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Physiological parameter measurements by Organic field effect transistors
Keywords: Organic Field-Effect Sensors, Physiological parameter monitoring, breathing rate monitoring, joint bending detection, posture detection
Research in biomedicine and engineering during the last years has led to a remarkable interest in sensor technologies for biomedical applications. Silicon technology is not suitable for manufacturing low-cost large-area sensor devices that are preferably light, flexible, and even disposable (for some biomedical applications). Its inherent high temperature fabrication processes make it very difficult to use inexpensive flexible substrate materials, resulting in high fabrication costs. It is well known that the mobility of organic materials is about three orders of magnitude lower than that of crystalline semiconductors but there are applications, as the recently suggested electronic skin, in which the lower speed is tolerable and the use of organic materials seems to be more beneficial than detrimental. In fact, being able to obtain large sensing areas is certainly a benefit for a wide set of applications and using printing techniques for creating sensing devices on unusual substrates could certainly widen the set of possible applications where sensing is required. Many body parameters can be measured by using non-invasive sensors, among them thermal parameters as body and skin temperature, chemical parameters as sweat composition, geometrical and mechanically related parameters as respiration rate and amplitude, heart rate, blood pressure, position, detection of falls, monitoring of various daily activities etc. The integration on the same substrate of different devices endowed with the properties of organic materials is especially interesting as it allows obtaining "smart", flexible surfaces that can be employed in emerging applications as the already mentioned electronic skin (for robotic applications) and smart textiles.
Fig.1: (a) Experimental set-up for breathing rate monitoring. (b) ID vs.Time curves for normal breathing and apnoea
Fig. 2(a) shows the experimental set-up for elbow joint movements monitoring. Also in this case the device was glued on a wearable elastic band. An example of the obtained results is shown in Fig. 2(b).
Fig.2: (a) Experimental set-up for elbow bending monitoring. (b) ID vs.Time for bent and unbent elbow.
This technology can also be used in order to monitoring the posture through the detection of pressure exerted on shoes. In this case the sensor was glued on the outsole of a shoe and used to detect the pressure exerted by the foot on the outsole. An example of this application is shown in Fig. 3(a) while the signal recorded from the sensor is shown in Fig 3(b).
Fig.3: (a) Experimental set-up for posture monitoring. (b) ID vs.Time for stending and on tiptoes position
A. Bonfiglio, I. Manunza, A. Caboni, W. Cambarau, M. Barbaro, "Organic field-effect based sensors for body parameters monitoring", Proc. SPIE Photonics 2007, S. Diego (USA) 26-31, August 2007
I. Manunza, E. Orgiu, A. Caboni, M. Barbaro and A. Bonfiglio, Producing smart sensing films by means of organic field effect transistors, Proc. 28th IEEE Engineering in Medicine and Biology Society Annual International Conference, EMBS '06, 4344 (2006)
I. Manunza, A. Sulis and A. Bonfiglio, Organic semiconductor field effect transistors for unconventional applications: flexible sensors and wearable devices, Proc. Int. Workshop on Wearable and Implantable Body Sensor Networks (BSN'06), IEEE 2006