The SmartStem®, consists of wireless tire pressure and temperature sensors embedded in an aircraft's tire inflation valve stem. These special tire inflation valve stems communicate tire pressure, temperature and other information to the cockpit, or to a handheld reader. The technology used is the Phase IV-developed passive SensIC™ RFID ASIC (Application Specific Integrated Circuit). This tiny ASIC measures temperature internally and can interface with many different sensor types such as pressure, strain, load, and more, and lends itself to be used in many diverse applications.
The ASIC in the SmartStem®, when interrogated by a reader, measures temperature and pressure data and then transmits this data back to the reader. (Shown left is the ASIC multi-chip module with three independent channels).
SmartStem® has been selected for the latest Onboard Tire and Brake Monitoring System (TBMS) for current production Boeing aircraft. This technology is passive, obtaining its operating power from an external reader or interrogator. When the reader is close to the coil attached to the ASIC, the circuit uses the reader's signal to power measurement and communication of identification or sensor information.
The advantage to this system is that there are no batteries, power sources, or wires. SmartStem® is an integral part of the Crane Aerospace & Electronics' brake control system that is now operational in the Boeing 777. It has also been designed into the new Boeing 787. For SmartStem applications that are not integrated into the plane, and for smaller planes manufactured by companies like Cessna, Phase IV developed a handheld reader for Crane Aerospace.