Defected Ground Circular Shaped Non- Invasive Microwave Sensor for Deep Brain Temperature Measurements

This paper presents a circular shape microwave sensor for passive measurement of deep brain temperature noninvasively. The structure of proposed sensor consists of electromagnetic band gap (EBG) based ground plane with double sided rings of C shaped having opposite openings in the circular patch. The microwave sensor is designed on FR-4 substrate with dimension $40 \times 30 \times 1.6 \mathrm{~mm} 3$. The measured reflection coefficient in vacuum is $-48 \mathrm{~dB}$ at resonance frequency 3.8 GHz. The observed impedance bandwidth is $2.75 \mathrm{GHz}(2.75-$ 5.5GHz) with total gain of $3.1 \mathrm{~dB}$. The simulated results with human head phantom show maximum SAR value $381.87 \mathrm{w} / \mathrm{kg}$, maximum volume loss density $4.088 \times 108 \mathrm{w} / \mathrm{m} 3$ and minimum detectable electric field $(\mathrm{v} / \mathrm{m})$ of $5 \mathrm{~dB}$ in brain tissue for lw of input power at the depth of $15 \mathrm{~mm}$ inside head. The proposed sensor is capable of measuring deep brain temperature in the range of $350-400 \mathrm{C}$ in active mode.