Pneumotachometer in a T-shirt

Canadians made a T-shirt with a breath monitor

Denis Strigun, Naked Science

The development of wearable electronics makes it possible to create mobile devices for monitoring vital signs. So, commercially available smart watches and fitness trackers are able to keep statistics, for example, heart rate, which simplifies early and remote diagnosis of heart disease. Most of these systems, however, cannot measure respiratory rate – although this could prevent complications from asthma, chronic obstructive pulmonary disease (COPD) and sleep apnea. Existing prototypes of such devices usually involve the connection of sensors or electrodes to the user's body, which may limit his movements and reliability.

Integration of wearable breathing monitors with textiles using the technology of ultra-wideband pulsed radio signals (Impulse RadioUltra WideBand, IR UWB) is considered more promising. Compared to analogues, it requires less cumbersome equipment and at the same time has an extremely high accuracy of data transmission. Nevertheless, now in "smart" clothing, IR UWB is usually implemented on the basis of relatively large patch antennas made of conductive filaments - for example, in the form of square petals – with a thickness of six to seven millimeters. To reduce the area of the device, Canadian engineers have developed an antenna in the form of fragments of an Archimedean spiral.

The principle of operation of the sensor

The prototype has two arcs with a total length of 10 centimeters and is made of quartz glass coated with polyimide and silver. The device has an electrical resistance of 3 ± 1 ohm per centimeter and operates at a resonant frequency of 2.45 gigahertz. As part of the tests, the authors glued the device to a cotton T-shirt at chest level: when inhaled, the chest expanded, stretching the arcs (without deforming the material), which, combined with a change in the dielectric constant of the lungs (from 20.51 to 48.45), "shifted" the resonant frequency of the antenna. Information about the antenna signal was continuously transmitted to the vector analyzer of electrical circuits (VNA) and then to the computer.

Thus, according to the "shifts", scientists could estimate the respiratory rate. The sensitivity of the sensor was 1.4 megahertz per millimeter. Thus, the movement of the chest by only 3.6 millimeters led to a significant change in the resonant frequency – by 30 megahertz. In addition to its small size and high sensitivity, the authors attributed the advantages of the device to the absence of skin contact, which allows it to be used in the examination of infants. At the same time, in natural conditions, instead of a vector analyzer, the antenna frequency can be monitored using other technologies, for example narrowband filters operating in the ISM bands, which include Bluetooth.

Article by Guay et al. Wearable Contactless Respiration Sensor Based on Multi-Material Fibers Integrated into Textile is published in the journal Sensors.

Portal "Eternal youth" http://vechnayamolodost.ru  23.05.2017