Magnetic Loss Tangent Research Articles

Low‐Temperature Sintering Li2MoO4/Ni0.5Zn0.5Fe2O4 Magneto‐Dielectric Composites for High‐Frequency Application

The coexistence of Li2MoO4 (LMO) and Ni0.5Zn0.5Fe2O4 (NZO) has been proven and their low‐temperature‐sintered magneto‐dielectric composites (1−x)LMO–xNZO (volume fraction factor x = 0.1, 0.3, 0.5, 0.7) were prepared by the conventional solid‐state reaction method and were sintered below 700°C. It is found that the optimal sample (x = 0.5) has good and relatively stable magneto‐dielectric performance in the frequency range from 10 MHz to 1 GHz with permittivity between 7.14 and 6.84, dielectric loss tangent between 0.09 and 0.02, and permeability between 5.23 and 3.30, magnetic loss tangent between 0.06 and 0.65, respectively. Furthermore, the verified chemical compatibility with silver indicates that the LMO–NZO ceramics are potential for low‐temperature cofired ceramic application and their multifunctional magneto‐dielectric properties also make them for potential applications in electronic devices.

Structure, Morphology, and Electromagnetic Properties of Manganese Dioxide with Ni Doping

Hydrothermal synthesis between (NH 4)2S 2O 8 and MnSO 4 was carried out to investigate the structure, morphology, and electromagnetic properties of Ni-doped MnO 2 with different doping amounts. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that all the final products were α-MnO 2 and few amounts of γ-MnO 2, and the morphology changed obviously with the increase of the Ni doping amount. The doping of Ni had a certain effect on the electromagnetic properties, and some other properties derived from electromagnetic performances were also investigated, such as dielectric and magnetic loss tangent and microwave-absorbing properties. All the reflection loss (RL) peaks of the final products were moving toward lower frequency with increasing thickness, and with the thickness of 2 mm, the final products all had the maximum effective absorption bandwidth (RL < −10 dB), and the Ni-doped MnO 2 had better reflection loss performance than the undoped MnO 2 in the range of high frequency.

Electromagnetic and microwave absorbing properties of raw and milled FeSiCr particles

FeSiCr alloy (Fe: 90%, Si: 7.9%, and Cr: 2.1%) with pre-milled flaky shape was re-milled in a planetary ball-mill for 30 h. The complex permittivity (ε′−jε″) and permeability (μ′−jμ″) are measured by using the transmission/reflection method for two different aspect ratios of flake-shaped FeSiCr/epoxy composites for 30%, 40%, and 50% weight ratios. Dielectric loss tangent and magnetic loss tangent of re-milled FeSiCr powder show larger electromagnetic wave energy dissipation than those of the raw flaky FeSiCr powder. For 30 wt. % of FeSiCr/epoxy absorbers with 2 mm thickness, the calculated reflection loss reaches −25 dB at 13.0 GHz for raw flaky powder, −40 dB at 11.4 GHz for the re-milled FeSiCr powder with higher aspect ratios.

Properties of Sub-Wavelength Spherical Antennas With Arbitrarily Lossy Magnetodielectric Cores Approaching the Chu Lower Bound

For a spherical antenna exciting any arbitrary spherical mode, we derive exact closed-form expressions for the dissipated power and stored energy inside (and outside) the lossy magneto-dielectric spherical core, as well as the radiated power, radiation efficiency, and thus the radiation quality factor. These expressions are valid for the entire range from zero to infinite material loss tangents, with any dispersion of the real parts and an inverse frequency variation of the imaginary parts of permittivity and permeability. For the dipole modes of a sub-wavelength antenna, we demonstrate how an increasing magnetic loss tangent initially leads to a decreasing radiation quality factor, but in the limit of a perfect magnetic conductor (PMC) core the dissipated power tends to zero and the radiation quality factor reaches the fundamental Chu lower bound.

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.

Quality Factor and Radiation Efficiency of Dual-Mode Self-Resonant Spherical Antennas With Lossy Magnetodielectric Cores

For spherical antennas consisting of a solid magnetodielectric lossy core with an impressed surface current density exciting a superposition of the TEmn and TMmn spherical modes, we analytically determine the radiation quality factor Q and radiation efficiency e. Also, we determine the relative mode excitation, as a function of the core material parameters, which ensures self-resonance. For the specific case of a dual- TEm1, TMm1 dipole antenna of half a wavelength circumference, we show quantitatively, how Q/e and e behave, and can be optimized as functions of permeability and magnetic loss tangent. We obtain Q/e values well below the Chu lower bound with fair efficiencies up to 71% - 84%.

