Learning is half the fun.
Electrolytic refers to the type of liquid inside of the cap that acts as a plate. Aluminum Electrolytic, Aluminum... I was referring to the same thing, sorry to confuse you.
With the 0.22uF, that's usually a really small value for those types of cap. May be able to fin them though.
You can also look at ceramic, disk caps, etc. That's probably what you'd want to use.
I'm not certain how they're using caps as detectors... but if it's on the input line in series, it's most likely being used as a coupler. Basically only allowing certain frequencies (or ranges) to pass into the circuit. If the circuit is trying to pick up specific signals at very low levels, then I can see them using something like that to filter out any unwanted 'noise.'
The impedance (capacitive reactance - basically a resistance) of the cap is based on the capacitance (the amount of farads) and the frequency of the signal. The size of the cap (referring to farads) when comparing high versus low will all depend on the frequency of the signal, and what you're trying to block or pass.
When used as bulk storage caps (as in switch mode power supplies) the cap comes into an energy storage role. This is not what your circuit is using them as, so far as I can tell.
The voltage rating on the cap is telling you how much voltage you can put across it without damaging it. A general rule of thumb is to rate your cap at twice the voltage it will see. For instance, if my cap will have 5 volts across it, I will source a 10V rated cap.