Respiration monitoring made easy with non-contact XeThru sensor technology
Respiration rate is an important vital sign that can provide insight into a person’s general state of health and quality of sleep. Breathing rate and breathing patterns are also considered good indicators of underlying medical conditions. While current technologies in today’s market promise accurate and dependable monitoring, the majority are less than ideal - either they are not accurate and require continual adjustment or are uncomfortable for subjects to use.
This article explores the various established methods for measuring and analyzing respiration to understand their limitations when applied to the requirements for daily health care and fitness tracking. Overcoming these challenges is not easy but Novelda’s XeThru sensor technology, based on an ultra-wideband (UWB) impulse radar implementation, provides a superior non-contact monitoring solution that is highly accurate, has an effective range up to 2.8m and is capable of ‘seeing through’ obstacles, such as clothing, while also being low cost and easy to use.
Respiration monitoring for healthcare
Breathing rate is the number of breaths a person takes per minute, and is best measured when a person is at rest. The rate may increase with fever, illness, and with other medical conditions. The most common method for measuring breathing rate is by physical assessment, observing a person’s chest and counting the number of breaths during one minute. Breathing rate on its own provides limited information but breathing patterns; measuring rate, amplitude and other characteristics; provide far more valuable information, which can be used for medical diagnostics as well as the evaluation of sleep quality.
Numerous monitoring technologies exist today. Some are invasive and measure actual airflow in and out of lungs, while others are electromechanical and require an elastic strap to be tightened around the subject’s chest. Other acoustic technologies require a device to be connected to a subject’s neck, while capacitive techniques require a special mattress or sensing unit to be installed in the bed, or on a subject’s body. These methods are mainly used in professional monitoring situations and provide accurate breathing pattern data. However, a fundamental challenge still remains, which is the physical connection of a sensor to the body, causing stress to the monitored subject. Any associated discomfort will in turn affect the subject’s breathing, and potentially invalidate the data.
Consumer respiration monitoring
In recent years, individuals have become much more conscious of and concerned about their health and well-being. Consequently the market has been flooded with healthcare and fitness monitoring devices, introduced to provide consumers with the means to track their physical activity and manage their personal health. These products use similar technology to their medically qualified counterparts, while further refinements of medical designs address a trend towards providing complete health assessments, by monitoring sleep quality and breathing patterns while at rest.
Of the many products in today’s market capable of measuring breathing rates, the majority take the form of fitness trackers involving body-worn contact sensors built into wristbands or chest straps. However, sleeping with a monitoring device connected to the body is uncomfortable and battery-operated units also require regular charging. More advanced sleep monitors, which provide a means of non-contact sensing, avoid these issues and provide quality sleep monitoring with greater comfort. These use technologies such as capacitive sensing, where sensor units are placed under bed sheets, or continuous wave (CW) radar solutions that monitor breathing movement from the bedside.
Even then there are limitations. While CW Doppler radar is highly sensitive to movement, and can easily detect the frequency of repetitive movements like breathing, it only provides phase information and cannot measure distance. Not being able to measure the actual mechanical displacement of the chest means this particular technique is incapable of differentiating between shallow and normal breathing.
Radar technology would seem to be the ideal choice for systems that are non-intrusive and can monitor breathing from a distance, especially as its signals can pass through materials such as clothing or bedding. But what is needed is an approach that can measure distance and precisely track breathing patterns from the subject’s chest movement. Achieving this with a low power, low cost solution is the real challenge.
The Ultimate Solution
With an appreciation of the limitations of current solutions, and understanding that consumers expect health and fitness products to be comfortable, safe and easy to use, it is clear that a truly unobtrusive respiration/sleep monitor needs to meet some pretty demanding design criteria. It should be able to accurately measure and record breathing from a distance and its placement shouldn’t be critical as long as the person is within a reasonable detection zone. The person’s orientation within that zone shouldn’t matter and the monitor should operate reliably despite reasonable obstructions e.g. through a duvet.
The technology should be suitable for use with people of all ages and sizes but should also be non-intrusive and preserve the privacy of the person being monitored – this typically precludes monitoring using any form of video surveillance. It should also be possible to monitor more than one person concurrently.
Further considerations in terms of the technical performance of a sensor that delivers on these goals are that it should be: safe to use, low cost, low power and ideally, for ease of integration into an end-equipment design, should also be small in size and provide a digital interface.
In pursuing a solution to address these criteria, Novelda concluded that an electromagnetic sensor using the principles of radar should be able to meet all the technical requirements provided other concerns could be overcome. While noting previously the shortfall of CW radar, in only being able to measure change in velocity and not distance, this limitation does not apply when using of ultra-wideband (UWB) impulse radar techniques that, by emitting and sampling signal pulses, can achieve highly accurate distance measurements determined by the time differences between transmitted and received pulses.
Furthermore, by using what is essentially a spread spectrum approach and employing digital signal processing (DSP) to recover the return signal, UWB radar can operate at much lower power levels than conventional radar. This overcomes the potential consumer concern of not wanting a high-power radar sitting on their bedside table. The spread spectrum nature of UWB also means it can coexist with other RF systems without causing, or being affected by, interference.
Radar is considered to be a complex and expensive technology, typically deployed in high-end market segments. Certainly this has been true in the past for traditional systems constructed from discrete components and using costly ceramic substrates. In most markets, especially consumer, the widespread adoption of integrated circuit technology has enabled products to be produced in volume and offered at affordable prices. The high level of integration possible today enables complete system-on-chip solutions with consequent benefits in size and power consumption.
So finally …
This is the approach Novelda has taken, implementing a UWB impulse radar as a CMOS integrated circuit. Its proprietary and patented design, branded XeThru, optimizes the cost and performance of the sensor modules that Novelda has then subsequently developed for respiration monitoring and other presence detection applications. These complete sensor modules, which contain everything from the antennas through to the signal processing chip, are available from Novelda as OEM units ready to be integrated into end-user products. For development and technology evaluation Novelda also offers its Inspiration Kit that includes a PC hardware interface and provides a complete software environment, with configuration, data capture and visualization tools.