Hand Gesture Recognition Using EGaIn-Silicone Soft Sensors

Rational design of a laminate-structured flexible sensor for human dynamic plantar pressure monitoring

Flexible sensors are essential components in emerging fields such as epidermal electronics, biomedicine, and human-computer interactions, and creating high-performance sensors through simple structural design for practical applications is increasingly needed. Presently, challenges still exist in establishing efficient models of flexible piezoresistive pressure sensors to predict the design required for achieving target performance. This work establishes a theoretical model of a flexible pressure sensor with a simple laminated and enclosed structure. In the modeling, the electrical constriction effect is innovatively introduced to explain the sensitization mechanism of the laminated structure to a broad range of pressures and to predict the sensor performance. The experimental results confirmed the effectiveness of the theoretical model. The sensor exhibited excellent stability for up to three million cycles and superior durability when exposed to salt solution owing to its simple laminated and enclosed structural design. Finally, a wearable sensing system for real-time collection and analysis of plantar pressure is constructed for exercise and rehabilitation monitoring applications. This work aims to provide theoretical guidance for the rapid design and construction of flexible pressure sensors with target performance for practical applications.

A new 3D, microfluidic-oriented, multi-functional, and highly stretchable soft wearable sensor

Increasing demand for wearable devices has resulted in the development of soft sensors; however, an excellent soft sensor for measuring stretch, twist, and pressure simultaneously has not been proposed yet. This paper presents a novel, fully 3D, microfluidic-oriented, gel-based, and highly stretchable resistive soft sensor. The proposed sensor is multi-functional and could be used to measure stretch, twist, and pressure, which is the potential of using a fully 3D structure in the sensor. Unlike previous methods, in which almost all of them used EGaIn as the conductive material, in this case, we used a low-cost, safe (biocompatible), and ubiquitous conductive gel instead. To show the functionality of the proposed sensor, FEM simulations and a set of designed experiments were done, which show linear (99%), accurate (> 94.9%), and durable (tested for a whole of four hours) response of the proposed sensor. Then, the sensor was put through its paces on a female test subject's knee, elbow, and wrist to show the potential application of the sensor as a body motion sensor. Also, a fully 3D active foot insole was developed, fabricated, and evaluated to evaluate the pressure functionality of the sensor. The result shows good discrimination and pressure measurement for different foot sole areas. The proposed sensor has the potential to be used in real-world applications like rehabilitation, wearable devices, soft robotics, smart clothing, gait analysis, AR/VR, etc.

Move With the Theremin: Body Posture and Gesture Recognition Using the Theremin in Loose-Garment With Embedded Textile Cables as Antennas

We present a novel intelligent garment design approach for body posture/gesture detection in the form of a loose-fitting blazer prototype, “the MoCaBlazer.” The design is realized by leveraging conductive textile antennas with the capacitive sensing modality, supported by an open-source electronic theremin system (OpenTheremin). The use of soft textile antennas as the sensing element allows flexible garment design and seamless tech-garment integration for the specific structure of different clothes. Our novel approach is evaluated through two experiments involving defined movements (20 arm/torso gestures and eight dance movements). In cross-validation, the classification model yields up to 97.18% average accuracy and 92% f1-score, respectively. We have also explored real-time inference enabled by a radio frequency identification (RFID) synchronization method, yielding an f1-score of 82%. Our approach opens a new paradigm for designing motion-aware smart garments with soft conductive textiles beyond traditional approaches that rely on tight-fitting flexible sensors or rigid motion sensor accessories.

Laser Direct Structured 3D Circuits on Silicone

Silicone rubber is a biocompatible elastomeric polymer, with great potential for mechanical and biologic sensing applications, if electrical circuits can be reliably integrated. Laser direct structuring is a bottom-up circuit fabrication process, whereby copper is chemically grown on laser exposed regions of a modified substrate, promoting adhesion by laser roughening the circuit tracks. In this Research Article, we successfully demonstrate this process using superflexible biocompatible silicone (30 hardness on Shore 00) with copper chromite additive, cast into both 2D planar and 3D contour substrates. A horseshoe pattern circuit, meander and Hilbert fractal inductors, and a 3D hemispherical helix trace are fabricated and tested. The range of laser power and copper chromite concentration are explored. Mechanical testing is performed to determine breakage strain and elastic modulus. Material stiffness and trace peel strength are shown to increase with copper chromite concentration. Peel strength is measured to be very high, from approximately 1 to 5 kN/m, depending on dopant loading. With high adhesion and conductivity, the simple laser-writing process presented here enables high-quality circuit integration into elastomeric silicone.