National Physical Laboratory

Specific Absorption Rate


NPL has the UK's National Standards for Specific Absorption Rate (SAR), and offers calibration services for SAR probes in head and muscle simulating liquids. Probes are calibrated using matched-waveguide systems, as recommended by IEEE and CENELC Standards. The systems are traceable to Primary National Standards and meet the calibration requirements for companies seeking accreditation for their SAR measurement services.

NPL has waveguide systems for calibrating SAR probes in liquids at TETRA (380 MHz to 460 MHz), GSM900, GSM1800, GSM1900 and Bluetooth (2450 MHz) frequencies. The calibration uncertainty for these measurements is ± 10% (at a level of confidence of 95%). Calibration in other frequencies and liquids is available by request. We are able to calibrate all models of probe from SPEAG, IndexSAR, Narda, Antenessa and Aprel Labs.

In addition to probe sensitivity in liquid, NPL has systems for characterising all other relevant performance characteristics of SAR probes. This includes probe linearity to pulse modulated and amplitude modulated signals, spherical isotropy, and spatial resolution. We are also able to calibrate the probe's sensitivity in air over the frequency range DC to 40 GHz, with uncertainties as low as ± 5% (at a level of confidence of 95%).

The complex permittivity of tissue equivalent liquids is measured using either coaxial probes or temperature controlled transmission cells, with a best measurement uncertainty of ± 1% (at a level of confidence of 95%). Measurements over a range of accurately controlled temperatures are also possible, and this allows the temperature coefficient of the permittivity to be established.

NPL offers calibration of systems for radio frequency (RF) dosimetry to researchers studying health effects of RF and microwave exposures. Our capabilities extend to the calibration of RF exposure systems used for medical research, including measurement of SAR induced in samples in vitro, thermal measurements and also computer simulation of these systems.


SAR Probe Calibration Services

  • Sensitivity in liquids for the following frequency ranges:
    • 380 MHz to 460 MHz
    • 800 MHz to 1000 MHz
    • 1750 MHz to 1950 MHz
    • 2300 MHz to 2600 MHz
  • Proximity effects - change in sensitivity when the probe is used near to the boundary of the phantom
  • Spherical isotropy in fluid at 900 MHz and 1800 MHz
  • Spatial resolution of the probe in fluid
  • Sensitivity in air from DC up to 40 GHz
  • Linearity to continuous wave, amplitude modulated and pulse modulated signals (including GSM, UTMS and TETRA signals) up to field levels of 2500 V/m in air
  • Dielectric measurements of liquids
  • Complex permittivity of tissue equivalent liquids, using either coaxial probes or transmission cells
  • Measurement of the temperature dependence of the permittivity


Customer Service tel: +44 20 8943 8538

Last Updated: 25 Mar 2010
Created: 8 Jun 2007


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