This PDF file contains the front matter associated with SPIE Proceedings Volume 11451, including the Title Page, Copyright information, and Table of Contents

The problem of detection and trajectory tracking of a group of small objects by a passive vision system is solved. The system consists of several space-oriented optical receivers that monitor the viewing area is considered. We propose an approach based on the distribution of optical receivers over stereo pairs, taking into account the orthogonality of the lines of sight on objects, and the redistribution of stereo pairs in the case of receiver failures to solve this problem. An appropriate algorithm has been developed to improve the reliability of the system, the probability of detecting all objects, and the accuracy of determining spatial coordinates. The results of the experimental examination of the developed algorithm are presented.

We discuss about a fully-staring THz video camera prototype intended for security screening. The camera utilizes so-called kinetic inductance bolometers to detect THz radiation in the bandwidth of 0.3-1 THz. The imaging distance is 2.5 m with the nominal field-of-view of 2 m × 1 m. The camera is equipped with a kilo-pixel detector array, intermediate-scale cryogenics operating at 6 K, and low-noise electronics to read out the whole detector array. Here, we focus on describing the wide field-of-view and close-looking optical system of the imager.

For over 28 years, INO has been developing microbolometer arrays for the infrared and Terahertz (THz) domains. INO’s microbolometer array is the key component of INO’s broadband THz cameras. Using this detector, INO has developed active Terahertz imaging systems ranging from 250 GHz to 750 GHz. See-through THz imaging is particularly well suited for security screening of persons and non-destructive inspection of objects. Materials such as cardboard, plastic, leather and denim are transparent to THz radiation and can provide insights on objects hidden from the naked eye or from infrared cameras. In addition, Terahertz provides high resolution images and is non ionizing. In particular, the frequency range of 150 – 550 GHz is of interest for its properties of see-through imaging that enable a wide variety of potential applications. In this paper, we present images obtained around 400 GHz and 200 GHz (corresponding to wavelengths of 0.76 mm and 1.52 mm). We have chosen these two wavelengths to allow for a wide range of objects and obscuring materials to be tested. The 400 GHz wavelength allows better image resolution, while the 200 GHz provides better penetration through the materials. The THz imaging system can obtain images of objects with dimensions up to 1 meter x 0.75 meter with subcentimeter resolution. To achieve this, we use diffraction-limited imaging optics with high numerical aperture and a microbolometer array detector. For each object, multiple images are acquired that are then stitched together. Each instantaneous image can be seen in real-time during the acquisition and has the same resolution as the global reconstructed image. In the context of an application, the operator does not need to wait until the scan has been completed to identify a hidden object if the size of its features is compatible with the instantaneous field-of-view. When a more global image is required, the reconstructed image shows the features of the whole object under investigation without resolution loss. Images are acquired in two different configurations: transmission and reflection. Each imaging configuration provides different information about the features inside the object as well as its composition. In summary, this paper demonstrates the potential for our THz imaging systems by providing see-through high-resolution THz images of large objects. An analysis of the impact of wavelength and imaging configuration on the image results is also provided.

Surrogate explosives and shrapnel weapons at a range of 2 metres have been measured using a full polarimetric radar operating over the band 18-26 GHz. Measurements of these items were made as they were standing by themselves and as they were placed on the body, under light clothing. These measurements were compared with measurements made of the divested human body. The polarimetric radar comprised a vector network analyser, and orthomode transducer and a waveguide conical horn antenna. The measurements were analysed using the Euler/Huynen decompositions and the Cloude/Pottier decompositions working on the coherency matrix, as derived from multiple time sequence measurements. The results conclude that the signature of threat items changes considerably when they are placed on the human body. The measured signature of the threat item on the body appears to be somewhere between that of the threat item when it is by itself and that of the divested human body.

