Holographic Imaging System Using Wideband Chirped Ultrasound
The application of the ultrasound imaging techniques is spreading in many fields such as nondestructive testing, medical diagnosis or underwater imaging. Especially the B-scan imaging which visualizes a two dimensional section of a specimen is the most popular technique. In the conventional B-scan imaging system, the lateral resolution is limited by the aperture of the transducers and range resolution is limited by the pulse width of the ultrasound. As for the range resolution, the use of a short time pulse improves the resolution, however it causes a degradation of the signal to noise ratio (SNR). Another possibility to improve the resolution is to employ the holographic technique. In this case, while the lateral resolution is greatly improved by the synthetic aperture, the range resolution gets worse because the coherent illumination must be used in the holographic imaging technique. This nature had been also a problem in the field of the microwave radar until the synthetic aperture radar (S.A.R.)(1) was developed. Since the success of S.A.R. is a result of combination of a holography and the pulse compression technique, it may be possible to employ the same technique in the acoustical imaging.
KeywordsEntropy Microwave Radar Tral Acoustics
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