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Remote environmental and industrial sensing based on multi-spectral or radar imaging today plays an important role in ensuring sustainability and protection of natural resources, in saving time and energy in industry and agriculture, and in many other applications. Numerous examples of such systems exist which provide information like product quality to manufacturers, crops growth parameters to farmers or structural integrity details to civil engineers. With recent developments in electromagnetic millimetre-wave (mm-wave) technology and artificial intelligence implementation, short range mm-wave remote sensing is experiencing strong growth with the market dictating new applications with increasingly higher levels of system autonomy. The objective of this paper is to demonstrate methodology and hardware used in short-range radar sensing and use it to build-up a database of scattering images which will allow us the extraction of key signal parameters for particular objects and subsequently allow autonomous object classification using machine learning principles.

The use of higher symmetries in periodic structures has made possible the development of new designs of microwave components with enhanced properties. Significant potential of this new way of making periodic structures can also be applied in design of electromagnetic band-gap (EBG) structures. This can simplify the manufacturing of components in gap waveguide technology, but at the same time it is necessary to respect some limitations and challenging design aspects. In this work, we will discuss the properties of EBG glide-symmetrical holey structures and how to apply them in the realization of gap waveguide technology.

Wireless sensing based on radar devices is used today in various environments to ensure sustainability and protection of natural resources, to save time and energy in industry and agriculture, and in many other applications. Development of radar technology, in particular in millimeter-wave frequency bands, has opened many new applications which are being currently developed. Important aspect of these systems is increased level of system autonomy based on the principles of machine learning or artificial intelligence. In order to exploit these advantages, we need to acquire as much as possible measured information which can be used later in various detection scenarios. Our aim is to perform a polarization sensitivity analysis for a simple S-band FMCW radar system. The acquired measured results demonstrate the differences when scanning the polarization and give us a indication on how this can be exploited in future systems with polarization diversity.

Design of medical sensor implants is very challenging due to numerous restrictions in terms of size and biological acceptability. In addition, large absorption and reflection of electromagnetic waves in body tissues significantly degrades the communication link capabilities. The usual assumption in calculating the link budget is that the permittivity and conductivity of the body tissues are known. However, biological tissues show considerable diversity in structure and consequently in dielectric properties. The first aim of this article is to determine how much the uncertainty of the body tissues’ constitutive parameters affects the prediction of the achievable radiation efficiency of the implant. The second aim is to understand the loss mechanism and thus which tissue permittivity and/or conductivity has the dominant influence on losses. The analysis is done by considering a spherical multilayer human phantom and applying spherical wave decomposition proposed in a previous article. The stochastic collocation method is used to estimate the uncertainty of power density outside the human body, and sensitivity on the uncertainty of each tissue parameter is performed using the analysis of variance (ANOVA) approach. Several test cases were considered and the results clearly indicate which constitutive parameters have dominant effect on uncertainty.

Recently, there has been an increased interest in exploring periodic structures with higher symmetry due to various possibilities of utilizing them in novel electromagnetic applications. The aim of this paper is to discuss design issues related to the implementation of holey glide-symmetric periodic structures in waveguide-based components. In particular, one can implement periodic structures with glide symmetry in one or two directions, which we differentiate as 1D and 2D glide symmetry, respectively. The key differences in the dispersion and bandgap properties of these two realizations are presented and design guidelines are indicated, with special care devoted to practical issues. Focusing on the design of gap waveguide-based components, we demonstrate using simulated and measured results that in practice it is often sufficient to use 1D glide symmetry, which is also simpler to mechanically realize, and if larger attenuation of lateral waves is needed, a diagonally directed 2D glide symmetric structure should be implemented. Finally, an analysis of realistic holes with conical endings is performed using a developed effective hole depth method, which combined with the presented analysis and results can serve as a valuable tool in the process of designing novel electrically-large waveguide-based components.

International audience; Fundamental limits on radiation performance of implantable antennas serve as the design quality gauge, facilitate the choice of the antenna type, and provide simple design rules to maximize the radiation performance. This study obtains the limits using two formulations 1) theoretical spherical-wave expansion using elementary magnetic and electric dipoles and 2) realistic full-wave 2D-axisymmetric models of TM10 and TE10 mode capsule antennas. Using both formulations, the optimal radiation conditions are investigated, the effects of antenna dimensions and its implantation depth are quantified. The results also demonstrate that an electric antenna operating close to the optimal frequency could achieve higher efficiency than a magnetic one. The latter, however, is more efficient below the optimal frequency range. © 2020 EurAAP.

