Time-frequency analysis of a pressure wave caused by impulse tree using wavelet transform

This paper describes results of time-frequency analysis of a pressure wave caused by impulse tree extension using wavelet transform. Pressure waves were measured by a piezo sensor which was located on the back of the plane electrode when high-voltage nanosecond pulses were applied to a point electrode in a low-density polyethylene block. Frequency of the pressure wave from induced charges on the plane electrode was higher than that of the pressure wave from tree. In addition, the frequency of the pressure wave from tree tended to decrease with increasing gap length because of the dispersion of the pressure wave during its propagation. When a large tree extension occurred between a 5-mm gap, pressure waves of about 10 MHz propagated from the tree tip and a pressure wave of ` MHz propagated from the tree stem. (C) 2002 Wiley Periodicals, Inc.