Frequency Characteristics of Pulse Wave Sensor Using MEMS Piezoresistive Cantilever Element

Abstract

Wearable sensor devices with minimal discomfort to the wearer have been widely developed to realize continuous measurements of vital signs (body temperature, blood pressure, respiration rate, and pulse wave) in many applications across various fields, such as healthcare and sports. Among them, microelectromechanical systems (MEMS)-based differential pressure sensors have garnered attention as a tool for measuring pulse waves with weak skin tightening. Using a MEMS-based piezoresistive cantilever with an air chamber as the pressure change sensor enables highly sensitive pulse-wave measurements to be achieved. Furthermore, the initial static pressure when attaching the sensor to the skin is physically excluded because of air leakage around the cantilever, which serves as a high-pass filter. However, if the frequency characteristics of this mechanical high-pass filter are not appropriately designed, then the essential information of the pulse-wave measurement may not be reflected. In this study, the frequency characteristics of a sensor structure is derived theoretically based on the air leakage rate and chamber size. Subsequently, a pulse wave sensor with a MEMS piezoresistive cantilever element, two air chambers, and a skin-contacted membrane is designed and fabricated. The developed sensor is 30 mm in diameter and 8 mm in thickness and realizes high-pass filter characteristics of 0.7 Hz. Finally, pulse wave measurement at the neck of a participant is demonstrated using the developed sensor. It is confirmed that the measured pulse wave contains signals in the designed frequency band.

Assessment of a Calibration-Free Method of Cuffless Blood Pressure Measurement: A Pilot Study

“…As in Eq.14, the filter coefficients need to calculate the frequency response and window function coefficients according to different FIR filter types and the size of the convolution kernel. The related research on pulse wave analysis shows that the pulse wave frequency ranges from 0.8Hz to 30Hz [38][39][40][41]. Therefore, we use a bandpass filter (Eq.15) and set the cutoff frequencies fc1 and fc2 to 0.6 Hz and 5 Hz, respectively.…”

An Arterial Compliance Sensor for Cuffless Blood Pressure Estimation Based on Piezoelectric and Optical Signals

“…The volume V within the chamber is the move distance L into the sensor generated by the rubber membrane and the cross-sectional area A of the rubber membrane itself. The volume value calculated by the product of L and A is the volume [25] inside the compression chamber, which makes the original volume change ∆V, as in the following Equation ( 2):…”

“…The intra-arterial MAP can be estimated by Equation (25), where β is a constant that reflects the local arterial stiffness during a cardiac cycle, independent of changes in arterial pressure during the measurement cycle [62,63]. After obtaining MAP and PP through the Pβ model, we can track the systolic BP (SBP) and diastolic BP (DBP) through the calculation method of Equation (26), where the coefficient k needs to be adjusted according to the results of the experiments.…”