The relatively high atmospheric propagation of millimeter-waves (MMW) was found to be one of the most critical reasons for the development of reliable sensors for MMW detection. According to previous research works, it has been already shown that incident MMW radiation on a glow discharge detector (GDD) can increase the discharge current. Hence, the electrical mode of detection can be employed to detect the presence of MMW radiation. In this article, a new design of a row detector using GDDs as pixel elements, and the influence of MMW incidence on GDD’s discharge current, were acquired using an elementary data acquisition (DAQ) platform. The DAQ system computes the averaged Fast Fourier Transform (FFT) spectrum of the time signal and returns the FFT results as magnitude based on the level of detection. An FFT-based signal acquisition proved to be a better alternative to the lock-in detection that was commonly used in MMW detection systems. This improved detection circuit provides enhanced noise filtering, thereby resulting in better MMW images within a short time. The overhead expense of the entire system is very low, as it can avoid lock-in amplifier stages that were previously used for signal enhancement. A scanning mechanism using a motorized translation stage (step motor) is involved to place and align the row detector in the image plane. The scanning can be carried out vertically to perform the imaging, by configuring the step motor after selecting the desired step size and position. A simplified version of the MMW detection circuit with a dedicated over-voltage protection facility is presented here. This made the detection system more stable and reliable during its operation. The MMW detection circuit demonstrated in this work was found to be a milestone to develop larger focal plane arrays (FPA) with very inexpensive sensor elements.

Focal plane arrays (FPA) constructed using glow discharge detectors (GDD) as the pixel elements proved to be an inexpensive methodology for generating MMW (millimeter wave)/THz (terahertz) images. In the abnormal glow mode of operation, the weakly ionized plasma (WIP) in GDDs can be more responsive while interacting with the incident MMW/THz radiations. It has explicitly been found that the major influence of MMW/THz radiation on the emitted light spectrum from the GDD is located in the near-infrared (NIR) zone of the electromagnetic spectrum which is around 800 nm– 1000 nm. Also, there is no influence of the MMW/THz on the visual band ranging from 500 nm–600 nm emitted from the GDD. The up-conversion method utilized here refers to the detection of variations in the intensity of emitted light from the GDD due to the incident MMW radiation. A charge-coupled device (CCD) camera is employed here to generate MMW/THz images by capturing the light output from the GDD pixel elements on the FPA located in the image plane. The DC bias voltage emitted light from the GDD is much stronger than the modulated light produced as a result of the incident MMW/THz radiation. The major challenge of this work is to measure this minute variation in the GDD light output caused by the MMW/THz radiation and to distinguish it from the intense DC bias operation light of the GDD. For achieving this, we propose using an optical long-pass filter as a part of the CCD camera component, thus enhancing the performance of the suggested up-conversion method. The addition of the long-pass filter eliminates most of the highly intense visual spectrum from the light output of the GDD, thereby decreasing noise and making the up-conversion imaging more effective. Here, we demonstrated the feasibility of implementing GDD-based FPAs using up-conversion readout for MMW/THz imaging applications in the NIR regime by testing with a single GDD whose detection impact was captured using a CCD camera whose zoom lens was coupled with a long pass optical filter.

Performance enhancement of a very inexpensive millimeter-wave (MMW)/terahertz (THz) sensor for MMW/THz imaging systems is experimentally demonstrated in this study. The MMW sensor is composed of a glow discharge detector (GDD) and a light-to-frequency (LTF) converter combination. The experimental results given in this study show an improvement in the performance parameters of the detector element, such as the minimum detectable signal, as well as the signal to noise ratio (SNR) and the noise equivalent power (NEP), when a NIR long-pass filter was inserted between the GDD and the LTF combination. A detailed derivation of the NEP of this unique sensor is presented in this work. Based on this derivation and the experimental measurements, the NEP value was calculated.

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.