Vibrating membranes in a vacuum: How apprentices can contribute to research
Three polymechanics apprentices at ETH Zurich have manufactured appliances for physics research equipment as part of their final project, gaining them full marks. Their custom-made apparatus help improve the measurement of magnetic fields.
The physicist and technician Urs Grob carefully removes the glass vacuum chamber from its insulating sheath. The entire experiment takes place inside the chamber: testing silicon nitride membranes as a way to measure magnetic forces. Precise research within, a work in progress all around. The temperature-sensitive chamber is surrounded by cables, an aluminium frame as tall as a man and four pulleys to lower the glass part of the vacuum chamber so that the researchers can open it.
“That’s how it is with research apparatus: it’s constantly being improved upon and so it can seem confusing,” he says with a smile. In future, a crank-operated lifting table will replace the makeshift pulley system and ensure that the chamber can be opened safely. “You don’t get parts like that off the peg,” Grob says.
Apparatus for cutting-edge research is custom made at the department’s in-house workshop (see D-PHYS News 27 January 2017). A technician for Professor Christian Degen’s Spin Physics group, Grob drew the plans for the necessary components himself and forwarded them to the central workshop in the Department of Physics. There, the apprentice polymechanics Jérôme de Meurichy, Marlon Margadant and Gian Curiger manufactured these components as their final practical exams, gaining them full marks.
The lifting table will replace the current makeshift rope and pulley arrangement for the vacuum chamber. Urs Grob tests the operation of the lifting table, which will be used under the vacuum chamber in future.
Sensitive “bed linen” for expanding MRI technology
Since manufacturing the lifting table was a bigger task, two apprentices – de Meurichy and Margadant – worked on it together. During their four-year apprenticeship, they had learned to manufacture accurate workpieces based on CAD blueprints and 3D models. For their final practical exams, they had to plan and organise the manufacturing process as well as the time management.
“We were able to manufacture the simpler workpieces on conventional turning and milling machines. For the more complex pieces, we used a computer-controlled CNC milling machine,” de Meurichy explains. First, the two apprentices simulated the milling process in a 3D program, which then generated an instruction code for the CNC milling machine. Even so, the CNC milling machine can’t do its job without human assistance: the apprentices must use the right tools, check the code, and calibrate and carefully monitor the machine.
The experiment in the vacuum chamber, for which the apprentices built the lifting table, allows the researchers in the nanomechanics lab of the Spin Physics group to test whether silicon nitride membranes are more accurate than standard sensors when measuring magnetic forces. To this end, the membranes are stretched inside the vacuum chamber where weak magnetic forces cause them to vibrate. “It’s a bit like how bed linen hung out to dry will flap in the wind,” Grob says. The physicists can measure the strength of the magnetic forces by the strength of the vibration. This means that membranes could be the key to the advancement of nanoscale magnetic resonance imaging (nanoMRI). In a similar way to the MRI used in hospitals, nanoMRI can scan and depict biological objects such as viruses in three dimensions with a resolution below one nanometre – that is 0.000000001 metres.
A cooling system for diamond-sensor microscopes
The Spin Physics group measures magnetic fields using not only such highly sensitive “bed linen” but also diamonds. And the apprentices had an assignment involving these, too. In the Diamond Lab, the researchers use a defect in the diamond to determine the magnetic forces at a specific point. In what is known as a nitrogen-vacancy centre, one carbon atom is missing from the diamond’s otherwise pure carbon lattice and a nitrogen atom sits in the place of an adjacent carbon atom. The resulting change in the number of electrons causes the defect to react sensitively to a magnetic field.
“Using this sensor, we can scan samples – like in atomic force microscopy – to measure magnetic fields on surfaces,” Grob says. “This is of interest to the hard disk industry, for example, which needs to characterise the thin layers of magnetic material with the utmost accuracy.”The researchers now offer such diamond-sensor microscopes through Qzabre, a spin-off from the Diamond Lab. “For some measurements, it’s useful to be able to apply an additional magnetic field from the outside,” Grob says.
As an add-on module to the microscope, Qzabre offers a magnet consisting of three coils, which makes it possible to control the strength and direction of the magnetic field. Since the coils heat up during use, Grob designed a cooling system, which polymechanic Gian Curiger turned into a reality. This sees the coils come to rest in an aluminium cone through which cooling water flows. Precisely designed boreholes channel the water around the coils in a multi-stage circuit. “To ensure optimum heat dissipation, the coils are also encased in copper,” Curiger adds. Finally, the individual parts are screwed together and made watertight with the help of laser-cut neoprene seals.
Learning from prototypes
Collaboration and assignments from research are what makes polymechanics training at ETH unique – and from time to time, these aspects also call for some “translation work” between the workshop and experimental physics: “We work on trials and prototypes – which means we mostly make one-offs,” Margadant says. All three apprentices are delighted by how varied their apprenticeship is. “At ETH, the training doesn’t just cover one area, you’re always learning something new,” Curiger says. If you want to get ahead, an apprenticeship at ETH is the way to go, de Meurichy says.
In the workshop, the total of 16 apprentices are treated as the employees’ equals and their input is appreciated. The apprentices also get on very well together. Their time at ETH ends with the completion of their apprenticeship. All three will now be moving to vocational high school. However, the results of their final practical exams will be staying at ETH to enable cutting-edge research. While the parts they built will be assembled only in the coming weeks, the apprentices can already be satisfied with their outstanding work.
The photos were taken by Monika Hanke and Emanuel Noe Schweizer. They are both budding interactive media designer from ETH vocational training.
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