Research On Metal Detector Sensor Bases On Enclosed Circular Coil System

With the rapid development of modern industry and the progress of science and technology, informatization and automation technology has already been applied to the field of industry,medical treatment and many areas of daily life. In daily life, the monitoring of food safety and pharmaceuticals have been attached more and more concern, because if any metal impurities are mixed in food and pharmaceuticals, it will cause disastrous effect to consumers. Besides,in the industrial production line, if any metal impurities are added in the processing of materials, it will damage the devices and thus results in large economic losses to manufacturers.In order to solve the problems mentioned above, it is necessary to introduce a metal detector in the monitoring of food safety and industrial production line.Metal detector are devices used to detect the existence of metal based on the theory of electromagnetic induction while among all of the electromagnetic induction sensors, the most commonly observed one is circular coil sensor which relies on the changes of mutual inductance to do measurement. By referring to the model of enclosed circle balancing coil, this thesis devises a metal-detecting sensor aimed at the production line, which is particularly capable of monitoring the metal efficaciously and removing the impurities to ensure the production safety and order. The major task and researching focus of this thesis is as follows:Firstly, the analysis of mutual inductance between two non-coaxial circular coils is analyzed. By means of the vector magnetic potential, Kim modificatory formula is derived in detail for calculating the mutual inductance between two non-coaxial circular coils, and the reason why Kim formula is wrong has been indicated. And by comparing the simulated results with the Neumann integral formula calculation results, it is verified that Kim modificatory formula is correct and computation efficiency is higher than Neumann integral formula.Then, the characteristic analysis of enclosed circular balanced coil sensors is analyzed. Based on the mathematical model about enclosed circular balanced coil for metal detector, in this thesis, the magnetic field distribution of transmitting coil is analyzed, and the change rules of the electromotive force before and after the entry of metal in the coil are studied.Last, the optimized design of enclosed circular balanced coil sensors is implemented. Through the analysis of the position of the metal, the frequency of the excitation signal and the influence of different metal materials on the output signal of the sensors, the optimal position of the conveyor belt and the best physical model of the sensors are-determined.Simulated results indicates that the electromagnetic induction sensors which are based on enclosed circular balanced coil can detect and identify metal effectively. This sensor has achieved the expected goal, providing theoretical basis for improving the detective accuracy and stability of metal detector.