Gerhard Troester

ETHOS: Miniature orientation sensor for wearable human motion analysis

Inertial and magnetic sensors offers a sourceless and mobile option to obtain body posture and motion for personal sports or healthcare assistants, if sensors could be unobtrusively integrated in casual garments and accessories. We present in this paper design, implementation, and evaluation results for a novel miniature attitude and heading reference system (AHRS) named ETHOS using current off-the-shelf technologies. ETHOS has a unit size of 2.5cm3, which is substantially below most currently marketed attitude heading reference systems, while the unit contains processing resources to estimate its orientation online. Results on power consumption in relation to sampling frequency and sensor use are presented. Moreover two sensor fusion algorithms to estimate orientation: a quaternion-based Kalman-, and a complementary filter. Evaluations of orientation estimation accuracy in static and dynamic conditions revealed that complementary filtering reached sufficient accuracy while consuming 46% of a Kalmans power. The system runtime of ETHOS was found to be 10 hours at a complementary filter update rate of 128Hz. Furthermore, we found that a ETHOS prototype functioned with a sufficient accuracy in estimating human movement in real-life conditions using an arm rehabilitation robot.

Development and evaluation of temperature sensors for textile integration

In this paper we report an approach to fully integrate micro fabricated sensors into textiles. We first developed platinum resistance temperature sensors (RTDs) on 500 µm-wide, 67.5 mm-long plastic stripes. After completing the sensor fabrication, we used a dicing saw to separate individual sensors by cutting the plastic foil into stripes, each containing an individual sensor and connecting lines. The resistance of the RTDs was 665 Ω +/− 10 Ω at room temperature. The temperature coefficient of the RTDs is 0.00223 K−1 with a the sensitivity of 1.52 Ω /°C at a drive current of 500 µA. Cutting the substrate did not affect the sensor functionality. We then tested the influence of strain on the stripe RTDs signal using a pulling tester to apply tensile strain. Longitudinal strain resulted in metal line break after 2 N applied force (at an elongation of 5 %) and in breaking of the Kapton stripe at 8 N applied force. Single sensor stripes spaced 10 mm apart were integrated into a textile band using a commercial band weaving machine.

The WearARM: modular, high performance, low power computing platform designed for integration into everyday clothing

Describes a low power high performance wearable computing platform, specifically designed for easy integration into everyday clothing. It combines a heterogenous, distributed, user reconfigurable system architecture, advanced power management features and highly miniaturized, mechanically flexible electronic packaging technology. As a result the WearARM system offers high performance for a wide range of application in a form factor that allows it to be worn without in any noticeable way interfering with your look and comfort.

Reconfigurable processors for handhelds and wearables: Application analysis

In this paper, we present the analysis of applications from the domain of handheld and wearable computing. This analysis is the first step to derive and evaluate design parameters for dynamically reconfigurable processors. We discuss the selection of representative benchmarks for handhelds and wearables and group the applications into multimedia, communications, and cryptography programs. We simulate the applications on a cycle-accurate processor simulator and gather statistical data such as instruction mix, cache hit rates and memory requirements for an embedded processor model. A breakdown of the executed cycles into different functions identifies the most compute-intensive code sections - the kernels. Then, we analyze the applications and discuss parameters that strongly influence the design of dynamically reconfigurable processors. Finally, we outline the construction of a parameterizable simulation model for a reconfigurable unit that is attached to a processor core.

Autonomous smartwatch with flexible sensors for accurate and continuous mapping of skin temperature

Epidermal sensors, which form an intimate and robust contact with the skin, are capable of providing clinically relevant information about cardiovascular health, electrophysiology and dermatology with high accuracy and in an unobtrusive manner. To enable clinical applications, however, continuous and long-term monitoring is necessary. In addition, wireless and energetically autonomous systems are highly desirable to eliminate the needs of tethers and cables for powering and data transmission. Such requirements call for devices that combine accurate and precise sensing with high performance electronics for signal treatment, communication and power management in formats which conformal laminate on the body. In this work, we present a novel system whose design leverages on the recent developments in low power wearable devices and flexible sensors. It consists of an ultra-low power smartwatch connected to flexible solar modules assembled on a strap and an array of epidermal temperature sensors which are mounted on the wrist. Preliminary experiments show how this platform is well-suited for long-term, accurate and continuous mapping of the temperature of the skin.

Optical bow position, speed and contact point detection

Sensor technologies for musical instruments enable musicians to capture playing parameters while playing and augment their instruments for enhanced musical expression. A further step into this direction is the following optical, contact free bowing sensing technique for string instruments. In string instrument playing, the combination of bowing speed, position, bow pressure and bow to string contact point and angle are the basic factors of the right hand sound production. To measure these parameters, we developed an optical, contactless sensor system to complete existing pressure measurement systems. It consists of emitters, infrared (IR) or colored light emitting diodes (LEDs) on the bow and IR or color receivers on the violin. The precision of the measurement data obtained with this setup is sufficient to investigate the main parameters of bowing and sound production.

2D Thin Film Temperature Sensors Fabricated onto 3D Nylon Yarn Surface for Smart Textile Applications

We report on micro fabrication methods used to integrate electronics into smart textiles. We have introduced a shadow mask fabrication method to pattern 2D thin film structures onto the 3D surface of yarn. We have demonstrated the fabrication of gold resistance temperature sensors (RTDs) onto 500 μm thick nylon yarn. The sensors are meander shaped and have lateral dimensions of 0.3 mm × 1 mm and the width and spacing of the meander is 20 μm. Two different fabrication methods are developed and evaluated: 1) a planar mask made of Kapton foil is patterned by dry etching and 2) a tube mask made of Kapton foil is patterned with a laser. Both methods have proven to be suitable for the fabrication of RTDs onto textile yarns. The fabricated sensors are measured in a climate chamber from 15 to 50°C. The temperature coefficient of the RTDs is 0.0026 ω/°C with a sensitivity of 0.74 ω/°C.

Impact of light coherence on depth of focus of wearable retinal displays

This paper discusses the impact of light coherence on the defocusing properties of a novel retinal projection display. The display is based on a liquid crystal display (LCD) illuminated by partially coherent light from a LED which projects the LCD-image directly onto the eyes retina. It is shown that the increase of the coherence level of the illumination light enhances on the one hand the contrast of a defocused image. On the other hand, however, the perceived image quality is affected by the occurrence of intermediate defocusing peaks as well as by coherence effects, such as edge-ringing. Measurements of both the modulation transfer function (MTF) and of the text readability when defocusing are presented using a bench model of the display system. The experimental results reveal that for text readability the best DOF can be achieved not for fully coherent illumination, but for partially coherent light of a coherence level σ ≈ 0.35-0.5. Further, it is shown that the optimum σ-level depends slightly on the targeted text size.