When most people think of wireless power transfer (WPT) devices or wireless charging devices, they most likely think of devices meant to charge smartphones, tablets, or wireless headphones. However, these aren’t the only devices that can be charged wirelessly. As technology has advanced, WPT has helped medical devices improve as well. Patients and doctors alike have the ability to easily charge medical devices more quickly and more conveniently than ever before.

This is a great advancement for these technologies, but just as SAR testing for medical devices is required to prove compliance, the wireless power transfer devices used to charge them must be tested as well. Keep reading to find out everything you should know about wireless power transfer devices, FCC SAR requirements for these devices, and how this affects wireless medical devices.

FCC Requirements for Near Field Charging Devices

It’s important for wireless power transfer devices to meet product safety requirements. These devices wirelessly transmit energy between a power source and a receiver and are used in close proximity to humans. This is why these products must adhere to FCC radio frequency (RF) emission guidelines. This makes SAR testing crucial for any wireless power transfer device.

According to these FCC SAR guidelines, any device sold in the US that is intended for WPT must undergo SAR testing to prove compliance. Some low power devices may be exempt, but these exemptions will be made on a case-by-case basis.

What is Wireless Power Transfer?

The most common technology for wireless power transfer, also known as near field charging, uses an electromagnetic field between two copper coils, but this requires the device to be close to the charging pad.

There are three types of WPT devices:

• Charging pads, which use tightly coupled electromagnetic inductive or non-radiative charging.
• Charging bowls or through-surface type chargers, which loosely couples or uses radiative electromagnetic resonant charging that is capable of transmitting a charge within a few centimeters.
• Uncoupled radio frequency (RF) wireless charging, which is able to transmit a trickle charge at distances of many feet.

Tightly coupled and loosely coupled devices operate on the principle that a time-varying magnetic field induces a current in a closed loop of wire.

Here’s how it works: a copper coil, or magnetic loop antenna, is used to generate an oscillating magnetic field, which then generates a current in receiver antennas. If the proper capacitance is added to make the loops resonate at the same frequency, the amount of current in the receivers will increase. This is known as inductive charging or magnetic resonance, and it enables power to be transmitted at large distances between the transmitter and receiver.

The size of the coil also influences how far this power can be transmitted. The larger the coil or the more coils are contained in the device, the greater the distance at which power can be transmitted.

Uncoupled radio frequency wireless power transfer devices allow a mobile device to be charged without it needing to be put down in a specific spot. They work similarly to wireless routers, sending out RF signals that are received by enabled mobile devices. These devices are made up of a small RF antenna, an application-specific integrated circuit, and software. 

WPT and Medical Devices

Although wireless medical devices emit RF energy and require SAR testing, the wireless power transfer devices used to charge them are required to prove SAR compliance as well. Devices like surgical tools, portable carts, implantable medical devices, and wearables are all devices that make use of WPT for charging.

Previously, these medical devices required the use of sockets in order to plug in and be charged when low on power. Unfortunately, this required cables that could cause a hazard and are sometimes difficult to keep sterile. In addition to this, many of these devices also have short battery life, requiring them to be plugged in and unable to be used or to be used while connected to cables that may not be properly sterilized.

Wireless power transfer, also known as near field charging, has the potential to greatly improve patients’ quality of life as well as user experience. 

Wireless Power Transfer Device Testing at RF Exposure Lab

Whether your wireless power transfer devices are designed to be used for medical devices, smartphones, or any other device, RF Exposure Lab is here to provide SAR testing. 

At RF Exposure Lab, we also go above and beyond to make sure our clients understand what we do and assist them in understanding how FCC regulations affect the testing required for your device. We strive to be as communicative and transparent as possible throughout the SAR testing process so you always know what’s going on with your product and are never left in the dark.

We offer SAR testing services for a variety of wireless devices including cell phones, laptops and tablets, medical products, survey equipment, wireless modems, and soon, wireless power transfer devices. If you’re looking for SAR testing help or have any questions about SAR testing for wireless power transfer devices, please contact us.