MAGNETIC SUBSTRATE FOLDED DIPOLE ANTENNA FOR UHF RFID METAL TAG

In this paper, magnetic material was applied in the design of a UHF-RFID metal tag to increase the reading distance. The in∞uence of the electromagnetic properties, especially the electromagnetic loss, of a magnetic substrate on the gain of the tag antenna is discussed by analyzing the re∞ection and the surface current distribution. As to folded antenna, the loss of energy caused by the magnetic substrate tends to occur in the folding edge of the antenna. Both simulations and experiments indicate that electromagnetic loss markedly reduces the gain rapidly when both the dielectric loss tangent (tan-) and the magnetic loss tangent (tan-m) are between 0 and 0.3. The reading distance drops from 3m to 1.5m when the tan-m of the magnetic composite substrate increases from 0.009 to 0.023. And tan-m should be less than 0.1 for the antenna working excellently. The conclusion ofiers meaningful guidance for future studies of magnetic substrate folded metal tag.

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.

Novel Frequency Dispersion of Permeability in Nickel Ferrites with Different Amounts of Cobalt Doping

The effect of cobalt doping on permeability spectra of nickel ferrites with excess iron ( Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.743-x</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.057</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.20</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , x=0-0.027) has been studied. With increasing amounts of Co-doping, the static permeability μi decreases at first, then increases to the local maximum at Co substitution of x = 0.018, and finally decreases again. The permeability spectra go through a modification of relaxation-resonance-relaxation dispersions. The samples with Co substitution of x = 0.018 and 0.021 have the static permeability of ~13, resonance frequency of 400 MHz, and sufficiently low magnetic loss tangents, over 1-250 MHz, make them promising candidates for high frequency applications.

Facile synthesis of α-MnO2 nanorods at low temperature and their microwave absorption properties

One-dimensional α-MnO2 nanorods were fabricated by using low-temperature water-bathing chemical precipitation method at 80 °C. The crystalline structures, morphological evolution process and microwave absorption properties were systematically investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and measurement of electromagnetic parameters. The results show that the morphological structures and electromagnetic properties have close relationship with the reaction time. With the prolonging of the treatment time, the as-synthesized products turn from microspheres constituted of tiny dendrites to nanorods with diameters of 20–30 nm and lengths up to 1–2 μm. The electromagnetic characterization shows that the dielectric constants and magnetic permeability values show decreasing trends with the increasing frequency, however, the dielectric and magnetic loss tangents all increase with frequency. The electromagnetic absorption properties of the products have close relationship with the morphologies and thicknesses of the samples. With a thickness of 3 mm, an absorbing peak value of −25 dB was achieved for the sample treated for 24 h. The microwave absorption properties of MnO2 can be attributed mainly to interfacial polarization, space charge polarization and relaxation phenomena.

A Novel Magnetodielectric Solid Solution Ceramic 0.4LiFe5 O8 -0.6Li2 MgTi3 O8 with Excellent Microwave Dielectric Properties

In this study, a novel spinel solid solution ceramic of 0.4LiFe5O8–0.6Li2MgTi3O8 (0.4LFO–0.6LMT) has been developed and investigated. It is found that the 40 mol% LiFe5O8 and 60 mol% Li2MgTi3O8 are fully soluble in each other and a disordered spinel phase is formed. The ceramic sample sintered at 1050°C/2 h exhibits both good magnetic and dielectric properties in the frequency range 1–10 MHz, with a permeability between 29.9~14.1 and magnetic loss tangent between 0.12~0.67, permittivity between 16.92~16.94 and dielectric loss tangent between 5.9 × 10−3–2.3 × 10−2. The sample also has good microwave dielectric properties with a relative permittivity of 16.1, a high quality factor (Q × f) ~28 500 GHz (at 7.8 GHz). Furthermore, 3 wt% H3BO3–CuO (BCu) addition can effectively lower the sintering temperature to 925°C and does not degrade the magnetodielectric properties. The chemical compatibility with silver electrode indicates that this kind of ceramics is a good candidate for the low-temperature cofired ceramic (LTCC) application.

