Exploring mem-element emulators: A review

A memory-based resistor, commonly referred to as a memristor, differs fundamentally from the three conventional passive circuit elements, such as a resistor, a capacitor, and an inductor, because of its ability to retain the history of the charge that has passed through it, thereby exhibiting memory characteristics. The memristor was theoretically postulated by Prof. Leon O. Chua in 1971 as the fourth fundamental passive circuit element. However, it was not experimentally realised until 2008, when researchers at HP Labs demonstrated the first practical memristor. Following this breakthrough, the concept of memory circuit elements was extended to include memcapacitors and meminductors, collectively known as memelements. Owing to their nonlinear, nonvolatile, and memory-dependent characteristics, these devices have attracted considerable attention for applications in neuromorphic computing, nonvolatile memory, artificial intelligence, analogue signal processing, and adaptive electronic systems. Since the large-scale fabrication and commercialisation of practical memristive devices remain challenging, researchers have proposed numerous memristor emulator circuits and simulation models to investigate their characteristics and potential applications. This review presents a comprehensive overview of recent developments in memristor emulators, including their mathematical modelling, circuit implementations, performance analysis, and emerging applications. It discusses future research directions in this rapidly evolving field.