| In this paper new kinds of Y-type and S-type dual-path mass-loading sensor devices fabricated on 128?rotated Y cut X propagating LiNbO3 substrate are reported.There are one input IDT and two output IDTs in these devices. SAW excitated by input IDT is divided axisymmetrily (Y type) or centrosymmetrily (S type) into two pathes and detected by their output IDTs.There is a mass loading area located accurately in each acoustic path and fabricated by photolithography technology in Y type and S type mass loading sensor devices.As the characteristics of SAW sensor are greatly influenced by temperature,these sensors have one acoustic path for reference another acoustic path for measurement in order to reduce the influence of temperature.In this paper 5 function modek equivalent circuit model and P matrix representation of IDT are expounded. The principle of energy transfer efficiency of energy transfer and frequency response of combinational acoustic pathes are also expounded.The principles structure types and developments of SAW sensors are introduced as well as applications in physical and chemical area. In the meantime , the commonly used piezoeletric materials are also introduced.Design principles and rules of Y type and S type sensors including input and output IDTs multistrip coupler and mass loading area are introduced in detail.Their operating frequency , bandwidth and insertion loss are 122MHz . 2.75MHz and 14dB respectively.Frequency responses of these sensors are simulated with MATLAB and fabrication processes of these sensors are also described summarily.Design and realization of mesurement system for these sensors are introduced. Delay line oscillator is composed of broadband amprifer adjustable attenuator and SAW sensor device.After output signal of delay line oscillator is smoothed,it mixes with 109MHz local oscillation signal.Its differential frequency signal is smoothed by low-pass filter trimmed by shaping circuit and processed by digital processing circuit. In its digital processing circuit, clock chip with high precision and temperature compensation is uesd as reference clock.High frequency reversible counter is used to count trimmed impulse signal forward or backward and two pathes SAW signals are selected timely by multichannel selector.Finally,its frequency shift is displayed by LED,which is caused by mass loading effect. Accuracy of the measurement system is verified by standard signal sources.Frequency tracking error does not reach 50Hz.The measurement system has merits of visual display and high accuracy,which is an ideal measurement system for dual-path SAW mass sensor.Y type and S type dual-path SAW mass sensors have been tested and analysed in detail.Their frequency domain characteristics and time domain characteristics have been tested under non-oscillatory mode.Transmission characteristics of Y type S type and "-" type SAW mass sensors are derived by P matrix representation. Primary delay signal triple reflection signal and quintuple reflection signal of these sensor devices have been analysed in detail. Results show that triple reflection signal and quintuple reflection signal of Ytype and S type are less 12dB, 16.67 dB and 11.8 dB, 17.3 dB than that of"-'"type SAW mass sensor device.Experiment results show that insertion loss (about 14dB)of the devices in center frequency is close to the theoretical value (about 16dB) developed by P matrix representation.Sensing characteristics of Y type and S type SAW mass sensors have been also tested and analysed in detail. Ethanol and pure water mixed solution containning trace NaCl is titrated into mass loading area of Y type and S type SAW mass sensors devices to detect their mass loading sensitivities. Their mass loading sensitivities are about 29.67ppm.cm2/ μ g (Y type) and 31.15ppm.cm2/μ g (S type),which are colse to the theoretical value 38.93ppm.cm2/μ g. Operating frequency as a function of temperature of these sensors has been tested. Their temperature coffcient of single acoustic path and differential temperat...
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