Some problems and challenges for applications of uncooled or slightly cooled detectors (not deeper than to 77 K) for sub-THz and THz (terahertz) arrays are briefly discussed. The possibilities to involve detectors based on plasmon resonance FETs (field effect transistors) and those based on warm electron effect narrow-gap semiconductor bolometers are speculated, as they seem to be promising for using in large format broadband arrays of low-cost systems, though they are still in the stage of research and optimization.
Analysis of four types 4×288 designed and manufactured readouts is presented. All the readouts have the direct injection input circuit with the circuits incorporated that allows testing procedure of readouts without the photodiodes attached to readout circuits. TDI registers have three delay elements between neighbouring inputs. Some characteristics of 4×288 FPAs with mercury-cadmium-telluride (MCT) arrays are presented too. Analysis have shown that in spite of different constructions of four readout types, different numbers of outputs and external service, rather similar parameters of FPAs have been obtained. Detectivity values measured for all 4×288 FPAs at operation temperature T ≈ 78 K with skimming mode included and background temperature Tb ≈295 K were in the range D*λ ≅ (1.2−1.7)×1011 cmHz1/2/W.
Room temperature linear arrays (up to 160 detectors in array) from silicon metal- oxide-semiconductor field-effect transistors (Si-MOSFETs) have been designed for sub- THz (radiation frequency 140 GHz) close to real-time direct detection operation scanner to be used for detection and recognition of hidden objects. For this scanner, the optical system with aspherical lenses has been designed and manufactured. To estimate the quality of optical system and its resolution, the system modulation transfer function was applied. The scanner can perform real-time imaging with the spatial resolution better than 5 mm at the radiation frequency 140 GHz and contrast 0.5 for the moving object speed up to 200 mm/s and the depth of field 20 mm. The average dynamic range of real time imaging system with 160-detector linear array is close to 35 dB, when the sources with the output radiation power of 23 mW (IMPATT diodes) are used (scan speed 200 mm/s). For the system with 32-detector array, the dynamic range was about 48 dB and for the single-detector system with raster scanning 80 dB with lock-in amplifier. However, in the latter case for obtaining the image with the sizes 20×40 mm and step of 1 mm, the average scanning time close to 15 min is needed. Convolutional neural network was exploited for automatic detection and recognition of hidden items.
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