Scanning Walthrough

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(03.22.08) Scanning Walththrough

Setting up the Scan Area

1. Mount the sample to be scanned to the Z-axis stage and get the stages as perpendicular to the horns as possible.

2. Turn on the Newport Motion Controller. After the initialization, the stage model numbers are shown on the Newport front panel display with the word 'off' appearing next to them. Press the button next to 'off' for both stages, this should change the display to 'on' for both axes.

3. Define current position as 'Home'. After aligning the sample between the near field probes in Step 1, you now need to use the wired remote control for the Newport Controller. To make sure nothing bad happens from the start, type in the following two commands, each followed by the 'ENTER' button

  • 1DH ('DH' stands for 'Define Home', 1 is the X axis)
  • 2DH ('DH' stands for 'Define Home', 2 is the Z axis)

This defines the current position of each axis as 'Home', and resets the position to (0.000, 0.000) mm. In the picture below we plan to scan a circular area given in red. We are viewing the object from the VNA side, or Reflected side.

Pictorial representation of our proposed scan area.
  • Red is the scan area
  • Blue is a 1mm minimum space to be left on the starting side of the scan for data processing purposes. Assuming 0.05mm steps in X, 1mm will give 20 vertical lines of data which will be used to calculate and remove any drift effects in phase or amplitude. It is safest to leave 1.5-2.0mm of space.
  • Yellow box is the start position
  • Yellow arrows define the scan direction, which will repeat as shown


4. Find and define the X-axis starting position. We will use the command (axis)PR(distance) to move along the X axis, where (axis)=1 and (distance) will be defined as we go. 'PR' stands for 'Position Relative', so we are going to do several relative moves until we find our starting position. Units are in millimeters. First type: 1PR1 (enter). Note which way the stage moves. You can also enter negative distance values, such as 1PR-3 to move -3mm. Use a series of moves until you are in your desired X=0 position as defined in the above picture. When you are happy, type 1DH to define this position as the X-axis home and set this position to 0.000mm.

5. Find the X-axis scan range. We will now use the command (axis)PA(distance). Instead of a 'relative' move, this will perform an 'absolute' move. For example, starting at the position X=1mm, typing 1PR2 will move you to X=3mm. Typing 1PA2 will move you to X=2mm. Easy. Just be sure you don't ram the sample into the probe tips. Should you accidentally type in the wrong direction, type 1ST to stop the X axis from moving further. Let us say that our scan limit in X is 20.00mm. Just remember (or write down) that value. Type 1PA0 to move the sample back to the X home position.

6. Find and define the Z-axis starting position. Just like step 4, use the PR command to find your starting point as defined in the picture. Once you have it, type 2DH to define it as home.

7. Find the Z-axis scan range. Repeat step 5 for the Z axis, remembering to use 2PA(distance), NOT 1PA(distance). Record your value, say 15mm for this example. Type 2PA0 to return the sample to the 'Home' position of the scan.


Setting up Labview

Run Labview 8.5

Open the file Modified ScanAll_20.vi, this is the control VI for the whole system. You will see a picture like this:

Screen shot of ScanAll_20.vi

The numbers in RED are the important parameters/button that we will describe in order.

  • 1. Enter the frequency, here it is 260GHz. Don't worry about the multiplier, that does nothing currently and will be removed.
  • 2. Enter X and Z scan parameters. XMotor=0, X Scan Distance=20, ZMotor=0, Z Scan Distance=15. This will scan from 0mm<X<20mm, 0mm<Z<15mm.
  • 3. Scan step. We usually use 0.05mm step size.
  • 4. 'Set Home' and 'Manual Control' buttons. Be sure both of these are highlighted. The 'Set Home' button just ensures that the current position of the stages is set as 'Home', or (X,Z)=(0.000mm,0.000mm). Manual control (I believe) ensures that the stages do not default to their hardware limits. More info coming on this as I recall more details.
  • 5. Enter a descriptive filename.
  • 6. Enable the 'Save Data' button, or you will be sorry. This will be enabled by default in the future.
  • 7. Start the VI code running with the arrow button.
  • 8. Since we are not taking a base, a popup box will appear saying 'saving data'. The 'Get Sample Ready' LED will turn green. Look over everything one last time. The last step is to press the 'Sample Ready' button.
  • Watch the first scan line to be certain the scan motion is following the correct course. To check on the scan from outside the lab, we have a VNC server running. Under linux, use vncviewer and log into Bose.mines.edu (192.168.12.23) using your username and password for Windows(?). Will check on this as well. From a windows system, download and install TightVNC viewer.
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