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Direct excitation of molecular vibrational motion by intense broadband THz pulses
摘要： We theoretically investigate molecular vibrational dynamics driven by intense and broadband THz pulses. The light-nuclei interaction is derived from a fully quantum-mechanical minimal coupling Hamiltonian to analyse direct excitation of vibrational modes by the THz pulses. We show that for diatomic molecules a "vibrational moment" can be defined in a manner similar to the dipole moment and that it has non-zero values only for heteronuclear diatomic molecules. Taking ultra-cold heteronuclear diatomic molecules as examples, we show that vibrational-mode excitation by THz pulse irradiation occurs almost stepwisely, especially for low vibrational modes. Coherent control method using frequency-controlled THz pulse sequence is also proposed.
关键词： quantum-mechanical minimal coupling Hamiltonian,vibrational moment,heteronuclear diatomic molecules,coherent control,molecular vibrational dynamics,THz pulses
更新于2025-09-09 09:28:46
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - A THz Imaging System Using Sparse Antenna Array for Security Screening
摘要： This paper presents our study on a THz imaging system using a sparse periodic linear antenna array (SPA) with large element spacing, consisting of only 14 transmitters and 16 receivers at 220GHz to achieve a horizontal field of view (FOV) of about 0.8m. The image of a realistic target scenario, i.e. the metallic objects concealed under a thin clothing in front of a human body phantom is reconstructed with data from an effective simulation based on a combined method between moment and ray launching-geometrical optics (RL-GO) algorithms in FEKOTM. The results have shown that a resolution of 3.5mm at 4m distance can be achieved in this THz imaging system. In addition, the study demonstrates compressive sensing (CS) reconstruction method is capable to provide a comparable image quality with a dramatic reduction of sampling data, which can also be applied in practical products to improve the imaging rate.
关键词： compressive sensing,THz imaging,security screening,sparse antenna array
更新于2025-09-09 09:28:46
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Hyperspectral Terahertz Tomography in Amplitude Contrast
摘要： Hyperspectral Terahertz Tomography in amplitude contrast is presented using a time-domain spectroscopy system in the spectral range 0.3 - 2.5 THz. The Fourier transformed signal data is used to reconstruct test objects’ cross-sections at multiple frequencies using standard filtered backprojection. The full hyperspectral set of images reconstructed at around 300 adjacent spectral points is used to trace the combined contribution of Beer-Lambert volume attenuation, Fresnel reflection losses and Rayleigh roughness scattering losses, which is in good overall agreement with the experimental results. The image quality for Styrofoam (refractive index around 1.02, attenuation coefficient < 1 mm-1) test objects is best in the range 0.8 - 2.0 THz depending on the porosity of the material.
关键词： THz,time-domain spectroscopy,hyperspectral imaging,Rayleigh roughness,hard-field tomography
更新于2025-09-09 09:28:46
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Modulation Mode Detection & Classification for in-Vivo Nano-Scale Communication Systems Operating in Terahertz Band
摘要： This work initiates the efforts to design an intelligent/cognitive nano receiver operating in Terahertz (THz) band. Specifically, we investigate two essential ingredients of an intelligent nano receiver—modulation mode detection (to differentiate between pulse based modulation and carrier based modulation), and modulation classification (to identify the exact modulation scheme in use). To implement modulation mode detection, we construct a binary hypothesis test in nano-receiver’s passband, and provide closed-form expressions for the two error probabilities. As for modulation classification, we aim to represent the received signal of interest by a Gaussian mixture model (GMM). This necessitates the explicit estimation of the THz channel impulse response, and its subsequent compensation (via deconvolution). We then learn the GMM parameters via Expectation-Maximization algorithm. We then do Gaussian approximation of each mixture density to compute symmetric Kullback-Leibler divergence in order to differentiate between various modulation schemes (i.e., M -ary phase shift keying, M -ary quadrature amplitude modulation). The simulation results on mode detection indicate that there exists a unique Pareto-optimal point (for both SNR and the decision threshold) where both error probabilities are minimized. The main takeaway message by the simulation results on modulation classification is that for a pre-specified probability of correct classification, higher SNR is required to correctly identify a higher order modulation scheme. On a broader note, this work should trigger the interest of the community in the design of intelligent/cognitive nano receivers (capable of performing various intelligent tasks, e.g., modulation prediction etc.).
