LONDON—Researchers at the Technical University of Eindhoven have developed a wireless temperature sensor that is powered by millimeter wavelength radio waves that are also used for communications.

Eindhoven student Hao Gao was due to receive a Ph.D. earlier this month for his thesis in which he discusses his development of the sensor that has an area of 2 square millimeters and weighs 1.6mg. The sensor is made using a 65nm CMOS manufacturing process.

A specially developed wireless router communicates with the sensor, which has an antenna on chip and picks up both energy and information from the millimeter wave signals. The current version of the sensor has a range of 2.5cm but researchers hope to extend this to a meter within a year.

The autonomous nature of the temperature sensor means it can be put behind plasterboard or included in a screed of concrete or paint.

The sensor stores the energy received and once there is enough switches on, measures the temperature and sends a signal to the router. Each temperature is indicated by a slightly different frequency at which the return signal can be sent. The router determines the temperature by the distinctive frequency.

The same technology could be used with other sensor types, such as motion, light and humidity. The tiny size of the silicon chip is expected to keep sensor costs down to around 20 cents in volume.

The title of Hao Gao’s thesis is Fully Integrated Ultra-Low Power mm-Wave Wireless Sensor Design Methods. The IC research was done in the Mixed-Signal Microelectronics group and also involved university groups specialised in electromagnetics and signal processing systems as well as the Center of Wireless Technology.