Abstract:  n recent years there has been a growing interest in using the Lamb wave devices to fabricate sensors applied to physical, chemical and biological fields. Because the sensitivity of the sensors is dependent on the shift of
the operation frequency induced by the measured physical quantity, the sensitivity of the sensors will increase if the oscillation frequencies increase. T herefore, many researches focused on the increase of the operation frequencies of
the devices, however, the fundamental frequencies of the devices cannot increase limitlessly due to the technical limitation for fabricating interdigital transducers ( IDT) . The propagation characteristics of the high order modes of
Lamb waves are studied here, and a new kind of oscillator using the high order modes Lamb wave excited by IDT is presented with which one can obtain a higher phase velocity and a higher oscillating frequency, and then sensitivity
will be greatly improved. Due to the dispersive and multi mode property of the Lamb wave, the fabrication of high frequency oscillators by using high order modes of the Lamb wave will be easier than the zero order mode Lamb
wave. To select the operating mode of the high mode Lamb wave oscillator, a high order mode selector is inserted between the Lamb wave delay line and the amplifier in the closed oscillating loop. The phase velocity of the
operating order modes Lamb wave is much higher than that of the zero order mode Lamb waves. Experimental measurements are performed on a 127   86 o rotated Y- cut, X propagating lithium niobate plate, with the ratio of the
plate thickness to the fundamental wavelength h/  = 0  94. By the measurement results of the dispersion curve of the Lamb wave, the relation between the wavelength and frequency can be calculated, which is used to determine the
operating frequency. A high order modes Lamb wave with the phase velocity 19 652m/ s is obtained in experiments, the oscillating frequency is 46   24 MHz, whereas the oscillation frequency of the oscillator using the a 0 mode of the
Lamb wave excited by the same IDT is about 8  75 MHz. Thus, the operation frequency, i. e. , the phase velocity, of the high order Lamb mode oscillator is 5.3 times higher than that of the a 0 mode. Therefore the high frequency
oscillator with operating frequency above UHF band can be fabricated much easier by this method, then the sensitivity of the sensor using the new oscillator can be increased greatly.