The extension of the abilities of human senses using synthetic devices or systems is of main concern for long time. So, the trend of developing remote sensing systems has attracted attention of electromagnetic researchers for its important applications such as Air-traffic control, Air defense, exploration geophysics, and several important applications in medicine. In this paper, the target identification of the conducting objects that have cavities with small apertures is considered. These apertures act as coupling windows. If the aperture couples waves to any cavity structure, for example the fuel tanks, internal resonant fields will be excited. The internal resonant fields appear as slowly damped sinusoidal signals in the late time. The internal modes are almost dominated over the target natural modes in the very late time. In this paper, a new scheme is proposed to identify targets via these internal modes. The validation of the algorithm is done using the backscattered signal from conducting structures simulated using our home made Moment Method software.