Is free-space wireless charging viable? Dialog thinks it’s worth a try

August 21, 2014 // By Graham Prophet
Dialog Semiconductor and Energous are to collaborate to develop market for Energous’ “Wattup” wire-free charging technology; the two companies aim to bring a combination of over-the-air wireless charging, and lowest power Bluetooth Smart, to wearable IoT devices.

Energous' technology promises charging of devices such as Smartphones, within a room or within around 3m of a charging point, with no connections to the hand-held or wearable device and with no requirement to lay it on a charging pad or mat.

Details of Energous’ exact technology have so far been sketchy, but the company says it is using “the same radio bands” as WiFi and other wireless communications standards – therefore, GHz RF. Within the operational range of the charging point (Energous calls the space a “pocket”) a compatible device is found and authorised for charging. Eventually devices may be native-Wattup-compatible: demonstrations so far seen are reported as requiring add-on Wattup “cradles” to add the charging function. Once identified, a phased-array of transmitting antennae form an RF beam that is focussed on the target device, and that tracks it if it moves. That RF is received, rectified and used as the power source. Nothing is revealed so far about exact frequency or frequencies (fixed? hopping? ultra-wideband?) or modulation schemes (CW? Pulsed?) or if the receive end of the link also needs a phased antenna array.

Other questions that will immediately occur to engineers include, how much power can actually be delivered in this way – a figure of 10W has been seen but it is not clear if this is the power available, or transmitted. And; what end-to-end efficiency is possible? Again, reported figures of 20% (mains-socket to battery terminal) for prototypes have been mentioned, with Energous expressing confidence that this can be raised. Inevitably, questions of safety will arise, even if power levels are modest.

Energous is playing in a space where Witricity has already staked a claim; this MIT spin-off company proposed magnetic resonance rather than RF as a means of sending power over a free-space distance (a standard called Rezence has support from some high-profile names) and has been associated with higher power levels such as