Monday, September 30, 2013

Does Wireless Charging Cause RF Interference?

USB-based device chargers can create noise that interferes with touchscreen operation especially when the chargers omit noise suppression features. So with the advent of wireless charging, one wonders whether noise will be added to the communication channels used by Wi-Fi or Bluetooth devices.

It appears that such corded charging creates noise in the 100 kHz to 1 MHz range, and should therefore not cause problems with Wi-Fi or Bluetooth devices.

But what about wireless charging? Granted, charging systems work by creating localized magnetic fields, which should not, in principle, interfere with radio frequency signals. But three major approaches to wireless charging (radio charging, inductive charging and resonance charging) do use radio frequencies.

Radio charging, intended to reach low-power devices operating within a 10-meter (30 feet) radius from the transmitter, is seen as a way to recharge batteries in medical implants, hearing aids, watches and entertainment devices.

The transmitter sends a low-power radio wave at a frequency of 915 MHz (frequency for microwave ovens) and the receiver converts the signal to energy. The radio charging method is closest to a regular radio transmitter.

But more common are wireless chargers using inductive charging featuring a transmit and receive coil in close proximity. Electric toothbrushes were one of the first devices to use this charging method, and mobile phones are the largest growing sector to charge without wires.

For larger batteries such as electric vehicles, resonance charging, or electro dynamic induction, is being developed, and at least some of those methods use the 915 MHz frequency.

When a new source is “radio” based, there is potential for signal interference. So far, nobody seems to think there will be a problem with magnetic fields and energy in the radio frequency bands.

Of the several systems being developed, including auto charging, the Qi (Wireless Power Consortium), Power Matters Alliance (PMA) and the Alliance for Wireless Power (A4WP) systems, all use localized magnetic fields to transfer energy.

The Cota charging system uses the same spectrum as Wi-Fi and Bluetooth. That naturally raises the question of whether adding a new electromagnetic source can interfere with radio frequency communications, perhaps by adding more noise into a channel.

Wireless charging uses a magnetic field to transfer energy from an alternating current source, using a localized magnetic field, to a device able to convert the magnetic energy into direct current. Of course, the process is inefficient. The only issue is how inefficient.

The point is that wireless charging is convenient, just not “green.”

1 comment:

Anonymous said...

All I know for a fact is when I use my wireless charger I lose TV antenna reception. The TV and antenna are 8-10 feet away from the charging device

Whose Free Speech is Protected?

First Amendment law admittedly is arcane, but occasionally becomes important in the context of how industries ought to be regulated. One tho...