Dielectric Cover Research Articles

Microwave-transparent metallic metamaterials for autonomous driving safety.

Maintaining the surface transparency of protective covers using transparent heaters in extreme weather is imperative for enhancing safety in autonomous driving. However, achieving both high transmittance and low sheet resistance, two key performance indicators for transparent heaters, is inherently challenging. Here, inspired by metamaterial design, we report microwave-transparent, low-sheet-resistance heaters for automotive radars. Ultrathin (approximately one ten-thousandth of the wavelength), electrically connected metamaterials on a millimetre-thick dielectric cover provide near-unity transmission at specific frequencies within the W band (75-110 GHz), despite their metal filling ratio exceeding 70 %. These metamaterials yield the desired phase delay to adjust Fabry-Perot resonance at each target frequency. Fabricated microwave-transparent heaters exhibit exceptionally low sheet resistance (0.41 ohm/sq), thereby heating the dielectric cover above 180 °C at a nominal bias of 3 V. Defrosting tests demonstrate their thermal capability to swiftly remove thin ice layers in sub-zero temperatures.

Wideband Millimeter-Wave MIMO Antenna with a Loaded Dielectric Cover for High-Gain Broadside Radiation

In a millimeter-wave terminal device, the use of a radome degrades the radiating performance of the broadside antenna, especially for the MIMO antenna system. In this study, a dielectric cover is de-signed and investigated to enhance the broadside gain of a millimeter-wave MIMO antenna, while keeping its wideband and high isolation performance. Firstly, a compact wideband ladder-shaped slot antenna is proposed with 21.9% bandwidth. The effectiveness of the dielectric cover design criteria over the wideband antenna is investigated. Then, this wideband antenna element is expanded to a 2 × 2 MIMO antenna by forming a center-symmetric structure and isolating it via the inserted metal vias. By loading the dielectric cover, this millimeter-wave MIMO antenna is verified with enhanced broadside gain for more than 2.1 dB. With the measured impedance bandwidth of 21.9% (57.0–71.0 GHz), peak broadside gain of 12.3 dBi, and high isolation over 15 dB, the proposed MIMO antenna is suitable for wireless gigabit terminal devices.

Ripple phenomenon and artifact elimination in millimeter-wave imaging of a hidden target.

In millimeter-wave imaging of a hidden target, the effect of the dielectric cover before the target is typically ignored. This results in ripple-corrupted images that pose challenges for target recognition. In this paper, we provide a perspective for understanding the image of the hidden target, which clearly reveals the origin of the ripples, and propose a separation method that not only gets rid of ripples, but also obtains the target's depth map. Reflections and transmissions during imaging are considered and decoupled to separately form images corresponding to each real or virtual object. An algorithm based on the range-direction spread function is developed to iteratively estimate the depth and reflectivity of the target. Imaging experiments with and without a cover are conducted to demonstrate the formation and influence of ripples and to verify the proposed algorithm. Our work deepens the comprehension of covered target imaging. Benefited fields might include non-destructive testing, through-wall imaging, subsurface imaging, and security screening.

Surface Susceptibilities as Characteristic Models of Reflective Metasurfaces

While metasurfaces (MSs) are constructed from deeply subwavelength unit cells, they are generally electrically large and full-wave simulations of the complete structure are computationally expensive. Thus, to reduce this high computational cost, nonuniform MSs can be modeled as zero-thickness boundaries, with sheets of electric and magnetic polarizations related to the fields by surface susceptibilities and the generalized sheet transition conditions (GSTCs). While these two-sided boundary conditions (BCs) have been extensively studied for single sheets of resonant particles, it has not been shown if they can correctly model structures where the two sides are electrically isolated, such as a fully reflective surface. In particular, we consider in this work whether the fields scattered from a fully reflective MS can be correctly predicted for arbitrary field illuminations, with the source placed on either side of the surface. In the process, we also show the mapping of a perfect electric conductor (PEC) sheet with a dielectric cover layer to bianisoptropic susceptibilities. Finally, we demonstrate the use of the susceptibilities as compact models for use in various simulation techniques, with an illustrative example of a parabolic reflector, for which the scattered fields are correctly computed using an integral-equation (IE)-based solver.

