Abstract
A new wireless and passive surface acoustic wave (SAW)-based chemical sensor for organophosphorous compound (OC) detection is presented. A 434 MHz reflective delay line configuration composed by single phase unidirectional transducers (SPUDTs) and three shorted reflectors was fabricated on YZ LiNbO3 piezoelectric substrate as the sensor element. A thin fluoroalcoholpolysiloxane (SXFA) film acted as the sensitive interface deposited onto the SAW propagation path between the second and last reflectors of the SAW device. The first reflector was used for the temperature compensation utilizing the difference method. The adsorption between the SXFA and OC molecules modulates the SAW propagation, especially for the time delay of the SAW, hence, the phase shifts of the reflection peaks from the corresponding reflectors can be used to characterize the target OC. Prior to the sensor fabrication, the coupling of modes (COM) and perturbation theory were utilized to predict the SAW device performance and the gas adsorption. Referring to a frequency-modulated continuous wave (FMCW)-based reader unit, the developed SAW chemical sensor was wirelessly characterized in gas exposure experiments for dimethylmethylphosphonate (DMMP) detection. Sensor performance parameters such as phase sensitivity, repeatability, linearity, and temperature compensation were evaluated experimentally.
Highlights
Chemical sensors with high sensitivity and fast response for organophosphorous compound (OC) detection in real time are necessary for responding to the threats of terrorism and environmental pollution
Typical surface acoustic wave (SAW)-based chemical sensor systems are composed of a differential SAW oscillator array and a chemical interface coated onto the SAW propagation path of the sensing SAW device
Wang et al proposed some passive SAW-based sensors for wirelessly sensing some toxic or harmful gases like CO2, NO2, and some other volatile organic compounds, where the phase signal from the reflectors of the SAW reflective delay line configuration induced by the gas adsorption between the sensitive interface and target gas was picked for gas sensing
Summary
Chemical sensors with high sensitivity and fast response for organophosphorous compound (OC) detection in real time are necessary for responding to the threats of terrorism and environmental pollution. Wang et al proposed some passive SAW-based sensors for wirelessly sensing some toxic or harmful gases like CO2, NO2, and some other volatile organic compounds, where the phase signal from the reflectors of the SAW reflective delay line configuration induced by the gas adsorption between the sensitive interface and target gas was picked for gas sensing. A wireless and passive SAW chemical sensor system was developed for OC sensing referring to a frequency-modulated continuous wave (FMCW)-based reader unit. Target OC concentrations can be extracted by evaluating the differential phase signals, Φsensor, as Φsensor = 2 ˆπf (∆τ32 ́ w ∆τ21), where f is the operation sensor frequency, ∆τ32 and ∆τ21 are the measured changes in time delays among the three reflection peaks from the peaks including the information of environmental temperature and target species concentration, and w is the ratio of the second-to-third reflector distance to the first-to-second reflector distance [13]. Combining the detection results of the phase detection module, the phases of the three reflected signals could be acquired and determined, respectively, and sent to the model building part, which is designed to determine the curve of the relation between phase shift and temperature and gas adsorption [24]
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