Optimizing a new blood pressure sensor for maximum performance based on finite element model

A new non-invasive, cuff-less, low-cost blood pressure (BP) sensor capable of continuous detection is optimized by this study for maximum performance. This blood pressure sensor module encapsulates specially-designed electrodes as a strain sensor to be attached to a flexible plate. In operations, the strain sensor is held stable with top surface contacting tightly with the human skin while the bottom surface under a low pressure exerted by a pressurizing wrist belt. The electrodes and plate are expected to vibrate in a synchronized fashion with artery pulsations as vibrations transmitted to the sensor through the module to vary the net (average) strain of electrodes, thus also varying its resistance. Employing a readout circuit of Wheatstone bridge, an amplifier, a filter, and a digital signal processor, the artery pulsations could be successfully converted to temporal voltage variations for calculating blood pressures via known algorithms. However, due to the small diameter of the artery, around 3 mm, mis-positioning (MP) of the sensor electrode area relative to the artery beneath is inevitable, which may lower sensor sensitivity due to smaller average strains. To remedy the problem, efforts are paid to conduct finite element modeling (FEM) and simulations on the electrodes, sensor module and the wrist including bone, tissue and other bio-structures to predict sensor output variations with respect to varied mis-positionings. Based on the predictions, the sensor optimal length is successfully found as 5 mm, which maximizes average strain, the sensitivity of the sensor.