Practical asymmetry and its effects on power and bandwidth performance in bi-stable vibration energy harvesters

Abstract

Scavenging energy from ambient vibrations using piezoelectric bi-stable energy harvesters (BEHs) has been a research focus in recent years. The typical assumption that BEHs have perfectly symmetric potential profiles is hardly attainable in practice. Unlike previous works which model asymmetry as a quadratic restoring force term, we present a physically quantifiable concept of practical asymmetry degree γ which can be utilized in both theory and experiment. Also, we optimize the nondimensional method by normalizing to the inherent parameters, which guarantees consistent and comparative model analysis. Based on above, a comprehensive study of practical asymmetry’s effect on BEH’s performance is experimentally validated. Results show that for stable inter-well oscillation, asymmetry increases BEH’s output power due to enlarged phase orbit space, but decreases BEH’s bandwidth due to elevated potential barrier. Compared with symmetric BEH, asymmetric BEH improves power by 57.56 % and 26.93 % but reduces bandwidth by 73.81 % and 57.38 % in simulation (γ = 4.08) and in experiment (γ = 4.11), respectively. Initial position in the shallow well improves both power and bandwidth of the asymmetric BEHs. Compared with deep well initial position, shallow well initial position exhibits 41.72 % power improvement and 50.00 % bandwidth increase in experiment (γ = 4.11). Sufficiently large excitation level is required to reach above conclusions, as asymmetric BEHs under small excitations might not reach optimal performance. These results provide instructive insights for designing practical BEHs with improved power and bandwidth performance.