Abstract
A small slot antenna has desirable characteristics for radio communications and location of an internal transceiver in-vivo medical applications. The effect of coupling between two identical antennas on the human torso was measured between 2.1 GHz antennas on the skin surface. The effect of an external field was measured as a function of the angle in the horizontal plane to quantify noise isolation. The perimeter separation loss was approximately 0.25 dB/mm. The external radio source induces currents in the soft conducting tissue resulting in a sinc radiation pattern for the antenna/body combination with a front-to-back ratio of approximately 12 dB. As the UHF band is commonly used in many non-medical applications, there is concern that external radio sources can result in a reduced signal to noise ratio and perturbed field strength measurements on the skin.
Highlights
A slot in a small conducting box has been suggested as a convenient wearable antenna for measuring the radio field on the skin surface from a subsurface transmitter [1]
This paper addresses two important characteristics of the antenna not yet reported, (a) the mutual coupling between two antennas on the skin surface, and (b) the effect of an in-band radio source on the field strength measurement and communications reliability
An inward-looking, resonant, slot antenna was designed for impedance matching to the human torso at 2.1 GHz
Summary
A slot in a small conducting box has been suggested as a convenient wearable antenna for measuring the radio field on the skin surface from a subsurface transmitter [1]. When the transmitter is embedded in the lossy media, lateral wave propagation effects can be observed on the surface evidenced by significant interference nulls [2], [4]. This interference is caused by the difference in the path attenuation and the time of arrival for the direct ray through the material and a surface wave propagating across the surface. When one half space is layered, trapped and ducted propagation paths can exist This effect is commonly observed in clear air propagation caused by temperature and humidity variations in layers close to the earth’s surface [5]
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