Permeability measurement and control for epoxy composites

et al. 2021

Sci Rep

Self Cite

The epoxy/magnetite nanocomposites express superparamagnetism under a static or low-frequency electromagnetic field. At the microwave frequency, said the X-band, the nanocomposites reveal an unexpected diamagnetism. To explain the intriguing phenomenon, we revisit the Debye relaxation law with the memory effect. The magnetization vector of the magnetite is unable to synchronize with the rapidly changing magnetic field, and it contributes to diamagnetism, a negative magnetic susceptibility for nanoparticles. The model just developed and the fitting result can not only be used to explain the experimental data in the X-band but also can be used to estimate the transition frequency between paramagnetism and diamagnetism.

Section: Permeabilitysupporting

confidence: 88%

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confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Frequency-induced negative magnetic susceptibility in epoxy/magnetite nanocomposites

et al. 2021

Sci Rep

Self Cite

Characterization of the lossy dielectric materials using contour mapping

Chao

Review of Scientific Instruments

2018

The imaginary part of the complex permittivity of a lossy dielectric material is large and couples with its real part. The resonant frequency of a cavity with the sample depends not only on the real part of the complex permittivity of the sample but also the imaginary part, resulting in serious ambiguity in determining the sample’s complex permittivity. This work proposes a contour mapping method to determine the complex permittivity. The full-wave simulation gives us the contours of the resonant frequency and the quality factor, which are functions of the relative dielectric constant and the loss tangent. By mapping the measured resonant frequency and the measured quality factor, one can uniquely determine the complex permittivity of the sample. Five liquids were examined, including three low-loss materials for benchmarking and two lossy materials. The measured complex permittivities of the three low-loss materials agree very well with the other methods. As for the lossy materials, the measured relative dielectric constant and the loss tangent of alcohol are 6.786 and 0.895, respectively. Besides, the measured dielectric constant of glycerin is 6.811, and its loss tangent is 0.562. The proposed contour mapping technique can be employed to measure the complex permittivity of liquids and solids from lossless to lossy materials.

Manipulating the permittivities and permeabilities of epoxy/silver nanocomposites over a wide bandwidth

Applied Physics Letters

2020

The electromagnetic properties of materials are generally frequency-dependent. Controlling the permittivities and permeabilities of composites is commonly achieved in a narrow frequency range. This work characterizes the electromagnetic properties of epoxy/silver nanocomposites using the transmission/reflection method. The silver nanoparticles serving as electric dipoles enhance the permittivity as the volume fraction increases. On the other hand, the rapidly changing magnetic field induces current on the conducting silver particles, resulting in a negative polarizability. The macroscopic magnetic susceptivities are negative under the long-wavelength limit. The electromagnetic properties are controllable and just slightly change over a very broad frequency range from 8 GHz to 110 GHz.