Inspection of high-attenuation and high-noise materials using ultrasonic pulse compression technique
- Iowa State Univ., Ames, IA (United States)
Within a highly attenuating material, it is often difficult to identify relevant target signals due to the system`s white noise that is elevated by high gain settings on a conventional ultrasonic system. Ultrasonic pulse compression technique resolves such problem. The ultrasonic pulse compression technique permits an ultrasonic system to operate with long transmitted pulses for an increased detection range, but without sacrificing the depth resolution by signal correlation. The data contains 2048 points sampled at 40 nsec interval using 256 bits long and 100 nsec wide (single bit) Golay codes. Typical pulse compression systems transmit random or pseudorandom codes such as Barker code, maximal-length sequence, and linear FM chirp. And the configuration of such systems varies depending upon the type of code and its generation and processing methodology. However, such systems suffer from inherent limitation, called self noise or range sidelobes when finite integration time limits are used to approximate the signal correlation. To reduce the self noise to a tolerable level, Center for NDE, Iowa State University, has implemented a set of complementary binary codes, known as Golay codes, into a laboratory prototype pulse compression system. Golay code is a set of complementary series of the same length, each has its own auto-correlation having one main response, but the relative polarities are opposite except the main peak. So, if these two correlation results are added, the main response doubles and all others cancel. These characteristics of the Golay codes allow us to obtain a correlated signal of an enhanced SNR without the range sidelobe that is normally produced in other random or pseudorandom codes.
- OSTI ID:
- 563460
- Report Number(s):
- CONF-960324-; TRN: 97:004031-0004
- Resource Relation:
- Conference: Spring conference and research symposium of the American Society for Nondestructive Testing, Norfolk, VA (United States), 18-22 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 ASNT spring conference and fifth annual research symposium - NDE the flagship of quality; PB: 252 p.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Application of the spread-spectrum technique in well logging
1. 06 micrometer wideband laser modulator: fabrication and life testing. Final report, 25 Jul 1974--25 Jul 1975