Research And Design Of SAW Temperature Sensor With Multilayer Structure

Surface acoustic wave (SAW) technology is a combination of acoustic, piezoelectricmaterials and microelectronics technologies. The sensors based on SAW technology has theadvantages of passive wireless, security and high stability, good sensitivity and have beenwidely used in the areas such as temperature real-time monitoring of electrical switchgearwith high-voltage.Compared with conventional SAW devices which has only a single substrate material,multilayer structure SAW devices are coated with different films on the base material, so itcan be targeted to improve some defects of the conventional SAW devices such as lowelectromechanical coupling coefficient, improves performance of the devices, and addsmany other features. Currently, multilayer structure SAW devices are primarily used forsignal processing in communication systems. This paper probes SAW application in thesensing field, studies its performance, then products. ZnO/quartz multilayer structure SAWtemperature sensor has been tested.The main content of this paper is divided into three parts:The first part is the study of SAW transmission characteristics of multilayer structuredevices. Combining with the laws of mechanics and electromagnetism and particle stressanalysis, the solving method for propagation velocity of SAW in piezoelectric material havebeen derived,and as a basis obtaining the state equation and its solving method whichdescribes the SAW propagation characteristics in multilayer structure devices. Then theexpression equation of surface effective permittivity, dispersion properties andelectromechanical coupling coefficient are all obtained using the theory above. At last, theaforementioned characteristics of ZnO/quartz structure SAW devices are calculated.The second part is the simulation and design for a multilayer structure SAWtemperature sensor. A modeling and simulation are conducted using Finite Element Method(FEM) software to research the device performance changing with the interdigital transducerstructure parameters on device performance. Then the traditional δ function model isimproved based on the dispersion characteristics of multilayer structure devices, andsimulate the multilayer structure SAW temperature sensor using the improved model. Finally,the prototype device has been tested,then the problem of the possible causes of the test have been analyzed.The third part is the study of composition of the passive wireless SAW temperaturesensing system, the operating principle of each part of the system and operating mechanismhave been researched.