In‐situ Near‐IR Spectroscopy Monitoring of Residual Strain in PEEK‐Coated Magnet Wires

Polyetheretherketone (PEEK) coatings are emerging as high‐temperature insulation for magnet wire in high‐voltage electric motors. Residual strain accumulated during coating extrusion and wire forming could undermine its dielectric reliability. This study demonstrates a rapid, non‐destructive protocol for quantifying the residual strain using near‐infrared (NIR) spectroscopy coupled with a two‐step optimized principal component regression (PCR) algorithm. Mid‐IR assignments and two‐dimensional correlation spectroscopy (2D‐COS) were applied to identify the strain‐sensitive NIR windows. After selecting the suitable spectral windows and applying baseline correction, a model trained on a single wire can predict strain values on new wires with an average R 2 of around 0.90. The model accuracy declined at varied deformation rates, indicating the need for rate‐specific model training or multi‐rate models for production use. An inline NIR monitoring setup design for a PEEK‐coated magnet wire production line is proposed for enabling closed‐loop control of processing parameters.