Search

This paper introduces a localization protocol that fills a gap among already existing methods, such as ground penetrating radar or methods based on inductive prospecting. The principle is to attach a radio frequency identification (RFID) tag to a non-metallic object of interest buried in a non-magnetic soil and deduce its depth from the magnetic induction in the near field regime between the buried tag and an RFID antenna. Electromagnetic propagation in soils has been extensively studied in geophysics. The higher the frequency, the lower the penetration depth. The standard frequency range in geophysics is lower than 100 kHz to reach penetration depth as high as several tens of meters and the soil conductance is the main influencing factor. When working with passive RFID tags, their received power and, consequently, the detection range in air grows with the frequency. A frequency tradeoff for the detection in media lies in the range of 10–50 MHz, where the authorized RFID frequency is 13.56 MHZ. In this range, the wavenumber in weakly saline soils depends essentially on the medium dielectric permittivity (see). In this paper, we calculate the precision of the estimation of the burying depth of the tag in terms of the standard deviation and the corresponding bias up to two uncertain parameters—the penetration depth and the activation field. The laboratory experiments provide results supporting the chosen model. [ABSTRACT FROM AUTHOR]

With the development of new integrated circuits to interface radio frequency identification protocols, inductive air interfaces have become more and more important. Near field communication is not only able to communicate, but also possible to transfer power wirelessly and to build up passive devices for logistical and medical applications. In this way, the power management on the transponder becomes more and more relevant. A designer has to optimize power consumption as well as energy harvesting from the magnetic field. This paper discusses a model with simple equations to improve transponder antenna matching. Furthermore, a new numerical analysis technique is presented to calculate the coupling factors, inductions, and magnetic fields of multiantenna systems. [ABSTRACT FROM AUTHOR]

We propose a circularly polarized antenna with a wide axial ratio (AR) beamwidth that consists of a normally magnetized ferrite disk mounted on a ground plane. The device uses the resonant modes of the disk, which rotate only in the clockwise or counter-clockwise sense in the frequency range where the effective permeability of ferrite is negative. A semianalytical model is derived for the antenna fed by a single, conventional current probe and is validated numerically by finite element method. For a yttrium iron garnet disk with the radius and height of 5 and 1 mm, respectively, the results show a 3 dB AR beamwidth of 90^\circ with an operation frequency, which can be tuned in the 4–4.5 GHz range by varying the magnetic bias field from 50 to 35000 A/m. Simulations show that higher AR beamwidths are achievable using finite ground conductors. Compared with previous papers, the fabrication requirements on this structure are not critical, which enhances its potential applicability. [ABSTRACT FROM PUBLISHER]

The low-frequency electromagnetic radiated field is utilized in this paper for the purpose of condition monitoring and fault diagnosis of electric components. The main purpose is to build arrays of receiving coils that can detect and monitor the radiated electromagnetic field around the electric component and accordingly utilizing the measured fields in condition monitoring and fault diagnosis of various power components. A flexible 3-D printed coil antenna is proposed to be built, which will detect the fault of the electric machines. Primarily, finding the optimum location of the coil antenna to capture the most sensitive stray field from the components is the objective. Using finite-element method, the most sensitive location for the antenna is first identified for the field around the vicinity of the machine in healthy condition. Then, the radiated field of the machine is observed while short circuit occurred in the coil and winding inside the component. Variation in the amplitude of the harmonic orders of the radiated field helps in the identification of the short circuits. The results are then compared based on the variations of the amplitudes of the healthy and faulty fields and sent to the signal processing unit for diagnosis. As the practical implication of the study, the nonintrusive 3-D printed sensor provides the opportunity to locate the faulty winding in various electric components based on their electromagnetic signatures. [ABSTRACT FROM AUTHOR]

A new model of the radio frequency identification antenna using the solenoid coil, surrounded by a coaxial ferrite toroid, is proposed in this paper. The truncated region eigenfunction expansion method is adopted to derive the expressions of the magnetic vector potential. Besides, due to the low conductivity and high permeability of the ferrite, a convenient solution region division is introduced to avoid solving the transcendent eigenvalue equation caused by the end effect as usual. Numerical calculations are performed, and the results are in excellent agreement with those obtained from the finite-element method simulations. [ABSTRACT FROM AUTHOR]

