Wearable Blood Pressure Sensing Based on Transmission Coefficient Scattering for Microstrip Patch Antennas

Figures

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  Figure 1. Relative permittivity (εr) in the frequency range from (2–3) GHz of the biological tissues selected for the heterogeneous simulated samples.

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  Figure 2. Cylindrical modeled multi-layer human arm model developed in ANSYS HFSS: (a) perspective view; (b) cross section of the top view (zoomed in).

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  Figure 3. (a) Conventional microstrip patch antenna versus (b) the proposed patch antenna.

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  Figure 4. Designed flat patch antenna on epoxy flexible material: (a) front view and (b) bottom view.

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  Figure 5. Structure and performance measurement of the fabricated patch antenna: (a) schematic of fabricated antenna with coaxial feed on a flexible substrate; (b) photos of different antenna bending angles at 20° and at 60°; (c) variation of measured (dotted lines) and simulated (solid lines) reflection coefficient for different bending angles at 20°, 40° and at 60° mm; (d) simulated and measured off-body 2-D radiation patterns at 2.4 GHz of the proposed antenna in flat and at different bending conditions.

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  Figure 6. The microstrip patch antenna on the simulated human arm model of (a) 45 mm radius versus (b) the fabricated microstrip patch antenna on real human arm subject of the same radius.

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  Figure 7. Simulated return loss with the presence of the simulated human arm model versus measured return loss on a real human arm of the same radius 45 mm as simulated.

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  Figure 8. Simulated SAR of on-body arm model.

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  Figure 9. Illustration of proposed method related to brachial artery h/R ratio variation in respect to blood pressure estimation. Healthy elastic arteries = Normal BP and elastic artery stiffening = increase CV risk. The arterial vessel is often modeled as an elastic cylindrical tube. The simulation would be performed at five instances of brachial artery diameters to mimic the condition of blood flow. Although the above simulation model lacks blood flow, the consideration of different arterial diameters partly compensates for the hemodynamic effects. The choice of different arterial diameters complies with the characteristics of the arterial system. It was reasonably assumed that the brachial artery diameter changes uniformly at each dielectric characteristic change of the flow of blood, fat, muscle, bone and skin.

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  Figure 10. Two fabricated antennas in free space separated by 6.5 cm.

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  Figure 11. The fabricated pair of antennas are placed on a real human arm of radius 45 mm to examine the transmission coefficient.

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  Figure 12. Axial ratios of the conventional and proposed patch antennas.