When an elastic wave travels through an elastic joint connecting two different waveguides, some of the incident power is transmitted while the rest is reflected due to mismatch in mechanical impedance between two waveguides. If an impedance-matching element is used, all of the incident power can be transmitted to mismatched waveguides. On the other hand, there exists a frequency band within which the elastic wave is not allowed to propagate inside the structure in periodic waveguide and this phenomenon being called the “band gap”. When the unit cell of periodic waveguides includes an impedance-matching element, interesting phenomena occur. This study investigates various aspects of such periodic waveguides with simulations