This paper investigates the online fault detection (FD) of the inter-turn short-circuit (ITSC) fault in direct torque control (DTC)-driven induction motors (IMs). We conducted the investigations of harmonic, inter-harmonic, and sub-harmonic contents for FD purposes. The harmonics in the flux leakage spectrum appear as a result of diverse causes including stator fault, DTC reaction to the fault, switching activities, and core saturation effect. Physics-based co-simulation was held through the coupling between a finite-element model (FEM) of the faulty IM and the circuit simulation of DTC. Its advantages are: 1) the IM harmonic contents including stator slots, rotor slots, saturation, switching activity, and fault are simulated and 2) dangerous experimentations of a faulty IM can be avoided. Therefore, we can safely study all the characteristics on a faulty IM. We exploited FEM for the verification of the experimental harmonic signatures of the scattered magnetic field. We verified the online FD technique based on the radiated magnetic field’s spectrum through the co-simulation and experimental results. This indicated that the method is able to correctly detect the ITSC faults with 1% severity factor. [ABSTRACT FROM AUTHOR]

In this paper, we present the most recent results on the development of magnonic holographic memory (MHM). MHM is a type of holographic device, which uses spin waves for data transfer and processing. The most appealing properties of MHM include parallel read-out and database search. We present experimental data showing parallel read-out of four magnetic memory states. In this experiment, the internal magnetic state is recognized by the level of the output inductive voltage produced by the spin-wave interference. We also present the experimental data showing database search in the MHM. In this experiment, the search for the maximum output is accomplished by utilizing spin-wave superposition. The experiments were carried out for six- and eight-terminal yttrium iron garnet-based prototypes. Potentially, magnonic holographic devices can be implemented as complementary memory/logic units to digital processors. Physical limitations and technological constraints of the spin-wave approach are also discussed. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid algorithm based on the genetic algorithm (GA) and the evolution strategy (ES) for the electromagnetic optimization problem. The GA is not good enough at times in searching the optimal solution from the view point of the convergence speed and the solution quality, while the ES has the risk of being trapped in a local minimum. The hybrid algorithm is composed of GA and ES in order to make up for these defects. First, we reached the vicinity of optimal solution using the GA. Then, the ES is used to find the accurate optimal solution. The switching point can be a main issue, which is also resolved in this paper. First, the performance of the convergence speed and the solution accuracy are comparatively tested using the known functions. In addition, the optimized design of the 2.45 GHz coplanar waveguide-fed circularly polarized antenna is carried out as a practical application. Only the GA and the hybrid algorithm reach the satisfactory value, and the more rapid convergence can be shown by the ES in this hybrid method after 380 iterations. [ABSTRACT FROM AUTHOR]

In this paper, the problem of connecting the unbalanced measurement setup on the balanced antenna of the near-field communication (NFC) system is addressed. The parameters of the antenna’s equivalent circuit were determined using quasi-static and full-wave vector field finite element simulations. Measurements and simulations are carried out on three different prototypes of 13.56 MHz NFC rectangular four turns antenna printed on FR4 substrate material. The obtained results concerning the RLC equivalent circuit parameters show that a direct connection of the unbalanced measurement devices to the balanced antenna structure impairs the accuracy of the obtained measurement data because of the mode mismatch at the antenna terminals. [ABSTRACT FROM PUBLISHER]

In this paper, soft magnetic Mn–Zn ferrite samples have been prepared through oxide processes. The magnetic properties and the phase structures were investigated. It was found that the optimal sintering temperature is about 1360 °C. The initial permeability of the samples is 1700–2300, Curie temperature Tc is about 140 °C−180 °C, and cutoff frequency fr is about 1 MHz. Moreover, the initial permeability of the samples is relatively stable, and its temperature coefficient is \sim 10^-6 /°C at the temperature range of 20 °C−60 °C. High-frequency simulation results show that the Mn–Zn ferrites samples are suitable for the application of the wireless sensor networks in theory. [ABSTRACT FROM AUTHOR]

