Design of the Squared Daisy: A Multi-Mode Energy Harvester, with Reduced Variability and a Non-Linear Frequency Response

Abstract

With the rise of the Internet of Things (IoT) and the ever-increasing number of integrated sensors, the question of powering these devices represents an additional challenge. The traditional approach is to use a battery; however, harvesting energy from the environment seems to be the most practical approach. To that end, the use of piezoelectric MEMS energy has been proven as a potential power source in a wide range of applications. In this work, a proof of concept for a new architecture for MEMS energy harvesters is presented. The influence of the dimensions and different characteristics of these designs is discussed. These designs have been proven to be resilient to process variation thanks to their unique architecture. This work presents the use of vibration enhancement petals in order to widen the bandwidth of the energy harvester and provide a non-linear frequency response. The use of these vibration enhancement petals has allowed the fabrication of three design variations, each using an area of 1700 µm by 1700 µm. These designs have an operating bandwidth between 3.9 kHz and 14.5 kHz and can be scaled to achieve other targeted resonant frequencies.

Control of Spring Softening and Hardening in the Squared Daisy

“…As marked in Figure 5 , the deflection of the central mass was considered as the measurement point. The deflection measurements of the free cantilevers will yield a similar response with a higher velocity due to the increased degree of freedom of such cantilevers, as shown in [ 27 ]. This can also be directly observed using the measurement of the mode shape of both variants presented in Appendix A .…”

“…its nonlinear behavior. This architecture was presented for the realization of a MEMS piezoelectric VEH in [ 27 ]. The SD structure can be partially simplified to the weighted string structure, as it consists of a central proof mass acting as the weight suspended by a predefined number of cantilevers of varying cross-sections, as shown in Figure 2 .…”

“…A basic analytical analysis of the resonant frequency in the SD structure was presented in [ 27 ], where it was shown that the fundamental resonant frequency of such a structure can be expressed as [ 27 ]: where E is the Young’s modulus of the material, I is the area moment of inertia, which depends on the physical dimensions of the device, is the radius of the proof mass, H is the height of the proof mass, is the density of the material, L is the length of the structure, and denotes the scaling factor.…”

“…This process provides cost-effective access to piezoelectric MEMS prototyping. In the literature, this process has been reported for the implementation of various MEMS-based resonators and VEH (e.g., [ 7 , 27 , 34 , 35 , 36 , 37 ]). The fabrication process includes five masks based on an N-type, double-sided, polished silicon-on-insulator (SOI) wafer.…”

“…The application of such a method to nonlinear MEMS resonators as presented in [ 23 ], and remains the exception. Accordingly, characterization methods that reduce the impact of hysteresis are not widely employed in the literature touching on the design and development of nonlinear MEMS resonators, as can be observed in [ 6 , 7 , 8 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 24 , 25 , 26 , 27 ]. Therefore, developing experimental characterization methods that allow for mitigation, or at least relative control of such hysteresis in nonlinear MEMS resonators is desirable.…”