We propose the use of 3D-printed helix antennas for millimeter-wave radar imaging. This concept is promising for a number of reasons: Additive manufacturing involving 3D-printing is a relatively cost efficient fabrication technique and offers increased geometrical freedom of design compared to conventional manufacturing processes. From an imaging point of view, using helix antennas is advantageous because of the circular polarization the antennas emit. That way, imaging thin dipole-like structures is possible regardless of their orientation. In contrast, imaging systems using linearly polarized antennas are unable to image dipoles orientated orthogonally to their polarization direction. Radar systems using circular polarization additionally enable polarimetric imaging and decomposition. In security screening this can achieve a higher classification accuracy in discriminating threat objects and reduce false alarms. Furthermore, the thin helix antennas (typical coil diameter: ca. 1.5 mm) can be mounted very closely to each other, which is interesting for array design. A security screening example was investigated for demonstration: A cardboard box with metallic and dielectric threat objects was screened at 70 GHz – 90 GHz by a quasi-monostatic synthetic aperture radar consisting of two 3D-printed helix antennas, one right-hand and one left-hand circularly polarized. As a reference, the same object was screened with split-block linearly polarized horn antennas. With the proposed setup, the resolution of the reconstruction images was comparable to that of the reference system. However, the circular polarization was able to depict thin structures in a better fashion than the linearly polarized reference system.

The results of the influence of Ti⁴⁺ + Сo²⁺ ions on the magnetic properties of ferrites are presented. It is shown that the increase in the content of Со²⁺ + ions Ti⁴⁺ in the structure of spinel ferrites can be controlled to change as the values of magnetic permeability and temperature of the phase transition to the paramagnetic state. Magnetic and dielectric properties of ferrites are closely related to their chemical transformations during synthesis and temperature treatment. Temperature treatment, provides homogenization and formation of ceramic structure. The paper considers ferrite systems as phases of variable composition formed in the process of temperature treatment. Specific examples are given of modern ideas about the physic-chemical nature of the processes of synthesis of ceramics. The obtained samples are characterized by high density, micron size of crystallites, uniform distribution of alloying impurities, chemical homogeneity.

The well known Y-Ba-Cu-O superconductor (oxygen rich) material also exhibits a semiconducting phase (oxygen depleted), which offers in its amorphous form (a-YBCO), an attractive solution for the easy fabrication of room temperature thermal radiation detectors. The operating mechanism is related to a sensitive pyroelectric response that originates from the permanent dipolar moment of the Y-Ba-Cu-O unit cell. In the first part of this paper, we investigate material aspects of a-YBCO thin films (surface morphology, electrical transport and optical properties) for a better understanding of the microstructure vs. conductivity relationship. In the second part, we report on the near-infrared (NIR) characterization of planar and trilayer detector devices fabricated on silicon substrates. These detectors exhibit a very fast response (time constant tau = 1.9 µs for a planar device; tau = 0.12 µs for a trilayer device) as compared to commercially available pyroelectric sensors. The best noise equivalent power (NEP) and detectivity D*, which are at the state of the art, were observed in the NIR at 10 kHz modulation frequency: NEP = 2.0 pW/rootHz and D* = 6.6×10^9 cm•rootHz/W for planar device; NEP = 2.6 pW/rootHz and D* = 5.7×10^9 cm•rootHz/W for trilayer device. Evolution towards THz detection is finally considered

Hot electron bolometers (HEB) exploiting the properties of the high-T_C superconductor (HTS) Y-Ba-Cu-O, are offering a competitive alternative to THz Schottky mixers, which require moderate cooling (e.g., 60 to 80 K). This arises from the HTS HEBs expected wide bandwidth (tens of GHz), and low local oscillator (LO) power requirements: tens of microwatts, whereas several milliwatts are necessary to pump Schottky diode LOs efficiently. In fact, the large instantaneous bandwidth is related to the extremely short electron to phonon relaxation time (1 to 2 ps, typically) in YBa- Cu-O. It is much longer in low-T_C superconductors (LTS), e.g., about 20 ns in NbN. Besides, as required for LTS materials, it is mandatory to fabricate high quality and ultra thin HTS epitaxial films, so to process nano-bolometers exhibiting good mixing performances (i.e., double sideband noise temperature T_n and conversion gain G). Most of all, the challenge for Y-Ba-Cu-O remains the chemical reactivity and the aging effects, as reported previously. The main objectives of this paper are: i) to predict Y-Ba-Cu-O HEB heterodyne mixer performances, and ii) to exploit those predictions to simulate a stand-off passive detection system for, e.g., screening or security applications.

