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We report a simple wireless power charging (WPC) antenna system (50 mm \times40 mm \times0.1 mm) for use in simulating power transfer efficiency ( \eta ) with and without ferrite and a metallic object (battery case), thereby identifying suitable magnetic parameters and ferrite sheet thickness. The simulation results suggest that magnetic loss tangent (tan ) and permeability ( \mu ' ) need to be less than 0.05 and higher than 125 at 13.56 MHz, respectively, to achieve at least 75% of the transfer efficiency ( \eta \mathrm {max} ) of the WPC antenna without ferrite and the metallic object. Accordingly, we have fabricated NixZn0.85–xCu0.15Fe2O4 (x = 0.32 – 0.38) spinel ferrites using a one-step sintering process and obtained relatively high \mu ' of 169 and low tan \delta \mu of 0.1 with a nickel (Ni) concentration of 0.38. This magnetic loss is still too high to achieve 75% of the \eta \mathrm {max} value. In order to further reduce the magnetic loss, a two-step sintering process was used. The two-step sintered Ni0.38Zn0.47Cu0.15Fe2O4 shows $\mu '$ of 132 and a tan \delta \mu of 0.03 at 13.56 MHz, respectively. Therefore, this ferrite meets criteria identified by the transfer efficiency simulation and is a good candidate for 13.56-MHz wireless power transfer charging antenna system. In addition, our designed WPC system is capable of evaluating other magnetic materials that are suitable for WPC antenna applications. [ABSTRACT FROM AUTHOR]

Miniature low-profile multiband ferrite antennas were designed with various BaCo1.4Zn0.6Fe16O27 hexaferrite loading configurations and fabricated for telematics applications. Experimental permeability ( \mu ^\prime ) of 2.0, permittivity ( \varepsilon ^\prime ) of 7.3, magnetic loss tangent (tan \delta \mu ) of 0.035, and dielectric loss tangent (tan \delta \varepsilon ) of 0.005 at 1 GHz were used for antenna performance simulations. It is observed that a hollow rectangular ferrite substrate loading shows simulated maximum ripple levels ( \Delta = E\theta \\max -E\theta \\min ) of 2.2, 3.0, and 1.9 dB at the first ( f1 ), second ( f2 ), and third ( f3 ) resonant frequencies, respectively, implying wider coverage than other loading configurations. Miniaturization factor is greater than that of air-core antenna, and the impedance matching and bandwidth are improved with the ferrite loading. Higher gain of the ferrite-loaded antenna than the air-core antenna was observed at f2 and f3 , while the gain at f1 remains almost the same. Moreover, the vertical component E\theta is greater than the horizontal component E\phi , showing the vertically polarized operation of the antenna. Based on the measured and simulated results, it is concluded that the BaCo1.4Zn0.6Fe16O27 substrate loading allows antenna miniaturization with enhanced antenna performance. [ABSTRACT FROM PUBLISHER]

ABSTRACT We demonstrate that electrically small ferrite antenna gain is significantly increased with a small dc magnetic field of compact Nd-Fe-B permanent magnet (9.5 × 4.6 × 1.5 mm3). The experimental magnetic tangent loss of the Ni-Mn-Co ferrite decreased by about 62%, which was from 0.509 with 0 Gauss to 0.192 with 750 Gauss. The antenna gain increased by 54% (from −10.58 to −4.81 dBi) when the magnetic field of 1600 Gauss was applied to the antenna. The ferrite antenna has the volume of 0.346 cm3 and shows omnidirectional patterns, which are suitable for hand-held mobile device applications. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1531-1534, 2014 [ABSTRACT FROM AUTHOR]

We demonstrated the size reduction of axial-mode helical antenna based on Co2Z hexaferrite-glass composite. Axial-mode helical antenna was employed to provide reliable communication for unmanned aerial vehicle (UAV) applications. The conventional axial-mode helical antenna uses an air core or low dielectric material, resulting in large antenna size. To increase the miniaturization factor n=(\mur\varepsilonr)^0.5, a Co2Z hexaferrite-glass composite was used as an antenna core. The 3-dimensional finite element method (FEM) simulation was performed to design a hexaferrite helical antenna and confirm the axial-mode operation at 2.44 GHz with gain of 2.0 dBi. The designed hexaferrite helical antenna showed 82% of volume reduction and good impedance matching compared to the air-core antenna. The axial-mode hexaferrite antenna was fabricated based on the designed structure and characterized in an anechoic chamber. The maximum gain of 0.541 dBi was measured with the pitch angle of 10^\circ at 2.39 GHz. Also, a two-element axial-mode antenna array was designed based on the miniature hexaferrite antenna to further improve antenna gain. Maximum gain of 4.5 dBi at 2.43 GHz was simulated for the antenna array. Therefore, high gain and miniature antenna can be achieved with the combination of Co2Z hexaferrite-glass composite and antenna design technology. [ABSTRACT FROM AUTHOR]

