Wireless power transfer, also known as near field charging or wireless charging, is best known for being used to recharge batteries for devices like smartphones or directly powering devices like LED lights by placing them on a wireless charging device. However, wireless power transfer can be used for a variety of devices, such as medical devices or even cars. In fact, as wireless charging has become more popular, wireless charging in cars has become possible. Many vehicles are now built with the capability of charging smartphones, smartwatches, and other wireless charging-enabled devices simply by placing them on a wireless charging device embedded into the vehicle.

However, all these devices require SAR testing to prove compliance and safety for users. Keep reading to learn what this means for manufacturers of wireless charging devices and how RF Exposure Lab can help!

FCC Requirements for Near Field Charging

Wireless charging devices, including wireless charging in cars, must meet the FCC’s product safety requirements. These devices wirelessly transmit radiofrequency (RF) energy between a power source and a receiver. They’re also used in close proximity to humans. Because of this, these products are required to adhere to FCC RF emission guidelines. This makes SAR testing crucial for any wireless charging device.

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

What is Wireless Charging?

The most common technology for wireless charging (or 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 wireless charging devices:

• Charging pads, which use tightly coupled electromagnetic inductive or non-radiative charging.
• Charging bowls or through-surface type chargers, which loosely couple 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.

Wireless charging works by using a copper coil to generate an oscillating magnetic field, which generates a current in receiver antennas. If the proper capacitance is added to make the coils resonate at the same frequency, the amount of current in the receivers will increase. This is what is known as inductive charging and it enables power to be transmitted at a large distance between the transmitter and receiver.

The size of the coil used also has an effect on how far power can be transmitted. The larger the coil or the more coils are in the device, the greater the distance at which power can be transmitted.

Uncoupled RF wireless charging devices allow a mobile device to be charged without it even needing to be put down in a specific spot. They work the same way as wireless routers, sending out RF signals that are received by enabled mobile devices. These devices consist of a small RF antenna, an application-specific integrated circuit, and software.

Wireless Charging in Cars

Wireless charging in cars currently involves embedded components that are installed inside cars and used to wirelessly charge smartphones, wearables, and other Qi (pronounced “chee”) enabled devices. These systems inside cars use induction coils to create an electromagnetic field that transfers energy from a transmitter unit to a receiver unit. The receiver then takes this energy and converts it into safe and efficient power that can wirelessly charge a variety of Qi-enabled devices.

What are Qi-Enabled Devices?

Qi-enabled devices are devices that follow the Qi system of wireless power transfer. This standard system is made up of two basic modules, the base station, and the mobile device. The base station includes one or more power transmitters, each of which can provide wireless power transfer functionality to one device at a time and consists of a power conversion unit and a control unit and communication.

Essentially, devices such as smartphones are Qi-enabled when they’re designed with wireless charging by default or designed to upgrade to wireless charging.

Both Qi-enabled devices, as well as the wireless charging devices, use RF energy, requiring them to undergo SAR compliance testing.

Near Field Charging Device Testing at RF Exposure Lab

Even when it comes to wireless charging in cars, wireless charging devices must prove compliance, and RF Exposure Lab is here to provide SAR testing. 

At RF Exposure Lab, our goal is to make sure that our clients understand what we do and assist them in understanding how FCC regulations affect the testing required for their devices. 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 wireless charging devices. If you’re looking for SAR testing help or have any questions about SAR testing for wireless power transfer devices, please contacts us for a quote.