Lin Wei, Fan Li, Gan Changming, Xu Boling, Zhu Zhemin
State Key Lab of Modern Acoustics and Institute Acoustic, Nanjing University, Nanjing 210093, China.
Ultrasonics. 2006 Dec 22;44 Suppl 1:e911-5. doi: 10.1016/j.ultras.2006.05.038. Epub 2006 Jun 5.
The dispersive characteristics of higher order mode Lamb waves (HOMLW) excited by interdigital transducers (IDT) are measured and analyzed, which are necessary for designing micro-sensor in ultrahigh frequency (UHF). A measurement system is set up, in which dispersive characteristics of HOMLW are obtained by the method of transform between frequency and time domains. The characteristics of amplitude-frequency and phase-frequency of Lamb wave are auto-measured by the system. By IFFT, the pulse response of the IDT device was obtained. Different modes were separated in time domain and dispersive curve of each mode is calculated by FFT. The best mode is chosen to design the micro-sensor in UHF. The phase velocity of HOMLW is greater than the surface wave (SAW) velocity and an oscillator in higher frequency can be made, so the absolute sensitivity of micro-sensor can be increased. In this paper, the dispersive characteristics of HOMLW excited by an IDT in a 127.86 degrees rotated Y-cut, X propagating lithium niobate plate is analyzed. An oscillator using a(13) mode is made, the phase velocity of which is measured about 19,652 m/s when h/lambda=0.94 (h=plate thickness, lambda=wavelength).
对由叉指换能器（IDT）激发的高阶模式兰姆波（HOMLW）的色散特性进行了测量和分析，这对于在超高频（UHF）设计微传感器是必要的。搭建了一个测量系统，通过频域与时域变换的方法获得HOMLW的色散特性。该系统可自动测量兰姆波的幅频和相频特性。通过快速傅里叶逆变换（IFFT）得到IDT器件的脉冲响应。在时域中分离出不同模式，并通过快速傅里叶变换（FFT）计算出每种模式的色散曲线。选择最佳模式来设计超高频微传感器。HOMLW的相速度大于表面波（SAW）速度，因此可以制作更高频率的振荡器，从而提高微传感器的绝对灵敏度。本文分析了在127.86度旋转Y切、X传播的铌酸锂板中由IDT激发的HOMLW的色散特性。制作了一个使用a(13)模式的振荡器，当h/λ = 0.94（h = 板厚，λ = 波长）时，其相速度测量值约为19,652 m/s。
