The electromagnetic parameters (permittivity and permeability) method, retrieved from the reflection and transmission coefficients of a slab, is presented. Improvements over existing methods, including the determination of the permittivity, permeability and impedance of the slab, are expressed as explicit functions of the S parameters for both the time-dependent factors, eiωt and e−iωt (ω is the angular frequency of the incident electromagnetic wave), and the proper selection of the sign of impedance and the real part of the refractive index. Moreover, based on the retrieving method, the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed, which confirm the validity of the technique for the retrieval of electromagnetic parameters.
The structural disorder of the black butterfly assists in capturing sunlight across a wider spectral and angular range, injecting infinite vitality for omnidirectional and stimuli-responsive wave-absorbing materials. Here, the disordered micro-pores responding to terahertz (THz) waves through electromagnetic simulations, and then prepared via ice templating technology are analyzed and optimized. The customized disordered aerogel makes possible perfect terahertz response property with incidence-angle-insensitive and ultra-broadband. Ti3C2Tx MXene/carboxymethyl cellulose aerogels realize excellent shielding effectiveness exceeding 70.32 dB and reflection loss of more than 43.02 dB over the frequency range of 0.3-1.5 THz. Tailoring the structural orientation of anisotropic aerogels functions as a versatile dynamic modulation approach along terahertz propagation direction. The porous structure with moderate conductivity gradually triggers the resonance effect of the cavity, approximating a resonance sphere (pore) and waveguide system (tube). Ultimately, gradient impedance aerogel is proposed integrating THz-infrared stealth, hydrophobicity, and mechanical strength. This inspired biomimetic structural strategy will also enable various terahertz applications such as terahertz imaging, line-of-sight telecommunication, information encryption, and space exploration.
The dielectric properties of multiwalled carbon nanotubes/silica (MWNTs/SiO2) nanocomposite with 10 wt % MWNTs are investigated in the temperature range of 373–873 K at frequencies between 8.2 and 12.4 GHz (X-band). MWNTs/SiO2 exhibits a high dielectric loss and a positive temperature coefficient (PTC) of dielectric effect that complex permittivity increases monotonically with increasing temperature. The PTC effect on the dielectric constant is ascribed to the decreased relaxation time of interface charge polarization, and the PTC effect on the dielectric loss is mainly attributed to the increasing electrical conductivity. The loss tangent strongly supports the dominating contribution of conductance to the dielectric loss.
The self-consistent nonlinear equations, which describe electron cyclotron maser under the condition of anomalous Doppler effect, have been developed. By employing an initially rectilinear electron beam and a guiding static magnetic field, an efficient energy transfer between electrons and microwave can be achieved. The results suggest potential applications in designing a compact and efficient microwave generation/amplification device.
A method using strong fluctuation theory (SFT) to compute the effective electromagnetic parameters of multiphase composite media, and common materials used to design radar-absorbing materials, is demonstrated. The effective electromagnetic parameters of ultrafine carbonyl-iron (DT-50) and fiber fabric, which are both multiphase composite media and represent coated and structured radar absorbing materials, respectively, are investigated, and the corresponding equations of electromagnetic parameters by using the SFT are attained. Moreover, we design a program to simplify the solutions, and the results are discussed.
Abstract Circulators, as passive non-reciprocal devices, have excellent potential for application in wireless communication and radar-signal processing. However, the construction of terahertz (THz)-frequency circulators is extremely difficult. Here, an electromagnetic matching model for metamaterials is proposed to support the design of a THz circulator with a wider operating bandwidth. The resulting circulator can work without an external magnetic field in the THz frequency range. The best isolation of this THz circulator is 20.9 dB, and its maximum directionality is 16.6 dB. These results validate a new method for the design of metamaterial-based THz devices.
Various materials have been examined to obtain permittivity and permeability values required for detailed investigations on functional materials like microwave-absorbing and high-permittivity dielectrics. We call for caution when samples exhibit negative imaginary permeability, whether containing a resonance peak or not. In the retrieval procedure, the Fabry-Pérot resonance (FPR) can produce a negative imaginary permeability, which should be classified as an extrinsic rather than an intrinsic physical attribute. In particular, for high-loss materials, the implicit FPR would bring a plausible negative imaginary permeability. Here we have listed a dielectric dispersion of FPR behavior for BiFeO3 samples.
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