Simulation and Experimentation Analysis of Dielectric Covers on Square Patch Antenna in Wireless Communications

In this paper the different dielectric covers affects on square patch antenna is investigated and compared their performance. The square patch antenna is designed at 2.4GHz with arlon diclad 880 substrate. The dielectric constant of substrate is 2.2 and thickness of substrate is 1.6mm. The different dielectric covers or superstrates are used whose dielectric constants are 2.2, 3.2, 4.8 and 10.2. The patch antenna is simulated using Ansoft electromagnetic simulator such as HFSS. The effect of dielectric cover at height (H) =0 on patch antenna, the result is the performance of antenna is slightly decreased and as increase the height of the dielectric cover above the patch performance antenna is slightly increases as increases height of the dielectric cover above the patch, but at optimum height, performance of the cover results which is same the antenna without dielectric cover. The uses of dielectric covers are used to providing protections from physical damage, rain and snow and also protecting the antenna from physical heat and other environmental hazards. This antenna designed specifications and frequency 2.4GHz is used in wireless applications.

A fundamental mode converter based on tapered LiNbO3-on-insulator photonic wire with a laterally asymmetric structure

We report a mode converter based on a tapered X-cut/Y-propagation ridge-type LiNbO 3 -on-Insulator (LNOI) photonic wire (PW) with a laterally asymmetric refractive index profile realized by introducing a semi-infinite dielectric cover layer on one side of the LNOI PW. The interplay of material and waveguide birefringence enables to realize mode hybridization, which is a prerequisite for realizing mode conversion. The introduction of the semi-infinite cover layer and the use of a taper structure modify mode index and electric field distribution, enabling to realize mode conversion. Aiming at 1.55 μm wavelength, we have simulated mode hybridization and conversion characteristics of the tapered, laterally asymmetric ridge-type LNOI PW. The results show that a conversion between fundamental TM 00 and TE 00 modes can be realized. The conversion efficiency can be optimized by choosing an appropriate cover layer material and/or adjusting its thickness. An ultra-compact device with a taper length <100 μm is expected. • A mode converter based on a tapered LNOI photonic wire (PW) is proposed. • The device has a laterally asymmetric refractive index profile. • Asymmetric index profile and taper structure enable to realize mode conversion. • A conversion between fundamental TM 00 and TE 00 modes is realized. • An ultra-compact device with a taper length <100 μm is expected.

Light trapping transparent electrodes with a wide-angle response.

The angle dependent transmission of light trapping transparent electrodes is investigated. The electrodes consist of triangular metallic wire arrays embedded in a dielectric cover layer. Normal incidence illumination of the structure produces light trapping via total internal reflection, virtually eliminating all shadowing losses. It is found that varying the external angle of incidence can affect the light trapping efficiency ηLT due to partial loss of internal reflection and increased interaction with neighboring wires. Despite these effects, a judicious selection of geometry and materials can reduce shadowing losses by more than 85% over a surprisingly large angular range of 120°. It is demonstrated that the angle-averaged shadowing losses in an encapsulated silicon solar cell under illumination with unpolarized light can be reduced by more than a factor of two for incident angles between -60° and +60° off-normal across the entire AM1.5 solar spectrum.

Dielectric Cover Layer Thickness Effect on Circular Microstrip Antenna Parameters

This paper studies the effect of dielectric cover layer thickness on circular microstrip patch antenna parameters such as gain, bandwidth, beam-width, radiation patterns, return loss and VSWR. The proposed antenna is designed with 2.4GHz frequency in S-Band region. This operating frequency useful in ISM band applications. Circular patch antenna is designed with cavity model analysis and simulated using HFSS simulation software (Electromagnetic simulator). The coaxial probe fed is used for antenna design. In this paper the effect of dielectric cover layer on antenna parameters studied experimentally and comparing their performance characteristics. The simulation results shows that the antenna without dielectric cover layer obtained gain is 4.11dB and antenna with dielectric cover the gain is reduced to 2.87dB to 5.88dB based on thickness of the dielectric cover layer. The antenna bandwidth obtained without dielectric cover is 3% and with dielectric cover its bandwidth is reduced from 0.012GHz to 0.052GHz based on thickness of the cover layer effect. Similarly other parameters are investigated and compared. This proposed circular patch antenna is used in wireless and Wi-Fi applications.

