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Detection Principle

Regardless of method it is a quite delicate task to detect sparsely occurring foreign bodies in a complex environment such as a food product. In physical terms the food product is a material that is inhomogeneous, turbulent and possibly also stratified. All detection technologies assume a certain contrast between the foreign bodies and the surrounding material, the bulk. The contrast, as experienced by the electromagnetic waves, is physically described by the difference in electromagnetic permittivity, or the dielectric “constant” between the two materials. The permittivity, which in its most general form is mathematical/physical very complex, and an important physical property determine transmission, reflection, attenuation and scattering of the electromagnetic radiation when it impinges on the foreign object. The fact that the dielectric permittivity is frequency and temperature dependant makes it even more complicated. Another important parameter is of course the physical shape of the foreign object. Thus, it can during some instances be easier to detect an object with sharp edges, than a spherical object. Our definition of contrast includes all the above mentioned differences between the bulk and the foreign body from a electromagnetic point of view.

Microwave field without bulk material

Microwave field in the presence of a ”bulk material”

Microwave field when a
foreign object is present

Food Radar software displaying the signal, the threshold and a detect.