Wireless charging gets universal antenna
“The rate limiting factor [in wireless charging] is not antennas but the battery circuit itself,” NuCurrent CEO Jacob Babcock told EE Times.
Babcock explained that a recharge cycle might miss a full charge by several watts if the battery gets too hot. In addition, the current will only flow around the outer edge of the wire causing longer charge times.
“NuCurrent invented the ML wire — it’s like bundling 100 drinking straws together to pass through liquid — then we optimized conductive area available based on skin depth of a frequency. We’re able to pass more current with lower resistance through that wire,” Babcock said.
Source: NuCurrent
NuCurrent produces multi-mode antennas for wireless charging. Its antennas can support Qi, Power Matters Association (PMA), and Association for Wireless Power (A4WP) standards, which all operate at different frequencies. Thus it must manage several skin temperature possibilities.
To help manage heat from various charges, NuCurrent uses the same coil for inductive Qi (110 and 205 kHz) and resonant PMA (200 to 300 kHz) standards. It uses a second coil for A4WP (6.78 MHz) resonant charging on the same board.
Higher quality, lower resistance antennas play a big role, Babcock said. “The reason that the higher quality factor matters is because we can achieve the necessary charging efficiency with thinner antennas; with smaller antennas we can keep your phone or whatever the device is cooler which allows us to maintain charging speed,” he said.
NuCurrent’s antennas are up to 0.08mm thin, and as small as 12.7mm x 12.7mm. They power mobile devices from 50mW – 2.5W and up to 50W. The antennas also have NFC capability.
Babcock said NuCurrent’s antennas are not designed for higher-power items like electric cars or appliances. However, they do offer a 70% charging efficiency for mobile and wearable devices.
“The devices that I think need wireless power the most right now are medical devices like neuro-stimulators, hearing aids, and wearables,” Babcock noted.
The Chicago-based company began developing antennas in 2009. It has partnered with Texas Instruments to develop wirelessly charged wearables and Molex on antenna manufacturing. NuCurrent is a member of the three major wireless charging standards groups, but believes the loosely-coupled coil patterns of resonant charging will become the dominant paradigm.
“Unless Qi resonant becomes more pervasive and…we don’t see the progress on the [Qi-based] Wireless Power Consortium’s resonant technology that we think is necessary for [WPC’s standard] to be pervasive,” Babcock said. “I think [the eventual standard] will be a form of resonant technology and as of right now, will more likely be A4WP because they have an 18-24 month start on Qi resonant.”
NuCurrent is also involved with Efficient Power Conversion Corporation (EPC), which uses Gallium Nitride (GaN) instead of silicon to make transistors. Using NuCurrent’s coil, EPC create a wireless power transfer demo capable of delivering up to 35 W into a DC load while operating at 6.78 MHz.
“I personally think what EPC is doing is the way of the future. As a company we’re happy to lend input to our customers…but whether transistors are silicon or GaN-based it doesn’t make a difference to us,” Babcock said.
— Jessica Lipsky, Associate Editor, EE Times
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