Abstract Additive fabrication of active materials with sub‐millimeter resolution can improve the performance and expand the functionality of sensing, actuation, and transduction in microsystems. In particular, the integration of soft magnetic materials of customized 3D geometries that guide and focus magnetic flux can increase inductive coupling and interaction forces. In this paper, a magnetic material extrusion method is used to fabricate flux concentration structures of arbitrary shapes. A magnetic permeability of 42 is experimentally demonstrated. Ring and H‐shape structures are used to evaluate their performance as inductive, power‐line energy harvesters. An output power density of 6.4 µW g −1 is demonstrated by open‐loop coupling to a 10 A, 500 Hz power line emulating an aircraft use case. The results are compared with similar ferrite and moulded material devices, which yield 17.3 and 2.4 µW g −1 , respectively. In line with a simulation analysis, the experimental results show that materials with moderate magnetic permeability can provide competitive transduction performance, while offering unique customisation, accessibility, and design‐to‐prototype speed benefits. The proposed customisable magnetic flux‐concentration approach provides a simple, effective, and accessible method for enhancing the performance of magnetic and inductive sensing, actuating, and energy transduction devices.