This study presents an electrically-controlled hybrid plasmon-induced transparency (PIT) metadevice leveraging on nematic liquid crystals for enabling active manipulation of terahertz slow light. Achieving Fano-resonant response via near-field coupling of chiral and achiral meta-atoms facilitates nonlinear terahertz generation and mitigates radiative losses. These findings highlight the potential of Fano-resonant active metasurfaces for advanced sensing and slow-light devices.
Currently, objects tracking issue in immersive Virtual Reality (VR) applications is important for various applications. It is related not only to determination of the position and orientation of the user himself but also as the tool that she/he exploits in the VR environment. Among numerous methods of objects tracking, the "Lighthouse" solution implemented in the SteamVR tracking system deserves special attention. One of the main reasons is the open concept of the SteamVR tracking system and the availability of simple analytical tools, which allows users to build their own tracker modules. For correct operation, these tools require accurate data both on the parameters of the sensors and the base stations of the system. This paper describes research on these parameters. The obtained results allow for a more accurate implementation of the simulations, which are the basis for the design process of Steam devices.
Fabrication of approx. 3 THz Al0.15Ga0.85As/GaAs QCLs grown by Molecular Beam Epitaxy equipped with Ta/Cu or Ti/Cu waveguide claddings will be presented.
Our previous studies showed that copper layers as the waveguide claddings are most promising in THz QCLs technology. The theoretical predictions showed that lasers with Ti/Cu or Ta/Cu claddings (where Ti and Ta play the role of diffusion barriers and improve adhesion) show the smallest waveguide losses when compared with other metals. The main important issue of the presentation will be the wafer bonding of the QCL active region and GaAs receptor wafer. We will compare the results of ex-situ and in-situ bonding technology. The structures were tested by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS). Our studies show that it was necessary to apply at least 5 nm-thick diffusion-barrier layers, as well as to keep all of the process temperatures below 400C in order to ensure the barrier tightness. The next important issue was control of composition of metallic claddings, in order to provide the control of the refractive index profiles of the claddings.
The ridge structure lasers were fabricated with ridge width in the range 100 – 140 µm, formed by dry plasma etching in BCl3/Cl2/Ar mixture in ICP RIE system.
The lasers operated with threshold current densities of approx. 1.2 kA/cm2 at 77 K and the Tmax = 130 K, when fed by 100-300 ns current pulses supplied with 0.3-1 kHz repetition frequencies.
*This research is supported by The National Centre for Research and Development (bilateral cooperation, project no. 1/POLTUR-1/2016) and TUBITAK (Scientific and Technical Research Council of Turkey) project number 215E113.
The paper describes the results of experimental research on the mobile verification of travellers based on fingerprints. Three-day tests were carried out at the border crossing in Terespol, Poland. The developed system automatically acquires personal and biometric data (fingerprints) from the Polish biometric passport, determines their quality and compares with the live data collected from the traveller. In addition, the system measures the time of individual stages of the process and determines total transaction time. For total number of correctly scanned travellers equal to 128, false acceptance rate equals to 0, while rejection rate is less than 1%. The average transition time of border check was 37 seconds.
Face re-identification is a challenging task which is aimed to check similarity of two faces shown in the images. Face recognition system have been investigated since many years mostly in visible domain. We investigate face recognition methods based on facial images acquired in far-infrared range (thermal spectrum). The main reason for using thermal infrared for face recognition is to observe people in night conditions. However, this task is not free of challenges. In this paper we investigate the impact of various head positions on efficiency of face re-identification. The paper presents our measurement approach, results of many series of tests as well as performance metrics of re-identification based on three state-of-the-art facial descriptors.
Biometrics refers to unique human characteristics. Each unique characteristic may be used to label and describe individuals and for automatic recognition of a person based on physiological or behavioural properties. One of the most natural and the most popular biometric trait is a face. The most common research methods on face recognition are based on visible light. State-of-the-art face recognition systems operating in the visible light spectrum achieve very high level of recognition accuracy under controlled environmental conditions. Thermal infrared imagery seems to be a promising alternative or complement to visible range imaging due to its relatively high resistance to illumination changes. A thermal infrared image of the human face presents its unique heat-signature and can be used for recognition. The characteristics of thermal images maintain advantages over visible light images, and can be used to improve algorithms of human face recognition in several aspects. Mid-wavelength or far-wavelength infrared also referred to as thermal infrared seems to be promising alternatives. We present the study on 1:1 recognition in thermal infrared domain. The two approaches we are considering are stand-off face verification of non-moving person as well as stop-less face verification on-the-move. The paper presents methodology of our studies and challenges for face recognition systems in the thermal infrared domain.
