Superluminality and amplifiers

Demonstration of negative signal delay with short-duration transient pulse

“…In 1990s, this negative group delay (NGD) phenomenon was also confirmed with several electronic experiments [22][23][24][25][26][27][28][29][30][31]. Firstly, by using an operational amplifier in negative feedback loop with passive networks based on R, L and C,…”

“…Chiao and his co-workers from the University of Berkeley proposed a topology of active circuit analogue to the resonant atomic system with negative refractive group index [22][23][24]. So, they have evidenced in time domain, an output Gaussian pulse peak in advance of about some hundreds of ms compared to the corresponding input.…”

“…So, they have evidenced in time domain, an output Gaussian pulse peak in advance of about some hundreds of ms compared to the corresponding input. They pointed out also that this NGD phenomenon does not forbid the causality [23][24][25]. To characterize this counterintuitive phenomenon, it is more general to use the group delay concept instead of the group velocity because in the electronic devices, the lumped component physical length is meaningless.…”

Neutralization of LC- and RC-Disturbances with Left-Handed and NGD Effects

“…(4) Since the early 1990s, the possibility to generate negative group delay (NGD) phenomenon has been confirmed in electronic domain thanks to the topology of circuit proposed by Chiao and his co-workers [19][20][21][22]. The first NGD circuit composed of an operational amplifier in feedback with passive networks mainly composed of resistor(s), inductance(s) and capacitance(s) as described in [23][24].…”

“…However, such NGD circuit operates only up to some hundreds kHz [23][24][25]. It was stated that the NGD effect does not contradict the causality principle [19][20][21][22][23][24][25][26]. In addition, the left-handed (LH) lumped passive circuit capable to generate NGD effect for microwave signals up to GHz has been introduced by the group of Mojahedi [15][16].…”