FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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This is a reasonable approximation if t(n,m) is the average value
of the depth over a circular area. The sum of the responses over
the six nearest neighbours of the location that is to be
investigated (n,,m) is calculated overt
F(n,m) = s(n-1,m) + s(n, m-1) + s(n, m+1) + s(n-1, m-1)
This can be expressed as
+ s(n+1, m-1) + s(n+1,m)
F(n,m) = 6t(n,m) + 2 t(n-1,m) + 2t(n,m-l)
+ 2t(n+l,m) + 2t(n,m+l) + 2t(n-1,m-1)
+ 2t(n+T,m-1) + 2t(n+2,m) + 2t(n-2,m)
+ 2t(n+1,m-2) + 2t{n+1,m+i) + 2t(n-1,m-2)
+ 2t(n-1,m+1) + t(n-2,m-1) + t(n-2,m+1)
+ t(n+2,m-1) + t(n+2,m+1) + t(n,m-2) + t(n,m+2)
The first sufficient approximation is t(n,m) = F(n,m)
6
This solution can be used for an iterative procedure for the
solution of n X m linear equations with n X m unknowns, thus
completing the transformation of the S matrix into a T matrix.
The values of the T matrix can then be color coded to produce an
image with depth indications. The above methodology applies both
to wire wound and printed circuit coils. This procedure, which
plots depth estimates at the center of each individual coil
core, can also be used in the dynamic case.
TESTS PERFORMED WITH THE TSI ARRAY
This array was prepared in house. In short, twelve coils were
arranged in a rectangular pattern of three by four coils, with
the distance between the nearest neighbours being 1.75 nm - The
individual coils serve both as driver and receiver.
The performance of individual coils was assessed, namely the
sensitivity to detect the shallow (.1mm deep by 2mm long)
slot (Figure 8). The coils picked up the defect with no
difficulties.
This array was also mechanically scanned over an aluminum plate
containing 3 3" hole. Figure 9 shows two isometric plots
obtained by scanning the array over 33 m hole.
We experienced some asymmetries: coils 1 to 6 had a larger left
peak than right peak with the opposite being the case for ^ to
12. This was due to the higher concentration of flux lines to