Biometrics is a science that studies and analyzes physical structure of a human body and behaviour of people. Biometrics found many applications ranging from border control systems, forensics systems for criminal investigations to systems for access control. Unique identifiers, also referred to as modalities are used to distinguish individuals. One of the most common and natural human identifiers is a face. As a result of decades of investigations, face recognition achieved high level of maturity, however recognition in visible spectrum is still challenging due to illumination aspects or new ways of spoofing. One of the alternatives is recognition of face in different parts of light spectrum, e.g. in infrared spectrum. Thermal infrared offer new possibilities for human recognition due to its specific properties as well as mature equipment. In this paper we present the scheme of subject’s verification methodology by using facial images in thermal range. The study is focused on the local feature extraction methods and on the similarity metrics. We present comparison of two local texture-based descriptors for thermal 1-to-1 face recognition.
Conditions of fabrication of first-order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10 μm are presented. The 1-μm-deep rectangular-shaped gratings with the period of about 1.55 μm and duty cycle in the range of 65% to 71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7 cm−1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15 to 25 μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1 nm/K in the temperature range of 77 to 120 K. The full width at half maximum of the emitted spectra is ∼0.4 cm−1.
Conditions of fabrication of first order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10μm are presented. The 1 μm-deep rectangular-shaped gratings with the period of about 1.55 μm and duty cycle in the range of 65-71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7 cm-1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15-25 μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1 nm/K in the temperature range of 77-120 K. The full width at half maximum of the emitted spectra is ~ 0.4 cm-1.
In this study common clothing and variety of textile materials were used in research on its influence on remote materials identification. Experimental setup was designed for the terahertz reflection spectroscopy of different materials located at a distance up to 5 m. The source of the radiation is a tunable solid-state optical parametric oscillator (OPO), which generates a narrow-band nanosecond pulses in the range of 0.7-2.7 THz. The signal is detected with hot electron bolometer (HEB). Investigations were carried out for 1 m, 3 m and 5 m distance between the examined sample and the system. Experiment was conducted in the 0.7 – 2.5 THz range. Fabrics subjected to testing were varied in terms of the fibers kind which they were made from and weights of test materials ranged from 53 g/m2 up to 420 g/m2. Also textiles with a composition consisting of several fibers with differing percentage of the fibers composition of each sample were measured. Information about textiles transmission was obtained in separate set of experiments. The study fabrics were made of viscose, polyester, cotton, spandex, wool, nylon, leather, flax.
Detection of explosives has always been a priority for homeland security. Jointly, terahertz spectroscopy and imaging are emerging and promising candidates as contactless and safe systems. In this work, we treated data resulting from hyperspectral imaging obtained by THz-time domain spectroscopy, with chemometric tools. We found efficient identification and sorting of targeted explosives in the case of pure and mixture samples. In this aim, we applied to images Principal Component Analysis (PCA) to discriminate between RDX, PETN and mixtures of the two materials, using the absorbance as the key-parameter. Then we applied Partial Least Squares-Discriminant Analysis (PLS-DA) to each pixel of the hyperspectral images to sort the explosives into different classes. The results clearly show successful identification and categorization of the explosives under study.
We report research results with regard to AlGaAs/GaAs structure processing for THz quantum-cascade lasers (QCLs). We focus on the processes of Ti/Au cladding fabrication for metal–metal waveguides and wafer bonding with indium solder. Particular emphasis is placed on optimization of technological parameters for the said processes that result in working devices. A wide range of technological parameters was studied using test structures and the analysis of their electrical, optical, chemical, and mechanical properties performed by electron microscopic techniques, energy dispersive x-ray spectrometry, secondary ion mass spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and circular transmission line method. On that basis, a set of technological parameters was selected for the fabrication of devices lasing at a maximum temperature of 130 K from AlGaAs/GaAs structures grown by means of molecular beam epitaxy. Their resulting threshold-current densities were on a level of 1.5 kA/cm2. Furthermore, initial stage research regarding fabrication of Cu-based claddings is reported as these are theoretically more promising than the Au-based ones with regard to low-loss waveguide fabrication for THz QCLs.
This paper presents results of computer simulation of 1D monolithic high refractive index contrast grating (MHCG) reflector also called surface grating reflector (SGR). We analyzed optical properties of the GaAs reflector designed for 980 nm wavelength with respect to the grating parameters variation. We also determined the electric field patterns after reflection from the structure in several cases of parameters variation. We show that thanks to the scalability and design simplicity, proposed design is a promising candidate for simple, next generation vertical cavity surface emitting lasers emitting from ultra-violet to infrared.
