Remote sensing of marine plastic is a relatively new field and research into the capabilities of radar for detecting and monitoring marine plastic pollution is lacking, with several interactions and mechanisms being largely unknown. Here, we exploit the use of a C- and X-band radar to understand the capabilities of radar for detecting and monitoring marine plastics. Our results show that backscattering differences in C- and X-band between ‘clean’ water and test water filled with plastics can be detected in some conditions (based on statistical analysis). With C- and X- band detecting statistical differences in 20 / 67 and 48 / 68 cases respectively. We also find that the difference in backscattering is dependent on the size and shape of the plastic object, as well as the wave conditions in which the plastic is moving. This work provides key information on the capabilities of radar for detecting marine plastic litter and provides details which can be used for future planning in regard to tackling remote sensing of marine plastic pollution.
One of the most challenging shoulder injuries is rotator cuff tear that increases with aging and particularly happens among athletes. These tears cause pain and highly affect the functionality of the shoulder. The motivation of this work is detecting these tears by microwave tomographic imaging. This imaging method requires the solution of an inverse problem based on a minimization algorithm, with successive solutions of a direct problem. We make use of parallel computation from the domain decomposition method and domain-specific language with the open-source FreeFEM solver. Results demonstrate the possibility to detect tendon tear in a simplified shoulder model.
Device-free localization (DFL) systems exploit the human-induced perturbations of the electromagnetic (EM) fields as a privacy-preserving sensing tool for passive detection, recognition, localization, and tracking. Without wearing any electronic device, the monitored subjects (targets) modify the EM field (e.g., the Received Signal Strength - RSS) in a way that depends on their location relative to the wireless devices. Thus, DFL systems exploit specific radio maps to reconstruct the body-induced alterations of the EM field and enable motion tracking. These maps can be learned from training data or obtained from a physical/EM model. Practical EM models are based on the scalar diffraction theory and predict the impact of subject motions on the radio propagation without requiring time-consuming computations. However, they are often limited by free-space propagation assumptions that are unsuitable for complex environments characterized by significant multipath effects. This paper discusses and extends the generic diffraction-based models by considering also the floor influence in indoor scenarios. The proposed model is validated by EM simulations and experiments. The impact of this model on the statistical characterization of the RSS is also analyzed for selected target locations.
A new type of antenna called modified comb antenna is proposed in this paper, it is also proposed a dedicated mathematical framework for the antenna design. The new antenna consists of parallel conductors, fed by a single fed. The results obtained from the analytical model were then compared with the simulated results, finding a 4% error in the calculated antenna size. A prototype of the antenna has been made to evaluate the radiation performance and the frequency response of the antenna. Concerning predicted curves, a 1.1% shift in the resonance frequency was found. The proposed modified comb antennas is appealing and of potential interest for innovative applications
We discuss forward and backward modes in one-dimensional (1-D) periodic bounded structures. First, it is shown that the conventional definition of the phase speed can incorrectly identify the forward/backward nature of modes. Therefore, we propose an alternative definition of the phase speed for modes in bounded periodic structures and demonstrate that this definition correctly identifies the nature of modes in a 1-D periodic corrugated parallel plate waveguide. The proposed phase speed is analyzed through simulations with commercial software and a circuit model.
We designed and simulated a 1 GHz planar dipole antenna that is cloaked in a band around 10 GHz. Relative to an uncloaked antenna it has a reduced extinction cross-section for the co-antenna polarization, at the cost of an increased cross-polarization. This reduced extinction cross-section characterizes a reduction in scattering and absorption, and so reduced interference to electromagnetic waves in the frequency of cloaking. The dipole antenna element is cloaked by the introduction of sub-wavelength capacitive strips surrounding its length. The cloaking results were obtained using full wave simulations, showing for the realistic, lossy design a reduction of at least 5 dB in the extinction cross-section over a bandwidth of more than 1.5 GHz in comparison with the uncloaked antenna.
This paper presents a design of probe fed dual beam 2x2 antenna array at 2.4 GHz. The dual beam of the antenna array was obtained by a simple technique of exciting the neighboring elements with phases of 180°. The characteristic mode analysis(CMA) was performed to get the better understanding of multiport structure. The critical parameters of CMA, such as modal currents, modal radiation patterns, modal significance, and modal weighting coefficient, were used to reveal the physical insight behind the dual beam behavior. It showed how the feed-induced phase reversal affects the surface currents to produce a dual beam. The dual beam was produced at the angle of 55° with a beamwidth of 61° and a peak gain of 8 dB. The antenna array showed stable gain with a cross-polarization level as low as -60 dB. The antenna elements were placed at a distance of 0.45λ from each other.