In this research, we present the design, fabrication and experimental validation of 3D printed mux/demux elements for terahertz frequencies. The devices consist of a set of in-line polystyrene (PS) rectangular waveguides, separated by 100 μm, 200 μm and 400 μm air gaps. The principle of operation for the proposed elements resides in coupled-mode theory. Q-factors of up to 3.4 are observed, and additionally, the experimental evidence demonstrates that adding fibers to the design improves the Q-factor by up to 0.62 per fiber added. Using two independent THz broadband channels, we demonstrate the first mux/demux device based on 3D printed in-line filters for the THz range. This approach represents a fast, robust and low-cost solution for the next generation of THz devices for communications.

Despite the rising interest in the human skin signature over the millimetre wave band there is relatively little information about the human skin reflectance and the dielectric properties of the human skin, and how these varying with locations and between gender, and hydration level of the skin. This paper has investigated the reflectance of the human skin over the frequency band 80-100 GHz, and comparing the reflectance of the human skin with the reflectance of porcine skin samples under normal and wet skin conditions. For a sample of 60 healthy participants (36 males and 24 females) the mean reflectance of the skin over all measurement locations was found to be ~0.606 with a standard deviation of ~0.086. The skin regions of the palm of the hand, the outer wrist and the dorsal forearm skin had reflectances 0.068, 0.058 and 0.0677 lower than the skin regions of the back of the hand, the inner wrist and the volar forearms respectively. Reflectance measurements of human skin under normal and wet state on the palm of the hand and the back of the hand regions indicate that the mean differences in the reflectance before and after the application of water is ~0.15 and ~0.075 respectively. A comparison in reflectance between human skin and porcine skin samples indicates similar trends in signatures between ex-vivo porcine skin samples and human skin. During the cycle of life, human skin is affected by many factors such as the age, the environment, the interaction with different types of radiation, genetic defects, dehydration, and accidents. These factors might cause diseases, temporal skin conditions, and permanent disorders. In response to this, the skin presents signatures, which can be measured using non-contact millimetre wave sensors that could quantify the degree of the damage. These unique findings enable millimetre wave radiometry to be used for detecting human skin signatures and anomalies under different conditions by identify unusually high or low levels of reflectance in tens of seconds.

Millimetre-wave beam-steering distortions are due mainly to unbalanced feeding amplitudes among the delay lines network. To compensate for this, active amplifiers or attenuators are employed, increasing the circuit complexity and costs, whilst compromising the passive array advantage. This work presents a passive millimetre-wave distortion-free beam steering solution with analog resolution in liquid crystal planar delay line technology. Enclosed coplanar waveguide (ECPW) tunable delay lines with 0-180˚ and 0-360˚ phase-shifting ranges are prototyped respectively. A novel impedance matching and mismatching approach for amplitude compensation is proposed and verified, as evidenced by the 67 GHz measured maximum insertion loss of –4.37 dB (variation up to 5%) for the 0-180˚ delay line, and –8.28 dB (variation up to 8%) for the 0-360˚ device. Based on a smart combination of the 0-180˚ and 0-360˚ ECPW, an optimised delay lines deployment scheme is proposed for two-dimensional beam steering with a fault tolerance capability and a minimised systematic insertion loss in total on the feeding network.

Terahertz radiation is the part of the electromagnetic spectrum ranging from hundreds of MHz up to several THz. Recent advances in detector technology enable us to develop compact and affordable systems able to generate and detect THz radiation, thus filling the so-called “terahertz gap". Terahertz cameras with thousands of pixels arranged in one or two dimensions allow for real-time imaging applications. THz imaging techniques can be used to detect materials that are opaque to that radiation, such as metal or ceramic objects embedded in THz-transparent materials (e.g. paper, textiles, etc.). Due to its non-ionising nature, THz radiation does not require special shielding precautions compared to X-ray systems, and can be safely applied to living tissue. Terahertz imaging can be employed to detect forbidden objects in security checks with parcels scanners and full body scanners. This paper will describe our recent developments towards an innovative application of a sub-THz imaging system based on a commercially available detector. The setup is used to detect objects inside parcels and packages using a conveyor belt and a THz imaging system. An automatic detection system based on convolutional neural networks has been developed allowing for a real-time selection of targets against a set of images. The performance of the setup will be shown and newest results on the recognition capability will be presented.

