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Wirelessly Powered Sensors Collect Data and Energy (MIT Technology Review)

Do battery-free sensors have a future in building automation?

A smart building can be host to thousands of sensors, gathering data about everything from light levels and temperature to vibration and sound. Wireless sensors still rely on batteries with finite life spans.

The exact location of a sensor can affect the worth of its data -- and wiring to a remote location can drive up the sensor's cost. Wireless sensors can transmit their data without copper tethers for data or power. They depend on various wireless data protocols that are known to be reliable, together with something known to eventually fail: an on-board battery.

Battery-free sensor technology

Enter a new kind of sensor that doesn't need a battery. Developed by Intel researcher Josh Smith, the sensor can collect environmental information and transmit it for much longer than a battery-powered sensor.

"The sensor uses an antenna similar to those found in battery-free RFID tags. When the sensor comes within range of an external device called an RFID reader, which emits radio waves, the antenna and circuitry harvest power from the radio signal to turn the sensor on."

Limited range limits applications

"Within range" is the key qualifier. As long as the sensor is within a meter of a reader, it collects and processes environmental information.

That range could be extended to about three meters, still not enough range to place sensors in long ducts or high skylights. (This would work in a trucking application, for example, where temperature sensors in frozen foods send data to a reader in the cab.)

One potential building application would be in dense sensor installations. Engineers could cluster these sensors around hubs containing the power-transmitting readers. The hubs could employ a mesh-network-like architecture to collect data and bypass points of failure, such as hubs with dead batteries.

The cost-benefit equation will depend on avoided maintenance -- changing batteries or whole sensors in hard-to-reach locations -- and the uninterrupted flow of valuable data as it translates to saved energy and infrastructure expenses.