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Sensitivity is a key parameter for microspeakers, especially in low-power applications such as consumer electronics, medical devices and Internet of Things. However, the sensitivities of most reported piezoelectric MEMS speakers are inferior to those of commercially available electrodynamic speakers. Design of high-sensitivity piezoelectric MEMS speakers requires an analytical expression of sensitivity, which is not yet available. In this paper, the analytical expression is derived, and an ultrahigh-sensitivity piezoelectric MEMS speaker is designed, fabricated and characterized. The sensitivities of the speaker in an ear simulator are 107 dB/mW, 104 dB/mW and 105 dB/mW at 250 Hz, 1 kHz and 10 kHz, respectively, which are the highest among piezoelectric MEMS speakers. The analytical calculation results and measurement data are perfectly matched. Furthermore, the speaker is based on thin-film AlN instead of commonly used thin-film PZT. This work demonstrates that the ultrahigh-sensitivity piezoelectric AlN MEMS speaker consumes 10 times less power than a typical 6 mm electrodynamic speaker; and the developed analytical expressions provide valuable design insights into piezoelectric MEMS speakers for high sensitivity and low power. [2022-0063] [ABSTRACT FROM AUTHOR]

The development of Internet of Things (IoT) requires demanding accurate and low-power indoor localization. In this article, a high-precision 3-D ultrasonic indoor localization system with ultralow power is proposed. A new piezoelectric micromachined ultrasonic transducer (PMUT) chip with a slotted membrane is designed and fabricated as a receiver, breaking the dilemma of low resonant frequency and wide field of view required for indoor localization. The system works based on the time difference of arrival (TDoA), and an improved quantum genetic algorithm (QGA) is used to estimate the location. The results show that the system achieves centimeter-level positioning precision, which is among the best solutions nowadays. Due to the high performance and small size endowed by the PMUT, the receiver footprint reaches as small as 0.25 cm2 and power consumption could reach as low as 0.1 mW, which are far better than that of current indoor localization systems. [ABSTRACT FROM AUTHOR]

This paper presents a 429 MHz flexible Lamb wave resonator based on lithium niobate thin films with a high figure of merit (FoM) of 205, which is about 10 times higher than the FoM of the flexible resonator presented in our previous work. The measured corresponding quality factor (Q) and electromechanical coupling coefficient (Kt2) are 1268 and 16.2%, respectively. The resonant frequency, Q, and Kt2 of the flexible resonator show maximum changes of only 0.11%, 0.37%, and 0.31%, respectively, under a repeated mechanical bending condition up to 10 000 times at a bending radius of 3 mm. We also found that FlexMEMS technology we proposed not only endows Lamb wave resonators with mechanical flexibility but also improves FoM by ∼180% compared to their counterpart, conventional Lamb wave resonators on rigid silicon substrates. The flexible resonators with much improved FoM will find applications as low-power radio frequency key components in emerging applications, especially Internet of Things. [ABSTRACT FROM AUTHOR]