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11 Myths About SAR-Compliant Chips in Connected Devices

April 27, 2023
Standards for specific absorption rates (SARs) keep people safe, but it’s one more engineering challenge when designing cell phones, laptops, and other electronic goods. It’s not impossible to meet those standards, though, despite what some rumors say.

This article appeared in Electronic Design and has been published here with permission.

What you'll learn:

  • What is SAR?
  • The challenges of achieving SAR compliance.
  • The role of proximity sensors.

In the consumer device industry, manufacturers face the ongoing challenge of improving device performance while maintaining compliance with stringent global standards. As the industry moves toward adopting 5G connectivity, the complexity of designing systems that meet international RF emission requirements continues to intensify.

By using proximity sensors in today’s most popular devices­­­—smartphones, laptops, and tablets—leading original equipment manufacturers (OEMs) can ensure compliance with specific-absorption regulations while supporting wireless standards from Wi-Fi 6 and sub-6-Ghz 5G to emerging 5G mmWave signals.

What follows are some of the myths and misinformation surrounding specific-absorption-rate (SAR) compliance standards and the challenges faced by industry’s most popular OEMs when designing consumer products.

1. SAR compliance requirements are the same globally.

SAR is a measure of the amount of RF energy absorbed by a body when a person uses a wireless device. Various standards bodies specify SAR requirements and the limits differ across different markets. The SAR compliance standard varies by country and devices must meet the requirements before shipping them to consumers.

In the U.S., the Federal Communications Commission (FCC) sets the exposure limit to be a SAR at 1.6 W/kg (over 1 g of tissue) with a separation distance of 25 mm from the user. The requirement is the same for Canada and Korea. The standard for the European Union, Australia, and Japan is 2.0 W/kg (over 10 g of tissue) with a separation distance of 5 mm from the user.

2. Proximity sensors can only detect the presence of a human.

A SAR-compliant subsystem built into consumer devices can detect humans as well as objects. It automatically adjusts RF emissions while ensuring the device runs at peak performance. If the subsystem could not detect humans, the measured SAR value would rise above its regulated limits when a human approaches.

To meet SAR requirements, RF power must be lowered so that the SAR value also lowers when close to a person (as opposed to an object). Simply, if you’re typing on your laptop and it’s sitting on your lap, your device regulates its RF levels to be lower to comply with SAR regulations. With the ability to distinguish between a human’s lap and desk, the laptop can adjust dynamically to get the best performance.

3. It’s not possible to enable 5G connectivity and remain SAR-compliant.

Smart sensors are vital to the future of widespread 5G access, implementation, and adoption. According to Juniper Research, 5G smartphones shipments are expected to reach $337 billion by 2025. This means most smartphones on the market will have to maintain SAR compliance and handle 5G and legacy network requirements.

This situation presents a challenge for OEMs. In the design process, RF engineers must add more RF antennas to accommodate additional network frequencies. With intelligent sensors, consumer devices can maintain SAR compliance while supporting various wireless standards, from 5G to Wi-Fi 6, giving users the best connectivity and speed.

4. Constant RF power reduction leads to improved range, bandwidth, and link quality.

With intelligent proximity sensors, OEMs can build products that reduce RF power only when necessary, thus ensuring optimal link quality and range. This is particularly the case with 5G smartphones, which require more antennas to support better connectivity and greater bandwidth.

5. Proximity sensors can only be used to detect a human presence on smartphones.

Many consumer devices include smart proximity sensors to detect a human presence and enable intelligent, real-time responses. Beyond smartphones, devices such as tablets and laptops also can use proximity sensors to detect humans. Other than human detection, proximity sensors can enable intuitive gesture controls such as auto on/off and advanced media controls on wearable devices.

6. Changes in ambient temperature don’t cause false proximity detection.

One of the main challenges with proximity sensors is that they must be accurate enough to differentiate an approaching human from environmental noise. In addition, temperature and other environmental factors can make capacitance vary significantly.

Smart proximity sensors help reduce temperature variation and enable stable monitoring over long durations. This limits the chances of false human detections if there’s a change in environmental temperature. A smart proximity sensor also can include auto offset compensation, which monitors and removes environmental effects to ensure the change in capacitance is caused only by a nearby human.

7. Maintaining SAR compliance isn’t required for device manufacturers.

SAR compliance is required for all device manufacturers. All consumer devices must be evaluated and certified before they hit the market. This testing ensures consumer devices meet all compliance requirements. The standardization of SAR compliance leaves no room for error—if products don’t meet the appropriate SAR regulations, they can’t be sold.

8. Proximity sensors aren’t reliable.

For OEMs, designing a subsystem that accurately differentiates an approaching human from environmental noise can be challenging. Smart proximity sensors with advanced analog front ends deliver exceptional performance that enables large detection distances with small sensor area. A smart proximity sensor can detect, then reduce, RF power when reliably close to a human.

9. Proximity sensors aren’t suitable for portable applications.

Proximity sensors have small footprints that offer versatility for a wide range of applications and products. The sensors’ low power consumption makes them ideal for battery-operated devices such as mobile phones, tablets, laptops, and wireless headsets.

10. It’s not possible to adjust the sensitivity of SAR sensors.

Capacitive sensing is the process of measuring a small variation of capacitance to detect the presence of humans or objects. Proximity sensors that employ capacitive-sensing technology can automatically calibrate the sensors and regularly adjust sensor sensitivity for changes in temperature, humidity, and electrical noise.

11. SAR compliance of wireless consumer products isn’t required in the United States.

U.S. manufacturers are required to ensure all wireless devices they ship meet FCC SAR standards. Consumers who want to know if their personal cell phone is compliant or not should visit FCC’s website to learn more. This online resource includes details and links to manufacturers’ websites along with detailed instructions on how to search each of the sites for SAR information.

About the Author

David Wong | Senior Director of Consumer Sensing Products, Wireless and Sensing Products Group, Semtech

David Wong is senior director of consumer sensing products for Semtech’s Wireless and Sensing Products Group.

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