'Smart' technologies, which encompass both 'Smart' materials and structures, are creating a sea-change in engineering practice. Their fusion of conventional structural materials with aspects of information technology offers the prospect of engineering systems which can sense their local environment, interprets changes in this envirnoment and respond appropriately. Demonstrator projects exist world-wide exploring the range of possible applications for 'Smart' technologies in sectors ranging from aerospace and civil engineering to automobile and marine. A common feature of such programs is their use of relatively sophisticated technologies, examples including the use of fiber optic techniques for sensing and actuation based on functional material such as piezoceramics, electro- and magnetistrictives and shape-memory alloys. The use of such advanced technologies is symptomatic of the strong technology push which has dominated the development of this field.
The paper presents Nitinol, a Nickel-Titanium shape memory alloy, as a smart material for medical implants and devices. The atomistic nature of shape memory and superelasticity of Nitinol and the associated unique changes in mechanical properties are described. The smartness of the material is exemplified by its use for self-expanding stents. Caused by the stress hysteresis of superelastic Nitinol, these devices exhibit a biased stiffness behavior, i.e. they exert a low chronic outward force on the vessel wall, but resist external deformation with much higher forces. Some recent developments of thin film Nitinol stents and filters are also discussed.
The main steps in transferring ideas from a biological context to an engneering one are: 8) recognizing the required function within the engineering context; 9) isolating a biological equivalent; 10) transferring the biological function to the engineering context. To illustrate this, there are many ways of joining two pieces of material together which can be displayed on Cartesian coordinates wiht the non-parametric variables of strength of interaction and permanence.
The construction and maintenance of the civil infrastructure represents between 10% and 20% of the public investment in most European countries. In the last decade we have however witnessed an increasing shift from investments in the construction of new structures to the maintenance and the lifetime extension of the existing ones. With the exception of the high-speed train lines, most of the transporataion network, including highways and railway, is completed and in service. However, the steady increase of the passengers and goods circulating in the continent, amplified by the free circulation policy introduced by the European Community, is putting the civil infrastructrue under a rude test. Many bridges and tunnels built a few tens of years ago need repair and in many cases an extension of their bearing capacity and lifetime that exceed the original plans. Besides the direct costs associated with these interventions, the disruption to the normal use of the structures causes additional inconveniences including traffic jams and accidents that carry additional hidden costs.
This paper gives an overview on what was expected to be achieved in smart structures and materials for aerospace and automotive applications about a decade ago and what so far could be achieved. Although initial goals turned out to be somewhat over-ambitious, achievements so far are worth to be discussed and pursued. Major ongoing activities being on the verge to be transferred into application are therefore summarized and referenced. A major lack in smart structures technology transfer has been identified being procedures on how to identify which technologies have the most likely chance to be transferred into application. A procedure for this successfully applied in market research and product development is therefore described and proposed here.
One of the principal activities of the ASSET Network was to summarise the state-of-the-art in smart structures technology. This paper presents a summary of these reports and endeavours to bring together the component enablers, sensors and actuators, the software tools principally signal processing and control algorithms, into a structural design philosophy. Whilst any design philosophy must be in the early phases of development the increasing importance of integrating advanced instrumentation systems within structural artefacts rapidly becomes evident.
The design of living systems is controlled by their evolutionary adaptation to their environment. At almost any scale at which they are observed, these systems can generally be classified as “complex”. In this paper, the appropriateness of biomimetic designs for engineered systems is explored. A number of related concepts are defined and discussed, and different measures of complexity are identified. Finally, the use of evolutionary system design and complex adaptive behavior in engineered systems is considered.
Active materials with adaptive acoustic impedance are materials with an acoustic characteristic which can be controlled using as external source of energy and a control circuit. Controlling the acoustic impedance means controlling the transmission, reflection and absorption properties of the material.
Good marksmanship is critical to infantry mission effectiveness. In combat there are intense external simulations such as incoming fire, loud noises. There is fear of the unknown and death, especially with the witnessing of loss of life. Unfortunately, the stress generated by all these pressures produces detrimental physiological effects. Studies have shown that the heart beat of a soldier in combat is aroudn 300 beats per minute. In addition to this, the soldiers breathing and muscle jerk increases, significantly reducing accuracy. This lost accuracy severely reduces the change of soldier survival, mission effectiveness and increase colateral damage and civilian casualiteis. These stressors are well known to the military.