Numerical Study of Extremely Wideband-Modified Biconical Radiation Structures for Electronic Support Measures Application

Using the finite difference time domain (FD-TD) method, this paper studies radiation structures that can have multiple tunable frequency bands between 0.4 GHz and 4 GHz, a fixed band in [3.97, 5.36] GHz and an extremely wideband from 6.14 GHz to 68.27 GHz, where a frequency band is defined by the voltage standing wave ratio (VSWR) less than or equal to two. The base radiation structure has a modified-biconical antenna configuration, called base MBA, and is fed by a square-coaxial line with characteristic impedance close to 50 ohms. A dielectric ring and an outer dielectric cover are used between the two modified cones to enlarge the frequency band and strengthen the structure. An equal number of metallic-rings can be stacked at both circular-ends of cones in the base MBA to tune the positions of the frequency bands that are lower than 4 GHz and to alter their vertical polarization (V-pol) patterns. However, compared with those of the base MBA, these stacked metallic rings do not make significant changes to the VSWR in the [3.97, 5.36] GHz and [6.14, 28.27] GHz bands and the radiation patterns in the [6.14, 28.27] GHz band. The simulation results show that the base MBA and its metallic-ring-loaded versions all have V-pol radiation characteristics at all frequency bands and have donut-shaped omnidirectional patterns only when the wavelength is bigger than the length of the structure. When the wavelength is less than the size of the radiation structure, the donut shape is modified with ripples on the V-pol radiation pattern. Sometimes deep notches could be observed when MBAs operated at the higher end of the extremely wideband. A 0.2 mm cube was used to construct the antenna structures with the consideration of using the 3D metal/dielectric printer technology to build the antennas in the future.

Metasurface Cloaks to Decouple Closely Spaced Printed Dipole Antenna Arrays Fed by a Microstrip-to-Balanced Transmission-Line Transition

In this work, we present a numerical study of 1D and 2D closely spaced antenna arrays of microstrip dipole antennas covered by a metasurface in order to properly cloak and decouple the antenna arrays operating at neighboring frequencies. We show that the two strongly coupled arrays fed by a microstrip-to-balanced transmission-line transition are effectively decoupled in 1D and 2D array scenarios by covering the dipole antenna elements with an elliptically shaped metasurface. The metasurface comprises sub-wavelength periodic metallic strips printed on an elliptically shaped dielectric cover around the dipole antennas and integrated with the substrate. We present a practical design of cloaked printed dipole arrays placed in close proximity of each other and demonstrate that the arrays are decoupled in the near field and operate independently in the far field with their original radiation characteristics as if they were isolated.

Performance Enhancement of 5G Millimeter Wave Antenna Module Integrated Tablet Device

This article describes the design and considerations for millimeter-wave (mmWave) 5G antenna modules embedded in a tablet device. The antenna module consists of eight-chain broadside antenna array and two pairs of four-chain endfire antenna array. A dual-polarized air-filled stacked patch antenna is designed for the broadside patch antenna. Although the performance can be deteriorated due to a plastic cover, the proposed antenna enables an adaptable design for a dielectric cover. A novel surface-mountable chip antenna is also proposed, to implement a vertical polarized (V-pol.) endfire antenna on a low-profile substrate. To integrate a dual-polarized endfire antenna in a confined space, a horizontal polarized (H-pol.) mesh grid antenna and a V-pol. chip antenna are collinearly integrated. In addition, a plastic cover on the tablet is modified to enhance the performance of the endfire antenna array. The cumulative distribution function (cdf) of effective isotropic radiated power (EIRP) is utilized to evaluate spherical coverage, based on the 5G standard of 3rd Generation Partnership Project (3GPP). The spherical coverages are presented by varying the types of plastic cover, the effects of the blockage, and the number of mmWave 5G modules.

Scale dependent performance of metallic light-trapping transparent electrodes.

The optical and electrical performance of light trapping metallic electrodes is investigated. Reflection losses from metallic contacts are shown to be dramatically reduced compared to standard metallic contacts by leveraging total internal reflection at the surface of an added dielectric cover layer. Triangular wire arrays are shown to exhibit increased performance with increasing size, whereas cylindrical wires continue to exhibit diffractive losses as their size is increased. These trends are successfully correlated with radiation patterns from individual metallic wires. Triangular metallic electrodes with a metal areal coverage of 25% are shown to enable a polarization-averaged transmittance of >90% across the wavelength range 0.46-1.1 µm for an electrode width of 2 µm, with a peak transmission of 97%, a degree of polarization of <0.2%, and a sheet resistance of 0.35 Ω/sq. A new figure of merit is introduced to evaluate the light trapping potential of surface-shaped electrodes.

