Riding the Wave

The surface acoustic wave (SAW) tyre pressure monitoring technology that Transense Technologies plc has specialised in since the company’s establishment in 1991 will be used to produce the automotive industry’s first piezo-electric surface acoustic wave (SAW) sensor based system. In mid-May Texas Instruments announced their selection of Transense Technologies’ TMS3 20F28X digital signal controller as a key component in the development of this new system, a decision that will see the Oxford-based company supplying a market where, come September 1, all new light motor vehicles registered must be equipped with tyre pressure technology that alerts drivers of significant tyre under-inflation.

The logic behind the US corporate giant’s choice of a small UK supplier becomes immediately apparent upon examining the technology on offer. The Transense digital signal controller is tiny, weighing less than 2 grams and measuring only 11x33mm. Such miniscule dimensions are possible as no power source is needed. And the battery free nature of the Transense sensor is arguably the main advantage afforded by SAW technology – not only is weight, a critical factor in objects fitted to a wheel or tyre, kept to a minimum, maintenance and end of life disposal issues are also all but eliminated. Furthermore the absence of the need to easily access any battery unit means that sensors may be embedded within the wheel or tyre, although the option of attaching them onto the wheel or the back of the valve still remains.

Rather than employing the direct active system that most tyre pressure monitoring technologies use, the Transense device places three passive piezo-electric SAW sensors at appropriate angles on a single substrate surface within a small gastight capsule. Pressure is transmitted via a diaphragm to deform the die and mechanically strain one of the elements, while all three elements see thermal strains. The sensors are interrogated by an RF signal, first exciting and then transmitting the three resonant SAW frequencies from which independent pressure and temperature are subsequently determined.

With approximately 1.2 billion tyres sold annually, the US Department of Transportation’s TREAD Act, when it comes into force on September 1, will greatly expand the TPMS market. And with this technology entering the mainstream, the merits of a virtually maintenance free system that leaves no batteries to dispose of are obvious. Indeed, despite losses of £1.33 million during the 2006 year Transense speak with confidence regarding the company’s medium-term revenue earning potential, sentiments shared by financial analyst Katie Allen, who earlier in the year wrote in the Guardian newspaper that “now that it is commercialising years of technology development the company could take off in 2007.” With this latest Texas Instruments deal joining previous agreements signed between Transense and both Michelin and Lear Corporation, Ms Allen’s forecast may well be right on the money.