New technique that could improve tests of soft materials

Scientists use various instruments to stretch, squeeze, and twist soft materials to precisely characterize their strength and elasticity. But typically, such experiments are carried out sequentially, which can be time-consuming.

Now, inspired by the sound sequences used by bats and dolphins in echolocation, MIT engineers have devised a technique that vastly improves on the speed and accuracy of measuring soft materials’ properties. The technique can be used to test the properties of drying cement, clotting blood, or any other “mutating” soft materials as they change over time. The researchers report is published in the journal, Physical Review X.

The technique improves and extends the deformation signal that’s captured by an instrument known as a Rheometer. Scientists refer to this shorter, faster, and more complex signals as a “chirp,” after the similar structure of frequencies that are produced in radar and sonar fields — and very broadly, in some vocalizations of birds and bats. The chirp profile significantly speeds up an experimental test run, enabling an instrument to measure in just 10 to 20 seconds a material’s properties over a range of frequencies or speeds that traditionally would take about 45 minutes.

The team analysed the chirp signals and optimized these profiles in computer simulations, then applied certain chirp profiles to their Rheometer in the lab. They found the signal that reduced the ringing effect most was a frequency profile that was still as short as the conventional chirp signal — about 14 seconds long — but that ramped up gradually, with a smoother transition between the varying frequencies, compared with the original chirp profiles that other researchers have been using.