We investigated the Fourier transform of memristor with various barriers and neuristor. To provide the different barriers we present a simple adaptive model dependent on input signal. We saw that there was no significant change of the harmonics with increasing barriers. Neurons provide an energy and area efficient and could be used in neuromorphic circuits. We used a neuron circuit that can be efficient to provide second and higher harmonics. Neuron circuit generates various spike shapes like regular spike, fast spike, initial bursting, chattering, etc. In this paper we analysed the Fourier transform of the most common spike shapes. The neuron or neuristor can be more efficient to generate second and higher harmonics compared to the other standard circuits.