Analysis of Upper Bound Power Output for a Wrist-Worn Rotational Energy Harvester from Real-World Measured Inputs

Abstract

Abstract. Energy harvesting from human motion addresses the growing need for battery-free health and wellness sensors in wearable applications. The major obstacles to harvesting energy in such applications are low and random frequencies due to the nature of human motion. This paper presents a generalized rotational harvester model in 3 dimensions to determine the upper bound of power output from real world measured data. Simulation results indicate much space for improvement on power generation comparing to existing devices. We have developed a rotational energy harvester for human motion that attempts to close the gap between theoretical possibility and demonstrated devices. Like previous work, it makes use of magnetically plucked piezoelectric beams. However, it more fully utilizes the space available and has many degrees of freedom available for optimization. Finally we present a prototype harvester based on the coupled harvester model with preliminary experimental validation. IntroductionEnergy harvesting has been a promising solution as the alternative to traditional systems powered by batteries when energy independence is required. As the power consumption becomes a major obstacle to the emerging market for wearable technologies, kinetic energy contained in human daily activities naturally appeals to the researchers in the field of energy harvesting. Due to the low and random frequencies of human motion, which usually occurs around 1 Hz [1], resonant harvesters cannot benefit from the peak dynamic magnification. The well-known Seiko Kinetic watch converts the kinetic energy of a rotor to electricity using an electromagnetic generator [2]. Such rotational designs with non-resonant configuration are the common approaches that researchers have adopted to overcome the limitation of conventional linear harvesters. While the Seiko Kinetic watch boosts its energy density by a sophisticated high-ratio gear train, another strategy, which is often referred to as frequency up-conversion, is to excite a higher-frequency resonance in a transducer via a slowerfrequency motion. Prior reported non-resonant harvesters include a piezoelectric harvester with inplane magnetic plucking based on a planar rotor model [3] and a magnetic spherical harvester [4]. The goal of this paper is to provide an estimate of the maximum power output from a rotational harvester regardless of the energy conversion mechanism using real-world measured data such as

Energy Harvesting Research: The Road from Single Source to Multisource

“…This idea has encouraged a large amount of research to investigate the possibility and feasibility of harvesting human biomechanical energy. Representative examples include shoe‐mounted generators in the heel or sole, medical implants, wearable devices harvesting head, wrist and arm motion, and backpack shoulder straps . There are comprehensive reviews available which focus on such biomechanical/human energy harvesting …”

Analysis of Magnetic Plucking Configurations for Frequency Up-Converting Harvesters

“…Plucking is one technique which applies such a strategy. Eccentric rotorbased wearable energy harvesters have been demonstrated in previous endeavors either using magnets [1] [2] or pins [3][4] to pluck piezoelectric beams. Magnetic coupling provides better reliability since it can be designed contact-free.…”

“…As shown in Figure 1, the direct repulsive configuration is listed alongside for later comparison as we have applied this orientation in our previous harvester prototyping with off-the-shelf components [2]. This paper will introduce the modelling, experimental validation and finally an implementation of the alternative magnetic configuration in a frequency up-converting energy harvester.…”

Piezoelectric Vibration Energy Harvester Using Indirect Impact of Springless Proof Mass

“…Frequency-upconverted electromagnetic transducers and piezoelectric generators using magnetic or impact-based systems are some of the examples [2,3]. Although utilization in a specific wearable device application would require further research efforts, harvesters having the form-factor of a conventional wristwatch have also been reported, which utilized the asymmetric rotor to convert the external vibration into a rotational motion and generate power [4,5]. Due to the straightforward operating principle and proven performance in the watch manufacturing industry, utilization of asymmetric rotor as a proof mass in energy harvesting device could potentially be a promising approach, but the improvement of output power and reduction of fabrication cost and complexity need to be accompanied.…”