HIFU Transducer –
High Intensity Focused Ultrasound

Welcome to Sonic Concepts video series on High Intensity Focused Ultrasound Steering.

Sonic Concepts H-300 Phased Array HIFU Transducer is featured through the following series of demonstrations.

The H-300 transducer is attached to the bottom of a water filled tank with its spherical bowl radiating upward. A black liquid thermochromic sheet is positioned co-planar to the transducer. The HIFU source focuses energy to the size of a grain of rice around the geometric axis of the HIFU array. A green laser is used to generate a plane of light passing through the central axis. This particular H-300 phased array is comprised of 128 elements arranged about the spherical aperture in the form of an Archimedean spiral. Each of the 128 elements is electrically driven to steer the focus using the Verasonics Vantage Research Ultrasound System.

The focus is visible as light spots on the black background. The black thermochromics material changes color as its temperature changes in response to the ultrasound. Initially, the focus is steered outside of the allowable steering range and grating sidelobes appear along the geometric axis. As the focus moves laterally across the frame and within its allowable range, the grating sidelobes disappear and a single elliptical spot appears at the intended focus.

The liquid crystal sheet is removed and the green laser now illuminates the water in the same plane. The power is turned up to transmit enough sound pressure to create vapor cavities within the focal region, commonly known as ‘Cavitation’. The intended focus, represented by the main cavitation zone, becomes very bright. Streaming appears beyond the focus as a strong radiation force pushes the bubbles that have not entirely collapsed. As the bubbles change the local acoustic velocities, the focal structure appears to divide into two zones.

Using the same acoustic power, the water surface is lowered to one centimeter above the focal plane. The view from above the water surface shows the laser’s illuminating plane. When the focus is positioned outside of the allowable range the focused sound pressure atomizes the water making fog that follows the turbulent air flow above the water. When steering outside the intended range high intensity sidelobe activity occurs at the water surface. When steering inside the intended focal range the pulsed HIFU reduces nebulization and can be tracked by plumes of water displacement.

A birds-eye view reveals accumulation of fog above the water level. The intense focus is seen ejecting large water droplets.

The power is increased and the water surface is lowered to the focal plane. An aerial view captures the violent water jets produced by high intensity displacements at the water to air interface. As the beam is laterally steered the pulsed HIFU energy creates the HIFU Geyser Fountain Effect.

Lastly, a view from underneath the water’s surface displays the jet displacement in combination with wave reflections within the water tank.