hey there
recently I've became interested in capacitive soil moisture sensors. they are pretty neat. here is a picture of them


as you can see there is a cupper plate in the center and a GND around it.
and here is a link to see how they work

my question is that how can this structure even work? the whole copper and GND plates are sealed with solder mask and even the water can not fill the space between copper and GND plates to affect its capacitance?

any ideas?

 

There are two capacitors in series.
One between the outer track and the soil, and one between the soil and the inner track.

 

There are two capacitors in series.
One between the outer track and the soil, and one between the soil and the inner track.

true, but is it possible for the Electrical waves to go outward from solder mask? I know my question might sound funny but it really confused me and I need to know

 

true, but is it possible for the Electrical waves to go outward from solder mask?

Yes! That single word answers your question. Now you will ask why!
The answer to why? is beyond circuit theory.