A Flexible Accelerometer System for Human Pulse Monitoring
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A Flexible Accelerometer System for Human Pulse Monitoring Yuanfeng Zhang1 and Woo Soo Kim1 1 School of Mechatronic Systems Engineering, Simon Fraser University, Surrey, B.C. Canada V3T 0A3 ABSTRACT Here we introduce a cost-effective and highly sensitive flexible accelerometer system, which can sense human pulse by detecting the pulsation. The accelerometer employs capacitive sensing with a structure of two parallel plate electrodes with the optimally designed top electrode pattern in order to achieve high sensitivity. This flexible light-weight sensor is fabricated by directprinting of silver nano-inks on pre-patterned flexible paper substrates. When the accelerometer is attached to the body surfaces: neck, inner elbow, or any other pulsation point, accurate pulse rates are obtained by reading out the voltage output signal.
INTRODUCTION MEMS technology is currently growing at a dramatically accelerated rate in the microelectronics industry. Its global market has approached several billions of units in recent years [1]. Typical MEMS devices, such as accelerometers, have been widely used in automotive industry, consumer electronics, structural health monitoring, and machine health monitoring. In addition to these fields, accelerometers also begin to gain much attention in biomedical applications such as motion detectors [2] and blood pressure sensors [3]. Although MEMS accelerometer is so attractive due to its tiny size, its time-consuming, complex and expensive fabrication processes limit its further advance [4]. Also, these micro machining processes are incompatible with flexible substrates in terms of high processing temperature and corrosive liquid etchants. On the contrary, printing technology is inexpensive, process-effective, fully compatible with flexible substrates, and able to pattern fine micro-scale structures on substrates. Besides, paper, readily available and light-weight, is a new alternative to serve as flexible substrates for MEMS devices with high potential for extremely low cost device fabrication [5]. And some paper-based MEMS devices have shown great performance in recent researches [6]. To combine accelerometers with novel printing technology, this work tries to develop a flexible printed accelerometer. In particular, this light-weight flexible accelerometer is an excellent candidate as wearable or attachable sensor for pervasive sensing in e-healthcare systems. We present the high sensitivity of this accelerometer to accelerations over a low frequency range, and its possibility to detect and measure body movement and human pulse by integration with an interface circuit.
EXPERIMENTAL DETAILS
In this approach, the capacitive structure of accelerometers is composed of two parallel membrane electrodes, where the proof mass as the movable plate electrode is in the top membrane and the bottom is the stationary electrode. Two electrodes are separated by a thin insulating layer [7].
Figure 1. Schematic of the capacitive membrane-based accelerometer: top view and cross-sectional view.
Figure 1 il
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