Sensor Tag Development
In addition to developing physical, chemical, and biological sensors based on SAW device technology, ASR&D is also developing individually coded SAW devices suited for use as wireless interface devices to external passive impedance varying or voltage producing sensors.
In this application, the coded SAW device can act as an interface device alone, allowing sensors that would normally have been used in a wired configuration (such as thermistors) to be individually identified and read wirelessly. If desired, the SAW device can combine both a tag interface function and a sensing function, for example measuring temperature in the SAW device and reading an external sensor as well. The goal of this work is elimination of the wiring harness currently required for numerous sensors in airframes and test facilities.
ASR&D has demonstrated that both coded and uncoded SAW devices can be used to wirelessly read external devices that respond to changes in their environment passively (i.e. without the need for an applied voltage, or battery). Devices tested include switches, thermistors, strain guages, and unpowered acoustic emission sensors. Devices such as thermistors, which are traditionally read in a wired configuration such as a Wheatstone Bridge, actually change resistance in response to changes in device temperature. While measuring these devices would normally require an applied voltage, they can in fact be read wirelessly and completely without any local power by attaching the thermistor to a SAW device. As temperature changes, the varying impedance of the thermistor modifies the RF signal that is reflected from the SAW device, and these modifications are directly related to the temperature.
Under a NASA Phase I SBIR (NNX09CE49P), ASR&D developed and wirelessly tested conventional single frequency RFID coded reflective delay line tags, dispersive RFID coded reflective delay line tags using both full and half pulse compression in the tag device, and simple uncoded and coded coded reflective differential delay line tags. All the tags tested demonstrated changes in wireless tag performance in response to changes in attached devices and sensors. Changes in device response of a few dB to over 35 dB were measured for specific sensor-tag combinations. A more detailed description of ASR&D's work under this project can be found in the NASA report section of this website, or by clicking here.