Abstract
A passive wireless impedance-loaded orthogonal frequency-coded (OFC) surface acoustic wave (SAW) sensor for wireless sensor networks was proposed in this paper. One of the chips on OFC SAW tag is connected to an external sensor, which could cause a phase shift in the time response of the corresponding part on the SAW device. The phase shift corresponds to the sensed quantity, which could be temperature, strain, vibration, pressure, etc. The OFC SAW tag is isolated by a proper package from the direct effect of the measurand on the device’s response which could avoid the multiple measurands coupling. The simultaneous work of multiple sensors is guaranteed by orthogonal frequency coding. By processing the response based on an extended matched filter algorithm, sensing information of the specific coded OFC device can be extracted from the superimposed response of multiple independent encoded sensors. Compared to previous methods, the proposed method can produce a more flexible passive (battery-free) wireless sensor suitable for large-scale wireless sensor networks. Simulation and experimental results demonstrate the effectiveness of the sensor.
Highlights
Wireless sensors could be used for structural health monitoring (SHM) systems which are desired on most of the aircraft for dynamic monitoring [1,2,3]
The device identification is accomplished by orthogonal frequency coding, and the measurand is sensed by an external sensor connected to the reflectors on the surface acoustic wave (SAW) device
Simulation results and experimental results show that the presented impedance-loaded orthogonal frequency-coded (OFC) SAW sensor could provide a large capacity for passive wireless sensor networks while avoiding the multiple measurand coupling effects on the SAW device
Summary
Wireless sensors could be used for structural health monitoring (SHM) systems which are desired on most of the aircraft for dynamic monitoring [1,2,3]. In the impedance-loaded SAW sensors, the SAW device is used as a transponder for device identification, while the measurand is sensed by an external sensor. To expand the capacity of SAW sensors, an OFC SAW sensor based on the principle of orthogonal frequency-coded division is proposed in [28,29,30]. The device identification is accomplished by orthogonal frequency coding, and the measurand is sensed by an external sensor connected to the reflectors on the SAW device. Simulation results and experimental results show that the presented impedance-loaded OFC SAW sensor could provide a large capacity for passive wireless sensor networks while avoiding the multiple measurand coupling effects on the SAW device
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