Smart materials including sensors and actuator applications are often based on Lead-Zirconate Titanate (PZT) as the active component in the system. PZT is often used because despite being a ceramic, it’s a fairly versatile material for manufacturing purposes. You can form wafers, fibers, composites, and thin films with PZT, and include it in a number of applications like airplane wings, car dashboards, shoes, micro-pumps, etc. In particular PZT thin films can be used for pumping and sensor systems for biomedical applications, but the problem here is that PZT includes Lead, and it wouldn’t really work without it.
And Lead is of course toxic, which makes it more or less not biocompatible and therefore not unuseable in biomedical applications for implantation in the body. Furthermore, with new Lead regulations in places like Europe, it’s basically very difficult or illegal to introduce products which contain lead, this was one of the big pushes a few years ago to put research funding into leadless solders for electronic products. So it was cool to read from New Scientist that researchers from the University of California, Berkeley including Robert Zeches and Ramamoorthy Ramesh have developed a piezoelectric-like material based on bismuth ferrite, which reatins properties similar to PZT, but without using any Lead. This could be a significant step for smart materials.
The bismuth ferrite material reacts to electrical fields and exhibits a strain of 1.5% when electrically driven. A strain of 1.5% might seen small for most structural smart materials applications. However, from previous research dealing with active fiber composites composed of PZT fibers and interdigitated electrodes, actuation strains on the order of 0.16% have been seen when driving the actuator at 4000 Volts. This AFC technology has been used to develop active rotor blades and active wing technology, so an actuation strain of 1.5% with a green smart material really isn’t that bad.
At the moment the bismuth ferrite exists as a thin film technology, but if developments are made in the manufacturing process to produce wafers or fibers, it could find many applications in aerospace and automotive applications on the industrial scale. For example, in active damping systems in cars, an application where it would be difficult to use Lead-based materials due to envirnomental regulations (Lead-free countries). And of course, those would need to be cost-effective manufacturing processes.
Publishing and distributing content to an audience has always been an interesting topic for me. While I was working on my dissertation on Active Fiber Composite (AFC) Reliability I also educated myself on blogging and photography topics. Via blogging I learned about Search Engine Optimization (SEO) when publishing internet articles and posting photos to sites like Flickr. So, it was natural I’d think about how to integrate these ideas with my research work. Not to research how to share information, but use what I know from blogging and apply it to the academic research world.
In the academic research world, things are still largely paper and journal based. This makes a lot of sense, you send an article to a journal, it’s reviewed by academic peers, and then published in a journal. For most dissertations, the goal is to publish a hardcopy, which sits in a library somewhere. More pro-active institutions allow you to download dissertations from a library website, and often times the content has also been published in journal form.
I’ve been thinking of how to publish and promote my dissertation online, to maximize its impact on the world. This just means, I want to make it as open as possible for search engines and interested researchers to find and to read. I thought about making it into a giant webpage, and am still working on converting it to a Joomla! website, but this isn’t automatic, although published it on a content management system like Joomla! or Wordpress offers the best mix of on-demand reading and SEO. In conjunction with a book I’m promoting, I decided to experiment with Issuu.com, where one can upload a PDF document and then embed a viewer (flash based) anywhere on the internet. This offers many advantages. For one, anyone can access the dissertation with a web browser, second, it can be easily embedded and distributed like an online magazine.
One primary drawback of Issuu is that is isn’t easy to quickly search through a document, which is really needed when going through a research document. That’s one reason why publishing on a CMS website is ideal, because the document is then fully optimized for searching and a reader can quickly find the most important parts of the research, which they can then use to further their own projects.
Having lofty goals is good for individuals. It motivates us think, more importantly to imagine the possibility of attaining things which should be impossible – when viewed from within the conventional idea of what is possible.
Google is littered with random stories about conspiricies and views on the fake moon landing. This missed the point. The moon landing wasn’t simply the act of placing living humans on the surface of the Moon. It was the momentum of inspiration and innovation, both physical and mental, as well as philosophical which embodies the true impact of the Apollo 11 mission, and the landing of humans on the Moon on July 20, 1969.
On July 21st, 1938 a climbing team including Heinrich Harrer, Anderl Heckmair, Fritz Kasparek and Ludwig Vörg began their asscent of the Eiger Nordwand. The climbing of the Alps, and of many mountains can be as phycologically daunting and mentally liberating as the idea of flying to the nearest planet. The idea of climbing a mass of rock on our planet might seem like an unlikely comparision to flying to the moon. But if you’ve ever looked up the face of a mountain, and tried to imagine a route up what appears to be a barren face, then you can understand the will requried to attain a feat such as launching people into Space. For, until it has been done, it’s nothing but fantasy, an idea to preoccupy the tohughts. But when the summit has been achieved, when a person has been landed on the moon, then we can look out again into the further unkown, and imagine another place to see, another idea to understand, and the Universe becomes a little less vast.
The i-net Basel Innovation Lounge is hosting an event promoting the topic of Biomaterials as an innovation topic. I was clued into the meeting via an invitation on an Amazee project (innovation networks).
Professor Thomas Scheibel is going to talk about the development of techniques in the biological materials realm, which enable the manufacture of synthetic spider silk via the development of proteins. The story of this product being brought to market is going to be covered.