The design of a specific antenna for a cranial implant is used to illustrate design and simulation issues linked to implantable antennas. After a brief introduction, we will review the requirements for the antenna, and go through the design process, discussing the tools used and the issues encountered. The final design will then be presented and discussed

With research of curved metasurfaces gaining more attention, adequate analysis methods are needed to allow for an efficient design of such structures. Previous works dealt with specific canonical problems, such as those with cylindrical geometry, which were mostly analyzed using Mode Matching approach. In this paper we present an analysis based on Method of Moments which can be used for any generally-curved metasurface structure situated in free-space, or for metasurfaces embedded in canonical multilayer supporting structures (e.g. spherical or cylindrical). We implement a solver for this method and verify the results against other computational approaches, as well as against measurements of a developed antenna pattern-shaping metasurface.

In-body implanted antennas are one of essential components of various medical devices being developed in order to help in monitoring patient’s condition more directly. Human body is, however, a very hostile environment from electromagnetic point of view, since the body, when viewed as dielectric medium, has very high losses. To study how this effects the radiation properties, in this paper we focus on the analysis of radiation efficiency as a function of the size and the position of the implant inside the body. We compare two scenarios where the body is approximated with spherical and cylindrical body models which are commonly used in similar investigations. Results confirm that in both scenarios the size and the position of the implant have a major effect on the efficiency, however, the observations have to take into account the frequency since different loss mechanisms dominate for different frequencies.

Using glide-symmetric structures with different dispersion properties has shown huge potential for novel electromagnetic applications. Our interest in this paper is to investigate how waveguide-based technology can be improved using glide-symmetric holey structures. The impact which glide-symmetric holey structure has on the waveguide losses when there is an unwanted gap in the waveguide structure is demonstrated using developed prototypes. Further, an analysis of realistic holes with conical endings is performed using developed effective hole length method which can serve as a valuable tool in the process of designing novel waveguide lenses based on these properties.

Fundamental radiation limitations of in-body or implantable antennas should give us an estimate on the feasibility of some desired system. It was shown that near-field effects and distance to the body - free space boundary are critical aspects, while the shape doesn’t play a major role in the achievable power. Through the frequency analysis of these limitations in this paper we provide another perspective and show how rigorous and approximate approach to near-field and reflection losses manifest in the results. This is demonstrated on a spherical body example which contains a small spherical implant which can be placed at different positions within the body in order to simulate different implant depths. The results reveal that reasonably accurate description of in-body loss mechanisms can be achieved using our previously defined fundamental radiation limitations for power density, however, depending on the frequency different loss aspects must be treated with special care.

Metasurfaces that manipulate electromagnetic waves have gained significant attention in recent years. The focus has primarily been on planar devices, while many applications require curved surfaces. In this study, the authors propose an analysis approach for cylindrical cascaded (multilayer) metasurfaces. The approach combines the concept of sheet impedance in the spectral domain with a new transmission matrix formulation that is applicable to stratified, canonical curved geometries. Approximate formulas for the sheet impedance of common planar, metallic patterns are also adapted to curved geometries. The reported analysis approach allows one to determine the optimal spectral-domain, azimuthal dependence of a sheet impedance, as well as the best geometrical elements to obtain the required azimuthal variation. The results are verified through several cylindrical metsurface examples.

Vibrations and their parameters can be measured through monitoring the speckle pattern of multimode optical fiber. In this paper a modified approach to realization of a specklegram based vibration sensor system is discussed. Replacing the (standard) camera detector with an array of several detector diodes improves the size and frequency range of the system. Different statistical methods for processing the signals from the diode array are presented, compared experimentally and discussed. The principal advantages of the specklegram vibration detection approach, low cost and distributed detection possibility, have been retained.

Realization of components in gap-waveguide technology can be expensive and time-consuming due to demanding manufacturing procedure. To reduce the costs of production we have investigated the characteristics of a 3D printed leaky wave antenna metallized using low-cost electroless process. As a proof of concept, leaky wave antenna is designed in groove gap-waveguide technology for operation at 30 GHz. The antenna was simulated, manufactured and measured to verify the design and the quality of the used copper plating process.