Ultra-High-Frequency Behavior of BaFe$_{12}$O$_{19}$ Hexaferrite for LTCC Substrates

M-type barium hexaferrite (BaFe12O19) is investigated with an aim of using with low temperature co-fired ceramic (LTCC) substrate material. The as-calcined powders from combustion synthesis at neutral and acidic precursor solutions are used, which exhibit excellent properties of low coercive field values (up to 1350 Oe) and high magnetization (up to 60 emu/g). With an appropriate amount of Bi2O3 as sintering aid, high density ferrites have been realized at LTCC processing temperatures. The sintered ferrites possess bulk resistivity in excess of 109 Ω·cm, indicating their suitability for high-frequency applications. Complex magnetic permeability and magnetic loss factors are studied up to 1 GHz frequency. Complex permeability between 1.2 to 2.2 and magnetic loss tangent between 0.05-0.5 have been realized for the sintered ferrites. The influence of Bi2O3 content on resistivity and high-frequency magnetic properties is discussed. It is observed that the sample prepared by employing neutral pH during combustion preparation and calcined at 1200°C for 12 h shows low coercivity of 1350 Oe. After sintering at 900°C with 2 wt% Bi2O3, the sample shows better results with permeability of 1.5-1.7, magnetic loss tangent below 0.3 up to 700 MHz frequency and a high resonance frequency of 140 and 715 MHz in VHF and UHF band, respectively. Since the synthesis conditions provide better control over basic magnetic properties, the use of combustion synthesized BaFe12O19 material augers well for magnetic materials applications in LTCC technology.

Ni3Zn ferrite octahedral nanoparticles with high microwave permeability and high magnetic loss tangent

Ni3Zn ferrite octahedral nanoparticles with grain size of about 40nm were synthesized via a low temperature hydrothermal route. The saturation magnetization (Ms) and coercive force (Hc) of the sample are 57.5emu/g and 197Oe, respectively. In 50MHz–8GHz frequency range, the complex permeability and complex permittivity for Ni3Zn ferrite/wax composites containing 60wt% ferrite powders were measured by a vector network analyzer. The real part μr' of the permeability exhibits high values between 4 and 1.65 in 50MHz–2GHz range, and the imaginary part μr'' of the permeability presents a broad peak with a maximum value of 1.53 at 2.1GHz, the calculated reflection loss of ferrite/wax coating with the thickness of 8mm reaches −13dB at 2.1GHz. The results indicate the as-prepared Ni3Zn ferrite octahedral nanoparticles can have applications in biomedicine, and microwave absorption and electric devices.

Complex permeability and permittivity variation of radar absorbing materials based on MnZn ferrite in microwave frequencies

The complex dielectric permittivity (ε) and magnetic permeability (µ) of Radar Absorbing Materials (RAM) based on magnetic particles (MnZn ferrite particles) embedded in a dielectric matrix (silicon rubber) have been studied in the frequency range of 2 to 18 GHz. The relative permeability and permittivity of MnZn ferrite-silicon composites for various mass fractions are measured by the transmission/reflection method using a vector network analyzer. The concentration dependence of permittivity and permeability on the evaluated frequency range is analyzed. In a general way, the results show ε' parameter presenting more significant variation among the evaluated parameters (ε", µ", µ'). The comparison of dielectric and magnetic loss tangents (ε"/ε' and µ"/µ', respectively) shows more clearly the variation of both parameters (ε and µ) according to the frequency. It is also observed that higher MnZn ferrite content fractions favor both dielectric and magnetic loss tangents.

Recent progress in some composite materials and structures for specific electromagnetic applications

This review aims to summarise the progress in some materials and structures for electromagnetic applications, such as microwave absorption, electric shielding and antenna designs, which have been developed in recent years. Composites with spherical powders for microwave absorption focus mainly on those based on ferrites (especially hexagonal), carbonyl iron and related alloys and various newly emerged nanosized materials. Composites with long conductive fibres as fillers will be summarised, with speical attentions to prediction, measurment and evaluation of their performances. Metamaterials include structures for microwave absorbing applications, tunable materials or structures with reflection or transmission coefficients that are tunable by external magnetic or electric fields, and specially designed structures for microwave absorbing applications, with thickness much smaller than that of conventional composite materials and performances that can be optimised by the physical properties of substrates, and new metamaterials constructed with ferrite cores wound by metallic wire coils that exhibited unique magnetic properties, with extremely high real and imaginary permeability, which are adjustable or tunable by varying their configurations. Magnetodielectric materials, with matching permeability and permittivity, together with sufficiently low magnetic and dielectric loss tangents, with potential applications in antenna miniaturisation, will be discussed.

