecting the sound pressure level (SPL) of piezoelectric microelectromechanical systems (MEMS) speakers is that the membrane vibration displacement of those with sealed membranes is small, while those with unsealed membranes suffer from acoustic loss. Presented here is a high-SPL piezoelectric MEMS speaker via a rigid-flexible coupling mechanism, which can maintain large vibration displacement of the unsealed membranes without acoustic loss. The ingenious deposition of Parylene C on the upper surface before etching the back cavity is the key process forming the rigid–flexible-coupling sealed vibration membrane. Compared with that of the proposed speaker without the flexible sealed Parylene C at 2 V, the SPL generated by that with the rigid–flexible-coupling sealed vibration membrane is 3.0–26.1% higher, the frequency range of the speaker with the sealed membrane is widened from 250 Hz–20 kHz to the human hearing frequency range of 20 Hz–20 kHz for SPLs exceeding 59 dB, and a 101.2-dB SPL is obtained at the resonance frequency of 6.7 kHz. This simple strategy represents a significant step toward practical applications of piezoelectric MEMS speakers, given the wide frequency band, high SPL, and low power consumption. [2021-0041]

Obtaining High SPL Piezoelectric MEMS Speaker via a Rigid-Flexible Vibration Coupling Mechanism

We design and fabricate electrostatically actuated micro-speakers with circular diaphragms and peripheral electrode configuration. The novel electrode configuration mitigates the squeeze film damping and increases pull-in voltage when compared with the conventional parallel plate electrostatic transducer design. Finite element analysis shows that under dynamic conditions, we can achieve diaphragm deflections as much as 80 times the gap between the electrodes because of the proposed design. We compare the conventional design of electrostatically actuated audio speakers – where typical electrode separation gaps are around 60 to $100~{\mu }\text{m}$ and actuation voltages are in the range of 10 to 200 volts – with the proposed peripheral electrode design with an electrode separation gap of $1~ {\mu }\text{m}$ and actuation voltage ≤100 volts. The SPL obtained is comparable to the existing designs and ranges from 40 to 60 dB at 1 kHz at 1 cm with different sizes of the micro-speakers. The efficiency achieved with the proposed design is 100−4% at resonance which is at least two orders higher than the typically observed value for electrostatic micro-speakers. [2020-0134]

A Novel MEMS Speaker With Peripheral Electrostatic Actuation

A novel structure for this microspeaker is composed of permanent magnet Neodymium Iron Boron (NdFeB) with the magnetization of 1.42 T, diameter 1.6 mm, a thickness 0.8 mm is bonded on the PDMS membrane and N-copper planar coil is fixed on the bottom wafer. The total size of the PDMS membrane is 3 × 3 mm2 and thickness 130 μm. The proposed microspeaker is designed for CIC (completely in canal) type hearing aid. The calculation results successfully confirmed that the proposed MEMS microspeaker have a better of electroacoustic performance and efficiency. The sound pressure level (SPL) is 99 dB and the maximum displacement is 5.8 μm at the resonance frequency of 630 Hz with the microspeaker efficiency is 0.06%. In addition, the aim of this structure is to get the low resonance frequency and high acoustic efficiency is validated.

A Novel Structure of Electromagnetic MEMS Speaker for Hearing Aid Application

We report on the realization of a biomimetic MEMS speaker inspired by field crickets. This speaker is at least five times thinner and four times more efficient than the current dynamic speakers used in portable electronics. We present results of the acoustic characterization of a single MEMS speaker. Computational extrapolation of the results suggests that an array of such thin speakers will be highly efficient compared to the existing speakers of equal area.

https://www.mdpi.com/2504-3900/1/4/345/pdf

Cricket Inspired High Efficiency MEMS Speakers

Audio speakers have become an integral part of our life. They are essential components in mobile phones, music players, televisions, laptops and medical devices like hearing aids. Traditional speakers are voice coil based, and hence quite bulky. With advancements in MEMS (Micro-Electro-Mechanical-Systems) technology, though long after MEMS microphones, accelerometers and numerous types of other MEMS sensors and actuators, speakers have joined the race towards miniaturization.

Meera Garud

Papers

A Novel MEMS Speaker With Peripheral Electrostatic Actuation

Cricket Inspired High Efficiency MEMS Speakers

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