报告题目：Low- and bandpass NGD circuit concept

报告时间：2018年07月17日（周二）上午9:00

报告地点：微波楼2楼会议室

报告人：Blaise Ravelo 副教授

主持人：万发雨 教授

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电子与信息工程学院

2018-07-13

专家简介：Dr. Blaise RAVELO is an associate professor Normandy University.  His research topic includes electronics circuit boards design/modelling, signal integrity and electromagnetic compatibility/interference (EMC/EMI) characterization. He is pioneer of the negative time-delay circuits and anticipated & advanced signal processing. He is (co-)authors of more than 210 scientific research papers in new technologies published in int. conf. and journals. With US, Chinese, Indian, European and African partners, he is actively involved and contributes on several research, development and innovation international research projects (ANR, FUI, FP7, INTERREG, H2020, Euripides², Eurostars…). He is the scientific chair of int. conf. ICONIC 2011, organizer and chairman of special sessions of int. conf.: META2012 (Paris), AES2012 (Paris), RADIO2014 (Mauritius), RADIO2015 (Mauritius) and EuCAP2015 (Lisbonne).

报告内容摘要：Since the classical monograph of Sommeferld and Brillouin, it has been known that in anomalously dispersive media wave packets can propagate at abnormal group velocities, i.e. velocities that are superluminal or even negative. It implies that the group delay can be negative. The fact that the group velocity can become negative in a spectral region of anomalous dispersion raised concerns about causality in the early days of special relativity. By considering a signal with a definite starting point, namely, a step-modulated sinusoidal waveform with a frequency near the absorption line of the dispersive medium, they pointed out that in the region of anomalous dispersion the group delay, which in general is neither the signal delay nor the energy propagation delay can be superluminal or negative. In this case, the medium exhibits a negative group delay (NGD) phenomenon. In 1970s, Garret and McCumber examined the propagation of a Gaussian pulse through a medium having a positive or negative absorption line and showed through analytic expressions that the pulse can propagate at superluminal group velocities while still remaining substantially Gaussian in shape for many absorption depths. In 1982, Chu and Wong employing picosecond laser pulses propagating in GaP:N samples experimented first time the NGD phenomenon. By using gain-assisted linear anomalous dispersion, Wang and his team reported the observation of NGD propagation in a 6-cm cesium gas cell. In an experiment that exploited the spectral region of anomalous dispersion between two closely spaced resonances in a laser-driven potassium vapor, Chiao and his team proposed an NGD resonant system. By identification, operational amplifier based NGD circuits were proposed in 1990s. But such NGD circuit are limited to hundred KHz. In 2000s, RF/microwave NGD passive circuits operating up to several GHz was inspired from metamaterial left-handed concept. But these passive NGD circuits generate losses more than 20dB in order to synthesize significant NGD level. In 2007, active microwave NGD circuit was proposed. This active circuits open potential RF/microwave applications of the NGD circuits notably for synthesizing independent frequency phase shifter, balun, power divider and combiner. In addition, signal and power integrity applications were also introduced with the NGD-based equalization technique. Despite the performed research works which confirm the existence of the NGD phenomenon, many efforts are still necessary to democratize the concept in both academic and industrial world. For this reason, basic theory on the NGD topologies is reported . An analogy between the NGD and linear filter theory was proposed. Simple low-pass and band-pass NGD circuits are defined. The main characteristics of these unfamiliar NGD circuits are proposed.