Wearable technologies for sweat rate and conductivity sensors: design and principles

Wearable sensors present a new frontier in the development of monitoring techniques. They are of great importance in sectors such as sports and healthcare, as they permit the continuous monitoring of physiological and biological elements, such as ECG and human sweat.

Until recently, this could only be carried out in specialized laboratories in the presence of cumbersome, and usually, expensive devices. Sweat monitoring sensors integrated onto textile substrates are not only part of a new field of work but, they also represent the first attempt to implement such an innovative idea on a system which will be worn directly on the body. The objective of this book is to present possible designs and technologies of low cost wearable sweat rate and conductivity sensors integrated onto a textile.

The first chapter deals with a preliminary introduction on sweat production and composition, and the applications of wearable devices. Further, the second chapter describes the conductivity sensor, i.e. the geometry, materials and the coupling which includes a temperature sensor for precise measurements are discussed.

This is followed by a chapter on the sweat rate sensor, and the technologies employed to fabricate it. Sensors that are based on a) conductive yarns coated with hydrophilic polymers, b) conductive polymer fibres, c) hydrophilic polymers between conductive fabrics and d) humidity sensors are described in detail.

Finally, the last chapter provides a study of sweat production in different body areas, the calibration procedure, and summarizes the results which arise from the tests on volunteers.

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Mini-Varicon Dielectric/Conductivity Sensor from Lambient Technologies

The Mini-Varicon dielectric/conductivity sensor, available from Lambient Technologies, is designed for use with molds, laminates, presses, and bulk materials. It is modeled on a polyimide substrate and can enable users to select high or low sensitivity utilizing the whole sensor or by cutting off portions of the array at an assigned line. The sensor can be supplied either with custom-length Teflon-insulated leads or without leads.

The Mini-Varicon sensor measures 1.5” (4.0cm) in length and 0.004” (100µm) in thickness, and its tin-plated electrodes contain 0.004” (100µm) widths and spaces. It can measure the given materials’ dielectric/conductive properties within approximately 0.004” (100µm) of the electrode surface.

The Mini-Varicon sensor is ideal for high pressure applications. It is suitable for evaluating the dielectric properties and cure state of epoxies, molding compound (SMC), bulk molding compound (BMC), RIM, thermosets, urethanes, silicones and composite materials.

Key Features

The main features of the Mini- Varicon dielectric/conductivity sensor are as follows:

• Thin, flexible dielectric sensor
• Modeled on a polyimide substrate
• Suitable for high pressure applications
• Tolerates temperatures up to 375°C without leads and operates up to 200°C with leads

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New Universal Inductive Conductivity Sensor Simplifies Accurate Process Measurement

Designed with matched dual toroidal magnetic coils for precision accuracy, the intelligent S80 Inductive Conductivity Sensor from Electro-Chemical Devices (USA) simplifies process measurement in rugged industrial water treatment applications.
The measurement of conductivity in liquid water-based solutions is an essential requirement in a wide range of municipal water treatment and industrial processes. Conductivity sensors measure the electrical conductivity of a solution, which correlates to the purity of the water or the amount of dissolved ions in the liquid.
The versatile S80 Inductive Conductivity Sensors are ideal for a wide range of rugged environment municipal and industrial water applications. They are suitable for service in applications that include: wastewater treatment effluent, petrochemical refinery cooling tower water, food/beverage concentration control and clean-in-place (CIP) systems, electronic component resin regeneration, rinsing systems for metals and mining production, paper pulp stock processes and electric power generation cooling tower water. The 0.75-inch diameter allows for easy installation using the fittings common to all S80 sensors.
The S80 Inductive Conductivity Sensors convert the analogue signals from their dual toroid magnetic coils into a digital protocol that allows two-way communications with ECD’s universal T80 transmitter. The identity of the sensor, the measurement type and the serial number are stored in the sensor’s memory along with three calibration registers.
When connected to an ECD digital analyser the sensor’s conductivity measurement information is uploaded from the sensor to the analyser. This system configures the displays and outputs of the transmitter to the values appropriate for the parameter measured by the sensor. Set-up is easy with this virtually plug-and-play sensor/transmitter/analyser technology.
The S80’s conductivity sensors feature a chemically resistant PVDF (KYNAR) body, which is excellent for highly corrosive industrial process environments. The standard contacting sensor configuration can measure from very low conductivity, < 50 µS, to very high conductivity ranges, but they can be subject to coating and corrosion issues in some applications. When those conditions are present the non-contacting configuration sensors excel. The contacting conductivity S80 sensors come in three ranges, low range, 0.05μS – 50μS, high range, 50μS – 50mS and Resistivity, 0 – 20MΩ. The inductive sensors measure from 50µS to 1000mS.
The S80 Sensors are designed for use with the ECD Model T80 transmitter, which is available as a single or dual channel transmitter for the measurement of conductivity, resistivity, pH, ORP, pION, dissolved oxygen and turbidity. The Model T80 transmitter digitally communicates with any ECD intelligent S80 digital sensor, automatically configuring the transmitter’s menus and display screens to the measured parameter.
The ECD S80 digital sensor product line facilitates two way communication with the Model T80 transmitters. With the optional SENTINEL configuration, the transmitter automatically activates a “remaining life” diagnostic graphic alert for the S80 sensor’s replaceable cartridge.

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