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It was chosen to orient this blind spot at 45° and further to rotate every other row by 90° so
that consecutive rows do not have the same blind spots. Because of this arrangement the
blind spot can be eliminated by measuring a DUT twice with a small physical shift between
scans.
For EMScanner & EMS Model
Each of the 1218 probes on the EMScanner is created from two overlapping loops to
increase their angular coverage. Even with this hybrid approach they do not have 360-
degree coverage. There is one orientation of magnetic field that the probes do not respond
to, essentially creating a blind spot. This blind spot can be eliminated by measuring a DUT
twice with a small physical shift between two scans. A scale model of the probes is shown
below. It effectively combines two separate loop probes into one “X Loop”.
This setup is to provide a cumulative sensitivity as shown in the figure below.
This is a small 5x5 array taken from the larger 29x42 scanner. The effect of this different
sensitivity on scan results sometimes shows up when
a device is rotated. If the device has only H-field components,
the scan results will be as shown in the top right
of the graph
on the right. If this device is rotated 90° then
results are as
expected and as shown below.