Inconsistent testing undermines triboelectric generator data and hinders comparison across studies.
(Nanowerk Spotlight) Every time a fingertip swipes a phone screen, a pen taps a notebook, or fabric brushes against skin, tiny bursts of electrical charge are exchanged between materials. This is the triboelectric effect—a basic physical phenomenon so ordinary it often goes unnoticed. But over the past decade, researchers have been trying to harness it in a very deliberate way.
They’re building devices called triboelectric nanogenerators, or TENGs, that turn surface contact into electrical power. The idea is simple: when two materials touch and then separate, they generate a voltage. Arrange this cycle into a repeatable motion, and you can produce alternating current. The word “nanogenerator” refers not to the size of the whole device, but to the scale at which charge is transferred—at contact points often measured in nanometers, where electrical exchange is most efficient. These devices typically use thin insulating layers just a few hundred microns thick, with surface textures engineered to enhance charge buildup at that tiny scale.
In principle, it’s a lightweight, low-cost approach to powering small electronics, wearable sensors, or environmental monitors—anywhere energy is scarce but motion is available.
But this deceptively simple concept faces a complicated problem. Different research groups often report very different performance numbers, even when working with similar materials. One study might claim a sharp increase in output from a new coating or surface structure; another finds no such benefit. Behind these inconsistencies is a deeper issue: testing conditions vary widely, and the most influential parameters are not always disclosed or controlled.
TENGs are unusually sensitive to how they’re built and tested. A small difference in contact force, surface alignment, or even how a wire is connected can significantly alter the electrical output. Misinterpreting these differences as evidence of improved materials or design leads to unreliable conclusions. This makes it difficult to compare results across studies, validate claims, or build a cumulative understanding of what works and why. For those developing real-world applications, it introduces uncertainty that makes engineering design and materials selection more difficult.
A framework for consistent performance testing
A new review published in Advanced Energy Materials (“How to Test Triboelectric Nanogenerators: Key Factors for Standardized Performance Evaluation”) addresses this issue directly. Written by Daniel Mulvihill and colleagues, the paper offers a structured framework for evaluating TENGs in the laboratory. It brings together insights from fabrication science, mechanical engineering, materials characterization, and electrical testing, organizing them into a guide that explains how to produce reliable, repeatable, and comparable measurements.
The authors divide the key influences on TENG performance into four categories: fabrication, mechanical, electrical, and environmental. These are treated not as isolated technical details, but as interdependent factors that shape every aspect of how a TENG performs.
Factors affecting TENG test results divided into the four subcategories addressed in this paper: fabrication, mechanical, electrical and environmental. (Image: Reprinted from DOI:10.1002/aenm.202502920, CC BY)
Fabrication details influence electrical behavior
Fabrication begins with the selection and preparation of materials. TENGs are made from layered components: triboelectric surfaces that contact and separate, electrodes that collect the charge, and sometimes spacers or insulating backings that guide the mechanical movement. The properties of these layers—thickness, elasticity, surface roughness, and even how flat and parallel they are—can influence both how much charge is generated and how consistently it flows.
For example, many research setups rely on commercially available adhesive tapes to create electrodes. But these can introduce air gaps or insulating layers at the interface, reducing performance in ways that may go unnoticed unless the device is carefully characterized.
Testing conditions vary more than expected
Mechanical testing introduces another layer of variation. In earlier studies, TENGs were often actuated by hand or with improvised rigs. These informal methods are now largely replaced by programmable machines—linear motors, electrodynamic fatigue testers, or tribometers—that apply contact with known frequency and force.
But even among these, the level of precision varies. A linear motor can control motion but often lacks fine control over the force between surfaces. Fatigue testers offer better force regulation but at higher cost. Tribometers, widely used in friction and wear studies, are especially useful for sliding TENGs, where surface movement is continuous rather than cyclical.
Real contact area drives output, not surface size
One of the most important variables, and one that is often overlooked, is contact area. There is a critical difference between the nominal contact area—the visible overlap between two surfaces—and the real contact area, where physical contact actually occurs at the microscopic scale. Because most surfaces are rough at some level, actual contact may occur only at isolated points.
The review highlights that TENG output increases with real contact area, not just the visible size of the surfaces. This means that surface alignment, local roughness, and material stiffness all shape the electrical response. Even small misalignments—on the order of a fraction of a degree—can cause sharp reductions in output.
Force, texture, and material properties interact
Another factor is contact force. As pressure increases, surfaces deform and more microscopic contact points come into play. This expands the real contact area and raises output, but only up to a point. At high loads, the effect tends to level off. The authors recommend that tests be performed under controlled and reported contact pressure, ideally normalized by the nominal area, so that different setups can be meaningfully compared.
Surface texture matters too, but its effects are complex. Some structured surfaces enhance output by increasing contact points or generating local strain gradients, which may induce polarization through a mechanism called the flexoelectric effect. In other cases, increased roughness reduces output by lowering the real contact area. The outcome depends on how the materials interact and deform. The review stresses the importance of replicating surface topography as closely as possible when comparing different materials or treatments.
Even the mechanical properties of the materials themselves—particularly their elastic modulus—play a role. Softer materials deform more under the same force, creating larger contact areas. They may also undergo more bond breakage during contact, which some theories suggest could boost charge transfer. However, these benefits come with trade-offs, such as increased wear or reduced mechanical stability over time.
Electrical measurements need careful isolation
Beyond the physical construction and movement, electrical measurement presents its own challenges. TENGs behave like high-impedance current sources, meaning that even small measurement errors—such as using a voltmeter with too low an internal resistance—can drain charge and distort results. The review outlines how to set up circuits that accurately capture open-circuit voltage and short-circuit current, using high-impedance meters and, where needed, amplification stages to isolate the true signal. Parasitic capacitance from wires or instruments can interfere with readings, especially at low frequencies or small signal levels, and needs to be carefully managed.
Environmental conditions affect repeatability
Environmental conditions also influence performance. Humidity can increase surface conductivity and lead to charge leakage. Temperature changes may soften polymers or alter surface properties. The authors emphasize that these parameters should be monitored and reported during testing. For real-world applications, environmental sensitivity might be a design consideration; for laboratory tests, it’s a source of variation that needs to be controlled.
Moving toward standardization
Rather than prescribing a single universal testing method, the review proposes a structured approach to standardization. The goal is not to reduce all experiments to a fixed script, but to make the sources of variation visible and reportable. By identifying which parameters influence output, and by encouraging their consistent documentation, the paper lays the foundation for meaningful comparison between studies. It also recommends the creation of an international standards committee to formalize test procedures through ISO protocols.
This shift in focus—from materials innovation to measurement discipline—may seem modest, but it’s essential for progress. Without consistent testing, advances in materials or design remain difficult to verify. By bringing clarity to how TENGs are evaluated, this work enables more reliable comparison, more reproducible results, and ultimately a stronger basis for engineering energy-harvesting systems that work as claimed.
If this article was useful, support our independent nanotechnology reporting with any amount.
Your contribution funds the next explainer and keeps Nanowerk open for everyone.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
