Electric field not reaching material across air gap (Electric Currents, Frequency Domain)

Diogo Pires TEMA – Centre for Mechanical Technology and Automation

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Hello everyone,

I’m currently working on a model in COMSOL Multiphysics (AC/DC Module – Electric Currents, Frequency Domain) and I’m facing an issue where the electric field does not seem to penetrate the material located across a small air gap.

Here is the setup: -Two planar electrodes (terminal and ground) placed side by side on a PCB substrate. -Above the electrodes, there is a thin polymer layer, then a 2 mm air layer, and finally a block of bone material. -Everything is enclosed by a cylindrical air domain. -Excitation: 3.3 V at 32 kHz (frequency domain study).

When the air layer is present between the electrodes and the bone, the electric field and current density completely vanish inside the bone, only the region in the air shows nonzero values. If I replace the air layer by the bone (so there’s direct contact), then I see the expected electric field inside the bone and i can see changes in capacitance, even when changing bone properties and material.

The strange part is that if I artificially set the air conductivity to something like 0.001 S/m, the field appears inside the bone again. But with σ_air = 0 S/m, it disappears entirely and capacitance dont change.

Thanks in advance for any advice or insight, I’ve been stuck on this for a while and would really appreciate any suggestions on how to make the field correctly propagate through the air and into the bone layer.

Best regards, Diogo Pires


1 Reply Last Post Oct 18, 2025, 3:22 a.m. EDT
Edgar J. Kaiser Certified Consultant

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Posted: 12 hours ago Oct 18, 2025, 3:22 a.m. EDT

Hi Diogo,

in ec-physics all domains must have a small conductivity. You can test how low you can go in air. It depends on the frequency too. Often even the solver is not converging when zero-conductivity domains are present.

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi Diogo, in ec-physics all domains must have a small conductivity. You can test how low you can go in air. It depends on the frequency too. Often even the solver is not converging when zero-conductivity domains are present. Cheers Edgar

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