Antenna Effects on Respiratory Rate Measurement Using a UWB Radar System

State-of-the-art advances in the field of radar technology have made it possible to design noninvasive sensing devices of vital signs. This paper presents the effects of antenna characteristics on an ultra-wideband (UWB) radar-based respiratory rate measurement system for tele-health-monitoring applications. The performance of three types of antenna for a UWB radar respiratory rate measurement system was studied in this paper. In this context, the proposed system was comprehensively evaluated using two experimental sets. First, a mechanical setup was used to provide a series of controlled frequency and distance motions for measurement test. The error analysis for various parameters associated with pulmonary activities such as breathing frequency and chest displacement was performed. Results indicated that the proposed sensing system used effectively as a respiratory rate measurement is less affected and shows less error when an antenna with directive radiation pattern, low cross-polarization, and stable phase center was used. Due to its good radiation characteristics and small form-factor, this antenna was selected to study the respiratory rates of ten test subjects. The results were compared with a standard respiratory-rate measurement using a respiration belt transducer. The measurement results using the proposed and the standard systems showed excellent agreement. The mean error value of the respiratory rate measurements was 0.03 Hz with a statistical standard deviation of 0.03 Hz.

I. Introduction

Respiratory rate is one of the most crucial vital signs used to assess human body functions and physiological stability. In fact, respiratory rate is helpful in predicting potential clinical events. For example, a sudden change in respiratory rate is considered a marker for cardiac arrest [1] and one of the strongest predictors of mortality [2]. Furthermore, respiratory rate is helpful in monitoring patient illness progression to determine the effective treatments that should be received [3].