Reply to Kevin’s Email

Ahh, the consummate skeptic and exactly what we need at this point.  The peer review committee for our eventual paper, if they are any good, will want these same questions answered!

There is a relation between cable heating vs time of power source applied as seen by the animated GIFs.

There are two ways to eliminate cable heating as the source of the movement:

  • Put the cavity on a scale (I will bring one this coming week)
    • First, put the cavity on it’s side on the scale to see if the EM fields inside the cavity have any effect on the scales measurement.  This is our baseline.  We should measure nothing.
    • Second, put the cavity facing downward, i.e. on it’s narrow end, then zero out the scale and we should see a weight gain.
    • Three, put the cavity facing upward, i.e. on it’s large end, zero the scale again and we should see a weight loss
  • Run four tests with the cavity rotated 90 degrees each time, but leave the cable the way it is.
    • For the 1st 90 degree test, if the cavity moves sideways, it is the cable heating, if the cavity moves forward, toward the narrow end, it is the cavity.
    • Repeat for the other 270 degrees and we should see movement toward the narrow end for each test.

Easier then trying to cool the room.

IF the movement was caused by the microwaves, the movement would be apparent in the 1st few seconds as the steady-state condition would have been met by then (Rambabu, please correct me if i’m wrong).

Two points here and they are related to a discussion I had with Rambabu about a graph that Shawyer published:

  1. The graph is from one of Shawyer’s earliest tests, before he could run the magnetron indefinitely.  It shows that the force he measured (blue and green lines) is not produced until 10 to 12 seconds after power (red) is applied.  i.e. the resonating EM waves take about 10 to 12 seconds to build up and because our cavity is about the same size or larger, we won’t see steady state until about the same time.
  2. In our case, whatever is causing the force, is causing a very small force and we can only compare the start and ending frame to see the movement.  It takes 75 seconds for the cavity to move just millimeters.

The movement will not be apparent in the first few seconds with the low force cavity.

Due to this, it is expected for the cavity to move back slowly rather than immediately after the power to the magnetron is switched off.

This is true, and we can test this with the first three tests we did, the 30 second, 45 second and 75 second tests. I haven’t look closely, but last frame on the 30 second test should match the first frame on the 45 second test and the last frame on the 45 second test should match the first frame on the 75 second, because we did them in that order and nothing was moved between those tests. The 90 second test is an exception because the cable was touched or the camera moved because the cavity is in a different location.

To prevent the loop of the cable, the current set-up can be modified to hang the cable (and cavity) straight directly from the waveguide to N-type transition with the orientation of the transition flipped (i.e. facing downwards). Slight arrangement for the items on the shelf may be necessary.

Yes, good idea.  Another idea is that we can put all the weight of the cavity on a wire, and take tension off the cable.

See you guys on Monday,