This paper presents and discusses a comparative numerical and experimental analysis of the electromagnetic (EM) phenomena arising in a laboratory phantom radiated by a radio-frequency field, simulating the exposure in a magnetic resonance imaging (MRI) context. A specific frequency-domain coupled finite element-boundary element solver, running in graphical processing unit environment, has been developed to analyze the EM effects as well in the presence of metallic objects simulating prosthetic implants. The experimental setup consists of an antenna radiating a cylindrical box filled with a tissue simulating liquid; a bulk metallic parallelepiped can be included to mimic the presence of a prosthesis. [ABSTRACT FROM AUTHOR]

This paper presents a practical methodology of obtaining a robust optimal solution for a multi U-slot PIFA (Planar Inverted F-Antenna) structure with triple bands of 433 MHz, 912 MHz and 2.45 GHz. Using evolutionary strategy, a global optimum is first sought out in terms of the dimensions of the slots and shorting strip. Then, starting with the optimized values, Taguchi quality method is carried out in order to obtain a robust design of the antenna against the changes of uncontrollable factors such as material property and feed position. To prove the validity of the proposed method, the performance of the antenna is predicted by general-purpose electromagnetic software and also compared to experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a novel 13.56 MHz microantenna using the microelectromechanical system technology is presented. The microantenna consists of a solenoid-type coil and a high-performance NiZnCu ferrite sheet magnetic core. The overall size of the microantenna is $< 10 \,\, \times \,\, 6.7 \,\, \times \,\, 0.46$ mm3. Test results show that the relative permeability of the ferrite sheet magnetic core reaches 156, and the tangent of loss is \sim 0.036$ at 13.56 MHz. The microantenna is designed and simulated using the high-frequency structure simulator software. The measurement results show that the sensitivity of the microantenna reaches up to 288.6 mV/ \mu \text{T} , and the communication distance is 52 mm with the power consumption of only 100 mW. [ABSTRACT FROM AUTHOR]

Finite-element techniques are applied to the frequency response computation of the input impedance of antennas with the eddy current losses taken into account. Both time-domain and frequency-domain approaches are discussed. Comparison to results for a dipole patch antenna with T-match obtained by assuming infinite conductivity is presented. [ABSTRACT FROM AUTHOR]

Functional electrical stimulation (FES) is a type of therapy used for paralyzed patients. In FES, the implant direct feeding method is an ideal stimulus method. In this method, small stimulators are implanted in the paralyzed limbs, and magnetic coupling is used to simultaneously power the implants and enable digital communication with the mounted system. To realize this method, we have developed an implant antenna (magnetic connective dual-resonance antenna) that can transmit as well as receive signals and a mounted communication system that is responsible for supplying power and communication from outside the body to the implanted antenna inside of the body. However, to guarantee safe stimulation, this system requires the closed-loop control function. For this purpose, we have proposed a communication protocol that is inexpensive, and a new communication system that supports bidirectional communication. In this paper, we present the new protocol, the composition and mechanisms of the proposed system, and the experimental results that verify the efficiency of this system. [ABSTRACT FROM AUTHOR]

In this paper, a new boundary formulation for the computation of the current and electromagnetic fields on a printed circuit antenna is presented. The state variables are the surface current density j on the metal, the electrical field e on the dielectric boundary, and the magnetic field h on the total boundary of the materials. We obtain very good results in a shorter central processing unit (CPU) time than with classical EFIE and MFIE formulations. [ABSTRACT FROM AUTHOR]

In this paper, a new time-domain integral equation solution method for arbitrarily shaped, perfectly conducting thin-wire antennas is presented. The space-time discretization of the circumferentially invariant electric current along the wire axis is achieved by employing higher order hierarchical polynomials for the spatial basis functions and discretely causal piecewise polynomial interpolation functions for the temporal basis functions. The solution of the transient current along the wire is obtained by marching-on-in-time (MOT). The hierarchical nature of the spatial basis functions enables the efficient assembly of the space-time impedance matrices. Rigorous evaluation of the time-domain wire kernels is presented. Numerical test cases demonstrate the validity, accuracy, and applicability of the new method. [ABSTRACT FROM AUTHOR]