Terahertz radiation is within the frequency range from 100 GHz to 10THz. This radiation has specific characteristics in
terms of imaging. The radiation is harmless to the human body because the energy transferred by electromagnetic waves
in this range of frequencies are very small thus there is no ionization of matter.
The development of imaging devices and exploration of new spectral bands is a chance to introduce new equipment for
assuring public safety. It has been proved that objects hidden under clothing can be detected and visualized using
terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition.
In order to determine the properties of terahertz imaging for detection of hidden objects several aspects need to be
considered. Taking into account the fact that the image captured by the terahertz camera reflects the spatial distribution
of the relative temperature of the observed objects, the effect of the measurement time on the imaging capabilities should
be examined. A very important aspect is the influence of the type (material composition) of coating material, as well as
the type of an object hidden under clothing (size and material).
The purpose of the studies is to investigate the time stability of passive THz imaging on 250 GHz for detection of
concealed objects. In the article, we present the measurement setup, the measurement methodology as well as the initial
results of measurements with various types of clothing and test objects.
We report our research on processing of AlGaAs/GaAs structures for THz quantum-cascade lasers (QCLs). We focus on
the processes of fabrication of Ti/Au claddings for metal-metal waveguides and the wafer bonding with indium solder.
We place special emphasis on the optimum technological conditions of these processes, leading to working devices. The
wide range of technological conditions was studied, by use of test structures and analyses of their electrical, optical,
chemical and mechanical properties, performed by electron microscopic techniques, energy dispersive X-ray
spectrometry, secondary ion mass spectroscopy, atomic force microscopy, fourier-transform infra-red spectroscopy and
circular transmission line method. On the basis of research a set of technological conditions was selected, and devices
lasing at the maximum temperature 130K were fabricated from AlGaAs/GaAs structures grown by molecular beam
epitaxy (MBE) technique. Their threshold-current densities were about 1.5kA/cm2. Additionally we report our initial
stage research on fabrication of Cu-based claddings, that theoretically are more promising than the Au-based ones for
fabrication of low-lossy waveguides for THz QCLs.
Detection of concealed dangerous objects is a very demanding problem of public safety. So far, the problem of detecting
objects hidden under clothing was considered only in the case of airports but it is becoming more and more important for
public places like metro stations, and government buildings.
The development of imaging devices and exploration of new spectral bands is a chance to introduce new equipment for
assuring public safety. It has been proved that objects hidden under clothing can be detected and visualized using
terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. On
the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some
conditions, as well as high image quality and big pixel resolutions.
The purpose of the studies is to investigate the possibilities of using various cameras operating in different spectral
ranges for detection of concealed objects. In the article, we present the measurement setup consisting of medium
wavelength infrared (MWIR), long wavelength infrared (LWIR), THz and visible cameras and the initial results of
measurements with various types of clothing and test objects.
We present results on the comparison of different THz technologies for the detection and identification of a variety of
explosives from our laboratory tests that were carried out in the framework of NATO SET-193 “THz technology for
stand-off detection of explosives: from laboratory spectroscopy to detection in the field” under the same controlled
conditions. Several laser-pumped pulsed broadband THz time-domain spectroscopy (TDS) systems as well as one
electronic frequency-modulated continuous wave (FMCW) device recorded THz spectra in transmission and/or
reflection.
In this paper a method for producing resonant structures using laser micromachining is presented. In the spot of laser
beam impact on AlN ceramics surface a conductive aluminum layer is formed. Compilation of process parameters allows
for the fabrication of structures with resistance at Rs ~ 0.01Ω/Rs. It has been also found out that the maximum value of resistance for which spiral resonator structures manifest their unique properties is at the level of Rs = 1.43 Ω.
Furthermore, the occurrence of mutual capacity which value is dependent on the arrangement of individual SR structures
with respect to each other was observed and examined. Based on satisfactory results for SR structures, it has been
attempted to produce a resonant structures dedicated to the THz range based on the process of direct metallization of
AlN ceramics surface. As a result, the Split Ring Resonator structure whose properties were verified by using the
THz -TDS method was manufactured. In case of the field E perpendicular to SRR structure and one resonance area for
0.50 THz with field E parallel to the structure, two characteristic resonant dips for 0.22 THz and 0.46 THz were
obtained. The studies confirmed that the method of direct metallization of AlN ceramics allows to produce resonant
structures in the THz range.
We report on a method for extracting the characteristic features of covered materials, including hexogen, in the range from 0.5 to 1.8 THz. This time-domain spectroscopy-based technique takes into account only part of the signal reflected from a covered sample and analyzes it by using the Fourier transform. The obtained power spectrum has distinctive peaks that correspond to peaks measured in the transmission configuration and can be used for further identification of the materials.
