Circuit Solutions Toward Broadband Piezoelectric Energy Harvesting: An Impedance Analysis

The literature on piezoelectric energy harvesting (PEH) systems underscores the role of circuit advancements in enhancing energy harvesting capability in resonance. Recent studies using phase-variable (PV) synchronized switch technologies have also shown potential in broadband PEH, thereby improving off-resonance energy harvesting. However, the electrically induced dynamics by existing interface circuits lack a comprehensive definition and demonstration, hampering the performance comparisons across different circuits. Regarding these gaps, this paper presents an impedance-based analysis and comparison of electromechanical joint dynamics in PEH systems employing various interface circuits. The focus is on their contributions to enhancing harvesting bandwidth. By introducing resonance tunability into the conventional ideal PEH model, this paper proposes a more generic impedance model. It reveals that the achievable dynamic ranges of practical interface circuits are subsets of the ideal arbitrarily tunable scenario. A detailed quantitative study on the attainable ranges of the PV synchronized switch circuit solutions is provided after the introduction of the ideal target. Simulation and experimental data from different interface circuits align well with theoretical findings. The paper concludes that resonance tunability hinges on the extent of the achievable reactive (imaginary) part of the equivalent impedance. Electromechanical coupling conditions and dielectric loss may further impact resonance tunability. The general ideal model and quantitative impedance analysis provided in this paper help guide the future design effort toward high-capability and broadband PEH systems.