*Microscale "artificial muscle" components fabricated with shape changing alloy microfibers"
The arena of nanotechnology is by no means confined to the specific realm of "replicators" or nanoassembler machine systems per se. Indeed, the entire genre of mechanical molecular manipulation and assembly as a manufacturing process can yield a potentially endless variety of engineered materials with exotic attributes. Indeed, with the advent of even current day developments such as fullerenes which can encapsulate atoms and even entire molecules of various elements and materials, matrices of seemingly "impossible" molecular combinations that would never occur naturally, begin to become possible.
But in yet another, perhaps even more obscure realm of exotic materials, there are a few lone researchers pioneering what may become one of the yet to be "discovered" areas of commercial applications development.
Consider for a moment a homogenous metallic alloy, with extraordinary tensile strength and durability characteristics, that can be "trained" to rapidly conform to a predetermined shape or volume as a function of an electrical, or thermal gradient stimulus. Consider further, if such a material could actually perform work during such shape transformations, be repeatably cycled between specific shapes, and instead of suffering from life cycle fatigue limitations, actually improve with continued usage. Translated into viable commercial applications, the possibilities include such diverse products as artificial muscle fibers (with considerably higher load bearing capabilities than most organic fibers), ultra miniaturized valve and actuator components, tactile response feedback devices, thermally or electrically induced assembly components, thermally sensitive medical devices, and so on.
Physicists and metallurgists have for years speculated on the theoretical aspects of certain classes of metals which are made up of crystal structures that have very specific state phase geometries. If the relative symmetry and geometry of the crystal matrices underwent a significant enough of a change as it was instigated to change from one state phase to the next, then the macroscopic structure of the material itself would actually perform work, and deform to a specific shape. Although many materials can be temporarily deformed to a specific shape via some form of external stimulus, very few materials actually perform this type of shape deformation repeatably between two specific predetermined shapes as a function of an applied stimulus. This type of behavior is referred to as Dual Shape Memory Effect, or DSME.
Unlike a bimetallic strip, where the key factor for deformation is differing
thermal coefficients between the two materials laminated together, a homogenous
alloy which can be cycled between two completely different crystal structures is
remarkably different. In the case of NITINOL, and various hybrids which are
being produced (FLEXINOL, for example), the applications are almost endless. Not
only is the state phase induced crystal structure change remarkably extreme, but
the cycle times can be very rapid (milliseconds). This is a material which can
actually perform measurable mechanical work during its shape change, and indeed,
its load bearing and displacement capacities can be startling even to a seasoned
materials development specialist. 
One of the early pioneers in exploring the potential of DSME alloys, and specifically NITINOL, is Dr. David Johnson. Although he now has his own company (TINI Alloy Company, San Leandro CA), and can be most often found in his laboratory along with a small but dedicated cadre of technical support staff, I personally had the extreme good fortune of working with him as a technician in the early 1970's at Lawrence Berkeley Lab. Back in those days, DOE (Department of Energy) actually funded alternative energy projects, and in general, supported related technical developments at several of the national laboratories. He was one of a very small number of physicists who had speculated on the concept of a thermally induced DSME material as a component for a solar engine.
Since then, he has become a recognized authority on the physics of DSME alloys, particularly in the realm of utilizing ion plasma deposition techniques to create molecular films of programmable shape changing alloy materials to silicon substrate micromachine structures.
Unlike the current genre of etched silicon
micro mechanical devices, the NITINOL thin film constructions do not suffer
from extreme fragility. In fact, by contrast, the NITINOL material is remarkably
hardy, and is an ideal candidate for extreme critical applications, such as
medical, aerospace, and industrial devices. Though some of his current
developments are not quite ready for public exposure, one product that is
emerging is a series of microscale diaphragm valves. These tiny valves can
switch either gas or liquid lines, and have extraordinary fatigue lifetimes.
In an entirely different area of development, another entrepreneur is actively pursuing the concept of "artificial muscle" fibers. Tucked away in a small, remote lab (San Anselmo, CA) is Roger Gilbertson, and his company, MondoTronics. In the current real world, various research teams here and abroad are struggling with the complexities of attempting to mimic the behavior "organic" beings with an interesting and diverse range of mechanical organisms. Aside from the obvious sensory and decision processing abilities that such an artificial organism would need to possess, the actual physiological hardware of the organism itself would also require special materials with "lifelike" properties.
The current genre of walking, hopping, and crawling insect-like mechanical organisms which are at the forefront of this area of research rely mostly on "traditional" mechanisms for generating mobility. However, an entirely different approach, one which much more closely mimics the behavior of actual muscle tissue, is seen by some as the real future of artificial organism construction.
