A sound argument
10 August 2017
When we buy a metre of timber, a kilo of potatoes, or a hectare of land, we know the measurements will be correct – there are national and international standards – but the same cannot be said for measuring sound waves.
Professor Jonathan Scott from the School of Engineering at the University of Waikato says current methods for measuring acoustic properties of things have not advanced much for decades. “They are tiresome, frequency by frequency and on a `best effort’ basis,” he says. He wants to change that, and has been awarded seed funding from the Science for Technological Innovation National Science Challenge to investigate.
He and his doctoral students are going to build an acoustic version of a vector-corrected network analyser, an AVNA. The microwave VNA is the most powerful tool available to microwave engineers.
“With an AVNA soundwaves will be measured hundreds of times faster, and with traceable accuracy,” says Professor Scott. The sort of things that might be measured, for example, are the sound damping of furnishings, pasture dry-matter yield, the sonar cross section of an insect or a torpedo, the reflectivity of a tumour surface, the quietening of a muffler or an air duct, or the impedance of a musical instrument.
What Professor Scott is proposing involves the confluence of many technologies, including “some magnificent mathematics” he says, and with PhD student Marcus Macdonnell and their collaborator John Cater at the University of Auckland they are going to make an AVNA that measures acoustic pressure waves. “It is complicated and precise, we’ll have to 3D print some of the components.”
Already Professor Scott and his graduate students have fabricated and tested directional couplers that separate forward and reverse sound waves. “We have shown that they possess sufficient directionality and can be scaled by means of 3D printing to cover a wide frequency range.”
They have built vector receivers connected to microphones, and calibrated a reflectometer using a dual acoustic directional coupler, and they’ve developed novel ways of synthesizing some acoustic standards. Now they seek to develop a full two-port system in the form of a test set for a commercial Vector Network Analyser (VNA), and from that they’ll do further testing.
Professor Scott is of the opinion that research is never wasted. His new investigation is based on research started nearly 50 years ago.
A scientist called P E Lagasse developed an acoustic directional coupler back in 1971, and it promptly sank into history. “But that component has turned out to be really valuable for us. It’s a great example of how mankind needs unfettered wild research! We will achieve traceable measurements by applying the lessons from six decades of research into fast, traceable, microwave electromagnetic (EM) network measurements to the acoustic domain using Lagasse’s forgotten toy.”
Seed funding for a second project was awarded to Professor Steve Reeves in Computer Science who, in a Vision Mātauranga project will investigate the potential for storing taonga and other valuable materials in the blockchain.