Wall Resonance Research Articles

Resonance sonomanometry for noninvasive, continuous monitoring of blood pressure.

Cardiovascular disease is the leading cause of death worldwide. Existing methods for continuous, noninvasive blood pressure (BP) monitoring suffer from poor accuracy, uncomfortable form factors, or a need for frequent calibration, limiting their adoption. We introduce a new framework for continuous BP measurement that is noninvasive and calibration-free called resonance sonomanometry. The method uses ultrasound imaging to measure both the arterial dimensions and artery wall resonances that are induced by acoustic stimulation, which offers a direct measure of BP by a fully determined physical model. The approach and model are validated in vitro using arterial mock-ups and then in multiple arteries in human subjects. This approach offers the promise of robust continuous BP measurements, providing significant benefits for early diagnosis and treatment of cardiovascular disease.

Crystal structure, microstructure, and magnetic properties of Ba3-xNdxCo2Fe24O41 hexaferrite ceramics with enhanced magnetic anisotropy

Crystal structure, microstructure, static and dynamic magnetic properties of Ba3-xNdxCo2Fe24O41 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were investigated. Samples were prepared via sintering at 1250 °C for 4 h, and XRD results revealed their crystal structure after Nd substitution. With the increase in Nd3+ ion dopant content, particle porosity increased, leading to slight decrease in volume density. Static magnetic data showed the weak effect of Nd-substitution on saturation magnetization strength and a slight increase in coercivity (from 52 Oe to 75 Oe at x = 0–0.5), while out-of-plane magnetic anisotropy rose significantly (from 10.1 kOe to 14.5 kOe at x = 0–0.5). Dynamic magnetic tests demonstrated noticeable decrease in permeability (from 17 to 8), whereas cutoff frequency increased from 0.8 GHz to 1.9 GHz and the maximum Snoek product reached 18.8 GHz for the sample with x = 0.4. The fitting of real part of permeability using domain wall resonance and natural resonance models revealed that resonance frequency and out-of-plane anisotropy both increased with Nd-substitution. Moreover, despite Nd doping, samples maintained low magnetic loss and high Q value within higher frequency range. Therefore, findings of this study provide a pathway to development of substituted Z-type barium (Co2Z) ferrites for high frequency applications.

Envisioning the structural and room temperature impedance spectroscopy study of praseodymium modified lanthanum ferrites

Praseodymium-modified lanthanum ferrites with general formula La1-xPrxFeO3 [x = 0.0, 0.1, 0.3, 0.5] were prepared using the sol-gel auto combustion technique. The X-ray diffraction patterns of all samples supported the orthorhombic crystal structure with the Pbnm space group. With increasing Pr concentration, it was discovered that the average crystallite size dropped from 44.29 to 29.83 nm. An LCR metre was used to evaluate the frequency-dependent dielectric characteristics between 100 Hz and 1 MHz at room temperature. A single semicircle on the Nyquist plots highlights the impact of grain resistance on electrical behaviour. The depressed semicircles at intermediate frequencies might be created by the grain boundary effect, while semicircles depressed at high frequencies imply grain conduction. The dielectric behaviour of lanthanum ferrites is explained based on Koop’s theory. The loss factor resulting from domain wall resonance displayed the same dielectric constant dispersion behaviour. At high frequencies, orthoferrites were shown to have lower dielectric losses. This is due to the constrained motion of the domain wall, which suggests that magnetically tunable filters and oscillators are possible practical uses.

Study on the influence of the degree of the easy-plane orientation on the high-frequency magnetic properties and power loss of SMC in the MHz band

