Tham khảo tài liệu 'microsensors, mems and smart devices - gardner varadhan and awadelkarim part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ACOUSTIC WAVES 313 Figure Wave generation on Love wave mode devices The basic principle behind the generation of the waves is quite similar to that presented in the description of an SH-SAW sensor. The only difference would be the fact that the Love wave mode would be the same SH-SAW mode propagating in a layer that was deposited on top of the IDTs. This layer helps to propagate and guide the horizontally polarised waves that were originally excited by the IDTs deposited at the interface between the guiding layer and the piezoelectric materia beneath Du et al. 1996 . The particle displacements of this wave would be transverse to the wave-propagation direction that is parallel to the plane of the surface-guiding layer. The frequency of operation is determined by the IDT finger-spacing and the shear wave velocity in the guiding layer. These SAW devices have shown considerable promise in their application as microsensors in liquid media Haueis et al. 1994 Hoummady et al. 1991 . In general the Love wave is sensitive to the conductivity and permittivity of the adjacent liquid or solid medium Kondoh and Shiokawa 1995 . The IDTs generate waves 314 INTRODUCTION TO SAW DEVICES that are coupled into the guiding layer and then propagate in the waveguide at angles to the surface. These waves reflect between the waveguide which is usually deposited from a material whose density would be lower than that of the material underneath surfaces as they travel in the guide above the IDTs. The frequency of operation is determined by the thickness of the guide and the IDT finger-spacing Toumois and Lardat 1969 . Love wave devices are mainly used in liquid-sensing and offer the advantage of using the same surface of the device as the sensing active area. In this manner the loading is directly on top of the IDTs but the IDTs can be isolated from the sensing medium that could as stated previously negatively affect the performance of the device Du et al. 1996 . It is again important that
