A Guide to RF Exposure and SAR Testing for Wireless Devices

A Guide to RF Exposure and SAR Testing for Wireless Devices

Do you have a wireless device in development that will require compliance testing for RF exposure? You’ve come to the right place. RF Exposure Lab is a SAR testing lab with a team of experts in compliance testing who are here to make things simple for you. 

We know that understanding best practices for SAR testing can be challenging, so we’ve put together this guide to help you out. Our team is also available to help you complete your projects and get your product to market as quickly as possible.

Keep reading to learn all about the best practices for compliance testing.

What is SAR and RF?

Specific absorption rate (SAR) is a unit of measurement that describes the quantity of radio frequency (RF) energy that is absorbed by the body when a wireless device is in use. SAR regulations apply to devices used within 20 centimeters or 8 inches of the body. 

SAR regulations provide a simple and clear way to measure the RF exposure characteristics of wireless devices to guarantee that they meet global safety guidelines. Wireless devices are required to be evaluated to meet the RF exposure limits that have been determined by federal governmental agencies around the world.

Product Classifications

Products are classified in one of three ways: fixed, mobile or portable. A product’s classification depends on how they’re installed and used.

A fixed product is a product with an antenna that is permanently affixed to a structure and can’t be easily moved. These products may require a license aside from the FCC’s Part 15 certification. 

Mobile and portable products are those that can be easily moved from one place to another and may be used in close proximity to your body. The main distinction between these two types of products is separation distance.  A mobile device is used 20 cm or more from the body, while portable devices are used less than 20 cm from the body. However, devices held in your hand, such as mobile phones, are classified as portable.

RF Exposure and SAR Testing in Design

We strongly recommend keeping SAR regulations in mind even in the initial stages of designing a product. Knowing what will be required of your product from the very beginning will help you avoid unpleasant surprises later in the process or when certifying your product. 

If it’s too late in the manufacturing process, being unable to pass SAR testing could require a costly change in the design of your product. This may also delay your product’s time to market, which increases costs as well.

Explaining the Importance of SAR Testing

Wireless products need to undergo SAR testing to ensure that all safety and compliance requirements are met. Different countries have introduced standards that limit the amount of RF exposure allowed from wireless devices. 

Although completely avoiding natural and man-made sources of radiation is impossible, SAR testing allows the amount of RF exposure from wireless devices to be measured and regulated.

Without the certification that comes from passing compliance testing, products will not be allowed onto the market in any country that requires certification.

How Testing Works and Which Devices Need Testing

Testing is conducted using regulated models of the human head and body. These models are filled with liquid to mimic the way RF is absorbed by different tissues in the body. Wireless devices are then tested in positions that simulate how users would typically hold them. During testing, these devices are operated at their highest power level in all the frequency bands in which they operate. While placed in these different positions, a robotic probe measures the electric field at specific locations within the model head and torso. 

While all of this data is submitted, only the highest SAR values for each frequency band are included in the final report to show that the device conforms to the FCC’s RF exposure guidelines.

When a device is certified it means that the device will not expose users to levels of RF exposure higher than what is allowed by federal guidelines.

Now we’ll discuss how RF energy is used, and what kinds of products require SAR testing. RF energy is usually used to provide telecommunications services. This includes the following: 

  • Radio and television broadcasting
  • Cellular phones
  • Personal communications services
  • Business radio
  • Radio communications for police and fire departments
  • Amateur radio
  • Satellite communications

It is also sometimes used for non-telecommunication products such as microwave ovens, radar, and industrial heating and sealing. RF energy is also used for medical reasons, such as magnetic resonance imaging (MRI) and diathermy. Some medical devices also use RF energy for wireless purposes, which requires proof of compliance.

Pre-Compliance SAR Testing

SAR compliance testing is required to be conducted at the end of the development process. However, when a wireless device is designed and developed without input from anyone with knowledge of SAR regulations, you may end up with a device that will fail the testing process. Once this happens, the only thing that can be done is to redesign the device, as proof of compliance is required to sell these devices.

Fortunately, all of this can be avoided with pre-compliance SAR testing. This entails testing during the product development phase as well as working with a SAR testing lab to get guidance on the product’s design. 