The concept of gap waveguide is based on using a finite quasi-periodic structure with an electromagnetic band-gap property to trap waves inside a parallel-plate waveguide. In order to efficiently analyze arbitrary components based on bed-of-nails gap-waveguide technology, we developed an analysis method that rigorously evaluates scattering from each pin using the mode-matching approach in combination with the multiple scattering analysis. The resulting program is very fast making it suitable for iterative optimization in the design process of various components.

The signal-to-noise ratio (SNR) of filtered incoherent light can be approximated from the product of the coherence time of the light and the equivalent (electrical) noise bandwidth of the detector. This approximation holds only for the light with very short coherence time, that is in the case where the optical bandwidth of the light is much larger than the electrical bandwidth. We present here an expression for accurate evaluation of the SNR of the filtered incoherent light, which computes SNR from arbitrary shapes of optical and electrical filter power spectral densities (PSD). The PSDs of the filters can be measured using optical and electrical spectrum analyzers. Using our expression, we show that the SNR reaches unity when the electrical filter bandwidth is becoming larger than the optical filter bandwidth. To prove the theory, we evaluate and directly measure SNR of an incoherent light source filtered with several optical filters with bandwidths larger and commensurate with the bandwidth of the detector. For later we used optical and electrical filters with 3-dB bandwidths of 15 GHz and 10 GHz, respectively. Using our expression to evaluate SNR we obtained results in a good agreement with directly measured SNR. The results also prove that the approximation for evaluating SNR does not provide accurate results. The PSD of the detector with large noise bandwidth is difficult to measure using spectrum analyzer. There- fore, we report here a method for measuring the electrical noise bandwidth of the detector using the heterodyne linewidth measurement technique with tunable laser.

The Wireless Body Area Network (WBAN) has become an important part of the wireless communication world in the past decade leading to the need for efficient antennas for In-, On- and Off-Body links. The design of such antennas depends critically on the understanding of their interaction with the host body, and thus on the propagation of waves in inhomogeneous lossy media of finite dimensions. To this aim, we propose a simplified spherical multishell model of the lossy body, and study its interaction with elementary sources placed within or on the latter.

The paper describes a systematic approach and a computer program for designing curved multilayer structures containing metasurface layers. Metasurfaces that manipulate electromagnetic waves have garnered significant attention in recent years. The focus has primarily been on planar devices, however many applications require curved surfaces. Curvature introduces additional challenges in the analysis, and we propose a analysis method based on the surface impedance approach in the spectral domain and on the algorithm for calculating Green's function of multilayer one-dimensional (1D) and two-dimensional (2D) structures.

International audience; With the development of generalized connectivity and the increased use of Body Area Networks, wearable antennas have become ubiquitous in the last decade. Their design presents a challenge, as they per definition are located at the interface between free space and an environment which is intrinsically lossy and hostile to the efficient radiation of electromagnetic waves. In this contribution, we propose a theoretical analysis of different canonical sources placed on biological tissues. Based on the insight gained, several simple design rules will be proposed and illustrated on a practical antenna design. © 2016 IEEE.

Many medical, environmental, and industrial sensing applications could take advantage of uncooled temperature-stable optical sources that are incoherent and un-polarized as such sources do not produce interference fringes, speckle patterns, or intensity variations due to polarization. For this purpose we propose an optical system for stabilization of light- emitting diodes over temperature exhibiting output power variation below 50 ppm/°C which does not employ any kind of TEC elements or even thermometers. This makes it especially suitable for handheld and battery operated instruments.

The objective of this work was to demonstrate a lightweight and inexpensive fiber-optic vibration sensor, built using 3D printing technology, for high-power electric machines and similar applications. The working principle is based on modulating the light intensity using a blade attached to a bendable membrane. The sensor prototype was manufactured using PolyJet Matrix technology with DM 8515 Grey 35 Polymer. The sensor shows linear response, expected bandwidth (< 150 Hz), and from our measurements we estimated the damping ratio for used polymer to be ζ ≈ 0.019. The developed prototype is simple to assemble, adjust, calibrate and repair.