Quasi-isotropic antennas have gained attention due to the emergence of the Internet of Things (IoT) and Wireless Sensing Networks (WSNs), for their orientation-insensitive communication ability. For those applications, electrically small (ES) antennas are usually preferred, which can save space for the IoT or sensing nodes, while reducing the material cost. Several compact isotropic antennas have been reported recently. However, only very few of them have shown dual-band operation ability. A novel design method to design a dual-band quasi-isotropic ES antenna is presented in this conference proceeding. The utilization of a band stop filter (BSF) enables the conventional single-band quasi-isotropic split ring resonator (SRR) antenna to behave in a dual-band operation, while maintaining the quasi-isotropic radiation for both bands. The proposed antenna is designed, fabricated, and measured, which shows a dual-band operation (both bands in ka<1 region) while maintaining decent performance.
This paper presents a novel ultra-thin slotted array antenna for automotive radar applications operating at E-band. A low-loss air-filled coaxial waveguide transmission line based on multilayer waveguide (MLW) technology is formed by vertically stacking three unconnected thin metal plates. The proposed antenna element consists of two series-fed columns of 6 slots which are combined with a power divider. In order to prevent any possible field leakage due to the air gaps between the layers, a periodic textured structure is used in the top and bottom layers. The desired patterns are fabricated by using chemical etching technique which is a fast and low-cost manufacturing process suitable for mass-production. The design, numerical simulations and experimental validation of the proposed antenna are presented in the frequency band from 76 to 81 GHz. The measurement results show a realized gain of around 15 dBi and a reflection coefficient better than -10 dB in the entire band of interest. The proposed coaxial MLW slot array antenna provides the advantages of low-loss, low-profile, low-cost and mass-production capability at millimeter-wave frequencies.
We consider the scattering of multimodal quantum light by the perfectly conducting cylinder and its emission by quantum two-element phased array antenna. For the scattering description, we use the well-known classical numerical technique based on the characteristic modes adapted to the quantum light. The method is applicable to cylinders of arbitrary cross-section and size relative to the wavelength. It is shown that the antenna emission and scattering are accompanied by the transformation of the quantum-statistical properties of light (the second-order far field correlation function becomes directional and the multimodal entanglement is created. The obtained results are promising for applications in various branches of quantum technologies.
We propose broadbeam geodesic H-plane horn antennas, potentially useful as simple primary feeds for reflectors. Since H-plane horn antennas are implemented in a structure similar to the parallel-plate waveguide, we show that a numerically efficient ray-tracing model can be used to describe wave propagation through them. Using the efficient ray-tracing tool, we optimize three different height profiles to obtain broad beams with different half-power beamwidths at the central operating frequency of 30GHz. All implemented structures have beamwidths larger than those of a planar reference counterpart.
This paper introduces a new antenna, payload and satellite testing facility, called HERTZ 2.0, currently under construction at the European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands. An overview of the building configuration, testing schemes capabilities and applications are provided.
In this paper, an eight-port quad-band multiple-input-multiple-output (MIMO) antenna system with an isolation enhancement technique is presented. The proposed isolation technique is used to improve the isolation between the ports with higher mutual coupling. This technique can also be repeatedly applied between other ports to improve the isolation without affecting the impedance bandwidth and other transmission coefficients. Each radiating element of the proposed system is excited using an offset-fed coaxial port. The multiple radiating elements are placed in a double-folded symmetry fashion to reduce the number of different parameters in the global S-parameter matrix. The designed quad-band 8-port MIMO antenna system is printed on Rogers RO4350B (ϵ r =3.55, tan δ=0.004) substrate with dimensions of 120×70×1.52 mm 3 . The proposed MIMO antenna system’s frequency bands lie in 5G n77, n78, n79, and n46 sub-6 GHz bands. The simulated and measured parameters are in good agreement.
This contribution discusses the applicability of a UAV as positioning and measurement system for antenna calibration in an arbitrary indoor environment. Since such an environment – unlike an anechoic chamber bears the possibility of multiple reflections the feasibility of time domain gating network analyzer measurements is investigated for the time-variant propagation channels due to the motion of the UAV. Based on a simple simulation time domain gating model taking into account the motion of a UAV and its influence on measurement parameters in the frequency domain it is shown that the motion of the UAV can be neglected. The propagation channel can be considered basically static provided a usual hovering flight with a typical motion uncertainty, the data of which is obtained from an exemplarily flight trajectory.
The obtention of highly absorptive surfaces over a wide frequency band and a wide angular range requires the complex manipulation of both electromagnetic properties and geometrical structure of materials. As a matter of fact, a periodic arrangement of sub-wavelength patterns can greatly improve the performance of an absorber with minimum thickness over a large set of conditions. Yet, this inevitably leads to a significant number of geometrical parameters making the design of absorbers fastidious and time-consuming. This paper presents a fast design methodology for microwave absorbers. An optimizer based on the algorithm Covariance Matrix Adaptation Evolution Strategy (CMA-ES) iterates over the results provided by a simulation code based on the Fourier Modal Method (FMM), in order to reach a targeted absorptivity of 1. To illustrate this fast design methodology, we present the optimization of a 10mm-thick structured microwave absorber made of a magnetodielectric material.
