Adaptive Impedance Matching Network for Contactless Power and Data Transfer in E-Textiles.

One of the major challenges associated with e-textiles is the connection between flexible fabric-integrated wires and rigid electronics. This work aims to increase the user experience and mechanical reliability of these connections by foregoing conventional galvanic connections in favor of inductively coupled coils. The new design allows for some movement between the electronics and the wires, and it relieves the mechanical strain. Two pairs of coupled coils continuously transmit power and bidirectional data across two air gaps of a few millimeters. A detailed analysis of this double inductive link and associated compensation network is presented, and the sensitivity of the network to changing conditions is explored. A proof of principle is built that demonstrates the system's ability to self-tune based on the current-voltage phase relation. A demonstration combining 8.5 kbit/s of data transfer with a power output of 62 mW DC is presented, and the hardware is shown to support data rates of up to 240 kbit/s. This is a significant improvement of the performance of previously presented designs.

Low-Cost Wearable Fluidic Sweat Collection Patch for Continuous Analyte Monitoring and Offline Analysis.

Sweat sensors allow for new unobtrusive ways to continuously monitor an athlete's performance and health status. Significant advances have been made in the optimization of sensitivity, selectivity, and durability of electrochemical sweat sensors. However, comparing the in situ performance of these sensors in detail remains challenging because standardized sweat measurement methods to validate sweat sensors in a physiological setting do not yet exist. Current collection methods, such as the absorbent patch technique, are prone to contamination and are labor-intensive, which limits the number of samples that can be collected over time for offline reference measurements. We present an easy-to-fabricate sweat collection system that allows for continuous electrochemical monitoring, as well as chronological sampling of sweat for offline analysis. The patch consists of an analysis chamber hosting a conductivity sensor and a sequence of 5 to 10 reservoirs that contain level indicators that monitor the filling speed. After testing the performance of the patch in the laboratory, elaborate physiological validation experiments (3 patch locations, 6 participants) were executed. The continuous sweat conductivity measurements were compared with laboratory [Na+] and [Cl-] measurements of the samples, and a strong linear relationship (R2 = 0.97) was found. Furthermore, sweat rate derived from ventilated capsule measurement at the three locations was compared with patch filling speed and continuous conductivity readings. As expected from the literature, sweat conductivity was linearly related to sweat rate as well. In short, a successfully validated sweat collection patch is presented that enables sensor developers to systematically validate novel sweat sensors in a physiological setting.

Smart sensor tights: Movement tracking of the lower limbs in football.

This article presents a novel smart sensor garment with integrated miniaturized inertial measurements units (IMUs) that can be used to monitor lower body kinematics during daily training activities, without the need of extensive technical assistance throughout the measurements. The smart sensor tights enclose five ultra-light sensor modules that measure linear accelerations, angular velocities, and the earth magnetic field in three directions. The modules are located at the pelvis, thighs, and shanks. The garment enables continuous measurement in the field at high sample rates (250 Hz) and the sensors have a large measurement range (32 g, 4,000°/s). They are read out by a central processing unit through an SPI bus, and connected to a centralized battery in the waistband. A fully functioning prototype was built to perform validation studies in a lab setting and in a field setting. In the lab validation study, the IMU data (converted to limb orientation data) were compared with the kinematic data of an optoelectronic measurement system and good validity (CMCs >0.8) was shown. In the field tests, participants experienced the tights as comfortable to wear and they did not feel restricted in their movements. These results show the potential of using the smart sensor tights on a regular base to derive lower limb kinematics in the field.

A wearable fluidic collection patch and ion chromatography method for sweat electrolyte monitoring during exercise.

This paper presents a method to continuously collect and reliably measure sweat analyte concentrations during exercise. The method can be used to validate newly developed sweat sensors and to obtain insight into intraindividual variations of sweat analytes in athletes. First, a novel design of a sweat collection system is created. The sweat collection patch, that is made from hydrophilized foil and a double-sided acrylate adhesive, consists of a reservoir array that collects samples consecutively in time. During a physiological experiment, sweat can be collected from the back of a participant and the filling speed of the collector is monitored by using a camera. After the experiment, Na+, Cl- and K+ levels are measured with ion chromatography. Sweat analyte variations are measured during exercise for an hour at three different locations on the back. The Na+ and Cl- variations show a similar trend and the absolute concentrations vary with the patch location. Na+ and Cl- concentrations increase and K+ concentrations seem to decrease during this exercise. With this new sweat collection system, sweat Na+, Cl- and K+ concentrations can be collected over time during exercise at medium to high intensity, to analyse the trend in electrolyte variations per individual.

On-chip contactless four-electrode conductivity detection for capillary electrophoresis devices.

In this contribution, a capillary electrophoresis microdevice with an integrated on-chip contactless four-electrode conductivity detector is presented. A 6-cm-long, 70-microm-wide, and 20-microm-deep channel was etched in a glass substrate that was bonded to a second glass substrate in order to form a sealed channel. Four contactless electrodes (metal electrodes covered by 30-nm silicon carbide) were deposited and patterned on the second glass substrate for on-chip conductivity detection. Contactless conductivity detection was performed in either a two- or a four-electrode configuration. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection setup. The four-electrode configuration allows for sensitive detection for varying carrier-electrolyte background conductivity without the need for adjustment of the measurement frequency. Reproducible electrophoretic separations of three inorganic cations (K+, Na+, Li+) and six organic acids are presented. Detection as low as 5 microM for potassium was demonstrated.