The Anatomy of the Chua circuit

Abstract: The Chua circuit, known to exhibit chaotic behaviour, has been constructed and studied. The goal was to investigate the experimental underpinning of the theory. The component relationship of the resistors, capacitors, inductors and operational amplifiers have been measured and established within their domain of validity. The system equations themselves cannot be directly validated through a traditional simulation vs. experimental study due to the chaotic property. Instead, a novel procedure is proposed where the system variables are split into groups, with each group being validated by obtaining the variables outside the group directly from experimental data. The method decisively confirms the equations and parameters values to be correct. To streamline the theoretical computations, the special piecewise linear structure of the system equations is used to obtain local analytical solutions, which are then pieced together by equation solving. Using the resistance as the control parameter, the different solutions to the equations are classified and qualitatively explained. A number of experimental tests are performed to investigate the correspondence between theory and experiments; the invariance under parity inversion, the position of the Hopf bifurcation and the equilibrium voltage as a function of resistance. Finally, chaos is quantified using the Lyapunov exponent. As its definition requires a metric, such is proposed based on energy consideration. The piecewise linear structure of the equation provides a very simple formula for the Lyaupnov exponent in terms of averaging over the Generalized Rayleigh quotient along a trajectory. The Lyaupnov exponent is evaluated as a function of resistance and compared with the qualitative conclusions about the circuit.