A Federal Aviation Administration (FAA) funded research program was performed to develop different technologies to improve the intelligence and reliability of aircraft electrical wiring and interconnector systems. One of the developed technologies is referred to as the SMART (Status and Motion Activated Radiofrequency Tag) sensor. The SMART sensor concept is based on a reversibly deactivated radio frequency identification (RFID) tag achieved through the addition of an electrical by-pass to the tag circuitry as shown in Figure 1. Regardless of the RFID tag design (examples in Figure 1 operate at 902 and 13.56 MHz), as long as the electrical by-pass remains intact and electrically closed, the RFID tag is deactivated and the information stored in the integrated circuit (IC) cannot be read. When the by-pass is removed/opened by a physical, thermal, electrical or chemical event/change (depending on the component incorporated into the by-pass), the RFID tag becomes readable (displays type/location of event) until it is replaced during the indicated maintenance action.
The SMART sensor concept allows one to continuously monitor aircraft wiring for specific detrimental events/changes that occurred during flight or landing without the need for power, algorithms or complex data acquisition systems. Since only the sensor(s) that has been activated by a specific event/change can be detected, a simple, hand-held RFID reader or cell phone can be used to read the activated sensor even though there may be thousands of other deactivated SMART sensors located in close proximity. Any RFID tag design can be converted into a SMART sensor through the addition of a by-pass so the issues of cost and manufacturability are minimal.
The original sensor concept was designed for detecting clamp failures and uses a push-button or steel dome switch to complete the by-pass (Figure 1) to produce a SMART clamp sensor. The sensor deactivates when the clamp (switch) is closed properly around a wire bundle (checks for proper installation) and is activated when the clamp fails causing the switch to open. Other SMART wiring sensor concepts were then designed for detecting thermal events (arcing, over-heating repairs, etc.) and intrusion by corrosive liquids (cleaning solutions, deicers, etc.) by using conductive traces to complete the by-pass (Figure 2). When the thermal sensor trace melts or the corrosion sensor trace corrodes/dissolves, the trace loses continuity and the SMART sensor activates permanently.
Although the SMART sensors were originally designed to monitor aircraft electrical systems, SMART sensors are also being designed for much larger consumer markets depending on the component used to complete the by-pass:
• Push-Button Switch: car/truck wire and hose clamps, E-passports, composite delamination
• Impact Switch: loose wiring striking wall, shipped package damage, helmets
• Brittle Trace: surface cracks, food/drug/electronics tampering, tread wear
• Meltable Trace: intermittent hot spots, body fevers, vaccine/frozen food integrity
• Corrodible Trace: bridge structures, coolant leaks, fluid intrusion, biocorrosion
• Relay Switch: loss of electrical power