The effects of the degree of the easy-plane orientation on soft magnetic composite (SMC) are studied, utilizing the α-Fe easy-plane soft magnetic composite (α-Fe EPSMC) as the study system. The relationships between the degree of the easy-plane orientation (DEPO) and magnetic properties as well as power loss are studied. It is found that the magnetic properties and the power loss are significantly improved with DEPO increasing. The permeability increases from 22 to 45, the domain wall resonance frequency increases from 22 MHz to 210 MHz, the natural resonance frequency increases from 0.125 GHz to 1.36 GHz, the frequency stability increases from 3 MHz to 100 MHz. The power loss decreases from 6560 kW/m3 to 568 kW/m3 (5 MHz, 8 mT). In addition to the obvious improvement in properties, it is more important to establish relationships between the DEPO and power loss. It is found that the DEPO is inversely proportional to the hysteresis loss and the excess loss. The high DEPO mainly achieves the decrease of hysteresis loss and excess loss by decreasing the angle between the magnetization vector and external magnetic field and increasing domain wall resonance frequency. This study proposes a novel type of SMC (α-Fe EPSMC) with ultra-low power loss and excellent magnetic properties. It is more important that this study provides new ideas and methods for decreasing the power loss of SMC in the MHz band and studying the power loss mechanism of SMC in the MHz band.

The excess loss analysis of an easy-plane FeSiAl@SiO2 soft magnetic composite with high permeability

The loss coming from the special eddy current caused by the inhomogeneous domain wall motion is usually used to explain the complex mechanisms of the excess loss below 200 kHz. In this work, an easy-plane FeSiAl@SiO2 SMC was fabricated to analyze the core loss. The prepared easy-plane FeSiAl@SiO2 SMC exhibits an initial permeability of 816 at 1 MHz and a domain wall resonance peak of 5.9 MHz. The core loss was measured up to 3 MHz and was separated into hysteresis loss, classical eddy current loss and excess loss. The excess loss was deeply analyzed by the theory of G. Bertotti. The results show the excess loss caused by localized eddy curreny is the main component of core loss in the range of 200 kHz to 3 MHz, and the domain wall resonance also exhibits the contribution on the core loss in the MHz band.

Structure Design, Surface Modification, and Application of CNT Microwave‐Absorbing Composites

AbstractElectromagnetic (EM) contamination has now become a non‐negligible problem. To solve the EM contamination problem, it is imperative to develop high‐efficiency absorption materials with thin thickness, light weight, strong absorption properties, and broad absorption bands. Carbon nanotubes (CNTs) have a special helical structure and chirality, which will lead to special EM effects and therefore can absorb EM microwaves through magnetic polarization attenuation such as hysteresis loss, domain wall resonance, and aftereffect loss. Moreover, they have the characteristics of light weight, good compatibility, wide absorption frequency band, and high electrical loss angle tangent. In this paper, the different structures of CNT microwave‐absorbing composites are reviewed and the effects of the composite structures on the microwave‐absorbing properties are systematically discussed. The methods and mechanisms of surface modification of CNT absorber composites and the effects of modification on the absorber properties are summarized in detail. The progress of two specific CNT microwave‐absorbing composites, namely flexible and high‐temperature microwave‐absorbing composites, is briefly described. The shortcomings and challenges in the application of CNT microwave‐absorbing composites are described and future research directions for CNT microwave‐absorbing composites are explored.

High-frequency magnetic properties of FeB nanochains based soft magnetic composites for potential antenna applications up to GHz

Soft magnetic materials are a kind of promising materials for antenna substrates because their permeability and permittivity are both greater than unity. However, their magnetic properties would deteriorate dramatically as the frequency reaches 1 GHz owing to Snoek limit and domain wall resonance, thus limiting their application at high frequency. Here, we report a low-dimensional soft magnetic composite (SMC) prepared by FeB nanochains, achieving the optimized magnetic loss tangent (tanδμ) of 0.09 and the real part of permeability (μ′) of 3.3 at 1 GHz, which is more competitive than the conventional spherical FeB SMCs. Such an optimization is ascribed to the change in the dominant mechanism of the magnetization process from domain wall motion to magnetic moment precession, associated with the transition of the magnetic domain structure of the particles from multi- to mono-domain. The SMC proposed in this work provides a significantly potential candidate for high-frequency and miniaturized 5G antennas. Furthermore, the design concept and preparation method can be extended to other SMCs, providing a guidance for the development of high-performance antenna substrate materials.