Terahertz imaging, is the latest entry into the crowded field of imaging technologies. Many applications are emerging for the relatively new technology. THz radiation penetrates deep into nonpolar and nonmetallic materials such as paper, plastic, clothes, wood, and ceramics that are usually opaque at optical wavelengths. The T-rays have large potential in the field of hidden objects detection because it is not harmful to humans. The main difficulty in the THz imaging systems is low image quality thus it is justified to combine THz images with the high-resolution images from a visible camera. An imaging system is usually composed of various subsystems. Many of the imaging systems use imaging devices working in various spectral ranges. Our goal is to build a system harmless to humans for screening and detection of hidden objects using a THz and VIS cameras.
A growing interest in terahertz technology finds support in a large number of applications. One of the most interesting applications of terahertz waves is imaging. The terahertz range of electromagnetic radiation has large potential in the field of hidden objects detection because it is not harmful to humans [1, 2]. However, the main difficulty in the THz imaging systems is low image quality due to low sensitivity and a small number of pixels in detecting modules of cameras Considering the fact that even THz images with low pixel resolution still provide valuable information, it is justified to combine them with the high-resolution images from a visible camera. Image fusion can be used in a wide range of security applications for example detection and identification of hidden objects. Our goal is to build a system harmless to humans for screening and detection of hidden objects using a THz camera. A very important aspect of applying various processing techniques to images is proper assessment of image quality. We propose a combination of two image quality assessment methods (IQA) as a methodology of assessing quality of the fused images and a method to compare image fusion algorithms.
We report on technical aspects connected with detection of the terahertz (THz) waves reflected from a small target which is situated at the distance of 5 meters. Details of experimental setup are presented. An optical parametric oscillator (OPO) was used as a THz nanosecond pulses radiation source and a hot-electron bolometer (HEB) was applied for pulse detection. A method of spectrum calculation from experimental data is described. Measured reflectance spectra of few materials are presented with explanation of the origin of water vapor hole burning in the reflectance spectrum.
We report on a new method for extracting the characteristic features of covered materials, including Hexogen, in the
range 0.5–1.8 THz. This time domain spectroscopy-based technique takes into account only part of the signal reflected
from a covered sample, and analyzes it by Fourier transform. The obtained power spectrum has distinctive peaks that
correspond to peaks measured in the transmission configuration and can be applied for further identification. We showed
results obtained for the samples of hexogen, lactose, and tartaric acid covered with commonly used packaging materials
such as plastic, foil, paper and cotton.
We report on measurements of transmission spectra of chosen materials (Hexogen, sugar, L-tartaric acid, 4-aminobenzoic
acid) in the range 0.7-2.0 THz. The measurements were carried out by means of a setup, which bases on the optical
parametric oscillator (OPO) combined with the hot electron bolometer (HEB). The setup consists of the commercially
available tunable OPO working in the range 0.7-2.0 THz with repetition rate 53 Hz, duration of the impulse of about
20ns and energy 10nJ. The beam was detected by the fast and sensitive HEB. The spectra were compared to results
obtained from a standard time domain spectroscopy (TDS) setup. Only small discrepancies between spectra measured by
both methods are observed. For the range 0.7-2.0 THz typical features can be identified using both methods. Above 2
THz the TDS setup seems to have better performance in terms of signal-to-noise ratio and sensitivity.
The SDA (Spectral Dynamics Analysis) method is used for the detection and identification of the PWM C4 explosive
with the surface having inhomogeneity, caused by action of the sandpaper with different grit on the explosive surface,
or with the surface having various curvature of its surface.
We show that the SDA-method is good tool for the detection and identification of the explosive using THz signal
reflected from the PWM C4 explosive. We propose (see as well [24]) integral criteria for the identification of
substances. These criteria allow to detect the explosive despite an influence of its shape on the THz spectrum.
Proposed assessments and algorithms for computation of the identification probability show both high probability of the
substance identification and a reliability of realization in practice.
We demonstrate the improvement of the quality of the image captured by TS4 - the commercially available THz passive
camera manufactured by ThruVision Systems Ltd. The measurements range of this device reaches 10 meters. Our
approach is based on application of novel spatial filters and algorithms, developed by us for computer processing of
passive THz images produced by the various THz cameras.
In our opinion, the most important result of this paper consists in a demonstration of the possibility of using a passive
THz camera to observe a difference in temperature on the human skin if this difference is caused by different
temperatures in the inside of the body. Such possibility was proposed by Vyacheslav Trofimov on the Conference in
Baltimore (April 2012) as well as and in [20]. We discuss two physical experiments, in which a person drinks hot and
cold water. After computer processing of images captured by passive THz camera TS4 we may see the pronounced
temperature trace on the human body. We illustrate this phenomenon by a series of images captured by passive THz
camera in real time.
