Compared with apodization, the piston-mode technique is a preferable solution to suppress the spurious transverse modes in surface acoustic wave (SAW) devices. This paper extends the technique to the SAW resonator (SAWR) strain sensors to achieve a high performance, that is, conquer some negative influence in the wireless strain sensing system caused by the spurious modes, such as low signal to noise ratio (SNR), high misreading rate and demodulation difficulty. The principle of piston-mode operation was presented and a modified expression was given for primary design of the piston-mode waveguide, which takes into account the anisotropy difference in different electrode regions. SAWRs based on the Al/ST-quartz with the conventional and two common piston-mode configurations were designed, simulated, fabricated and measured. The experiments to evaluate the wireless performance and strain sensitivity of the SAWR strain sensors with different electrode configurations were performed.

Wearable measurement of center of pressure (COP) coordinates is the key of obtaining the measurement of natural gait. Plantar pressure insole is the right sensing unit for plantar pressure monitoring for long-term outdoor measurements and the control of walking assisting exoskeleton robot. It’s necessary to study the configuration of pressure sensing cells. This study explored the sensing cell configuration for the plantar pressure insole. The data of plantar pressure of walking is collected for layout variants. The RMSE of COP coordinates estimations are used as the evaluation criteria. The RMSE of COP coordinates decreases from 8.00 to 3.20 mm as the amount of pressure sensing cells increases from 2 to 7. The size of pressure sensing cells contribute to reduce the RMSE of COP coordinates and 7 pressure sensing cells, with the size of 2.0–2.5 cm have the satisfying performance. Adding pressure sensing cell in the heel and hallux area increase the accuracy of estimating COP coordinates. Comparison results indicate that the configuration of 7 pressure sensing cells has a satisfying measurement performance.

Since surface acoustic waves (SAWs) are composed of multiple displacement components, their slowness curves sometimes exhibit a more complex shape rather than elliptical or hyperbolic. As a result, the parabolic approximation of 2-D coupling-of-modes (2-D COM) equations is invalid for analysis of waveguiding in such SAW devices. Thence, this paper develops a new general form of 2-D COM equations based on the basic 2-D wave equations of SAWs which contain two displacement components. The fundamentals of the equations were established and the procedures for determining 2-D COM parameters were presented in detail. The new equations were embedded in the partial differential equation (PDE) mode of COMSOL for the simulation of different types of SAWs, including Rayleigh and shear-horizontal (SH) SAWs on ST-quartz and 42°YX-LiTaO3 (42-LT) substrates, respectively. By comparing the calculated results with 1-D COM, parabolic 2-D COM, extended thin plate model, 3-D finite-element method (FEM) calculated results, and the measured result, the applicability of these equations was verified.

In digital holography (DH), the quality of the reconstructed images relies on the accuracy of the reconstruction distance. Existing autofocusing approaches primarily determine the reconstruction distance by evaluating the sharpness of the features in reconstructed images under different reconstruction distances. The maximum sharpness corresponds to the optimal reconstruction distance. However, the existing approaches often fail for diffuse samples and specular ones with no features. The main challenges are as follows: (1) The spatial features, including edge, contrast, and sparsity do not vary obviously by varying the reconstruction distance. (2) The spectral features do not vary obviously as well by varying the reconstruction distance. Therefore, we propose an autofocusing approach based on phase difference to tackle the above problems. The proposed approach consists of three steps: (1) introducing a phase difference into the measured sample as an artificial feature; (2) recording two holograms before and after the phase change and obtaining the phase difference by reconstruction; and (3) taking the phase difference image as the feature and determining the optimal reconstruction distance by using image sharpness evaluation algorithms. According to simulation and practical experiments, the proposed approach has successfully solved the autofocusing problem of the specular samples with no features and diffuse samples.

The high-pressure vortex tube is one of key equipment in the skid-mounted package liquefied CBM. The high pressure gas strong rotating flow in vortex tube is the key issues of energy separation. There are many problems that the current experimental methods for the strong high-pressure in three-dimensional rotating turbulent flow and heat transfer measurements. The flow field and temperature field structure characteristics in the high-pressure vortex tube are analyzed under different external pressure by numerical simulation model. The design of high-pressure vortex tube hot region should be focused on solving the problem of gas accumulation. This works provide guidance on the development of the high-pressure vortex tube of fluidified CBM.

The lateral distortion of a surface measuring Fizeau interferometer may cause distorted image features in the lateral direction, as well as the surface form error in the axial direction (which is a source of the retrace error). Traditional method for lateral distortion measurement requires a high-accuracy calibration plate featuring a grid pattern. Such a calibration plate is not always available, especially when the required accuracy of the grid pattern comes to the order of sub-micrometer or even nanometer level. To remove the dependence on the plate accuracy, we propose a self-calibration method for the measurement and correction of lateral distortion in Fizeau interferometer. The self-calibration technique may separate the lateral distortion and the geometric error of the calibration plate. This method is verified using a 108-mm-aperture Fizeau interferometer. The experiments show that the form measurement error of a surface tilted at approximately 5° and 16° can be reduced from 92 nm to 43 nm and from 251 nm to 144 nm (peak-to-valley value), respectively, after the distortion correction.