An enhanced 3-D alternating-direction implicit finite-difference time-domain method for the systematic analysis of double negative metamaterial-based waveguide and antenna devices is presented in this paper. Being fully frequency-dependent, the new scheme introduces a set of generalized multidirectional operators which incorporate the suitable Lorentz-Drude model and subdue inherent lattice deficiencies for broad spectra. So dispersion errors, as time-steps exceed the Courant limit, are drastically minimized yielding fast and accurate solutions for propagating and evanescent waves. The technique is applied in the design of microwave structures, realized via the prior model or networks of thin wires and split-ring resonators. Numerical results certify its merits, without requiring elongated simulations and excessive overheads. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is one of the next generation data storage technologies that aims to increase the areal data density to beyond 1 TB/in2. Near-field transducer (NFT), which is a type of plasmonic nanoscale antenna, is a key component of the HAMR system. The laser in an HAMR system typically operates in the near infrared wavelength range between 700–900 nm. We explore the plasmonic behavior and performance of a number of NFTs at longer wavelength of 1550 nm. The different plasmonic modes in the NFTs at different wavelengths are analyzed, and the correlation of the NFT performance with variations in the geometrical design is investigated. Thermal performances of NFT are also studied and compared with the thermal performances when NFTs are operated near 800 nm. It is found that there is a significant improvement in the figures of merit when using longer wavelengths and this can provide an important strategy to realize higher performance data storage devices. [ABSTRACT FROM PUBLISHER]

Monodomain NiCuZn ferrites were investigated for use in the design of a high-efficiency terrestrial digital multimedia broadcasting antenna with reduced physical dimensions. The results show that the reported monodomain design is effective. Specifically, monodomain ferrite with 1 wt% Co2O3 doping has a high miniaturization factor (~14) and very low loss factors (tan $\delta _{{\mu }} = 0.017$ and tan $\delta _{{\varepsilon }} = 0.012$ , respectively). It also reveals equivalent permeability and permittivity ( $\mu ^\prime = 14.05$ and $\varepsilon ^\prime = 14.12$ , respectively) at the frequency of 200 MHz, implicating the convenient impendence match in the antenna application and consequent miniaturization. The magnetic spectra of the monodomain samples were studied with a numerical fitting method to obtain guidelines for preparing high-quality materials. The results indicate that it is necessary to lower relaxation frequency $\omega _{{{\text{r}}}}$ and maintain the other dispersion parameters as moderate to achieve a high real part of permeability and low tan $\delta _{{\mu }}$ . Furthermore, we demonstrate that appropriate Co2O3 doping is a feasible way to adjust the dispersion parameters. [ABSTRACT FROM AUTHOR]

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]

Heat-assisted magnetic recording (HAMR) is the next-generation data storage technology that can address the challenge of increasing data storage capacity. The key to the design of an HAMR system is the near-field transducer (NFT) that focuses light to a very small scale in the range of tens of nanometers with a very high intensity. This is also associated with unwanted self-heating of the NFT, which is detrimental to the functionality of the NFT, and hence there is a need to improve NFT designs. We investigate a third dimension in the typical planer NFT design by introducing a taper in the model of an E antenna NFT design and study its effect on the optical and thermal performances of the NFT. We find that the proper optimization of the taper geometry gives rise to improved operation of the NFT. In addition, in terms of thermal figures of merit, its performance is also significantly superior. [ABSTRACT FROM PUBLISHER]

In this work, a simple method is proposed to simultaneously reduce the size and cross-polarization level (XPL) of quarter-wave microstrip antennas by reconstructing the magnetic currents along the radiation edges. A design example of five shorted elements is given with a comparison of the quarter-wave microstrip antennas at 1.88 GHz. Measured results show an over 64% size reduction and 17-dB cross-polarization suppression enhancement for the proposed scheme as compared with the conventional one. Moreover, the proposed scheme exhibits good broadside radiation patterns with a gain of 5.4 dBi and the half-power beamwidths of about 104° in the E-plane and 84° in the H-plane. [ABSTRACT FROM AUTHOR]

