Abstract: A method of determining a concentration of magnetic powderly material in a sample is disclosed. In this method, a pair of series-connected exciting coils are disposed in such a manner that magnetic fields generated from the respective exciting coils oppose to each other. A detecting coil is disposed at a position where the magnetic fields from the pair of exciting coils cancel out each other. A sample mixed with magnetic powder is inserted into one of the pair of exciting coils. Then, the method detects a voltage induced in the detecting coil in association with the insertion of the sample into the exciting coil and determines the concentration of the magnetic powder in the sample based on the detected voltage.

Abstract: An ozone gas sensor comprising a film type semiconductor element including a substrate and a semiconductor film consisting of a metallic oxide formed on the substrate, and a layer of silica formed on a surface of the film type semiconductor element. At least one thin film layer of one or a plurality of types selected from metals and metal oxides is interposed between the semiconductor film and the layer of silica.