Novel Compact Design and Investigation of a Super Wideband Millimeter Wave Antenna for Body-Centric Communications

This paper presents a novel design for a multiple band millimeter wave antenna with a wide active region in the extremely high frequency (EHF) range. The antenna's performance was tested at three evenly separated frequencies: 60 GHz within the V-band region, 80 GHz within the E-band region, and 100 GHz. Simulation exhibits satisfactory results in terms of gain and efficiency, although the efficiency falling tendency for higher frequency persists. As millimeter wave antennas have miniature-like dimensions and low penetration depth into human body layers, the performance of these antennas is less disturbed by the presence of a human body, making them ideal for body-centric wireless communication (BCWC) applications. Thus, a human body model was created virtually with the necessary property data. Simulations are repeated at the same frequencies as before, with the antenna kept close to the constructed human body model. The results were promising as the gains found increased radiation patterns and return loss curves remained almost identical, except some efficiencies that were considered. Some H-plane radiation patterns are changed by the presence of a human body. Although all three frequencies present satisfactory results, 60 GHz is found to be more balanced, but 100 GHz shows better gain and directivity. Multiple band operability makes this antenna suitable for various applications. Finally, a distance-based analysis was conducted to realize the in-depth characteristics of the antenna by placing the antenna at five different gaps from the human body. The result verifies the antenna’s category as suitable for body-centric communications.

Bandgap Energy of TiO₂/M-Chlorophyll Material (M=Cu²⁺, Fe³⁺)

The bandgap energy (Egap) of TiO2 material modified with metal-chlorophyll complex compounds (M = Cu2+, Fe3+) was observed. Chlorophyll (Chl) was isolated from cassava leaves, and its UV-Vis spectra showed absorption peaks in the Soret band region (410 nm) and in the Q band region (665 nm), which is the typical peak of chlorophyll. Copper(II)-chlorophyll complex was prepared from the reaction between chlorophyll and CuSO4.5H2O, while the iron(III)-chlorophyll was synthesized from chlorophyll and FeCl3.6H2O in methanol solvent under reflux at 65°C. The presence of copperand iron metals in the chlorophyll metal complexes was identified using Atomic Absorption Spectroscopy in methanol solution. The absorption of copper measured in Cu2+-Chl was 0.0488 (0.4805 mg/L), while the iron atom in Fe3+-Chl was 0.0050 (0.0195 mg/L). The UV-vis spectra demonstrate the hypsochromic shift of the Soret band to 405 nm (Cu2+-Chl) and 402 nm (Fe3+-Chl). The Infrared spectra of chlorophyll after being complexed with copper(II) shows the increase of vibrational absorption wavenumber of the C=N group from 1225.06 cm-1 to 1241.94 cm-1 indicates the coordination of the metal ion on the N atom in the pyrrole ring. The shift in the absorption band on the Fe3+-Chl spectrum was seen for the C=O ester group from 1720.49 cm-1 to 1721.10 cm-1 indicating the metal ion bonding in the C=O group of esters. The DR-UVis analysis of TiO2/metal-chlorophyll shows a bathochromic shift towards the visible light region. By using the Tauc plot method, it was observed that the Egap of TiO2 reduces from 3.08 eV to 2.89 eV and 2.93 eV in the compound of TiO2/Cu2+-Chl and TiO2/Fe3+-Chl, respectively.

Performance analysis on double-pass thulium-doped fiber amplifier for 16-channel WDM system at S-band

In this paper, the performance of single and double-pass thulium-doped fiber amplifiers (SD-TDFA and DP-TDFA) is analyzed in the short wavelength (S-band) region. The effect of thulium-doped fiber (TDF) length, input signal power, and input pumping power on the amplifier’s performance is comprehensively investigated on basis of gain and noise figure (NF). DP-TDFA showed a higher gain compared to single-pass configuration and that is due to double-propagation of the forwarded and amplified spontaneous emission (ASE) signal into the TDF which maximizes the achievable gain in the S-band region. At a gain medium length of 8 m, the proposed DP-TDFA showed higher gain enhancement over SP-TDFA at an input power of −20 dB compared to −40 and 0 dB input signal powers. The gain enhancement at 1470 nm is 5.6 dB, while the maximum recorded gain with the proposed double-pass configuration is 14.7 dB.

Modulation of the optical properties of chiral porphyrin dimers by introducing bridged chiral amide-bonds

The d/l-enantiomers of a series of three Zn(II)tetraarylporphyrin dimers were synthesized and isolated by incorporating a bridging amide-bonded xanthene moiety at the para-position of one of the meso-aryl rings. The electronic structures and optical properties were modulated by incorporating chiral amino acid moieties into the amide-bonding moieties of the xanthene bridge that contain methyl, tolyl and 2-methylindole substituents. A cofacial dimer was formed in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) resulting in a significant red shift of the B band, due to a relative destabilization of the HOMO, which has large MO coefficients on the pyrrole nitrogens. The sign sequences observed in the B band region of the CD spectra due to the presence of the chiral amino acid moieties were modified due to this change in geometry. Significant CD intensity is also observed in the B band region of the CD spectra of anion radical species during in situ spectroelectrochemical measurements.