The Science behind the Passive Millimeter Wave Camera was discovered in the 1930’s and is known as Radio Astronomy. Scientists and engineers heard noise coming from their perfect radios and wondered from where the noise was coming. They discovered that the noise was generated by us and all that we see around us. All matter generates radio-waves and as it turns out us humans are very noisy. Radio-telescopes are pointed into the universe and when pointed at distant planets and galaxies they detect the radio “noise” generated by these bodies. The void of space is for the most part very quiet. Based upon the characteristics of the radio waves received, scientists can determine if there is water, oxygen or other matter present.

Millimeter waves are naturally occurring forms of electromagnetic wave energy that are much larger than light waves. Because millimeter wavelengths are large relative to the microstructure of most materials, millimeter waves tend to pass through most materials such as clothing whereas light waves and infrared waves, which both have much smaller wavelengths, are not able to pass through many of these same materials.

All objects emit, absorb, and reflect energy at various wavelengths. The intensity of the emitted or reflected energy at any particular frequency is determined by the internal structure of the object. Objects also reflect and absorb the thermal energy in the environment and almost all objects emit some amount of thermal energy.

Just as regular cameras detect visible light energy and infrared cameras detect thermal energy in the infrared portion of the spectrum, millimeter wave cameras detect energy in the millimeter wave portion of the spectrum. Unlike regular cameras, however, passive millimeter wave cameras rely on the energy being emitted from or reflected by the objects in the scene (radiometric imaging) and require no external illumination, at millimeter or other wavelengths.

MMW (Millimeter Wave) cameras are made to detect and amplify the reflected MMW energy of an object. MMW energy is reflected by an object. Different objects and materials have different levels of emissivity and reflectivity because of their structure. Very dense materials possess high reflectivity and low emissivity. The human body being 90% water has a relatively high emissivity. Dense materials such as metal, composites and plastics have higher levels of reflectivity and more of the MMW wave energy is reflected and the object appears cooler than the human body. This causes the object to show up as a black image in front of the human figure.