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Soft Inkjet Circuits: Rapid Multi Material Fabrication of Soft Circuits Using a Commodity Inkjet Printer
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Despite the increasing popularity of soft interactive devices, their fabrication remains complex and time consuming. We contribute a process for rapid do-it-yourself fabrication of soft circuits using a conventional desktop inkjet printer. It supports inkjet printing of circuits that are stretchable, ultrathin, high resolution, and integrated with a wide variety of materials used for prototyping. We introduce multi-ink functional printing on a desktop printer for realizing multi-material devices, including conductive and isolating inks. We further present DIY techniques to enhance compatibility be-tween inks and substrates and the circuits’ elasticity. This enables circuits on a wide set of materials including temporary tattoo paper, textiles, and thermoplastic. Four application cases demonstrate versatile uses for realizing stretchable devices, e-textiles, body-based and re-shapeable interfaces.
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September 2019
... There has been considerable exploration and research in the field of human-computer interaction regarding the design and production of flexible electronics for thin-film circuits (Corzo et al., 2020). Common methods in the maker and DIY communities include using CNC machines to engrave copper foil (Yan et al., 2022;Yang et al., 2023), achieving complex and refined circuit designs through etching copper foil (Du et al., 2018;Heibeck et al., 2015) or using screen printing or inkjet printing with conductive inks (e.g., conductive silver glue: Feng et al., 2023;Wang et al., 2020a) and carbon-based inks: Kawahara et al., 2013;Khan et al., 2019). ...
... One such technique is inkjet printing, which allows printing on flexible substrates and facilitates the fabrication of resistors, coils, sensors, and other components and devices. Inkjet printing offers a wide range of applications [8], limited primarily by printing time and ink properties [9]. To be suitable for inkjet printing, inks must possess stability and low viscosity to facilitate printhead usage [10] but have a high particle loading to enable the printing of structures with significant height. ...
Capacitors play a crucial role in modern electronics as they are widely employed for energy storage, signal processing, radiofrequency tuning and matching, and signal filtering. This paper presents a novel approach to chip‐scale capacitor fabri- cation utilizing the laser‐induced forward transfer (LIFT) technique, a versatile 3D printing method that offers a flexible and cost‐effective alternative to conventional manufacturing processes. Plate capacitors were fabricated through dot‐by‐dot printing of titanium di‐oxide and silver paste layers, and their performance evaluated. Optimal dot circularity at a diameter of 130 μm were achieved with printing parameters of 120 mW for 4 ms, with no noticeable surface defects. Using smaller dots enabled higher resolution, but this compromised the quality of the printed surface. The fabricated capacitors demonstrated a mean capacity of 40.1 ± 2.2 pF at 100 MHz, making them suitable also for high‐frequency applications. The resistivity of the printed silver tracks was 1.2 × 10−7 Ωm, measured over 16 structures, and closely matched the manufacturer's specifications for the silver ink. The achieved resolution from the dot‐by‐dot method used in this paper provided greater flexibility in transfer in comparison to previously reported results using a square‐shaped transfer geometry.
... Inherently conductive objects can act as the touch sensor [Sato et al. 2012]. A common approach for sensing on a wider range of objects is to print a deformable touch sensor on different materials using inkjet printing [Kawahara et al. 2013;Khan et al. 2019;Pourjafarian et al. 2022] or screen printing [Olberding et al. 2014]. Moreover, existing objects can be enhanced with a thin sensing layer through hydrography [Groeger and Steimle 2018], by spraying functional materials on the objects [Wessely et al. 2020;Zhang and Harrison 2018;Zhang et al. 2017], or by attaching functional stickers or patches [Cheng et al. 2020;Klamka et al. 2020;Strohmeier et al. 2018]. ...
Mutual-capacitive sensing is the most common technology for detecting multi-touch, especially on flat and simple curvature surfaces. Its extension to a more complex shape is still challenging, as a uniform distribution of sensing electrodes is required for consistent touch sensitivity across the surface. To overcome this problem, we propose a method to adapt the sensor layout of common capacitive multi-touch sensors to more complex 3D surfaces, ensuring high-resolution, robust multi-touch detection. The method automatically computes a grid of transmitter and receiver electrodes with as regular distribution as possible over a general 3D shape. It starts with the computation of a proxy geometry by quad meshing used to place the electrodes through the dual-edge graph. It then arranges electrodes on the surface to minimize the number of touch controllers required for capacitive sensing and the number of input/output pins to connect the electrodes with the controllers. We reach these objectives using a new simplification and clustering algorithm for a regular quad-patch layout. The reduced patch layout is used to optimize the routing of all the structures (surface grooves and internal pipes) needed to host all electrodes on the surface and inside the object's volume, considering the geometric constraints of the 3D shape. Finally, we print the 3D object prototype ready to be equipped with the electrodes. We analyze the performance of the proposed quad layout simplification and clustering algorithm using different quad meshing and characterize the signal quality and accuracy of the capacitive touch sensor for different non-planar geometries. The tested prototypes show precise and robust multi-touch detection with good Signal-to-Noise Ratio and spatial accuracy of about 1mm.