An array of ferrite and air-core inductors was fabricated on silicon wafer to characterize inductor performance. The 1 \mu\m and 2.5 \mu\m thick ferrite films for the fabrication of inductors were prepared by dc magnetron sputtering. The inductance of the ferrite inductor increased with the thickness of ferrite film from 45.5 nH for 1 \mu\m thick ferrite to 50 nH for 2.5 \mu\m thick ferrite. The maximum Q-factor was obtained to be 59 at 2.87 MHz from 2.5 \mu\m thick ferrite inductor, which is higher than 49.3 at 2.26 MHz for 1 \mu\m thick ferrite inductor and 23.2 at 1.56 MHz for air-core inductor. Superimposed dc current of 1 \mu\m and 2.5 \mu\m thick ferrite inductors was estimated to be 2.5 A and 2.15 A, respectively, corresponding to a 5% drop in L at 10 MHz. In addition, the power efficiency of the buck dc-dc converter based on the studied ferrite inductors was calculated to be 91.7% for 2.5 \mu\m thick ferrite inductor and 90.1% for 1 \mu\m thick ferrite inductor at load current of 0.647 A. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetic properties and ferromagnetic resonance (FMR) frequency of Ni0.7Mn0.3-xCoxFe2O4 ferrites (NiMnCo: x = 0.00, 0.04, 0.06, and 0.10) were controllable with the concentration of cobalt (Co). The measured saturation magnetization remains almost constant at 57 emu/g in the studied range of the Co content. However, the coercivity increased to 72 Oe (x = 0.10) from 12 Oe (x = 0.00). Ferromagnetic resonance frequency increased from 129 MHz to the GHz frequency with increasing the Co content from x = 0.00 to x = 0.10, but the real part of permeability decreased to 1.6 from 16.7. This is because FMR frequency increases with the magnetocrystalline anisotropy (Hk) of the Co according to fr = (γ/2π)Hk. The permeability decreased with the Co content by µ = 1 + (4πMs/Hk). Temperature coefficient, in the range of 20-100 °C, was 0.002 for Ni0.7Mn0.3Fe2O4 (x = 0.00) and 0.008 for Ni0.7Mn0.2Co0.1Fe2O4 (x = 0.10). The results suggest that Ni0.7Mn0.3-xCoxFe2O4 ferrites have excellent temperature stability, and also are applicable to very high frequency: 30-300 MHz) and ultra high frequency: 300 MHz-3 GHz) devices. [ABSTRACT FROM AUTHOR]

We have studied soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite for T-DMB (terrestrial digital media broadcasting) antenna applications. The effect of magneto-dynamic properties on antenna size, bandwidth, and radiation efficiency was investigated. The soft M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite (Co/Ti-substituted BaM) was synthesized by a combination of ball-milling and two-step sintering processes. Permeability and loss tan δµ of the Co/Ti-substituted BaM were measured to be 4.5 and 0.039 at 200 MHz, respectively. The Wheeler cap method and network analyzer were used to evaluate antenna radiation efficiency and measure return losses, respectively. Our experimental results show that the low-loss Co/Ti-substituted BaM is an excellent soft magnetic material for VHF (very high frequency: 30-300 MHz) miniature antenna applications. [ABSTRACT FROM AUTHOR]

We report a low magnetic loss Ba 3 Co 2 Fe 24 O 41 (Co 2 Z) hexaferrite for use in gigahertz (GHz) antennas. Acid-etching was very effective in removal of unwanted Y-type hexaferrite (Ba 2 Co 2 Fe 12 O 22 ) from calcined Co 2 Z powder. It is found that the calcined and acid etched (AE) Co 2 Z hexaferrite shows a low magnetic loss tangent (tan δ μ ) of 0.012 and 0.037 at 1 and 2 GHz, respectively. These low tan δ μ are attributed to removal of Y-type hexaferrite, which possesses a lower anisotropy field ( H k ) than W-type hexaferrite (BaCo 2 Fe 16 O 27 ). The figure of merit (FOM) of the AE Co 2 Z hexaferrite is 141.7 and 48.7 at 1 and 2 GHz, respectively. These FOM are much higher than the FOM of previously reported low-loss magnetic materials. Therefore, the AE Co 2 Z hexaferrite can be a good candidate for GHz antenna application in the ultra-high frequency (UHF) band. [ABSTRACT FROM AUTHOR]