In this paper, we explore the design and development of passive soft 3D-printed structures whose deformation can be sensed accurately without any wired connection. By 3D printing tangible interfaces consisting of flexible TPU (thermoplastic polyurethane), made from lattice structures with bespoke geometries and mechanical properties, and ferromagnetic elements using metal-infused filaments, we enable the detection of structural deformations through inductive sensing. We investigate how different ferromagnetic core configurations within flexible substrates, guided by key design parameters, influence the sensitivity, responsiveness, and deformability of the sensing system. We demonstrate that our 3D-printed inductive sensing approach allows users to switch their fully passive tangible interfaces for specialized tasks without assembly or the need to unplug wires. Our sensing approach can be integrated in portable applications, such as a smart bottle cover that captures subtle deformation to measure liquid intake, or in wearable applications, such as monitoring foot pressure in smart shoes.

We introduce a knitted inductive flex sensor which seamlessly integrates a coil and a capacitor into a soft and flexible tubular knit. By knitting enameled copper wires, we form a self-supporting coil, whose inductance changes with stretching and bending. Knitting both a coil and a parallel-wire capacitor, we create a textile resonant LC circuit, while preserving the softness, elasticity, and breathability of knitted textiles. In this paper, we present the fabrication process using an industrial knitting machine, evaluate sensor sensitivity and hysteresis over 100 bending cycles, and demonstrate the sensors versatility across joints of different radii. Our results show that knitted inductive sensors combine the wearability of soft textiles with the stability of inductive sensing, opening new sensing opportunities in healthcare, rehabilitation, and interactive electronic garments.

We introduce SqueezeMe, a soft and flexible inductive pressure sensor with high sensitivity made from ferromagnetic elastomers for wearable and embedded applications. Constructed with silicone polymers and ferromagnetic particles, this biocompatible sensor responds to pressure and deformation by varying inductance through ferromagnetic particle density changes, enabling precise measurements. We detail the fabrication process and demonstrate how silicones with varying Shore hardness and different ferromagnetic fillers affect the sensor’s sensitivity. Applications like weight, air pressure, and pulse measurements showcase the sensor’s versatility for integration into soft robotics and flexible electronics.

The direct fabrication of thin-film transistors (TFTs) based on Indium-Gallium-Zinc-Oxide (IGZO) on a flexible polyurethane (PU) substrate is presented. Polyurethane, with its mechanical flexibility, durability, and potential for environmental sustainability, offers a promising platform for flexible electronics. Here, a custom polyurethane film was synthesized and a low-temperature fabrication process (T ≤130◦C) was developed for the realization of oxide-based electronics on this flexible material. The fabricated TFTs exhibited an effective mobility of 15.3cm2V−1s−1, an on/off current ratio exceeding 105, and a threshold voltage of 0.8V. Additionally, the devices demonstrated long-term stability, retaining functionality after over 12 years of storage. The performance of the TFTs on PU is also compared to similar devices realized on a variety of other polymer substrates. The results demonstrate the feasibility of integrating IGZO transistors on polyurethane substrates for flexible electronic applications. Hence PU can open up a path towards unobtrusive and environmentally friendly wearable systems exhibiting mechanical adaptability, long-term reliability, or repairability.