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100 I-CONNECT007 MAGAZINE I FEBRUARY 2026 A RT I C L E BY Z AC K S C H A N E R , F L E X I B L E C I R C U I T T EC H N O LO G I ES T-type Thermocouples in Foil Heater Technology T his article examines the use of T-type ther- mocouples implemented with flexible printed circuit and etched foil heater technology, focusing on their design, fabrication, and integra- tion into advanced thermal management systems. I'll give particular attention to how their low-profile construction, accuracy at low temperatures, and mechanical robustness make them well-suited for critical devices operating in demanding environ- ments. These characteristics enable reliable tem- perature monitoring in applications where space constraints, environmental exposure, and perfor- mance requirements are especially challenging. Flexible T-type thermocouples are temperature sensors fabricated using polyimide as a dielec- tric, along with copper and constantan forming the sensing junction. When the junction between these foils experiences a temperature difference relative to a reference junction, a thermoelectric voltage is generated through what is known as the Seebeck effect, producing a predictable electromotive force that can be correlated with temperature. These sensors are particularly well-suited for low- temperature measurements, offering high accuracy and stability over a range of approximately −200°C to +200°C (with a tolerance of approximately +/- 1°C). The linear response and well-established material properties of T-type thermocouples con- tribute to their reliability in precision sensing appli- cations under extreme conditions. Compared to thermistors and RTDs, T-type ther- mocouples offer several advantages, especially in flexible printed circuit and etched foil heater appli- cations. As inherently passive devices, they require no excitation current, which eliminates self-heat- ing errors and simplifying circuit design. Thermo- couples can be fabricated as extremely low-profile structures—down to approximately 0.004" thick—