Magneto-dielectric Substrate Research Articles

Antenna array bandwidth enhancement using polymeric nanocomposite substrate

A 4 × 2 array antenna is developed using a new nanocomposite polymeric magneto-dielectric substrate. The permittivity and permeability factors have been accounted in designing the proposed array antenna at the frequency of 2.6 GHz. A pure polydimethylsiloxane (P-PDMS) (er = 2.7) solution is mixed with ferrite III oxide (μr = 1.2) to generate this new nanocomposite polymeric magneto-dielectric (NPMD) substrate. The NPMD surface is then hardened and located in between two P-PDMS layers. The 4 × 2 radiating elements are immersed to the top of P-PDMS layer, while SMA coaxial feeder is fed from underneath the ground layer. This sealing technique enabled the proposed antenna to be waterproof and flexible. This combination contributes to bandwidth enhancement of 52.65 %, size miniaturization of 176 × 156 mm2 and high gain of 10.8 dB. The measured results show a good agreement with simulations.

COMPACT PATCH ANTENNA ON STRUCTURALLY MODIFIED MAGNETODIELECTRIC SUBSTRATE

Magnetodielectric substrate gives a new dimension for reducing the size of the planar antennas. In this article, the patch size is reduced by taking a substrate with nano-sized nickel ferrite inclusions in LDPE polymer matrix. The antenna is made to operate in X and Ku bands by engraving T slots along the resonant length of the patch. Structural modification of the substrate geometry as a step profile is incorporated along the slotted patch edges to enhance performance. The T-slots, along both the resonating lengths with the magnetodielectric stepped substrate show four resonant frequencies in both X- and Ku-bands with S11 < −15 dB and a maximum −10 dB bandwidth of 22.4%. A miniaturization factor of 2.97 is obtained.

Polymer (PDMS-Fe3O4) magneto-dielectric substrate for a MIMO antenna array

This paper presents the design of a 2 × 4 multiple-input multiple-output (MIMO) antenna array fabricated on a nanocomposite magneto-dielectric polymer substrate. The 10-nm iron oxide (Fe3O4) nanoparticles and polydimethylsiloxane (PDMS) composite is used as substrate to enhance the performance of a MIMO antenna array. The measured results showed up to 40.8 % enhancement in terms of bandwidth, 9.95 dB gain, and 57 % of radiation efficiency. Furthermore, it is found that the proposed magneto-dielectric (PDMS-Fe3O4) composite substrate provides excellent MIMO parameters such as correlation coefficient, diversity gain, and mutual coupling. The prototype of the proposed antenna is transparent, flexible, lightweight, and resistant against dust and corrosion. Measured results indicate that the proposed antenna is suitable for WLAN and ultra-wideband biomedical applications within frequency range of 5.33–7.70 GHz.

Y-type hexagonal ferrites for microwave absorber and antenna applications

This article examines the potential of the Y-type hexagonal ferrites, BaSrCo2−xNixFe12O22, as passive microwave absorbing materials and magneto-dielectric antenna substrates. To this effect, we investigated the electromagnetic properties of the fabricated samples up to 18GHz, in conjunction with the composition, microstructure and static magnetic characteristics. It was found that the Ni substitution yields the increase of permeability μ* and permittivity ε* as a consequence of the weaker magnetocrystalline anisotropy and enhanced dielectric orientation polarization. By virtue of their different ε* and μ* spectra, the Co-rich hexagonal ferrites appear as appropriate for narrowband-yet tunable-reflection reduction in the 2.6–18GHz range (>20dB), whereas with Ni addition wideband attenuation of the transmitted waves (>20dB) is attained in the 7–18GHz band. In addition, the persistence of high refractive index up to 1GHz enables the utilization of these hexagonal ferrites in UHF antenna designs with smaller dimensions. Among them, designs with Co2-Y compound are liable to higher radiation efficiency, while Ni2-Y favours the achievement of wider bandwidth. On this basis, the performance of the produced materials in high frequency applications is evaluated and certain improvement directions are indicated.

