E. Printed Piezoresistive Fabric realized by serigraphy technology

Coated fabric sensors have been realized with a conductive silicone, not designed for application in textile field. The viscosity of this material has been reduced to allow the use of an industrial coating process. Print screening technology has been evaluated as textile approach to coat the elastic substrate with the conductive elastomer. This approach allows to print on the fabric, the desired sensors topography as well as to solve the connection issue by using the same materials for both the functions: sensorial and circuital.

F. Mechanical characterization of Fabric Strain Sensors

In order to investigate the properties of piezoresistive fabric sensors, a protocol of mechanical characterization has been implemented. The fabric strain sensors have been subjected to predetermined mechanical stimuli imposed by a PC controlled system. Corresponding variations of electrical resistance have been collected through voltage divider, gathered by an acquisition card (National Instruments PCIMIO- 16E-4)) with sampling rate of 64 Hz.

Several samples of strain sensors have been subjected to different uniaxial mechanical stimuli following signals such as step and trapezium, both of them with variable strain amplitudes, and sinusoidal cycles with variable strain amplitudes at selected frequencies. Uniaxial mechanical stimuli have been applied along the length of both kinds of piezoresistive sensors.

The mechanical characterization aims to study the electrical response of fabric strain sensor as a function of the external mechanical stimuli.

G. Acquisition of Biomechanical Signals through Fabric Strain Sensors

Fig. 3: Knitted system for the acquisition of abdominal and thoracic respiratory activity

In order to evaluate the performances of knitted piezoresistive fabric sensors for biomechanical monitoring, the knitted piezoresistive sensors have been tested to detect both the respiration signal as a function of thorax movement and the elbow bends. A seamless t-shirt with fabric strain sensors has been realised respiratory signal, see Fig. 3.

Strain fabric sensors signals have been acquired using a voltage divider to convert resistance to voltage, gathered by an acquisition card (National Instruments PCI 6036) with sampling rate of 1000 Hz.

The respiration signals acquired with textile sensors have been compared with a respiratory effort transducer; model SSL5B, contained in the BIOPAC MP30 system.

The knitted piezoresistive fabric sensors are sensitive to changes in thoracic or abdominal circumference that occur during the respiratory activity.

The elbow bends signal detected by knitted piezoresistive fabric sensors has been compared with a commercial movement tracking system (electrogoniometer by Biometric).

The piezoresistive sensors performances allow the detection of movement index, while the printed piezoresistive sensors showed to be more efficient in the realisation of wearable kinaesthetic systems for gesture and posture monitoring [6],[7].