Luap.
No, that sort of output is very rarely used and the frequency is nowhere near high enough to be a big microwave.
The output power is set automatically at the start of the scan, to be just enough to precess your protons to the required angle.
I'm confused by that. Surely the 'transmit - receive' rate is not at those frequencies?
I can't imagine the vast coils being able to conduct current in Mhz, the voltages would have to be astronomic at those frequencies.
I thought they just needed to give a short rise-time pulse, and detect the response. I'd imagined this in the hundreds of Hz, not millions.
I'm not sure if you are refering to an MRI here? The transmit pulse is a rather attractive (on an oscilloscope) waveform 'envelope' lasting milliseconds, but containing the 63Mhz carrier. Then transmit is switched off and recieve is turned on by high speed PIN diode switching.
An MRI is not one, but many coils. There is the main 'solenoid' coil, a superconducting coil with about 740 Amps at Nil Volts energising it. This does not change. Additionally, there are 18 superconducting 'shim coils' placed around the main magnet, to ensure a homogenous field.
Inside that physically is a double coil, which is actually concentric fibreglass tubes with a series of coils 'printed' on them. These are the 'Gradient coils' and they actually form the 'mechanism' for selecting the voxel being 'read'. These are resistive coils, driven by a very powerful linear amplifier for each axis, capable of pulses of 200Amps at 2000Vdc!
Inside that again, is the 'tube former' of the RF coil. I am not an 'aerial' man at all, but the coil is a 'birdcage' type antenna. I hope none of you need to be scanned on an MRI, for obvious reasons, but if you have been, you will know that they are very, very noisy.
This is the gradient coil pulsing and the minute amount of contraction the coil imposes on the two ton, resin bonded fibreglass tube, acting like a loudspeaker coil.
Sorry to go so far off thread, but the question was asked.
Roger.