16 April 2026 | Shaoxiao Nie, Karlsruhe Institute of Technology, Germany | Blog
Sensors everywhere
You may not realize it, but sensors are everywhere. They measure signals, monitor conditions, and quietly collect information from places we cannot easily see. From cities and industrial systems to medical devices, sensors have become the invisible building blocks of modern life. They are small, silent, and often hidden — yet they help keep our complex world running smoothly.
Power problem
In most cases, sensors are powered either by cables or batteries, and everything seems to work just fine. However, both approaches come with limitations. Cable systems require infrastructure — wiring, installation, and maintenance — which can be costly and sometimes impractical, especially in complex or distributed environments, where sensors are spread over large areas. Batteries, on the other hand, offer flexibility, but introduce a different challenge. They eventually run out and need to be replaced or recharged, which is not always easy, and often costly. Imagine sensors deployed in remote or hard-to-reach locations — for example, in underground pipelines or agricultural landscapes — where batteries are the only option. This creates a strong need for alternative ways to power these systems.
Figure: Outdoor weather sensor in green foliage (Photo by Kilian Königs, Pexels).
Waste heat conversion
But what if the energy we need is already around us? If you look closely, energy is everywhere: light, motion, and heat. For small sensors, the required power is actually very low — often just tiny amounts. The challenge is not the lack of energy, but how to convert it into a usable form. This is where things become both interesting and challenging. Among various energy sources, waste heat stands out. It is abundant, often overlooked, and present almost everywhere. In fact, a large portion of global energy is eventually lost as heat — much of it at relatively low temperatures below 100°C [1]. This kind of “low-grade” waste heat is everywhere, yet it is rarely reused. If we could reuse even a small fraction of this wasted energy, it could make a big difference.
What we are exploring
Of course, turning this vision into reality is not straightforward. In fact, harvesting low-grade waste heat — especially below 100°C — is surprisingly difficult. Converting it efficiently into electricity remains a major challenge.
This is exactly what the Heat4Energy project is trying to address. In this project, we explore ways to convert low-grade waste heat into electricity using thermomagnetic materials and devices. As a PhD researcher, my focus is on developing miniature-scale generators that operate in the microwatt range.
If you have followed the previous blogs, you may know that there are different approaches to thermomagnetic energy conversion. So, what makes our approach different? The approach I am working on is based on a concept called ‘resonant self-actuation’ [2]. While the term may sound complex, the basic concept is quite intuitive. You can think of it as a tiny mass attached to a spring, moving back and forth. What makes it special is that this motion is generated by the temperature difference between a heat source and ambient — without any external driving force. The motion is also stable and periodic, meaning it naturally oscillates at a certain frequency.
By combining this self-driven motion with miniature-scale structures, the device can operate at relatively high frequencies (over 100 Hz), while maintaining a stable and significant movement. Using a pick-up coil or a piezoelectric layer, the motion is converted into electricity. This resonant motion helps improve the overall energy conversion performance.
My work involves designing, modeling, and testing these devices — from understanding their behavior at the system level to fabricating and evaluating real prototypes, and gradually improving their performance.
Gap to vision
We are still far from a world where sensors never need charging. Today, most energy harvesting technologies can only provide limited power, and often under specific conditions. In many real-world situations, completely replacing batteries is still not feasible. However, their lifetime can be extended, reducing the need for frequent replacement or maintenance. This points to a different way of thinking about energy — not just generating more, but using what is already available around us.
Why it still matters?
The amount of energy we are dealing with may seem insignificant. Microwatts are tiny — far from the scale of power plants or even household devices. It is easy to wonder whether such small amounts of energy really matter. But in a world where billions of sensors are being deployed, the picture starts to change. Individually, each device consumes very little. Collectively, they form a massive and growing energy demand — along with the need for batteries, maintenance, and replacement. In this context, even small improvements — when scaled across millions or billions of devices — could have a meaningful impact.
So, what if sensors never needed charging?
We are not there yet.
But by rethinking how we use and generate energy — even at very small scales — we are taking steps in that direction.
If you are interested in our research and want to see how we are paving the way for the next generation of energy, please follow our updates in this Blog, YouTube and LinkedIn.
References
[1] European Commission, Directorate-General for Energy, EU energy in figures: statistical pocketbook 2024, Publications Office of the European Union, 2024.
[2] Joseph, Joel, et al. “A Gd‐Film Thermomagnetic Generator in Resonant Self‐Actuation Mode.” Advanced Functional Materials 33.22 (2023): 2301250.
Attribution: Originally published by HEAT4ENERGY. Reposted with permission. Original article: https://heat4energy.eu/blog/blog-9-what-if-sensors-never-needed-charging