Foamed concrete composites: Mn–Zn ferrite/carbon fiber synergy enhances electromagnetic wave absorption performance

In order to achieve multi-functional integration of materials and reduce electromagnetic pollution in the building environment, this paper uses foam concrete as a base, combined with magnetic loss absorbing material Mn–Zn ferrite (MZF) and resistance absorbing material carbon fiber to prepare a composite material with outstanding electromagnetic wave (EMW) absorption performance. The EMW absorption performance and mechanisms of the composites in the 0.2–5 GHz frequency range were studied, and the mechanical properties, hydration products, aperture parameters, and conductivity of the composites were analyzed. The results demonstrate that the magnetic loss of MZF in composites primarily comes from eddy current loss, domain wall resonance loss, and natural resonance loss. The combination of MZF and carbon fiber not only synergizes the electromagnetic loss capability, but also improves the impedance matching of the composite material, significantly enhancing the EMW absorption effect. The minimum reflection loss of the composite material in the tested frequency band is −28.75 dB (2.10 GHz, thickness 10 mm) and the effective absorption bandwidth is 1.46 GHz (2.29–3.75 GHz) at a thickness of 5.8 mm.

Particles size-dependent magnetic properties of a FeSiAl soft magnetic composite with hybrid insulating coating for MHz applications

In this work, organosilane modified water-soluble silicone resin coated spherical-FeSiAl soft magnetic composites with different particle sizes were prepared, and the effects of the particle size on the permeability, magnetic loss, and DC bias were investigated. For large particles composite, multi-domain lead to the introduction of domain wall resonance, which restricts the permeability in low frequency. As the particle size decreases, the particles tend to be single domain particles resulting in a decrease of the domain wall resonance component and an enhancement of the spin rotation one. Two stages with different loss mechanisms were investigated and the sudden increase of the loss near 70 kHz is ascribed to the short circuit of the insulating coating in high frequency due to the space charge polarization. Furthermore, electrochemical analysis also demonstrates the insulation of this soft magnetic composite. This ultrafine FeSiAl composite may promote the development of MHz frequency semiconductor power devices.

Magnetic and absorption properties in hundreds of megahertz band for a FeSi@SiO2 composite with brick stacking structure and crystallographic orientation

Electromagnetic (EM) pollution in the 0.1–1 GHz band is increasing with the rapid advancement in 5G communication technology. However, there are barely any absorption materials in the said band. Herein, we report a high-performance EM wave absorption composite with brick stacking structure and crystallographic orientation prepared using flake-like FeSi@SiO2 particles. The permeability of this composite with such novel structure is increased by more than ten times compared with conventional composites, reaching 42 at 1 MHz. The reflection loss (RL) can reach −40 dB around 0.3 GHz and the effective absorption bandwidth (RL 〈−10) can cover 0.2–1 GHz, which is significantly better than previous reports. Such a high permeability is ascribed to easy magnetization plane and low demagnetization factor parallel to the flake-like particles plane. The excellent absorption is attributed to the intrinsic loss introduced by the enhanced domain wall resonance, and the interference loss generated by quarter-wavelength cancellation. Particularly, the composite proposed in this study has great business and application value in the field of EM wave absorption, and the preparation method can be extended to other EM wave absorption composites, which provides a considerable guidance for the preparation of magnetic metallic absorption composites.

Radar-absorbing composite materials based on ferrite powders

The paper studies the effect of particle sizes of hexagonal ferrite powders on their electrodynamic properties. SrTi0.2Co0.2Fe11.6O19 and BaSc0.2Fe11.8O19 hexaferrites were used as the objects of research. Grinding in a high-energy planetary mill for up to 60 minutes made it possible to obtain hexaferrite powder particles with the average size successively decreasing from 1.5–2 μm to 0.05–0.15 μm. A scanning electron microscope was used for the analysis. Samples were prepared in a mixture with a polymer binder (70% ferrite + 30% polymer), and their electromagnetic radiation (EMR) absorbing capacity was studied in the microwave range from 30 to 50 GHz. It was shown that there is practically no peak corresponding to ferrimagnetic resonance in the composite with ferrite, with a decrease in the average particle size of BaSc0.2Fe11.8O19 hexaferrite powders to 50–150 nm. The dependences of the real and imaginary parts of the magnetic permeability and dielectric constant are given in the frequency range from 107 to 109 Hz. There was no domain wall resonance in the frequency dependence of magnetic losses for a ferrite-based composite mechanically activated for 60 min. SrTi0.2Co0.2Fe11.6O19 ferrite was milled in a bead mill to particles with an average size of 150–300 nm, and then to drying, pressing, sintering at 1360 °С and subsequent grinding to a size of 200–500 μm to obtain similar composites in a bond with a polymer. It was found that the properties of compositions change significantly with a change in the magnetic component synthesis technology: no resonant pattern of EMR absorption was observed. The Curie temperature was measured using the Faraday method. It was shown that it is ~340 °С for the studied material. Therefore, the effect of precursor milling on changes in magnetocrystalline anisotropy was identified.

