Architecture-independent power bound for vibration energy harvesters

E Halvorsen,P D Mitcheson,E M Yeatman,C P Le

doi:10.1088/1742-6596/476/1/012026

Abstract

The maximum output power of energy harvesters driven by harmonic vibrations is well known for a range of specific harvester architectures. An architecture-independent bound based on the mechanical input-power also exists and gives a strict limit on achievable power with one mechanical degree of freedom, but is a least upper bound only for lossless devices. We report a new theoretical bound on the output power of vibration energy harvesters that includes parasitic, linear mechanical damping while still being architecture independent. This bound greatly improves the previous bound at moderate force amplitudes and is compared to the performance of established harvester architectures which are shown to agree with it in limiting cases. The bound is a hard limit on achievable power with one mechanical degree of freedom and can not be circumvented by transducer or power-electronic-interface design.

Highlights

In designing energy harvesters, an important question is how to adjust the parameters of a chosen harvester architecture in order to optimize the performance? This question has been resolved for a number of harvester architectures under various operating conditons [1, 2, 3, 4] and resulted in guidelines on which among the known architectures to choose for given operating conditions [2]
Another important question is to what extent it is possible to significantly improve ouput power beyond that of the known architectures by inventing new device concepts, either related to the mechanics, the electromechanical conversion or the power electronic interface? In order to answer this question, it is necessary to know the ultimate limits on power without having to specify the details of the transducer and electronic interface, i.e. an architecture-independent power bound is needed
In this contribution we present a new theoretical bound that takes linear mechanical damping into account without making any a priori assumptions on the the details of the transducer or the electronic subsystem beyond the transducer having only one mechanical port

Summary

Introduction

An important question is how to adjust the parameters of a chosen harvester architecture in order to optimize the performance? This question has been resolved for a number of harvester architectures under various operating conditons [1, 2, 3, 4] and resulted in guidelines on which among the known architectures to choose for given operating conditions [2]. In order to answer this question, it is necessary to know the ultimate limits on power without having to specify the details of the transducer and electronic interface, i.e. an architecture-independent power bound is needed Such a bound based on input-power exists [5, 6], but does not account for parasitic losses which can amount to as much as half the input power even under optimal conditions [1]. Ta ta ta for a time interval [ta, tb] and seek the displacement waveform x that maximizes this quantity This approach is equivalent to optimizing the average of the power (F − bx )xtransferred at “1” in figure 1 and for long times it gives an upper bound on the power flow at later stages, such as the opportunity power at the output of the electromechanical transducer (”2” in the figure) or the final output power to a load or to a storage unit

Unrestricted proof mass motion

Strict limits on proof mass motion and periodic forcing

Optimum operation for a time harmonic force