| Summary: | 碩士 === 國立勤益科技大學 === 機械工程系 === 101 === The energyof propagationof surface acoustic wave (SAW) is concentrated within the surface of substrates and the energy lossof SAW is less than the bulk wave.The properties of propagation depend on the material of substrates and boundary condi-tion.In this study, we detect the surfactants by SAW devices. The composition of the SAW devices were piezoelectric substrates sputtered with interdigital transducers and then surface acoustic waves were excited. In the propagation path, we designed metal and free surface, the loading liquid with various effect of acoustic-electricwould lead to affect the properties of SAW, we can identifythe loading liquid by detect the change of SAW.
First, we choice the material of 41°YX LiNbO3 as substrate, which can be ex-cited SH SAW and have the characters of higher Electromechanical coupling factor, faster phase velocity and stable temperature coefficient. Using the technology of MEMS, we design resonators with split IDT and the central frequency is 59.9M Hz. The split IDT have lower insertion loss than normal IDT. One group of resonators deposit Al thin film on sensing region to exclude electrical characteristics of liquid to achieve accurately detect the types of surfactants. In this study, we measure the prop-erties of surfactants (SNDS, SDBS, SLS,TritonX-100, ..etc.) using immersion mea-surements, the sensor immersed in the liquid under test can effectively rule out the liquid quality and environmental impact of interfering factors on the velocity, and real-time monitoring of changes.
Experimental results show split type SAW sensor refers to a center frequency of 60.4947MHz, compare to the theoretical calculation approximately 1% error. In the free surface propagation path, the order of attenuation of energy is wa-ter&;lt;SLS&;lt;TritonX-100&;lt;DN-60. In terms of the metal-film surface propagation path, the order of attenuation of energy is water&;lt; TritonX-100&;lt; SLS&;lt; DN-60. Therefore, we can identify the surfactants by detect the attenuation of energy.
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