Paper on rapid absorption cross-section in a reverberation chamber

Paper on the rapid measurement of absorption cross-section in a reverberation chamber accepted for publication in IOP Measurement Science and Technology.

This paper presents a measurement methodology for polarisation and angle of incidence averaged electromagnetic absorption cross-section using a reverberation chamber. The method is optimised for simultaneous rapid and accurate determination of average absorption cross-section over the frequency range 1 to 15 GHz, making it suitable for use in human absorption and exposure studies. The typical measurement time of the subject is about eight minutes with a corresponding statistical uncertainty of about 3% in the measured absorption cross-section. The method was validated by comparing measurements on a spherical phantom with Mie Series calculations.

The efficacy of the method was demonstrated by measuring the ACS of a subject in different body postures obtaining the results shown in the figure above. We also looked at the effects of clothing on the measured absorption which are important considerations for the practical design of experiments for studies on human subjects.

This work was primarily done as part of the High Intensity Radiated Field Synthetic Environment (HIRFSE) research project. Within HIRFSE the results were used to quantify how human bodies affect the electromagnetic field inside aircraft cabins. The measurement method was also used to obtain a large body of data for human exposure assessment (Flintoft et al., 2014).

The full details are in the paper (Flintoft et al., 2015).

References

1. Flintoft, I.D., Melia, G.C.R., Robinson, M.P., Dawson, J.F. and Marvin, A.C., 2015. Rapid and accurate broadband absorption cross-section measurement of human bodies in a reverberation chamber. Measurement Science and Technology, 26(6), p.065701.
   

   A measurement methodology for polarisation and angle of incidence averaged electromagnetic absorption cross-section using a reverberation chamber is presented. The method is optimised for simultaneous rapid and accurate determination of average absorption cross-section over the frequency range 1 to 15 GHz, making it suitable for use in human absorption and exposure studies. The typical measurement time of the subject is about eight minutes with a corresponding statistical uncertainty of about 3% in the measured absorption cross-section. The method is validated by comparing measurements on a spherical phantom with Mie Series calculations. The efficacy of the method is demonstrated with measurements of the posture dependence of the absorption cross-section of a human subject and an investigation of the effects of clothing on the measured absorption which are important considerations for the practical design of experiments for studies on human subjects.

   @article{Flintoft2015a,
     author = {Flintoft, I. D. and Melia, G. C. R. and Robinson, M. P. and Dawson, J. F. and Marvin, A. C.},
     title = {Rapid and accurate broadband absorption cross-section measurement of human bodies in a reverberation chamber},
     journal = {Measurement Science and Technology},
     year = {2015},
     volume = {26},
     number = {6},
     pages = {065701},
     month = jun,
     issn = {0957-0233},
     note = {© 2015 IOP Publishing. This is an author created, uncopyedited version of an article accepted for publication in IOP Measurement Science and Technology. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.1088/0957-0233/26/6/065701.},
     doi = {10.1088/0957-0233/26/6/065701},
     file = {:pdfs/MST26-Flintoft-065701.pdf:PDF},
     keywords = {absorption cross-section, reverberation chamber, specific absorption rate},
     owner = {idf1},
     postprint = {https://pure.york.ac.uk/portal/files/43360130/MST26_Flintoft_et_al_065701_postprint.pdf},
     timestamp = {2016.10.12}
   }
   

2. Flintoft, I.D., Robinson, M.P., Melia, G.C.R., Marvin, A.C. and Dawson, J.F., 2014. Average absorption cross-section of the human body measured at 1-12 GHz in a reverberant chamber: results of a human volunteer study. Physics in Medicine and Biology, 59(13), pp.3297–3317.
   

   The electromagnetic absorption cross-section (ACS) averaged over polarization and angle-of-incidence of 60 ungrounded adult subjects was measured at microwave frequencies of 1–12 GHz in a reverberation chamber. Average ACS is important in non-ionizing dosimetry and exposure studies, and is closely related to the whole-body averaged specific absorption rate (WBSAR). The average ACS was measured with a statistical uncertainty of less than 3% and high frequency resolution for individuals with a range of body shapes and sizes allowing the statistical distribution of WBSAR over a real population with individual internal and external morphologies to be determined. The average ACS of all subjects was found to vary from 0.15 to 0.4 m 2 ; for an individual subject it falls with frequency over 1–6 GHz, and then rises slowly over the 6–12 GHz range in which few other studies have been conducted. Average ACS and WBSAR are then used as a surrogate for worst-case ACS/WBSAR, in order to study their variability across a real population compared to literature results from simulations using numerical phantoms with a limited range of anatomies. Correlations with body morphological parameters such as height, mass and waist circumference have been investigated: the strongest correlation is with body surface area (BSA) at all frequencies above 1 GHz, however direct proportionality to BSA is not established until above 5 GHz. When the average ACS is normalized to the BSA, the resulting absorption efficiency shows a negative correlation with the estimated thickness of subcutaneous body fat. Surrogate models and statistical analysis of the measurement data are presented and compared to similar models from the literature. The overall dispersion of measured average WBSAR of the sample of the UK population studied is consistent with the dispersion of simulated worst-case WBSAR across multiple numerical phantom families. The statistical results obtained allow the calibration of human exposure assessments made with particular phantoms to a population with a range of individual morphologies.

   @article{Flintoft2014,
     author = {Flintoft, I. D. and Robinson, M. P. and Melia, G. C. R. and Marvin, A. C. and Dawson, J. F.},
     title = {Average absorption cross-section of the human body measured at 1-12 GHz in a reverberant chamber: results of a human volunteer study},
     journal = {Physics in Medicine and Biology},
     year = {2014},
     volume = {59},
     number = {13},
     pages = {3297--3317},
     month = may,
     issn = {0031-9155},
     note = {Date of acceptance: 06/05/2014. This is an author created, uncopyedited version of an article accepted for publication in IOP Physics in Medicine. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.1088/0031-9155/59/13/3297.},
     doi = {10.1088/0031-9155/59/13/3297},
     file = {:pdfs/PMB59-Flintoft-3297.pdf:PDF},
     owner = {idf1},
     postprint = {https://pure.york.ac.uk/portal/files/43360156/PMB59_Flintoft_et_al_postprint.pdf},
     timestamp = {2016.10.12}
   }