Stress field design in vibro-acoustography beam forming

Vibro-acoustography produces images of the acoustic response of a material to a localized harmonic motion generated by ultrasound radiation force. Proper beam forming for the stress field of the probing ultrasound is very important because it determines the resolution of the imaging system. Three beam forming geometries are studied: amplitude modulation, confocal, and x-focal. The profiles of radiation stress amplitude on focal plane and beam axis are derived from each geometry´s pressure field. The theory is validated by experiments where a small sphere is scanned in all geometries. Sphere motion measured by a laser vibrometer is used to infer the exerted radiation stress. The theory and experimental technique may be useful in future transducer design for vibro-acoustography.