Facile In-Tube-Center Packaging of Flexible Airflow Rate Microsensor for Simultaneous Respiration and Heartbeat Measurement

Respiration and heartbeat are among the important vital signs of living beings. Taking advantage of the physical attachment of the lung and heart, measurements of both can be performed simultaneously using airflow rate microsensors to measure the respiration airflow. For such airflow rate sensors, the packaging is crucial to define and encapsulate the airflow region. In this study, we propose a facile packaging technique for flexible airflow rate microsensors. The thermal calorimetric sensing structure was fabricated through a standard microfabrication technology on a thin polyimide (PI) film. The film was packaged at the center of a resin tube utilizing its buckling. We also proposed an approach to improve the time response by limiting the thermal capacity around the sensing structure through the implementation of a thin substrate for the sensing structure supported by a thicker film. The strategy successfully improved both the time response and sensitivity of the airflow rate sensor. Finally, the utilization of the sensor for simultaneous respiration and heartbeat measurement was demonstrated through an animal experiment using a small animal, namely rats.

I. Introduction

The measurements of respiration and heartbeat are crucial indicators of the health and well-being of living beings. Respiration measurements can provide information about one’s lung function and can be used to detect respiratory problems such as asthma or pneumonia [1]. The significance of respiration is emphasized by the widespread impact of pneumonia caused by the COVID-19 pandemic [2], [3], [4]. Meanwhile, heartbeat measurements can provide information about one’s cardiovascular health and can be used to detect issues such as coronary artery disease [5]. Both respiration and heartbeat measurements can also be used to monitor one’s response to medical treatment and to detect changes in one’s condition. Both parameters are critical since pulmonary and heart diseases are major contributors to global mortality rates [6], [7].