Zekun Feng

Preparation and characterization of ferrite with Co substituted NiCuZn sheets application for 13.56 MHz radio frequency identification communication

The electromagnetic (EM) shielding sheets could be an effective solution to increase the detection distance of the RFID (Radio Frequency Identification) tags attached on metal. The eddy current induced on the metal surface can be reduced when a ferrite sheet sandwiched between RFID tag and metal. The magnetic spectra of Ni0.36Cu0.19Zn0.45Fe1.92O3.88 ferrite added with BiBSi-glass and CoO were investigated. It shows that the real part of permeability could reach above 150 while the imaginary part maintains below 2 at 13.56 MHz with 0.2 wt. % CoO and 0.4 wt. % BiBSi-glass doping content. The ferrites could be fabricated as EM shielding sheets by laminate process. The experimental results show that the doped ferrites could be a good candidate for EM shielding sheet. The final sheet size could be as large as 135 mm × 135 mm while the thickness is 0.1 mm and the density is above 5.0 g/cm3. By inserting the EM shielding sheet between the RFID antenna and metal surface, the improved communication performances ar...

Electromagnetic properties of Fe-Si-Al/BaTiO3/Nd2Fe14B particulate composites at microwave frequencies

Ferroelectric/ferromagnetic (soft and hard) three-phase microwave absorption composites, consisting of Fe-Si-Al/BaTiO3/Nd2Fe14B, are presented, which were fabricated by mechanical ball milling. The microstructure, magnetic, and microwave properties were measured, demonstrating significant improvement in magnetization and coercivity, compared to those single phase materials. In particular, either ferroelectric or hard magnetic phase presents a strong tunability of permeability and permittivity with frequency, which can tailor a frequency band of microwave absorption. The experiments indicate that an optimal reflection loss of the Fe-Si-Al/BaTiO3/Nd2Fe14B was tuned from 2 to 9.52 GHz, whereas the peak value was remarkably enhanced by 62.8%. Therefore, the three-phase microwave absorption composites may remain thin but have great potential to be used at high frequency range.

Ferromagnetic resonance induced large microwave magnetodielectric effect in cerium doped Y 3 Fe 5 O 12 ferrites

In recent years, multifunctional materials contained simultaneous ferroelectric and ferromagnetic ordering have been realized. Here, a real time room temperature adaptive materials system, which demonstrates an RF magnetodielectric (MD) response, i.e., CexY3−xFe5O12 (x = 0, 0.05, 0.1, 0.15, 0.2), is reported. The magnetic and dielectric properties of Ce-doped YIG microwave ferrites processed by a traditional ceramic route have been measured over a frequency range of 4–8 GHz (C-band). The substitution of Ce not only enhances the microwave electromagnetic properties of the YIG, but also modulates the magnetodielectric response. The maximum magnetodielectric response in Ce-doped YIG sample ranges in magnitude from approximately +5% to −5% under an applied field of 1.78 kOe. This effect was attributed to electron fluctuations on the Fe cation sites. Furthermore, the magnitude of the MD response was shown to be enhanced by the cerium content. It is believed that research of the magnetodielectric effect in YIG ferrites is of great importance to the development of next generation multifunctional adaptive microwave materials, devices and integrated circuits.

High frequency permeability and permittivity spectra of BiFeO3/(CoTi)-BaM ferrite composites

Low magnetic loss ferrite composites consisting of Ba(CoTi)1.2Fe9.6O19 and BiFeO3 (BFO) ferrite were investigated for permeability, permittivity, and high frequency losses at 10 MHz–1 GHz. The phase fraction of BiFeO3 was quantitatively analyzed by X-ray diffraction measurements. An effective medium approach was employed to predict the effective permeability and permittivity for the ferrite composites, which was found to be in good agreement with experimental data. The experiment demonstrated low magnetic losses (<0.128), modified by BFO phase fraction, while retaining high permeability (∼10.86) at 300 MHz. More importantly, the BFO phase resulted in a reduction of magnetic loss by 32%, as BFO phase increased from 2.7 vol. % to 12.6 vol. %. The effect of BFO phase on magnetic and dielectric properties revealed great potential for use in the miniaturization of high efficiency antennas.

Low loss Sendust powder cores comprised of particles coated by sodium salt insulating layer

Toroid-shaped Sendust powder cores were prepared from cold pressing mechanically pulverized Fe-Si-Al powder that had been coated using an inorganic insulating layer. The present work focuses on the effect of the sodium salt-coated Sendust particles upon the high frequency magnetic properties. Sendust powders, having a particle size range of ∼125 μm, exhibit a high saturation magnetization of 118.9 A·m2/kg and a low coercivity of 56 A/m. The experiments indicate that the sodium-based glass insulating layer synthesized from sodium metaphosphate and sodium metaborate can effectively reduce the change in permeability with frequency or DC bias field, yielding high effective permeability (μe) of ∼113 over a wide frequency range from 10 kHz–1 MHz. Furthermore, the effective permeability is measured at ∼27 at H = 7854 A/m, indicating stable and high effective permeability under a DC bias field. The measurements of permeability under DC bias field indicate a peak in the quality factor (Q) values corresponding to a...