Pedestrian fatal accidents in the USA are almost 15% of the total traffic deadly accidents; besides pedestrians account fo 85% of the fatal accidents without considering the vehicle's occupants. In Europe such percentages are even higher. Furthermore more than 50% of killed pedestrians are involved in an accident with a passenger's car, and between them almost 90% of killed pedestrians are hit by the front of the car.
This paper describes the wind tunnel aeroelastic testing of a Remotely Piloted flight Vehicle (RPV) with adaptive piezoelectric wings. The aeroelastic response to gusts and performance of the RPV wing using traditional aerodynamic control surface methods is compared to the results obtained using piezoelectric (PZT) actuation. Additionally, piezoelectric shunting, a passive form of control is used in order to create system redundancy, thus improving the RPV flight safety in the flight envelope worst-case scenario. Finally, implementation guidelines in terms of power requirements, miniaturization aspects, and the hardware in the loop required for the successful flight testing of the adaptive RPV are also provided.
Isolating a piece of delicate equipment from the vibration of a base structure is of practical importance in a number of engineering fields. Examples are the isolation of instrument boxes in aeroplane and the isolation of telescopes and antennas in satellites. In the majority of cases, the base is flexible and vibrates with an upredictable waveform which has a broadband spectrum. The active isolation of a vibration-sensitive equipment structure from a vibrating base is studied in this paper. Passive anti-vibration mounts are widely used to support the equipment and protect it from severe base vibration. However, conventional passive mounts suffer from an inherent trade-off between high frequency isolation and amplification of vibration at the fundamental mounted resonance frequency. General the best isolation performance is achieved by using an active system in combination with a passive mount, where the fundamental resonance can be actively controlled without reducing the high frequency performance.
When trying to control flexible structures by means of model-based control strategies, the necessary model reduction by means of discretization schemes may completely change the behavior of the 'true' or reference structure to be controlled. For example, the exact pointwise displacement control of a beam, once discretized by standard low-degree finite elements, is the solution of an ill-posed problem, resulting in wildly oscillating controls and suggesting the beam be less and less controllable when the mesh gets refined, whereas the continuous, or reference, model is exactly controllable, and although the mentioned finite elements yield a converging approximation of the statics and of the free dynamics of the structure. Moreover, the closed-loop spectrum associated with optimal control may get closer to the imaginary axis when the mesh is refined, even in cases when the reference model is uniformly exponentially stable.
A fuzzy model of a smart composite beam actuated by piezoceramics (PZT) and electro-rheological fluids (ERF) is formed. Then a fuzzy controller for vibration suppression of the beam is designed by using Lyapunov’s stability theory.
The problem of damage detection and identification has a natural hierarchical structure. At the higher levels, one might require the diagnostic to return say, information about the expected time to failure of a structure, while at the lowest level, the question is simply of whether a fault is present or not. In many ways, the latter is the most fundamental. In response to the need for robust low-level damage detection strategies, the discipline of novelty detection has recently evolved. The problem is simply to identify from measured data if a machine or structure has deviated from normal condition, i.e., if the data are novel. The method requires a bank of normal condition data against which the possible damage condition data are compared.
Electrically controllable glasses can be used to control daylight and solar energy in buildings and in automotives in order to improve quality of life and to save energy spent on lighting, cooling and heating. The paper discusses the case of switchable glazings using liquid crystal/polymer micro-composites. A comparison with other technologies (like inorganic electrochromics, thermotropic gels and dispersed particles) is drawn.
Many techniques are in development to detect and quantify damage in Carbon Fiber Reinforced Polymers (CFRP) structures. All the techniques have advantages and disadavantages in accuracy, expense, robustness and level of instrumentation. Almost all involve sensing of strains or acoustic waves using embedded or surface mounted optic fibesr or piezo transducers. An alternative, relatively unexplored, is the electrical potential technique, whcih exploits the electical conducitivyt of carbon fiber as a damage sensing element. The technique consists of measurement of potential distribution in CFRP laminates before and after delamination damage is formed by an impact or other event.
A new central railway station - Lehrter Bahnhof - is being built in Berlin. Because of construction activities in immediate vicinity and because of difficult soil conditions, vertical displacements will be expected. In order to avoid damage to the bridges and to a widely spanned glass roof which will be supported by two concrete bridges these two bridges have to be monitored right from the beginning of construction until commissioning as well as later on for several years. For this purpose, a long-term monitoring concept has been developed. Sensors with excellent long-term stabilty have been chosen to carry out the concept. This paper describes the measuring concept as well as components of the system. Especially techniques to monitor settlements and heaves and to measure strain and inclination of the prestressed concrete bridges are described. All measures are redundantly monitored. Measurements on-site are referenced by measurements on two large-scale beam models well-defined loaded under laboratory and field conditions.
