![metal detector metal detector](https://cdn.thewirecutter.com/wp-content/media/2021/08/metaldetector-2048px-0202.jpg)
However the single channel metal detection sensor has not shown sensitivity resolution through wide range of metal sizes from mm to cm scale. Active researches have been performed for the various kinds and shapes of metal in metal sensor head.
![metal detector metal detector](https://www.refrigeratedfrozenfood.com/ext/resources/RFF/Mettler-Toledo/MT-metal-detector-GC-conveyor-series.jpg)
The structure of sensor head in metal detector plays an important role in terms of sensitivity, and relevant studies have been conducted in this regard. The parent body containing metal piece is important from the point of selectivity, and the effort to detect foreign pieces in powder has been attempted. On the other hand, there were attempts to enhance visibility of metal piece through signal processing. Theoretical analysis and sensitivity analysis along with the shape of metal sensor have been performed to explore the sensitivity of electromagnetic metal sensor. However the method using electromagnetic wave is dominant, and recently the method using superconducting coil has been attempted. The demand for metal detection is high in food industry, and recently the detection methods by using X-ray and light have been already applied for this. Among these foreign materials, the detection for metal pieces is important in food industry, and various researches are concentrating on this. Other methods are envisaged to detect these materials which are not detectable by using metal sensor. Foreign materials are not only metal but also wood, ceramics, and germs, which are not detectable by using metal sensor. The metal detection sensor is now widely used in not only food processing industry but also defense industry to detect metal pieces in surrounding object, and considerable efforts have been devoted to enhance sensitivity and selectivity. Thus it was feasible to operate two sensors, having different sensitivity range, simultaneously and to extend detection range from mm to cm scale, within practically acceptable interference. The effect of interference, while in simultaneous operation of two sensors, resulted in reduced output response, but still within usable detection range. And metal detection channel having sensitivity in cm scale showed more uniform sensitivity distribution with the flexibility for future modular construction. Metal detection channel, having sensitivity in mm scale, showed detectable sensitivity to moving ferrous sphere, with diameter down to 0.7 mm, at 50 kHz exciting frequency and enhanced sensitivity distribution. The characteristics of the two metal detection sensor channels were investigated, respectively, and the interference effect, while in simultaneous operation, between two sensor channels was discussed. Two-channel metal detector, having two sets of perpendicularly oriented sensor antennas, is proposed to expand detectable size, ranging from mm through cm scale, of metal sensor, while conventional metal sensor is dedicated for detection only in mm or cm scale.