ECG Electrode (Sensor) printing with Ion Sensitive Membrane on Flexible substrate

Globally 30% deaths occur due to Cardio Vascular Diseases(CVD). ECG is one of the way to monitor this circulatory disease. Ag/Agcl Gel based ECG electrodes have their inherent problems, for prolonged continuous monitoring of ECG, connecting to a Cellular Mobile Phone, carried for early warnings. ECG electrodes with solid electrolyte connectable to mobile phones for Digital Signal Processing(DSP) is the alternative, in such continuous monitoring requirement. There are three fundamental ways of measuring ECG. These are electron conduction current, displacement current and Ionic conduction current measurements. ECG Bioelectric signals are due to electric conductivity or polarization/depolarization of the heart muscles, involving ions as charge carriers. So, electron conduction or displacement current measurements have side effects, reflected in the form of additional noise and signal vander when compared to direct ion current measurements. Unlike in current ECG electrodes, where electron current is picked up for ECG, along with various related electron current noise potentials, ideally speaking, ion current need to be picked up for very good noise and vander free Electro Cardio Gram(ECG). In Picking up such signals, there is involvement of interaction with Ionic charge carriers of the body and to transduce Ionic currents in to electron currents required for the signal carrying wires and interface electronics. Nernst potential of the dry electrode, for specific Ion like K+ and Na+ play crucial role, in these ECG electrodes. Over Potential or Over Voltage in these electrodes is due to excess polarization of the electrolyte, which is not desired. Perfectly, polarizable electrodes, pass a current between the electrode and electrolyte solution, by changing the charge distribution within the electrolyte near the electrode. So, nano-polarizable electrode structures, with good characteristics are to be preferred, for very good ECG measurements. Ion sensitive Thin Film Transistors (TFT) with Ion selective membranes at the skin interface is one of the alternative to sense Ion currents emanating from the human body. In order to rap around the body, a flexible substrate is more suitable for forming printable ECG electrodes with Ion sensitive membrane interface. Fully printable SWCNT (Single Wall Carbon Nano Tube) based Thin Film Transistors(TFT) with Top Gate structure are realizable on flexible substrates. The Ion transport or charge carrier transport, in general is through the intrinsic Frenkel or Shottky defects and 1-dimensional, 2-dimensional and 3-dimensional defects of the crystals or nanocrystals of the membrane. These Ion selective membranes are also printable, thus leaving the scope of ECG electrode to printable electronics, for online ECG applications. In the publication, based on Ion conduction path analysis of the electrode, a methodology is evolved for printable ECG electrodes on Flexible substrates, considering the existing research results in, Printable Thin Film Transistor field and Printable Ion selective membranes and reference electrodes. After analyzing methods of individual subsystems, best combination is chosen, for evolving the integrated methodology for Printable ECG electrodes, to form Ion conductive path for 10M concentration and 7 to 8 KΩ/Sq resistance per membrane layer, to suite the two stage skin electrical model.