Inherent to the experimental practice of wideband waveform-based acoustic emission technology is computer-based waveform-gathering equipment and computer-based analysis of the data. For multi-channel experiments, it is not unusual to record one or more gigabytes of raw data per single test using a waveform-based AE measurement unit. This contrasts with files from feature-based acoustic emission systems which are typically much smaller since only a handful of features for each analog acoustic emission signal (e.g., peak amplitude, duration, "energy", etc.) are measured and recorded.

We believe it is necessary to record waveform "hits" at approximately the same rate that feature-based "hits" have been and are currently recorded (a "hit" is one acoustic emission signal sensed and recorded by one acoustic emission channel). Typical feature-based AE systems can be ready to gather the next hit signal within less than 500 µs after the previous hit signal has been measured. Thus, it is a challenging task for a waveform-recording unit to be ready within a similar 500 µs timeframe because of the inherently larger amounts of data to be recorded when using a multiple channel acoustic emission waveform system. Commercial multi-channel waveform-based acoustic emission systems in use today typically require tens of milliseconds of time after a hit before they can record the next hit(s). This state of affairs does not seem to be acceptable since the generation of acoustic emission signals is a random process; hence there is no guarantee that the acoustic emission signals of significance in a particular case are nicely spaced out in time so they can all be recorded. Further, the AE signals of interest may possibly be a small minority of the total signals generated (even after attempts to minimize the non-significant signals have been implemented).

In the light of these facts, we have been monitoring the progress of a SBIR project (funded by the Department of Transportation) to develop a waveform-based multi-channel system which will be able to record 12 bit data, 4,096 points per waveform up to 40,000 hits per channel with up to 12 channels with a deadtime between hits of less than 500 µs on each channel. This system is PC based at the operator level, but has an industry standard VXI buss at the non-operator level with extensive RAM in each channel.

We believe that the other key design features of a sophisticated waveform based system include all of the following:

• A 12-bit dynamic range to be consistent with the dynamic range of wideband preamplifiers.
• Digitization rates up to 0.1µs/pt.
• Adjustable ranges of pre-trigger length and signal length.
• A means to inhibit triggers on the extended reflections of signals already measured.
• A real-time means to process the signal differently in order to decide whether to trigger and store the raw signal (not processed in the same fashion prior to storage).

At this point, there are no references of our publications dealing with the advanced waveform acoustic emission system as described above.

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