TNO at Holst Centre develops smart sensor mat that detects heart rate, breathing rate, and posture
TNO at Holst Centre has developed an ultrathin conformable smart sensor mat that can detect a person's breathing rate, heart rate and posture. The multi-modal sensing mat consists of a combination of printed piezo-resistive and piezo-electric sensors. In one implementation, the mat can be placed under a bed sheet, enabling long-term monitoring of patients in a hospital bed or babies sleeping at home. The mat can also be integrated into the seat and back of an office chair, increasing and extending the vitality of our work force. When used in a car seat, the mat can monitor posture and driver alertness. TNO at Holst Centre continues to develop the sensor mat to include monitoring of additional vital signs.
Approximately 26% of people between the ages of 30 and 70 suffer from sleep apnoea worldwide. People with sleep apnoea are four times more likely to have a stroke and many die each year from cardiovascular diseases caused by this condition. As the healthcare costs involved are increasing rapidly across the globe, the demand for a cure is on the rise.
People suffering from sleep apnoea are often monitored in so-called sleeping centres, having to sleep there several nights under less-than-ideal circumstances. Peter Zalar, program manager Large-Area Sensors at TNO at Holst Centre, explains: "The posture, breathing rate, and heart rate of a person laying on a bed can be ascertained using a large-area matrix of piezo-electric and piezo-resistive force sensors. Because these sensors are printed on a thin elastomer, they are very sensitive, quickly picking up a signal again even if the patient has moved. This maximises data quality, enabling patient monitoring to be performed completely remotely and reliably. Since the sensors are unobtrusive and do not cause discomfort, the patient does not notice the device – allowing for the accumulation of vast amounts of unbiased data. Furthermore, by combining multiple data sources, the state of the patient's health can be determined with greater certainty."
The smart sensor mat enables long-term monitoring, as it is a non-intrusive device. The mat simply disappears into the object in which it is integrated. There are many possible applications to use the sensor mat, for example in a baby bed to monitor an infant's activity and breathing rate.
Peter Zalar: "Another field of application is in cars. When used in a car seat, the mat can monitor sitting posture and heart rate and give an indication of the driver's alertness level. Even with the advent of autonomous driving technologies, the driver formally still needs to pay attention, but the chance of being distracted or dosing off increases due to driver inactivity. The mat could prevent people from falling asleep behind the steering wheel, which could help save lives."
Zalar continues: "When integrated in an office chair the mat can signal when it is necessary to change position or even to get up and get some exercise. This helps increase and extend the vitality of our work force. Additionally, it could help designers of office furniture to create more ergonomic chairs by identifying areas of a chair which can cause discomfort or harm to a person."
Existing solutions for large-area pressure sensors are rigid and often based on capacitive sensors that are difficult to implement in practice. The sensor mat is entirely developed in-house, using a unique set of materials and design features. Peter Zalar explains: "At TNO at Holst Centre we have optimised the technology of large-area, multilayer screen printing and lamination, which means that a sensor array can be printed on substrates as large as 90x200cm. We have also introduced the use of elastomeric substrates and laminates for piezo-electric sensors, increasing their sensitivity. Furthermore, in order to improve the sensitivity to compression, which is used to detect heartbeats, the piezo-electric sensor geometry has been optimised. To validate our approach, we have developed basic software and algorithms, as well as a new fast readout system to keep up with the volume of data produced by all the sensors. We have three submitted patents around these innovations."
The number and ratio of piezo-electric and piezo-resistive sensors within the matrix structure can be adjusted. This makes the mat highly cost effective in the long term, as more or fewer of either sensor type can be used on a larger or smaller surface. The algorithms can also be adjusted, so both the hardware and the software can be tailored to the application. Peter adds: "TNO at Holst Centre is currently working on adding new sensor modalities, such as (printed) temperature sensors, to broaden the application possibilities and prediction qualities of algorithms that take advantage of this data."
Caption: The smart sensor mat unobtrusively monitors a sleeping baby (photo: TNO at Holst Centre)