Broadbanding of circularly polarized patch antenna by waveguided magneto-dielectric metamaterial

Design of bandwidth-enhanced circularly polarized (CP) patch antenna using artificial magneto-dielectric substrate was investigated. The artificial magneto-dielectric material adopted here takes the form of waveguided metamaterial (WG-MTM). In particular, the embedded meander line (EML) structure was employed as the building element of the WG-MTM. As verified by the retrieved effective medium parameters, the EML-based waveguided magneto-dielectric metamaterial (WG-MDM) exhibits two-dimensionally isotropic magneto-dielectric property with respect to TEM wave excitations applied in two orthogonal directions. A CP patch antenna loaded with the EML-based WG-MDM (WG-MDM antenna) has been proposed and its design procedure is described in detail. Simulation results show that the impedance and axial ratio bandwidths of the WG-MDM antenna have increased by 125% and 133%, respectively, compared with those obtained with pure dielectric substrate offering the same patch size. The design of the novel WG-MDM antenna was also validated by measurement results, which show good agreement with their simulated counterparts.

A theoretical and numerical approach for selecting miniaturized antenna topologies on magneto-dielectric substrates

An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.

Propagation Analysis and Antenna Miniaturization on a Magneto-dielectric Composite Substrate by Manipulating the Permeability and the Permittivity

Propagation Analysis and Antenna Miniaturization on a Magneto-dielectric Composite Substrate by Manipulating the Permeability and the Permittivity

Compact, Wearable Antennas for Battery-Less Systems Exploiting Fabrics and Magneto-Dielectric Materials

In this paper, we describe some promising solutions to the modern need for wearable, energy-aware, miniaturized, wireless systems, whose typical envisaged application is a body area network (BAN). To reach this goal, novel materials are adopted, such as fabrics, in place of standard substrates and metallizations, which require a systematic procedure for their electromagnetic characterization. Indeed, the design of such sub-systems represents a big issue, since approximate approaches could result in strong deviations from the actual system performance. To face this problem, we demonstrate our design procedure, which is based on the concurrent use of electromagnetic software tools and nonlinear circuit-level techniques, able to simultaneously predict the actual system behavior of an antenna system, consisting of the radiating and of the nonlinear blocks, at the component level. This approach is demonstrated for the design of a fully-wearable tri-band rectifying antenna (rectenna) and of a button-shaped, electrically-small antenna deploying a novel magneto-dielectric substrate. Simulations are supported by measurements, both in terms of antenna port parameters and far-field results.

Low loss NiZn spinel ferrite–W-type hexaferrite composites from BaM addition for antenna applications

A series of NiZn ferrite composites with various BaFe12O19 hexaferrite (BaM) additions (x) were successfully synthesized by the solid-state reaction method for their potential application as magneto-dielectric antenna substrate materials. XRD and energy-dispersive spectrum analyses reveal that a W-type hexagonal phase is formed when the mixture of NiZn ferrite and BaM are sintered at 1200 °C, and diphase composite ferrite that consists of NiZn spinel ferrite and BaW hexaferrite is finally obtained. The composites display much smaller grain size and a refined microstructure. With the increasing x, the initial permeability decreases from ∼84.5 to ∼15.5, while the cut-off frequency is dramatically improved from 75 to 570 MHz. BaM addition significantly inhibits the frequency dispersion of permittivity spectrum and stable permittivity ε′ around 15 is observed for the doped samples from 1 MHz to 1 GHz, which is proved to be closely related to the refined grains according to Koops' theory. Besides, compared with the undoped NiZn ferrite, both the magnetic loss and dielectric loss are found to be reduced in the doped samples. Almost equal values of μ′ and ε′ is obtained in the sample with x = 30 wt%. Related magnetic and dielectric mechanisms are also discussed.

Performance enhanced miniaturized and electrically tunable patch antenna with patterned permalloy based magneto-dielectric substrate

Perspective magneto-dielectric materials with high permeability are potential substrates to miniaturize the patch antenna without deteriorating its performance. Besides its high permeability at high frequency, patterned Permalloy (Py) also presents tunable permeability by applying DC current. A performance enhanced miniaturized and electrically tunable patch antenna with patterned Py thin film is first presented and developed in this paper. To suppress the magnetic loss, the Py thin film layer is consisted of an array of 2 μm × 2 μm square Py patterns between the copper patch antenna and dielectric substrate. The DC current could be applied directly on Py patterns through the copper strip lines beneath the Py patterns along the length of patch antenna. The copper strip lines are specially designed with the same width of Py patterns and the thickness much less than the skin depth at the operating frequency, which can reduce their deteriorating effects to the performance of antenna. The structure of the antenna is presented and simulated with high frequency structure simulator. The results show that compared with non-magnetic antenna, the performance of Py thin film based antenna is improved with 50% bandwidth increase from 4 MHz to 8 MHz and 1.2 dB gain enhancement from 1.16 dB to 2.36 dB. The resonant frequency of the antenna could be continuously tuned from 937 MHz to 911 MHz with the permeability of Py thin film changing from 1750 to 1 900 by applying the DC current.

