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We use a high pattern-fidelity technique on piezoelectric electrodes to selectively excite high-order vibration modes, while isolating other modes, in multi-layered through-wall ultrasound power transfer (TWUPT) systems. Physical mechanisms, such as direct and inverse piezoelectric effects at transmitting and receiving piezoelectric elements, as well as wave propagation across an elastic barrier and coupling layers, all contribute to TWUPT. High-order radial modes in a TWUPT system feature strain nodes, where the dynamic strain distribution changes sign in the direction of disks' radii. This study explains theoretically and empirically how covering the strain nodes of vibration modes with continuous electrodes results in substantial cancelations of the electrical outputs. A detailed analysis is given for predicting the locations of the strain nodes. The electrode patterning for creating the transmitter and receiver shapes is determined by the regions where local force and charge cancelation do not occur, i.e., the two modal principal stress components have the same sign. Patterning for creating the electrode shapes is performed by high-fidelity numerical modeling supported by experiments. Using differential excitation on the transmitter side while monitoring transmitted power and efficiency on the reception side at various vibration modes is made possible by the unique nature of TWUPT systems. Due to an improvement in system quality and power factors, it is determined that employing the proposed electrode pattern designs enhances overall device efficiency and active power. The suppression of other modes makes up a filter feature that is paired with the enhancement at the mode under consideration. 

Mode couplings associated with elastic wave propagation through three-dimensional multiplex structures, as manifested by asymmetric eigenmodes and dissipation, determine the efficiency of electromechanical structures. As a result, it is critical to predict electroelastic symmetric modes such as thickness expander and radial modes, as well as asymmetric flexural modes, while accounting for material losses. Multiplex electromechanical structures include multi-layered through-wall ultrasound power transfer (TWUPT) systems. Physical processes that support TWUPT include vibrations at a transmitting/acoustic source element, elastic wave propagation through a barrier and coupling layers, piezoelectric transduction of elastic vibrations at a receiving element, and spatial resonances of the transmitting and receiving elements. We investigate mode couplings in an optimized modal TWUPT system, including their physical origins, models used to describe them, and regimes of weak and strong couplings. The system layout optimization is defined in terms of size (volume), operating frequency, and matching circuit load optimization. A computational model is developed and utilized in conjunction with experimental modal characterization to highlight the impact of eigenmode features on optimization results. Several behavioral modes are identified and analyzed. The interaction of symmetric radial and asymmetric flexural modes causes the system damping to increase and the device's overall efficiency to decrease. The electromechanical coupling factor value is likewise reduced as a result of this. Such occurrences are explained by the flow of energy between modes as they interact. The present work also proposes design guidelines to improve the performance of TWUPT systems based on exploiting inherent physical phenomena.