New Type of Thermal Moisture Sensor for in‐Textile Measurements

Abstract

The measurement of moisture in textile materials worn on or near the skin can be performed for a variety of reasons, for example, to analyze the amount of perspiration in clothing, wound fluid in bandages or even urine in diapers or bed sheets. Conventional moisture measurement methods, such as electrical resistance or capacitance measurement, can be susceptible to cross sensitivities to electrical fields or ionic impurities, often occurring in measurements close to the human body. The very reliable gravimetric methods are too bulky and difficult to be integrated in portable and online measurements. In this paper, the authors present a “transient heat moisture sensor” (THMS) which is small and comparatively easy to integrate into textiles. The authors describe the measurement principle and present a sensor element manufactured with thin film technologies. The analytical description of the sensor fits to both, experimental data and the result of first numerical analysis (COMSOL Multiphysics). The authors demonstrate how to limit the sensors spatial sensitivity to a thin layer of textile without being influenced by the adjacent environment by proper timing of the signal readout.

Miniaturized and Thermal‐Based Measurement System to Measure Moisture in Textile Materials

“…We already presented and explained the THMS method in detail in an earlier study . It uses the changing thermal properties of porous materials when they absorb water .…”

“…Under certain simplifications, the temperature rise of the sensor with transient heating can be assumed to be approximately linearly dependent on the root of the heating time . Ultimately, it can be described as a function of time ( t ), of heating power per area ([ q ] = J s −1 m −2 ), and of the thermal effusivity ( e ) of the environment…”

“…The THMS method differs from other moisture measurement methods. It enables to measure in very thin layers with a low energy effort and with low cross‐sensitivity to, e.g., salinity, contact with the human body, or changing ambient temperature . Because THMS‐based sensors are very slim, integration on or between thin textile layers is easily possible.…”

Monitoring Body Fluids in Textiles: Combining Impedance and Thermal Principles in a Printed, Wearable, and Washable Sensor

“…Prof. Gustafsson developed the transient plane source (TPS) method in 1979, as an alternative technique to measure the thermal conductivity of materials . Based on this work, Schönfisch et al presented the moisture content assessment on textiles applying the TPS method and the sensor consisted of a cleanroom microfabricated heater on polyamide foil . The initial part of this article focuses on the inclusion of the TPS and impedance sensors into a single wearable textile platform.…”

“…presented the moisture content assessment on textiles applying the TPS method and the sensor consisted of a cleanroom microfabricated heater on polyamide foil. 40 The initial part of this article focuses on the inclusion of the TPS and impedance sensors into a single wearable textile platform. Selection of textile as the sensor substrate ensures conformability and feasibility for all range of wearable applications.…”