Traditional thermoelectric modules struggle with performance across broad temperature gradients, as most single materials lose efficiency outside their optimal temperature ranges. Addressing this limitation, the team devised a segmented approach, combining materials tailored for specific temperature regimes within the same module. The module features p-type legs segmented with mid-to-high temperature optimized germanium telluride (GeTe) and low-temperature optimized bismuth-antimony telluride (BST), paired with n-type legs made of structurally refined skutterudite (Yb₀.₃Co₄Sb₁₂, SKD).

Through multiphysics finite element modeling, the researchers optimized the module’s architecture, determining three critical shape factors to maximize performance. The segmentation ratio, height-to-area ratio, and p- to n-leg area ratio were finely tuned to 0.35, 0.67 mm⁻¹, and 1.85 respectively. This strategic geometrical refinement ensures balanced thermal and electrical transport properties, enabling the module to operate optimally under a substantial temperature difference of 500 K.

A significant breakthrough came from integrating an ultrathin nickel foil at the interface between GeTe and BST segments. Remarkably, this nickel layer serves as a diffusion barrier, preventing elemental intermixing and ensuring structural integrity under high temperatures. Concurrently, it acts as a metallization layer that minimizes internal contact resistance, a common bottleneck in thermoelectric device performance.

Experimental validation demonstrated the module achieving a power output of approximately 0.43 watts at 500 K temperature differential. This equates to a power density of 0.35 W/cm² per module surface area and 143 W/kg per module weight. Notably, considering only the active TE material area, the effective power density soared to an impressive 1.51 W/cm², showcasing the module’s remarkable energy harvesting capability.

Compared to baseline unsegmented modules, the segmented design boosts power density and conversion efficiency by 35% and 21%, respectively. These enhancements underscore the transformative potential of broad-temperature leg segmentation combined with precise structural optimization.

This research opens avenues for more efficient industrial waste heat recovery systems and deep-space power sources, where reliability and performance across variable temperature spans are critical. The solid-state nature of thermoelectric modules also offers advantages in durability and absence of moving parts, positioning them as promising candidates for next-generation sustainable energy solutions.

The study appears in the journal ENGINEERING Energy, highlighting a pivotal step forward in thermoelectric materials science and device engineering.

Subject of Research: Thermoelectric energy conversion, solid-state energy harvesting, thermoelectric module design
Article Title: Achieving 12.7% energy conversion efficiency in segmented GeTe/BST-SKD thermoelectric modules via broad-temperature and structural optimizations
News Publication Date: 30-Jun-2026
Web References: DOI 10.1007/s11708-026-1081-1
Image Credits: Ge Fu, Shangchao Lin, Yang Liu, Yiling Duan, Yixuan Liu & Qilin Zhang

Keywords

Thermoelectric modules, waste heat recovery, segmented thermoelectrics, GeTe, Bi₂₋ₓSbₓTe₃, skutterudite, energy efficiency, power density, solid-state power generation

Traditional wireless sensing devices, especially those used for continuous physiological monitoring like electroencephalography (EEG), demand substantial energy to maintain functionality over extended periods. This energy requirement typically translates to bulky batteries or frequent maintenance, constraints that drastically limit the usability and deployment of such systems in routine, long-term health monitoring. The University of Osaka’s research team confronted this challenge head-on by designing a novel energy-harvesting mechanism aimed at eliminating dependence on conventional power sources.

Central to this technology is the exploitation of thermoelectric energy derived from the temperature gradient between human skin and the surrounding environment. Despite ambient temperatures frequently approaching or even matching body temperature during hot summer days—conditions typically considered disadvantageous for thermoelectric harvesting—the system maintains continuous operation. Remarkably, during their live demonstration at Expo 2025, the wireless EEG device functioned flawlessly at ambient temperatures exceeding 32 degrees Celsius, underscoring the robustness and practicality of the approach.

Achieving persistent wireless EEG transmission with such a limited energy budget required an innovative approach beyond simply harvesting thermoelectric energy. The team employed compressed sensing—a sophisticated signal processing technique that drastically reduces the volume of data needed to reconstruct high-fidelity signals. By randomly undersampling the EEG signals at the transmitter side, the system significantly conserves energy otherwise spent on data acquisition and transmission. The critical challenge of reconstructing the original EEG signals from this compressed data is addressed by advanced algorithms located on the receiver side, which faithfully restore signal integrity despite the undersampling.

This architectural innovation not only reduces power consumption but also streamlines data handling, thus enabling the EEG system to operate without an external power source. The implications are profound: continuous EEG monitoring can now become viable in everyday settings, liberated from the limitations of battery life or wired connections. This could propel forward the practical application of brain-wave monitoring across healthcare and neurotechnology, allowing for seamless, long-term recording that is insensitive to user interference or maintenance interruptions.

An important aspect of the project lies in its successful translation from controlled laboratory conditions to a challenging real-world environment. The demonstration involved outdoor operation in the hot and humid summer climate of Osaka, where ambient temperatures matched closely with that of the human body. Traditionally, such small temperature differentials drastically reduce the power that can be harvested thermoelectrically, but the team’s system overcame this obstacle by maximizing efficiency in energy conversion and data processing.

The success of this system reflects a multidisciplinary confluence of bioengineering, electrical engineering, and signal processing expertise. By harnessing insights from applied physics and energy harvesting techniques, the researchers crafted a prototype that integrates complex electronics into a low-power, wearable form factor suitable for routine biomedical monitoring without compromising data quality or transmission reliability.

Looking forward, this wireless EEG technology demonstrates the viability of battery-free wearable devices powered by human body energy. The principle it embodies—leveraging minute environmental energy gradients and sophisticated data compression for sustainable operation—has vast potential applications. Beyond health monitoring, it could revolutionize environmental sensing, smart city infrastructures, and other domains where continuous, untethered, and maintenance-free data acquisition is desirable.

Furthermore, the researchers emphasized that improvements in low-power sensor design, combined with energy-harvesting strategies like theirs, will broaden the spectrum of feasible self-powered devices. As the Internet of Things (IoT) landscape expands, such innovations are critical to creating sensors that are not only ubiquitous but also environmentally sustainable, requiring no battery replacements or external charging.

The University of Osaka’s project, funded by prestigious bodies including the Japan Society for the Promotion of Science and NEDO, highlights the potential for national and international cooperation in advancing transformative technologies that merge human physiology and ambient energy sources. This breakthrough aligns with global efforts to reduce electronic waste, promote energy efficiency, and enable constantly connected health systems that empower individuals and healthcare providers alike.

In summary, the wireless EEG system powered by the body’s ambient temperature difference signifies a pivotal advance in medical electronics and sustainable technology. Its demonstrated capacity to operate reliably in demanding outdoor settings without an external energy source paves the way for a new generation of health monitoring solutions that are both practical and environmentally friendly. As this technology matures, it promises to make continuous brain activity monitoring accessible, unobtrusive, and truly maintenance-free—ushering in a new era where human health data can be captured seamlessly and sustainably.

Subject of Research: Not applicable

Article Title: A Battery-Free Wireless EEG Transmission System Using Compressed Sensing and Powered by Body-Ambient Temperature Difference: Outdoor Demonstration at Expo 2025

News Publication Date: 5-Feb-2026

References: DOI: 10.1109/ICCE67443.2026.11449878

Image Credits: Daisuke Kanemoto

Keywords: Applied sciences and engineering, Bioengineering, Energy harvesting, Electronics, Electronic devices, Bioenergy, Biotechnology, Applied physics, Signal processing