A new sensor developed at the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) measures the tiniest cosmic waves — as small as a few femtometers (a millionth of a billionth of a meter) — with a 10 to 100 millisecond period (10 Hz to 100 Hz).

Vibration sensor. Source: Joris van HeijningenResearcher Joris van Heijningen had already developed the world's most sensitive inertial vibration sensor and now proposes a design, using cryogenic temperatures, that is 50 times more sensitive at frequencies below 10 Hz.

The Earth vibrates constantly, yet imperceptibly to humans, from, for example, gravitational waves, ocean waves and human activity. Van Heijningen explained that the amount of vibration varies depending on the location and, when plotted, vibrations fall between two lines called the Peterson Low and High Noise Models (LNM/HNM). The best commercial vibration sensors have a sensitivity below the LNM and are sensitive enough to measure all places on Earth with a decent signal-to-noise ratio, he said.

Currently, the Laser Interferometer Gravitational-Wave Observatory (LIGO) uses seismic isolation for this purpose. The demand for even more advanced and precise vibration sensors to prevent these vibrations from affecting scientific measurements is growing. Van Heijengen explained that the huge detectors that are being developed must be extremely stable because the smallest vibration can interfere with detections.

"Essentially getting the system close to zero degrees Kelvin (which is 270 degrees below zero Celsius) drastically reduces the so-called thermal noise, which is dominant at low frequencies. Temperature is a vibration of atoms in some sense, and this minuscule vibration causes noise in our sensors and detectors," said van Heijningen. For this reason, future detectors will need to cool down to cryogenic temperatures, which is not easy to accomplish. Once scientists achieve that, taking advantage of the cryogenic environment will improve sensor performance, as his design shows.

As a research scientist at UCLouvain in Belgium, van Heijningen plans to prototype this sensor design and test its performance for The Einstein Telescope.

The paper recently published in the IOP Science Journal of Instrumentation reveals a prototype of the next generation of seismic isolation systems with sensitivity down to 1 Hz, using cryogenic temperatures — lower than 9.2° and above the absolute zero.