In mechanical structures, the impact force is related to the structural damage. To identify the location where impact force occurs, the triangle method has long been used. This method requires three acceleration signals or strain signals to be measured on the mechanical structure. Time delay among these signals is useful information to estimate the location of the impact force. It is very difficult to estimate time delay by using the raw data of three signals because the propagation wave of the structure is a dispersive wave. Therefore, three signals should be analyzed in the time and frequency domain in order to estimate the time delay at each frequency. For the time-frequency analysis of highly non-stationary signals like impulse signals, time-frequency methods or time scale methods have been used. These methods use the first or second order statistical characteristics of the signal. This paper outlines the higher order Wigner method to obtain time and frequency information of a signal. Since it uses the high order statistics of signals, this method is useful for identifying the impact signal embedded in the background. It has a better time-frequency resolution for a non-linear signal than other time-frequency and time scale methods. This method can be applied to estimate the location of an impact force, which becomes a cause of damage of mechanical plants. Finally, in order to prove this method, experimental work was conducted on an aluminum plate in the laboratory.