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Updated: July 8th, 2008 05:26 PM CDT

First Automotive Surface Acoustic Wave (SAW) Sensor Coupled With TI Controller Enhances Fuel Efficiency and Safety

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DALLAS , May 14 /PRNewswire/ -- As automotive tire pressure monitoringsystem (TPMS) mandates come into effect and torque sensing applications likeelectronic power steering (EPS) become standard on even low- to mid-rangecars, Texas Instruments Incorporated (TI) (NYSE: TXN) today announced thatTransense Technologies plc is using their TMS320F28x digital signalcontrollers as a key component in the automotive industry's first targetedpiezo-electric surface acoustic wave (SAW) sensor based systems. Operating inenvironmentally harsh or remote automotive and industrial applications, theTransense sensor units operate wirelessly, require no power source and aretypically 11 mm by 3 mm and less than 2 grams in weight. By using the F28x-enabled SAW TPMS, braking distances and the risk of accidents due to tireunder inflation or failure are reduced. Fuel efficiency is also enhanced by upto ten percent through properly inflated tires and engine drag reductionthrough the elimination of the hydraulic pump in EPS systems.

SAW Sensor Uses Acoustic Wave for Measurement

SAW sensors utilize a radio frequency electric field to generate anacoustic wave which spreads over the piezo-electric substrate surface,transforming back to an electric field and re-transmitting for measurement.32-bit DSP performance and high integration of the F28x digital signalcontrollers perform essential real time data handling, calculation andreporting functions. The F28x device calculates the spectrum of the SAWimpulse response, finds the frequency of natural oscillations of the SAWsensor and can handle additional tasks such as system communication via theon-chip CAN BUS for instance. A radio frequency (RF) application specific IC(ASIC) dual channel controls RF transmission and reception.

SAW Sensors Answer US Mandated Tire Pressure Monitoring RequirementsAccording to the US Department of Transportation (DOT), up to 27 percent ofpassenger cars and 33 percent of light trucks operate with under inflatedtires, resulting in an estimated 23,000 crashes and 535 fatalities each year.As part of the November 2000 enacted Transportation, Recall Enhancement,Accountability and Documentation (TREAD) Act -- which affects all light motorvehicles registered after September 1, 2007 -- TPMS technology must alertdrivers of significant under-inflation of their tires.

Most existing TPMS are direct active systems utilizing a siliconmicro-electro-mechanical system (MEMS)-based sensor inside each tire poweredby a battery. Pressure and temperature information is transmitted by radiofrom each of the wheels to an electronic control unit (ECU) and displayed aseither a number or a warning indicator. Batteries inside tires add weight,have limited life and cannot be replaced. With 1.2 billion tires soldannually, this waste represents an increasing environmental hazard. Thepassive Transense SAW sensor incorporates a three element die within a smallgastight capsule. Pressure is transmitted via a diaphragm to deform the dieand mechanically strain one of the elements, while all three elements seethermal strains. The sensor is interrogated by an RF signal -- no battery isrequired -- first exciting, then transmitting the three resonant SAWfrequencies from which independent pressure and temperature are subsequentlydetermined.

Electronic Power Steering Becoming Standard on Many Cars

By 2010 half of all the cars sold in Europe are projected to be equippedwith electronic power steering (EPS) systems that reduce both installation andproduction time for manufacturers and save fuel and maintenance costs forconsumers. A vital part of the EPS control system is a torque sensor thatmeasures the driver steering input. Existing EPS systems typically employpotentiometers or optical transducers mounted on a length of steering shaftwith reduced section to increase local twist and hence measurementsensitivity. This approach tends to reduce driver feel and increases thesensor production cost.

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