New Beam Pattern Offers Unparalleled Sharpness to Ultrasound Images

Miguel Alonso, professor of optics, (right) and Kevin Parker, the William F. May Professor of Engineering, illustrate the �analytically beautiful mathematical solution� Alonso devised for the new beam pattern they describe in a recent paper. (University photo / J. Adam Fenster)

University of Rochester researchers have devised a new beam pattern, which is likely to offer unparalleled sharpness to radar and ultrasound images, burn precise holes in man-made materials at a nanoscale - even etch novel properties onto their surfaces.

These are just some of the items with potential applications for the beam pattern that Miguel Alonso, professor of optics, and Kevin Parker, the William F. May Professor of Engineering, illustrate in a recent paper published in Optics Express.

The pattern is the result of what Parker calls “an analytically beautiful mathematical solution” that Alonso devised. It causes a sound or light wave to collapse inward, developing - during a mere nanosecond or less - an extremely thin, intense beam prior to the wave expanding outward again.

All the energy fits together in time and space so it comes together—BAM!—like a crescendo. It can be done with an optical light wave, with ultrasound, radar, sonar – it will work for all of them.

Kevin Parker, Professor, University of Rochester

Most traditional beam patterns maintain a constant shape provided that the source is operating. However, they are not as powerful as the beam produced by Parker and Alonso, which the researchers call a “needle pulse beam.”

It is very localized, with no extensions or side lobes that would carry energy away from the main beam,” says Alonso.

Side lobes, radiating off a beam similar to halos noticed around a car headlight at times, are in particular problematic in ultrasound.

Side lobes are the enemy. You want to direct all of your ultrasound wave to the one thing you want to image, so then, whatever is reflected back will tell you about that one thing. If you’re also getting a diffusion of waves elsewhere, it blurs the image.

Miguel Alonso, Professor, University of Rochester

As it is extremely narrow, the new beam “makes it possible to resolve things at exquisite resolutions, where you need to separate tiny things that are close together,” Parker says, adding that the beam is likely to have applications not only for ultrasound, but radar, microscopy, and sonar.

According to Alonso, industrial applications would probably include any form of laser materials processing that involves putting as much light as feasible on a given line.

The concept for the needle pulse beam is credited to Parker, an expert in ultrasound, who for inspiration frequently peruses mathematical functions from a century or more ago that are found in the “ancient texts.”

I could see a general form of the solution; but I couldn’t get past the equation. So I went to the person (Alonso) who I consider the world’s leading expert on optical theory and mathematics.

Miguel Alonso, Professor, University of Rochester

They developed a number of expressions that were “mathematically correct,” Alonso says, but corresponded to beams needing an unlimited amount of energy. The solution, “a particular mathematical trick” that could be applied to a beam with finite energy, dawned on him while swimming with his wife in Lake Ontario.

Many of the ideas I have do not happen at my desk,” Alonso says. “It happens while I’m riding my bicycle, or in the shower, or swimming, or doing something else—away from all the paperwork.”

Parker states that this discovery continues a global quest that started at the University of Rochester. In 1986 - in the face of universal skepticism - a University team including Joseph Eberly, the Andrew Carnegie Professor of Physics and professor of optics, provided proof of a surprising new, diffraction-free light form. The so-called Bessel beam is widely used nowadays.

“It had been decades since anyone formulated a new type of beam,” Parker says. “Then, as soon as the Bessel beam was announced, people were thinking there may be other new beams out there. The race was on.

“Finding a new beam pattern is a like finding a new element. It doesn’t happen very often.”

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