As we believe, these experiments allow us wide applications of passive THz cameras for the detection of objects
concealed in the inside of the human body because the difference in temperature that will be reflected on the human
skin. Modern passive THz cameras have not enough resolution in temperature to see this difference. However, computer
processing allows us to enhance it for this application.
Using computer processing one may enhance the image quality and delete noise on the images. In some cases, it is
possible to achieve full de-noising of the image.
Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.
Detection of nanosecond pulses by fast and sensitive Hot Electron Bolometer (HEB) is reported. Pulses were generated
by an Optical Parametric Oscillator (OPO)-based source. The laser can be tuned in the range 0.7-2.5 THz; its repetition
rate equals to 53Hz, duration of the pulse is about 10-20ns, energy is 10nJ and spectral width 50GHz. HEB operates at
temperature of about 8.8K in a cryogenic refrigeration system. A sensitive element is a bridge from a 4-mm thick NbN
film integrated with a planar logarithmic spiral antenna on a high-resistive silicon. HEB works in 0.3-3THz range with
NEP ~3x10-13 W/Hz1/2 and dynamic range 0.1 uW. Thanks to exploitation of hot electrons in superconducting state, the detector is very fast with minimum response time equals to 50ps. The THz radiation is focused with a silicon lens, and then is coupled to a sensitive bolometer using the planar antenna. THz radiation from the OPO, through a set of mirrors and attenuators, was coupled to the detector. The distance between the source and detector was about 3m. Full Width at Half Maximum of the recorded pulses was about 20 ns. Moreover, we measured linearity of the detector in the range 0.7- 2.0 THz by rotation of the polarizer axis. The pulses were averaged and integrated for better stability. We obtained a good similarity to the theoretical curve of the polarizer.
The SDA (Spectral Dynamics Analysis) method was applied for the detection and identification of ceramic explosives (a
mixture of Al2O3 with Hexogen or Penthryte) hidden under different coverings - thin, rough, thick layers of
Polyethylene foils and a layer of cotton. We analyzed THz pulses reflected from the samples at different angles - nearly
90° (Stand-Off reflection) and 45° (Specular reflection). We showed that in some cases the presence of covering can
significantly distort the spectral properties of the reflected THz signal. Nevertheless, it is possible to find the identifiers
characterizing the presence of explosive under the covering analyzing the spectrograms and dynamics of spectral lines of
the main pulses and the sub-pulses following the main pulse.
Screening cameras working in millimetre band gain more and more interest among security society mainly due to their
capability of finding items hidden under clothes. Performance of commercially available passive cameras is still limited
due to not sufficient resolution and contrast in comparison to other wavelengths (visible or infrared range). Testing of
such cameras usually requires some persons carrying guns, bombs or knives. Such persons can have different clothes or
body temperature, what makes the measurements even more ambiguous. To avoid such situations we built a moving
phantom of human body. The phantom consists of a polystyrene manikin which is covered with a number of small pipes
with water. Pipes were next coated with a silicone "skin". The veins (pipes) are filled with water heated up to 37 C
degrees to obtain the same temperature as human body. The phantom is made of non-metallic materials and is placed on
a moving wirelessly-controlled platform with four wheels. The phantom can be dressed with a set of ordinary clothes and
can be equipped with some dangerous (guns, bombs) and non-dangerous items. For tests we used a passive commercially
available camera TS4 from ThruVision Systems Ltd. operating at 250 GHz. We compared the images taken from
phantom and a man and we obtained good similarity both for naked as well as dressed man/phantom case. We also tested
the phantom with different sets of clothes and hidden items and we got good conformity with persons.
The SDA (Spectral Dynamics Analysis) method was applied for the detection and identification of two mixtures of
explosive (Hexogen-Trinitrotoluene-Penthryte and
Hexogen-Trinitrotoluene-Octogen) hidden under various
coverings - the thin, rough, thick layers of Polyethylene foils and a layer of cotton. The main difficulty for identification consists in
fact that the mixtures have practically identical spectral properties both in the Stand-Off (reflection nearly at 90°) and
Specular (reflection at 45°) mode. The presence of covering makes additional difficulties for identification because it
distorts the spectral properties of the reflected THz signal. Nevertheless, it is possible to find the identifiers
characterizing the presence of the individual explosive in the mixtures under the covering analyzing the spectrograms
and dynamics of spectral lines of the main pulses and the sub-pulses following the main pulse.
We investigate the efficiency of spectral dynamics analysis (SDA) method for the detection of both explosives hidden
under various substances and explosives in their mixture. The detection occurs using the THz signal reflected from the
substance. The main difficulty concludes in multi-reflection of THz wave from the substance, in which the explosive is
packed. Our investigation shows that because of their structure these substances can be opaque for THz radiation at
certain frequencies. Nevertheless, this question requires additional investigation.
