Magneto-dielectric Materials Research Articles

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.

Matching permeability and permittivity of Ni0.5Zn0.3Co0.2In0.1Fe1.9O4 ferrite for substrate of large bandwidth miniaturized antenna

Nickel zinc cobalt indium ferrite of nominal composition Ni0.5Zn0.3Co0.2In0.1Fe1.9O4 was synthesized by a co-precipitation technique. The effect of sintering temperature on structural and electromagnetic properties was studied over the frequency range of 10 MHz to 6 GHz. The crystallite size increases from 45 to 60 nm, with an increase in sintering temperature from 800 to 1000 °C. The relative permeability (μr) and relative permittivity (er), both varies between 5 and 8 with sintering temperature and remains consistent up to 700 MHz, but ferrimagnetic resonance frequency reduces from 900 to 700 MHz. For sintering temperature of 900 °C, almost matching value of permeability and permittivity equals to 5.5 and 5.3 respectively were obtained up to 700 MHz. The loss tangent are found to be of the order of 10−2 in the same frequency band. Matching values of er (~5.3) and μr (~5.5) are very effective in proper impedance matching of substrate material with free space. Analysis in High frequency structural simulator verifies that the synthesized magneto-dielectric material based antenna can miniaturize size (~65 %), lowers reflection losses (RL) by 15 %, higher −10 dB RL bandwidth (8–12 %) and higher voltage standing wave ratio bandwidth (9–13 %) at resonant frequency of 450 MHz. The observed matching values also result in higher gain and radiation efficiency. Hence, the excellent electromagnetic properties obtained in our investigation for the suitably sintered Ni0.5Zn0.3Co0.2In0.1Fe1.9O4 ferrite shows a lot of potential to be used as a substrate material in miniaturizing microstrip antenna for futuristic electronic devices.

Theory of radiation pressure on magneto–dielectric materials

We present a classical linear response theory for a magneto–dielectric material and determine the polariton dispersion relations. The electromagnetic field fluctuation spectra are obtained and polariton sum rules for their optical parameters are presented. The electromagnetic field for systems with multiple polariton branches is quantized in three dimensions and field operators are converted to 1–dimensional forms appropriate for parallel light beams. We show that the field–operator commutation relations agree with previous calculations that ignored polariton effects. The Abraham (kinetic) and Minkowski (canonical) momentum operators are introduced and their corresponding single–photon momenta are identified. The commutation relations of these and of their angular analogues support the identification, in particular, of the Minkowski momentum with the canonical momentum of the light. We exploit the Heaviside–Larmor symmetry of Maxwell’s equations to obtain, very directly, the Einsetin–Laub force density for action on a magneto–dielectric. The surface and bulk contributions to the radiation pressure are calculated for the passage of an optical pulse into a semi–infinite sample.

Extraction of Permittivity and Permeability for Ferrites and Flexible Magnetodielectric Materials Using a Genetic Algorithm

A hybrid approach, based on the two-dimensional finite-element method (2-D-FEM) and a genetic algorithm (GA) optimization, is used to extract relative permittivity and permeability of ferrites and flexible magnetodielectric composite materials over wide frequency bands. S-parameters of a material under test (MUT) placed into a coaxial fixture are measured by a vector network analyzer and simulated using the 2-D-FEM code. The GA optimization procedure is then used to minimize the discrepancies between the measured and simulated S-parameters by iteratively searching the possible best permittivity and permeability. Multiterm Debye models of wideband complex permittivity and permeability are employed here for a frequency-dispersive MUT. This greatly reduces the number of unknowns in the GA optimization. The proposed method is tested with PTFE and a virtual magnetic material.

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.

Low loss Co2Z hexaferrite with matched permeability and permittivity in HF and VHF bands

Magneto-dielectric materials with matched permeability and permittivity have significant advantages for miniaturization and efficiency improvement of antennas. In this study, we adopted the Z-type hexaferrites in series (Ba0.5Sr0.5)3Co2Fe24O41+xSnO2 (where x=0, 0.1, 0.2, 0.4, and 0.6wt%) to produce the magneto-dielectric material. It was found that moderate SnO2 could obviously enhance mass transfer and densification of the ferrites, while there was no significant increase in grain size, which favored to obtain low magnetic and dielectric losses. However, excessive SnO2 led to the appearance of Co2W phase and slight decrease of sintered density. The samples with 0.1 and 0.2wt% SnO2 could obtain relatively high refractive index with real permeability and permittivity around 15. And the former presented the lowest magnetic and dielectric losses; the latter presented the best matched permeability and permittivity. Both of them are suitable for applications of antenna miniaturization between 3 and 300MHz (HF and VHF bands).

