Radiation force balance power meters are commonly used
to measure output acoustic power of ultrasound transducers.
Two types of targets are usually used in these devices:
a flat perfect absorber, or a cone-shape perfect reflector.
What would be the angle for a cone perfect reflector in order to
get identical power readings for a given ultrasound exposure
with two different type of targets? Assume that the two targets have
equal surface areas.
You must provide a proof for your answer.
Question: Lecture notes 2.1.6.4. Radiation Pressure When ultrasound is incident on a body consisting of medium that either absorbs, scatters or reflects the radiation, a force will be exerted that consists of two components. The first is an oscillatory component with a time-average of zero, arising from time varying acoustic pressure acting on the body. The second is a steady component that is known as the radiation pressure. The presence of radiation pressure is an inherent property of the nonlinear relation between pressure and density in the propagation media. Thus for a medium that behaves in a perfectly linear manner there would be no radiation pressure. Two types of radiation pressures are generally identified depending on the measurement conditions: the Langevin radiation pressure and the Rayleigh radiation pressure. For most practical situations, the Langevin radiation pressure is the dominant one. Radiation pressure will also be present within a fluid medium and will cause the fluid to be displaced in the direction of the pressure gradient. This phenomenon, known as acoustic streaming, is a direct result of the radiation pressure. Understanding the physics and obtaining accurate equations to describe the radiation pressure is fairly complicated and requires a full knowledge of nonlinear acoustics. Below are simplified equations of the Langevin radiation pressure for two ideal