ABSTRACT
This chapter is a gentle introduction to the energy band theory. Instead of presenting the quantum mechanical band theory in solid-state physics, it explains energy band formation in periodic structures using circuit theory. First, periodic networks consisting of inductors and capacitors are shown to support wave propagation. Then, transmission line theory is briefly described. It is shown that periodically loaded transmission lines exhibit qualitatively similar behavior to solid crystals. It is pointed out that the frequency-domain wave equations for a transmission line and the one-dimensional time-independent Schrödinger equation describing an electron have the same mathematical form. The well-known Kronig-Penney model of one-dimensional crystal can be formulated as both a quantum mechanics problem and a transmission line problem, and the results are almost the same. The energy band formation in periodic structures is a universal phenomenon common to various systems that can support wave propagation and is not exclusive to quantum mechanics.
