Design and development of a wearable inductive textile sensor to monitor back movements

This thesis focuses on the design and development of a wireless and wearable platform that employs an inductive sensor to track trunk movements when the user bends forward. The inductive textile sensor was designed based on the anthropometrical dimensions of the trunk’s lumbar area of a healthy female. The chosen shape of the sensor was a rectangular flat coil. The inductance behavior was investigated using theoretical calculations and simulations. Formulas developed by Grover and Terman were used to calculate the inductance to validate the inductive textile design. The simulations were used to analyze the change of the inductance when the area, perimeter, height, and width of the rectangle was modified, as well as the effect of the number of turns of the rectangular flat coil. Results from the theoretical calculations and simulations were compared. The inductive textile sensor was integrated at the lumbar section of a sleeveless garment to create a smart wearable platform. The performance of the smart garment was evaluated experimentally on a healthy participant, and it was shown that the designed sensor can detect forward bending movements. The evaluation scenario was further extended to also include twisting and lateral bending of the trunk, and it was observed that the proposed design can successfully discriminate such movements from forward bending of the trunk. An interference test showed that, although moving a cellphone towards the unworn prototype affected the sensor readings, manipulating the cellphone when wearing the prototype, did not compromise the capability of the sensor to detect forward bends. The proposed platform is a promising step towards developing wearable systems to monitor back posture to prevent or treat low back pain associated with poor posture

A fabric-based textile stretch sensor for optimized measurement of strain in clothing

Fabric stretch sensors are available as planar fabrics, but their reliability and reproducibility are low. To find a good working setup for use in an elastic sports garment, the design of such sensors must be optimized. The main purpose of this study was to develop resistive strain sensors from stretchable conductive fabric and investigating the influence of stretchability on conductivity/resistivity. The influence of using the sensor in a sweat rich environment was also determined, in order to evaluate the potential use of the sensor in sporting garments. The sensor resistivity performance was analyzed for its sensitivity, working range, and repeatability and it was determined what makes the sensitivity when elongated or stretched. The resistivity was found to decrease with elongation if no sweat is present, this can be due to molecular rearrangement and a higher degree of orientation that improves the conductivity of a material. The result from this finding also shows that for wearable applications the commercial EeonTexTM conductive stretchable fabric did not show a considerable resistivity increase, nor a good sensitivity. The sensitivity of the sensor was between 0.97 and 1.28 and varies with different elongation %. This may be due to the mechanical deformation characteristics of knitted samples that lead to changes in conductivity. We advise that the testing performed in this paper is done by default on new stretch sensitive textile materials, so practical use of the material can be correctly estimated

Development of a miniaturized motion sensor for tracking warning signs of low-back pain

Low-back pain (LBP) is a widespread disease which can also be highly disabling, but physicians lack of basic understanding and diagnosis tools. During this study, we have designed and built a new wearable device capable of detecting features helpful in LBP follow-up while being non-invasive. The device has been carefully validated, and shows good metrological features, with small noise level ($\sigma$ = 1{\textdegree}) and no observable drift. Two simple exercises were proposed to two young volunteers, one of them with LBP history. These exercises are designed to target two characteristics: the lumbar lordosis angle and the hip \& shoulder dissociation. Even if no general rules can be extracted from this study, we have shown that Inertial Measurement Units (IMU) are able to pick up those characteristics and the obtained values are meaningful refereeing to LBP disease. Henceforth, we are confident in going to clinical studies to investigate the link between back related feature and LBP, in particular the hip \& shoulder dissociation which is poorly documented

