This Extremely Tiny Temperature Sensor Is Powered By Radio Waves

The tiny sensor on the finger of PhD-student Hao Gao, the lead engineer. Bart van Overbeeke

Technology these days just keeps on shrinking, with complex computer systems that would once outweigh several cars now more likely to be one of many tiny components that fit into your smartphone.

Following this trend, a new miniscule, wireless temperature sensor weighing just 1.6 milligrams – no more than a grain of sand – has been developed by engineers at Eindhoven University. Not only is it just 2 square millimeters in size, but it never needs a battery: it’s powered solely by radio waves from the wireless network it uses to communicate its data.

Functioning in much the way contemporary digital thermometers do, this chip contains a thermoresistor, a small device that changes its resistance as it experiences changes in temperature. This resistance is then converted into an understandable temperature reading by a computer, which in most cases is on board the same device.

This new tiny sensor broadcasts its changing resistance to a nearby wireless router through a matching frequency of radio wave, which itself works out the temperature. Attached, more complex mechanical devices, such as the heating elements in an office, can use this information to decide when to become operational.

The sensor also contains an extremely small antenna, which receives radio waves from the associated router. The radio waves excite the free electrons in the sensor’s antenna, which creates a small electrical current. This is enough to power the sensor.

Image credit: Future cities will feature increasingly "smart" technologies that are self-reliant and autonomous. Peshkova/Shutterstock

The world’s infrastructure continues to become increasingly “smart;” it’s not surprising to encounter lights that only power on when you’re nearby, heating that knows when to turn on and cool down, or escalators that move only when you approach them. Future buildings will therefore need to contain sensors that do not require batteries to power them, otherwise they will require constant charging, making them somewhat environmentally unsustainable and reliant on an external power source.

This new miniature thermometer represents a new generation of sensor, one that is entirely self-reliant. Future variants could measure not just temperature, but light levels, movement, and humidity, using the exact same operating hardware. According to the research team, mass producing the chip, which is built using pre-existing technology, will only cost $0.20 (£0.13) apiece.

The sensor can only transmit its signal 2.5 centimeters (1 inch) unfortunately, but the researchers hope to get it up to 5 meters (16 feet) within the next few years without compromising its small size. Even in its present form, it is able to work beneath a layer of paint, plaster or concrete, suggesting that it could indeed be used in the near future in smart buildings.

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