A study of the microwave absorbing properties of coatings based on bulk samples of W-type hexaferites is presented. The link between dielectric and magnetic permeability makes it possible to control their magnetic properties by doping the original composition. Hexaferrites are the most stable system, showing a good rate of absorption and reflection of electromagnetic radiation in the microwave range. The substantiation of the choice of material for the manufacture an absorber of electromagnetic radiation and a brief description of the technology of obtaining a composite absorber based on W-type hexaferrite are given. The results of studying the characteristics of reflection and absorption of electromagnetic radiation based on W-type hexaferrite powder in the frequency range 1 MHz –40 GHz are presented. Recommendations are given on the use of the proposed composite material as an absorber of electromagnetic radiation. It is shown that the use of a composite material for shielding and absorbing EMP has great prospects, while the shielding efficiency depends, first of all, on the type of ceramic material.

This paper demonstrates the development of the analytical method of suppression of radiation pattern (RP) side lobes which is based on Woodward-Lawson method with three basic functions. The considered method allows to suppress the side lobes of the RP in a wide range of angles. It also allows to suppress RP side lobes in a desired direction. This approach can be used in digital antenna systems and the multibeam active phased antenna arrays. In the first part of the paper, linear phased antenna array (LPAA) consisting of isotropic equispaced radiators and methods of suppression of side lobes and creation of the operated minimum in a LPAA radiation pattern are considered. In the second part of the paper partial diagram method is considered. It is shown how to control the RP side lobes in wide range of angles. In the third part of the paper it is shown how to suppress RP side lobes in a desired direction. The fourth part of the paper shows how to synthesize amplitude and phase distribution to control RP side lobes. The method presented in this work allows to reduce the level of the side lobes of the radiation pattern by more than 50 dB in a wide range of angles, or in a given direction. Expressions for calculating the amplitude and phase distributions forming a minimum RP in a given direction are presented. Using LPAA with a given number of emitters, the use of the technique is demonstrated.

The paper presents an assessment of the accuracy of the method of choosing an integration variable for the numerical solution of the Cauchy problem in terahertz range. An example of using the method to determine ray paths in inhomogeneous media in the approximation of geometric optics is given. Unlike numerical methods of integration, where one pre-selected variable is used as an integration variable, in the considered method the integration variable is selected at each step. This approach reduces the risk of shifting to adjacent phase trajectories, which is especially important in the terahertz range. In addition, we note that using this approach allows you to effectively use computer resources. The integration method with the choice of the integration variable at each step is described. A feature of the method is that the variable with the highest rate of change is selected as the integration variable. The accuracy of the method is investigated by the example of a problem with a well-known analytical solution. The dependence of the relative error of the solution on the grid pitch is investigated. Extreme values of the grid pitch at which the relative error drops sharply are calculated. The dependence of the relative error of the solution on the direction of propagation of the rays is investigated. Shows the application of the numerical modeling algorithm for the example of constructing ray paths in inhomogeneous media in the approximation of geometric optics for geometry with three spatial coordinates. The ray paths in 3D space are presented.

Effective design of micromechanical switches for operation in various frequency ranges is impossible without mathematical models including the correlation of electrophysical parameters with the design and technological parameters of their fabrication. This task is complicated by the fact that different technologies and materials are used to create RF MEMS switch. An earlier analysis of the creation of the MEMS switch allowed us to identify groups of factors that have a significant impact on the electrophysical and frequency characteristics. To assess the influence of technological factors on the electrophysical and frequency properties, technological parameters such as the etching time of various layers, the processing temperature, and material properties such as electrical conductivity, Young's modulus, permittivity, and electrical resistivity were selected. And as design parameters, changes in thickness during the formation of the dielectric layer and the membrane, the thickness of the gap between the membrane and the dielectric layer were considered. In this paper, we construct a MEMS switch model including the influence of design and technological parameters on the characteristics of the switch in the on and off state. Another task is to assess the impact of technological uncontrolled effects that occur under certain conditions in the fabrication of a switch. Electrodynamic modeling of the switch was performed by the finite element method using the mathematical model that includes design and technological parameters. The operation voltage, switching time, the frequency of natural vibrations of the membrane, and the voltage characteristic of the switch were studied. The mathematical model of a micromechanical switch, including the technological parameters of its fabrication, will allow developing technological processes for the fabrication of MEMS switches that match the requirements in the specified frequency ranges and have low losses.