Elimination of Severe Near-Field Spatial Variations of Ultrasonic Transducers Using γ-Power Bessel Function Amplitude Distribution

Many published biomedical and chemical experimental results involving ultrasound suffer inconsistencies. One of the main reasons is due to the nonuniform field produced by conventional piston-type ultrasonic transducers; severe intensity fluctuation occurs in the near-field region where most experiments are conducted. We show both theoretically and experimentally that if the transducer surface vibration can be controlled to have an amplitude distribution in the form of J0[(ρ/R0)γU1], where ρ is the radial coordinate, R0 is the radius of the acoustic source, γ≥ 1, and U1 is the first zero of the zeroth-order Bessel function of the first kind J0(r), then the pressure amplitude space variation in the near-field can be eliminated to produce a three-dimensional (3D) cylindrical region with uniform pressure distribution near the transducer surface. The width of the cylindrical region increases while its height decreases with γ, which gives the flexibility of manipulating the shape of the uniform pressure field region. The presented design is beneficial for many biomedical and chemical experiments, as well as industrial applications that require uniform pressure sonication.