Research On Key Technologies Of An Intelligent ECG Monitoring System With Flexible MEMS-based Dry Electrode Array

Electrocardiogram(ECG) is the main basis for the prevention and treatment of cardiovascular diseases. At present, the bioelectrode most commonly used to monitor ECG is gel-type silver/silver chloride(Ag/AgCl) electrodes. However, gel electrodes are inconvenient because they require aggressive skin preparation and use an electrolytic solution to ensure ECG quality. Besides, the gel also dries over time, causing a dramatic decrease in signal quality. In recent years, with the rapid development of flexible MEMS technology and bioelectronic technology, dry surface electrodes on flexible substrates have been considered as replacements of conventional Ag/AgCl electrodes for long-term monitoring applications, because they have good flexibility and do not require an electrolyte layer. Moreover, the flexible dry electrode is an important component of the electronic skin(E-Skin), which is gradually becoming an important development direction of vital signs monitoring. Therefore, it is very necessary and important to study on flexible dry electrodes.Nowadays, the most commonly used flexible substrates are polyamide(PA), parylene(PPX), polyimide(PI), and polydimethylsiloxane(PDMS). However, PA materials required special treatment to improve the biocompatibility, and PPX coats should be deposited by special apparatus and the deposition process is complex. Besides, PI and PA materials undergo plastic deformation when large tensile or bending stresses are applied and cannot return to their original state completely. PDMS, a polymer biomaterial, which is non-toxic, does not irritate the surrounding tissue and has lower Young’s modulus than PI and PA, has been widely used in many fields including biomedical devices. Nevertheless, wrinkles and cracks are observed frequently in the metal film deposited on a PDMS substrate. The wrinkles and cracks could not only result in the resistance increase of the thin metal film, but also in the conductivity decrease. Therefore, reducing wrinkles and cracks of metal film deposited on PDMS has profound meaning to reliable and efficient flexible electronics fabricated on PDMS substrate, especially to the flexible PDMS-based dry electrode.The dissertation first investigated the methods of reducing wrinkles and cracks of metal film on PDMS substrate, proposed a flexible PDMS-based dry electrode array with micro domes, and then developed an intelligent ECG monitoring system. Concrete research content including following several aspects: methods of reducing wrinkles and cracks of metal film on PDMS substrate, fabrication of PDMS-based dry electrode array with micro domes, the ECG preprocessing and QRS detection algorithm and design of the intelligent ECG monitoring system. The main contributions and innovations of this dissertation are as follows:1、Winkles and cracks are occurred frequently in metal film deposited on a PDMS substrate, which would greatly impacts the conductivity and reliability of PDMS-based flexible electronics. To solve this problem, the dissertation proposed two kinds of methods to reduce the wrinkles and cracks: modification of PDMS by blending with nano particles and modification of PDMS by hexanes and(3-aminopropyl)triethoxysilane(APTES). The experimental results showed that the wrinkles and cracks of metal were reduced obviously on the modified PDMS substrates. Besides, the adhesion between metal and PDMS was greatly enhanced, and the conductivity of metal film was improved remarkablely.2、A flexible PDMSbased dry electrode array with micro domes was presented. The dry electrode array was fabricated on a PDMS substrate with high quality metal film through various kinds of MEMS technologies, such as melting photoresist, double PDMS moulding and pseudo-flip-chip bonding. The experimental results showed that the novel dry electrode array could produce good ECG signals.3、An ECG signal denoising algorithm based on single-step lifting wavelet transform and a QRS detection algorithm based on discrete Marr wavelet transform were proposed according to the characteristic of ECG signals recorded by the flexible PDMS-based dry electrode array. The experimental results showed the baseline drift and electromvographical interference were successfully removed, and QRS complex were fully recognized.4、This dissertation developed an intelligent ECG monitoring system with flexible PDMS-based dry electrode array. After transmitted via Bluetooth wireless, the ECG data was compressed in mobile intelligent terminal, and then uploaded to a central server, where ECG denoising and QRS detection were carried out. The results of processing were finally synchronized to a remote ECG monitoring website, so it is convenience for doctors to diagnosis the cardiovascular disease.