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Newsletter October 2023 | Menu of Newsletters

This Cal Poly Case Study was a wnining submission in
Minus K 's 2016
Educational Giveaway.

Cal Poly’s 2D solid experiment: A self-made interfacial shear rheometer of the two circular coils that create magnetic forces to deform the sample material in a glass dish and measured by the microscope suspended above, all sitting on a Minus K 100BM-1 negative-stiffness vibration isolator.

Vibration Isolation Supports the Search for Memory in Soft, Amorphous Solids

The Soft Mechanics Laboratory at California Polytechnic State University (Cal Poly is researching soft, amorphous solids like foams, concentrated emulsions and bulk metallic glasses to determine whether these materials remember deformations that were applied repeatedly in the past, and how this information could be encoded in their microscopic structure and behaviors.

Nathan Keim, Assistant Professor of Physics at Cal Polys Soft Mechanics Laboratory in San Luis Obispo, has for well over a decade been conducting research on memory, self-organization and other non-equilibrium behaviors of soft materials under deformation.

This includes experimental studies of the mechanisms of plasticity in disordered solids, and liquid interfaces. With his students, the lab conducts experiments on interfacial materials, made up of microscopic particles adsorbed at an oil-water interface, using these two-dimensional systems as models of soft, amorphous solids like foams, concentrated emulsions and bulk metallic glasses.

Amorphous solids like foam, sand, and ice cream feature many particles crowded together. Each particle is fully constrained by its neighbors, but the material is disordered so these constraints vary greatly, said Professor Keim. When the material is put under sufficient stress, we know that local groups of particles rearrange by squeezing past one another, but the way these microscopic processes organize and give rise to macroscopic behaviors of the material is still not well understood.

We focus on deformations that are large enough to cause these rearrangements and change the material, but too small to disrupt the material completely and cause it to start flowing. explained Professor Keim. This creates the possibility that the material can retain a detailed memory of how it was deformed in the past. Exploring how these memories are stored and how they can be retrieved is an opportunity to learn more about the mechanisms at play when these materials deform.

Interfacial Shear Rheometer and Managing Vibrations
To facilitate this research, Professor Keim and his team have constructed an instrument, a kind of interfacial shear rheometer, which allows a two-dimensional amorphous solid to be deformed while measuring its mechanical properties.

The apparatus uses a pair of magnetic coils to move a magnetized needle embedded in the material, deforming the material with pN (piconewton) forces. By simultaneously recording the motion of tens of thousands of particles in the material, they can connect what is happening on the microscopic and macroscopic scales a rare and highly desirable ability in the study of materials.

Since our research basically takes place on the surface of a dish of water, the experiment is especially sensitive to low-frequency vibrations that excite surface waves and agitate the material under study, added Professor Keim. The building where the physics department, and the Soft Mechanics Lab is housed, has severe vibrations at 5 Hz due to the many fume hoods in the building, as well as the HVAC system.

When these vibrations are too strong, they do not just introduce noise, but actually trigger rearrangements of the particles within the sample material essentially altering the sample during the measurement. Even when they do trigger rearrangements, low-frequency disturbances also add noise to the mechanical measurements and limit the ability to deform the material precisely and repeatedly

For vibration isolation, the experiments were being conducted on a tabletop platform resting on passive balloon isolators. But this was not sufficient to dampen vibrations satisfactorily. So the lab began performing experiments at night when the chemistry fume hoods were not in operation, which helped mitigate the problem, but still required considerable computer processing afterwards to stabilize imaging.

These vibration limitations had grown more important as we began to examine our materials response when the exact same deformation is applied hundreds of times, in order to study the possibility of learning and memory effects, continued Professor Keim.

Having looked at both optical air tables and active vibration cancellation systems as potential solutions for the vibration problem, and determined that neither was satisfactory for cancelling vibrations at very low frequencies, the lab selected Negative-Stiffness vibration isolation.

2D solid material sample: A layer of polystyrene particles at the interface between oil and water. The black bars at the top and bottom are the boundaries that are moved to shear the material.

Article continued...

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The LC-4 Ultra Compact Low Frequency Vibration Isolator

Low Freq. Horiz LC-4
4.75" W x 4.75" D x 7" H
(121mm W x 121mm D x 178mm H)

Ultra Low Freq. Horiz LC-4U
4.75" W x 4.75" D x 8" H
(121mm W x 121mm D x 203mm H)

The LC-4 is an ultra compact, low-frequency negative-stiffness isolator. It comes in two configurations, our low horizontal frequency performance of 1.5 Hz or our ultra low horizontal frequency performance of 0.5 Hz. Both configurations offer our signature 0.5 Hz vertical natural frequency.

