arXiv subjects

Yasutaka Amagai

Publications and source records attributed to Yasutaka Amagai.

4 recordsLinked to original sources

arXiv2026

Quantitative comparison of heat flow, guarded-heater and AC Harman methods for thermoelectric module efficiency

The evaluation of thermoelectric conversion efficiency remains challenging owing to the lack of internationally standardized measurement protocols. Commonly used techniques -including the heat flow, guarded heater, and AC Harman methods-differ fundamentally in their operating principles and sensitivity to heat losses. In this study, we benchmark three module-level efficiency measurement techniques -the heat-flow, guarded heater, and AC Harman methods- using commercial Bi2Te3-based modules with different module architectures. The conversion efficiencies obtained using the heat flow and guarded heater methods showed closely consistent central values and similar temperature-dependent trends over the investigated range. In contrast, the efficiency derived using the AC Harman method was systematically lower by approximately 16 % to 30 %, depending on the module architecture. Steady-state finite-element calculations of heat conduction and radiation indicated that the open thermal boundary condition used in the Harman configuration produces module-architecture-dependent internal temperature distributions and effective temperature differences, consistent with the experimentally observed trend. These results demonstrate that module-level efficiency estimated using the AC Harman method can be affected by nonideal thermal environments and emphasize the necessity of accounting for radiative and substrate-related heat losses. Nevertheless, the AC Harman method remains useful for rapid performance screening, provided that its module- and boundary-condition-dependent systematic bias is appropriately considered. Our results provide a quantitative benchmark for major measurement techniques and support the development of best practices, method-selection guidelines, and future methodological standardization in module-level thermoelectric metrology.

physics.app-ph↗

arXiv2026

Reverse heat flow with Peltier-induced thermoinductive effect

The concept of "thermal inductance" expands the options of thermal circuit design. However, the inductive component is the only missing components in thermal circuits, unlike their electromagnetic counterparts. Herein, we report an electrically controllable reverse heat flow, in which heat flows from a low-temperature side to a high-temperature side locally and temporarily in a single material by imposing thermal inertia and an ac current. This effect can be regarded as an equivalent of the "thermoinductive" effect induced by the Peltier effect. We derive an exact solution indicating that this reverse heat flow occurs universally in solid-state systems and that it is considerably enhanced by thermoelectric properties. A local cooling of 25 mK is demonstrated in (Bi,Sb)2Te3, which is explained by our exact solution. This effect can be directly applied to the potential fabrication of a "thermoinductor" in thermal circuits.

physics.app-ph↗

arXiv2025

Current comparator for both AC and DC ratio measurements with 10-8-level accuracy

Accurate measurements of alternating current (AC) and direct current(DC) ratios are fundamental to electric power metrology. However, conventional current comparators for AC and DC typically rely on distinct technologies-electromagnetic induction for AC and superconducting quantum interference devices for DC. This technological divide leads to a fragmented and complex traceability system. Bridging this gap is critical for developing unified current standards that meet the demands of emerging power technologies. In this work, we present a compact, room-temperature AC/DC current comparator that integrates a diamond-based magnetometer using nitrogen-vacancy centers. The device achieves an accuracy of 10-8 for both AC and DC signals and supports a system bandwidth up to 300 Hz, without the need for cryogenics. It surpasses the performance of typical AC comparators, offering ten-fold higher accuracy, and matches that of state-of-the-art DC comparators. This unified, cryogenics-free solution not only enhances precision and versatility but also expands the applicability of the system to DC resistance bridges in quantum electrical standards.

quant-ph↗

arXiv2020

Large-scalable fabrication of improved Bi-Te-based flexible thermoelectric modules using a semiconductor manufacturing process

Among the several flexible thermoelectric modules in existence, sintered Bi-Te-based modules represent a viable option because of their high output power density and flexibility, which enables the use of arbitrary heat sources. We have fabricated Bi-Te-based modules with a large-scalable fabrication process and improved their output performance. The reduction in the interconnection resistance, using thick electrodes of the flexible printed circuit, significantly improves the module's output power to 87 mW/cm$^{2}$ at $ΔT$ = 70 K, which is 1.3-fold higher than a previous prototype module. Furthermore, the establishment of the fabrication for the top electrodes by using the surface mount technology makes it possible to realize a high-throughput manufacturing of the module. Our durability tests reveal that there is no significant change in the internal resistance of the module during 10000 cycles of mechanical bending test and 1000 cycles of thermal stress test.

physics.app-ph↗