Pre-compliance SAR testing can help you save time and money by helping you determine if a product will pass testing throughout the design and development process. If you find that there are any issues with the product, you can quickly correct them without a significant loss of time or money. 

Although pre-compliance testing can result in slightly increased costs, the benefits it provides, and the time and money it will save your business, make up for these added costs.

OTA Testing

Over-the-air (OTA) testing is a method used to forecast the performance and reliability of wireless devices in the real world. The device is placed in a free-space environment within a test chamber, where real-life situations are simulated. The device is then subjected to multiple test conditions to observe how it responds to each situation. This testing measures the device’s signal path and antenna performance to ensure that it will be able to perform as intended.

Products that use MIMO technology may include phased antenna arrays of 4-by-4 or 8-by-8, making it necessary to determine how to conduct SAR testing for these devices based on OTA testing. 

A particular concern when conducting compliance testing for devices using MIMO technology is that all testing is conducted in the near-field reactive region. Testing radiated signals also raises the challenge of ensuring that stray signals won’t obscure SAR testing results for these devices. 

It’s necessary to figure out how to test these devices in a functional environment that won’t have outside interference or allow signals to be transmitted externally. This requires the use of specific testing chambers for MIMO devices.

Variability in Global Regulations for SAR Measurements 

Exposure limits for SAR testing vary between different countries. Authorities such as the Federal Communications Commission (FCC), European Union (EU) and Innovation, Science and Economic Development Canada (ISED), and more countries have regulations for SAR testing and SAR limits. RF Exposure Lab is able to provide compliance testing for these countries.

In the United States and Canada, the wireless device must meet a SAR limit of 1.6 watts per kilogram, average measured from 1 g tissue volume. This means that to receive FCC or ISED certification and be sold in the markets, the devices’ maximum SAR level must not exceed this level. In the European Union, to receive CE certification, the devices’ maximum SAR limit is 2.0 W/kg average measured from 10 g tissue volume.

Overall, the European Union’s SAR guidelines are broader than those in the United States and Canada. Although the UK is typically included when referring to Europe, certain regulations differ. For example, some EU countries use the Wi-Fi UNII-3 band, but the UK does not. Manufacturers planning to sell products in the UK should keep this in mind when going through compliance testing.

In addition to this difference for products in the UK, ANSES, a French agency, necessitates that a separation distance of 0mm is taken into consideration for devices that operate higher than 20 mW and are used within 20cm of the body.

FCC compliance guidelines are generally more complex than European regulations. This is because the FCC has differing guidance for specific devices and technologies, such as LTE, 3G, Push-to-Talk devices, WLAN, and more. In comparison, European regulations are applied broadly rather than created specifically for each technology.

The FCC has also determined that low-power devices can prove compliance according to their output power rather than undergoing SAR testing. However, this depends on the device’s separation distance, power and the frequency it operates in.

Like the US, Canadian SAR limits are 1.6W/kg measured from 1g tissue volume according to ISED. However, in addition to ISED setting its regulations for measurements, FCC, IEC, and IEEE procedures are accepted as well. This can make obtaining certification in Canada more challenging than in other countries. 

Advancements in Wireless Technology & SAR Testing 

There are recent technologies as well as upcoming technologies that are changing SAR testing. For example, 6G, the next generation following 5G technology, will use even higher frequencies than 5G, providing devices with greater data capacity and reduced latency. Communication will also be significantly faster and will even work with AI to determine the best areas for computing. However, 6G and the following generations will require updates to SAR testing for devices using this technology.

Complete Your SAR Testing Projects With Help From RF Exposure Lab

We hope that this guide has helped you learn a bit more about SAR testing and regulations for RF exposure, but we also know that there is much more to compliance testing than can be fit into one guide. 

When you need RF or SAR testing for a project, come to the experts here at RF Exposure Lab. The importance of working with an experienced, A2LA accredited testing lab can’t be overstated. Working with an experienced testing lab as early as possible in the manufacturing process will help you successfully get through the maze of regulations and ensure that your product is compliant.

We offer RF exposure testing services for a variety of wireless devices, such as

As well as many more devices! If you’re looking for compliance testing help that is provided with expertise, speed, accuracy, and integrity, contact us to learn more about our services or to get a quote.