This low frequency vibration isolator is for weight loads from 15 to 130 lbs. and 1/2 Hz performance vertical and horizontal.

LC-4 isolators can be combined into multi isolator systems to support heavier payloads while taking up very little room themselves. The isolators are passive, manually-adjustable and require no air or electricity. More...
  • Vertical natural frequency of 1/2 Hz or less can be achieved over the entire load range.
  • Horizontal natural frequency is load dependent. 1 1/2 Hz (low horiz. freq.) or 1/2 Hz (ultra low horiz. freq.) or less natural frequencies can be achieved at or near the nominal load.
  • See performance for a typical transmissibility curve with 1/2 Hz natural frequency.

Pricing & specs for LC-4

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Vibration Isolation Improves Specimen Examination at the
Natural History Museums of Los Angeles County

The museums' microscope is supported by negative-stiffness vibration isolation, which enables precise clarity of specimens being viewed at high magnification and high resolution

The Natural History Museums of Los Angeles County (NHMLAC), which include the Natural History Museum in Los Angeles' Exposition Park, the La Brea Tar Pits, and the William S. Harding Museum, is the largest natural and historical museum in the western United States, holding one of the world’s most extensive and valuable collections of natural and cultural history—more than 35 million specimens and artifacts covering 4.5 billion years of history.

The NHMLAC collections are strong in many fields, but the mineralogy and Pleistocene paleontology collections are among the most impressive, the latter thanks to the wealth of specimens collected from the La Brea Tar Pits located in the heart of Los Angeles. The worlds most powerful gateway to the Ice Age, the asphalt seeps at the La Brea Tar Pits represent the only active urban fossil dig site in the world. The site contributes an ongoing wealth of extraordinary specimens, like saber-toothed cats, mammoths, dire wolves, and mastodons, as well as the tiny microfossils of insects, plants, mammals, and reptiles from the last 50,000 years.

Fundamental to the activities of NHMLAC is research. Essentially, close examination of these objects, artifacts, and specimens for the purposes of illustration, preparation of scientific papers for publishing, and photography for displays within the museum. Much of this research is conducted with the use of microscopy, viewing specimens at high magnification and high resolution to observe and examine fine details.

Researchers at the Natural History Museum in Exposition Park, for example, are examining the structure of prehistoric fish teeth, minerals, insects, and other small creatures, said Brian Brown, PhD, curator of the Entomology Section. Even ancient feathers from 100 million years ago encased in amber. Amber influences clarity and distorts and changes the viewability of the feathers. Very high microscopy resolution is needed to examine minute, fine details from these and other specimens..
For the examination of its specimens, the museum uses a digital microscope.

Digital microscopes incorporate observation, image capture, and measurement capabilities while providing an on-screen interface for viewing objects. Compared to conventional optical microscopes, digital microscopy provides superior imaging capabilities. Even at higher magnification, images are fully focused due to a large, depth- of-field composition function.

The digital imaging system gives us up to 1,000 times magnification, continued Brown. The microscope allows us to view great detail and fidelity in our specimens.

Vibration problem
For several years ambient vibrations severely plagued the microscopes ability to deliver precision images.

At high magnifications things get very sensitive, added Brown. This requires great stability. But our microscope is located on the third floor of the Entomology Section in the museum, in a cantilevered room extending from the main building. An elevator is located right next to the room, so we were constantly dealing with vibration issues that were affecting the quality of our images. We would wait for periods of relative stability, like between elevator movement, to view images. Even if the elevator was not running, we would still get ambient vibrations from people walking around in the department.

Vibration can be caused by a multitude of factors within a building. Every structure is transmitting noise. Within the building itself the heating and ventilation system, fans, pumps, compressors, elevators, doors closing, and footfall are just some of the sources that create low-frequency vibration that will affect microscopy imaging and data sets. Depending on how far away the microscopy instrumentation is from these vibration sources, and where in the structure the instrumentation is locatedwhether in a basement or in a cantilevered roomwill determine how strongly the instrumentation will be influenced.

External to the building, sensitive instrumentation can be influenced by vibrations from truck movement, road traffic, nearby construction, loud noise from aircraft, and even wind and other weather conditions that can cause movement of the structure.

Essentially, we were getting so-so results from the microscope, and we knew the problem was coming from the ambient vibrations in the room, explained Brown. We tested an active cancellation vibration isolation system, but found it hard to set up, and it really did not cancel vibrations very well. We then did a demonstration of a negative- stiffness passive vibration isolation system and found it to perform very well.

Article continued...

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