Dr. Who, a British Broadcasting Corporation science fiction television programme, has an enormous following worldwide. I am not one of those followers as you might have guessed from the headline, which means I didn’t understand this pop culture reference, from the April 23, 2012 news item on Nanowerk,
For fans of the hit series Doctor Who, the Sonic Screwdriver will be a familiar device. But now an international team of EU-funded researchers has taken equipment designed for magnetic resonance imaging (MRI)-guided focused ultrasound surgery and demonstrated a real Sonic Screwdriver, lifting and spinning a free-floating 10 cm-diameter rubber disk with an ultrasound beam.
I’m going to concentrate on the project first since this EU (European Union) funded project has a somewhat confusing configuration, which I’ll try to tease apart later in this posting. From the news item,
Dr Mike MacDonald, of the Institute for Medical Science and Technology (IMSAT) in the [University of Dundee, Scotland] United Kingdom, comments: ‘This experiment not only confirms a fundamental physics theory but also demonstrates a new level of control over ultrasound beams which can also be applied to non-invasive ultrasound surgery, targeted drug delivery and ultrasonic manipulation of cells.’
The theory the team were testing had not previously been proved in a single experiment; it is valid for both sound and light, and is used in fields like quantum communications and biophotonics. The theory states that the ratio of angular momentum to energy in a vortex beam is equal to the ratio of the number of intertwined helices to the frequency of the beam.
Dr Christine Demore from IMSAT comments: ‘For the first time, our experimental results confirm directly the validity of this fundamental theory. Previously this ratio could only be assumed from theory as the angular momentum and power in a beam had only ever been measured independently.’
The ultrasound beam generated by the researchers resembles the ‘double-helix’ structure of DNA but with many more twisted strands, or helices. This vortex beam generates a rotating, angular component of momentum that can exert torque on an object. In the recent publication, they showed how they could generate vortex beams with many intertwined helices, using a 1 000-element ultrasound transducer array as an acoustic hologram. These beams are so powerful they can levitate and spin the 90 g-disk made of ultrasonic absorber in water.
Here’s a 30 secs. video of the ‘sonic screwdriver’,
Ray Walters in his April 20, 2012 article for Geek.com offers a description using measurements that are more commonly used in Canada and the US for what we’re seeing in the video [I have removed a link from the following passage],
Depicted in the video above, the “Sonotweezers” [aka, sonic screwdriver] project as it’s officially known, uses an ultrasound beam that is structured like a strand of DNA. The difference being that there are many more twisted strands that can be used to bring torque to bear on objects for movement. The team has used its device to levitate and spin a 3.17 ounce, 10cm diameter rubber disk that was suspended in water.
To make this happen, the research team used a 1000-element ultrasound transducer array to create what’s called an acoustic hologram.
The project known as ‘Sonotweezers’ at the University of Dundee, is part of a larger European Union project, Nanoporation, which is investigating drug delivery to cancer cell using MRI (magnetic resonance imaging) and guided focused ultrasound. The larger project includes a couple of Israeli teams, neither of which seem to be involved with the Sonotweezers/sonic screwdriver project. I gather some of the funding for the Sonotweezers project comes from the UK’s Engineering and Physical Sciences Ressearch Council (EPSRC). You can find out more about the Scottish team at the University of Dundee, Sonotweezers, and EPSRC in the April 19, 2012 press release on the University of Dundee website.