A Wristwatch-Based Wireless Sensor Platform for IoT Health Monitoring Applications
2. Comparison of Wireless Performance in the 868 MHz and 2.45 GHz ISM Bands
2.1. Free Space Path Loss
2.2. Radio Frequency (RF) Attenuation in Indoor Environment
2.3. Co-Existence Issues
2.4. Power Consumption
2.5. Wireless Communication Range
3. System Design
3.1. System Hardware Architecture
3.2. System Software Design
3.2.1. Wireless Network Protocol
- Bidirectional communication;
- Minimum throughput that allows the reliable transfer of sensor data and control commands;
- Handle a burst of data of 500 bytes;
- Determine sleep/active cycles of the wristwatch to enable power saving.
3.2.2. System Workflow
3.3. Working Principle of the PPG Sensor
4. Antenna Design
4.1. Antenna Simulations
4.2. Impedance Matching and Bandwidth Enhancement
4.3. Antenna Prototype Fabrication
- 3D part fabrication or selection: The 3D part/object on which the metal has to be printed can be fabricated using standard 3D printers. The commercially available thermoplastic parts, such as metals, plastics, glass, FR4, can also be used. In this work, the antenna structure is printed on an ASA thermoplastic wristwatch enclosure from OKW enclosures ;
- Part coating with ProtoPaint epoxy: The part is covered with the LPKF ProtoPaint LDS epoxy layer;
- Laser direct structuring: The LPKF laser system creates an outline of the conductive pattern of the design. In this step, the laser removes some of the epoxy material and forms a rough surface on which the copper can firmly adhere during metallization;
- Metallization: This step involves the electroless copper plating of the region exposed by laser etching. The photograph of the antenna track during the metallization process is shown in Figure 11. The metallization of the antenna track was completed in the following four steps:
- Step 1: In order to get a low resistance electrical continuity through the activated track on the plastic, copper electroless deposition of the surface was required to make it possible to electroplate it. Using an in-house developed, dimethylamine borane (DMAB)-based copper electroless deposition solution, the track was metallized with copper. The sample was immersed in the bath for 60 min at 70 °C, pH9;
- Step 2: The electroless copper deposited on the sample needed to be electroplated up with copper. A Schlotter commercial copper bright bath, ACG8, was utilized for this process. The sample was plated for 60 min, 2 A/dm2 at room temperature;
- Step 3: Utilizing an in-house developed, low stress nickel-sulphamate-based electroplating bath, the sample was plated for 10 min, 3 A/dm2, at 60 °C. The minimum thickness (tmin) of the electroplated copper is 14.8 μm, as shown;
- Step 4: To avoid oxidation of the nickel surface, a commercially available gold Ormex immersion solution by Engelhard was used to finish the surface with gold. The thickness of the gold finish is less than 0.11 μm. This process took 7 minutes at a temperature of 85 °C.
4.4. Antenna Measurements
5. Communication Range Measurements of the Sensor Platform
6. System Implementation and Clinical Trials
Conflicts of Interest
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|Parameters||868 MHz||BLE 4.0|
|Transmit power limit (dBm)||14 ||10 |
|Receiver sensitivity (dBm)||−110 ||−95 |
|Wristwatch Tx antenna gain (dBi)||−4.86 (Measured)||0|
|Receiver antenna gain, assumed (dBi)||0||0|
|Maximum communication range, d (m)||2333||456|
|Without MiWi stack||25.84||No security option|
|Using MiWi, Tx only||19.13||Security Disabled|
|Using MiWi, Tx only||9.60||Security Enabled|
(Both Tx and Rx at the same time)
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Kumar, S.; Buckley, J.L.; Barton, J.; Pigeon, M.; Newberry, R.; Rodencal, M.; Hajzeraj, A.; Hannon, T.; Rogers, K.; Casey, D.; O’Sullivan, D.; O’Flynn, B. A Wristwatch-Based Wireless Sensor Platform for IoT Health Monitoring Applications. Sensors 2020, 20, 1675. https://doi.org/10.3390/s20061675
Kumar S, Buckley JL, Barton J, Pigeon M, Newberry R, Rodencal M, Hajzeraj A, Hannon T, Rogers K, Casey D, O’Sullivan D, O’Flynn B. A Wristwatch-Based Wireless Sensor Platform for IoT Health Monitoring Applications. Sensors. 2020; 20(6):1675. https://doi.org/10.3390/s20061675Chicago/Turabian Style
Kumar, Sanjeev, John L. Buckley, John Barton, Melusine Pigeon, Robert Newberry, Matthew Rodencal, Adhurim Hajzeraj, Tim Hannon, Ken Rogers, Declan Casey, Donal O’Sullivan, and Brendan O’Flynn. 2020. "A Wristwatch-Based Wireless Sensor Platform for IoT Health Monitoring Applications" Sensors 20, no. 6: 1675. https://doi.org/10.3390/s20061675