Low-loss NiCuZn ferrite with matching permeability and permittivity by two-step sintering process

Magneto-dielectric materials with matched permeability and permittivity are promising candidates as loading materials to reduce the physical dimensions of low-frequency antennas. In this study, NiCuZn ferrites were prepared by both the traditional final-stage sintering process and the two-step sintering process to obtain the magneto-dielectric materials. It was found that the samples sintered by the two-step sintering process tended to obtain microstructure with dense, homogeneous, and small average grain size, which was favorable to obtain low magnetic and dielectric losses. The sample sintered by the two-step sintering process with high temperature 950 °C and holding temperature 900 °C could obtain almost equal permeability and permittivity of around 11.8. And the magnetic and dielectric loss tangents were lower than 0.015 in a frequency range from 10 to 100 MHz. These properties make the material useful to the design of miniaturized antennas.

Control of magnetic loss tangent of hexaferrite for advanced radio frequency antenna applications

We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.

ARTIFICIAL MAGNETIC MATERIALS SYNTHESIS WITH GENERIC METALLIC BROKEN LOOPS

We propose a methodic approach to design Artiflcial Magnetic Materials (AMM) with desired magnetic properties. The design procedure is deflned based on a novel formulation for characterizing AMMs. The employed formulation expresses the efiective permeability and the magnetic loss tangent (MLT) in terms of the geometrical and physical parameters of the inclusions. The method comprised four steps. In the flrst step, the feasibility of the design is checked through a set of constraints. The second and third steps provide an iterative procedure to capture the desired magnetic properties. Finally, the geometrical elements, i.e., the area and perimeter of inclusions, are calculated. The technique is applied to design of an AMM structure based on Rose curve resonators. The design based on the proposed methodology is verifled by the numerical simulation of the AMM.

Gain Enhancement in Microstrip Patch Antennas Using Hybrid Substrates

A substrate design that uses a ferrite ring to enhance the gain of a microstrip patch antenna without compromising the bandwidth is proposed. This design forces constructive interference between the incident and reflected fields inside the substrate. The interference is created by introducing a ferrite ring at a distance d1 from the circumference of the patch with a ring width d2. Initial values of d1 and d2 of one-quarter of the free-space wavelength ( d1 = d2 = λ0/4) are selected. An unbiased ferrite, with relative permeability of μr2 = 14, relative permittivity of er2 = 10, dielectric loss tangent tan δe = 0.0017, and magnetic loss tangent tan δm = 0.0391, is used. Using HFSS, the results of the patch antenna above a conventional substrate (i.e., no ferrite ring) and above the hybrid substrate (which includes the ferrite ring) are compared. Enhancements of about 4 dB in gain and nearly 1% in impedance bandwidth are obtained by using the hybrid substrate instead of the conventional one.

A Novel Magneto‐Dielectric Solid Solution Ceramic 0.25LiFe5O8–0.75Li2ZnTi3O8 with Relatively High Permeability and Ultra‐Low Dielectric Loss

In this study, a 0.25LiFe5O8–0.75Li2ZnTi3O8 solid solution ceramic was developed via the solid‐state reaction method. Its phase evolution, microstructure, and sintering behavior were investigated and it was found that the 25 mol.% LiFe5O8 phase is almost fully soluble in Li2ZnTi3O8, and only the Li2ZnTi3O8 type spinel phase was formed in the 0.25LiFe5O8–0.75Li2ZnTi3O8 ceramic. The ceramic sample sintered at 1050°C for 2 h was found to possess both good magnetic properties and dielectric properties in the frequency range from 1 to 10 MHz, with permeability between 38.2 and 15 and magnetic loss tangent between 0.25 and 0.75, permittivity between 19.6 and 19.3 and dielectric loss tangent between 8 × 10−3 and 2 × 10−3. The sample also possesses good microwave dielectric properties with a relative permittivity of 19.1, a high quality factor (Qf) ~11,770 GHz (at 6.84 GHz). The ceramic is a novel magneto‐dielectric ceramic with both high permeability and good dielectric properties, which might be a good candidate for the applications in novel electronic devices.