Fiber optic temperature sensor for use in experimental microwave hyperthermia

Temperature measurement in electromagnetic environments is often accomplished with radiofrequency immune temperature sensors, like those based on optical fibers. This paper describes the development of an intensity-based fiber optic sensor, for use in the evaluation of microwave hyperthermia applicators. It measures the temperature based on the variation of optical power transmitted along the fiber. This variation is caused by the replacement of a small part of the optical fiber cladding by an oil whose refraction index is temperature dependent. A multimode 62.5/125 μm patch cord with ST type connectors was used. The sensor was built baring the fiber in the middle of the patch cord and replacing the cladding by a purified vegetable oil. The oil was contained inside a thin walled glass tube. The constructed sensor is cylindrical, with 1.1 mm of external diameter and 30 mm of length. It possesses a very low thermal time constant (<2 s) and an excellent repeatability. The fabrication procedure of the sensor is very simple and the required materials are relatively inexpensive.