A Novel Orthogonal Electromagnetic Sensing Method for Metal Detection

In this article, for electromagnetic (EM) target sensing, the effect of primary- and secondary-field spatial coupling characteristics has been studied. Such investigation holds promises for metal detection. A novel orthogonal EM sensing method is proposed where the primary field is applied along the
${z}$
-axis and the secondary field is picked up along the
${x}$
-axis. When the second field is orthogonal to the primary one, the metal target incurred weak magnetic perturbation can be extracted much easier than the traditional parallel manner. Based on the theoretical analysis, a metal detection system based on a tunneling magnetoresistive (TMR) sensor and a driving coil is developed. The sensor’s sensing direction is orthogonal to the excitation field. Such metal detector has been used to detect a metal small target with increased high secondary field to the primary-field ratio (SPR) and signal-to-noise ratio (SNR) by 9.8 dB compared to the traditional parallel configuration.