A high-sensitivity phantom-implantable E-field probe for studies in bioelectromagnetics

The authors address the design, development, and evaluation of a high-sensitivity RF sensor that is useful in measuring specific absorption rate (SAR) that occurs when a full-size human phantom is exposed to radio-frequency (RF) radiation. The probe consists of a small dipole connected to a zero-bias Schottky diode. The detected and filtered DC signal is preamplified and applied to a voltage-controlled oscillator (VCO). The VCO output is transmitted to a receiver by a fiber-optic link. The preamplifier and VCO use very-low-power devices which permit minimum battery drain. The zero-bias detector has a near-zero cut-in (forward) voltage and detects low-level field intensities. The fiber-optic link eliminates RF interference, and the relatively small diameter of the probe permits determination of localized SAR in phantom models. Details concerning prototype development and testing are presented. Initial evaluation of the probe indicated a VCO frequency shift of 1.0 kHz for an internal 29.9-MHz electromagnetic-field intensity of approximately 82 V/m