New wireless thermometer for RF and microwave thermal therapy using an MMIC in an Si BJT VCO type

A new wireless thermometer is proposed for thermal therapy that uses a silicon bipolar transistor voltage-controlled oscillator (Si VCO), based on three-dimensional monolithic-microwave integrated-circuit (MMIC) technology. A theoretical analysis of heating characteristics was conducted using the finite-element method. The result suggests the MMIC thermometer may be used for RF/microwave thermal therapy in a strong electromagnetic wave circumstances. The fundamental characteristics of an Si VCO MMIC are examined experimentally. As a result, the VCO's oscillation frequency (around 4.35 GHz) is extremely linear against temperature in the range from 30/spl deg/C to 50/spl deg/. Tests using a phantom material show that a prototype thermometer can be detected at depths of more than 8 cm of soft tissue.