BiFeO3 tailored low loss M-type hexaferrite composites having equivalent permeability and permittivity for very high frequency applications

Co–Ti substituted M-type hexaferrite composites, consisting of Ba(CoTi)1.2Fe9.6O19 with various amounts of Bi2O3 (0–8wt%), were successfully synthesized by conventional ceramic processes. The effects of Bi2O3 upon the composite microstructure, magnetic properties, and magnetic and dielectric properties sintered at low temperatures were systematically investigated. The present studies aim to develop magneto-dielectric materials possessing equivalent values of permeability and permittivity, as well as low magnetic and dielectric losses, which allow for miniaturizing efficient antennas at the very high frequency band (VHF, 30–300MHz). The present experiments show that addition of BiFeO3, observed in the polycrystalline hexaferrite composites, acts to reduce loss factors (i.e., tan δμ/μ′=0.014, tan δε/ε′=0.00071) while concomitantly retaining high and equivalent values of permeability and permittivity (i.e., μ′∼12 and ε′∼12 at 300MHz).

Observation of direct magneto-dielectric behaviour in Lu3Fe5O12-δ above room-temperature.

The coupling of dielectric and magnetic order is highly nontrivial and seldom observed in rare-earth iron garnets. Careful investigations on polycrystalline Lu3Fe5O12-δ, prepared by the solid state route, establish a direct correlation between the magnetic and dielectric order parameters. A dielectric anomaly at the magnetic ordering temperature supports this correlation. The dielectric permittivity at various magnetic fields is measured using an indigenously developed connector setup. Lu3Fe5O12-δ exhibits a magneto-dielectric coupling of ∼6% at room temperature, which is significant in the case of a single-phase magneto-dielectric material at low fields. Rietveld refinement of the X-ray diffraction pattern, bond valence sum method, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy indicate two different oxidation states of Fe. Complete structural optimizations performed using the density functional theory establish a ferrimagnetic ground state and provide structural parameters in agreement with experimental values. Electronic structure analysis shows that Lu3Fe5O12 exhibits insulating behavior both in ferromagnetic and ferrimagnetic configurations. The capability of Lu3Fe5O12-δ to exhibit room temperature magneto-dielectric response is a key factor in designing and fabricating various electronic devices and sensors.

High Gain Resonant Cavity Antenna with Meta-material Inspired Superstrate

Abstract A high gain planar Resonant Cavity Antenna (RCA) inspired by metamaterial superstrate is proposed operating at C-band. The RCA is modelled using simple ray tracing method. The unit cell metamaterial consists of Artificial Magnetic Conductor (AMC) and square patch laminated on either side of magneto-dielectric material, is used as the superstrate to design RCA. Square patch is capacitive type and that AMC as inductive. Effects of the reflection phase of the substrate decides the gain of the antenna. A cylindrical dielectric resonator antenna (CDRA) has been used as the primary radiator. The metamaterial unit cell structure is characterized and its effective material parameters are extracted through its S-parameters simulation. The proposed antenna achieves 12.5dBi gain with only 2x2 array superstrate.The results of upto 12 x 12 array superstrate with multiple layers can be demonstrated for higher gain over wide frequency range.

Tunable Ultrawideband Phase Shifters With Magnetodielectric Disturber Controlled by a Piezoelectric Transducer

A new tunable ultrawideband phase shifter with magnetodielectric disturber controlled by a piezoelectric transducer has been developed in this paper. With their high relative permeability, magnetodielectric materials show great potential in microwave circuit and device designs. Novel ultrawideband phase shifter designs with conductor-backed coplanar waveguide were compared and investigated. NiCo-ferrite films were adopted to laminate the magnetodielectric material perturber on a dielectric Rogers material substrate. A maximum relative phase shift of 384° at 20 GHz with respect to the unperturbed condition has been achieved for the conductor backed coplanar waveguide structure.

A laminate of ferromagnetic films with high effective permeability at high frequencies

The paper reports on development of magnetodielectric material with high microwave permeability. The material is a laminate of multi-layer permalloy films deposited onto a thin mylar substrate by magnetron sputtering. The deposited films are arranged into a stack and glued together under pressure to obtain the laminate. With the content of ferromagnetic component in the laminate being 22 % vol., its measured quasistatic permeability is 60. The peak value of imaginary permeability attains 50 and the peak is located near 1 GHz. As compared with the multi-layer films, which the laminate is made of, it exhibits lower magnetic loss tangent at frequencies below the magnetic loss peak and may therefore be useful for many technical applications. Lower low-frequency loss may be attributed to pressing of the glued sample. This rectifies wrinkling appearing due to sputtering of rigid multi-layer film onto flexible mylar substrate and, therefore, makes the magnetic structure of the film more uniform.

Magnetodielectric effects in hybrid magnetorheological suspensions

The magnetodielectric material obtained is a hybrid magnetorheological suspension (MRS-hybrid) which contains polyurethane sponge foam, magnetorheological suspensions (MRS) and polymerized silicone rubber. We create a plane capacitor based on MRS-hybrid. Using a programmable bridge we measure the capacitance C and the dissipation factor D of the capacitor as a function of intensity H of a constant magnetic field, and as a function of frequency f of an electric field. We determine the components ϵ′ (relative dielectric permittivity) and ϵ′′ (dielectric loss factor) of the complex dielectric permittivity ϵ* of MRS-hybrid. We present and discuss the obtained results.

