In this paper, we propose an unsealed piezoelectric microelectromechanical systems (MEMS) speaker with rigid-flexible composite membrane, which can eliminate the membrane separation and the vibration displacement limitation at high driving voltage compared to that with the sealed rigid-flexible coupling membrane demonstrated in our previous work. Measurements performed on encapsulated prototypes mounted to an artificial ear simulator have revealed that in the human audible range of 20 Hz–20 kHz, higher than 68.5 dB SPLs are obtained at 2 V, and greater than 89.6 dB SPLs are achieved at 10 V. Moreover, the SPL distribution and effective SPLs at each moment when playing the same song exhibit similar characteristics to those of a commercial electromagnetic one. This piezoelectric MEMS speaker achieves high SPLs meeting the basic hearing needs of the human, and will have excellent prospects for future wearable audio electronics.

Medium and high entropy alloys (MEAs and HEAs) have emerged as promising materials in materials science and engineering, offering exceptional mechanical properties and intriguing low-temperature physical characteristics. In the study of superconducting mechanisms, high-quality, large single crystals are essential for obtaining reliable experimental data. Here, we report the first successful growth of high-quality MEA HfNbZrTi single crystals using the Floating Zone Method and present a comprehensive investigation of their superconducting properties, vortex dynamics, and specific heat. Notably, the specific heat jump extracted from experimental data yields ΔC/γT _c = 1.43, while the superconducting gap Δ(0) is 0.92 meV, precisely matching the theoretical prediction of the weak-coupling Bardeen–Cooper–Schrieffer model. Furthermore, we report the first investigation of magnetic relaxation in MEA single crystals, revealing an exceptionally low relaxation rate (S < 0.02 at 2 K). These findings not only provide strong experimental evidence supporting the application of MEAs and HEAs superconductors but also open new avenues for the development of superconductors with ultralow magnetic relaxation rates.

Piezoelectric micromachined ultrasound transducers (pMUTs) are essential for ultrasonic communication as well as energy harvesting and transmission. While pMUTs typically demonstrate lower energy conversion efficiency and narrower bandwidths compared to traditional sandwich ultrasound transducers, their larger counterparts often present size constraints in specific applications. This paper introduces a sandwich pMUT (SpMUT) designed to enhance ultrasound transmission and reception. The SpMUT features a silicon substrate with a scandium aluminum nitride thin film, a dual electrode layer, and a three dimensional printed horn. The horn acts as a mechanical intermediary, amplifying the mechanical strain generated by the piezoelectric layer or an external sound field. Our experiments yielded a fractional bandwidth of −6 dB at 107% with a center frequency of 421 kHz in water. By optimizing the ratio of the horn's back and front diameters, we achieved maximum amplification factors of 8.59 for transmission and 8.1 for reception. The SpMUT shows significant potential for enhanced ultrasound signal amplification in biomedical and nondestructive testing applications.

Conventionally designed edge-bound type piezoelectric Micro Electro Mechanical Systems (MEMS) speakers with Si supporting layer still suffer from the problem of low sound pressure level (SPL) and high total harmonic distortion (THD). In this paper, we demonstrate a center-bound type piezoelectric MEMS speaker based on flexible supporting layer, which meets the minimum SPL requirement for human hearing, and achieves a lower THD over a wider continuous frequency band compared with the reported state-of-the-art works, and demonstrates good reliability and durability. Test results in an acoustics test adaptor show that at a driving voltage of 1 V ${}_{\mathbf {rms}}$ , greater than 52dB SPLs are obtained in the human audible range of 20Hz-20kHz, basically meeting the minimum auditory requirements for human beings. The applicable working frequency range for THD of this device spans the medium and high frequency band of 500 Hz-20 kHz. Compared with state-of-the-art reported works, it achieves a THD of $\le 5$ % over a significantly wider continuous frequency range. Moreover, this speaker produces no abnormal sound, shows no fracture after dropping from a height of 5meters, and maintain at least 90% of the SPLs after playing music continuously for 100 hours. The proposed center-bound type piezoelectric MEMS speaker with flexible supporting layer is expected to drive its own development and practical application by offering new perspectives and design concepts to researchers and enterprises. [2025-0116]

Conventionally designed piezoelectric micro-electro-mechanical systems (MEMS) speakers with thin-film-type, piston-type, and cantilever-type vibration membranes still adopt a Si supporting layer, which not only hinders the improvement of sound pressure level (SPL) but also lacks characterization of reliability. In this paper, we propose a fixed-end beam–cantilever piezoelectric MEMS speaker with a flexible supporting layer, achieving an SPL comparable to that of traditional three types of piezoelectric MEMS speakers with a Si supporting layer, and displaying good reliability. The measured results performed on encapsulated prototypes mounted to an acoustic test adaptor demonstrate that under a driving voltage of 1 V_rms, the SPL exceeds 51.6 dB in the human audible frequency range of 20 Hz–20 kHz, the total harmonic distortion (THD) remains below 3.4% above 430 Hz, satisfying the basic requirements for human auditory perception. Moreover, further experiments also prove its reliability by revealing no abnormal sound output, no fracture after being dropped from heights of 1 to 5 m, and the retention of over 92% SPL following 100 h of continuous music playback. This fixed-end beam–cantilever piezoelectric MEMS speakers with a flexible supporting layer provide researchers and enterprises with brand-new design ideas and a fresh perspective, which may potentially promote their development and practical application.

MEMS vector hydrophones are poised to become the core devices of miniaturized underwater acoustic sensing. However, existing MEMS vector hydrophones suffer from low sensitivity and shallow concave point depth, which hinders long-range detection. In this work, we present an axisymmetric bionic seal whisker–type piezoelectric MEMS vector hydrophone (ASWVH) that leverages bioinspired geometries and stress-concentration regions to amplify piezoelectric output, yielding enhanced directivity and high sensitivity. The optimal microstructure dimensions for ASWVH were determined using COMSOL 5.6 simulations. The biomimetic seal whisker structure not only ensures an operational frequency bandwidth of 20–2000 Hz but also expands the effective acoustic reception area, thereby further enhancing sensitivity. The unique wavy bionic sealing whisker shape provides high sensitivity, and the measured X-axis and Y-axis sensitivities are -171.7 dB and -173.2 dB@2 kHz (re. 1 V/μPa), respectively. Moreover, the device exhibits an exceptional “8”-shaped directivity pattern with concave point depth exceeding 40 dB in both channels, rendering it well-suited for high-precision passive underwater detection.