Terahertz (THz) Generator and Detection

In the whole research process of electromagnetic wave, the research of terahertz wave belongs to a blank for a long time, which is the least known and least developed by far. But now, people are trying to make up the blank and develop terahertz better and better. The charm of terahertz wave originates from its multiple attributes, including electromagnetic field attribute,photon attribute and thermal attribute, which also attracts the attention of researchers in different fields and different countries, and also terahertz technology have been rated as one of the top ten technologies to change the future world by the United States. The multiple attributes of terahertz make it have broad application prospects in military and civil fields, such as medical imaging,astronomical observation, 6G communication, environmental monitoring and material analysis. It is no exaggeration to say that mastering terahertz technology means mastering the future. However, it is because of the multiple attributes of terahertz that the terahertz wave is difficult to be mastered. Although terahertz has been applied in some fields,controlling terahertz (such as generation and detection) is still an important issue. Nowadays, a variety of terahertz generation and detection technologies have been developed and continuously improved. In this paper, the main terahertz generation and detection technologies (including already practical and developing) are reviewed in terms of scientific and engineering principles,in order to provide a systematic and up-to-date reference for researchers in terahertz field

High-Dimensional Information Detection based on Correlation Imaging Theory

Radar is a device that uses electromagnetic(EM) waves to detect targets; it can measure the position parameters and motion parameters and extract target characteristics information by analyzing the reflected signal from the target. From the perspective of the radar theoretical basis of physics, the more than 70 years of development of radar are based on the EM field fluctuation theory of physics. Many theories have been developed towards one-dimensional signal processing. For example, a variety of threshold filtering have widely used as methods to resist interference during detection. The optimal state estimation describes the propagation process of the statistical characteristics of the target over time in the probability domain. Compressed sensing greatly improves the reconstructing efficiency of the sparse signal. These theories are one-dimensional information processing. The information obtained by them is a deterministic description of the EM field. The correlated imaging technique is from the high-order coherence property of the EM field, which uses the fluctuation characteristic of the EM field to realize non-local imaging. Correlated imaging radar, a combination of correlated imaging techniques and modern information theory, will provide a novel remote sensing detection and imaging method. More importantly, correlated imaging radar is a new research field. Therefore, a complete theoretical frame and application system should be urgently built up and improved. Based on the coherence theory of the EM field, the work in this thesis explores the method of determining the statistical characteristics of the EM field so that the high dimensional target information can be detected, including theoretical analysis, principle design, imaging modes, target detecting models, image reconstruction algorithms, the enhancement of visibility, and system design. The simulations and real experiments are set up to prove the theory's validity and the systems' feasibility

Sensors for Vital Signs Monitoring

Sensor technology for monitoring vital signs is an important topic for various service applications, such as entertainment and personalization platforms and Internet of Things (IoT) systems, as well as traditional medical purposes, such as disease indication judgments and predictions. Vital signs for monitoring include respiration and heart rates, body temperature, blood pressure, oxygen saturation, electrocardiogram, blood glucose concentration, brain waves, etc. Gait and walking length can also be regarded as vital signs because they can indirectly indicate human activity and status. Sensing technologies include contact sensors such as electrocardiogram (ECG), electroencephalogram (EEG), photoplethysmogram (PPG), non-contact sensors such as ballistocardiography (BCG), and invasive/non-invasive sensors for diagnoses of variations in blood characteristics or body fluids. Radar, vision, and infrared sensors can also be useful technologies for detecting vital signs from the movement of humans or organs. Signal processing, extraction, and analysis techniques are important in industrial applications along with hardware implementation techniques. Battery management and wireless power transmission technologies, the design and optimization of low-power circuits, and systems for continuous monitoring and data collection/transmission should also be considered with sensor technologies. In addition, machine-learning-based diagnostic technology can be used for extracting meaningful information from continuous monitoring data

Study of electromagnetic wave propagation and scattering in Low-THz automotive radar

The development of a new generation of sensors for autonomous vehicles requires the increase of the number of automotive radars on the roads, leading to an inevitable problem of overcrowding of the electromagnetic spectrum in the allocated 77 GHz band. The solution proposed in this research is the migration of the automotive radar operation frequency towards the low-THz band. This thesis reports, firstly, an experimental study on the feasibility of deploying automotive radars working at frequencies above 100 GHz. The study analyses the possible additional attenuation of the electromagnetic waves in adverse weather conditions and the differences in targets reflectivities, in comparison to the performances of current automotive radars. A comprehensive library of reflectivity signatures of a number of road actors is established, to provide a basis for the development of low-THz automotive radars. Secondarily, the thesis discusses and demonstrates the advantages of the employment of low-THz signals to improve the imaging capability of automotive radars, to allow identification and classification of road targets based on high resolution images and micro-Doppler signatures

An electromagnetic imaging system for metallic object detection and classification

PhD ThesisElectromagnetic imaging currently plays a vital role in various disciplines, from engineering to medical applications and is based upon the characteristics of electromagnetic fields and their interaction with the properties of materials. The detection and characterisation of metallic objects which pose a threat to safety is of great interest in relation to public and homeland security worldwide. Inspections are conducted under the prerequisite that is divested of all metallic objects. These inspection conditions are problematic in terms of the disruption of the movement of people and produce a soft target for terrorist attack. Thus, there is a need for a new generation of detection systems and information technologies which can provide an enhanced characterisation and discrimination capabilities. This thesis proposes an automatic metallic object detection and classification system. Two related topics have been addressed: to design and implement a new metallic object detection system; and to develop an appropriate signal processing algorithm to classify the targeted signatures. The new detection system uses an array of sensors in conjunction with pulsed excitation. The contributions of this research can be summarised as follows: (1) investigating the possibility of using magneto-resistance sensors for metallic object detection; (2) evaluating the proposed system by generating a database consisting of 12 real handguns with more than 20 objects used in daily life; (3) extracted features from the system outcomes using four feature categories referring to the objects’ shape, material composition, time-frequency signal analysis and transient pulse response; and (4) applying two classification methods to classify the objects into threats and non-threats, giving a successful classification rate of more than 92% using the feature combination and classification framework of the new system. The study concludes that novel magnetic field imaging system and their signal outputs can be used to detect, identify and classify metallic objects. In comparison with conventional induction-based walk-through metal detectors, the magneto-resistance sensor array-based system shows great potential for object identification and discrimination. This novel system design and signal processing achievement may be able to produce significant improvements in automatic threat object detection and classification applications.Iraqi Cultural Attaché, Londo

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium