Inkjet-Printed RTDs on Kapton for Integrated Sensing Platforms: A Preliminary Metrological Evaluation

Introduction

Driven by the increasing demand for compact, lightweight, and comfortable devices, flexible sensors have attracted growing research interest. This motivates the development of inkjet-printed resistance temperature detectors (RTDs) on flexible polymeric substrates. However, before a printed RTD can be reliably used as part of an integrated sensing platform, its metrological behavior should be evaluated under controlled conditions. The present work focuses on the primary metrological evaluation of inkjet-printed RTDs as a preliminary step toward their future integration with other printed sensing elements.

Methods

The printed RTDs were characterized under a controlled laboratory setup. Each DUT was mounted on a custom test platform that provided mechanical support and electrical access without directly modifying the sensing element. The platform included a co-located NTC used as the reference temperature sensor. The DUT resistance was measured in a four-wire configuration using a Rigol M300 data acquisition/multimeter system with 6½-digit resolution. A dedicated LabVIEW interface was developed for subsequent post-processing.

Results

The present study uses the square-spiral layout as the first metrological validation case. The heating and cooling branches were evaluated separately. The equivalent hysteresis was below approximately 0.6 °C, while the TCR variation across repeated tests remained limited. Using the appropriate baseline-referenced interpretation, the square-spiral RTD showed promising temperature reconstruction performance under controlled steady-state conditions. For the best-performing device, the branch-specific calibration resulted in a low dispersion of the temperature reconstruction residuals, generally below 0.1°C, while maximum absolute temperature errors were mostly below 0.5 °C.

Conclusion

The results indicate that, although the sensor response is highly linear under steady-state conditions, practical use requires branch-specific calibration and baseline referencing to account for hysteresis and repeated-test variations. These results support the next transition toward a portable setup, where packaging, contact stability, and mounting conditions must be validated before integrated sensing applications.