Magnetodielectric effects in composite materials based on paraffin, carbonyl iron and graphene

We present the fabrication and testing of a composite magnetodielectric material based on paraffin, carbonyl iron microparticles (CI) and graphene nanoparticles. Dependence of relative dielectric permittivity with an external magnetic field of intensity H was investigated for two plane capacitors with dielectric materials based on the new composite, at two different volume concentrations (with ratio 1:3) of CI. By increasing the volume concentration of CI, the relative dielectric permittivity of magnetodielectric changes from a linear increase to a downward parabola-like variation and the magnetodielectric becomes a magnetoresistor. The observed effects can be applied for fabrication of magnetic field sensors.

Printed inverted‐F antennas over lossy magneto‐dielectric materials: Theoretical approach and validations

Closed-form formulas for radiation efficiency and bandwidth predictions, suitable for printed inverted-F antennas (PIFAs) over lossy magneto-dielectric materials, are proposed. The formulation uses the field expressions inside the cavity for the first resonant-mode (fundamental mode) based on the cavity model. It includes the substrate effective permittivity (εre) and permeability (µre) in addition to the radiation from both the shorting-pad and the slot. The derived expressions for efficiency and bandwidth are validated with measurements and full-wave CST simulations based on the finite integration technique. Various sizes and types of magneto-dielectric materials are considered. It is noticed that magneto-dielectric materials having √(εreµre) > εr or simply with µr > εr are advantageous for both radiation efficiency and bandwidth enhancement.

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.

A Magneto-Dielectric Handset Antenna for LTE/WWAN/GPS Applications

A compact multiband internal antenna covering LTE/GSM/GPS/DCS/PCS/UMTS bands (748-960 and 1575.42-2690 MHz) is presented for mobile terminals. The antenna combines a coupled-fed scheme and a magneto-dielectric material, which has low loss properties (magnetic loss tangent <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$ &lt; 0.08$</tex></formula> ) up to 3 GHz, thereby achieving not only reduced antenna size but also improved bandwidth. In addition, a T-shaped monopole feeding line generating parasitic capacitance is applied to the proposed antenna. It plays an important role to shift the resonances, especially in the low band. The overall size of the antenna is only <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$35 \times 15 \times 4~\hbox{mm}^{3}$</tex> </formula> , corresponding to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$0.0875{\lambda _0} \times 0.0375\ {\lambda _0} \times 0.01\ {\lambda _0}$</tex></formula> ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\lambda _0}$</tex></formula> is the wavelength at 750 MHz). The design process and the measured results of the proposed antenna are presented in detail.

How we intended the world's best hub for high-frequency welding

This paper represents contribution of improvement for energy parameters of high frequency inductive welding of steel tubes. This improvement was shown through lessened consumption of electric energy . The function of concentrator is to transfer and convert electromagnetic energy into heating energy in the best possible max. Optimal concentrator with Fluxtrol A magneto-dielectric material was projected and made. Practical results provide us most one of the best solutions in this field in the world, with the proven criteria.

Miniaturized Antennas With Reduced Hand Effects in Mobile Phones Using Magneto-Dielectric Material

In this letter, magneto-dielectric (MD) material is proposed to reduce the antenna volume without significant performance degradation and mitigate the efficiency decrease by the human hand. The MD ceramic, which has small magnetic loss tangent around 0.1 or less at 2 GHz, is developed using hexagonal ferrites. This ceramic material is mixed with polymers to form the MD composites, which can be easily applied to the complex-shaped substrates of mobile antennas. Inverted-F antennas (IFAs) on the composites are simulated for studying of the antenna miniaturization and hand effects. Mobile antennas using the composites are manufactured by injection molding and plating processes. Then, the radiation efficiencies are measured with and without the hand phantom. The test results show that the MD composites are useful for miniaturizing antennas and reducing hand effects in the mobile phones.

Low-Loss Magneto-Dielectric Materials: Approaches and Developments

Magneto-dielectric materials with matching permeability and permittivity have significant advantages for miniaturization and efficiency improvement of antennas. The main requirements for this kind of magneto-dielectric material include a high refractive index, matched permeability and permittivity, and low magnetic and dielectric losses at the application frequency. However, it is very difficult to meet these requirements simultaneously. This review presents the approaches and developments of magneto-dielectric materials of three types: spinel-based, hexagonal-based, and composite magneto-dielectric materials. It is proved that choosing the proper type of magneto-dielectric material is very important to obtain a higher refractive index and matched permeability and permittivity in the application frequency band. When the application frequency is low (less than 30 MHz), adopting composites of spinel ferrite and high-dielectric material is the best choice to improve the refractive index. When the application frequency is between 30 MHz and 100 MHz, it is better to choose spinel-based magneto-dielectric materials in consideration of both their relatively high refractive index and low losses. When the application frequency increases to 100 MHz to 500 MHz, hexagonal-based magneto-dielectric materials offer better performance. Finally, when the application frequency is beyond 500 MHz, to obtain matched permeability and permittivity, choosing composites of hexaferrite and an organic medium is recommended. Solutions for how to decrease magnetic and dielectric losses and expand the application frequency range are also discussed.