Optical sources with highly temperature-stable output intensity and low power consumption are desired in portable devices for metrology, and in medical applications, communications, and illumination. This paper introduces and demonstrates an optical stabilization scheme that uses the drift in peak-emission wavelength of light emitted from an LED as a temperature feedback signal to realize output intensity temperature coefficients below 100 ppm/K. The control principle relies on a conventional feedback loop but with a specially designed weakly polarizing optical interference coating that exhibits different transmittivity/reflectivity ratio dependence on wavelength for two different polarizations and by using a weighted sum of two polarizations as the output power correcting signal in a feedback loop. The method does not need a thermometer or temperature control stage, and its calibration can be performed electronically, adding to the simplicity of the design and making it also suitable for portable and battery-operated instruments.

A metasurfing concept is demonstrated and applied in the design of Luneburg lens antennas. Using an array of size-varying circular patches on a dielectric substrate inside a parallel-plate waveguide (PPW) structure variable surface impedance is obtained, which realizes an equivalent refraction index as that of a Luneburg lens. The obtained lens has good bandwidth characteristics and significant fabrication advantages with respect to conventional dielectric lenses. Based on this PPW lens, an H-plane antenna has been designed and simulated.

Complexity and needed computation time of moment method analysis approach for conformal antennas is reduced by applying particular series acceleration techniques to the partial sums encountered in these problems. The Wynn’s ε-acceleration technique is investigated and modified in order to achieve better convergence. The results show excellent convergence properties when applying this method to the analysis of antennas printed on cylindrical and spherical substrates.

This paper presents a novel hybrid method for analysing convex multilayered conformal array antennas. The hybrid method is based on the spectral domain approach in combination with the ray-based UTD (Uniform Theory of Diffraction) method. The analysis is divided in two parts. First, the spectral domain approach is accelerated by using an asymptotic extraction technique where the extracted term of the Green’ s function is calculated using UTD. It is shown that this new approach results in significant acceleration of the existing spectral domain algorithm without losing accuracy. The modified spectral domain method is then used in the second part where generally shaped convex multilayered surfaces are analysed by using sets of canonically shaped surfaces (spheres and/or circular cylinders). Their radii are obtained using the UTD formulation, which contains important information such as distance and curvature of the generally shaped surface along each geodesic. The results obtained using the new algorithm are compared to the available results (calculated and measured) for different conformal antennas, showing very good agreement.

This article presents a rigorous mathematical analysis of spherical stacked-patch arrays with emphasis on the physical interpretation of mutual coupling mechanisms present in doubly- curved convex structures. The analysis method is based on electromagnetic field representation in terms of spherical harmonics where each harmonic has the same angular variation as the spectral source component. To obtain the spectral representation the vector-Legendre transformation is applied to currents and fields. A novel approach to the mutual coupling calculation within the Moment Method (MoM) analysis of spherical arrays is applied. By expressing the patch current in terms of two suitable potential-like auxiliary functions, it is possible to avoid the use of Euler’ s formulas for coordinate system rotation and the related lengthy integrations. Instead, the rotation of antenna elements and corresponding current distributions can be done in closed form with the help of Vilenkin’ s addition theorem for associated Legendre functions. It is shown that the new approach results in significant acceleration and improved accuracy of the analysis of spherical patch antenna arrays. The algorithm is successfully tested against a commercially available EM software and measurements performed on the developed laboratory model, confirming its accuracy for both input impedance and mutual coupling calculation and with only a small difference between the predicted and measured resonant frequencies, due to limitations in the experimental model. The influence of the structure parameters on mutual coupling level is extensively investigated, including all coupling mechanisms and leakage of energy due to curvature of the structure. It is shown that stacked-patch antennas can have reduced coupling level comparing to single patch antennas with possible deep nulls above the antenna resonant frequency.

Recent advances in the development of self- seeded WDM-PON communication systems employing modulation averaging are presented. Optical transmitter containing extended-cavity resonator with modulation-averaging reflector at the remote node improves the link margin and allows for a wider range of bias conditions at the transmitter. The developed modulation- averaging reflector is a passive optical device and therefore the remote nodes in our proposed WDM-PON system remain passive. Optimization of WDM-PON system components, in particular optimization of modulation-averaging reflector, is discussed in the paper.

We investigate the influence of temperature on multimode Fabry-Perot laser output in a proposed colorless WDM system with self-seeding via modulation averaging reflector and with BLS-seeding. In particular, we investigate the connection between the information about the optical laser output from the laser integrated monitor photodetector and optical power output of the entire system with temperature change of the laser diode.