关键词： nano-scale communication,Expectation-Maximization algorithm,Kullback-Leibler divergence,Gaussian mixture model (GMM),modulation classification,Terahertz (THz) band,modulation mode detection
更新于2025-09-09 09:28:46
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An <i>ex</i> <i>vivo</i> comparative study of occlusal and proximal caries using terahertz and X-ray imaging
摘要： Objectives: To examine the effectiveness of terahertz (THz) pulsed imaging (TPI) in comparison to intraoral photostimulable phosphor late (PSP) and cone beam CT (CBCT) for the detection of dental caries ex vivo. Methods: Newly extracted 32 human permanent teeth surfaces (16 with caries and 16 without caries) were serially sectioned mesiodistally and imaged by using four image sets as follows: (1) CBCT; (2) PSP; (3) THz movie video; and (4) THz static images. All images were evaluated twice separately by two calibrated observers for the presence/absence of caries using a 5-grade rating/confidence scale. Weighted κ coefficients were calculated. Different image sets were compared with the histological gold-standard using the receiver operating characteristic and area under curves for each image set were compared using χ2 tests, with a significance level of α = 0.05. Results: Intra- and interobserverκ-values for all image sets were almost excellent ranging between 0.777 and 0.988. Mean Az values of observers and readings were 0.898 for CBCT, 0.888 for PSP images, 0.853 for THz static images and 0.781 for THz video movie. No statistically significant differences (p > 0.05) were found between Az values for the different image sets. When observer scores were evaluated according to caries location again no statistically significant differences (p > 0.05) were found between Az values for the occlusal and proximal caries for the four image sets. conclusions: Terahertz pulsed imaging was found to be successful for the detection of dental caries ex vivo.
关键词： THz imaging,radiology,caries detection
更新于2025-09-09 09:28:46
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[IEEE 2018 15th Workshop on Positioning, Navigation and Communications (WPNC) - Bremen, Germany (2018.10.25-2018.10.26)] 2018 15th Workshop on Positioning, Navigation and Communications (WPNC) - 100 Gbps and beyond: Hardware in the Loop experiments with PSSS modulation using 230 GHz RF frontend
摘要： The terahertz frequency range provides abundant bandwidth (25GHz ~ 50 GHz) to achieve ultra-high-speed wireless communication and enables data rates up to and above 100 Gbps. Parallel Sequence Spread Spectrum (PSSS) is a physical layer (PHY) baseband technology which is suitable for ultra-high speed wireless communication since the receiver architecture is straightforward and can be implemented almost entirely in analog hardware. In this paper, a PSSS modulated signal at a chip rate of 20 Gcps with a spectral efficiency of 4 bit/s/Hz is transmitted using a 230 GHz RF-front-end operating in the linear range to achieve 80 Gbps. The PSSS transceiver models are implemented in MATLAB/Simulink. The PSSS transmitter generates the PSSS modulated symbols that are loaded into an Arbitrary Waveform generator (AWG) and are then transmitted using the available 230 GHz wireless frontend. A Real-Time Oscilloscope samples and stores the received signal. The PSSS receiver performs synchronization, channel estimation, and demodulation. For a coded data rate of 80 Gbps, a BER of 2.072?10-3 has been measured. Thus, PSSS modulation is the promising modulation technique to achieve a data rate up to or above 100 Gbps in the Terahertz domain
关键词： PSSS,100 Gbps,broadband receiver,THz,wireless,PHY layer,submillimeter-wave,Hardware-In-The-Loop
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE 5G World Forum (5GWF) - Silicon Valley, CA, USA (2018.7.9-2018.7.11)] 2018 IEEE 5G World Forum (5GWF) - CHRONOS: A Cloud based Hybrid RF-Optical Network Over Synchronous Links
摘要： This paper presents CHRONOS, a Cloud based Hybrid RF-Optical Network Over Synchronous Links. The primary goal of this project is to design, build and maintain a multi-node, heterogeneous, wideband, scalable, hybrid and synchronous Cloud Radio Access Network (Cloud RAN or C-RAN), specifically to support emerging applications requiring both THz-optical and conventional sub-6GHz technologies like Wi-Fi and cellular networks. The novelty of the testbed is in enhancing the core capabilities of C-RAN in multiple directions by integrating synchronous RF and Optical links that is not considered for contemporary C-RAN deployments. The long term goal of this project is to utilize the testbed to enable practical research in wireless and optical communication with emphasis on new hardware and software architecture for signal processing. In this paper, we present the design, implementation and initial results of CHRONOS, in an indoor setting, with a clear path to a scalable and real-time network. Our results show synchronous reception across multiple edge nodes while achieving an aggregate bandwidth of 108Mbps using 20MHz OFDM waveform in each RF and optical paths.