Design, Simulation and Experimental Analysis of Square Microstrip Patch Antenna with Superstrates at 2.4GHz

Microstrip antenna is used in wide area of applications such as high speed vehicles, missiles, tanks and satellite communications. In these applications dielectric superstrate (or cover) is used above the square patch antenna for providing the protections from severe environmental conditions such as rain, snow, heat, and damage etc. The proposed square microstrip patch antenna is designed using coaxial probe feed technique and transmission line model and operated at center frequency of 2.40 GHz, which is lying in the S-band region. The proposed model is used in linear polarization applications. The square patch is fabricated on low loss dielectric substrate material having dielectric constant is 2.2 and loss tangent of the substrate material is 0.0009. Ansoft electromagnetic simulator software such as HFSS is used for simulating proposed model and studied the effect cover or superstrate on different parameters of square patch antenna. This paper mainly focuses on the performance of square patch antenna without superstrate, and with superstrate at different height of dielectric superstrate above the patch antenna. The result found of patch antenna without superstrate the bandwidth is 0.04GHz and gain is obtained 8.9 dB and 7.51 dB in azimuth and elevation respectively. The result observed of patch antenna with dielectric cover (or superstrate) at height H =0, the antenna performance characteristics are slightly degraded and also comparing the antenna with the bandwidth is decreased to 0.02GHz from 0.04 GHz and gain is decreases to 6.44 dB and 6.6 dB from 8.9 dB and 7.51 dB in both azimuth and elevation plane respectively. The decreased performance characteristics of antenna will be improved by varying height of the superstrate above the patch antenna.. At particular optimum height, the performance characteristics patch antenna will be almost same as the patch antenna without superstrates. The obtained simulated results good match with measurement results.

Wakefields in conducting waveguides with a lossy dielectric channel

The resonant properties of the impedance of a two-layer circular metal-dielectric waveguide are investigated by taking into account the finite conductivity of the metallic pipe and the dissipation of the radiated energy in the dielectric layer. The dispersion relations for azimuthally symmetric monopole TM modes are analyzed. It is shown that, for an outer metallic layer with finite conductivity and a thin internal dielectric cover, the waveguide has only a single slowly propagating ${\mathrm{TM}}_{01}$ mode. The point charge longitudinal wake potentials are evaluated for thin and thick internal layers.

Low-Profile Wideband Conjoined Open-Slot Antennas Fed by Grounded Coplanar Waveguides for $4\times4\,\,5$ G MIMO Operation

Four grounded coplanar waveguide (GCPW)-fed open-slot antennas conjoined into a cross shape with a central circular slot are presented for $4\times4$ fifth-generation (5G) multi-input multi-output (MIMO) operation in 3.3–4.2 GHz. The four conjoined slot antennas have a 1 mm low profile (about $0.01\lambda $ at 3.3 GHz) and a compact size of 42 mm $\times42$ mm (about $0.46\lambda \times 0.46\lambda $ at 3.3 GHz) to provide four wide operating bands (about 24% centered at 3.75 GHz) with antenna efficiency better than 40%. The conjoined circular slot leads to enhanced operating bandwidth of the four slot antennas and good decoupling thereof. Owing to the 1 mm low profile, the conjoined slot antennas are promising to be integrated within the dielectric back cover of the 5G terminal device, thereby decreasing the antennas’ volume inside the device. Details of the GCPW-fed conjoined slot antennas for 5G-MIMO operation are presented.

Rigorous Evaluation of Losses in Uniform Leaky-Wave Antennas

General formulas are proposed for thoroughly evaluating the radiation efficiency of traveling-wave antennas operating in any radiating regime. Indeed, existing theoretical models only work in the scanned-beam region, where the radiating mode is considerably above cutoff and the perturbation method applies. The analysis provided here extends the application of the perturbation method close to the cutoff condition, thus providing a correct estimation of the losses even in the case of broadside radiation. This case is particularly important for Fabry-Perot cavity leaky-wave antennas (FPC-LWAs) based on partially reflecting screens (PRSs), which are commonly designed to generate a broadside pencil beam. However, the previous works on FPC-LWAs always assume either a lossless PRS, or a lossless dielectric cover layer thus neglecting metal and dielectric losses: a hypothesis that is no longer fulfilled at high frequencies, such as millimeter-wave and submillimeter-wave frequencies. An original theoretical framework is thus developed to derive analytical formulas for a rigorous evaluation of losses when either lossy PRS or lossy dielectric cover layers are employed. Interestingly, the equivalence between a lossy PRS and a lossy dielectric cover layer is shown from a theoretical viewpoint. All the findings derived here are validated through full-wave simulations to corroborate the proposed analysis.

