Journal of Infrared, Millimeter, and Terahertz Waves最新文献

A dual-band metamaterial absorber (MMA) for fifth-generation (5G) applications is discussed in this work. The suggested absorber works at frequency bands of 28 GHz and 38 GHz. The suggested MMA unit cell with a size of 5.8 mm × 5.8 mm (0.54 λ₀ × 0.54 λ₀ at 28 GHz) is designed on 1.5 mm (0.14 λ₀) low-cost FR4 substrate and composed of two metallic ring resonators. The suggested MMA is investigated to validate its performance for different polarization for transverse electric (TE) and transverse magnetic (TM). Both normal and oblique angles are studied. The MMA has a simple structure with a compact size. Different parameters such as the currents, electric field distributions, and normalized impedance are studied. The array of 10 × 10 unit cells is utilized to verify the simulated outcomes. The suggested MMA is fabricated and tested, and its outcomes are compared to the simulated outcomes. The MMA is operated at dual bands 28/38 GHz with high absorption rates of 98 and 98.4%, respectively, under the normal incidence for both outcomes. A good matching between the two outcomes is observed, which supports the MMA for 5G applications.

We present a novel electrically scalable, reconfigurable frequency selective surface (FSS) far-IR filter fabricated on transparent, and flexible polyimide substrate. Our proposed method of reconfigurabilty is achieved by employing phase change materials (PCMs). The PCM primarily considered in this proposal is vanadium dioxide (VO₂) due to its relatively low temperature reversible metal to insulator transition and conformity to common fabrication techniques. Here, the proposed reconfigurable filter covers 15–17 μm with a stopband center wavelength that can switch between 15.5 and 16.1 μm with the activation of VO₂. Although the design provided is intended for the far-infrared, it can easily be scaled to meet the needs of longer wavelength and lower frequency applications.

Glass-based materials, including polymer/glass stack ups, are attractive structural blocks for packaging substrates supporting 5 G and 6 G microelectronic modules and components. We present the first broadband characterization of AGC Inc. EN-A1 alkali-free boroaluminosilicate glass and of Ajinomoto Build-up Film (ABF) laminated on soda-lime float glass substrate from 200 GHz to 2.5 THz with a commercial terahertz time-domain spectroscopy (THz-TDS) system. The refractive index (n(nu )), attenuation coefficient (alpha (nu )), permittivity (varepsilon '(nu )), and loss tangent (tan delta (nu )) of EN-A1 glass as well as laminated ABF are (n_mathrm{EN-A1}=2.376), (alpha _mathrm{EN-A1}=31.1) cm(^{-1}), (varepsilon '_mathrm{EN-A1}=5.64), (tan delta _mathrm{EN-A1}=0.062), and (n_textrm{ABF}= 1.9), (alpha _textrm{ABF}= 30) cm(^{-1}), (varepsilon _textrm{ABF} = 3.8), (tan delta _textrm{ABF}= 0.072), all at 1 THz. Our results validate the promising perspective of both EN-A1 glass and ABF polymer materials as microwave and THz packaging solutions.

We consider the possibilities of producing wideband chaotic terahertz-range radiation in gyrotrons with excitation of cyclotron harmonics. The transition to the chaotic generation mode in gyrotrons requires a significant excess of the operating current over the starting value, which excludes selective operation at cyclotron harmonics due to the intensification of mode competition. At the same time, it is attractive to use a competition-free frequency multiplication effect that arises due to the nonlinear properties of the electron beam. The implementation of the frequency multiplication regime is simplified when using low-energy electron beams. Based on the averaged model of electron-wave interaction, we simulate generation in a 250-GHz low-voltage gyrotron and demonstrate the regime of a double frequency multiplication providing 0.5 THz chaotic radiation with a bandwidth of about 20 GHz and an average power of 0.5 mW. A significant expansion of the spectrum is achieved through to additional resonant interaction at the intersection points of the dispersion characteristics of the operating mode and the electron beam at the second cyclotron harmonic.

Calculations are presented for an electron-optical system that makes it possible to produce a helical electron beam with an energy of 250 keV, a current of 100 A, and a pitch factor of 1.1 for a 0.3 THz gyrotron with the operating mode of TE_33.2. Based on averaged stationary equations with a non-fixed field structure, the cavity profile is optimized and the possibility of obtaining an output power of about 8 MW with an electronic efficiency of more than 30% is demonstrated. Within the framework of particle-in-cell three-dimensional simulation, the processes of establishing oscillations are considered. Besides, it is shown that in the range of magnetic fields from 14.7 to 15.1 T, selective excitation of oscillations in the operating mode with a maximum power of about 7 MW is possible.

Off-axis parabolic mirrors (OAPMs) are widely used in the THz and mm-wave communities for spectroscopy and imaging applications, as a result of their broadband, low-loss operation and high numerical apertures. However, the aspherical shape of an OAPM creates significant geometric aberrations: these make achieving diffraction-limited performance a challenge, and lower the peak electric field strength in the focal plane. Here, we quantify the impact of geometric aberrations on the performance of the most widely used spectrometer designs, by using ray tracing and physical optics calculations to investigate whether diffraction-limited performance can be achieved in both the sample and the detector plane. We identify simple rules, based on marginal ray propagation, that allow spectrometers to be designed that are more robust to misalignment errors, and which have minimal aberrations for THz beams. For a given source, this allows the design of optical paths that give the smallest THz beam focal spot, with the highest THz electric field strength possible. This is desirable for improved THz imaging, for better signal-to-noise ratios in linear THz spectroscopy and optical-pump THz-probe spectroscopy, and to achieve higher electric field strengths in non-linear THz spectroscopy.