We demonstrate a fiber-optic sensor for monitoring mechanical vibrations in high-power electric machines built using 3D-printing. We describe the design, mechanical and optical modeling, and the results of its preliminary characterization. The measurements show linear sensor response in the frequency range 10 to 150 Hz.

Fiber Bragg grating (FBG) sensors have become quite common in many applications for monitoring strain, temperature and similar. These systems are usually fixed since the FBG interrogation unit is sensitive to the environment and therefore mounted into the equipment cabinet. However, a portable FBG interrogation unit would be of great benefit in applications where there is no need for continuous monitoring. For this reason here we propose a portable interrogation system based on a temperature stable SLED broadband source, calibrated tunable optical filter and an adaptive peak search algorithm.

Gap waveguide structures combine the ideas of parallel plate waveguides and electromagnetic bandgaps to form novel efficient high frequency waveguiding structures. Since the concept relies on the use of periodic structures with bandgap properties the analysis is very complex. Our proposed analysis approach is based on efficient use of Method of Moments / Mode-matching to rigorously determine the scattering of each element in the grid. To achieve this, the currents on the elements are first determined by using the Green's function of a single element in a parallel-plate waveguide. The solution is then expanded to all the elements from which dispersion properties can be determined. The results of our approach are verified using full-wave commercial software. They show excellent agreement, but it is important to point out that they are obtained in a fraction of the time compared to the full-wave software.

Analysis of electromagnetic components that contain periodic structures is a difficult and time-consuming task. The first design of such components can be made in a short period of time using the Green's function for canonical structures where the periodic structure is taken into account in the asymptotic sense. In this way it is possible to determine the basic structure parameters of the designed electromagnetic component, and therefore significantly shorten the time needed to obtain the final design (which is done using a general electromagnetic solver). Furthermore, with the help of the simplified analysis it is possible to calculate the electromagnetic parameters of interest (e.g., radiation pattern, mutual coupling level, etc.). This paper will present several models of periodic structures that accurately describe the observed structure, i.e. in which all the relevant mechanisms linked to the guiding and interaction of electromagnetic waves are considered. By comparing the results obtained using general electromagnetic solver and using the presented method we have demonstrated the accuracy and benefits of the proposed method in the design of electromagnetic components that contain periodic structures.

This paper presents an overview of complex conical beams and techniques developed for their application in the analysis of reflectors and reflector antenna systems, realised either as full PEC surfaces or quasi-periodic, frequency selective surfaces. The various techniques link complex conical beams with Physical Optics, Spectral-Domain method and the Uniform Theory of Diffraction. The method is tested on several examples, including a frequency-selective dual-reflector system of the Gregorian type, designed for the operating frequency of 25 GHz.

This paper presents a combined analysis approach suitable for analyzing complex reflector antenna systems comprised of both simple PEC reflectors and frequency selective surfaces. The approach joins several methods and models, including Complex Conical Beams, Physical Optics, Spectral-Domain method and the Uniform Theory of Diffraction. The method is tested on a frequency-selective dual-reflector system of the Gregorian type, designed for the operating frequency of 25 GHz.

Modeling of gap-waveguide structures with single and multiple transmission lines is performed using spectral domain Green's functions approach. The approach is extended using even/odd mode analysis in order to also estimate the crosstalk levels between neighboring transmission lines. The results of this analysis are compared with the results of a commercial electromagnetic solver and with the measured results.

Concept of variable or non-uniform metasurfaces allows a very high level of control over the electromagnetic wave paths. In this paper this control is achieved by gradually modifying the geometry of subresonant printed patches on a grounded dielectric substrate. This allows us to change the phase velocity or the propagation path of the guided wave. This property was used to design a Luneburg lens which was then inserted into an H-plane horn to improve the horn's radiation characteristics. The results of this idea are demonstrated using full wave simulations, showing the applicability of this concept.

This paper demonstrates the design and the analysis of a novel type of horn antennas with a potentially higher directivity. The idea is to replace one plate of an H-plane horn antenna with a plate that has specially designed surface impedance. In our case we generated the surface impedance variation that corresponds to a Luneburg law, thus obtaining the Luneburg lens effect and consequentially increasing the directivity and reducing the overall horn length.