This work presents a novel technique for designing chipless radio frequency identification (RFID) tags which, unlike the traditional tags with complex geometries, are both compact and printable. The tags themselves are alphabets, which offers the advantage of efficient visual recognition of the transmitted data in real-time via radio frequency (RF) waves. In this study, the alphabets (e.g., a, b and c) are realized by using copper etching on a thin dielectric substrate (TLX-8) backed by a ground plane. It is shown that the original signature of the frequency response of the backscattered radar cross-section (RCS) of the letter, displays dips that are unique to the individual letters. The tags have been simulated, fabricated and their monostatic cross-sections have been measured by using a dual-polarized Vivaldi antenna in the frequency band ranging from 6 to 13 GHz. The study also includes, for the first time, a detailed analysis of the impact of changing the shape of the tag owing to variation in the font type, size, spacing, and orientation. The proposed letters of the alphabet are easily printable on the tag and provide an efficient way to visually recognized them and, hence, to detect them in a robust way, even with a low coding density of 2.63 bit/cm2. The advantages of the proposed novel identification method, i.e., utilization of the both co- and cross-polar RCS characteristics for the printable clipless RFID tags are the enhancement of the coding density, security and better detection of the alphabet tags with different fonts by capturing the tag characteristics with better signal to noise ratio (SNR). Good agreement has been achieved between the measured and simulated results for both co- and cross-polarized cases.

An eight-element antenna system operating at sub 6 GHz is presented in this work for a future multiple-input multiple-output (MIMO) system based on a modified E-slot on the ground. The modified E-slot significantly lowers the coupling among the antenna components by suppressing the ground current effect. The design concept is validated by accurately measuring and carefully fabricating an eight-element MIMO antenna. The experimentation yields higher element isolation greater than −21 dB in the 3.5 GHz band and the desired band is achieved at −6 dB impedance bandwidth. The E-shape slot occupies an area of 17.8 mm × 5.6 mm designed on an FR-4 substrate with dimensions of 150 mm × 75 mm × 0.8 mm. We fed the I-antenna element with an L-shape micro-strip feedline, the size of the I-antenna is 20.4 × 5.2 mm2, which operates in the (3.4–3.65 GHz) band. Moreover, our method obtained an envelope correlation coefficient (ECC) of <0.01 and an ergodic channel capacity of 43.50 bps/Hz. The ECC and ergodic channel capacity are important metrics for evaluating MIMO system performance. Results indicate that the proposed antenna system is a good option to be used in 5G mobile phone applications.

This study presents, for the first time, a novel design of ultra-wideband (UWB), circularly polarized and highly directive log-spiral THz photoconductive antenna. The proposed antenna is simulated in High Frequency Structure Simulator using gold as the antenna electrode material which is backed by a quartz substrate (ε r = 3.78, tan δ = 0.0001) and hemispherical silicon-based lens with a diameter of 140 μm. A comprehensive detailed parametric study of the antenna design parameters is performed in the frequency range of 1 to 6 THz for the optimal design of the developed antenna structure. The optimal antenna structure with integrated lens has UWB characteristics with −10 dB impedance bandwidth of 5 THz and 3 dB axial ratio bandwidth of around 4 THz. The observed directivity and half-power beam width of the presented design varies in the range 5 to 12 dBi and 34 to 62 , respectively, for the frequency range of 1 to 4 THz. The wideband, high directivity as well as highefficiency (>50%) characteristics of the proposed design make it a favorable choice for the THz sensing and imaging applications.

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A Vivaldi dipole rectenna system for infrared (IR) energy harvesting is investigated. First, a parametric study on the Vivaldi dipole antenna is performed to collect the maximum electric field between the Vivaldi poles. The antenna arms were optimized to achieve a high-efficiency rectenna system. The two arms of the antenna were formed using two different metals, that is, gold and titanium. These two metals have different work functions, which facilitate the diode operation through tunneling at zero bias. The two arms of the Vivaldi dipole are overlapped, and a suitable insulator layer is injected in the overlapped area to form the metal-insulator-metal (MIM) diode. The MIM diode is an ideal candidate for this operation as it works without any bias, provided the two metals have different work functions. For rectenna operation, it is crucial that the rectifying diodes should work without any aid of external bias. The Al 2 O 3 is the insulator layer of the MIM diode. We have chosen Al 2 O 3 because it has a low dielectric constant at terahertz frequency regime, which allows us to match the operational cutoff frequency, that is, 28.3 THz. A parametric study of the Al 2 O 3 insulator layer is performed to increase the captured received intensity. At the end, the nano-antenna operates at a frequency band of [26 … 30 THz] to harvest IR energy from the environment with good efficiency and demonstrate its capacity to capture incident waves and obtain high-intensity values within its gap. It is a development that could eventually boost electricity generation.