Variable frequency field conjugate lenses for ultrasound hyperthermia

Abstract

This paper describes variable frequency focusing with field conjugate lenses designed to mimic the multiple-focusing capabilities of large two-dimensional phased arrays. Simulations, experiments, and Fresnel diffraction analysis are used to show that both the size and the depth of a field conjugate lens focus may vary with frequency. Examples are given for field conjugate lens focusing with planar transducers, focused transducers, and ordinary refracting lenses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>