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Monitoring of respiration and cardiac activity based on piezoelectric textile sensors
| Content Provider | Semantic Scholar |
|---|---|
| Author | Wristel, David Lund, Anja Rundqvist, Karin Nilsson, Erik Hagström, Bengt Sandsjö, Leif |
| Copyright Year | 2014 |
| Abstract | Monitoring health and health related mechanisms is a growing area of interest. In a laboratory environment it is possible to measure most of these aspects, but in a real situation outside the lab where resources are limited some difficulties may occur. In this study, the focus has been to monitor respiratory and cardiac activity using a recently developed textile sensor which potentially can improve health monitoring and be easier applied in long-term investigations in real/everyday situations. The sensor is made of fibres which have piezoelectric characteristics, and has been proven to stand the forces involved in a weaving process, and can thus be weaved into fabrics. When a force is applied to such fabrics an electrical signal is generated. In an earlier study it was shown that the fabrics can detect stimuli at a few Hertz, but this is not sufficiently low to monitor respiration, which requires a system sensitive to at least tenths of Hertz. The aim of this report was to investigate whether it is possible to extend the low frequency characteristics of the sensor in order to use these fibres/fabrics to monitor respiration and cardiac activity. A signal conditioning circuit has been created which main circuits are a voltage follower and a charge amplifier. By this configuration the input impedance can be sufficiently high for the conditioning circuit to reproduce the weak electric signal from the piezoelectric sensor. Depending on different aspects such as; the force applied to the textiles, dimensions of the textiles and input impedance of the signal conditioning circuit, different amplification levels may be needed, but is in the order of 100 times. A trade-off of extending the low frequency range to be able to monitor respiration is a slow system response with time lag. These two aspects needs to be considered and balanced in relation to the intended application. In order to evaluate the entire sensory system, i.e. the textile sensor and the signal conditioning circuit, a test setup was created where repeatable and controllable measurements could be performed. The test setup enabled three different signals: 1) a sinusoid generated by an ex-centric point at DC motor shaft, 2) a step generated by a dropped weight at steady state and 3) a motor-driven ramp followed by a step. Using this setup, the sensors and signal conditioning circuit proved to have its low end sensitivity lower than 17 mHz, which is well below requirements of monitoring respiration. Due to the fact that varied circuit characteristics may be required for different textile samples and applications, the signal conditioning circuit can be adjusted in gain and offset to match the analogue to digital converter of the transferring unit, in terms of maximum output and resolution. The transferring unit could be a bluetooth unit (in this case an Arduino board) which transfers the signal to a computer for real time presentation of the signal. Finally, the sensor system was compared to a previously suggested textile solution to monitor respiration, based on piezoresistive textiles in a Wheatstone bridge. By comparing both textile solutions it was found that the piezoelectric system is limited to dynamic forces and needs less manual adjustments/calibration prior to measurements while the feeding of a comparative bridge can exchanged to an amplifier. The suggested system was proven to be useful, but needs further development for practical use. Nevertheless it was found that piezoelectric fibres can be used to measure low frequency forces, close to static levels. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://publications.lib.chalmers.se/records/fulltext/208881/208881.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