DESIGN OF LIGHT WEIGHT MICROSTRIP PATCH ANTENNA ON DIELECTRIC AND MAGNETODIELECTRIC SUBSTRATE FOR BROADBAND APPLICATIONS IN X-BAND

A modiflcation in the structure of a substrate has been carried out to reduce weight and improve the performance of microstrip patch antenna in X-band. A step proflle is incorporated in the substrate along the radiating edges of the patch. The design is tested on both dielectric and magnetodielectric substrates. Return loss of antenna with varying step riser height and step tread length shows improvement in i10dB bandwidth to 13.2% for the dielectric and to 12.3% for the magnetodielectric as compared to about 4.8% and 6.9% for unproflled substrate geometry in dielectric and magnetodielectric respectively. As compared to the unproflled planar antenna, maximum weight reduction for the stepped antenna on dielectric substrate is 54.75 % and for the magnetodielectric is 58.9% is observed. An equivalent circuit modeling for the stepped structure is carried out for the proposed structure.

Low Loss ${\rm NiZn/Co}_{2}{\rm Z}$ Composite Ferrite With Almost Equal Values of Permeability and Permittivity for Antenna Applications

A series of NiZn-ferrite/Co2Z-hexaferrite composite ferrites were successfully synthesized by the solid-state reaction method for their potential application as magneto-dielectric antenna substrate materials. It is found that, with the increasing amount of NiZn ferrite (x) from 55 wt% to 70 wt%, the real permeability μ' at low frequencies is improved from ~10 to ~19, while the real permittivity e' varies slightly with value around 14. The sample with wt % has almost equal values of μ' and e', large miniaturization factor about 15, as well as sufficiently low dielectric and magnetic loss (1-50 MHz). This composite ferrite is very useful to the design of miniaturized antenna with good impedance-matched to free space.

Numerical and experimental characterization of a button-shaped miniaturized UHF antenna on magneto-dielectric substrate

The design and characterization of a new broadband small patch antenna, based on an innovative magneto-dielectric material and suitable for wearable applications at 868 MHz, is presented. To reduce antenna dimensions, while preserving its radiation and matching performance, a barium-strontium hexaferrite Ba0.75Sr0.25Fe12O19 has been synthesized as the antenna substrate to achieve magnetic permeability double than vacuum in the band of interest. First material realization is characterized and dispersive permittivity and permeability behaviors are included in the design of a small patch antenna with a shorting-plate. A button-size realization is obtained and its suitability for wearable applications is numerically and experimentally demonstrated on body with and without the presence of conductive shielding. Very good agreement with measurements is demonstrated for both matching and radiation performance of the antenna.

Exploitation of a novel magneto-dielectric substrate for miniaturization of wearable UHF antennas

A new magneto-dielectric material for wearable antenna applications at 868MHz is presented. A barium–strontium hexaferrite is synthesized in order to achieve the best compromise between antenna dimensions and performances, exploiting the miniaturization properties offered by relative permeability greater than unity. The electrical properties of the substrate are then experimentally characterized and the corresponding material model is derived and used during the EM-simulation-based design of a patch antenna. The maximum antenna dimension is about λ/20 with a maximum directivity of 6.4dBi. Broadband simulations and measurements of the reflection coefficient and of the radiated far-field are finally compared and demonstrate the reliability of the proposed design. A shielding solution by a conductive fabric allows to minimize back radiation and thus to avoid EM interference with human body tissues.

Small global positioning system patch antennas with self-biased NiCo-ferrite films

Magneto-dielectric substrates with thin ferrite films show great potential in realizing small antennas with improved omni-directional performance than those realized on dielectric substrates.This article introduces self-biased NiCo-ferrite films as a practical means to tune a patch antenna by loading a commercially available dielectric substrate. Novel antenna designs with self-biased ferrite films were investigated, and these magnetic antennas have improved the axial ratio from 1.45 to 1.0 dB with respect to the central frequency ranging from 1.575 to 1.561 GHz in the simulations. Experimental global positioning system patch antennas with/without ferrite films were fabricated and tested. The measured results demonstrate that antennas with ferrite films can miniaturize the geometrical dimension by shifting down the resonance. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1162–1165, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25909

Miniaturization of a Microstrip Antenna Using a Compact and Thin Magneto-Dielectric Substrate