Effects of nitriding and Ni doping for the frequency of domain wall resonance peak and high-frequency magnetic performance of easy-plane Y2Fe17

Rare earth soft magnetic alloys have potential in high frequency applications due to strong easy-plane anisotropy. As the research progressed, a new resonance peak in the MHz frequency band, the domain wall resonance peak was observed, which seriously affects applications of magnetic materials in power device. A way to decrease it is by increasing domain wall resonance frequency (fdw). In this paper, the composites of easy-plane Y2Fe17 and polyurethane were presented and the easy-plane Y2Fe17 were treated by nitriding and doping. It is found that both nitriding and doping are effective in increasing the permeability. And the frequency of domain wall resonance peaks is varied due to the variation in exchange interaction by nitriding and doping. These results provide insight into soft magnetic properties of soft magnetic composites (SMCs) in the MHz frequency band, particularly for SMCs in power devices applications.

Static magnetic, complex dielectric and complex permeability properties of aluminum substituted hexagonal barium ferrites based on doping concentration

The regulation of magnetic and dielectric properties for hexagonal barium ferrites by ion doping is highly desirable in magnetic recording and microwave absorption. Herein, aluminum (Al)-substituted barium hexaferrite with the general formula of BaFe12−xAlxO19 (x: 0, 0.6, 1,2, 1.8) was obtained. The influences of the Al3+ doping concentration on the crystal structure, microstructure, static magnetic, complex dielectric and permeability properties of hexagonal barium ferrites were studied. The morphologies and crystal structure characterizations confirm the Al3+ ion has effective doping in the hexagonal barium ferrites and substituted for Fe3+ in positions of 2b site. The lattice parameters and grain size of the hexagonal barium ferrites were dependent on the doping concentration. The magnetic characterization displays the saturation magnetization decrease while the coercivity increase with the doping concentration. The high-value about 8249 Oe of coercivity can be obtained at x = 1.8. The dielectric properties measurement further indicates that Al doping could improve both real and imaginary parts of permittivity. The highest value of the real part of permittivity was obtained at x = 1.2. Lastly, the complex permeability spectrum displayed the doping of Al ions not only regulate the complex permeability but also influence the domain wall resonance frequency, which is significant for controlling the application frequency.

Wide band direct on-chip EMI shielding layer with metallic/magnetic multilayer

A new type of direct on-chip electromagnetic interference (EMI) shielding layer for the 10 MHz to 1 GHz frequency range is investigated. A multilayer system consisting of non-magnetic metal layers and magnetic layers is found to exhibit a larger shielding effect than a conventional Cu layer owing to multiple reflections of electromagnetic waves. A multilayer stack of Cu (400 nm)/[Ta (5 nm)/Ni-Fe-Cu-Mo (50 nm)]4/Cu (400 nm) is found to exhibit a larger shielding effect than Cu (3 µm) in the frequency range of 200–400 MHz. A Ta break layer is found to reduce the coercivity of Ni-Fe-Cu-Mo layer and contribute to enhancing the peak in this frequency range. Another type of multilayer stack of [Cu (100 nm)/Ni-Fe-Cu-Mo (100 nm)]10 is found to exhibit a larger shielding effect than Cu (3 μm) over the wide frequency range of 20 MHz to 1 GHz. One remarkable feature of this sample was a peak in the shielding effect at around 60 MHz. The combination of this peak with the ferromagnetic resonance peak creates a wide-band shielding effect. Weak magneto-static coupling between magnetic layers may contribute to the peak at 60 MHz via domain wall resonance. By using these multilayer structures, a thin direct-on-chip shielding layer that covers a wide frequency range can be obtained. This technology is suitable for application in mobile devices and electric vehicles, where EMI in the MHz range, which is due to switching power modules is an issue.

