Collimation of ultrasonic linear array transducer

DETAILED DESCRIPTION Improved ultrasonic linear arrays are realized whose elements exhibit the desired angular resonse and approach the ideal beam properties.
Collimation via critical angle effects is used to change the beam characteristics of individual array elements.
The generation of significant ultrasonic energy outside the designated acceptance region is eliminated, while not altering significantly the beam characteristics within the acceptance region.
The illustrative embodiment is a phased array transducer in a sector scan imaging system which performs wide angle (90.
degree.
) sector scans.
The transducer array has a collimator in the form of a sheet of polyethylene approximately one wavelength in thickness at the lowest useful emission frequency.
Acoustic waves whose angle of incidence is less than the critical angle (47.
degree.
-55.
degree.
for human tissue) are transmitted and waves whose angle of incidence is greater than the critical angle are totally reflected.
The angular range of transmitted waves is equal to or greater than the angular extent of the sector of the body which is scanned and imaged by the system.
The critical angle is approximately equal to the maximum scan angle of the imager.