Wireless temperature sensors need no batteries

Paul Boughton

Senseor is launching three innovative wireless temperature sensors based on SAW (surface acoustic wave) technology, suitable for demanding industrial applications. More than a rudimentary wireless sensor, Senseor's innovative products are also totally passive; the sensors are only powered by the energy of radio waves emitted by the associated reader unit when remotely interrogating the devices in real-time. The ensuing benefits are therefore claimed to be unique.
First, without any batteries or active electronic components at sensor level, these sensors are suitable for use in explosive atmospheres or irradiated environments at temperatures reaching +175 degrees C (current in-house research and development efforts are aiming at 350 degrees C) with almost unlimited autonomy. In addition, by avoiding problematical wires, these maintenance-free and lightweight sensors can either be mounted onto an extensive range of rotating and moving machinery parts or be installed in inaccessible places.
As a result, two thermowell-packaged wireless temperature probes, namely the SED-100 and SED-120, are being launched. Furthermore Senseor is introducing a novel system to monitor surface temperature, known as the SA-D003.
Each measurement system comprises a reader unit (also referred as an interrogator) and the sensor mounted with its associated antenna. The interrogation distance between the sensor and the reader unit can reach up to several metres in open space.
In short, the technological advantage behind surface acoustic waves relies on the reverse piezoelectric effect. On the one hand, the electromagnetic wave sent by the interrogator is received then converted into an acoustic wave by means of a transducer located at the surface of a piezoelectric crystal (typically quartz). Temperature variations related to the nearby environment of the SAW sensor trigger a modification of the acoustic wave's physical properties when propagating along the surface of the device. In return, the modified acoustic wave is transformed back into an electromagnetic wave to be retrieved by the reader unit.
The integrated building block of those above-presented sensing systems, SE-AS10 SAW sensor, is also commercially available a standalone device, capable of sensing temperatures ranging from -20 to +175 degrees C with a measurement precision of +/-2 degrees C. This tiny sensing element (only 5 x 5 x 1.5mm3) can be associated with different types of customised antennas, depending on the environment characteristics as well as implementation constraints.
Andreas Jagtøyen, the general manager for machinery instrumentation at Kongsberg Maritime AS (Norway), a partner who has industrialised a SAW-based in-engine bearing temperature sensor for vessel motors, confirms: "We have installed thousands of systems working in the toughest conditions – and none of the sensors has ever failed. We will use this technology for other breakthrough applications".
Besides this application already in production, Senseor is also strongly involved in several customer projects with world-leading companies in the fields of energy, industry and transportation, aiming to industrialise even more successful prototypes. There are also some developments in the medical sector.
The non-exhaustive range of applications that can be covered by SAW sensing comprises temperature measurements inside tyres at 250km/h, at the surface of an electric motor's rotor at 5000rpm, or even inside high-voltage breaker boxes.
For more information, visit www.senseor.com