A size-distinguishing miniature electromagnetic tomography sensor for small object detection

Electromagnetic tomography (EMT) is an emerging imaging technique that presents the property distribution of conductive or magnetic materials based on signals from the coil array on the EMT sensor. However, conventional EMT researches generally involve large-size EMT sensors, which are ineffective in detecting and discerning the size of small objects due to limited spatial resolution, sensitivity and relatively high noise level. As such, this paper presents a novel miniature EMT sensor, which incorporates 8 small coils around the circumference for imaging and 2 larger horizontal coils that generate a vertical field for target size distinction. Moreover, a novel equivalent theory is proposed to approximate the effect of the horizontal coils by the cumulative effect of the 8 small coils. An EMT testing system is established with the proposed sensor array and the multi-channel instrument developed in our lab. Experiments based on multiple sample distributions and different reconstruction algorithms validate the ability of the sensor to detect and distinguish the size of small objects of different materials. Furthermore, the equivalent theory was validated through the experiments.