Measurements at a distance: the missing link to chronic monitoring
Remote sensing comprises several sensing mechanisms for the continuous monitoring of vital signs. They all operate without physical contact to the subject, hence the term noncontact sensing that is sometimes used.
Remote sensing is a concept that comprises multiple sensing techniques, some of which have gained increased interest recently.
The field of remote sensing holds great promise for lifelong and chronic monitoring of vital signs. Key to achieving that goal is the invisible and completely unobtrusive integration into everyday objects, such as bed sheets, office/car chairs, couch or PC screen. In this case, the strength is not in the quality of the acquired signals, but the longitudinal nature, with the potential to reveal slowly changing patterns - possibly symptoms from underlying physiological changes. The analysis of such datasets, currently largely unexplored, will provide new insights into normal versus pathological patterns of changes over very long periods of time.
Another area where remote sensing could play an important role, is in monitoring of patients that cannot withstand continuous skin contact, such as neonates.
Relevance for the Electronic Components and Systems (ECS) industry
Remote sensing and monitoring holds a great promise in the prevention and very early detection of pathological symptoms. Remote sensing and monitoring has the potential to become embedded into everyday life objects, such as furniture, TV sets, etc. It is targeting the entire population.
Technological challenges are foreseen in
Miniaturization and integration;
Distributed data analytics and intelligence;
Enabling technology platforms
Several distinct techniques are being explored for the implementation of remote sensing, where each technique has a unique set of properties and matching use cases.
Sensing of ballistic forces relies on motion created by the heart and bloodflow, which can be captured remotely with force sensors or accelerometers integrated in bed or chair. The method is very sensitive to the presence of other forces and vibrations.
Optical sensing techniques can be used for remote reflective photoplethysmography, since well-perfused areas of facial skin changes tone on every heartbeat. Standard RGB cameras can be used for this purpose, and ambient light can act as light source. Novel hyperspectral cameras can improve the sensitivity of the measurement. In theory, heart rate, respiration rate and even blood oxygen levels could be measured in this way. Technical challenges are found in low light conditions, darker skin tones and under conditions of motion.
Capacitive sensing techniques can capture the body’s electrical activity through non-conductive layers (e.g. clothing, bed sheets or seat cover). It allows for remote measurement of ECG and bio-impedance from which heart rate, heart rate variability and respiration rate and (relative) depth can be derived. The distance between the measurement electrodes and patient should be small, so approaches can be utilized in which arrays of electrodes are applied such that pairs of electrodes can be chosen to optimize signal quality.
Radar sensing techniques use electromagnetic waves to measure tiny chest displacements. A beating heart, as well as normal respiratory activity, can cause chest displacements that can be measured with radar techniques from a large distance (10’s of meters) and through walls. Obviously, displacements of the user cause big artefacts in the recorded signal.
As multiple techniques exist, each with their unique set of advantages and disadvantages, it is likely that the deployment of remote monitoring system will be multi-modal, with fusing techniques to smart analytics to unify the data into usable information. All remote sensing techniques are very sensitive to artefacts, which calls for smart algorithms to continuously quantify signal quality, preferably close to the source (edge computing).
Another challenge is related to the power source of the sensors. The furniture in which sensors are envisioned to be embedded into, is typically not connected to mains power. As a consequence, the sensors might have to be powered from a battery, ideally with a single battery over the lifetime of the sensor. This calls for novel ultra-low power sensing, processing and wireless transmission techniques.
A final challenge is the integration itself. For example, integration of capacitive sensors into bedsheets comes with a washability challenge, integration of radar sensing into a TV set comes with a challenge of antenna integration, etc.