###### Abstract  
Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the two extracted components on the performance of TRP are studied experimentally. The results show that the two time intervals, in which the waveforms are extracted, have great influence on the accuracy of damage detection of the time reversal method (TRM). What is more, it requires a large number of experiments to determine these two time intervals. Therefore, this paper proposed an efficient time reversal method (ETRM). Firstly, a broadband excitation is applied to obtain response at a wide range of frequencies, and ridge reconstruction based on inverse short-time Fourier transform is applied to extract desired mode components from the broadband response. Subsequently, deconvolution is used to extract narrow-band reconstructed signal. In this method, the reconstructed signal can be easily obtained without determining the two time intervals. Besides, the reconstructed signals related to a series of different excitations could be obtained through only one actuating-sensing step. Finally, the effectiveness of the ETRM for damage detection in composite laminates is verified through experiments. L 2019 9 11 10.3390/app9010011 10.  
techniques rely on comparing the test signal with the baseline signal. Since the test signal varies with the environment and boundary conditions, subtle signal changes due to damage may be masked. To address this issue, researchers have done numerous work regarding baseline-free damage detection in the past decade [9; 10]. Specifically, the TRP has been widely used for Lamb wave-based damage detection, as it can not only achieve dispersion self-compensation but also realize baseline-free damage detection in composite laminates [11; 12; 13; 14; 15]. In the TRP, an excitation signal is injected in one actuator, the response signal that captured by sensor is then time reversed and re-emitted at the sensor position. Therefore, the frequency components that arrive later will be re-emitted earlier, followed by the components with higher velocities. After the TRP, all the frequency components with different velocities will arrive at the original excitation position concurrently, and thus the dispersion could be compensated. For a healthy structure, the final signal will be the same as the original input signal. In contrast, the two signals will be different from each other if there is any damage present along the propagation path. Therefore, baseline-free damage detection could be realized by comparing the waveform of the reconstructed signal with that of the original input signal. Researchers have done a lot of work to improve the performance of TRP. [PERSON] et al. [13] combined a wavelet-based signal processing technique with TRM to enhance the time-reversibility of Lamb wave in composite laminates. [PERSON] et al. [16] proposed a modified TRM, which uses a single actuator and multiple sensors. That is, the initial input signal and the secondary excitation signal are actuated by the same actuator. [PERSON] et al. [17] presented a virtual time reversal algorithm which only needs one actuating-receiving step to obtain the reconstructed signal. [PERSON] et al. [18] investigated the influences of adhesive layer between the transducer and the host plate, the excitation parameters, the transducer size and the plate thickness on the performance of the TRP to develop an effective damage detection strategy. [PERSON] et al. [19] investigated the effects of single-mode and two-mode Lamb waves on the effectiveness of time reversal damage detection process through theoretical and experimental analysis. And they concluded that, under narrow-band excitation, the time reversibility of single-mode Lamb waves could be greatly improved. [PERSON] et al. [20] and [PERSON] et al.