The magnetic and dielectric properties of the composites Ni0.35Cu0.18Zn0.45Co0.02Fe1.95O4 + x wt% BaTiO3(x = 0, 5, 10, 15, 20, 25) were investigated. All samples were sintered at 1080 °C for 3 h to obtain approximately equal real permeability and permittivity. X-ray diffraction results indicated that there had no obvious reaction between the NiCuZnCo ferrite and the BaTiO3 in all samples. BaTiO3 powder could obviously suppress grain growth of the composites. The sample Ni0.35Cu0.18Zn0.45Co0.02Fe1.95O4 + 15 wt% BaTiO3 presented a real permeability of $\sim 29$ (loss tangent $\sim 0.02$ ) and a real permittivity of $\sim 28.3$ (loss tangent $\sim 0.002$ ), respectively, over 3–30 MHz. This composite material had potential prospects in antenna miniaturization at HF band (3–30 MHz). [ABSTRACT FROM AUTHOR]

The possibility of tuning the magnetic properties of materials with voltage (converse magnetoelectricity) or generating electric voltage with magnetic fields (direct magnetoelectricity) has opened new avenues in a large variety of technological fields, ranging from information technologies to healthcare devices and including a great number of multifunctional integrated systems, such as mechanical antennas, magnetometers, and radio frequency (RF) tunable inductors, which have been realized due to the strong strain-mediated magnetoelectric (ME) coupling found in ME composites. The development of single-phase multiferroic materials (which exhibit simultaneous ferroelectric and ferromagnetic or antiferromagnetic orders), multiferroic heterostructures, as well as progress in other ME mechanisms, such as electrostatic surface charging or magneto-ionics (voltage-driven ion migration), have a large potential to boost energy efficiency in spintronics and magnetic actuators. This article focuses on existing ME materials and devices and reviews the state of the art in their performance. The most recent progress on different ME devices based on ME heterostructures is presented but with a larger emphasis on ME antennas and sensors due to the significant advances achieved in these applications. The rapid development of mechanically actuated ME antennas has been observed over the past several years, producing ME antennas that are miniaturized by 1–2 orders compared to conventional antenna size. Magnetic sensors based on simple ME composites are potentially promising alternatives to conventional magnetometers due to their very good detectivity (

A number of systems require high-resolution, non-perturbative thermal mapping. This need is especially apparent for heat-assisted magnetic recording (HAMR), a technology developed to increase the areal density of magnetic storage. In HAMR, plasmonic antennas are used to heat magnetic media by hundreds of degrees in a nanoscale region. Understanding the antenna’s temperature is critical, but the available methods for high-resolution thermal mapping are dominated by experimental artifacts. In order to measure the temperature distributions of a plasmonic antenna without a major perturbation, a new technique, polymer imprint thermal mapping (PITM), was developed, which relies on the thermal response of a thin polymer film to report temperature. The polymer permanently cross-links upon heating, so the thermally induced height change of the polymer film is directly correlated with the sample temperature. It is experimentally shown that PITM creates thermal maps that are far superior to conventional scanning thermal microscopy. In addition, the modeled thermal distributions show remarkable agreement with the measured PITM thermal maps. [ABSTRACT FROM AUTHOR]

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 \mu^\prime at low frequencies is improved from \sim10 to \sim19, while the real permittivity \varepsilon^\prime varies slightly with value around 14. The sample with x=65 wt % has almost equal values of \mu^\prime and \varepsilon^\prime, 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. [ABSTRACT FROM AUTHOR]

