ASA 124th Meeting New Orleans 1992 October

4aEA12. Pulse-tube measurements with conditioned signals.

R. E. Moore

J. J. Dlubac

S. C. Schreppler

R. J. Deigan

Code 1945.1, Ship Acoust. Dept., David Taylor Res. Ctr., Bethesda, MD 20084-5000

Operation of pulse tubes typically involve a gated signal, either a tone or a bandlimited impulse. The incident and reflected signals are separated in time and Fourier transformed to determine the response of the test sample in the pulse tube. Both gated tones and impulses, however, suffer from the inevitable turn-on transients of the transducer and the receiver which corrupt the desired spectral output. Since the transfer function between the signal generator and the receiver can be determined using convenient digital-processing techniques it is possible to condition the output at the receiver. This method is applied to modify broadband impulses so as to maintain the desired spectral output at the receiver. The technique requires one iteration to converge to an optimal waveform input to the transducer from the signal generator. The technique is demonstrated using data collected in a 2-in. diamx72-in. pulse tube.