About the helix plasma antenna: effective factors on characteristics of radiation

ABSTRACT In this paper, a plasma waveguide including a dielectric cover surrounded by metallic helical sheath is investigated as a helix plasma antenna. By solving the wave equation, the components of electric and magnetic fields of hybrid modes for each region is calculated. The collisional approximation for background plasma is used at first and in the second stage a magnetized plasma will be considered as the electromagnetic media in the helical sheath. Applying suitable boundary conditions, the dispersion relation of slow waves in terahertz frequency region is investigated for two configurations mentioned above. Effect of several parameters such as the helix angle, the geometry dimensions, the dielectric constant of dielectric layer, the cyclotron frequency and the plasma frequency on the population of dispersion branches of lower hybrid modes, is investigated. Also, the graphs of normalized radiation power in plasma region to the radiation power in vacuum region are presented.

Solar PV soiling mitigation by electrodynamic dust shield in field conditions

Soiling of solar photovoltaic (PV) modules by dust accumulation can cause significant loss in electricity production. Electrodynamic dust shield (EDS) is a potential anti-dust solution that can be used to repel dust from a PV module surface, but so far there have been few studies of EDS performance in the field. In this study, we fabricated prototype PV modules with integrated EDS electrodes, and carried out field tests of the EDS function. Each prototype was made by fabricating EDS electrodes on the front glass of a base module and insulating the electrodes with a polymer dielectric cover. Three units, comprising two EDS-integrated PV modules and one reference PV module without the EDS electrodes, were tested in a solar test facility at Doha, Qatar for six months. The soiling loss of each solar module was quantified by comparing the module’s temperature-corrected performance ratio to that of the clean module. The EDS efficiency was in turn assessed by comparing the soiling loss of the EDS-PV module with EDS activation to that of the EDS-PV module without activation. When activated hourly at 9 kVpp, EDS could reduce soiling loss by 16–33%, while at 6 kVpp activation voltage EDS had no observable soiling mitigation effect. Further research with larger sample sizes and longer testing time is needed to better understand the soiling mitigation capability of EDS in field conditions.

The design theory for a flat microwave absorber with a protective cover

To achieve a complete absorption for a microwave absorber with a protective cover, which is a practical assembly, it is important to establish a general design theory for such an assembly. The equations that elucidate the relations of the electromagnetic parameters of the absorber and its dielectric cover for a zero reflection are established by inverse solving the equations obtained by transmission line model used to calculate the reflection of the assembly. This design theory is applied to three kinds of practical polymers (PTFE, epoxy resin and phenolic resin) at three given frequencies (2, 10, and 18 GHz) as examples. For a given cover material and a given frequency, the complex electromagnetic parameters and the thickness of an absorber are determined by solving these equations and the results are graphically represented in the loss-angle plane and the possible use of these design curves is illustrated. For a certain cover material, the required relative thickness of a magnetic absorber is thinner than that of an electric absorber and the required electromagnetic loss should be weak when the ratio of the real part of relative complex permittivity and permeability of the absorber is small. For different cover materials, the design curves show a similar tendency. For a cover with strong dielectric properties, for example, phenolic resin, to achieve a total absorption, the required dielectric loss of an electric absorber is strong, while the required magnetic loss of a magnetic absorber is weak.

A Novel Integrated Yagi–Uda and Dielectric Rod Antenna With Low Sidelobe Level

A novel antenna integrated the advantages of the Yagi–Uda and the dielectric rod antenna (DRA) is presented in this communication. The antenna mainly consists of a tapered printed Yagi–Uda, a tapered dielectric cover, and a periodic dielectric rod. First, a tapered printed Yagi is designed as the primary feeder and embedded inside a tapered dielectric rod to improve the directive gain, radiation efficiency, and sidelobe levels. The influence of the dielectric cover to the Yagi is discussed. Then, a dielectric rod with triangular periodic surface is also loaded to the end of the dielectric cover to obtain higher gain and better front-to-back ratio. Finally, a sample of the antenna working at 8.5–9.7 GHz with 18 dBi maximum gain and −23.37 dB sidelobe level is designed. A prototype is fabricated and tested; the measured results match well with the simulated. Compared with the traditional Yagi–Uda antenna and DRA with the same length, the presented integrated antenna has higher gain with lower sidelobe level.