关键词： CHRONOS,Cloud RAN,sub-6GHz,THz-optical,Synchronous Links,cellular networks,RF-Optical Network,Wi-Fi
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE Photonics Conference (IPC) - Reston, VA, USA (2018.9.30-2018.10.4)] 2018 IEEE Photonics Conference (IPC) - THz Photonic Transmitters with Type-II Hybrid Absorber UTC-PDs and Dual-Ridged Horn Antennas for High-Power and Extremely wide Fractional Bandwidth Performances
摘要： Waveguide-coupled THz photonic transmitters, which have novel design of dual-ridged horn antenna and ultra-fast photodiodes, demonstrate extremely wide 3-dB fractional O-E bandwidth (100%; 0.1-0.3 THz). A reasonable power (31.6 μW; 0.24 THz) can be detected in the receiving-end through wireless transmission.
关键词： Extremely wide fractional bandwidth,High-power,THz photonic transmitters,Dual-ridged horn antennas,Type-II hybrid absorber UTC-PDs
更新于2025-09-09 09:28:46
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Current-Driven Dyakonov-Shur Instability in Ballistic Nanostructures with a Stub
摘要： We develop a compact model for the THz plasmonic unstable structures with tunable narrow-channel regions of an increased width (called plasmonic “stubs”) using the transmission line analogy and derive the dispersion equations describing unstable plasmons. The solutions of the dispersion equations in the plasmonic systems with the electron drift, which are derived using the hydrodynamic model and generalized to account for the stubs, illustrate the device physics and can be used for design and characterization of THz plasmonic-electronic sources. Our results show that adding stubs allows one to control the Dyakonov-Shur instability in plasmonic ?eld-e?ect transistors by optimizing the boundary conditions, controlling the plasma velocity, and making it possible to drive periodic plasmonic structures wirelessly, thus avoiding the contact problems.
关键词： THz plasmonic,hydrodynamic model,plasmonic stubs,Dyakonov-Shur instability,ballistic nanostructures
更新于2025-09-09 09:28:46
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Effective Medium Model of Periodic Nanolayered Transparent Shields
摘要： An innovative effective medium model based on the transfer matrix method is proposed for the simulation of 1D-periodic subwavelength metal–dielectric laminated structures excited by TM- or TE-polarized plane wave with oblique incidence angles. The homogeneous medium of each period is characterized by TM or TE complex effective permeability and conductivity. The resulting effective single layer (ESL), having the same total thickness of the multilayer laminate, is represented by a transfer matrix given by the product of the transmission matrices of the periods composing the structure. Notice that this model allows the homogenization of n-layer periods, while the effective medium approximation method is formulated for only two-layer periods. The ESL is used to compute the transmission and reflection coefficients and the shielding effectiveness of 1D-periodic nanolayered transparent coatings made by alternating layers of silver, zinc oxide, or titanium dioxide films, in the frequency range from 100 MHz up to 10 THz. The propagating wave performances of the ESL are compared with the ones given by the rigorous multilayer model. Finally, two different screens made of transparent coatings over glass are proposed and analyzed.
关键词： 1D-periodic multilayer (ML) coating,Effective homogeneous model,terahertz (THz) shielding effectiveness
更新于2025-09-09 09:28:46