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Author: search.filters.author.Ono, TakahitoSubject: search.filters.subject.Radiative cooling

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    Flexible thermoelectric cooler with optimized fill factor and radiative cooling integration for energy-efficient wearable thermal management
    (2025-12-01)
    Gobpant, Jakrit
    ;
    Sakulkalavek, Aparporn
    ;
    Sriniratkul, Pannarai
    ;
    Sa-I, Saowanee
    ;
    Rudradawong, Chalermpol
    The growing demand for skin-interfaced electronics in health monitoring, sports, and personal comfort highlights the need for compact, energy-efficient, and conformable cooling systems. However, existing thermoelectric coolers (TECs) are rigid, bulky, and power-intensive, making them unsuitable for wearable applications. To address this limitation, we present a flexible thermoelectric cooler (FTEC) with a compact footprint of 40 × 40 × 2.26 mm<sup>3</sup>, featuring discrete p- and n-types thermoelectric leg arrays with systematically varied fill factors (FF = 9 %, 16 %, 25 %, and 36 %). Optimization revealed that the 16 % FF configuration provides the most energy-efficient architecture, achieving a cold-side temperature of −5.9 °C and a coefficient of performance (COP) of 3.25 at 6 W input, while balancing cooling capacity and electrical loss. To improve heat dissipation without increasing bulk, ultrathin graphite and radiative cooling (RC) layers were integrated. Three configurations, including baseline (no thermal layer), graphite-enhanced, and RC-enhanced FTECs, were systematically evaluated. Under ambient conditions (33 °C), the RC- enhanced FTEC maintained a cold-side temperature of approximately 23 °C for 6 h during low-current operation of 0.3 A. Beyond intrinsic performance, the optimized FTEC was benchmarked against both commercial rigid TEC modules and state-of-the-art flexible TECs. Compared to widely used Peltier devices (TEC1–12705 and TEC1–12710), our FTEC achieved comparable ΔT with nearly 65 % lower power consumption, owing to fill factor optimization and RC-enhanced heat rejection. Mechanical flexibility was validated through bending tests, confirming both thermal and electrical stability. Finally, integration with an ESP32-based proportional–integral–derivative (PID) control system enabled real-time wearable cooling, successfully reducing skin temperature from 33 °C to 31 °C in on-body trials. This work demonstrates.
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    Flexible thermoelectric generator with radiative cooling for body-heat-driven self-powered Bluetooth low energy sensing system
    (2025-10-01)
    Gobpant, Jakrit
    ;
    Van Toan, Nguyen
    ;
    Ono, Takahito
    ;
    Tuoi, Truong Thi Kim
    ;
    Tran, Ngoc Dang Khoa
    Wearable electronics and wireless IoT sensors are increasingly expected to operate in a self-powered manner. However, their practical deployment remains limited due to the lack of compact, flexible, and sustainable energy sources. Thermoelectric generators (TEGs), which convert body heat into electricity, present a promising solution but are typically hindered by small temperature gradients and the requirement of bulky heat sinks that compromise flexibility. To address these challenges, we developed an ultra-thin flexible thermoelectric generator (FTEG) integrated with a radiative cooling (RC) layer that passively enhances heat dissipation under natural convection. The device, fabricated using high-performance thermoelectric materials on a soft silicone substrate, maintained a total thickness of just 2.26 mm. Finite element modeling and experimental validation confirmed that the RC layer effectively increased the temperature gradient across thermoelectric legs, significantly improving the output power compared to conventional graphite-based or no-cooling designs. The FTEG achieved a maximum normalized power density of 3.51 μW/cm<sup>2</sup> under temperature conditions representative of wearable use (T<inf>skin</inf> of 32 °C and T<inf>ambient</inf> of 26 °C). The harvested energy was then stored using a power management circuit and capacitor. This stored energy was successfully used to power a Bluetooth Low Energy (BLE) sensing module, enabling stable wireless transmission driven entirely by body heat. These results highlight the practical potential of integrating passive radiative cooling into flexible thermoelectric systems, paving the way for high-performance, battery-free wearable electronics and autonomous IoT applications.