The Random Phase Transducer : A New Tool for Scattering Medium
In pulse echo measurement, interference between scatterers observed with a coherent transducer, leads to scalloping in spectral estimation (attenuation measurement) and to speckle noise in envelope detection (imaging).
In order to get rid of these effects, Miller has proposed phase insensitive transducers (CdS transducer and array of point like detectors). These transducers have shown promising results, but suffer from a lack of sensitivity.
We have developed a new approach to control the degree of spatial coherence of ultrasonic transducers.
Random Phase (R.P.) transducers consist in one or two rotating random phase screens (R.P.S.) located in front of a coherent transducer. The ultrasonic beam generated by the transducer is then transmited and received through the moving R.P.S.. Spectral analysis and envelope detection are processed by averaging the data on a set of locations of the R.P.S. Optimal choice of the location of the R.P.S. will be discussed in order to get spectral smoothing and speckle reduction. Experimental results will shown the strong efficiency of the R.P. transducer in attenuation measurement of tissue like phantom and in low constrast specular reflector detection.
KeywordsGraphite Attenuation Foam Rubber Coherence
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