The preparation and high-frequency electromagnetic properties of Co80Ni20 alloy particles for potential antenna applications

A magneto-dielectric substrate material with high permeability and low loss at high frequency is necessary for a miniaturized antenna. Keeping the loss low is essential, in order to restrain the eddy current effect and to possess a high magnetic resonance frequency. In this work, the effects of the NaOH concentration and soaking time on crystal structures and morphologies of Co80Ni20 alloy particles are studied based on a polyol process. The results reveal that the size of particles increase with the promotion of the concentration of NaOH and soaking time. The electromagnetic (EM) properties of Co80Ni20 alloy particles/ polyurethane composites with various soaking times are studied at the NaOH concentration of 1.5 mol/L. The results reveal that the real part of permeability (μ'), the real part of permittivity (ε'), the magnetic loss tangent (tanδμ), the dielectric loss tangent (tanδε) of the composite with the soaking time of 3 h are 2.0, 11.0, 0.09, and 0.057 at 1 GHz, respectively, and the eddy current effect is suppressed effectively. The calculation of the permeability shows that the composite possesses a high domain wall resonance frequency. This work is significant for developing a magneto-dielectric substrate material using at 1 GHz.

Structure, electromagnetic and dielectric properties of Ti-substituted lithium--zinc ferrite

Li0.35+0.5xZn0.3TixFe2..35–1.5xO4 (x = 0–0.4) ferrites waere prepared via a solid-state method. XRD refinement results show that diamagnetic Ti4+ ions enter octahedral lattice and replace Fe3+ at B site, resulting in the redistribution of B sublattice magnetic moment and ultimately reducing saturation magnetization. This mechanism is analyzed from the perspective of ion occupying distribution and substitution law. Globus relation is used to qualitatively analyze the law of initial permeability change with temperature and titanium content, and the main influencing factors are revealed. The variation of initial permeability and permeability loss with frequency and its causes have been explored, which are attributed to domain wall displacement, domain rotation and various resonance effects, especially domain wall resonance. The dominant characteristics and main influencing parameters of the three types of power losses in different frequency bands were studied quantitatively, and the transition law of the main mechanism of power losses with the change of frequency was explored. The variation of dielectric properties with frequency, titanium content and temperature was studied and analyzed utilizing polarization mechanism and Koops model.

Fabrication of heterostructure composites of Ni-Zn-Cu-Ferrite-C3N4-Poly(vinylidene fluoride) films for the enhancement of electromagnetic interference shielding effectiveness

In this report the emphasis has been given on the influence of carbon nitride (C3N4) semiconducting fillers for the enhancement of the electromagnetic interference shielding effectiveness. This is the first ever report where the inexpensive composite nanomaterials of Ni-Zn-Cu-Ferrite-C3N4-Poly(vinylidene fluoride) are fabricated by very simple solution casting method. Structural and chemical studies have confirmed the presence of all the required phase of the component materials in the heterostructure composite films. The magnetic NZCF nanoparticles are responsible for the generation of the high magnetic loss in terms of domain wall resonance. Also, C3N4 semiconducting fillers all around the NZCF nanoparticles and the interactions between these binary nanofillers and the β-phase reach PVDF matrix are responsible for the generation of polarization loss, conduction loss and eddy current loss by their interactions with the electromagnetic (EM) wave of GHz frequency range. The presence of these binary nanofillers (Ni-Zn-Cu-Ferrite-C3N4) inside the matrix of PVDF are responsible for the improvement of the shielding effectiveness due to absorption and shielding effectiveness due to reflection. High value of total shielding effectiveness of −71.5 dB and −88 dB has been observed corresponding to the X-band and Ku-band for these NZCF-C3N4-PVDF composite films. Such high value of attenuation of >99.999999% and the corresponding wide bandwidth of NZCF-C3N4-PVDF composite films offers a completely new insights for the fabrication of microwave absorber to combat against electromagnetic pollution.