This is the stuff which is truly awesome to hear about, bridging the great divide between engineering and biologically inspired materials, which make use of the design which has gone into different natural biological materials. Animals and plants, insects and all manner of tiny organisms have gone through millions of years of design iterations to reach their present form. By comparison, a car engine has likely gone through what, maybe 10 or so real design iterations and an equal number of significant design refinements over the course of a decade?
Electroactive polymers (EAP) represent a relatively new (as compared with Nitinol) class of smart materials. EAPs can exhibit very high deformations coupled with low forces and are classified in two forms, dielectric and ionic based.
In the dielectric form polymers are layered with electrodes and a voltage is applied, the electrostatic forces then lead to deformation of the material. Dielectric EAPs therefore rely on the electrostatic forces between electrodes to induce actuation by expansion of the polymer layer. When a high voltage is applied electrostatic attraction between the electrodes leads to an expansion in the plane of the actuator.
Ionic EAPs function via the displacement of ions in the polymer. The required driving voltages are generally on the order of a few volts, less than that required for dielectric EAPs. However, a larger driving current is required. Common applications for EAPs include artificial muscles, body sensors, and peristaltic pump designs. Due to the viscoelastic nature of the base polymer material, EAP actuators generally exhibit low response times.
At the present time, the commercialization of EAP materials is not sufficiently advanced to provide a characterized material source to be considered for a smart materials characterization study. The long-term reliability of EAP actuators is also a concern, dielectric actuators need to be pre-stressed but degradation of the pre-stress stiffness can occur. The advent of new polymers will no doubt lead to improvement in EAP designs and reliability.
The Shape Memory Alloy (SMA) category of smart materials is made up of metallic alloys with shape memory effects, which rely on a temperature driven phase transformation to realize shape change in the material. Essentially, a material can be deformed, and returned to its original shape by heating. Materials that heal themselves, actuators, nanotechnology, numerous medical devices, and many other applications exist for SMAs.
The most common SMA is Nitinol (Ti3Ni4), and research into it dates back to research by the United States Navy, hence it’s name, Nickel Titanium Navy Ordinance Labs (Nitinol). The morphing affect of SMAs relies on the temperature dependent phase transformation between austenite and martensite. The shape memory effect is possible through reversibility of the martensite transformation via self-accommodation of martensitic plates.
Shape memory alloys rely on a transformation sequence between martensite and austenite. A shape memory material may be mechanically deformed while exhibiting a martensitic phase, and return to its original shape when heated above its transformation temperature. When heated, the material goes through a reverse transformation, the phase changing from martensite to austenite. Upon cooling from the austenite phase, the material crystallography returns to martensite. The transformation is rather versatile, enabling the manufacture of three different types of shape memory effects: one-way, two-way, and mechanical shape memory.
The narrow composition tolerance of Nitinol, and cost of the raw materials makes it difficult to manufacture in large bulk. Advances are being made in the area of iron and copper based SMAs, which offer a lower material cost. Super elastic tendons and texture-changing surfaces are common applications of Nitinol-based smart material system designs.
However, the phase transformation dependence on temperature renders a poor actuation response time unless the material can be heated and cooled at high rates. This implies that the surface area to volume ratio of a Nitinol actuator should be very high, such as occurs with a Nitinol coating as opposed to a Nitinol beam actuator. Despite a great deal of research expenditure, Nitinol based smart material designs have seen limited success. One drawback of SMAs such as Nitinol is the accumulation of dislocations in the crystal lattice, which can limit the service life and long-term reliability of Nitinol actuators. Over millions of fatigue cycles degradation in shape recovery can be seen.
Engineering fields have traditionally focused on using uni-functional materials with set mechanical properties to design and build structures and products which fulfill certain design intents. Materials such as wood, concrete, and metals have served vast uses throughout history; allowing the construction of cities and industries. The industrial introduction of metals such as titanium or aluminum alloys and fiber-based composite materials have allowed the production of lightweight structures such as airplane fuselages and numerous inventions. While great strides have been made in the field of materials, modern science and engineering does not tell how to design and manufacture multifunctional materials, which can be designed for multiple design intents such as actuation and sensing in addition to fulfilling load-bearing requirements.
Traditional materials such as wood, concrete and metals are generally highly engineered and optimized to certain design requirements. Systems in Nature however, use complex materials, which are genetically optimized through natural selection to accommodate the changing conditions of a certain operating environment. In many ways current material design concepts are being rethought with an eye towards systems, which integrate active components into traditional materials to create material systems which interact with their environment.One method of accomplishing this goal is the integration of sensors and actuators into laminate materials. This allows the engineering of multi-functional products, which can sense and respond to changes in their environment and thereby increase the functionality of the original design. The field of smart materials seeks to fill the gap between traditional uni-functional and controllable multifunction materials.
The goal of smart materials research is to enable the design of materials that can function beyond the traditional design interests such as strength, stiffness, thermal conductivity, etc. An active or smart material system can generally be thought of consisting of three essential elements, the active material, the passive material, and the control system.
The active material is defined as the actuator or sensor element. As a sensor, the device exists to receive information from the operating environment (such as vibration or mechanical deformation). As an actuator the device enables interaction with the environment via shape or vibration control. The term “passive material” or “host structure” denotes the material that the device is integrated into. Finally, the control system refers to the mechanism or program which collects information from the sensor elements and controls actuation of the material. Modeling of various control systems has been addressed in numerous works, but research into the coupling between device and structure is infrequently addressed. Ideally, the same device should be able to act as a sensor and actuator, thereby lending greater flexibility to fulfilling the specific design requirements of any given application.
