64 3 20 14 43 3 129 1 10 37 376 2 32 2 90 6 9 3 52 6 90 3 8 4 80 3 90 17 74 3 45 3 90 27 16 4 66 3 ff 24 13 5 144 3 ff 37 11______________________________________ it is interesting to note that the eddy current instrument eci and the impedance analyzer ia agreed only for the 2 mhz probe at 3 mhz which applicants interpret as coincidental since all other data indicate the eddy current measurement as highly inaccurate inaccuracies generally were noted on the order of plus or minus 10 to 20 degrees rendering the data unacceptable test results on the other eddy current instruments were similar as those presented in table 1 use of eddy current for the field inspection of graphite epoxy will require eddy current instruments to provide accurate high frequency phase detection selection of the appropriate frequency requires knowledge of the material resistivity if the entire thickness of the material is to be inspected then the frequency lowest frequency in a multifrequency approach must provide penetration of the electromagnetic field through the thickness of the material if the frequency is much lower than necessary some defect sensitivity is lost the frequency selected is determined by the resistivity of the material and on.