This paper presents a novel and effective characterization method for giant piezoresistive properties of silicon nanowires by using the reference structures. This contrast detection approach investigates the influences of quantum size effect and surface defects effect on piezoresistive coefficients of silicon nanowires by direct comparison of the resistivity change ratio of silicon wires with nanoscale-to-microscale width under the same applied stress conditions. The characterization experiments based on four-point bending tensile test demonstrate that piezoresistive coefficient of small nanowidth silicon nanowire can be significantly increased to about five times higher levels than that of bulk silicon under the same impurity concentration, which indicates that the silicon nanowire can have giant piezoresistive effect. On the other hand, to solve the problem on nanowires pick-up, we proposed a nanowire piezoresistive detection approach, whose validity is confirmed by the dynamic LDV resonance test. Meanwhile, to investigate the influence of undercut arising from the wet chemical release process of the suspended silicon nanowire, a three-dimensional finite element simulation is also carried out for the fundamental resonant frequency using ANSYS software. The numerical and experimental results show that our piezoresistive detection is accurate and effective and the undercut should be carefully considered in the design of the high frequency resonator and mixer. The findings of this paper provide some useful references for the piezoresistive effect measurement and the piezoresistive pick-up in nanoelectromechanical system.

The dry bias of MEMS humidity sensor induced by solar radiation heating seriously affects the accuracy of the relative humidity (RH) measurement. To solve this problem, this paper presents a novel numerical analysis method for the error correction of RH based on computational fluid dynamics (CFD). Firstly, considering the solar radiation, the distribution of temperature field of MEMS humidity sensor is simulated from the ground to 32km altitude by using CFD soft under the boundary condition of fluid-solid coupled heat transfer. Secondly, the numerical analysis model of RH is put forward for solar radiation dry bias (SRDB) correction based on the working principle of the MEMS capacitive humidity sensor and the definition of RH. The results of numerical analysis show that the error of RH caused by solar radiation is nonlinearly increased with the altitude. Meanwhile the errors decrease with the reflectivity of sensor or of solder point increase. The simulation data also indicate that the SRDB can be reduced by improving the reflectivity of sensor or of solder point, adopting the substrate material with high thermal conductivity or choosing the suitable thickness of sensor. However, the SRDB should be corrected, for it still is more than 20% under the low atmospheric pressure. In this paper, the method based on fluid dynamics simulation provides a new way to correct the error of radiosonde MEMS humidity measurement caused by solar radiation heating.

Airborne cloud liquid water content (CLWC) sensors have been used in weather observation and weather modification for years. However, traditional CLWC sensors are relatively bulky and heavy. Additionally, it is inconvenient to use wind tunnel to calibrate traditional sensors. In order to meet the need of wind tunnel calibration tests, reduce the wind signal interference and reduce the cooling effect of high water content cloud, two new types of hot-wire water meter content sensors are designed in this paper. Using steady-state heat transfer theory, a finite element method is used to simulate temperature distribution of the new water content sensors, including the scenario in which cloud water droplets evaporates as colliding the sensors. In order to minimize sensor error, convection is also considered in the finite element model. Through the numerical analysis of the two new types of hot-wire water content sensors, it is concluded that the sensors designed in this work are able to reduce the wind interference error and extend the CLWC measurement range of the instrument.

A theoretical model based on the constitutive equations of piezoelectrics and magnetostrictor is introduced to discuss the magnetoelectric (ME) coupling in freebody bilayer containing magnetostrictive and piezoelectric phases. The ME coupling at low frequency of Ni0.8Zn0.2Fe2O4–PZT bilayer have been studied by using the model and the corresponding material parameters of individual phases. The results show that the ME voltage coefficients can increase to a maximum at a given volume fraction of piezoelectric phase. An approximately linear increase of the maximum has been obtained with strengthening interface coupling. Analysis shows that large magnetostriction, appropriate volume fraction and ideal interface coupling are key ingredients for obtaining excellent ME performance.