The action of the THz pulse, inclined at various angles to the sample surface, on substance is analyzed. It should be
stressed that at inclined falling of THz wave, one can get more information about explosive in comparison with the case
of normal falling of THz wave. As a result, the growth of the detection probability takes place.
New features demonstrate the mixture of explosives. Under certain conditions on concentrations of substances in the
mixture, the compound substance displays own properties not as mechanical combination of properties of initial
substances during the time interval of action the main THz pulse. For the detection and identification in this case, one
needs to use the long time interval signal from the substance. Other requirement consists in inclined falling of THz pulse
to detect and identify the explosive.
The paper presents the concept of a multisensor system for perimeter protection, suitable for stationary and moving
objects. The system consists of an active ground radar and thermal and visible cameras. The radar allows the system to
locate potential intruders and controls an observation area for system cameras. The multi-sensor system concept ensures
significant improvement of the probability of intruder detection and reduction of false alarms, thus increasing the
functionality and performance of the whole system. Effective ranges of detection depend on the quality of the applied
sensors and the observed scene itself. One of the most important devices used in such systems are IR cameras. The paper
discusses the technical possibilities and limitations to use uncooled IR cameras in such a multi-sensor system for
perimeter protection. The role of IR cameras in the system was discussed as well as a technical possibilities to detect a
human being. The operational distances for perimeter protection are rather high, considering the performance of
commercially available thermal cameras. The required spatial resolutions for detection, recognition and identification
were calculated and then the detection ranges were estimated using NVTherm software. The results of analysis were
finally presented and the comparison of exemplary IR cameras.
The aim of this paper was the verification of our identification model. The main assumption of our model was the
possibility of the distinction between indicated compounds based on several narrow band detectors of terahertz
radiation. Achieve of this frequency points was done with measurement data from FT-IR obtained in vacuum.
The influence of absorption in water vapor was added numerically from Hitran simulation. The verification
procedure was carried out with Time Domain Spectroscopy (for distance below 20 cm) and with narrow band
sources (for distances above 20 cm). This verification was prepared in laboratory, controlled conditions. Our
results confirm the possibility of application of the model in real THz stand-off security system.
We report on analysis of epoxy composite reinforced with a glass fiber mat by means of Time Domain Spectroscopy
(TDS) technique in reflection way. The samples consisted of 2 or 3 layers with the beveling angle of the layers equal to
90° and thickness up to 2 mm. Two samples with artificially induced air-bubbles (~1-2 mm in diameter) and a sample
which consisted of the 2 layers of epoxy and a layer of an air-bubble foil between them were also investigated. The
measurements shown that all layers as well as defects can be identified.
The nature of the recent military conflicts and terrorist attacks along with the necessity to protect bases, convoys and
patrols have made a serious impact on the development of more effective security systems. Current widely-used
perimeter protection systems with zone sensors will soon be replaced with multi-sensor systems. Multi-sensor systems
can utilize day/night cameras, IR uncooled thermal cameras, and millimeter-wave radars which detect radiation reflected
from targets. Ranges of detection, recognition and identification for all targets depend on the parameters of the sensors
used and of the observed scene itself. In this paper two essential issues connected with multispectral systems are
described. We will focus on describing the autonomous method of the system regarding object detection, tracking,
identification, localization and alarm notifications. We will also present the possibility of configuring the system as a
stationary, mobile or portable device as in our experimental results.
The method of spectral dynamics analysis (SDA-method) is used for the detection and identification of explosive RDX
and harmless substances in pellets with different weight and hidden under the thin layer of polyethylene or cotton by
reflected THz signal. The signal was measured on the long-term interval with duration about 180 ps and contains not
only the main reflected THz pulse but the subpulse with less intensity. Two cases of the reflection were investigated - at
90° and at 45° from the sample. SDA method allows to obtain the spectrogram - 2D THz signature of the substance, and
to analyze the dynamics of many spectral lines of the signal by one set of measurements. The identifiers characterizing
the presence of substance in the sample were found in all investigated samples - they contain in the corresponding
spectrograms and dynamics of spectral lines. We showed that the analysis of the reflected signal over the short time
intervals (less than 50 ps) is insufficient for reliable identification of the substances, especially of hidden ones, because in
some cases the characteristic features of the substances can be found only in the subpulses. The influence of window
shape in Fourier-Gabor method on the dynamics of spectral lines was discussed too.
