Polyimide-Based High-Performance Film Bulk Acoustic Resonator Humidity Sensor and Its Application in Real-Time Human Respiration Monitoring

Abstract

Respiration monitoring is vital for human health assessment. Humidity sensing is a promising way to establish a relationship between human respiration and electrical signal. This paper presents a polyimide-based film bulk acoustic resonator (PI-FBAR) humidity sensor operating in resonant frequency and reflection coefficient S11 dual-parameter with high sensitivity and stability, and it is applied in real-time human respiration monitoring for the first time. Both these two parameters can be used to sense different breathing conditions, such as normal breathing and deep breathing, and breathing with different rates such as normal breathing, slow breathing, apnea, and fast breathing. Experimental results also indicate that the proposed humidity sensor has potential applications in predicting the fitness of individual and in the medical field for detecting body fluids loss and daily water intake warning. The respiratory rates measured by our proposed PI-FBAR humidity sensor operating in frequency mode and S11 mode have Pearson correlation of up to 0.975 and 0.982 with that measured by the clinical monitor, respectively. Bland–Altman method analysis results further revealed that both S11 and frequency response are in good agreement with clinical monitor. The proposed sensor combines the advantages of non-invasiveness, high sensitivity and high stability, and it has great potential in human health monitoring.

The application of impantable sensors in the musculoskeletal system: a review

“…A thin PI film is also used as the diaphragm in capacitive pressure transducers for implantable cardiovascular applications ( Hasenkamp et al, 2012 ). Zhu et al (2022) introduced a PI-based film bulk acoustic resonator humidity sensor with high sensitivity and stability. This sensor was applied for the first time in the real-time monitoring of human respiration.…”

Highly Sensitive Self-Powered Biomedical Applications Using Triboelectric Nanogenerator

“…By analyzing the rate of breathing, people can sense the other physical activities, such as abnormalities in the lungs, heart, sleeping, exercise, and the emotional states of human body [88][89][90]. Researchers have developed a lot of sensors for the early diagnosis of breathing rate abnormalities, as these sensors are highly necessary for providing proper medical assistance [91][92][93][94][95]. Among the various types of sensors, research on self-powered sensors has emerged as a topic of mass interest.…”

“…In this matter, in 2018, Xudong Wang and his co-workers proposed an air-flow-driven TENG for self-powered real-time respiratory monitoring. Here, the authors developed a flexible TENG using the nanostructured surface of PTFE film and copper for tribo-materials [95]. This was a wavy-shaped PTFE film on flat copper film in an acrylic box where one end of the PTFE film was attached to the acrylic box and the other end was free to vibrate for the effective friction, with the flat copper film attached to the acrylic plane, as shown by the schematic in Figure 9a.…”

Editorial for the Special Issue on Piezoelectric Transducers: Materials, Devices and Applications, Volume III

“…Energyscavenging structures are discussed in two contributions, one of which analyzes a piezoelectric heterostructure employing magnetic springs for harvesting mechanical energy from human foot strikes [25] and the other of which examines a dual-frequency vibration-based energy harvester based on coupled resonators [26]. Transducers oriented towards sensor development are also considered in this Special Issue, with demonstrations of polymeric tactile sensors being used for hardness differentiation during the palpation process [27] and a polyimide-based film bulk acoustic resonator used as humidity sensor [28]. Finally, a review paper on flexible ultrasonic transducers presented recent advances in their development and practical applications in imaging systems [29].…”