How to ensure SAR compliance in connected consumer devices
Article By : David Wong
Intelligent proximity sensors enable users of laptops and tablets to provide optimal connectivity and long battery life, but they must meet SAR compliance.
During the past two years, how many of you worked from a coffee shop or your home office? Working from anywhere is the new normal. This flexibility gives people better work-life balance and increased reliance on their connected devices. According to a Pew Research Center survey, 61% of Americans are choosing to work from the comfort of their own home rather than going back into the workplace. With 6-out-of-10 U.S. workers working remotely, high performing laptops and tablets will be required to enable them to work from anywhere at any time.
With the help of intelligent proximity sensors, integrated by original equipment manufacturers (OEMs), laptops and tablets can provide optimal connectivity and long battery life, which are essential when working remotely. Furthermore, the top U.S. carriers have launched 5G networks with more 5G-enabled devices going live daily. To ensure that these products work with the fastest 5G networks and support the higher bandwidths, OEMs design additional radio frequency (RF) antennas into the devices to improve connectivity. OEMs balance the improvement in RF performance without comprising the device’s battery life or form factor. These devices are efficient, powerful and convenient for today’s remote worker.
With devices running at optimal performance, there is no need to worry about network lags or loss of signal during a video conference. Embedded intelligent sensors can support all wireless signals, from Wi-Fi 6, 5G Sub-6, to emerging 5G mmWave networks, providing the best connectivity for users at all times while maintaining compliance.
Industry compliance in connected devices
There are compliance regulations for connected consumer devices such as smartphones, laptops and tablets. OEMs produce devices that comply with Specific Absorption Rate (SAR) standards. SAR is a measure of the rate at which energy is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. The standards vary by country and regulatory body for each country. In the U.S., the Federal Communications Commission (FCC) mandates SAR compliance. According to the FCC, the SAR limit is 1.6 W/kg (over 1g of tissue) with a separation distance of 25mm. For Europe, the SAR limit is 2.0 W/kg (over 10g of tissue) with a separation distance of 5mm. In order to meet these standards, OEMs build wireless devices with compliant RF levels.
Smart sensors allow RF power to be regulated when devices get close to humans. For example, if you are typing on your laptop and your laptop is sitting in your lap, your device lowers the RF exposure to stay compliant with SAR regulations while ensuring optimal performance. If your laptop is sitting on your desk and you are typing on it through a wireless keyboard, the device can transmit at optimal RF power since direct human touch is not present.
Let us explore how these sensors work.
An example of a proximity sensor that can detect human presence in a laptop or tablet is the SX9330 as shown in the diagram. Using this SAR sensor, devices can accept up to four sensor inputs and can accurately distinguish between an inanimate object and a human body. Typically, the sensor input is rather simple and not much more than a standard copper plate on a PCB surrounded by a ground shield for noise immunity. When the processor senses a human body in close range, it sends an alert to its host processor via I2C serial bus to indicate detection.
Smart sensors identify the presence of a conductive object such as a finger or a palm by monitoring the capacitance on the sensor inputs. If there is no conductive object nearby, the sensor only recognizes an inherent capacitance value created by the interaction of its electric field and the environment. An approaching conductive object modifies the electric field around the sensor, and the total capacitance the sensor sees will rise.
For OEMs, designing a system that can accurately differentiate an approaching human from environmental noise can be challenging. Similarly, temperature and other factors may also make capacitance vary over time and cause false detection. To address this, the sensor can include an auto offset compensation mechanism, to monitor and remove environmental effects to ensure that the sensor accurately detect human presence only.
Typical features to look for in proximity sensors include:
- High performance analog front end (AFE), enabling greater detection distance or smaller sensor area. This also delivers high signal-to-noise ratio and ensures strong noise immunity.
- Built-in smart human sensing capability to accurately differentiate between human and inanimate object to enhance detection accuracy.
- Stability: delivering low temperature variation over long durations and limiting the chances of false human detections.
- Small sensor footprint to provide versatility for a variety of applications and product implementations.
- Sensors offer low power consumption, making them ideal for battery-operated devices.
Conclusion
Today, tablet and laptop manufacturers design products that balance high performance and connectivity needed, while also ensuring SAR compliance. Intelligent sensors built into these consumer devices are able to detect human presence and automatically adjust RF emissions yet keep devices running at peak performance. Appropriate smart sensors make it possible to trust that a laptop will operate at its highest performance, enabling you to continue to work from anywhere.
This article was originally published on Embedded.
David Wong is senior director of consumer sensing products for Semtech’s wireless and sensing products group. He obtained his BS in electrical and electronics engineering from the University of Southern California.