Magnetoresistive power sensor for measurement in situ of RF power absorbed by tissue

A new magnetoresistive sensor for use in medical RF heating and hyperthermia is presented. This sensor has dc output proportional to RF power absorbed in tissue. The operating principle of the sensor consists of multiplication of the instantaneous value of the RF current and voltage in a microstrip transmission line using a magnetoresistive element. At an operating frequency of 915 MHz in a 20% bandwidth, it has a sensitivity of 22 μV/W, insertion losses less than 0.1 dB and nonlinearity less than 3% up to 300 W. The uncertainty caused by the reflected waves with arbitrary phase is less than 3.5% up to the voltage standing wave ratio (VSWR) equals 3