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Special communications for remote health monitoring
It's hard to imagine a modern world today without wearable devices. The mobility, compactness and performance of these devices are important features that engineers and scientists around the world are continually working to improve. Wearable devices, whose purpose is to monitor the user's health, are one of the most important aspects of digital medicine. But like any other personal device, they need an advanced infrastructure to transmit signals from the device to the data centre. The problem is that this infrastructure does not exist everywhere. Scientists at the University of Arizona (Tucson, US) have developed a new device that can transmit data up to 24km away without access to a satellite infrastructure. What is this device, how does it work and how efficient is it?
Research base
Wearable sensors can extract highly accurate information from basic physiological processes and transmit this information wirelessly for aggregation and research. Devices designed for these applications typically implement short-range communication, Bluetooth Low Energy or Wi-Fi as communication methods. Although these communication protocols are reliable and well developed, their use is limited due to inherent infrastructure requirements such as adequate cellular coverage, internet connectivity for interaction with applications, and basic power supplies for long term operation. It seems that in places where such infrastructure is lacking, portable monitoring devices become just a jewel. Although some solutions have attempted to address this problem through the use of satellite communications, power requirements, equipment and deployment costs have prevented widespread deployment in resource-constrained areas. To address this problem, low-power wide area network (LPWAN) protocols such as ultra-narrow band (UNB), LoRa and SigFox have been implemented.
Recent advances in the architecture of wearable biosymbiotic devices, combined with the proliferation of complementary electronics to exploit long-distance transmission, offer a promising path to realising this technology.
Study results
The given device uses a single antenna at 915 MHz, which allows both energy harvesting from a commercially available 915 MHz power transmitter and long-distance transmission using LoRa communication protocols. The use of a single antenna allows for a smaller device footprint, increased flexibility and lower manufacturing costs.
LoRa is a patented communication protocol that is a derivative of spread spectrum frequency modulation with built-in direct error correction and uses wideband transmission to cope with possible frequency and noise changes. The LoRa receiver unit can decode transmissions with power well below the minimum noise level, providing reliable long-range communication schemes. Operating in the lower frequency ISM band (915 MHz) in the US, this communication scheme is an attractive alternative to traditional communication technologies operating in the higher frequency ISM bands (Wi-Fi and Bluetooth), which have limited communication distances and require extensive infrastructure. In addition, LoRa-based communication offers the possibility to extend communication distances to hundreds of kilometres by using multiple gateways and by implementing LoRa wireless networks (LoRaWAN).
The device attaches to the dorsal side of the forearm, allowing the optical sensor to be placed near the palm of the wrist to record physiologically relevant information. The sensor is encapsulated and has a low thermal and mechanical mass (device weight < 400 mg), allowing measurements with high sensitivity. This device also provides digital communication with an integrated optical sensor for photoplethysmography recording (PPG from photoplethysmography).
The sensor uses a TPU mesh cutout and a laminated elastomeric material coated with black dye (5% by weight) to ensure conformal contact with the body and protect the sensor from ambient optical noise, significantly reducing motion artifacts and allowing data collection during physical activity.
Novel method of reading the biosymbiotic platform is demonstrated by optically recording physiological processes using a PPG chip to detect the user's heart rate in the palm region of the wrist. In this case, the change in infrared absorption caused by volume changes in the underlying vascular network can be used to monitor heart rate.
To demonstrate the capabilities of this platform in practice, scientists have created a biosymbiotic device to be placed on the dorsal side of the forearm. The distance between the subject and the receiver was 15 miles (24 km). The subject was then asked to walk a pre-determined route, which consisted of moderate mountainous terrain with elevation differences (± 98 m). The device was programmed to transmit at approximately 5 MHz and used the average heart rate over 5 samples, resulting in a calculation time of 9.2 seconds. Temperature was also recorded at 5 MHz.
The researchers note that their device was designed for use in a "rural" area, i.e. in an open space. However, it is capable of transmitting data up to 0.5 miles without line-of-sight in a densely populated area with tall buildings around the user. To demonstrate the long-term performance capabilities in an urban environment, a 7-day experiment was conducted.
During this experiment, the device operated continuously at 5 MHz and recharged when the user was near a power transmitter located in high-traffic areas, such as the nightstand and office. Battery voltage was monitored at regular 8-hour intervals, with green shaded areas indicating proximity to the energy emitter. Heart rate and skin temperature data (shaded in red) were collected continuously. During periods of moderate activity, such as walking, a less pronounced increase in heart rate was also observed. The device demonstrated reliable performance in several different scenarios in urban environments, ensuring continuous collection and transmission of biosignals with high accuracy regardless of activity.
Scientists have described this invention as a wearable device designed to collect and transmit user biosignals. Such devices already exist, but these described are distinguished from their competitors by the ability to operate in the absence of the necessary communication infrastructure. Their realization is capable of transmitting user data up to 24 km away. The secret of this device's success lies in its use of LPWAN (low power wide area network), which provides a range 2400 times greater than Wi-Fi and 533 times greater than Bluetooth. The new system uses LoRa, a patented LPWAN technology. At the same time as implementing this protocol, researchers developed a circuit and antenna that could be incorporated into a soft wearable device. Another feature of the device is the possibility of contactless recharging at a distance of more than 2 metres from the base.
In the future, scientists plan to continue working on the device, namely to try to increase the communication range by introducing LoRa wireless gateways that can serve hundreds of square kilometers and hundreds of device users using only a small number of connection points.
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