Magnetic thin film access card system

A system is described for a low-cost access card system which exhibits a high resistance to conventional decoding and inspection techniques. The system described utilizes the uniaxial anisotropic characteristics of thin magnetic films deposited onto a code card and then encapsulated. Methods of depositing the magnetic materials are discussed and card fabricating and coding techniques are described. Mathematical equations are given for the binary one and zero output voltages from the sensor as a function of the system parameters. Experimental data are given for several magnetic samples. Comparisons are made between the calculated and experimental results. Four-pole transducer configurations for maximum prevention of code simulation are described.