Though microwave emissions in association with hypervelocity impacts have been confirmed experimentally, the emission characteristics and the emission mechanism have not yet been made clear. For example, whether the emission is noise or a coherent signal is not known. In this paper, two kinds of analyses, output waveform analysis and spectral analysis, are discussed. Regarding output waveform analysis, microwave pulses are simulated on the basis of a microcrack model in consideration of discharge current, and are compared with experimental pulses in terms of the pulse shape and width. Regarding spectral analysis, the intensity and phase of waveforms are calculated in the frequency domain to examine the frequency characteristics. The spectral intensity is nearly flat and the phase has coherency. Accordingly, the microwave emission is not noise but a sequence of independent pulses.

A technique was developed to reduce ECG data efficiently within a controlled accuracy. The sampled and digitized data of the original waveform of an ECG is transformed in three major processes. They are the calculation of a beat-to-beat variation, a polygonal approximation and the calculation of the difference between consecutive node points. Then, an adaptive coding technique is applied to minimize redundancies in the data. It was demonstrated that the ECG waveform sampled in 200 Hz, 10 bit/sample, 5 µV/digit could be reduced with the bit reduction ratio of about 10% and within the reconstruction error of about 2.5%. A polygonal approximation method, called MSAPA, was newly developed as a modification of the well known method, SAPA. It was shown that the MSAPA gave better reduction efficiency and smaller reconstruction error than the SAPA, when it was applied to the beat-to-beat variation waveform. The importance of the low-pass filtering as a preprocessing for the polygonal approximation was confirmed in concrete examples. The efficiency of the proposed technique was compared with the cased in which the polygonal approximation was not used. Through these analyses, it was found that the redundancy elimination of the coding technique worked effectively in the proposed technique.