This paper presents some potentially interesting aspects of spectroscopic transmission measurements of explosive
materials in Far-Infrared (Terahertz) range: preparation of the samples, influence of covering by clothes and influence of
phlegmatization of explosives (addition an agent to an explosive material to stabilize or desensitize it). Moreover, two
commonly used techniques - Far Infrared Fourier Spectroscopy and Time Domain Spectroscopy are presented and
compared. We also shown and compared spectra of materials obtained in two Time Domain Spectroscopy reflection
configurations: specular (45° incident angle) and stand-off with distance 30 and 40 cm to a sample.
We report on measurement of transmission spectra of commonly used explosives (RDX, PETN, HMX) covered by
popular materials: paper, polyester and cotton in THz range (0.3-2.5 THz). Explosives were prepared as pellets, where
Teflon was applied as the matrix material. We made use of Time Domain Spectroscopy and Fourier Transform Infrared
Spectroscopy, which are described and results are compared. We show that characteristic features of explosives can be
still identified up to 2.0 THz.
Detection and recognition of covered explosive materials in the THz range can be devided into two areas - passive and
active systems. Passive systems in the submilimeter (100÷300 GHz) as well as the terahertz (0.3÷3 THz) range base on
thermal emissivity of exemined bodies. Such devices are designed to control persons and baggage in airports mainly at
the temperature about 300K. Thermal emissivity of real bodies can be obtained from the Planck's formula for perfect
black bodies and an emissvity coefficient. The emissivity coefficient of the real bodies can be determined from
laboratory measurements of spectral transmission and reflection for the specific materials. However, values of the
thermal emissivity detected in real cases depend strongly on surface of the material, direction of detection in relation to
normal to the emitting surface, atmosphere and covering materials. These factors introduce attenuation of the emissivity
what can cause camouflage of the characteristic features of individual materials and makes them difficult to identify. In
this paper we present the value of the emissivity of hexogen (RDX) based on transmission measurements in FTIR
spectrometer. The obtained emissivity is used to simulate intensity of radiation on an aperture.
Introduction of a ground multispectral detection has changed organization and construction of perimeter security
systems. The perimeter systems with linear zone sensors and cables have been replaced with a point arrangement of
sensors with multispectral detection. Such multispectral sensors generally consist of an active ground radar, which scans
the protected area with microwaves or millimeter waves, a thermal camera, which detects temperature contrast and a
visible range camera. Connection of these three different technologies into one system requires methodology for
selection of technical conditions of installation and parameters of sensors. This procedure enables us to construct a
system with correlated range, resolution, field of view and object identification. The second technical problem connected
with the multispectral system is its software, which helps couple the radar with the cameras. This software can be used
for automatic focusing of cameras, automatic guiding cameras to an object detected by the radar, tracking of the object
and localization of the object on the digital map as well as identification and alarming.
In this paper two essential issues connected with multispectral system are described. We focus on methodology of
selection of sensors parameters. We present usage of a spider-chart, which was adopted to the proposed methodology.
Next, we describe methodology of automation of the system regarding an object detection, tracking, identification,
localization and alarming.
We report our experimental investigation on characterization of Index-Guiding Photonic Crystal Fibers (PCF)
from their far field intensity distribution. The below presented algorithm makes it possible to determine the
geometrical parameters of the PCF (core diameter, air hole spacing and air hole diameter) from its far field
pattern. We obtained good agreement with the manufacture data for all used fibers.
Photonic crystal fibers (PCFs) constitute a new class of optical sensors because of its diverse advantages. Large possibilities of tailoring different parameters and sensing properties of PCFs by means of geometry design are very promising and are extensively investigated. One of research fields of the PCF are interferometer sensors, where demodulation (processing) of an output signals needs a phase sensitivity to a measurand. We present our theoretical research of phase sensitivity of the Photonic Crystal Fibers with different geometry. In our computations, we make use of the Multipole Method for calculation of an effective refractive index of the fiber. On this basis we determined the phase changes caused by the mechanical disturbances (elongation, bending) as well as temperature changes.
The dislocation sensor based on the contrast phenomenon in an unbalanced fiber optic Michelson interferometer with a 3 x 3 coupler and a semiconductor multimode laser. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. A conception of the elongation sensor that based on linearization of contrast oscillations is shown. Next, a setup of the sensor and signal processing scheme of the sensor is presented. During measurements, for 1-m long sensor we obtained 5-mm measuring range with ±28-μm uncertainty. Explanation of these differences and conclusion to further research are formulated.