This paper presents the results of a 5-month diary study into the practices and routines that develop around technological making in the home, particularly focused on the experiences of women, as they continue to be an underrepresented group in the maker community. In this study, we provided participants with an entry-level electronics making kit. Over the course of twenty weeks, the participants documented their making activities via photos, videos, text messages and taking part in interviews. By means of interpretative phenomenological analysis, we identified six core themes related to women’s experiences with technological making in the home. These experiences ranged from positive—feeling challenged, proud of accomplishments, inspired; to negative—feeling frustrated, guilty due to lack of progress or confused and overwhelmed. These experiences are discussed and contextualized by aspects related to hurdles experienced by the participants, and success factors that contribute to proactive engagement with making in the home.
Research Highlights Twenty-week photo diary study and interpretative phenomenological analysis. Identification of six core themes based on empirical data on experiences with technological making in the home context. Discourse around thresholds to engage women in technological making and the maker community. Design and research directions to reduce barriers in technological making.
This paper introduces LASEC, the first technique for instant do-it-yourself fabrication of circuits with custom stretchability on a conventional laser cutter and in a single pass. The approach is based on integrated cutting and ablation of a two-layer material using parametric design patterns. These patterns enable the designer to customize the desired stretchability of the circuit, to combine stretchable with non-stretchable areas, or to integrate areas of different stretchability. For adding circuits on such stretchable cut patterns, we contribute routing strategies and a real-time routing algorithm. An interactive design tool assists designers by automatically generating patterns and circuits from a high-level specification of the desired interface. The approach is compatible with off-the-shelf materials and can realize transparent interfaces. Several application examples demonstrate the versatility of the novel technique for applications in wearable computing, interactive textiles, and stretchable input devices.
Stretchable electronics is an emerging technology that creates devices with the ability to conform to nonplanar and dynamic surfaces such as the human body. Current stretchable configurations are constrained to single-layer designs due to limited material processing capabilities in soft electronic systems. Here we report a framework for engineering three-dimensional integrated stretchable electronics by combining strategies in material design and advanced microfabrication. Our three-dimensional devices are built layer by layer through transfer printing pre-designed stretchable circuits on elastomers and creating vertical interconnect accesses using laser ablation and controlled soldering. Our approach enables a higher integration density on stretchable substrates than single-layer approaches and allows new functionalities that would be difficult to implement with conventional single-layer designs. Using this engineering framework, we create a stretchable human–machine interface testbed that is based on a four-layer design and offers eight-channel sensing and Bluetooth data communication capabilities. By combining strategies in material design and advanced microfabrication, three-dimensional integrated stretchable electronic devices can be created, including an eight-channel sensing system with Bluetooth communication capabilities that can be used to extract an array of signals from the human body.
We present a scalable Do-It-Yourself (DIY) fabrication workflow for prototyping highly stretchable yet robust devices using a CO2 laser cutter, which we call Silicone Devices. Silicone Devices are self-contained and thus embed components for input, output, processing, and power. Our approach scales to arbitrary complex devices as it supports techniques to make multi-layered stretchable circuits and buried VIAs. Additionally, high-frequency signals are supported as our circuits consist of liquid metal and are therefore highly conductive and durable. To enable makers and interaction designers to prototype a wide variety of Silicone Devices, we also contribute a stretchable sensor toolkit, consisting of touch, proximity, sliding, pressure, and strain sensors. We demonstrate the versatility and novel opportunities of our technique by prototyping various samples and exploring their use cases. Strain tests report on the reliability of our circuits and preliminary user feedback reports on the user-experience of our workflow by non-engineers.
E-Textiles are fabrics that integrate electronic circuits and components. Makers use them to create interactive clothing, furniture, and toys. However, this requires significant manual labor and skills, and using technology-centric design tools. We introduce Sketch&Stitch, an interactive embroidery system to create e-textiles using a traditional crafting approach: Users draw their art and circuit directly on fabric using colored pens. The system takes a picture of the sketch, converts it to embroidery patterns, and sends them to an embroidery machine. Alternating between sketching and stitching, users build and test their design incrementally. Sketch&Stitch features Circuitry Stickers representing circuit boards, components, and custom stitch patterns for wire crossings to insulate, and various textile touch sensors such as pushbuttons, sliders, and 2D touchpads. Circuitry Stickers serve as placeholders during design. Using computer vision, they are recognized and replaced later in the appropriate embroidery phases. We close with technical considerations and application examples.
