between two layers of Kapton (25 mm thickness), in close contact with the material to be investigated. The double metal spiral serves both as the heat source and as a resistance thermometer. When making measurements in solid bodies, the spiral is clamped between two surfaces of the same material, as shown in the Figure 1. The radius of the sensor can very between 2 mm and 30 mm thus, the sample size can vary between 8 mm and 120 mm or larger.