This paper presents investigation results of a new generation of the fibre optic perimeter sensor in a two Sagnac interferometers configuration. This system can detect a potential intruder and determine its position along a protected zone. A multiresolution wavelet analyses of the signal is used to determine its start point. First, we made use of decomposition, thresholding and reconstruction of the signal by means of a Daubechies wavelet. Consequently, high-frequency noise was removed from the signal. Next, the signal was exposed to an approximation process by means of a multiresolution Haar wavelet. Statistical analysis of this signal enabled us to determine an amplitude criterion for calculation of a start point for slowly-changeable signals. The criterion was a standard deviation of the amplitude increase of the signal after approximation. Arrangement of a laboratory model of the sensor and its signal processing scheme is presented. During research of a laboratory model, it was possible to detect the position of the disturbance with resolution of about 20 m along a 6-km long section.
Modal Interference Fiber Optic Sensor (MIFOS) for permanent monitoring of the network is presented. A mechanical disturbance of a fiber cable influences on intensity distribution at the end-face of a multimode fiber. Variations in interfering images are analysed by means of a digital processing unit that determines the alarm in case of unauthorized access along the whole length of the fiber. A contrast of an interference pattern and a procedure of fiber optic selection for the sensor are shown. A simple criterion that bases on changes of local maximums positions of the interference patterns is applied. A laboratory arrangement of the sensor and its experimental research are shown.
The theoretical analysis of sensitivity of the Sagnac interferometer-based sensor is presented. This setup has wide range of implementation -- one of them is a perimeter sensor for security systems. Sensor sensitivity is determined firstly by a frequency-phase sensitivity, which is connected with the interferometer principle of operation and, secondly, by electronic noise of a processing unit and attenuation of used fiber optic.
Theoretical description of a contrast in an unbalanced fiber optic Michelson's interferometer with a multimode laser was shown. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. Required characteristic features of the contrast for an elongation sensor were determined. Influences of laser spectrum parameters (wavelength, halfwidth and mode spacing) as well as laser mode amplitudes on the contrast were simulated. Optimal spectrum for the dislocation sensor was determined theoretically. A laser which parameters fulfilled the requirements was found and its spectrum was measured. The measured contrast function was very similar to the optimal theoretical plot what proves correctness of the calculations.
The dislocation sensor based on the contrast phenomenon in an unbalanced fiber optic Michelson interferometer with a 3 x 3 coupler and a semiconductor multimode laser. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. A conception of the elongation sensor that based on linearization of contrast oscillations is shown. A virtual model of the sensor was built for simulations. For real parameters of 1-m long sensor, 5-mm measuring range with 12-mm uncertainty was obtained. Next, a setup of the sensor and signal processing scheme of real sensor is presented. During measurements we obtained 5-mm measuring range with ±28-mm uncertainty. Explanation of these differences and conclusion to further research are formulated.
Security issues of telecommunication networks present complicated and versatile problems. Data transfer of classified information should be secure and in compliance with the law. Presented fiber optic sensors make it possible to adjust electronic business to currently-in-force requirements for network protection. The proposed implementations of fiber optic sensors into telecommunication networks, apart from signalling of an unauthorized access, in more sophisticated arrangements localize a place where an attempt to connection is made. Interferometric fiber optic sensors with distributed sensitivity both with multimode and monomode fibers are presented. Computer simulations shows a possibility of a disturbance point localization along a fiber optic cable. Conceptions of sensors for data transfer security in links, cables and networks by means of proposed sensors is also presented.
Influence of laser spectra on a fiber optic Michelson interferometer's contrast is mathematically described and simulated. Proposal of using contrast-based setup as elongation meter as well as method of measuring range increasing and algorithm for signal processing is also presented. Experimental setup and software were worked out. We obtained 5-mm measuring range, where the biggest difference between real and measured elongation is 25 μm.
The dislocation sensor based on the contrast phenomenon in an unbalanced fiber optic Michelson interferometer with a 3 x 3 coupler and a semiconductor multimode laser used as a source is described. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. So direct contrast-sensitive elongation measurement is limited only to one 200-μm long slope. In this paper we present a method of measuring range expansion up to 8 mm by linearyzation of contrast slopes. Elongation modulator in a reference arm of the interferometer
is used. Experimental setup and software were worked out. For 1-m long sensor the 8-mm measuring range was obtained, where the highest difference between real and measured elongation is 25 microns
The paper presents a theoretical analysis and investigation on temperature and strain sensitivity of Fiber Bragg gratings verified in a laboratory setup. On these ground studies, researches of Fiber Bragg Grating Dislocation Sensor were conducted. Differences between real and measured strain at a constant temperature are depicted.
The results of fiber-optic polarizer preparing in base of a fused biconical taper technology are presented. A new element of this work is use of a high-birefringence fiber with D-type cladding. The received results have been compared with theoretical investigation obtained for suitable prepared substitute model of polarizer structure. All results ware made for elements working on visible range oflight (He-Ne laser).
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