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Harvester could capture energy from ambient rf signals

imec and the Holst Centre, along with the Delft University of Technology and the Eindhoven University of Technology, have designed and fabricated a self calibrating rf energy harvester which may pave the way towards capturing energy from ambient WiFi or GSM signals.

According to the researchers, the device can harvest rf energy at lower input powers than current solutions. Measurements taken in an anechoic chamber in the 868MHz band show a -26.3dBm sensitivity for 1V output and 25m range for a 1.78W rf source in an office corridor. The maximum end to end power conversion efficiency is said to be 31.5%.

The key blocks are a five stage cross connected bridge rectifier, a high Q antenna and a 7bit capacitor bank. The capacitor bank and the rectifier are implemented in standard 90nm cmos and are esd protected.

The design is said to overcome several limitations of existing rf energy harvesters, including poor sensitivity, the need for calibration, the need for a special technology process and a large chip/antenna area.

The device features a smaller antenna area and operates at lower frequencies and is believed to be suitable for powering small sensor systems in applications where other energy sources are not available.

Graham Pitcher

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