Ultrasonic transducers are vital components for transmitting and receiving sound waves, which are customized to specific applications based on their operating frequencies.Small-sized high-frequency ultrasonic transducers have gained considerable attention and adoption in medical ultrasound imaging and small pipe flow testing. However, the significant impact of attenuation on high-frequency ultrasound restricts detection distance and degrades the signal-to-noise ratio. Additionally, thin-film high-frequency ultrasound transducers exhibit low output sound pressure, due to their low resonance displacement. In this study, we present an innovative approach to address these challenges through the design of an integrated small-size honeycomb-type top, two-electrode aluminum nitride (AIN)-based high-frequency ultrasonic transducer. A comprehensive investigation of the relationship between transducer size, sensitivity, and transmitted sound pressure levels is conducted. Leveraging microelectromechanical systems (MEMS) micro-nano-machining technology, we fabricate a 14 x 13 array with a unit diameter of 50 mu m, and a matching circuit is employed to enhance the transducer's amplitude. Experimental results demonstrate remarkable transmit sound pressure levels (SPL) exceeding 210 dB (re:1 mu Pa/V) at a distance of 2 cm, with a maximum transmit SPL of 233 dB, and the receive sensitivity surpasses - 175 dB (re:1 V/mu Pa) and, at the 5 MHz resonance, the sensitivity reaches - 143 dB (re:1 V/mu Pa). Moreover, the transmit and receive linearity values demonstrate 99% and 98%, respectively. Our findings highlight the significant potential of the proposed high-frequency ultrasonic transducer for a diverse range of applications.

Ultrasound is widely used in industry and the agricultural, biomedical, military, and other fields. As key components in ultrasonic applications, the characteristic parameters of ultrasonic transducers fundamentally determine the performance of ultrasonic systems. High-frequency ultrasonic transducers are small in size and require high precision, which puts forward higher requirements for sensor design, material selection, and processing methods. In this paper, a three-dimensional model of a high-frequency piezoelectric micromachined ultrasonic transducer (PMUT) is established based on the finite element method (FEM). This 3D model consists of a substrate, a silicon device layer, and a molybdenum-aluminum nitride-molybdenum (Mo-AlN-Mo) sandwich piezoelectric layer. The effect of the shape of the transducer’s vibrating membrane on the transmission performance was studied. Through a discussion of the parametric scanning of the key dimensions of the diaphragms of the three structures, it was concluded that the fundamental resonance frequency of the hexagonal diaphragm was higher than that of the circle and the square under the same size. Compared with the circular diaphragm, the sensitivity of the square diaphragm increased by 8.5%, and the sensitivity of the hexagonal diaphragm increased by 10.7%. The maximum emission sound-pressure level of the hexagonal diaphragm was 6.6 times higher than that of the circular diaphragm. The finite element results show that the hexagonal diaphragm design has great advantages for improving the transmission performance of the high-frequency PMUT.

For the development of supercapacitors, electrode materials with the advantages of simple synthesis and high specific capacitance are one of the very important factors. Herein, we synthesized g-C N and NiCo O by thermal polymerization method and hydrothermal method, respectively, and finally synthesized NiCo O /g-C N nanomaterials by mixing, grinding, and calcining g-C N and NiCo O . NiCo O /g-C N nanomaterials are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The microscopic morphology, lattice structure, and element distribution of NiCo O /g-C N nanomaterials were characterized by scanning electron microscopy (SEM), transmission electron microscopy, high resoultion transmission electron microscopy, and mapping methods. The electrochemical performance and cycle stability of NiCo O /g-C N were tested in a 6 M KOH aqueous solution as electrolyte under a three-electrode system. Due to the physical mixing structure of g-C N and NiCo O nanomaterials, the electrochemical energy storage performance of NiCo O /g-C N supercapacitor electrodes is better than that of NiCo O supercapacitor electrodes. At a current density of 1 A/g, the capacitances of NiCo O and NiCo O /g-C N are 98.86 and 1,127.71 F/g, respectively. At a current density of 10 A/g, the capacitance of NiCo O /g-C N supercapacitor electrode maintains 70.5% after 3,000 cycles. NiCo O /g-C N electrode has excellent electrochemical performance, which may be due to the formation of physical mixing between NiCo O and g-C N , which has broad application prospects. This research is of great importance for the development of materials in high-performance energy storage devices, catalysis, sensors, and other applications.

For the development of supercapacitors, electrode materials with the advantages of simple synthesis and high specific capacitance are one of the very important factors. Herein, we synthesized g-C3N4 and NiCo2O4 by thermal polymerization method and hydrothermal method, respectively, and finally synthesized NiCo2O4/g-C3N4 nanomaterials by mixing, grinding, and calcining g-C3N4 and NiCo2O4. NiCo2O4/g-C3N4 nanomaterials are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The microscopic morphology, lattice structure, and element distribution of NiCo2O4/g-C3N4 nanomaterials were characterized by scanning electron microscopy (SEM), transmission electron microscopy, high resoultion transmission electron microscopy, and mapping methods. The electrochemical performance and cycle stability of NiCo2O4/g-C3N4 were tested in a 6 M KOH aqueous solution as electrolyte under a three-electrode system. Due to the physical mixing structure of g-C3N4 and NiCo2O4 nanomaterials, the electrochemical energy storage performance of NiCo2O4/g-C3N4 supercapacitor electrodes is better than that of NiCo2O4 supercapacitor electrodes. At a current density of 1 A/g, the capacitances of NiCo2O4 and NiCo2O4/g-C3N4 are 98.86 and 1,127.71 F/g, respectively. At a current density of 10 A/g, the capacitance of NiCo2O4/g-C3N4 supercapacitor electrode maintains 70.5% after 3,000 cycles. NiCo2O4/g-C3N4 electrode has excellent electrochemical performance, which may be due to the formation of physical mixing between NiCo2O4 and g-C3N4, which has broad application prospects. This research is of great importance for the development of materials in high-performance energy storage devices, catalysis, sensors, and other applications.

A piezoelectric micromachined ultrasonic transducer (PMUT) is a microelectromechanical system (MEMS) device that can transmit and receive ultrasonic waves. Given its advantages of high-frequency ultrasound with good directionality and high resolution, PMUT can be used in application scenarios with low power supply, such as fingerprint recognition, nondestructive testing, and medical diagnosis. Here, a PMUT based on an aluminum nitride thin-film material is designed and fabricated. First, the eigenfrequencies of the PMUT are studied with multiphysics coupling simulation software, and the relationship between eigenfrequencies and vibration layer parameters is determined. The transmission performance of the PMUT is obtained via simulation. The PMUT device is fabricated in accordance with the designed simple MEMS processing process. The topography of the PMUT vibration layer is determined via scanning electron microscopy, and the resonant frequency of the PMUT device is 7.43 MHz. The electromechanical coupling coefficient is 2.21% via an LCR tester.

Since black silicon was discovered by coincidence, the special material was explored for many amazing material characteristics in optical, surface topography, and so on. Because of the material property, black silicon is applied in many spheres of a photodetector, photovoltaic cell, photo-electrocatalysis, antibacterial surfaces, and sensors. With the development of fabrication technology, black silicon has expanded in more and more applications and has become a research hotspot. Herein, this review systematically summarizes the fabricating method of black silicon, including nanosecond or femtosecond laser irradiation, metal-assisted chemical etching (MACE), reactive ion etching (RIE), wet chemical etching, electrochemical method, and plasma immersion ion implantation (PIII) methods. In addition, this review focuses on the progress in multiple black silicon applications in the past 10 years. Finally, the prospect of black silicon fabricating and various applications are outlined.