That's because the larger the wireless charging router, the more antennas it can house to transmit power, according to Holmes.
Energous' WattUp wireless routers use radio frequency (RF) transmissions to send up to 4 watts of power in a 15-ft. radius. The Pleasanton, Calif.-based company raised nearly $25 million when it went public earlier this year.
The WattUp transmitter works much like a wireless router, sending RF signals that can be received by enabled mobile devices such as wearables and mobile phones. A small RF antenna in the form of PCB board, an ASIC and software make up the wireless power receivers.
The Bluetooth wireless communication specification is used between WattUp transmitters and receivers.
Energous' routers are only limited by the number of antennas they have, but the company has chosen to keep the size of its routers at 12-in. x 12-in., allowing them to overlap transmissions to cover areas larger than 15 feet, Holmes said.
"Overlapping circles of coverage gives you a better overall coverage area," Holmes said.
Within 5 feet of a WattUp wireless router, a mobile device can be charged at the same rate as if it were plugged into a wall socket, Holmes added.
Energous is currently focused on powering small mobile devices rather than laptops that require charging capacities greater than 4 watts. Energous has also created a mobile app that manages which devices are authorized to connect to a WattUp wireless charging router. Holmes said one key market for the transmitters would be mini-refrigerators for college dorm rooms because students tend to be the biggest users or new mobile tech that requires charging.
A single WattUp transmitter can charge up to 24 devices. The maximum amount of power — 4 watts — can only be delivered to four devices simultaneously. So as more enabled and "authorized" devices enter a room, the charge to each device is reduced.
Also, as the distance between transmitter and receiver becomes greater, the power transfer dissipates. For example, a WattUp transmitter can stream 4 watts within a 5-foot radius. At a range of 5-to-10 feet, that power drops to 2 watts per device; at 10-to-15 feet, the router puts out 1 watt per device (4 watts total).
WattUp's RF transmission, which operates at 5.7MHz and 5.8MHz, is referred to in the industry as "far-field" wireless charging. Energous is not the first company to come up with the idea.
Startup uBeam landed $750,000 in seed funding for technology that uses ultrasound waves to transmit electricity to mobile devices. The specifics may differ, but the principle is similar to the approach Energous has taken, according to Ryan Sanderson, an analyst at IHS.
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