Study of multi-functional surface acoustic wave sensor using Langmuir-Blodgett (LB) method

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A surface acoustic wave(SAW) sensor and its system for measuring the environment are presented. SAW devices have been widely used as a chemical and physical sensor for measuring the environment. In general most of the SAW device using as the sensor is coated with a thin film that capable of interaction with the chemical of interest through physical and chemical absorption. Sensitivity, response time, and reproducibility of the sensor are closely related with the characteristics of the sensing film. Therefore, the selective coating film is very important for a stability and reproducibility of the SAW sensor. There are numerous methods to coat a selective film, such as air brushing, dip cast, and spin coating of the SAW devices with good reproducibility.In this paper, first the SAW sensor incorporating an ultra thin selective film is presented. Ultra thin organic films are currently gaining interest in many areas such as integrated optics, sensors, and nano technology. The ultra thin fil … More ms were made by both self-assembled(SA) method and by Langmuir-Blodgett(LB) method. SAW delay lines were fabricated on a 128 Y cut X propagating LiNbO3 substrate and the propagation path was coated with the selective polymer deposited by these transfer technique. The polystyrene sulfonic acid sodium was used as an SA film material and the phosphatidylethanolamine was used as a LB film material. Due to sorption of molecules, the density, permittivity and electrical conductivity of these selective film change. The effects caused to reduce the velocity of the SAW Experimental results showed that the SAW velocity change was quite linear in proportion to the concentration on organic gases. Rapid and totally reversible responses were obtained by using the thin monolayer film. Moreover, it is shown that the thin film is suitable to obtain good linearity, high sensitivity and rapid response.Moreover, a new functional sensor also has been designed by using reflecting delay line. A reflecting SH-SAW delay line was constructed on a 36 YX LiTaO_3 substrate and the right angle(90-degree) edge has been used to reflect the SAW. Six-channel reflecting delay lines have been fabricated on one substrate. Each channel has a different length and the responses are obtained in time domain. Both the phase and amplitude of the reflected SAW on the each delay line were measured as a sensor response.Several experiments were performed to verify the performances of the edge reflection sensor. The basic characteristics of the reflecting SAW sensor were obtained by measuring the amplitude and phase of reflected wave when the SH-SAW is incident to a perpendicular corner. The obtained results showed that the reflecting SH-SAW sensor was very effective for sensing the gas and liquid phase.Wireless systems are also suggested for the effective operation of the reflecting SH-SAW sensor. The electronic measurement system for accurately measuring the phase characteristics of a reflected wave from the multi-channel sensor is proposed. In particular, it is shown that the wireless sensing system is very suitable for remote sensing. Finally it will be shown some applications of the wireless SH-SAW sensors on the measurement of the conductivity and viscosity of sample liquids. Less