Sharif Digital Repository

We present here a simulator that solves the main semiconductor charge and transport equations coupled to Maxwell equations to study receivers based on photoconductive antennas (R-PCAs). Making use of this tool we were able to correctly characterize the operation of these antennas. In doing so, we compared simulations with the results of the semi-empirical expression ITHz(r) ∝σc(t)∗ ETHz(t) employed to evaluate the detected photocurrent by means of the convolution between the photoconductivity in the receiver and the electric field linked to the emitter antenna. We were able to accurately reproduce experimental data with our simulation tool. These kinds of... 

The factors affecting the quality of material identification by simulating a simple THz spectroscopy system in the frequency range of 0.5–1 THz, have been investigated. Two methods, using the Kramers-Kronig relation and the derivative of the reflection coefficient, are applied to identify the C-4 material. Also, the optimal incident angle to minimize the sensitivity of the reflectance to the incident angle has been obtained theoretically. To improve the THz spectroscopy of rough objects, two methods are proposed including transmitter displacement and rotation. Using the relations between the scattered waves and the spatial frequencies, the proposed methods are theoretically analyzed and... 

We have modelled and simulated a simple THz spectroscopic system to identify materials. A Vivaldi antenna with suitable specifications was used as a transmitter in the simulation. In order to characterize the object, we applied two different methods based on the derivative of the reflectivity and the Kramers-Kronig relations. Also, to obtain the optimized incident angle, we calculated the reflection sensitivity of the sample to the angle of incidence using the Fresnel equations and verified our result by simulation. © 2021 IEEE  

Terahertz spectroscopy is a useful and an efficient method for detection of pure materials and also mixture compounds. In the present study the terahertz spectra of the α-lactose, high explosives RDX and also the binary mixture of mentioned materials has been obtained in the transition mode. The obtained spectra of the pure materials were in a very good agreement with literatures in the range of 0.1 to 1.5 terahertz. The spectra of mixture samples which show the specific fingerprint characters of each component, declare that terahertz spectroscopy can be used effectively for the detection of explosives and chemical compounds even in the mixture samples. © 2016 IEEE  

Dirac leaky-wave antennas (DLWAs) are derived from photonic crystals exhibiting Dirac cone dispersion around their Γ-point. DLWAs provide high directive beams and continuous frequency beam scanning, non-fluctuating leakage constant and real non-zero Bloch impedance at and around broadside, due to the closed and linear Dirac dispersion relation around broadside. These features, along with their inherent compatibility for higher frequency designs (larger unit cells compared to metamaterials), make DLWAs an ideal candidate for the upper microwave, mm-wave and terahertz frequencies, and for applications such as radar, 5G, spectroscopy, etc. In this review, we cover the recent developments on... 

The infrared range optical absorption mechanism of carbon-copper composite thin layer coated on the diamond-like carbon buffer layer has been investigated. By consideration of weak interactions between copper nanoparticles in their network, optical absorption is modelled using their coherent dipole behaviour induced by the electromagnetic radiation. The copper nanoparticles in the bulk of carbon are assumed as a chain of plasmonic dipoles, which have coupling resonance. Considering nearest neighbour interactions for this metallic nanoparticles, surface plasmon resonance frequency (ω 0) and coupled plasmon resonance frequency (ω 1) have been computed. The damping rate against wavelength is...