Varifocal imaging using an optical lens that employs acoustic radiation force and a viscoelastic material and that has no
mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic
transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration
mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of
the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a
We report on the measurement of sound pressure in water utilizing the modulation of the optical reflectivity at the end of
an optical fiber. First, we develop a new experimental setup comprising a low-coherent light source to suppress the
interference noise. Then, we formulate the relation between the sound pressure and the modulation in the reflected light
intensity, and theoretically analyze the performance of this method with emphasis on the directivity and the sensitivity.
A compact, high-speed variable-focus liquid lens using acoustic radiation force is proposed. The lens consists of an annular
piezoelectric ultrasound transducer and an aluminum cell (height: 3 mm; diameter: 6 mm) filled with degassed water and
silicone oil. The profile of the oil-water interface can be rapidly varied by applying acoustic radiation force from the
transducer, allowing the liquid lens to be operated as a variable-focus lens. A theoretical model based on a spring-mass-dashpot
model is proposed for the vibration of the lens. The fastest response time of 6.7 ms was obtained with silicone oil
with a kinematic viscosity of 100 cSt.