Interview

Abstract

Hiroya Tanaka from Toyota Central Research and Development Laboratories in Japan talks about the work behind the paper ‘Memristance enhancement by external voltage source’ on page 1446. Hiroya Tanaka I was engaged in the research of mobile antennas and radio wave propagation analysis during my Ph.D. Afterwards, I joined Toyota Central Research and Development Laboratories, Inc.. A lot of electric and electrical components are used in recent vehicles for energy management and advanced control. My current interests are nano-structured electromagnetic devices, nonlinear circuit elements and electromagnetic compatibility management for automotive applications. The result reported in the Electronics Letters paper is an output from the current research activity. An amazing finding has been reported by Professor M. Di Ventra's group. They have indicated that memristance is enhanced by white noise due to the nonlinear phenomenon of stochastic resonance. In our Letter, an alternative approach for the enhancement is proposed. The proposed circuit uses an external voltage source instead of white noise. The external voltage source has higher amplitude and frequency than the original signal. The numerical analysis reveals the increase of the memristance. Moreover, the current-voltage characteristic of the original signal is modulated by the external voltage source and then the hysteresis characteristic is enlarged. In our approach, the memristance is enhanced by the external voltage source instead of the white noise. The white noise level is tuned by temperature variation. On the other hand, the amplitude and frequency of external voltage source can be arbitrarily and easily tuned. Therefore, the proposed system is suitable for circuit implementation. The results in our Letter indicate that the memristance enhancement and hysteresis loop can be engineered by modulating memristance. In the past two decades, the role of fluctuation in system enhancement has been discussed in the context of nonlinear physics. One of the famous phenomena is ‘stochastic resonance’, which is induced by noise. The other example is ‘vibrational resonance.’ In this scheme, the noise is replaced by a periodic signal. The proposed system is included in the scheme of the vibrational resonance. The nonlinear physics based on the fluctuation has been applied to the field of signal processing. Various applications have been theoretically investigated, such as signal detection, imaging and wireless communication. The memristors are among interesting nonlinear circuit elements. Therefore, we have explored the possibility of memristors. Adequate parameters of the external voltage source – the amplitude, frequency and relative phase – should be set to maximise the memristance enhancement. In our Letter, the optimum parameters are determined numerically. Optimum condition of the external voltage source is strongly desired for maximising the circuit performance in the viewpoint of design. In the next step, I will derive the framework of designing the effective external voltage source. I am currently analysing the time response of memristance in the circuit using the external voltage source. The optimum condition of memristance enhancement circuit using external voltage source will be discussed in a later publication. The scheme of stochastic and vibrational resonance has often been discussed theoretically. And then the great enhancement of signal processing performance has been reported. However, to the best of our knowledge, there has been no successful example in practical applications. This is because the applied fluctuation should be controlled adaptively following the environment to maximise the signal processing performance. In addition, the memristive devices giving the maximum enhancement of the system performance should be developed. We have a big challenge in applying the interesting nonlinear physics to the real-world applications. Various schemes of memristive devices have been investigated theoretically and experimentally. Those include not only memristors but also memcapacitors and meminductors. Combinations of memristive systems with fundamental circuit elements will bring novel functions and advantages into the current analogue and digital circuit. Various applications of memristive devices have been investigated, such as digital memory, logic, neuromorphic circuits, learning circuit and programmable circuits. The memristive devices will be put into these practical applications in the near future.