Could some electronics guru please help ? Suppose a high frequency(approx. 30 - 40 Mhz) oscillator connected across a aimple
1 cm x 1 cm plate area parallel plate capacitor, with a 1 mm thick dielectric plate in between, material FR4. Now how do I detect that indeed the signals are being transmitted between the plates, given that a capacitor is a short to AC.
Also, if I connect a simple rectifier diode e.g., 1N4007 after the capacitor, and then a small electrolytic capacitor, after that in the signal return path, would the capacitor indicate a DC voltage across it ?
I have done some experiments regarding this idea, but am confused by the results.
Any hints, suggestions would be welcome. Thanks in advance for your help.
detect current flow by detecting V drop across an R detect low impedance of the FR4 cap, eg by feeding it frmo a 50ohm source and noting the voltage drops low etc
You'd need a rectifier that lets current flow both ways in the FR4. So minimum 2 diodes.
First of all, if you just hook a diode to a cap like that, it will only put out any voltage until the cap charges up. If you ever have to rectify off a cap you need to either use a doubler, or either a coil or resistor to gro und, and the latter methods are not efficient but might be useful for instr umentation.
Since there was a first of all, second of all, to what end are you doing th is ? Building some secret weapon ? If so count me in.
Or are you interested in the dilectric properties of FR-4 ?
Might help if we know what you're shooting for here.
Are you looking for transmission of power? Or, for a signal of some sort? Or multiple signals?
Power metering requires both a magnetic and electric field sensor, and access to the rest of the circuit, not just one two-terminal component, unless you want to know the power that's being dumped into heat in the dielectric "FR4".
Now that you mention it... In fact if he tries to put any power through it, he will get smoke likely even way below its design limits.
For measuring, he is probably best off with a pair of Schotkeys configured as a doubler. And of course a small correction factor for their Vf, which w ill be lower than other high speed diodes. And we don't even know how much power he wants to try to push through this thing. If he does not know the 1 N4007 won't work, he might not have much of an idea about this - yet.
If this is a purely academic experiment that is one thing. but if there is an application involved it really helps to know what that is. He might be t rying to build a capacitively coupled battery charger, which is not the wor st idea in the world. If I had to do that I would lean toward an inductivel y coupled system though. Trying to get power through a capacitor like that implies he wants a high degree of isolation, which may well be better provi ded by a transformer. Some electric cars charge by that method IIRC. I was thinking, years ago, of a cordless phone that would be totally waterproof. Some sort of shrink wrap around the whole thing but with the coil embedded. Might have been able to even make a kit, or retrofit or something for exis ting models. But at this stage of the game they got them pretty much done. A buddy of mine has a cellphone like that, says you can just dump it in a b ucket of water and nothing happens.
I do believe the capacitive approach to that would result in enough EMI tha t the FCC sends the SWAT team to your door though. They DO have a SWAT team .
Now a guy starts a thread bitching about me asking about the purpose of thi s whole endevour. HA. (they are tearing him up...)
t, he will get smoke likely even way below its design limits.
d as a doubler. And of course a small correction factor for their Vf, which will be lower than other high speed diodes. And we don't even know how muc h power he wants to try to push through this thing. If he does not know the 1N4007 won't work, he might not have much of an idea about this - yet.
s an application involved it really helps to know what that is. He might be trying to build a capacitively coupled battery charger, which is not the w orst idea in the world. If I had to do that I would lean toward an inductiv ely coupled system though. Trying to get power through a capacitor like tha t implies he wants a high degree of isolation, which may well be better pro vided by a transformer. Some electric cars charge by that method IIRC. I wa s thinking, years ago, of a cordless phone that would be totally waterproof . Some sort of shrink wrap around the whole thing but with the coil embedde d. Might have been able to even make a kit, or retrofit or something for ex isting models. But at this stage of the game they got them pretty much done . A buddy of mine has a cellphone like that, says you can just dump it in a bucket of water and nothing happens.
hat the FCC sends the SWAT team to your door though. They DO have a SWAT te am.
his whole endevour. HA. (they are tearing him up...)
Thanks to each of you for your feedback. I have worked with inductive power coupling, and now I am experimenting with capacitively coupled power transfer, for example, for battery charging. I am aware that 1N4007 is not a good chpice, but at this stage, I am more interested in ensuring that capacitive coupling works, before going to the next step.
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