Herein, the development of complex 3D intelligent structures such as robotic hands using innovative designs and multimaterial additive manufacturing technology is presented. The distal phalanges of the 3D printed hand presented herein have inherent soft capacitive touch or pressure sensors and embedded electronics. Materials such as thermoplastic polyurethane (TPU), silver paint, conductive polylactic acid composite, graphite ink, etc. are explored to develop five different variants of the sensors using a modified 3D printer, which is capable of extruding conductive ink, metal paste, and polymers. The best‐performing 3D printed soft capacitive touch sensors, formed with silver paint and soft rubber (Ecoflex 00‐30), are integrated on the distal phalanges of the 3D printed robotic hand. These sensors exhibit a stable response with sensitivity of 0.00348 kPa−1 for pressure <10 kPa and 0.00134 kPa−1 for higher pressure. To demonstrate the practical applicability, the 3D printed hand with embedded soft capacitive touch sensors is used for interacting with everyday objects. The tightly integrated sensing elements within the 3D printed structures, as presented herein, can pave the way for a new generation of truly smart material systems that can possibly change their appearance and shape autonomously.

This paper presents a novel additive manufacturing method to obtain bendable smart sensing structures having printed strain sensors and interconnects to gain access to embedded electronic components. The presented smart structure is obtained by simultaneous printing of functional materials along with conventional polymer-based 3D printing materials. To this end, a low-cost open-source 3D printer was augmented with a silver palladium metallic paste extruder. The strain sensors in the presented 3D printed smart structure are particularly useful for wearable motion sensing applications such as knee joint motion analysis. The printed interconnects allow for electrical connection with the Light Emitting Diodes (LEDs) embedded within the 3D printed structure. With electronic components embedded in the flexible 3D printed structure, this work also demonstrates a novel method for soft packaging of electronic and sensing components. The electrical tests conducted on the smart structure show excellent electrical continuity. The 3D printed strain sensors, tested in static and dynamic bending conditions, showed a linear response of resistance. Under no strain, the resistance of the sensor was measured to be 0.9671 Ω (resistivity of 9.671×10-6 Ω.m) and during testing it exhibited a gauge factor of 1. Multi-material additive manufacturing demonstrated in this paper opens a new direction for fabrication of complex 3D structures with embedded sensors and electronics and offers significant advantages for rapid prototyping and packaging.

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This paper presents a tilt sensor comprising of 3D printed capacitive sensors located at the four ends of a '+' shaped channel to provide the orientation of objects by using the capacitive fluid level measurement concept. The interdigitated capacitive sensors were developed by 3D printing and the channel was filled with ecoflex and silicone oil to obtain two variants of tilt sensor. The results show a change in the capacitance of ~11.5% and ~9.53% for ecoflex and silicone oil-based sensors respectively. A drift of ~2.6% is observed for ecoflex and ~0.16% for silicone oil. Considering the lower viscosity and the lower drift, the silicone oil-based tilt sensors were further investigated and two tilt sensors with varying silicone volumes (1ml and 1.5ml) were fabricated and compared for tilt angles ranging from 0 o to 30 o. The result from all four interdigitated capacitive sensors in the tilt sensing structure show similar rate of change in capacitance (~0.67% per degree increase in the tilt angle) with a standard deviation of ~±0.1%. However, the sensor with higher volume of silicone oil (1.5ml) saturated at a tilt angle of ~20 o which is ~10 o smaller than the response of the sensor fabricated with 1ml of silicone oil (saturated at 30 o). We also demonstrate the possibility of extending the sensor range by optimizing the volume of fluid and the channel's fluid capacity. With integration of fabricated tilt sensor with a robots' body, white cane or smart objects etc., it will be possible to obtain the information about orientation.

Herein, the design and implementation of a transparent 3D touch‐enabled surface for richer user interaction with midair 3D virtual objects in a touch‐interactive pseudo‐holographic display are presented. Frustrated total internal reflection (FTIR)‐based touch sensing is used in combination with a four‐sided pyramidal pseudo‐holographic projection. The developed system allows gesture‐based control and smooth touch interaction through facile and inexpensive hardware and open‐source software tools. A software application is also developed as the interface between the touch/gesture‐sensing system and the optical display. By bringing the virtual and real world closer through touch‐based interaction, the presented system will enrich user experience and enable advances in areas such as education, entertainment, gaming, retail, and museums where holograms are currently used.