Passive Millimeter Wave Imaging System Based On Focal Length Agility

Millimeter wave imaging has good penetrability for clothing and sensitive identification of metal objects.Due to shorter wavelength,better resolution can be obtained in imaging,and because passive millimeter wave imaging system does not radiate millimeter waves to the outside world,so it's safe and harmless to the human body.It is widely used for concealed dangerous goods detection and security imaging.In this paper,we use the digital refocusing principle of the light field camera to invite a passive millimeter wave focal length agile imaging system that is applied to security imaging which is more convenient and efficient.The passive millimeter-wave-based focal-distance agility imaging system presented in this paper concludes the following research sections :(1)The principle analysis of light field imaging,the establishment of a four-dimensional coordinate system,and the method of the dual-plane parameterization to describe the light field.(2)The establishment of the quasi-optical path model,including the calculation of the main lens,the microlens array,and the radiometer array.Calculationg of the surface equation of the lens,and the optimization of the system.(3)Research of digital refocusing algorithm.The collected light field information is expresse d as a five-dimensional matrix format.Get multiple sub-aperture images,then refocus the image by moving the slice of the light field to the same depth and then adding the images of all the subapertures.With the verification of the light field data,we can see the focal plane of the image is changed.(4)Co-simulation of the whole model,the specific information of the millimeter wave band radiation field is obtained and expressed as a five-dimensional matrix,then achieve the focal distance agility by th e refocusing algorithm.The mentioned various originals of the passive millimeter-wave focal-range agile imaging system above have been established corresponding model in the electromagnetic simulation software FEKO.After the simulation,we can get the millimeter wave radiation field information.Process this data and then digitally refocus,the change of focal plane in the results can clearly distinguished.