A Digital Lock-in Amplifier Based on Adaptive Kalman Filter for Rail Defect Detection

Figure 3

Sweep frequency response curves. (a) f_o = 0.5 kHz, (b) f_o = 1 kHz, (c) f_o = 10 kHz, and (d) f_o = 50 kHz.

(a)

(b)

(c)

(d)