Fast Surface Mount MRI Protection Diodes: there are two principal applications for which the MML4400 series are intended…
The first is MRI receiver protection from high-RF energy fields, including long RF pulses and RF spike pulses present in most MRI machines. The MML4400 series acts as a passive protector (limiter) for the MRI receiver’s low-noise amplifier (LNA).
The diode assembly exhibits extremely low insertion loss, both in the ‘on’ state (high power present) and the ‘off’ state (receiver power present), so that the receiver’s noise figure is not increased by the protector circuit.
The second principal application is passive switching of surface-coil detuning and blocking circuits. In this case, the flow of the loop current during transmitter pulses turns on the diodes, without the use of a switch driver.