Design, fabrication and metrological evaluation of wearable pressure sensors

Abstract

Pressure sensors are valuable transducers that are necessary in a huge number of medical application. However, the state of the art of compact and lightweight pressure sensors with the capability of measuring the contact pressure between two surfaces (contact pressure sensors) is very poor. In this work, several types of wearable contact pressure sensors are fabricated using different conductive textile materials and piezo-resistive films. The fabricated sensors differ in size, the textile conductor used and/or the number of layers of the sandwiched piezo-resistive film. The intention is to study, through the obtaining of their calibration curves, their metrological properties (repeatability, sensitivity and range) and determine which physical characteristics improve their ability for measuring contact pressures. It has been found that it is possible to obtain wearable contact pressure sensors through the proposed fabrication process with satisfactory repeatability, range and sensitivity; and that some of these properties can be improved by the physical characteristics of the sensors.

Easy-to-Build Textile Pressure Sensor

“…The designed sensor works on the basis of the resistance variation through pressure application. The sensor itself is based on a structure proposed in [ 36 ] and consists of a sandwich made of two conductive Shieldex NoraDell woven fabric sheets [ 37 ] with a Low Density Polyethylene (LDPE) sheet between the conductive fabrics, which makes it different from previous designs in literature [ 36 ]. The Shieldex NoraDell woven fabric sheets have been largely used for microwave applications due to its good conductivity and radiation efficiency characteristics [ 38 , 39 , 40 , 41 ], having a surface resistance lower than 0.009 Ω/sq and a maximum thickness of 0.13 mm.…”

“…Specifically, pressure sensors have different ways of measuring the pressure variation [ 32 ]. These sensors can work either measuring capacitive changes [ 24 , 29 , 33 ], piezoelectric voltages generated by pressure [ 34 ], or resistance variation generated by pressure [ 31 ], where piezo-electrical [ 35 ] and piezo-resistive [ 36 ] polymers are widely used for these purposes.…”

A Linear Wide-Range Textile Pressure Sensor Integrally Embedded in Regular Fabric

“…Moreover, as shown in [4] and [6], current piezo-resistive textile pressure sensors of similar structure could only sense up to 800 kPa, which is insufficient for some applications such as gait analysis that requires approximately 1,000 kPa [7]. This letter presents an improved design and prototype of a textile pressure sensor that can be integrally embedded in regular cotton fabric using intarsia knitting technique.…”

“…For example, a textile force sensor whose capacitance changes with thoracic expansions is proposed for breath sensing [2], while piezo-electric pressure sensors are used for heart-beat sensing in a cardiorespiratory monitoring application in [3]. A type of textile pressure sensors is constructed by having one or more layers of active polymer, commonly piezo-electric [1] or piezo-resistive [4] polymer, sandwiched between two conductive plates [5], [6]. Both types of polymers are very thin for comfort wear.…”

Characterization of Bespoke Force Sensors for Tailored Applications

“…One study has evaluated force sensors made with elastic electrodes yet with a non-elastic piezo resistive layer [10]. Similarly, a study has investigated the repeatability, sensibility and range of these low cost resistive sensors while modifying the number of electrodes and piezo resistive layers [11]. The performance of commercially available thin and flexible sensors has been studied before [12].…”