Standards: Exposure Limits for Brief High Intensity Pulses of Radiofrequency Energy Between 6 and 300 GHz

Overview

This Standards paper examines the exposure limits defined by the International Commission on Nonionizing Radiation Protection (ICNIRP) and the IEEE (C95.1-2019) concerning "brief exposures" to radiofrequency electromagnetic fields (RF-EMF), especially when exposures fluctuate significantly within the 6-minute averaging period specified in the current guidelines.

Relevant Exposure Scenarios

• Cellular base stations using MIMO antennas with beamforming technology, which sweep beams dynamically across the service area.
• Exposure to pulsed RF-EMF with high peak power and low duty cycles.

Findings

• Both ICNIRP and IEEE limits for brief RF-EMF exposures between 6 and 300 GHz were assessed with numerical and analytical approaches using a one-dimensional thermal tissue model.
• The study analyzed skin heating effects for both rectangular RF-EMF pulses (sudden exposure) and impulsive energy events.
• The research revealed that these guidelines provide varying levels of protection against transient skin heating—with IEEE guidelines being notably more conservative than ICNIRP's.
• The paper proposes a straightforward adjustment to existing pulse fluence limits to enhance protection consistency against excessive temperature increases, irrespective of pulse duration and frequency.

Limitations and Further Risks

• ⚠ Nonthermal hazards and thermoacoustic effects—produced by brief, extremely high amplitude RF-EMF pulses—are not addressed in this analysis, despite the potential for biological impacts due to rapid temperature changes, even if absolute temperature increases are small.

Conclusion & Research Needs

⚠ The current guidelines exhibit inconsistencies in safeguarding against transient heating. Further research and development are urgently needed to establish and refine exposure limits for pulsed RF-EMF to ensure adequate health protection.