Smart Devices and Systems for Wearable Applications

Wearable technologies need a smooth and unobtrusive integration of electronics and smart materials into textiles. The integration of sensors, actuators and computing technologies able to sense, react and adapt to external stimuli, is the expression of a new generation of wearable devices. The vision of wearable computing describes a system made by embedded, low power and wireless electronics coupled with smart and reliable sensors - as an integrated part of textile structure or directly in contact with the human body. Therefore, such system must maintain its sensing capabilities under the demand of normal clothing or textile substrate, which can impose severe mechanical deformation to the underlying garment/substrate. The objective of this thesis is to introduce a novel technological contribution for the next generation of wearable devices adopting a multidisciplinary approach in which knowledge of circuit design with Ultra-Wide Band and Bluetooth Low Energy technology, realization of smart piezoresistive / piezocapacitive and electro-active material, electro-mechanical characterization, design of read-out circuits and system integration find a fundamental and necessary synergy. The context and the results presented in this thesis follow an “applications driven” method in terms of wearable technology. A proof of concept has been designed and developed for each addressed issue. The solutions proposed are aimed to demonstrate the integration of a touch/pressure sensor into a fabric for space debris detection (CApture DEorbiting Target project), the effectiveness of the Ultra-Wide Band technology as an ultra-low power data transmission option compared with well known Bluetooth (IR-UWB data transmission project) and to solve issues concerning human proximity estimation (IR-UWB Face-to-Face Interaction and Proximity Sensor), wearable actuator for medical applications (EAPtics project) and aerospace physiology countermeasure (Gravity Loading Countermeasure Skinsuit project)

Developable Rotationally Symmetric Kirigami‐Based Structures as Sensor Platforms

Developable surfaces based on closed‐shape, planar, rotationally symmetric kirigami (RSK) sheets approximate 3D, globally curved surfaces upon (reversible) out‐of‐plane deflection. The distribution of stress and strain across the structure is characterized experimentally and by finite‐element analysis as a function of the material and cut parameters, enabling the integration with strain gauges to produce a wearable, conformal patch that can capture complex, multiaxis motion. Using the patch, real‐time tracking of shoulder joint and muscle behavior is demonstrated. The facile fabrication and unique properties of the RSK structures potentially enable wearable, textile‐integrated joint monitoring for athletic training, wellness, rehabilitation, feedback control for augmented mobility, motion of soft and traditional robotics, and other applications.This work introduces a new paradigm for realizing 2D to curved, 3D, functional surface transformation using rotationally symmetric kirigami as a platform for deploying wearable sensors; here it is demonstrated for real‐time tracking of complex motion of joints within the body and circumventing longstanding tradeoffs in the design of materials, structures, and devices for conformable, wearable electronics.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153082/1/admt201900563-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153082/2/admt201900563.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153082/3/admt201900563_am.pd

Stretch sensors for measuring knee kinematics in sports

The popularity of wearable technology in sport has increased, due to its ability to provide unobtrusive monitoring of athletes. This technology has been used to objectively measure kinetic and kinematic variables, with the aim of preventing injury, maximising athletic performance and classifying the skill level of athletes, all of which can influence training and coaching practices. Wearable technologies overcome the limitations of motion capture systems which are limited in their capture volume, enabling the collection of data in-field, during training and competition. Inertial sensors are a common form of technology used in these environments however, their high-cost and complex calibration due to multiple sensor integration can make them prohibitive for widespread use. This thesis focuses on the development of a strain sensor that can be used to measure knee range of motion in sports, specifically rowing and cycling, as a potential low-cost, lightweight alternative to inertial sensors which can also be integrated into clothing, making them more discreet. A systematic review highlighted the lack of alternate technologies to inertial sensors such as strain sensors, as well as the limited use of wearable technologies in both rowing and cycling. Strain sensors were fabricated from a carbon nanotube-natural rubber composite using solvent exchange techniques and employed a piezoresistive sensing mechanism. These were then characterised using mechanical testing, to determine their electrical properties under cyclical strain. The strain sensors displayed hysteretic behaviour, but were durable, withstanding over 4500 strain cycles. Statistical analysis indicated that over 60% of the tests conducted had good intra-test variability with regards to the resistance response range in each strain cycle and sensor response deviating by less than 10% at strain rates below 100 mm/min and less than 20% at a strain rate of 350 mm/min. These sensors were integrated into a wearable sensor system and tested on rowing and cycling cohorts consisting of ten athletes each, to assess the translational use of the strain sensor. This preliminary testing indicated that strain sensors were able to track the motion of the knee during the rowing stroke and cycling pedalling motion, when compared to the output of a motion capture system. Perspectives of participants on the wearable system were collected, which indicated their desire for a system that they could use in their sport, and they considered the translation of this system for real-life use with further development to improve comfort of the system and consistency of the sensor response. The strain sensors developed in this project, when integrated into a wearable sensor system, have the potential to provide an unobtrusive method of measuring knee kinematics, helping athletes, coaches and other support staff make technical changes that can reduce injury risk and improve performance.Open Acces