Effect of Sn doping on the room temperature magnetodielectric properties of yttrium iron garnet

The structures, magnetic properties, permittivity spectra, and magnetodielectric (MD) effects of polycrystalline Y3Fe5−xSnxO12 compounds prepared by solid state reactions were systematically investigated. The substitution of Sn4+ leads to lattice expansion and the donation of excess electrons in ceramics, which affects the concentration of Fe2+, space charge, and electric dipole. As a result, as the amount of Sn dopant increases, so does saturation magnetization and permittivity in the low frequency band. The MD coefficient ([er(H) − er(0)]/er(0)) of lightly doped samples (x ≤ 0.05) is negative in the entire frequency band, reaching −2.3% at 350 MHz and 0.6 T for Y3Fe4.95Sn0.05O12 ceramics. The MD coefficient of heavily doped samples (x > 0.05) is positive in the low frequency band, reaching 0.83% at 10 MHz and 0.6 T for Y3Fe4.925Sn0.075O12 ceramics, and then decreasing with the increasing frequency, gradually becoming negative in the high frequency band. A detailed explanation is provided based on the or...

Microwave Bandpass Filters Tuned by the Magnetization of Ferrite Substrates

C-band (around 5 GHz) microwave bandpass filters fabricated on yttrium-iron-garnet (YIG) and Al-doped-YIG ferrite substrates are tuned by an external magnetic field of 0 to 720 Oe. The filters on Al-doped YIG with lower saturation magnetization exhibit lower tuning ranges and sensitivities but reduced insertion losses and expanded bandwidths. The tunabilities of the filters are related to their partial or full magnetization states. Full magnetization states have three regimes: low field, resonance, and high field. The resonance regime cannot be used for bandpass filters. The detailed tuning mechanism is analyzed based on the dynamic magnetization states of magnetic materials. The results will provide a framework for the design of magnetically tunable bandpass filters.

Magnetic spectra and Richter aftereffect relaxation in CexY3−xFe5O12 ferrites

The static and dynamic magnetic properties of cerium (Ce) doped yttrium iron garnet CexY3−xFe5O12 (x=0, 0.05, 0.1, 0.15, 0.2) ferrites (YIG) have been reported in this work. The ferrites were fabricated by the traditional solid-state reaction method. All ferrite samples reveal pure garnet structure identified by x-ray diffraction (XRD). The substitution of cerium not only enhances the saturation magnetization of the samples, but also regulates the magnetocrystalline anisotropy constant K1. Obvious differences in permeability spectra over a frequency of 1 MHz - 1 GHz can be observed. It is verified that the permeability dispersion and magnetic losses of Ce-doped YIG ferrite contain the contribution of Richter aftereffect relaxation due to the existence of Fe2+ ions. The fitting results of the permeability spectra applied three-mechanism model is in good agreement with experimental data, which successfully explains the mechanisms of magnetic losses observed at 1 MHz to 1 GHz for Ce-doped YIG ferrite. In add...

Low power loss and field-insensitive permeability of Fe-6.5%Si powder cores with manganese oxide-coated particles

Fe-6.5%Si alloy powders coated with manganese oxides using an innovative in situ process were investigated. The in-situ coating of the insulating oxides was realized with a KMnO4 solution by a chemical process. The insulating manganese oxides with mixed valance state were verified by X-ray photoelectron spectroscopy analysis. The thickness of the insulating layer on alloy particles was determined to be in a range of 20–210 nm, depending upon the KMnO4 concentration. The powder core loss and the change in permeability under a DC-bias field were measured at frequencies ranging from 50 to 100 kHz. The experiments indicated that the Fe-6.5%Si powder cores with a 210 nm-thick manganese oxide layer not only showed a low core loss of 459 mW/cm3 at 100 kHz but also showed a small reduction in permeability (μ(H)/μ(0) = 85% for μ = 42) at a DC-bias field of 80 Oe. This work has defined a novel pathway to realizing low core loss and field-insensitive permeability for Fe-Si powder cores.

Effect of Co 2 O 3 Addition on Stability of Permeability to an Impulse Magnetic Field in NiCuZn Ferrites

The NiCuZn ferrites doped with Bi2O3 and Co2O3 were prepared by the solid-state reaction method. Micrographs were obtained by SEM. The complex permeability spectra were measured by Agilent E4991A and 16454A. Variation of the permeability under a magnetic field impulse was measured by Agilent 4284A. Effect of the Co2O3 content on the permeability spectra of the NiCuZn ferrite samples before and after exposing to an impulse magnetic field was discussed. The corresponding permeability spectra of the samples were decomposed into the domain wall motion component and the spin rotation component. The results show that the permeability at 1 MHz decreases and the resonance frequency increases with more Co2O3 content, and Co2+ have different effect on the two kinds of magnetic susceptibility components. Different variation was revealed for the domain wall motion component and the spin rotation component after exposing to an impulse magnetic field. The decline rate of susceptibility by domain wall motion is smaller than that of susceptibility by spin rotation.