Wireless SAW Sensing
SAW technology has very successfully been used in the telecommunications industry to build frequency controlled oscillators and band pass filters. This same technology also has the capability of providing wireless and sensing capabilities. SAW sensing elements can also be powered without an external power supply. When connected to an antenna, they can be powered by wirelessly harnessing energy from electromagnetic bursts from a near by transmitter, very much like RFID. The transduced signals from the sensing element can then be transmitted to a receiver through the same antenna thereby providing an effective wireless and energy-passive sensing mechanism.

SAW Pressure Sensing
The figure below shows a SAW wireless pressure sensor. The sensor consists of three SAW devices that are used to measure temperature and pressure. Each SAW device has Inter-digital Transducers (IDTs)(comb-like pattern of metal structures that interchangeably convert electric signals into mechanical stress). The SAW devices are activated by electromagnetic bursts generated by a wireless transceiver. Antennae attached to the SAW devices convert the electromagnetic bursts into electrical pulses, which are then funneled through IDTs to induce acoustic waves in the SAW devices. The temperature and pressure to which the SAW devices are exposed modifies their resonant frequency. The acoustic waves are reconverted back into electrical signals by the IDTs and further re-converted to electromagnetic signals. The response signals generated by the SAW devices are processed to deliver temperature compensated pressure measurements. The sensor operates in the 433 MHz Industrial, Scientific and Medical (ISM) radio band. Interrogation distances, i.e. the range within which the sensors can operate, typically range between 1.0 to 3.0 meters.

Figure: Wireless SAW Pressure Sensor

Typical and Potential Applications
A key application of the wireless SAW pressure sensor is in tire pressure monitoring systems (TPMS). The United States government recently passed legislation that requires from September 2007 all new passenger vehicles and light trucks under 10,000 pounds of gross vehicle weight to be equipped with tire pressure monitoring systems. The ability of vehicles, especially critical transport vehicles, to carry the specified load is a direct function of maintaining correct tire pressure. The correct pressure results in the avoidance of catastrophic failure and allows for increased fuel economy and tire life.

Further, there is a significant market opportunity in the commercial, agricultural and construction vehicle markets, where continuous monitoring of tire pressure offers opportunities for operating cost reductions and elimination of expensive manual maintenance programs. Industrial applications for wireless pressure sensors include HVAC industries, medical applications, semiconductor fabrication plants and process control requirements.

What SenGenuity Offers Today
SenGenuity manufactures wireless pressure sensors for TPMS and industrial applications. Click here to view the TFSS433E wireless pressure sensor specification sheet. Should you have any questions or would like to lean more, please contact us at sensors@sengenuity.com.