Miniaturization of a rectangular microstrip antenna using a magneto-dielectric substrate is discussed theoretically and experimentally. A compact magneto-dielectric substrate is designed using a metamaterial structure that can reduce the antenna dimensions by increasing the constitutive parameters of the substrate. Furthermore, the proposed structure is thin enough to be embedded in a single dielectric substrate. The area of the microstrip antenna with the proposed magneto-dielectric substrate at 2.4 GHz is reduced up to about 65% compared to a conventional dielectric microstrip antenna. The bandwidth of the miniaturized antenna is almost unchanged due to the increase of the magnetic permeability at the designed 2.4-GHz frequency. Finally, a fabricated version of the miniaturized antenna is tested and measured. The results of the measurement and simulation are in good agreement.

CIRCULARLY POLARIZED MICROSTRIP PATCH ANTENNA USING ARTIFICIAL MAGNETO-DIELECTRIC SUBSTRATE WITH GRID STRUCTURE

We propose a circularly polarized microstrip patch antenna that use an artiflcial magneto-dielectric (AMD) substrate. The proposed antenna has a square patch with dual feeding points and uses a Wilkinson power divider in order to achieve a circularly polarized radiation pattern. The AMD substrate is constructed with a two-dimensional array of single split ring resonators. The antenna has an axial ratio of less than 1.7dB, peak gain of 0.55dBic, and exhibits a right handed circular polarized radiation pattern at Korean UHF RFID service band. The size of the antenna is 100mm £ 100mm £ 5:2mm and the radiating patch measures 65mm£65mm (0:199‚0£0:199‚0).

Broadband, Miniaturized Stacked-Patch Antennas for L-Band Operation Based on Magneto-Dielectric Substrates

Design of stacked-patch antennas using magneto-dielectric substrates was investigated. In particular, special types of substrates with identical relative permittivity and permeability were considered. The optimal design parameters were determined using a genetic algorithm. It will be shown that by employing these matched magneto-dielectric substrates, a significant miniaturization of up to 60% can be achieved while providing a large operating bandwidth (20%). Several design examples were considered and their performance was evaluated using a full-wave analysis technique based on the method of moments. The tradeoff between antenna gain and degree of miniaturization for a fixed bandwidth was also investigated. A fabrication methodology for obtaining the required matched magneto-dielectric substrate materials is also proposed.

Miniaturized Antennas and Planar Bandpass Filters With Self-Biased NiCo-Ferrite Films

Miniaturized microwave devices are realized by using magnetodielectric substrate comprising thin magnetic films that exhibit both high permittivity and high permeability at gigahertz frequency. We have fabricated and tested miniature circular patch antennas and hairpin bandpass filters with the alumina and Rogers substrate loaded with self-biased NiCo-ferrite films that exhibit excellent uniformity and low loss at frequencies exceeding 1.5 GHz. The measured results of magnetic hairpin bandpass filters have improved the central resonant frequency shift from 1.55 to 1.44 GHz, and a large resonant frequency tunability of about 23%-34% of the - 3-dB bandwidth was achieved. For the circular patch antenna, we observed an improvement of 0.8 dB in gain and a large resonance frequency tunability of 100%-320% of the antenna -10-dB bandwidth.

Tunable Miniaturized Patch Antennas With Self-Biased Multilayer Magnetic Films

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Magneto-dielectric substrates with thin magnetic films show great potential in realizing electrically small tunable antennas with enhanced bandwidth, improved directivity, and high efficiency. This communication introduces self-biased NiCo-ferrite magnetic films as a practical mean to tune a patch antenna by loading single layer and multilayer self-biased ferrite films. The central resonant frequency of the unloaded patch antenna is measured at 2.1 GHz with a bandwidth of 18 MHz. However, with ferrite loading of the alumina substrate, this frequency is shown to be tunable within a range of 12 MHz–40 MHz, and the antenna efficiency is increased from 41% of the non-magnetic antenna to 56%, 65%, and 74% for the three magnetic antennas. The omnidirectional radiation pattern is significantly enhanced with the <formula formulatype="inline"> <tex Notation="TeX">${-}5$</tex></formula> dBic gain beamwidth increased from 140<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> to 155<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula>, 156<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> and 160<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula>, respectively for the three ferrite loaded antennas. In addition, the gains of the three magnetic antennas are enhanced by 0.32, 0.77, and 1.1 dB, respectively, over the unloaded antenna. </para>