A dielectric elastomer planar actuator consists of a polymeric film included between two compliant electrodes. A voltage difference applied between the electrodes generates an electrostatic pressure which compresses the flim thickness and expands its surface. The high performances and low costs of dielectric elastometers, belonging to the class of electroactive polymers, suggest their advantageous use for the actuation of small scale devices. The following figures present some possible simple applications of such actuators.
Real-time health monitoring of composite and metal structures has attracted considerable attention over the past years. Lamb waves were first described by Horace Lamb for homogeneous isotropic material. They are elastic waves that can be generated in a solid plate with free boundaries and are also known as plate waves. They can be divided in symmetric (Sn) and anti-symmetric (An) modes according to their displacement pattern.
Non-destructive Testing and Evaluation (NDT&E) is critical in the safety assurance of modern engineering structures, particularly when using high performance materials. Frequently, such materials are subject to mechanisms of damage uncommon in conventional structures. Additionally, many high performance alloys such as advanced aerospace aluminiums are more susceptible to fatigue failure than more traditional metals. In all such cases, it is essential to have good knowledge of the defects present in a component in order to assess its soundness. One of the most common and verstaile techniques used in NDT&E is ultrasonic testing, where the integrity of a component is characterized using acoustic waves.
Since a few years, Lamb waves have been seriously considered as a potential technique for integrated damage assessment systems. Since they are easily propagated over long distances in plate-shaped structures and are able to interact with inner material defects, Lamb waves are seen indeed as a most promising technique. Real-time, continuous health monitoring applications require the development of thin piezoelectric Lamb wave transducers intimately coupled to the structure to be monitored.
Magnetostriction occurs in the most ferromagnetic materials and leads to many effect. The most useful one to refer to is the Joule effect. It is responsible for the expansion or the contraction of a rod subjected to a longitudinal static magnetic field. In a given material, this magnetostrian is quadratic and occurs always in the same direction whatever is the field direction. Giant Magnetostrictive Materials (GMM), especially Rare erath-iron discovered by AE Clark, feature magnetostrains which are two orders of magntitude larger than Nickel. Among them, bulk Tb0.3Dy0.7Fe1.9, called Terfenol-D, presents the best compromise between a large magnetostrain and a low magnetic field, at room temperature. Positive magnetostrains of 1000 to 2000 ppm obtained with fields of 50 to 200 kA/m are reported for bulk materials. In the 90s, bulk magnetostrictive composite materials have been developed for high frequency ultrasonic applications. More recently, high magnetostrains have also been obtained in rare earth-iron thin films.
A comb-drive is a structure of interdigitated conductive fingers from which one part is able to move. Electrostatic forces allow the structure to function as an actuator whereas capacitance changes give way to use the structure as a sensor. Such structures became feasible on micrometer scale with the advent of surface micromachining in the late eighties. Since then there has been an overwhelming number of applications of comb-drives both in micro-actuation and sensing. This paper gives an overview of the basic operation of a comb-drive and its applications in sensing and actuation.
Next generation lithograph tools, such as x-ray, ion or electron beam use thin film membrane windows for the exposure masks. Systematic aberrations due to heat distortions during exposure and other influences are inevitable. The possibility of integrating an active correction system by mechanical stretching with precision actuators is investigated. The basic idea is to measure the placement error of the mask at a finite number of precision points and use these errors measurements to stretch the membrane with in-plane actuators back to their proper locations. The actuation could be implemented by micro-actuators that are monolithically attached directly to the mask membrane. In order to implement such a system, the following are required: 1) A metrology system that precisly measures the displacement of a set of precision points; 2) Micro-actuators that can be directly attached to the mask and offer sufficient force and displacement to strain the mask; and 3) A control algorithm and system that correlates 1 with 2.
CMOS photodiodes have increasingly been used for biomedical purposes. They offer many technical and economic advantages for their on-chip integration and system miniaturization. With the aim of developing portable instruments for micro-analysis, we have investigated the CMOS BDJ detector for fluorescence detection. Like conventional photodidoes, the CMOS BDJ detector can be used as a photodetector. In addition to that, it can also be employed as a wavelength-sensitive device.
