In this letter, we present a sapphire direct bonding method using plasma surface activation, hydrophilic pre-bonding, and high temperature annealing. Through the combination of sapphire inductively coupled plasma etching and the direct bonding process, a vacuum-sealed cavity employable for high temperature applications is achieved. Cross-sectional scanning electron microscopy (SEM) research of the bonding interface indicates that the two sapphire pieces are well bonded and the cavity structure stays intact. Moreover, the tensile testing shows that the bonding strength of the bonding interface is in excess of 7.2 MPa. The advantage of sapphire direct bonding is that it is free from the various problems caused by the mismatch in the coefficients of thermal expansion between different materials. Therefore, the bonded vacuum-sealed cavity can be potentially further developed into an all-sapphire pressure sensor for high temperature applications.

This study presents a highly sensitive wireless passive flexible pressure sensor. The sensor employs an ionic film as the dielectric layer, utilizes a spiral coil as the antenna for transmitting and receiving signals of the sensor, and adopts a sandwich process to complete the fabrication of the sensor. This study validates through circuit analysis and simulation that the sensor can be used for wireless passive detection of pressure information. Firstly, the performance of the ionic film is examined. The sensor fabricated with the ionic film has high sensitivity (38.74 N ^-1 ), fast response time (100 ms), and high stability. This study also tests the wireless transmission performance between the sensor and the antenna. The test results indicate that the sensor can achieve wireless signal detection within a range of 13 mm. The pressure sensitivity of the sensor in the range of 0 - 0.5 N is 394.94 MHz/N. When the applied pressure increases from 0.5 N to 10 N, the resonant frequency of the sensor decreases from 210 MHz to 160 MHz, and the pressure sensitivity is 4.15 MHz/N. The sensor can realize palm bending detection, breathing, and voice recognition, and has extensive application prospects in the fields of human-computer interaction and wearables.

The behavior of the magnetic field sensitivity of nitrogen-vacancy (NV) centers as a function of microwave power and the inhomogeneous distribution of MW fields was systematically studied. An optimal structure for exciting spin structures by MW signals was designed using two parallel loop antennas. The volume of the homogeneous regions was approximately 42 mm³, and the associated diameter of the diamond reached up to 5.2 mm with 10¹⁶ NV sensors. Based on this structure, the detection contrast and voltage fluctuation of an optically detected magnetic resonance (ODMR) signal were optimized, and the sensitivity was improved to 5 nT/√Hz. In addition, a pulse sequence was presented to fully eliminate the MW broadening. The magnetic field sensitivity was improved by approximately one order of magnitude as the π-pulse duration was increased to its coherence time. This offers a useful way to improve the sensitivity of spin-based sensors.

Large-area, highly uniform microwave field radiation and efficient excitation of fluorescence are the key to achieving high sensitivity sensing of the NV (nitrogen-vacancy) magnetometer. In this paper, we report a compact multipass-laser-beam antenna for NV ensemble color centers sensing. The antenna not only provides a tridimensional uniform magnetic field, but also can be used for efficient excitation of the NV fluorescence. The optimal size of the antenna and the angle of laser incidence are determined by the multi-physics field simulation software COMSOL. For an equivalent excitation power, the designed structure increases the path length of the excitation beam by up to three orders of magnitude, up to the level of m, compared to the conventional direct beam mode. Finally, this method increased the sensitivity by a factor of 60 realized a magnetic field sensitivity of 2.8 nT/√Hz in the range of 10–100 Hz. This work provides an experimental method for the design of integrated NV magnetometers.