The question can only be answered by the Manufacturer of the Medical device in question.
Various Standards may make a reference, but may not specify the exact frequency.
My experience is that 40 KHz is one of the most popular frequency at which surgical RMDs are processed.
There may be ultrasonic cleaners which employ 25 KHz, while there may be some which employ 125 KHz
However, the most important thing to know here is what do these frequencies imply.
The lower the frequency, the more violent (harsher) is the ultrasonic action. Of course, this could even damage certain delicate items. If we are to ultrasonic a heavy mass, or a large thick item (mallet, Osteotome etc), a lower frequency may be okay.
If we are looking at a processing a delicate item (Otis knife, Skin hooks, Cardiac bull dog clamps etc), going below 40 KHz may not be a good idea.
Imagine a tooth brush head of 1 cm x 3 cms.
If we had to cover the entire area by say 20 bristles, these bristles would need to be very thick. However, if we were to cover the area by 300 bristles, the individual bristles would be 10 times finer.
Obviously, the abrasive action of the thicker bristles would be way more violent as compared to those of the finer bristles.
At the same time, the finer bristles would reach smaller cavities, which the thicker bristles would not effectively penetrate.
If you are looking at purchasing a new Ultrasonic cleaner for your facility, It would be a good idea to invite the prospective vendors and show them your typical instrumentation. They will be able to provide more information.
At the same time, you may refer to IFUs supplied by various manufacturers of your existing RMDs
I hope the above was helpful.