Avihai Aharon Akram

Inexpensive THz Focal Plane Array Imaging Using Miniature Neon Indicator Lamps as Detectors

Development of focal plane arrays (FPAs) for mm wavelength and THz radiation is presented in this paper. The FPA is based upon inexpensive neon indicator lamp Glow Discharge Detectors (GDDs) that serve as pixels in the FPA. It was shown in previous investigations that inexpensive neon indicator lamp GDDs are quite sensitive to mm wavelength and THz radiation. The diameters of GDD lamps are typically 3-6 mm and thus the FPA can be diffraction limited. Development of an FPA using such devices as detectors is advantageous since the costs of such a lamp is around 30-50 cents per lamp, and it is a room temperature detector sufficiently fast for video frame rates. Recently, a new 8 × 8 GDD FPA VLSI control board was designed, constructed, and experimentally tested. First, THz images using this GDD FPA are given in this paper. By moving around the 8 × 8 pixel board appropriately in the image plane, 32 × 32 pixel images are also obtained and shown here, with much improved image quality because of much reduced pixelization distortion.

W-Band Chirp Radar Mock-Up Using a Glow Discharge Detector

Chirp or frequency-modulated continuous-wave (FMCW) radar is a very well-known method for range applications. Using the current technology, conventional FMCW radar for W-band waves requires the use of expensive microwave mixers and low noise amplifiers (LNA). A uniquely simple and inexpensive solution is presented using very inexpensive glow discharge detectors (GDDs). The use of GDDs enables direct beating between the electric field of the target signal and the reference signal eliminating the requirement for expensive millimeter wave mixers, sources, and LNAs. This unique solution to FMCW radar is proven to be capable of determining range to target, and creating 3-D radar images. In this paper, a proof of concept of chirp/FMCW radar detection using a GDD in the W-band regime is demonstrated experimentally. The GDD chirp radar system has the following advantages: 1) much simpler realization in short range applications; 2) rigid, room temperature operation; 3) sub-microsecond response time; 4) large dynamic range; and 5) immunity to high-power radiation.

Super resolution and optical properties of THz double row array based on inexpensive Glow Discharge Detector (GDD) pixels

The properties of terahertz (THz) radiation are well known. They penetrate well most non-conducting media; there are no known biological hazards, and atmospheric attenuation and scattering is lower than visual and IR radiation. Thus THz imaging is very attractive for homeland security, biological, space, and industrial applications Recently we have found experimentally that inexpensive miniature neon indicator lamp Glow Discharge Detectors (GDD) can be used as THz detectors. Based on the GDD we designed, constructed, and experimentally tested an 8×8 GDD array. In order to improve the performance and the resolution of the THz images a larger array is required. In this work we use a special double row 2×18 moving array detector. The 2×18 GDD array enables us to employ scanning method in order to obtain 36×36 pixel THz images. Furthermore, using this double row array it will be possible to employ super resolution methods. Optical properties such as optical transfer function and measurement of point spread function are presented, as well as first results for the 2×18 GDD array.

mm wave and THz imaging using very inexpensive neon-indicator lamp detector focal-plane arrays

Development of focal plane arrays (FPA) for mm wavelength and THz radiation is presented in this paper. The FPA is based upon inexpensive neon indicator lamp Glow Discharge Detectors (GDDs) that serve as pixels in the FPA. It was shown in previous investigations that inexpensive neon indicator lamps GDDs are quite sensitive to mm wavelength and THz radiation. The diameter of GDD lamps are typically 3-6 mm and thus the FPA can be diffraction limited. Development of an FPA using such devices as detectors is advantageous since the costs of such a lamp is around 30-50 cents per lamp, and it is a room temperature detector sufficiently fast for video frame rates. Recently a new 8×8 GDD FPA VLSI board was designed, constructed, and experimentally tested. First THz images as well as DSP methods using this GDD FPA are demonstrated. Super resolution was achieved by moving the 8×8 pixel board appropriately in the image plane so that 32X32 pixel images are also obtained and shown here, with much improved image quality because of much reduced pixelization distortion.

Switching and Fast Operation of Glow Discharge Detector for Millimeter Wave Focal Plane Array Imaging Systems

Applications of millimeter waves (MMWs), especially MMW imaging, are required in medicine, homeland security, communication, and space technology. The lack of a fast and inexpensive room temperature detector makes it difficult to realize those applications. Recently we found that the commercially available miniature neon lamps, known as glow discharge detectors (GDD), can be used as room temperature, sensitive, and inexpensive MMW detectors. Furthermore, they have shown a fast response time of about one microsecond. The disadvantages of using the GDD are high power consumption and for relatively large bias current, aging of the electrode coating due to electrode bombardment by heavy ions inside the plasma. Those disadvantages can be overcome by electronically switching on the detector bias current during detection period only, leaving the detector OFF most of the time. In this paper, the influence of the detector aging on the responsivity is investigated experimentally, and an electronic circuit for fast ON/OFF switching operation is demonstrated.