Desktop inkjet printers are ubiquitous and relatively inexpensive among the variety of available printers. These inkjet printers use an array of micro fluidic pumps, nozzles based on piezoelectric actuation, to dispense individual picoliter volume ink droplets at high speed. In this paper, we show that individual pumps in desktop printers can be accessed to dispense droplets on demand. Access was obtained using the printer’s command language programming. A detailed description of the access procedure is discussed. Droplets were printed on a paper as it rolled underneath the printhead, and with a minor hardware modification, they were also printed on a glass substrate. With this access, individual droplets were deposited, the smallest having an average diameter of 62 μm with a standard deviation of 6.9 μm, with a volume of ∼4 pL. From the intended position, the droplets had a standard deviation of 5.4 μm and 8.4 μm in the vertical and horizontal directions, respectively. The ink droplets were dispensed at a rate of 7.1 kHz. A circularity factor of 0.86 was obtained indicating that the dispensed droplets are of good quality. By replacing the ink in the cartridges with liquids of choice (e.g. cells, proteins, nanoparticles etc.), we believe it provides an opportunity for low-cost, high-speed, high-precision, picoliter volume printing for a variety of applications.
This paper introduces Tacttoo, a feel-through interface for electro-tactile output on the user's skin. Integrated in a temporary tattoo with a thin and conformal form factor, it can be applied on complex body geometries, including the fingertip, and is scalable to various body locations. At less than 35µm in thickness, it is the thinnest tactile interface for wearable computing to date. Our results show that Tacttoo retains the natural tactile acuity similar to bare skin while delivering high-density tactile output. We present the fabrication of customized Tacttoo tattoos using DIY tools and contribute a mechanism for consistent electro-tactile operation on the skin. Moreover, we explore new interactive scenarios that are enabled by Tacttoo. Applications in tactile augmented reality and on-skin interaction benefit from a seamless augmentation of real-world tactile cues with computer-generated stimuli. Applications in virtual reality and private notifications benefit from high-density output in an ergonomic form factor. Results from two psychophysical studies and a technical evaluation demonstrate Tacttoo's functionality, feel-through properties and durability.
Skin-based touch input opens up new opportunities for direct, subtle, and expressive interaction. However, existing skin-worn sensors are restricted to single-touch input and limited by a low resolution. We present the first skin overlay that can capture high-resolution multi-touch input. Our main contributions are: 1) Based on an exploration of functional materials, we present a fabrication approach for printing thin and flexible multi-touch sensors for on-skin interactions. 2) We present the first non-rectangular multi-touch sensor overlay for use on skin and introduce a design tool that generates such sensors in custom shapes and sizes. 3) To validate the feasibility and versatility of our approach, we present four application examples and empirical results from two technical evaluations. They confirm that the sensor achieves a high signal-to-noise ratio on the body under various grounding conditions and has a high spatial accuracy even when subjected to strong deformations.
With the proliferation of flexible displays and the advances in smart materials, it is now possible to create interactive devices that are not only flexible but can reconfigure into any shape on demand. Several Human Computer Interaction (HCI) and robotics researchers have started designing, prototyping and evaluating shape-changing devices, realising, however, that this vision still requires many engineering challenges to be addressed. On the material science front, we need breakthroughs in stable and accessible materials to create novel, proof-of-concept devices. On the interactive devices side, we require a deeper appreciation for the material properties and an understanding of how exploiting material properties can provide affordances that unleash the human interactive potential. While these challenges are interesting for the respective research fields, we believe that the true power of shape-changing devices can be magnified by bringing together these communities. In this paper we therefore present a review of advances made in shape-changing materials and discuss their applications within an HCI context.
This paper focuses on manual screenprinting as a DIY fabrication technique for embedding interactive behavior onto a rage of substrates such as paper, fabric, plastic, wood, or vinyl. We frame screenprinting as a process that operates at the intersection of art, technology, and material science and iteratively examine its potential in two STEAM contexts. We conducted youth and adult workshops whereby participants worked with our low-cost thermochromic, UV-sensitive, and conductive screenprinting inks to develop a range of concepts and final projects. Our findings highlight several unique features of screenprinting: it affords a low barrier to entry for smart material fabrication, supports a collaborative maker practice, and scaffolds creative engagement with STEAM concepts. By being widely-accessible and substrate-agnostic, screenprinting presents exciting opportunities for TEI: DIY fabrication of smart materials in domains such as fine arts, information visualization, and slow technology; and bridging diverse disciplines through STEAM screenprinting initiatives at youth and adult levels.