Thermoelectric needle probe for temperature measurements in biological materials

In certain biological and medical applications it is important to measure and follow temperature changes inside a body or tissue. Any probe inserted into a tissue causes damage to tissue and distortion to the initial temperature distribution. To minimize this interference, a fine probe is needed. Thus, thin film technology is advantageous and was utilized by us to produce sensitive probes for these applications. The resulting probe is a small thermocouple at the tip of a thin needle (acupuncture stainless steel needle, approximately 0.26 mm in diameter and length in the range 5-10 cm was used). The junction was produced at the needle's tip by coating the needle with thin layers of insulating and thermoelectric materials. The first layer is an insulating one and is composed of polyacrylonitrile (PAN) and polymide produced by plasma polymerization and dip-coating respectively. This layer covers all the needle except the tip. The second layer is a vacuum deposited thermoelectric thin layer of Bi-5% Sb alloy coating also the tip. The third layer is for insulation and protection and is composed of PAN and polyimide. In this arrangement the junction is at the needle's tip, the needle is one conductor, the thermoelectric layer is the other and they are isolated by the plastic layer. The probe is handy and mechanically sturdy. The sensitivity is typically 77 microV/degrees C at room temperature and is constant to within 2% up to 90 degrees C. The response is fast (less than 1 sec) the noise is small, (less than 0.05 degrees C) and because of the small dimension, damage to tissue and disturbance to the measured temperature field are minimal.