Polarization effects on heterodyne detection and imaging using Glow Discharge Detector at millimeter wavelengths

A miniature neon indicator lamp, also known as a Glow Discharge Detector (GDD), costing about 50 cents, was found to be an excellent room temperature THz radiation detector. Polarization effects on heterodyne detection were investigated in this work. In heterodyne detection, because of the dot product relationship between signal electric field (ES) and local oscillator (LO) electric field (Elo), optimal operation of heterodyne detection is obtained when ES and Elo are of the same polarization. Preliminary results at 300 GHz showed better sensitivity by a factor of 20 with only 56 microwatt local oscillator power using heterodyne compared to direct detection. Further improvement of the detection sensitivity can be achieved if the LO power (Plo) is increased. In this work investigation of polarization effects in heterodyne detection using neon indicator lamp GDD was carried-out. Experimental results of heterodyne detection at 300 GHz showed that an intermediate frequency (IF) signal was obtained for orthogonal polarization of the LO and signal, in contradiction to the theory. Also, our latest imaging results using Glow Discharge Detector at millimeter wavelengths will be shown in this work.

Sub-wavelength resolution of MMW imaging systems using extremely inexpensive scanning Glow Discharge Detector (GDD) double row camera

The properties of terahertz (THz) radiation are well known. They penetrate well most non-conducting media; there are no known biological hazards, and atmospheric attenuation and scattering is lower than visual and IR radiation. Thus THz imaging is very attractive for homeland security, biological, space, and industrial applications. In the other hand, the resolution of MMW images is lower comparing to IR and visual due to longer wavelength. Furthermore, the diffraction effects are more noticeable in THz and MMW imaging systems. Thus the MMW images are blurred and unclear and thus it is difficult to see the details and small objects. In recent experimental work with 8X8 Glow Discharge Detector (GDD) Focal Plane Array (FPA) we were able to improve the resolution of MMW images by using oversampling methods with basic DSP algorithms. In this work a super resolution method with basic DSP algorithms will be demonstrated using the 2X18 double row camera. MMW images with sub wavelength resolution will be shown using those methods and small details and small objects will be observed.

Low cost plasma Terahertz heterodyne image detection

Miniature inexpensive neon indicator lamp plasma glow discharge detectors (GDD) are excellent candidates to serve as room temperature, low cost, terahertz (THz) radiation detectors and as pixels in THz imaging systems. Heterodyne amplification of low power signals via higher power reference beams is very important for THz imaging systems because it permits detection of much lower object beam intensities. An experimental result of 300GHz heterodyne detection by a single commercial GDD device costing about 30 cents is presented here. In heterodyne image detection a picture is taken of interference fringes or a hologram deriving from a coherent reference wave and a coherent wave reflected from or transmitted through an object. Transmission with in-line or zero angles between those two waves is important to widen the fringes. The GDD detector is transparent, so that its possible to receive radiation from both sides, at 0 and 180 degree. This permit receiving the wave reflected from or transmitted through an object at 0 degree and the reference wave from the opposite direction at 180 degree. Such interference fringe widening can permit heterodyne direct imaging of the object instead of imaging the interference pattern.

THz imaging using Glow Discharge Detector (GDD) focal plane arrays and large aperture quasi optic mirrors

The properties of terahertz (THz) radiation are well known. They penetrate well most nonconducting media; there are no known biological hazards, and atmospheric attenuation and scattering is lower than for visual and IR radiation. Recently we have found that common miniature commercial neon glow discharge detector (GDD) lamps costing typically about 30 cents each exhibit high sensitivity to THz radiation, with microsecond order rise times, thus making them excellent candidates for such focal plane arrays. Based on this technology we designed, built and tested 4X4 and 8X8 GDD focal plane arrays. A line vector of 32 GDD pixels is being designed in order to increase the number of pixels in such arrays and thus the image resolution. Unique large aperture quasi optic mirrors were design and tested experimentally in this work. A new technology of light weight large aperture mirrors is proposed in this work. In this case a metal coating on plastic substrate is demonstrated. According to first experiments this technology proves to reliable with minimal deformation in LAB conditions. THz Images at 100 GHz were taken using this new inexpensive technology with good quality and resolution.

MMW/THz imaging using upconversion to visible, based on glow discharge detector array and CCD camera

An inexpensive upconverting MMW/THz imaging method is suggested here. The method is based on glow discharge detector (GDD) and silicon photodiode or simple CCD/CMOS camera. The GDD was previously found to be an excellent room-temperature MMW radiation detector by measuring its electrical current. The GDD is very inexpensive and it is advantageous due to its wide dynamic range, broad spectral range, room temperature operation, immunity to high power radiation, and more. An upconversion method is demonstrated here, which is based on measuring the visual light emitting from the GDD rather than its electrical current. The experimental setup simulates a setup that composed of a GDD array, MMW source, and a basic CCD/CMOS camera. The visual light emitting from the GDD array is directed to the CCD/CMOS camera and the change in the GDD light is measured using image processing algorithms. The combination of CMOS camera and GDD focal plane arrays can yield a faster, more sensitive, and very inexpensive MMW/THz camera, eliminating the complexity of the electronic circuits and the internal electronic noise of the GDD. Furthermore, three dimensional imaging systems based on scanning prohibited real time operation of such imaging systems. This is easily solved and is economically feasible using a GDD array. This array will enable us to acquire information on distance and magnitude from all the GDD pixels in the array simultaneously. The 3D image can be obtained using methods like frequency modulation continuous wave (FMCW) direct chirp modulation, and measuring the time of flight (TOF).