Structural and Magnetic Properties of NiZn Ferrite Nanoparticles Synthesized by a Thermal Decomposition Method

Ni1−xZnxFe2O4 (x = 0.5, 0.6, 0.7) nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by X-ray diffraction analysis, and they were calculated to be 46–51 nm in diameter by the Scherrer equation, depending on the composition. In the FE-SEM image, the ferrite nanoparticles have spherical shapes with slight agglomeration, and the particle size is about 50 nm, which was consistent with the value obtained by the Scherrer equation. The lattice parameter of the ferrite nanoparticles monotonically increased from 8.34 to 8.358 Å as the Zn concentration increased from 0.5 to 0.7. Initially, the saturation magnetization value slowly decreases from 81.44 to 83.97 emu/g, then quickly decreases to 71.84 emu/g as the zinc content increases from x = 0.5, through 0.6, to 0.7. Ni1−xZnxFe2O4 toroidal samples were prepared by sintering ferrite nanoparticles at 1250 °C and exhibited faceted grain morphologies in the FE-SEM images with their grain sizes being around 5 µm regardless of the Zinc content. The real magnetic permeability (μ′) of the toroidal samples measured at 5 MHz was monotonically increased from 106, through 150, to 217 with increasing the Zinc content from x = 0.5, through 0.6, to 0.7. The cutoff frequency of the ferrite toroidal samples was estimated to be about 20 MHz from the broad maximum point in the plot of imaginary magnetic permeability (μ″) vs. frequencies, which seemed to be associated with domain wall resonance.

Simple and fast prediction of train-induced track forces, ground and building vibrations

A simple and fast prediction scheme is presented for train-induced ground and building vibrations. Simple models such as (one-dimensional) transfer matrices are used for the vehicle–track–soil interaction and for the building–soil interaction. The wave propagation through layered soils is approximated by a frequency-dependent homogeneous half-space. The prediction is divided into the parts “emission” (excitation by railway traffic), “transmission” (wave propagation through the soil) and “immission” (transfer into a building). The link between the modules is made by the excitation force between emission and transmission, and by the free-field vibration between transmission and immission. All formula for the simple vehicle–track, soil and building models are given in this article. The behaviour of the models is demonstrated by typical examples, including the mitigation of train vibrations by elastic track elements, the low- and high-frequency cut-offs characteristic for layered soils, and the interacting soil, wall and floor resonances of multi-storey buildings. It is shown that the results of the simple prediction models can well represent the behaviour of the more time-consuming detailed models, the finite-element boundary-element models of the track, the wavenumber integrals for the soil and the three-dimensional finite-element models of the building. In addition, measurement examples are given for each part of the prediction, confirming that the methods provide reasonable results. As the prediction models are fast in calculation, many predictions can be done, for example to assess the environmental effect along a new railway line. The simple models have the additional advantage that the user needs to know only a minimum of parameters. So, the prediction is fast and user-friendly, but also theoretically and experimentally well-founded.

The Effect of DC Bias Current on Domain Wall Resonance Property of Thin-Film Magnetoimpedance Element

We investigated the influence of the dc bias current on the domain wall resonance of thin-film magnetoimpedance (MI) elements. When the intensity of dc bias current is relatively low (0-0.5 mA), the impedance profile shows a domain wall resonance behavior, which shows another peak and rapid drop of inductance in the low-frequency region. The peak height and resonance frequency do not depend on the dc bias current in this range. On the other hand, though the impedance profiles still show domain wall resonance, the behavior strongly depends on the dc bias current; the impedance peak height and amount of inductance drop decrease as well as the resonance frequency shifts to lower frequency with increasing dc bias current. The domain wall resonance completely disappears at 2 mA in this study. On the static field dependence of impedance with dc bias current, the profile shows asymmetric with respect to the Z-axis, which is the same as the property observed in higher frequency. The slight increment of impedance and inductance changes was admitted around the resonance frequency.