Contactless monitoring of respiratory activity using electromagnetic waves for ambient assisted living framework: feasibility study and prototype realization.

Respiratory rate is a vital parameter of primary importance in medicine, sport/fitness and wellness in general, especially for most vulnerable categories of people like children and elderly people. Contactless determination of breathing activity provides a powerful and essential mean for evaluating this parameter in subjects who cannot accommodate physical sensors on their bodies. In hospital such subjects may be intensive care patients, prematurely born children and hosts of burn units. Moreover, also for long-term measurements of healthy people, for example, an elder living in home alone or in a care centre, invasive systems prove to be uncomfortable and annoying. Even for a night-time diagnosis of respiratory sleep disorders, like apnoea and hypopnoea, they demonstrate to interfere with the sleep regularity. Therefore, in the last decades many electronic devices have been conceived and realized to detect such an important parameter along with different branches of physics: strain gauges, ultrasounds, optics, thermometry, etc. This chapter presents the theoretical studies, the design and realization of a standalone Electromagnetic (EM) system for contactless determination of breathing frequency and subject's activity. Two major EM solutions are already known in the literature, continuous wave (CW) systems, and ultra-wideband (UWB) systems. The first evaluates the Doppler effect caused by the chest displacement during breathing at a single frequency, and the other one is a radar that detects the body motion by measuring the time shifts of sequential pulses.An intermediate solution thatjoins the advantages ofboth and overcomes their drawbacks is proposed. Through the use of a frequency sweep, in fact, it is possible to retrieve the equivalent information that UWB pulses are able to give, yet keeping the same contained hardware complexity of a CW system. At the same time, the proposed system proves to be robust and insensible to environmental changes. The theoretical studies have aimed at the demonstration that the solution under study helps in avoiding the blind frequencies that affect CW systems, because of sensitivity issues that depend on the variability of the reflection coefficient from the frequency and, as proved, from the harmonic content of the monitored motion. Supported by such theoretical studies, the preliminary tests are performed using laboratory instrumentation (a VNA and a commercial double ridge antenna) for a thorough campaign of measurements on assorted frequency bands, both in a controlled environment (anechoic angle) and in a concrete house, that inherently clutter the received signal. The second step involves the design and realization of a custom antenna, to be used in place of the double ridge and operating in a narrower band, which has demonstrated the same reliability of the commercial one. It has been verified in different conditions that the proposed system is able to detect both the position of the subject (i.e. distance from the antenna) and his breathing frequency, without any need for collaboration from the subject under measure. The final activity is the realization of a prototype of the device that implements the algorithms that have been studied. It is worth to highlight that the proposed system can be profitably adopted for Ambient Assisted Living framework, since it is not invasive and does not infringe the privacy of the end user, and yet it provides many valuable information about the subject's health status.