Li Yi

Terahertz (THz) imaging techniques have attracted significant attention and have developed rapidly in recent years. However, despite several advances, these techniques are still not mature, and their high cost and system complexity continue to limit their applications. In this article, the techniques for achieving a practical imaging system with a compact THz transceiver are addressed, while considering the limitations of the current technique. The aim is to provide a brief review of related top

Three-dimensional (3D) imaging remains an expensive and challenging task in the THz band. In this study, a frequency-modulated continuous-wave photonic radar system was presented in the 300-GHz band, instead of using electronic-based devices. The proposed system can obtain a 6-dB bandwidth of 120 GHz to achieve a range resolution of ∼1.1 mm. The frequency sweep linearity of a laser source was calibrated with respect to the imaging distance and range resolution, through which a maximum detectable

With the development of 5G and other technologies, radar imaging techniques in high-frequency bands up to the terahertz (THz) range have attracted considerable attention. In particular, the photonic radar technique benefits from the unique advantages of optical devices, including an ultrawide and flexible bandwidth of more than 100 GHz, leading to submm-order range resolution, reduced phase noise, and flexible optical links. This article reviews recent progress in photonic radar systems from the

Electrical capacitance tomography (ECT) is a promising technique applied in many fields. However, the solutions for ECT are not unique and highly sensitive to the measurement noise. To remain a good shape of reconstructed object and endure a noisy data, a Rudin–Osher–Fatemi (ROF) model with total variation regularization is applied to image reconstruction in ECT. Two numerical methods, which are simplified augmented Lagrangian (SAL) and accelerated alternating direction method of multipliers (AA

We propose a high-resolution velocity analysis method to estimate the electromagnetic wave propagation velocity in subsurface medium. The estimation is achieved by applying the ℓ-1 norm regularized least-squares method to the conventional common-midpoint (CMP) velocity analysis algorithm. The proposed method can provide not only higher resolution than the conventional velocity analysis method, but can also be applied with a coarse sampling array system, such as our array ground penetrating radar

We propose a new iterative interpolation method for ground penetrating radar (GPR) data based on projection onto convex sets (POCS) and frequency-wavenumber (f-k) zone-pass filtering. The main purpose of this method is to simplify the three-dimensional (3-D) GPR data acquisition; it can also be used for conventional GPR data that include some missing traces. This approach allows the reconstruction of the image from sparsely sampled data that violate the Nyquist criterion. The method can fully us

It is important to identify the thin cracks within the airport pavement layers. To achieve this goal, a practical interferometric approach using the Yakumo multistatic ground-penetrating radar system was developed to detect the slight variability in wave propagation velocity and/or thickness caused by the thin cracks. In comparison with the conventional common midpoint (CMP) velocity estimation method, the proposed method can provide much higher-resolution estimations of slight deviations in the

Abstract The implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on–off keying is crucial to further boost the terahertz (THz) communications speed. Thereby, carrier phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, the photonic-based THz sources and the phase noise problem are briefly summarized. Then, a low phase-noise photonic source based on the st

We investigated a velocity analysis algorithm for the new array Ground Penetrating Radar (GPR) system “Yakumo”. The common mid-point (CMP) data, which is used to estimate the vertical profile of subsurface velocity can be acquired easily with this system. However, each CMP data set acquired by Yakumo includes only 8 GPR traces with more than 20 cm trace interval. In order to estimate the velocity with this sparse GPR data, we proposed a reversible normal move-out (NMO) processing to remove alias

To identify the slight spatial variability in the electromagnetic(EM) signal propagation velocity and thickness of an asphalt layer caused by the presence of thin cracks within the layer, a practical interferometric approach using the multistatic ground-penetrating radar system YAKUMO was introduced in this study. It was demonstrated that several parallel distributed common midpoint (CMP) datasets can be acquired at each position while moving the system in real time, which makes it possible to a

A resonant tunneling diode (RTD) is a promising device for future terahertz (THz) applications owing to its capacity to operate as both a transmitter and a receiver of THz waves. It is noteworthy that the RTD can simultaneously detect incoming terahertz signals while operating as an oscillator. In this study, we investigated the possibility of employing a single RTD transceiver module as both a source and a detector in THz sensing applications. Such a configuration can greatly simplify THz imagi

This paper presents an efficient use of telecom-based photonics technologies in millimeter-wave and terahertz systems, which include high-speed wireless communications in the 300-GHz and 600-GHz bands, and ultra-broadband millimeter-wave radars equipped on the drone.