Integration of Lower-Power Sensors in a Textile

In the modern sense, actual portable bio signals health monitoring solutions are not wearable like usual clothes. A number of electrodes are needed for clinical measurements such as ECG (Electrocardiograph).

Furthermore, a lot of patients would benefit from daily long-term monitoring, according to a panel of consulted doctors. Sadly, the available solutions which can acquire medical ECG are far from being adapted to a daily use such as this.

So, because of limited observability for reasons like usability and comfort, and crucially, due to the irritations and disagreements from the long-term use of adhesive gel electrodes and straps there is a corresponding lack in the prevention of heart illnesses.

So, in order to address the integration of sensors with dry electrodes in garments, CSEM has developed the technology of 'cooperative sensors' and is further pushing toward system integration into textiles.

This article outlines the ongoing activities and the expected achievements to be attained through the realization of a first demonstrator, which will be available for first testing in 2020.

Long-term monitoring of the electrical activity of the cardiovascular system with an ambulatory electrocardiogram (ECG) device, so-called Holter devices, is required for the diagnosis of different heart conditions (e.g., arrhythmias and other conduction abnormalities).

ECGs should be recorded for periods as long as possible (weeks to months) in order to capture a complete image of the health state of the heart, particularly in the attempt to capture fleeting and rare events.

A number of miniature Holter devices have been brought to the market in recent years, they are quite simple to use but have only a limited number of leads and, crucially, are uncomfortable to wear over long periods, mainly because of the adhesive of the gel electrodes and straps, the cables to the electrodes, the resulting maintenance and handling, and the size and weight of the electronics.

So, CSEM is developing a 12-lead Holter monitor, which is comfortable to wear even over long periods of time. Dry, adhesive-free active electrodes are utilized and integrated in a tight-fitting vest together with the electronics, which is in contrast to most other ambulatory ECG recorders (including patches).

The system is built via CSEM's patented cooperative-sensor technology in order to achieve this. It permits connecting a large amount of active electrodes with just a 1-wire bus while preserving ECG signal quality at least to the level of conventional devices.

With respect to previous developments, by reducing the size and the weight of the cooperative sensors thanks to an ultra-low-power ASIC the wearing comfort is enhanced even more.

For the first time, this enables the power of the active electrodes of the cooperative sensors remotely via the same 1-wire bus used for the measurement of ECG. The current return is attained by the body itself.

Although the wire must be insulated for correct operation, a failure of insulation, due for instance, to wear and tear or to the presence of body fluid (e.g., sweat) is safe because the powering current is limited to a value which is below the maximum permitted by the medical standard IEC 60601-1.

Only the recorder and its battery must be removed, the vest is washed together with its embedded sensors. Finally, by utilizing recent technologies from the sport textile industry, a high wearing comfort of the sensor garment is achieved.

As seen in Figure 1, the ASIC is housed in each of the sensors and is optimized for ultra-low power and meeting the best ECG signal quality compatible with medical use, in particular in motion and in environments disturbed with electromagnetic noise. The ASIC includes the following building blocks:

• A digital logic for sensor synchronization and time-sharing
• A low-noise wideband unity-gain buffer to address the high-impedance contact with the skin
• A power management unit responsible for harvesting power from the recorder and for delivering a clean power supply to the other circuits of the ASIC

As seen in Figure 1, up to 10 sensors are embedded in the textile garment. The textile garment must fulfill three key functions:

1. It must be comfortable to wear
2. It must apply the sensors with slight pressure on the skin at defined spots
3. It must connect the sensors and the recorder via a 1-wire bus

CSEM is working with sport fashion designers on a highly stretchable seamless apparel with printed conductive tracks in order to achieve these objectives. Another challenge comes from the fact that, from one person to another, body shape varies a lot.

As the positioning of the sensors and their skin contact is crucial, easily adaptable garments are developed to which healthcare professionals can attach the sensors so that their positions and preload can be custom-fitted easily to any body type.

A solution based on a wrapping garment with a freely adjustable waist circumference is demonstrated in the drawing shown in Figure 1.

Figure 1. Drawing of the developed vest showing the sensors, conductive tracks, and pads allowing custom fine positioning of the electrodes as well as the ASIC embedded in the cooperative sensors. Image Credit: CSEM

Furthermore, as the cooperative sensors have only one connection to the 1-wire bus, printed conductive pads on the vest allow healthcare professionals to pin the sensors to the right spots freely and so achieve fine adjustment of electrode position.

In conclusion, this development brings electronics integration and textile solutions together to attain comfort and usability for the long-term measurement of ECG of outpatients.

Acknowledgments

Produced from materials originally authored by A. Fivaz, M. Crettaz, J. Wacker, O. Chételat, B. Bonnal, K. Badami, M. Pons Solé and S. Emery from CSEM.

This information has been sourced, reviewed and adapted from materials provided by CSEM.

For more information on this source, please visit CSEM.