Remote Super-Resolution Mapping of Wave Fields

Mapping wave field in space has many applications such as optimizing design of radio antennas, improving and developing ultrasound transducers, and planning and monitoring the treatment of tumors using high-intensity focused ultrasound (HIFU). Currently, there are methods that can map wave fields remotely or locally. However, there are limitations to these methods. For example, when mapping the wave fields remotely, the spatial resolution is limited due to a poor diffraction-limited resolution of the receiver, especially when the f-number of the receiver is large. To map the wave fields locally, the receiver is either subject to damage in hazardous environments (corrosive media, high temperature, high wave intensity, and so on) or difficult to be placed inside an object. To address these limitations, in this article, the point spread function (PSF)-modulation super-resolution imaging method was applied to map pulse ultrasound wave fields remotely at a high spatial resolution, overcoming the diffraction limit of a focused receiver. For example, to map a pulse ultrasound field of a full-width-at-half-maximum (FWHM) beamwidth of 1.24 mm at the focal distance of a transmitter, the FWHM beamwidths of the super-resolution mapping of the pulse wave field with a spherical glass modulator of 0.7 mm diameter at two receiver angles (0 degrees and 45 degrees) were about 1.13 and 1.22 mm, respectively, which were close to the theoretical value of 1.24 mm and were much smaller than the diffraction-limited resolution (1.81 mm) of the receiver. Without using the super-resolution method to remotely map the same pulse wave field, the FWHM beamwidth was about 2.06 mm. For comparison, the FWHM beamwidth obtained with a broadband (1-20 MHz) and 0.6-mm-diameter polyvinylidene fluoride (PVDF) needle hydrophone was about 1.41 mm. In addition to the focused pulse ultrasound wave field, a pulse Bessel beam near the transducer surface was mapped remotely with the super-resolution method, which revealed high spatial frequency components of the beam.