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The current gold standard in hypertension monitoring is the cuff based pressure measurement i.e. the Ambulatory Blood Pressure Monitoring. The current solution offers intermittent measurements every 15 minutes – 30 minutes throughout a period of 24 hours. In critical patients it is needed to be able to measure their arterial pressure at a higher frequency for a longer period of time. Technologies have been appearing to overcome the need of continuous blood pressure measurement. One of this technologies are LC resonance based sensors, where a capacitive component changes its value in response to pressure. This technology allows for battery-less and remote solutions while maintaining high fidelity of data acquisition.

The design process of an LC resonant circuit requires the definition of its two components. The inductor and the capacitor. These design parameters can be overcome through COMSOL Multiphysics environment. The inductor coil was designed within the electromagnetic waveform module and the capacitive pressure sensitive plate utilised the MEMS module by combining the electrostatic module and mechanical module.

The inductor model is based on Modelling of a 3D inductor example [1]. The simulation was ran using the magnetic field module where the spiral coil was defined as a coil within the physics. The capacitor model follows the COMSOL’s capacitive pressure sensor example [2] where one quarter of the capacitive plate was simulated using symmetries to define the full volume of the 3D model. In the case of this work the capacitor dielectric material is composed of two materials. The first material is a fluid cavity which was simulated with the Enclosed cavity feature and defined as a deforming domain. The second layer was defined as a nearly incompressible hyperelastic material with a Neo Hookean model. A uniform pressure was applied to the top electrode, and swept from 0 mmHg to 200 mmHg. The inner dielectric materials where define as solid for the PDMS layer and the polyimide substrate layer, and as fluid dielectric material for the enclosed cavity with air as its content. In both cases the models were define as parametric designs to allow flexibility of modification. After completing the simulation their results were combined to compute the expected operation resonance frequency of the LC sensor through (1).

f0=\frac{1}{2\pi\sqrt{LCs}}

Simulation results show that the sensor design would have an expected sensitivity of 14.5 kHz/mmHg. Verification of the simulation results with fabricated sensor is still pending for analysis.

In conclusion, the utilisation of an FEM model for the design and optimisation of a blood pressure sensor with a capacitive pressure sensitive element can be achieved with a certain degree of accuracy. As the model does not take into account human error of the fabrication process there is a slight deviation between the sensitivity of the model and the measured response.