MMW imaging system based on GDD focal plane array with improved technology for detection of concealed objects

Abstract

Millimeter and sub-millimeter wave (50GHz – 20,00GHz) radiation has recently gained global attraction and is becoming more popular in the field of imaging concealed objects. We demonstrate here the employment of an inexpensive millimeter wave (MMW) imaging system using a focal plane array based on glow discharge detectors (GDDs) that can be used for these applications. The electrical detection method is used here, which refers to the detection by measuring the change in current between the GDD electrodes due to the incident radiation from an MMW source. A data acquisition (DAQ) platform is used here to acquire the readings from the sensor element, which is controlled by a LabVIEW code. The system measures the change in current passing through the GDD as a result of modulated radiation. We have implemented a DAQ platform with 8 channels that can be used to convert an analog signal to a digital one. Here we utilized a suitable digital algorithm that performs strong filtering of the noise and allows receiving a detection signal even for extremely low radiation intensities. A quasi-optical setup was composed of an MMW source, an off-axis parabolic mirror (OPM), and an imaging mirror. Calibration and alignment were carried out in order to locate the focal plane array (FPA) at the reflective focal length of the OPM. The salient advantages of the technology employed here are the low cost of detectors and the absence of a receiving antenna as exists in most detection systems. We currently construct a single row of detectors and propose to expand it to 64X64 pixels by using oversampling at sub-pixel resolution. Expansion and refinement of the concealed object detection systems can be achieved using image processing methods. The simplified version detection circuit implemented in this detection system is also capable of capturing images within a relatively short time with improved noise suppression.