Low-loss Ni-Zn porous ferrite ceramics have been obtained (porosity close to 40%) after appropriate heat treatment and shaping of nanosized powders. The key point in this process is a moderate reaction sintering that promotes desired value of porosity. Measured complex permeabilities and permittivities in the [10^7\ \Hz–10^10\ \Hz] frequency range are presented. The developed materials show almost constant refractive index value n close to 5 up to 900 MHz. The sum of the magnetic and dielectric losses shows moderate values up to a frequency value f, unusual for spinel ferrites: \tan\delta\mu+\tan\delta\varepsilon<0.083 at f=600\ MHz. Their efficiency for miniaturization and performances improvement of several new antennas for Digital Video Broadcasting Handheld (DVB-H) devices (frequency ranging: 470–862 MHz) are presented. High miniaturizations (about 40% to 60% when compared to not loaded antenna) are obtained. Low loss, wide bandwidth and good radiation efficiency are measured. Antennas performances are enhanced. A new antenna is also presented. Its dimensions are very small and it covers the entire DVB-H band. Suitability of Ni-Zn porous ferrites ceramics for antenna miniaturization for DVB-H applications is demonstrated. [ABSTRACT FROM AUTHOR]

Miniaturized 0.026 λ Co2Z hexaferrite and Ni-Mn-Co spinel ferrite T-DMB antennas were fabricated and characterized for antenna performance. The Co2Z hexaferrites were prepared with two different processes that are water quenching and air cooling. The water quenched Co2Z hexaferrite antenna shows - 6.5 dB of 3-D average gain at 190 MHz and 37 MHz of bandwidth at -10 dB. A magnetic tangent loss of water-quenched Co2Z hexaferrite was lower than that of air-cooled Co2Z hexaferrite. Compared to the hexaferrite antennas, the Ni-Mn-Co ferrite antenna shows higher frequency performance. Its gain and bandwidth were measured to be - 5.83 dB at 215 MHz and 41 MHz, respectively. Omnidirectional gain pattern was observed from all fabricated ferrite antennas. [ABSTRACT FROM AUTHOR]

If N ports are defined on the moment method model of a radiating structure, so-called characteristic port modes may be computed, using the moment method operator matrix, with respect to these ports. This results in N port excitation vectors (each of length N). Each vector excites a radiated field which is orthogonal to the fields excited by any of the other N excitation vectors. It is shown that this may be usefully employed in the design of antennas for multiple-input multiple-output (MIMO) communications, and that recent multimodal/multipolar approaches for MIMO antenna design may be interpreted in terms of such port modes. [ABSTRACT FROM AUTHOR]

An extended polarization-dependent generalized characteristic-mode theory for a radiating structure is given. We show how these modes can be computed and employed in the design of closely located multiple-input multiple-output multiantenna sets with low interantenna envelope correlation and good mean effective gain under realistic incoming power distribution scenarios found in mobile communications. [ABSTRACT FROM AUTHOR]

The iterative absorbing boundary condition (IABC) is a flexible and accurate way of truncating the computational domain for finite-element analysis of electromagnetic wave scattering, particularly when the element orders are adjusted carefully to minimize overall computational cost. The method is here extended to antenna problems, taking into account the feed modeling. Discretization and boundary errors in the feed reflection coefficient or in-the radiated field are balanced during the iteration. Results for a waveguide terminated in a flange, a horn antenna, and a microstrip patch antenna demonstrate the accuracy of the approach, and the computational savings relative to the use of the same element order during the whole iteration. [ABSTRACT FROM AUTHOR]

A magnetic material with high permeability and low loss characteristics at high frequency is required for miniaturizing electronic components such as antennas. The key factors to keeping low magnetic loss are a high magnetic resonance frequency and the suppression of the eddy currents. We have fabricated a low-loss magnetic composite material by dispersing Ni78Fe22 (permalloy) fine flakes in polymers; the thickness of the flakes was less than skin depth. The magnetic loss decreased with increased stirring time, and the minimum value occurred when the agglomerated particles decreased and most of the particles were deformed into flakes. Moreover, Zn5Ni75Fe20 composite material indicated high permeability when the flakes were oriented in the direction of sheets. The effect of wavelength shortening by permeability enhancement and the low loss characteristic were confirmed by experimental results of a rod antenna loaded with the developed magnetic composite material. [ABSTRACT FROM AUTHOR]