During industrial processing, it is possible for food to be contaminated with physical objects such as metal, plastic and glass. This can have health and safety repercussions as well damage the companies reputation. There are several technologies for instance X-rays, thermal imaging, near infrared spectroscopy that are used for food imaging. However, each technology has limitations. For instance, X-rays are not able to detect contaminants with a similar density to the medium they are in.

A novel method is proposed by Bill Heffernan which aims to detect such contaminants using Electromagnetic Sensing and Tomography in homogeneous mixtures. This technique differentiates the contaminants based on their conductivity by passing a sinusoidal current through the homogeneous mixture. When there is no contaminant, the current is uniform in the pipe. However, when there is a contaminant, the current distorts. This distortion results in distortion in the magnetic field. Low noise electronics hardware was designed, simulated and developed to measure the magnetic field around the pipe. Two Printed circuit boards (PCBs) were designed for the project: the sensor board and the main board. The sensor board consisted of a search coil, a two-stage amplification circuit and an ADC, and was found to have a voltage noise of 2 nV/ √ Hz . Originally the system was designed for 8 sensor boards, daisy chained together but due to limitations in the data transfer rate, this was changed to 3 sensor boards which were then rotated to take multiple static measurements. The main board supplied the power and retrieved the data from the sensor boards and sent them to the PC.

The estimated amplitude of the voltage induced in the search coil was recorded when phantoms made from three different contaminants were added inside a pipe; namely aluminium, Polylactic Acid (PLA) plastic and ferritic steel, in line with the sensor board ring. The results showed an increase in amplitude in the circumferential flux in the vicinity of aluminium and a decrease in the vicinity of PLA plastic. The ferritic steel also showed an increase in amplitude but at a slightly different angular position.

The experiments were then repeated at different vertical positions and the changes in the longitudinal flux were measured. The results showed that the direction of transverse current switches direction between when the contaminant is above or below the sensor ring. Furthermore, the direction of transverse current is also reversed between conductive and non-conductive materials.