I want to make a fixture to measure the permittivity of liquid at fairly low frequencies (1.8 to 144 MHz). I was thinking of using a 50 Ohm transmission line about 200 mm long, but making it out of a U shaped channel, rather than cylindrical, so its possible to clean the fixture. The inner conductor will be cylindrical.
I'm trying to think what would be the best material to make the inner conductor from. Clearly this will bend under its own weight, and I'm thinking the bending might not be insignificant. If so, the impedance in the centre is going to be less than at the ends.
I suspect that a larger diameter transmission line will suffer less bending than a smaller one, although I'm not sure about that. Obviously a larger conductor will have more mass, but I suspect it will bend less than a thin one that is lighter. This seems intuitive, but it maybe incorrect. I know a thin beam will bend less than a thick one with the same weight on it, but if the only weight is its own weight, my intuition might be wrong.
You can see I did not study much mechanical engineering!