In an actual organic muscle fiber, an electrical stimulus pulse causes the fiber to contract, thus performing work as it pulls on the limb it is tendoned to. To this end, Roger has constructed a series of "insects", some as small as a grasshopper. Indeed, even smaller machines are quite possible, and as one might suspect, the potential for applications are extraordinary.
Besides being considered as a possible candidate for micro robotics applications on the planned Martian landing mission, the range of possible industrial, technical, and even entertainment products is very interesting. Also in the lab were such items as a radio controlled actuator unit, and a miniature NITINOL "tweezers" which was actually being used to flap the wings of a butterfly mounted on small support rod.
This material can perform remarkably well after it has been appropriately
"trained", even under considerable loads. Improvements in various aspects of
both the manufacture and post-processing stages of material fabrication are
providing a glimpse of what this promising technology may have to offer in the
future .
Besides observing "Boris" the insect negotiate its way around a field of
small lava rocks at the MondoTronics lab, I also had the opportunity to observe
some of the long range development project concepts. Perhaps the most intriguing
is the concept of prosthetic and other medical assistance devices. Though this
entire area of research is still in its infancy, this is not science fiction.
Time will tell where these early explorations into DSME alloys and their
applications will lead into the future.
In the case of NITINOL, however, the transition is extreme, and therefore
causes a measurable shape change throughout the material. When the crystals are
in their martensitic state, they are in an orthorhombic, elongated form, and the
overall consistency of the material is relatively limber and deformable. This is
the circumstance when the material is "cold", or below austenitic threshold.
When the material is heated above its austenitic threshold (which can be set
both by alloy composition and post foundry "training"), the crystals within the
material very rapidly switch to a much tighter, cubic form, which causes the
material to contract and perform kinetic work. What makes NITINOL so interesting
is the extreme nature of this transformation.
A wire or foil made of this material can perform a visible shape
transformation in a matter of milliseconds, and is actually quite startling to
observe. Even more interesting is that this state phase transition can be
triggered electrically, and as such, can perform a wide variety of tasks,
particularly where rapid and precise deformation or shape change is required.
Indeed, in this context, the material behaves remarkably like an organic muscle
fiber. There are, however, many other applications where complex shape memory is
the critical feature of interest.
One example of this unique feature was a dish antenna designed for NASA,
which consisted of a wire mesh ball. After being launched into space, the ball
could be thermally triggered to unfold into a large hemispherical wireframe
dish. Surgeons now use wires of NITINOL to push cholesterol deposits out of
clogged arteries. When a "pre-trained" wire is inserted into the target artery
and is subsequently warmed by body heat, it stiffens to a pre-determined shape,
and pushes out the offending cholesterol. Cryogenic couplings of NITINOL are now
used routinely for critical high pressure line applications. A sleeve of NITINOL
can be brought to an assembly site in a dewar of liquid nitrogen. In this state,
it is a "loose" fit around a pair of lines being coupled. Once the NITINOL
coupling warms up to room temperature, it swages down on the lines, creating an
extremely robust leakproof joint.
As is the case with many "discoveries", this material was basically brought
to life via an accident. Originally part of a routine investigation at a Naval
metallurgical research facility (hence the "Naval Ordinance Laboratory" part of
the NITINOL acronym), billets of various titanium alloy samples were being cast
and tested at the lab. A lab technician, having bumped into a table and knocking
over a few of the sample billets onto the floor, noticed that some of the
billets landed with a "tinkle", while others landed with a "thud". He had noted
that the billets with the tinkle landing had been near a desk lamp, and were
therefore warmer than the other thud billets. This was duly noted in a lab
report, which was then filed away in an obscure file cabinet in the facility,
where it resided for over a decade. In the early 1970's, while physicists and
other re- searchers were pondering the possibility of DSME materials being
potentially useful as a thermal to kinetic conversion scheme for solar and
industrial waste heat energy systems, a chance mentioning of this "mystery
material" having been observed at the naval laboratory prompted some poking
around in various records, and eventually led to the lab notes in question.
Now, a mere 30+ years later, researchers are actively investigating a diverse
range of possible applications. This is still an area of research in its
infancy, and there is certainly any number of new niche products which will no
doubt evolve over the coming years.
Particularly in the realm of molecular films, and micromechanical structural
components and arrays, the possibilities for shape changing alloy applications
are intriguing.
About NITINOL
NITINOL (acronym for Nickel Titanium Naval Ordinance
Laboratory) is one of a very few materials which possess an unusual property
referred to as "Dual Shape Memory Effect", or DSME. In a particular class of
metals, which include nickel and titanium, the crystals within the material can
be cycled between two specific geometric states, referred to as martensites and
austenites. In fact, the martensitic/austenitic state phase change is common in
other metallic alloys, but the characteristics are so minute that they represent
only a technical interest.
Copyright © 1995 Nanothinc. Reprinted with permission from Midnight
Engineering.
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