Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC TR 62630: Evaluating Exposure from Multiple Electromagnetic Sources
IEC TR 62630:2010 provides technical guidance for evaluating human exposure to electromagnetic fields (EMF) when multiple sources contribute simultaneously. As wireless infrastructure proliferates — with cellular base stations, Wi-Fi access points, broadcast towers, and personal devices all contributing to the ambient RF environment — methods for assessing cumulative exposure become essential for compliance with safety limits.
Key Challenge: Real-world EMF exposure is rarely from a single source. Mobile phone users are simultaneously exposed to signals from their own device, nearby base stations, Wi-Fi routers, and broadcast transmitters — all at different frequencies and power levels.
1. Source Classification and Exposure Scenarios
The report classifies EM sources along two key axes:
| Classification Axis | Category | Characteristics | Examples |
|---|---|---|---|
| By intended use | User-centric | Device operates near the body; exposure dominated by near-field | Mobile phones, tablets, laptops |
| By intended use | Node-centric | Fixed installation; exposure from far-field at distance | Base stations, broadcast towers |
| By spectral characteristics | Single-channel | Narrowband emission at one frequency | FM radio, GSM carrier |
| By spectral characteristics | Band-wide | Broadband emission across frequency range | UWB devices, CDMA/WCDMA |
2. Combined Exposure Evaluation Methods
2.1 Uncorrelated Sources
When multiple EM sources emit uncorrelated signals, the combined exposure is evaluated by summing individual exposure ratios:
Total exposure ratio (TER): Sum of (Ei/Elimit,i)2 over all sources i
For SAR-based limits, the total SAR is the sum of SAR contributions from each source. This linear summation is valid when the sources operate at different frequencies or are sufficiently separated in space.
2.2 Correlated Sources
When signals exhibit correlation — for example, multiple antennas in a MIMO system or sector antennas on a shared tower — the field vectors may add coherently, requiring vector summation rather than power summation. The report provides:
- Accurate estimate: True field vector sum using complex phasor representation
- Conservative bound: Upper-bound estimate using scalar sensor measurements with a correction factor
Practical Guidance: For most public exposure assessments, uncorrelated power summation is conservative and appropriate. Vector summation is necessary only for tightly coupled sources (e.g., MIMO antennas).
3. Exposure Metrics and Limits
| Frequency Range | Exposure Metric | Basic Restriction | Reference Level |
|---|---|---|---|
| 100 kHz – 10 MHz | Current density (J) | f/500 A/m2 | E = 87 V/m |
| 10 MHz – 400 MHz | Specific absorption rate (SAR) | 0.08 W/kg (whole body) | E = 28 V/m |
| 400 MHz – 2 GHz | Specific absorption rate (SAR) | 0.08 W/kg (whole body) | E = 1.375 f1/2 V/m |
| 2 GHz – 300 GHz | Power density (S) | 10 W/m2 | S = 10 W/m2 |
Engineering Note: When evaluating combined exposure from sources operating in different frequency bands, the frequency-dependent basic restrictions must be applied individually and then weighted. A source at 900 MHz and another at 2.4 GHz cannot be simply compared using the same exposure metric.
Engineering Design Insights
- Site-specific assessment is essential — generic exclusion zones for individual antennas are insufficient when multiple sources share a tower; combined field calculations must account for spatial overlap of beams
- Time-averaging considerations — exposure limits are typically averaged over 6 minutes for occupational and 30 minutes for general public; fast-fading signals require statistical treatment
- Measurement vs. simulation — while measurement is the gold standard for compliance, full-wave simulation (FDTD, MoM) is more practical for predictive assessment during the design phase of multi-antenna installations
- Uncertainty management — combined exposure evaluations accumulate uncertainties from each source; a root-sum-square approach with coverage factor k=2 is recommended for compliance decisions
- Public communication — total exposure ratios below 0.1 (10% of limit) are generally considered negligible by regulators and provide a useful benchmark for community reassurance
FAQs
Q: Why is evaluating combined EM exposure important?
A: As wireless devices and infrastructure multiply, people are increasingly exposed to multiple EM sources simultaneously. Individual compliance assessments may underestimate cumulative exposure, potentially exceeding safety limits when all sources are considered together.
Q: Can I simply add the power density from all sources?
A: For uncorrelated sources (different frequencies, random phases), power density addition is appropriate. For correlated sources, vector addition may be needed. The report provides guidance on when each approach is applicable.
Q: How does the report address 5G and massive MIMO?
A: The report provides the foundational framework for correlated source evaluation. Beamforming arrays present a complex case where the field distribution changes dynamically; statistical approaches based on time-averaged exposure patterns are recommended for 5G systems.
