Temporally advanced signal detection: A review of the technology and potential applications

In recent years, a physical phenomenon referred to as Negative Group Delay (NGD) or superluminal wave propagation has been implemented in electronic circuitry and shown to temporally advance the detection of analog signals. Specifically, the output of such a circuit precedes the complete detection of its input as the group (and therefore time) delay through the circuit is negative. In this article we describe the background and theory behind this phenomenon, discuss its implementation in electronics and demonstrate a specific biomedical signal application (the human ECG). We discuss some key NGD circuit design considerations/configurations and potential applications in which this technology could offset or eliminate entirely, closed-loop control system delays.