Laterally pumped GaAs/AlGaAs quantum wells as sources of broadband terahertz radiation

In this work we consider lateral current pumped GaAs/AlGaAs quantum wells as sources of incoherent terahertz radiation. The lateral field heats the electrons in a two-dimensional quantum layer and increases the population of higher subbands, hence also increasing the radiation power generated in spontaneous intersubband emission processes. Digitally graded quasi-parabolic and simple square quantum wells are considered, and the advantages of both types are discussed. Calculations at lattice temperatures of 77 K and 300 K, for electric fields up to 10 kV/cm, show that the optical output power of ~100−200 W/m2 may be achieved for the 7 THz source. The main peak of the spectrum, at 7 THz, of the quasi-parabolic quantum well exceeds the black body radiation at 300 K by approximately a factor of two and by two orders of magnitude at 77 K

MILITAAROBJEKTIDE VALVETEHNOLOOGIA ARENG

Artikkel analüüsib viimastel aastatel maailmas käivitunud infotehno loogilisi arenguhüppeid, mis on toonud olulisi muutusi valvesüsteemide alale. Militaarobjektide valvesüsteeme on käsitletud nii sensorseadmete, süsteemi arhitektuuri kui ka üha rohkem tehisintellekti kasutava andmetöötluse vaates. Käsit luse süstematiseerimiseks on esile toodud neli põhilist alamsüsteemi ning teema sidu miseks maailma arengusuundadega on analüüsitud kaheksa olulise infotehnoloogilise uurimisteema kasvukõveraid. Detailsemalt käsitletud sensorseadmed on järgmised: 1) valvekaamerad nähtava valguse, lähiinfrapuna ja soojuskiirguse diapasoonidele; 2) sensoritega varustatud targad piirdetarad; 3) süsteemid mehitamata õhusõidukite avastamiseks ja jälgi miseks. Kaamerate puhul on analüüsitud kujutise sensorite arengutendentse ja DORI (detekteerimine, jälgimine, eristamine, identifitseerimine) tuvastusstandardit. Artiklis käsitletakse olulisemaid termineid ning arengusuundi, pidades silmas materjali võimalikku kasutamist tehniliste erialade väljaõppes Kaitseväe Akadeemias ja mujal

Improved C5D Electronic Realization of Conductivity Detector for Capillary Electrophoresis

The axial C4D (Capacitively Coupled Contactless Conductivity Detection) measurement electronics for capillary electrophoresis is considered and a new improved C5D compensated detection concept is proposed and tested. Using the idle compensation channel with inversed signal and immediate analogue summation of the active and idle channel currents yields effective suppression of the influence of the parasitic stray capacitance. Preliminary experiments have confirmed at least three-fold improvements of measurement resolution. Realisation of electronics allows flexible tuning of frequency from 0.2 MHz to 2 MHz. The relatively high voltage supply of 15 V for the AC measurement units together with 24- bit accurate analogue-to-digital converter yields additional improvement for the sensitivity

HÜPERSPEKTRAALSENSOORIKA RAKENDAMINE MILITAAROBJEKTIDE SIGNATUURIDE TUVASTAMISEKS JA VARJAMISEKS: Application of Hyperspectral Sensor Technology for the Detection and Concealment of Military Objects

Spectral distribution of the reflected light over wavelength values is a unique signature that can be used to distinguish different objects. Hyperspectral (HS) technology represents a new modern supersensor technology that can provide the detailed spectral content of the visible, ultraviolet or infrared light for every pixel in the image field. Multispectral cameras, precursors to the HS camera, appeared in the beginning of the 1980s and were able to register the image field only for a restricted number of wavelength values. The expensive HS cameras, capable of registering hundreds of wavelength values, were put into military application at the end of the 20th century but, at that time, their price remained too high for civil applications. In scientific literature, the appearance of publications on HS technology may be associated with the year 2001. The explosive exponential growth of HS research publications started around 2010–2011 when the cost of this efficient technology had dropped to a sufficiently low level to facilitate its wider take-up. This article gives an overview of the new capabilities offered by HS techno logy, able to transcend the capabilities of the human eye, which is limited to an only 3-color biological sensor system supporting a relatively narrow colour distinction wavelength window of 450–650 nm. Thus, for example, the strong “red step” between 700 and 750 nm that is an essential feature of all forests and backgrounds, and critical for all military concealment and detection tasks/operations, cannot be observed by the human eye without additional infrared vision devices. The experiments conducted with two HS cameras for the 400–1700 nm range emphasize the overall conclusion that in the modern information age, the concealment of objects has become more difficult and therefore we must begin the development of corresponding defence technologies to counter those threats. In particular, the measurements show that, although the colours of the Estonian Defence Forces correspond to the requirements of NATO standards (4360, 2836, 4698 + NATO AEP 59–65) in the infrared range, vehicles are clearly visible with hyperspectral cameras. The most serious attention should be paid to wavelengths between 600 and 700 nm, where the colour tones of the vehicles and also that of the soldiers’ clothing differ significantly from natural background colours due to the lack of chlorophyll and other biochemical compounds. In summary, the Estonian Defence Forces need a better concealment methodology that protects both military objects and people from hyperspectral monitoring systems. It is still a good idea to use natural ingredients to imitate natural backgrounds. However, for the development of effective concealment methods, modern HS technology is definitely required

Compact Empirical Model for Droplet Generation in a Lab-on-Chip Cytometry System

This study describes the construction of a droplet generation speed compact empirical mathematical model for a flow-focusing microfluidic droplet generator. The application case is a portable, low-cost flow cytometry system for microbiological applications, with water droplet sizes of 50-70 micrometer range and droplet generation rates of 500-1500 per second. In this study, we demonstrate that for the design of reliable microfluidic systems, the availability of an empirical model of droplet generation is a mandatory precondition that cannot be achieved by time-consuming simulations based on detailed physical models. When introducing the concept of a compact empirical model, we refer to a mathematical model that considers general theoretical estimates and describes experimental behavioral trends with a minimal set of easily measurable parameters. By interpreting the experimental results for different water- and oil-phase flow rates, we constructed a minimal 3-parameter droplet generation rate model for every fixed water flow rate by relying on submodels of the water droplet diameter and effective ellipticity. As a result, we obtained a compact model with an estimated 5-10% accuracy for the planned typical application modes. The main novelties of this study are the demonstration of the applicability of the linear approximation model for droplet diameter suppression by the oil flow rate, introduction of an effective ellipticity parameter to describe the droplet form transformation from a bullet-like shape to a spherical shape, and introduction of a machine learning correction function that could be used to fine-tune the model during the real-time operation of the system