Conductivity and Permittivity Measurements of Children and Adult's Hands Covering Mobile Communications Frequency Bands

This paper investigates the use of a simple open-ended coaxial line probe for measuring in vivo the relative permittivity and conductivity of human hands at microwave fre- quencies. In particular, we investigate how these properties are afiected by the force with which the probe is pushed into the skin and the time over which the probe is in contact with the skin. Results show these two variables have a large in∞uence on the measured results. We identify a suitable test procedure for use on a large scale volunteer study and present initial relative permittivity and conductivity results from more than 150 volunteers, ranging from ages 11 to 65. 1. INTRODUCTION Smart phones have become more than simple communication devices; for many they are indispens- able accessories capable of running sophisticated applications. The use of these smart phones by children is becoming more widespread. In this changing climate, possible health efiects of radiation from mobile phones on children in particular, takes on an added importance. In order to assess the Speciflc Absorption Rate (SAR) in human tissue, the relative permittivity and conductivity of the tissue must be studied. These properties of biological tissues at microwave frequencies have been investigated over a number of decades (1{4). Researchers have used live and dead animals as well as adult volunteers to measure the electrical properties of tissues. Numerous full-body human phantom models are now available for EM simulations of SAR. Although a number of studies have developed mathematical functions to extrapolate child data from adult, actual measured conductivity and permittivity data for children is much harder to source. As part of a large volunteer based study looking at how the hand holding a mobile phone afiects the power absorbed in the head, this study evaluates the use of the open-ended coaxial line (OECL) probe technique for measuring palm relative permittivity and conductivity of human participants. First we investigate how the force with which the probe is pushed into the palm afiects the relative permittivity and conductivity. With increasing force, we expect the blood to be forced away and the contact point to become closer to the underlying muscle, which will then change the dielectric properties. With the probe making contact with the palm, we also investigate how the measured results change with time. The aim is to develop a suitable measurement protocol that can be used on child and adult volunteers. Finally, we present relative permittivity and conductivity data collected from more than 150 participants and demonstrate how these properties change with age. 2. OPEN-ENDED COAXIAL LINE PROBE CONSTRUCTION AND CALIBRATION