Feng-mei Zhou

Influence of surface conductivity on sensitivity of acoustic wave gas sensors based on multilayered structures

The influences of the surface conductivity on the velocity of an acoustic wave (AW) in a multilayered material are studied theoretically with the transfer matrix method and the conductivity sensitivity of the AW sensor is presented. It is found that the velocity of the AW increases with decreasing surface conductivity and vice versa. The result is used to explain the abnormal response of AW sensors, in which the central frequencies of AW sensors increase after they sorb the detected gases. Meanwhile, the conductivity sensitivity is found to be related to the dielectric constants of the multilayered material and the electromechanical coupling coefficient of the sensor. Finally, the sensitivities of AW sensors based on multilayered structures are optimized by considering the influences of the surface conductivities of the sensors with different initial conductivities and thicknesses of the sensitive layers.

High piezoelectricity of Pb(Zr,Ti)O3-based ternary compound thin films on silicon substrates

Pb(Zr,Ti)O3 (PZT)-based ternary compound thin films, 0.06PMnN-0.94PZT(50/50) (PMnN-PZT), are deposited on Si-based heterostructures by rf magnetron sputtering system. The intrinsic PZT(50/50) thin films are also deposited on the same kind of substrates for comparison. The PMnN-PZT thin films show the similar polycrystalline structures as those of PZT with highly (111) oriented perovskite phase. The PMnN-PZT thin films show excellent piezoelectricity and ferroelectricity which are distinctly better than those of PZT thin films prepared with the same deposition conditions. Besides, the cantilevers of PMnN-PZT thin films on the heterostructure substrates also exhibit higher sensitivities than the PZT thin film cantilevers.

Experimental study of Love-wave immunosensors based on ZnO/LiTaO3 structures

Experimental study of Love-mode immunosensors based on structures of ZnO/36 degrees YX-LiTaO3 is presented, in which the ZnO films with c-axis (002) orientation have been successfully grown on the 36 degrees YX-LiTaO3 substrates by RF magnetron sputtering technique. Then the Love-mode immunosensors based on the ZnO/36 degrees YX-LiTaO3 structures and monitoring antibody-antigen immunoreactions in aqueous solutions in real time are fabricated. The experimental results show that the optimal thickness of ZnO layers is about 1.20 microm in the structures deposited on 36 degrees YX-LiTaO3 substrates, which is much less than that of SiO2 overlayers about 6 microm. The antibody-antigen immunoreaction experiments also show that the frequency shifts of the sensors with 1.33 microm ZnO films are proportional to the concentration of antigen in solution as the concentration range less than 100 microg/ml.

Study on sensitivities of Love-wave immunosensors based on SiO2/36°YX-LiTaO3 and ZnO/36°YX-LiTaO3 structures

Love-wave immunosensors based on SiO2/36°YX-LiTaO3 or ZnO/36°YX-LiTaO3 structures coated by special sensitive films have been fabricated and studied experimentally. A theoretical model using the partial wave theory of elastic waves propagating in three-layer structures covered by liquid loads is built up to calculate the sensitivities. To determine the elastic constants of the guiding layers, the phase velocities of the corresponding Love-wave devices are measured by a network analyzer, and the theoretical fitting of the experimental data are carried out. Then the relationships between the sensitivities of the Love-wave immunosensors and normalized thicknesses of the guiding layers are obtained, and there are optimized thicknesses of the guiding layers for getting maximum sensitivities. The experimental measurements and numerical calculations of the sensitivities of the Love-wave immunosensors show that both results are essentially consistent with each other.

Study of Love-mode immunosensors based on ZnO/36°YX-LiTaO 3 structures

Love-mode immunosensors based on ZnO/36degYX-LiTaO3 structures are studied. The ZnO films are grown on the 36degYX-LiTaO3 substrates by RF magnetron sputtering technique. The crystalline structures of the ZnO films are investigated by the X-ray diffraction (XRD) analysis, which show that the highly orientated (002) films are obtained. Then the Love-mode sensors are fabricated for monitoring antibody-antigen immunoreactions in aqueous solutions in real time. The results show that the Love-wave sensors based on ZnO/36degYX-LiTaO3 structures have higher mass sensitivity than those with the similar structures, such as SiO2/36degYX-LiTaO3 structure sensors.

Subharmonic vibrations in plates excited by high-intensive ultrasonic pulses

In this paper, the experimental and theoretical studies on the excitations of the subharmonic vibration in metal plates by the intensive ultrasonic pulses injected via an ultrasonic horn are presented. A series of experiments is performed to study the subharmonic vibration behaviors of rectangular stainless steel plates. The experimental results show that the excitations of the subharmonics change remarkably with different materials, sizes and fix (boundary) conditions of the plates, as well as the preload forces between the horn and plate. Meanwhile, a vibro-impact dynamical model is put forward to explore the generation mechanism of the subharmonics in the plates. According to the model, the intermittent contact between horn and plates is the reason for the generation of subharmonic vibration in plates. The numerical results are in agreement with the subharmonic phenomena observed in the experiments.

Experimental study on Love-wave sensors with SiO 2 /LiTaO 3 structures

In this paper, a kind of Love wave sensors with SiO2/36degYX LiTaO3 structures for monitoring antibody-antigen immunoreactions in aqueous solutions in real time is presented. In this study, the devices with low insertion losses are achieved when the devices are in direct contact with the solutions. In the immunosensing measurements, a goat anti human-immunoglobulin G (HigG) is immobilized on the device surface as a receptor layer for detecting HigG in buffer solution. The results show that the structures have high sensitivity, which demonstrate that the sensors are very effective for biological and chemical sensing applications in liquid environments.