[Paper Review] Smart materials and structures for energy harvesters

Tian Liu, Sanwei Liu+4 more|arXiv (Cornell University)|Sep 1, 2017

Innovative Energy Harvesting Technologies41 references3 citations

TL;DR

This paper reviews smart materials and structural designs for vibrational energy harvesters, focusing on piezoelectric materials and carbon nanotubes to enhance energy conversion efficiency. It addresses challenges like narrow bandwidth and low-frequency operation by analyzing transduction mechanisms and advanced techniques, contributing a comprehensive framework for optimizing harvesters in real-world applications with variable vibrational sources.

ABSTRACT

Vibrational energy harvesters capture mechanical energy from ambient vibrations and convert the mechanical energy into electrical energy to power wireless electronic systems. Challenges exist in the process of capturing mechanical energy from ambient vibrations. For example, resonant harvesters may be used to improve power output near their resonance, but their narrow bandwidth makes them less suitable for applications with varying vibrational frequencies. Higher operating frequencies can increase harvesters power output, but many vibrational sources are characterized by lower frequencies, such as human motions. This paper provides a thorough review of state of the art energy harvesters based on various energy sources such as solar, thermal, electromagnetic and mechanical energy, as well as smart materials including piezoelectric materials and carbon nanotubes. The paper will then focus on vibrational energy harvesters to review harvesters using typical transduction mechanisms and various techniques to address the challenges in capturing mechanical energy and delivering it to the transducers.

Motivation & Objective

• To analyze the state of the art in energy harvesters using diverse energy sources, including mechanical, thermal, electromagnetic, and solar inputs.
• To identify key challenges in capturing mechanical energy from ambient vibrations, particularly narrow bandwidth and low-frequency operation.
• To evaluate smart materials such as piezoelectric materials and carbon nanotubes for improved transduction efficiency.
• To explore structural and design techniques that enhance power output and operational robustness across varying vibrational frequencies.
• To provide a systematic review of transduction mechanisms and strategies for improving energy harvesting performance in real-world applications.

Proposed method

• Systematic review of vibrational energy harvesters using piezoelectric and carbon nanotube-based transduction mechanisms.
• Analysis of resonant harvesters and their limitations, particularly narrow bandwidth and sensitivity to frequency shifts.
• Evaluation of techniques to broaden operational bandwidth, including nonlinear mechanics and multi-degree-of-freedom designs.
• Investigation of high-frequency operation strategies to increase power output despite low-frequency ambient sources.
• Examination of structural configurations that optimize mechanical-to-electrical energy conversion efficiency.
• Synthesis of material and structural innovations to improve energy harvesting performance under variable vibrational conditions.

Experimental results

Research questions

• RQ1 How do resonant energy harvesters perform under varying vibrational frequencies, and what limits their practical deployment?
• RQ2 What role do smart materials like piezoelectric materials and carbon nanotubes play in enhancing energy conversion efficiency?
• RQ3 What structural and mechanical design strategies effectively broaden the operational bandwidth of vibrational energy harvesters?
• RQ4 How can energy harvesters be optimized for low-frequency sources such as human motion?
• RQ5 What are the most effective transduction mechanisms for converting ambient mechanical vibrations into usable electrical energy?

Key findings

• Resonant harvesters exhibit high power output near their resonance frequency but suffer from narrow bandwidth, limiting their utility in variable-frequency environments.
• Piezoelectric materials are widely used due to their high energy conversion efficiency and compatibility with microfabrication techniques.
• Carbon nanotubes show promise due to their high mechanical strength and tunable electrical properties, enabling efficient energy harvesting at the nanoscale.
• Techniques such as nonlinear mechanics and multi-mass configurations significantly broaden the operational bandwidth of vibrational harvesters.
• High-frequency operation increases power output, but many ambient sources operate at low frequencies, necessitating innovative structural designs to match input conditions.
• The integration of smart materials with optimized structural geometries enhances energy harvesting performance across diverse and unpredictable vibrational inputs.