This Metamaterial Could Turn Earthquakes & Explosions Into Electricity While Helping Protect Buildings

Imagine a material that does not need to be tuned to one particular vibration frequency to harvest energy. Whether it is pushed, pulled, shaken, or hit with a sudden disturbance, the material could capture the incoming energy, guide it to a specific location, and convert part of it into useful electrical power.

Researchers Hwang and Arrieta have proposed a remarkable approach based on nonlinear metamaterials and transition waves. Their work shows how a one-dimensional chain of specially designed bistable elements could potentially transmit, concentrate, store, and harvest mechanical energy in a way that is largely independent of the frequency or strength of the incoming excitation.

The concept could eventually lead to structures that not only protect buildings and infrastructure from extreme events but also recover some of the energy produced by those events.

The Problem With Conventional Vibration Energy Harvesting

Vibration-based energy harvesting is not a new idea. Researchers have developed devices that use vibrations from machines, vehicles, buildings, and other structures to generate electricity.

The problem is that conventional harvesters usually work efficiently only within a relatively narrow frequency range.

This happens because many energy harvesters depend on mechanical resonance. A structure vibrates particularly strongly when it is excited near its natural frequency. If the incoming vibration moves away from that frequency, the amount of harvested energy can fall dramatically.

Researchers have tried to overcome this limitation using nonlinear systems, phononic crystals, and metamaterials. These approaches can provide greater flexibility, but many still depend on specific frequencies, excitation conditions, or carefully tuned structures.

There is another problem at low frequencies. Generally, achieving a very low natural frequency requires a larger structure. That makes conventional resonant energy harvesters difficult to scale for applications involving slow or irregular movements.

Hwang and Arrieta approach the problem from a different direction.

Using Transition Waves Instead of Resonance

The key to their concept is a special type of nonlinear wave called a transition wave.

The researchers use a one-dimensional lattice made from bistable elements. A bistable element has two stable mechanical states. Think of it somewhat like a switch that can remain comfortably in either of two positions.

When one element switches from one state to the other, it can trigger the neighboring element to switch as well. That process can continue through the chain, producing a wave of mechanical transitions.

Unlike ordinary vibration waves, these transition waves can travel through the lattice while being much less dependent on the precise frequency of the input.

This creates an important opportunity for energy harvesting.

Instead of designing a harvester that must respond perfectly to one frequency, the lattice can use the incoming disturbance to initiate a transition wave. The wave then carries energy through the structure.

The Lattice Can Store Mechanical Energy

One of the most interesting aspects of the system is that the bistable lattice can effectively behave like a mechanical capacitor.

When the bistable elements are moved between their stable configurations, mechanical energy can be stored within the lattice.

That stored energy does not necessarily have to be released immediately.

The lattice can transmit the energy as a transition wave, allowing it to travel toward a selected region where it can eventually be converted into electricity.

This is different from simply attaching a generator to a vibrating structure. The material itself becomes part of the energy-management system.

The lattice can receive energy, store it, guide it, concentrate it, and then release it for harvesting.

Turning the Lattice Into an Energy Harvester

To make the concept capable of producing electricity, Hwang and Arrieta introduce an electromechanical transduction mechanism directly into the unit cells.

In simple terms, the mechanical movement of the lattice is coupled to a mechanism that can convert mechanical energy into electrical energy.

This makes energy harvesting an intrinsic property of the metamaterial rather than something that has to be added separately at the end of the structure.

The approach is also potentially versatile because the researchers focus on generic bistable unit cells. Different physical architectures could potentially be used to create these bistable elements.

That means the underlying concept is not restricted to one particular mechanical design.

Defects Can Tell the Energy Where to Go

The researchers discovered another powerful feature: engineered defects can be used to manipulate the waves.

A defect here does not necessarily mean damage. Instead, it is an intentionally designed change in the otherwise repeating lattice.

For example, researchers can modify the mass of selected elements or change the forces between neighboring elements.

These small changes can alter how the transition wave moves through the structure.

By carefully positioning such defects, the incoming energy can be directed toward a desired location.

This is particularly important for energy harvesting because concentrating energy at one location makes it easier to install an efficient transduction mechanism there.

Instead of allowing energy to spread throughout the entire structure, the metamaterial can effectively act as a mechanical pathway that guides energy toward a chosen harvesting point.

A Surprising Breather-Like Mode

The simulations revealed an even more unusual phenomenon.

The researchers observed a breather-like mode in this type of bistable lattice.

A breather is a localized oscillatory state in which energy remains concentrated around a particular region instead of simply traveling away.

In this system, such a localized state can help transform the energy carried by a transition wave into sustained oscillatory motion.

That is useful because electrical generators often benefit from having mechanical motion continue over a longer period rather than receiving one extremely short burst of energy.

According to the researchers, introducing these effects improved the harvesting performance by approximately an order of magnitude.

In other words, the engineered dynamics could increase the amount of practically usable energy by roughly ten times compared with the corresponding baseline configuration.

More Than Just an Energy Harvester

The potential applications extend beyond simply powering small electronics.

Because the system can redirect incoming mechanical energy while simultaneously harvesting it, it could potentially become part of a new generation of protective metamaterials.

Imagine a structure designed to experience a powerful mechanical disturbance.

Instead of allowing all of that energy to propagate randomly through the structure, the lattice could redirect it along a controlled path. Some of the energy could be concentrated and harvested, while the structure itself helps manage the disturbance.

This could be relevant to extreme events such as earthquakes, tsunamis, explosions, or other sudden impacts.

For example, a future protective structure might redirect destructive mechanical energy away from sensitive components while converting a portion of that energy into electricity.

That electricity could potentially help power local sensors, monitoring systems, communication equipment, or emergency electronics after an event.

A New Way to Think About Energy Harvesting

The most important idea behind this research is that energy harvesting does not always have to depend on matching a device to a particular vibration frequency.

Instead, the material's nonlinear dynamics can determine how energy moves through the structure.

The bistable lattice provides a way to receive mechanical disturbances, convert them into transition waves, guide those waves, concentrate energy at engineered locations, and potentially store and release that energy over time.

Because the mechanism can operate independently of many details of the incoming excitation, it offers a fundamentally different approach to vibration energy harvesting.

The researchers' concept therefore combines several functions within one material architecture: energy transmission, energy concentration, mechanical storage, and electromechanical conversion.

If these principles can be successfully developed into practical large-scale structures, future metamaterials could do more than simply withstand extreme mechanical events.

They could manage those events and recover useful energy from them.

That possibility makes nonlinear, transition-wave-based metamaterials an intriguing direction for the future of both energy harvesting and protective engineering.

Reference: Hwang, M., Arrieta, A.F. Input-Independent Energy Harvesting in Bistable Lattices from Transition Waves. Sci Rep 8, 3630 (2018). https://doi.org/10.1038/s41598-018-22003-7