The work presented in this paper utilizes the physics of guided wave propagation for structural health monitoring (SHM) transducer designs. Both the theoretical and experimental studies illustrated the importance of guided wave mode selection for SHM applications. Guided wave mode control is realized with an annular array transducer design on a PVDF polymer piezoelectric film. A sample problem on a 1mm thick aluminum plate is presented. Numerical calculations of the wave structures and guided wave power flow distribution inside the plate provide quick guidelines for the wave mode selection in structural health monitoring. Experimental study illustrates the importance of mode control with the comparison of PVDF annular array transducers and PZT ceramic disc transducers. The characteristics of wave mode reflections to defect depth and the defect sizing effect are also discussed in this paper.