The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAWs) on bonded structures consisting of a quartz (Qz) thin plate and a Qz support substrate with different Euler angles were investigated theoretically. By using both an X-cut Qz thin plate and a Qz support substrate with optimal Euler angles, we obtained LLSAWs with a larger coupling factor, a smaller attenuation, and a lower temperature coefficient of frequency than those on a single Qz substrate. Furthermore, from the resonance properties simulated by the finite element method, the bonded structures were found to exhibit a large admittance ratio and a high quality factor, which could not be obtained when using a single Qz substrate; the bandwidth however was as small as 0.016-0.086%.
This paper deals with experimental results on detection of toluene dispersed in water by means of a new and simple plastic optical fiber (POF) sensor. Its sensing part consists of swelling polymer cladding layer such as high density polyethylene (HDPE) with slightly larger refractive index n 2 than that of poly(methyl methacrylate) (PMMA) core with n 1 . When is exposed to toluene dispersed in water, HDPE cladding layer causes swelling and the value of n 2 decreases quickly. Then the POF structure in the sensing part changes from leaky-type to guided-one and the output light intensity increases dramatically. By measuring this light intensity change, it becomes possible to detect toluene concentration. In addition, as compared with the popular evanescent-wave detection principle type, this sensor operation does not depend on the wavelength of light source. Therefore, we can use an inexpensive LED or LD in visible region. In experiment, detection of less than 1 wt% toluene in water was easily obtained with fast response about only 1 s. Furthermore, this sensor can detect pure toluene even for a small amount below 1 ml.
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