Microwave Radiation-Pattern Measurements in the Presence of Biological Specimens

Power density is used extensively as an index of hazard to living systems from microwave radiation. To assess this, the biological effect observed in test specimens is related to power density, as measured in the absence of the specimen. The usefulness of power density as a biologically meaningful parameter has often been questioned and other alternatives have been proposed. In this paper, the authors show the restricted applicability of power density as an indicator of both biological hazard and beneficial effects caused by microwave fields. Power density measurements, at X-band microwave frequencies, were carried out in an anechoic chamber. Measurements were conducted in the absence and in the presence of biological specimens (animals and plant vegetation), with the aid of an isotropic microwave probe. Dramatic differences in the radiation patterns were observed, attributable to the large disturbance introduced by the biosystem on the imposed electromagnetic fields. Thermographic analysis (IR scanning) and microwave radiometry complemented the investigation.