While resistors with memory, sometimes called memristive elements (such as
ReRAM cells), are often studied under conditions of periodic driving, little
attention has been paid to the Fourier features of their memory response
(hysteresis). Here we demonstrate experimentally that the hysteresis of
memristive systems can be unambiguously distinguished from the linear or
non-linear response of systems without hysteresis by the values of certain
Fourier series coefficients. We also show that the Fourier series convergence
depends on driving conditions, and introduce a measure of hysteresis. These
results may be used to quantify the memory content of resistive memories, and
tune their Fourier spectrum according to the excitation signal