The photonic sensing technology is an area of very rapid growth and increasing interest nowadays. This is due in part to devices such as Fiber Bragg Gratings (FBG), whose inherent characteristics make them very suitable for different sensing fields such as civil engineering, aeronautics or medicine just to mention a few. Among the characteristics that make these devices so versatile, one can find their electromagnetic immunity due to the fact that they are made of dielectric material, both their low size and weight, and their ability to be multiplexed in the same fiber. Even more important is the fact that the information is wavelength encoded and so it is not altered by the attenuations of the transmission channel. This last characteristic transforms these devices into very reliable ones. A new FBG-based transducer for monitoring civil engineering structures is presented in this paper. It is able to monitor both strain and temperature at the same time, giving them very useful information about the actual behavior of their host structure. These transducers were fully characterized and tested in laboratory in order to evaluate their performance. The paper is organized as follows: first of all a brief theoretical introduced to FBG is given, and after that the design of the trasnducer is discussed. Then the characterization process, as well as its results, are presented. At the end, the final laboratory test in a well-known structure is described.
In recent years fiber Bragg gratings have been successfully introduced as sensors for strain, temperature and pressure variations. Their performance and reliability has been proven in many practical applications including strain monitoring in civil engineering and tunneling, downhole monitoring in oil reservoirs and flow assurance monitoring in pipelines. The gratings have great potential to at as true structurally integrated sensor elements. They can be embedded in typical structural or reinforcing elements of civil and geotechnical buildings. Several methods of interrogation schemes are established depending on the desired accuracy and resolution of the measurement. The most important methods are the linear discriminator, the tunable Fbry-Perot filter technique, and several interferometer setups.
Structural health and behavior monitoring have always been both a common concern and need in civil engineering. Several classical approaches have been given to this problem including the widley used strain gauges as well as the topographic measurements. These two techniques are almost always used to monitor the behavior of the structures whereas the health monitoring is accomplished by a simple periodic visual inspection. These approaches present serious problems that limit their practical use in real structures such as: lack of fiability, long-term drift, impossibility of full-time measurements, or lack of thoroughness. Centering the discussion in the strain gauges, for being the most representative of the classical civil engineering monitoring methods, it must be said that due to their electric nature they are exposed to both electromagnetic interference and corrosion. The latter greatly reduces their operating life time pushing it typically to less than one year after installation. That is whey new ways of monitoring civil structures were looked for, and that is how photonic fiber sensing came up. Characteristics shared by all fiber senors are their electromagnetic immunity for being manufactured using a dielectric material, low weight, small size, and compatibility with construction materials. As can be seen these inherent characteristics make them very suitable for their use in civil engineering structures. An example of a quasi-distributed transducer is presented in this communication. First the theoretical fundamentals of the transducer and its behavior is explained, and an in-field experiment consisting on monitoring a bridge is described and its results reported.
The output information delivered of an optical fiber sensor embedded in concrete depends on mechanical coupling between material, transducer body and optical fiber. We tried to estimate the 'filtering' function by numerical approach and experiment.
The availability of miniaturized spectrometers and bright LEDs makes possible the implementation of compact spectrophotometers which can be used for monitoring parameters in a wide range of industrial and biomedical applications. The introduction of fiber optic technology presents several advantages for online spectroscopy. This work presents compact portable instrumentation for absorption and reflection spectroscopy in the visible spectral range that uses optical fiber technology to conduct automatic online monitoring without sampling. It is suitable for any kind of industiral process control where continuous colorimetry of liquid samples or surfaces is a prime requisite.
The applicability of fiber optic sensors to the automotive field was evaluated within a national project, in which the Fiat Research Center, RTM and CNR-IROE are involved. The measurement of the mechanical deformations on a vehicle windshield was considered as a case study. This paper refers mainly to the validation phase of the project and in particular to the deformation measurements on a windshield of a FIAT 'Brava' using fiber Bragg gratings. The results were compared with data collected by using strain gauges and thermocouples. A brief description of the manufacturing and characterization of the grating and of the interrogation system is also provided.
AOS Technology is a UK-based SME which develops advanced optical solutions to challenging measurement and communication problems. Operating across the development spectrum from concept to consumer, the Company manufactures a range of products including a significant portfolio of complete and sub-systems for its clients. Active in the area of smart structures since its inception in 1996. AOS has recently released its GRATIS family of multi-channel, Bragg grating interrogation systems, capable of low drift, high resolution and high accuracy measurements and fast sensor update rates. AOS has also announced a commercial partnership with the FBG manufacturer, AOS GmbH, which will enable both companies to provide turnkey transducer and interrogation system packages.