1. RF Safety Measurements IOSH meeting Emley 4 th July 2013 www.radhazonline.com

2. What’s New?

3. Measurement & Monitoring Equipment n Survey Equipment –For making quantitative measurements ‘Broadband’ instruments Frequency selective instruments n Personal Monitors –For monitoring worker exposure levels n Area Monitors –Continuous monitoring

4. Survey Equipment vProvides a relatively accurate assessment of field strength and can be used to determine the level of compliance to a particular standard. vRequires a reasonable level of training before it can be used with confidence. vDoes not provide continuous monitoring against sudden equipment failure.

5. Types of Field Sensing Probe  Probes measure either the Electric and/or Magnetic field components.  Usually broadband without frequency selection capability.  Usually isotropic although anisotropic probes used for leakage measurement.  May provide “flat” or “shaped” response.

6.  Shaped Response  ‘Flat’ Response Types of Field Sensing Probe

7. Shaped Probes  Shaped probes have a frequency response weighted in accordance with a given safety guideline or standard. Shaped probes read out in “% of Std.” e.g. ICNIRP rather than in normal field units.  Shaped probes are useful for multiple emitter environments (multiple frequencies with different permissible exposure levels).  Shaped probes are also useful when surveying unknown or classified frequencies.

8. Freq. PWR STD. %STD (MHz) W/m 2 W/m 2 148 2.5 10 25 900 5.0 22.5 22 2100 20 50 40 Total = 27.5 W/m 2 87% 30 100 300 1310 MHz GHz Power Density (W/m²) 50 10 40 30 20 Determining Compliance in a Multi-Emitter Environment

9. Freq. PWR STD. %STD (MHz) W/m 2 W/m 2 148 10 10 100 900 5.0 22.5 22 2100 12.5 50 25 Total = 27.5 W/m 2 147% 30 100 300 1310 MHz GHz Power Density (W/m²) 50 10 40 30 20 Determining Compliance in a Multi-Emitter Environment

10. Magnetic Fields are measured with loops Ammeter Flux Lines Flux lines passing through loop generate current. Maximum indication if flux lines are perpendicular to loop. Mutually orthogonal loops are used in most survey probes. Magnetic field measurements  Narrowband operation compared to E-field probes.  May generate large out-of-band responses.

11. Low frequency Electric fields are measured with plates. Field lines strike perpendicular to plates and the resultant dieletric current is measured. ELF Measurements

12.  Electric fields are measured with a mutually orthogonal array of diode dipoles or thermocouples. Measurement of RF Electric Fields  Thermocouples exhibit extremely good adherence to the square of the field strength, and their output is relatively independent of ambient temperature. Typically have wide frequency operation (0.3 to 100GHz). Limited sensitivity, minimum measurement around 6 V/m (10  W/cm²). Relatively low overload level. Relatively expensive.

13.  Diode Based Detection –Better “zero stability” and overload handling but higher temperature sensitivity. –Good at low field levels, when diode is in it’s “square-law” region. A diode is a non-linear device, which when operated at higher levels will detect peak rather than average levels. Not recommended for multiple signal or pulsed signal environments. Measurement of RF Electric Fields

14. Types of Detectors - Diode Power In Voltage Out (A 2 + B 2 + C 2 ) (A + B + C) 2 “Square Law” Response

15. Measurement Uncertainty Three basic approaches to measurement uncertainty:  Direct comparison (or shared) risk approach - Measurement is taken as read. Uncertainty just quoted. May lead to poor quality measurements.  Additive approach - Maximum permissible exposure level is inset from the given safety guideline level by the amount of uncertainty. Can be overly restrictive.  Hybrid Approach - If uncertainty is kept inside a given limit e.g. 4dB, the measurement can be taken as read. If uncertainty exceeds the stated limit then the additional uncertainty is applied to the recorded value.

