Feasibility of conductive embroidered threads for I2C sensors in microcontroller-based wearable electronics

In recent years, the importance of flexible and textile electronics in the field of wearable devices has continuously increased, as they are expected to replace conventional wires that exhibit limited resistance to the mechanical stress occurring in on-body applications. Wearable health devices (WHDs) can provide physiological information about various body parts and employ distributed sensor networks. Among the sensors typically integrated within WHDs, those based on the I2C communication protocol are very common and exploit signals transmitted at frequencies up to hundreds of kilohertz. Therefore, robust communication is required to guarantee a proper transmission of the signal at those frequencies. In this context, we have realized embroidered conductive threads exhibiting a lower resistance, appositely designed to replace conventional wires in a microcontroller-based wearable device employing I2C sensors. A commercial conductive thread (silver coated polyamide) was used to embroider the conductive lines on to cotton fabric. Preliminary measurements were performed to characterize the response of these materials to signals typically operated within the I2C communication protocol at different path lengths. Resistive measurements have also been performed to stimulate different environmental conditions, that is, temperature, the effect of sweating, and repeated washing cycles, also apply mechanical stress, i.e. twisting, with promising results that validate our conductive paths for digital signal communication

Reflex: A Closed-Loop Tactile Feedback System for Use in Upper Limb Prosthesis Grip Control

Tactile sensing provides valuable insight to the environment in which we interact with. Upper limb amputees lack the sensations that generates the necessary information to stably grasp the wide variety of objects we interact with on a daily basis. Utilizing tactile sensing to provide feedback to a prosthetic hand provides a mechanism for replacing the grip control functionality of the mechanoreceptors found in human skin. Novel customizable, low cost tactile sensors for monitoring the dynamics of an object grasped by a prosthetic hand are developed and presented as part of this thesis. The response of sensors placed on a prosthetic hand provides information regarding the state of a grasped object, particularly contact and slip. The sensors are made up of various textile materials, including stretchable interfacing layers and conductive traces. Essentially a force sensitive resistor, each sensor is shaped into stretchable cu ff that can be placed around the finger of a prosthetic hand. An outer rubber layer on the sensor provides compliance, which is found to enhance grasping performance with a prosthesis. Two control algorithms were developed as part of the closed-loop tactile feedback system, called Reflex, to enhance grasping functionality with a prosthesis. A Contact Detection strategy uses force information to effectively reduce the user's electromyography (EMG) signals, which are used to control the prosthesis. Essentially, the goal of this strategy is to help a user grab fragile objects without breaking them. A second strategy, Slip Prevention, uses the derivative of a force signal to detect slip of a grasped object. Instances of slip trigger electrical pulses sent from the prosthesis control unit to close the hand in an effort to prevent additional slip. The Reflex system, comprised of two control strategies along with flexible textile based force sensors on the fingers of a prosthesis, was shown to improve the grasping functionality of a prosthesis under normal use conditions. Able body participants were used to test the system. Results show the sensors' ability to greatly enhance grasping fragile objects while also helping prevent object slip. The compliant nature of the sensors enables users to more confidently pick up and move small,fragile objects, such as foam peanuts and crackers. Without sensors and tactile feedback, users had a higher likelihood of breaking objects while grabbing them. The addition of sensors reduced this failure rate, and the failure rate was reduced even further with the implementation of control algorithms running in real-time. The slip prevention strategy was also shown to help reduce the amount of object movement after a grasp is initiated, although the most benefit comes from the compliant nature of the sensors. Reflex is the first closed-loop tactile feedback system with multiple control strategies that can be used on a prosthetic hand to enhance grasping functionality. The system allows one to switch between Contact Detection or Slip Prevention control strategies, giving the user the ability to use each control as needed. Feedback from the textile sensors directly to the prosthesis control unit provides valuable information regarding grasping forces. This research aims to help improve prosthetic technology so that one day amputees will feel as if their device is a natural extension of their body

Extending the Design Space of E-textile Assistive Smart Environment Applications

The thriving field of Smart Environments has allowed computing devices to gain new capabilities and develop new interfaces, thus becoming more and more part of our lives. In many of these areas it is unthinkable to renounce to the assisting functionality such as e.g. comfort and safety functions during driving, safety functionality while working in an industrial plant, or self-optimization of daily activities with a Smartwatch. Adults spend a lot of time on flexible surfaces such as in the office chair, in bed or in the car seat. These are crucial parts of our environments. Even though environments have become smarter with integrated computing gaining new capabilities and new interfaces, mostly rigid surfaces and objects have become smarter. In this thesis, I build on the advantages flexible and bendable surfaces have to offer and look into the creation process of assistive Smart Environment applications leveraging these surfaces. I have done this with three main contributions. First, since most Smart Environment applications are built-in into rigid surfaces, I extend the body of knowledge by designing new assistive applications integrated in flexible surfaces such as comfortable chairs, beds, or any type of soft, flexible objects. These developed applications offer assistance e.g. through preventive functionality such as decubitus ulcer prevention while lying in bed, back pain prevention while sitting on a chair or emotion detection while detecting movements on a couch. Second, I propose a new framework for the design process of flexible surface prototypes and its challenges of creating hardware prototypes in multiple iterations, using resources such as work time and material costs. I address this research challenge by creating a simulation framework which can be used to design applications with changing surface shape. In a first step I validate the simulation framework by building a real prototype and a simulated prototype and compare the results in terms of sensor amount and sensor placement. Furthermore, I use this developed simulation framework to analyse the influence it has on an application design if the developer is experienced or not. Finally, since sensor capabilities play a major role during the design process, and humans come often in contact with surfaces made of fabric, I combine the integration advantages of fabric and those of capacitive proximity sensing electrodes. By conducting a multitude of capacitive proximity sensing measurements, I determine the performance of electrodes made by varying properties such as material, shape, size, pattern density, stitching type, or supporting fabric. I discuss the results from this performance evaluation and condense them into e-textile capacitive sensing electrode guidelines, applied exemplary on the use case of creating a bed sheet for breathing rate detection