Printed Sensors on Textiles for Biomedical Applications

The respiratory rate is an important biomedical parameter to monitor human physical condition and investigate potential respiratory dysfunctions. The pulmonary plethysmography (PP) is a technique for measuring changes in tidal volume during the respirator

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1  Sensor Implementation Technique The plane geometry of the plethysmographic sensor had been chosen exploiting the results obtained in [5]. In particular, the sinusoidal geometry is the best configuration for the sensor due to a high impedance value and a low breaking factor. Two plethysmographic sensors, called sensor A and sensor B and shown in Fig. 1a, b, respectively, had been designed and implemented with different geometries: in particular, the sensors differ in the number of meanders and in the height. The sensor had been designed trying to increase the impedance change without losing the elastic features. The trace thickness is measured 5 mm: a lower thickness increased the resistance value, and, on the contrary, an upper thickness increased the quality factor but decreased the sensitivity due to the increase of the stiffness. The sensor implementation technique is based on the industrial screen printing process, known as serigraphy, which permits the passage of the tight amount of paste through the mesh of the screen. At the beginning, a heat sealable vinyl film was applied on the T-shirt as support, so that it was possible to print on the conductive material. The silver conductive paste DuPont 5000 was printed on the support by using mask with the same sinusoidal form of the heat sealable vinyl film. The conductive paste was subjected to sinterization process positioning the T-shirt into an oven at 125 °C for about 30 min. A protected layer was performed with the same procedure: the dielectric paste DuPont 5018 was printed on the conductive layer, but the sinterization was produced by UV ray. The first paste has an excellent conductivity, less than 15 mΩ/sq/mil, while the dielectric paste has a high insulation resistance, more than 10 GΩ/sq/mil. Both the pastes have allowed to produce a flexible thick film in accordance with the stretching movement of the sensors. A. Dionisi (*) • E. Sardini • M. Serpelloni Department of Information Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy e-mail: [email protected]

C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_84, © Springer International Publishing Switzerland 2014

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440 Fig. 1  View of the two plethysmographic sensors implemented by printed method, (a) sensor A and (b) sensor B. The dimensions of the two sensors are shown in the figures, respectively

A. Dionisi et al.

a

5 mm 1.8 cm 5.5 cm

26 cm

b

5 mm

7.8 cm 5 mm 26 cm

2  Sensor Characterization The modulus and the phase of the sensor impedance were measured by an impedance analyser (HP4194A) in order to characterize the two sensors. The resulted trends have represented the typical behaviour of a resistance RS and an inductance LS in series configuration. A capacitor CP = 330 pF was connected to the plethysmographic sensors in parallel in order to create a resonance frequency under 10 MHz whose qual

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