Accurate synthesis of acoustic holograms using field matching

Current methods for hologram design do not accurately encode the target phase distribution, mainly because the complex topology of these lenses results in a rich wave physics which is usually not considered in the design. In this work, we present a method to design acoustic holograms and lenses that accurately synthesize a target field using a phase-matching approach. Rather than producing a phase distribution over a holographic plane, the method matches the phase of the field produced by the lens to the target phase in a whole volume. For simple focused lenses, we theoretically demonstrate that classical methods result in a hyperbolic lens profile for higher-than-one refraction index materials, while the present method results in elliptic profiles, which are optimal. For lower-than-one refraction index, both methods result in hyperbolic profiles, but field matching method produces sharper focal spots, larger gain, and lower focal shifts, especially for low f-numbers. Finally, we observe that the structural similarity index of complex acoustic images produced at shorter distances is larger for the current method. The present technique goes beyond traditional methods to design acoustic holograms and might be used in emerging therapeutic ultrasound applications where an accurate control of the acoustic beam is needed.