ABSTRACT
Antennas as part of communication devices, sensors or radars can be mounted in close vicinity to the human body or even inside the body. The body is composed of many materials which affect the behavior and the performance of the antennas in different ways. Thus, the design of antennas, mounted near the body, should take into account the configuration of electromagnetic waves in boundaries between air and matter. When a plane wave that propagates in free space hits the human body, part of the energy is reflected back to air and part of the energy penetrates into the body. Some of the penetrating energy continues to propagate inwards into the body and some is absorbed by the tissues and the bones.
The design of antennas in the vicinity of the human body requires an accurate knowledge of the electrical properties of various tissues. Experimental data concerning the dielectric constant and the dielectric loss in human tissues have been published in the public domain. The variations of data from specimen to specimen and the dependence on the water content suggest that each antenna should be designed and optimized for its specific location near or inside the body. The design can include simulations, experiments on phantoms and experiments on live tissues (as long as low power of less than 10 mW is involved).
This chapter brings readers to the actual world of the design and measurement of antennas in close vicinity to the human body. Detailed reviews of such developments, either external or internal to the body (implantable), can be found in the literature. The small antennas under consideration were mounted on a human body (neck, belly, chest, etc.) or inside a phantom of the body, at different frequencies from VHF to S band. The chapter describes the effects of the human body in several aspects—detuning of the working frequency, additional loss by the live tissue, effects on the radiation patterns and the gain, and possible polarization rotation. Some commonly used measures to minimize the effects of the body are described and compared: choice of antenna shape, control of the distance to the body, isolating the antennas by a metallic sheet, use of absorbing materials and others. The chapter emphasizes the actual realization of the antennas and naturally it provides detailed examples with essential “tips” from an experimentalist point of view.
The five case studies presented here range from antennas attached to the body to antennas inside the body.
Wearable UHF radio-frequency identification tag on the neck.
Short-range link through the body at 2.4 GHz.
Measurement of body parameters with electrocardiogram pads.
Cellular antenna on a phantom.
Small antennas inserted into a phantom.
