Resonant frequency range utilized electro-mechanical impedance method for damage detection performance enhancement on composite structures

One of the problems when using EMI method on composite structures with large surface areas can lead to unsuccessful damage detection due to a vague change in the impedance signature. In addition, a threshold value is usually defined to differentiate a damaged case from an intact case. Therefore, the change in the impedance signature subjected to damage must be significant enough to overcome the effects from other factors which can also cause a change in the impedance signature. In this study, a concept of enhancing the damage detection ability of EMI method using a piezoceramic (PZT) material is reported. The proposed technique eliminates the trial-and-error approach when determining a suitable frequency range by using a resonant frequency range acquired in the lower frequency range below 80 kHz, covering a large sensing area. The main idea is to create peaks in the impedance signature in a peak free zone by sacrificing the sensing area in order to significantly increase the sensitivity of the damage detection ability. The major advantages of the proposed technique is the utilization of the lower frequency range for damage identification using EMI method, while eliminating the time consuming problem of the trial-and-error method.