Piezoelectric patches are used in structural health monitoring (SHM) to generate diagnostic acoustic waves traveling in a structure and to gather the electro-mechanical impedance (EMI) signatures of structures. Piezoelectric patches are generally bonded to structures by means of adhesive layers. The adhesive layers could affect both the amplitude of the generated acoustic waves and the EMI signature of the structure. This article describes an analytical model to account for the power losses incurred by the adhesive layer used to bond a circular actuator to a structure at resonance. Validation of the model was carried out by actuating various sensors mounted with epoxy adhesive thickness ranging from 20 to 640 цт on aluminum plates. Experimental results confirmed that the thickness and the tangent loss modulus of the adhesive layer might play a significant role in the energy dissipated. In addition, this article explains how to interpret low-frequency EMI signature to assess the quality of a bond and estimate the thickness of the adhesive layer.