16. Measurement Uncertainty 10. Uncertainty NBM550 & EF0391 (Broadband equipment) Source of uncertaintyUncertainty Value (dB) Probability DistributionDivisorStandard Uncertainty (dB) Variation due to probe isotropy 1Rectangular1.730.58 Variation in linearity response 0.5Rectangular1.730.29 Variation due to frequency response 1.25Rectangular1.730.72 Calibration uncertainty1.52 (k=2)0.75 Variation due to temperature 0.2Rectangular1.730.12 Repeatability2.0Normal2 (k=2)1.0 Combined standard uncertainty 1.58 Expansion factor1.96 Expanded uncertainty3.1 Expanded uncertainty (%)50% See EN50413 for further information.

17. Frequency Selective Survey Meter Combines the features of a hand-held spectrum analyser and an isotropic probe. Utilises an active antenna ideal for high sensitivity applications. Expensive compared to conventional broadband equipment. Limited frequency range 100kHz/27MHz to 6GHz.

18. Frequency Selective Survey Meter

20. Induced Current Measurements  Induced body current & contact current measurements occasionally may be relevant for frequencies up to 110MHz. RF induces voltage in ungrounded conductor Person acts as current path to ground by touching charged conductor RF induces voltage flow in person Current flows to ground

21.  Most UK telecoms and broadcast companies utilise personal monitors as part of a RF safety programme. simple to use simple to use have a wide operating frequency range (100 kHz to 100 GHz) have a wide operating frequency range (100 kHz to 100 GHz) shaped alarm threshold shaped alarm threshold  expensive  not accurate enough to be used for quantitative readings Personal monitors

22. The small print:  Polarization - Personal monitors should have the ability to detect all polarizations equally as an acute failure or near field applications will not have a predictable polarization.  Detection Angles - Personal monitors should have the widest possible detection angles, typically 45 to 90 degrees  Detection Angles - Personal monitors should have the widest possible detection angles, typically 45 to 90 degrees. Personal monitors

23. The small print: The small print:  Directivity. Most personal monitors are not omnidirectional, by function of their design they do not detect rf emissions to the rear of the unit. Accuracy should not be affected by presence of the human body.  Dosimetry. Personal monitors are not required to be true dosimeters - however some models do have data logging capability. Personal monitors

24. Area Monitors There are two main applications for area monitors:  Constant monitoring of an area near high power systems such as radar. Typically used for occupational applications.  Constant monitoring and datalogging of relatively low power signals near cell sites, radio masts etc. Typically used in public areas.

25. What to use?   For general public measurements: - - Telecoms & broadcast – usually Electric field only - - Frequency Range? - - Measurement Sensitivity? - - Broadband or frequency selective? - - Measurement uncertainty often less critical as recorded values will be tiny percentages of permissible exposure levels.

26. What to use?  For occupational measurements: -Frequency range? -Broadband or frequency selective? -Measurement range? -Overload (CW & Peak)? -Electric and/or Magnetic field? -Time or spatial averaging? -Meter memory? -Diode or thermocouple detectors? (Simple diode detectors not recommended for multiple signal or pulsed signal environments)

27. Measurement equipment  The small print: -Frequency sensitivity -Isotropy -Linearity -Out of band response -Temperature response -Unwanted response to the E or H component -Minimum measurement distance -Calibration standard

28.  No automatic need for measurement or monitoring equipment. Risk assessment can be by calculation.  Measurement or monitoring equipment should be backed up with appropriate training.  Measurement or monitoring equipment should be used as part of a RF safety programme.  Note requirements of EN50499 ‘Determination of workers exposure to electromagnetic fields’ etc. Occupational Exposure

29.  Measurement & monitoring equipment can be an important part of an RF safety programme but do not forget common sense and a basic risk assessment, you need to identify; -output power from source(s) -distance to source(s) -exposure period -operating frequency Occupational Exposure

30. Safe?Unsafe? Near Hz detector blah V 2 /m 2 %*~!! And finally……. Any Questions? www.radhazonline.com