In this series, Verkotan will dive into the world of SAR testing, an essential part of assessing the safety of modern wireless devices. SAR, or Specific Absorption Rate, measures the amount of radiofrequency energy absorbed by the human body from wireless devices like mobile phones, tablets, and other electronic gadgets. SAR testing is crucial as it helps ensure that these devices do not expose users to harmful levels of radiation.

SAR testing involves a complex scientific process, examining how wireless devices affect the body at various frequencies and power levels. Throughout this series, we will explore what SAR is, how it is measured, and why it’s so important for our health. Our goal is to provide readers with a thorough understanding of the scientific principles behind SAR testing and its role in the development of safe and effective technology.

History of SAR Testing and Limits

The Specific Absorption Rate (SAR) is a measurement in wireless technology area ensuring that mobile devices comply with safety standards to protect users from excessive radiofrequency (RF) energy exposure. But how did SAR testing come about, and how have the limits evolved over time? This article explores the history of SAR testing, the scientific developments behind it, and how regulatory standards have shaped the way we use mobile devices today.

The Early Concerns About RF Exposure

The study of electromagnetic radiation’s effects on the human body dates back to the early 1900s when scientists began investigating the biological effects of radio waves and microwaves. As radio and television broadcasting expanded in the 1950s and 1960s, concerns were raised about the long-term effects of RF exposure.

During the 1950s and 1960s, military research, particularly from radar systems, provided early data on how RF radiation interacts with biological tissues. These studies primarily focused on thermal effects, where RF energy absorbed by the body led to tissue heating. This research laid the foundation for understanding exposure risks and the need for safety standards.

Animal Studies in Early RF Research

Animal studies played a crucial role in early RF research, helping scientists to understand how the RF energy interacts with biological tissues. Many studies have documented the behavioural and physiological reactions of laboratory animals like rodents and rabbits to the thermal effects of RF energy at frequencies above 10 MHz.

These studies contributed to the understanding of RF energy absorption and helped develop the foundational principles of SAR testing. The localized SAR limit is derived from animal studies. It has been observed that a local SAR exposure 100 W/kg causes adverse effects on rabbit’s eyes.

Evolution of SAR Limits

SAR is measured in watts per kilogram (W/kg) and it indicates how much energy a tissue absorbs when exposed to RF fields. The introduction of SAR as a metric allowed for systematic testing of RF exposure and the establishment of safety guidelines. Studies showed that exposure to high-intensity electromagnetic fields can cause biological effects. In particular, exposure rates above 4 W/kg for whole body in primates were found to result in harmful behavioral effects, linked to body temperature increases that primates thermoregulatory systems could not manage.

A safety factor was applied to the findings from primate studies to ensure human health protection. A factor of 10 was applied for workers, and an additional factor of 5 for the general public. This resulted in SAR limit of 0.08 W/kg averaged over the whole-body for the general public.

Local SAR limits were established differently across the regions. In USA and Canada, a safety factor of 20 was applied to whole body SAR limit, resulting in a local SAR limit of 1.6 W/kg averaged over 1 gram of tissue for head/trunk. In Europe and many countries outside the Europe, such as Australia, International Commission on Non-Ionizing Radiation Protection (ICNIRP) set local SAR limits based on studies showing that the exposure rate of 100 W/kg could cause adverse effects on rabbits eyes. Considering that the human eye weights about 10g, safety factor of 50 was used to set the local SAR limit to 2 W/kg averaged over 10 grams of tissue for the head/trunk. For limbs, the local SAR limit is set at 4.0 W/kg averaged over 10 grams of tissue, and this limit is used worldwide.

Conclusion

The history of SAR testing highlights the efforts to ensure mobile device safety against RF exposure. Early studies, particularly on animals, established the basis for SAR metrics to measure energy absorption and its biological effects. As scientific understanding grew, safety factors were introduced to protect human health, leading to the development of SAR limits across different regions. Today, SAR testing remains crucial for ensuring that mobile devices comply with safety standards, balancing technological progress with the protection of public health.

Stay tuned for the next article in our Inside SAR! series, where we’ll explore how we mimic the human body in our testing. 

With over 20 years of SAR testing expertise, we guide you through every stage of product development, ensuring safety and reliability. Our in-depth knowledge of CE, FCC, and ISED certification helps you navigate the conformity process with confidence. 

Let us help you with your next project. Get a quote here! 😊