29-10-2012, 12:05 PM
Smart Materials
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Abstract
Sensors and Actuators designs have mimicked nature to a large extent. Similar to our five senses - sight, sound, smell, taste and touch -correspondingly visual/optical, acoustic/ultrasonic, electrical, chemical and thermal/magnetic sensors have been developed. The response from these primary sensors is converted to electrical signals, which are transmitted to the brain (central processing unit) for further processing. In addition to the processing, the role of the processor is to make decision based on these inputs. This is currently done manually by an experienced operator who has an understanding of the sensing and processing technology. To aid the operator in making a more judicious decision, the conditioned signal has to be presented with as much pertinent information displayed in an arresting way. A further development would be to provide the virtual machine itself to make the judgment - smart sensor. The next stage in this would be for the processor to decide on the course of action and the actuation mechanism to respond accordingly. Virtual human robots can be equipped with sensors, memory, perception, and behavioural motor. This eventually makes these virtual human
robots to act or react to events. The design of a behavioural animation system raises questions about creating autonomous actors, endowing them with perception, selecting their actions, their motor control and making their behaviour believable and the behaviour should be spontaneous and unpredictable.
INTRODUCTION
There is an increasing awareness of the benefits to be derived from the development and exploitation of smart materials and structures in applications ranging from hydrospace to aerospace. With the ability to respond autonomously to changes in their environment, smart systems can offer a simplified approach to the control of various material and system characteristics such as light transmission, viscosity, strain, noise and vibration etc. depending on the smart materials used [1]. There are a number of materials that act as both sensors and actuators that can monitor and respond to their environment. However, with the ability to also modify their properties in response to an environmental change, they can be 'very smart' and, in effect, learn. While the scope of sensors and actuators is quite broad, three main sub-programs have been identified – Smart Structures and Materials, Miniature Sensor and Actuators and Automated Testing, Inspection Monitoring and Evaluation. These are exciting times for Sensors and Actuators with the maturing of the enabling technologies of Photonics and Electronics paving the way for inventive and innovative system designs. For the modelling of sensor behaviours, the ultimate objective is to build intelligent autonomous virtual humans with adaptation, perception and memory. These virtual humans should be able to act freely and emotionally. They should be conscious and unpredictable. The virtual humans are expected in the near future to represent computer the concepts of behaviour, intelligence, autonomy, adaptation, perception, memory, freedom, emotion, consciousness, and unpredictability. Behaviour for virtual humans may be defined as a manner of conducting themselves. It is also the response of an individual, group, or species to its environment.
Intelligence may be defined as the ability to learn or understand or to deal with new or trying situations[1].
VIRTUAL REALITY APPLICATION
Virtual human robots (Fig. 1) can be equipped with sensors, memory, perception, and behavioral motor. This eventually makes this to act or react to events. The design of a behavioral animation system raises questions about creating autonomous actors, endowing them with perception, selecting their actions, their motor control and making their behaviour believable and the behavior should be spontaneous and unpredictable. They should give an illusion of life, making the people believe that that they are really alive. A virtual human can be developed which include the basic components of a smart system embedded sensor(s), an information processing (software) system for data analysis, logic and decision making and system hardware (e.g., multiplexers, actuators
etc) interfaced to a computer for control, actuation and feedback [4].
Environmental Requirements
The sensor implanted humanoid has to survey the construction and, if possible, the whole life span of the structure. During the construction phases, the sensor is exposed to a hostile environment and has therefore to be rugged enough to protect the fibers from external agent. Chemical aggression has to be taken into account since concrete can be particularly aggressive because of its high alkalinity. These requirements are often contrasting with the ones of the previous point. To protect the fiber one tends to isolate if from the environment by using thicker or multiple layers of coating. This has the side effect to impede the strain transmission from the structure to the fiber. Finally, the sensor must be easy to use by humanoid and has to be installed rapidly without major disturbance to the building yard schedule respond to all these requirements. Humanoids may be embedded with all these requirements so that the sensors can either be embedded into concrete, installed on the surface of an existing structure or secured inside a borehole by grouting.
BACKGROUND
Smart Materials are materials that respond to environmental stimuli, such as temperature, moisture, pH, or electric and magnetic fields. For example, photochromic materials that change colour in response to light; shape memory alloys and polymers which change/recover their shape in response to heat and electro- and magnetorheological fluids that change viscosity in response to electric or magnetic stimuli. Smart Materials can be used directly to make smart systems or structures or embedded in structures whose inherent properties can be changed to meet high value-added performance needs. Smart Materials technology is relatively new to the economy and has a strong innovative content. According to work by the Materials Foresight Panel, the use of smart materials could make a significant impact in many market sectors. In the food industry, smart labels and tags could be used in the implementation of traceability protocols to improve food quality and safety e.g. using thermo chromic ink to monitor temperature history. In construction, smart materials and systems could be used in 'smart' buildings, for environmental control, security and structural health monitoring e.g. strain measurement in bridges using embedded fibre optic sensors (Fig. 4). Magneto-rheological fluids have been used to damp cable-stayed bridges and reduce the effects of earthquakes. In aerospace, smart materials could find applications in 'smart wings', health and usage monitoring systems (HUMS), and active vibration control in helicopter blades. In marine and rail transport, possibilities include strain monitoring using embedded fibre optic sensors. Smart textiles are also finding applications in sportswear that could be developed for everyday wear and for health and safety purposes [8]-[12].
SMART MATERIALS AND STRUCTURE
SYSTEM
The use of smart materials (Fig-6) could make a significant impact in many market sectors. In the food industry, smart labels and tags could be used in the implementation of traceability protocols to improve food quality and safety e.g. using thermochromic ink to monitor temperature history. In construction, smart materials and systems could be used in 'smart' buildings, for environmental control, security and structural health monitoring e.g. strain measurement in bridges using embedded fibre optic sensors. Magneto-rheological fluids have been used to damp cable-stayed bridges and reduce the effects of
earthquakes. In aerospace, smart materials could find applications in 'smart wings', health and usage monitoring systems (HUMS), and active vibration control in helicopter blades. In marine and rail transport, possibilities include strain monitoring using embedded fibre optic sensors. Smart Structures, e.g. structures, with integrated sensors and actuator materials, which might eliminate the need for heavy mechanical actuation systems or damping systems through their functionality for shape change or vibration control. Self-monitoring, Control and Selfrepair, e.g. applications of functionally graded layers capable of a response tailored to their environment. This will involve use of sensor and actuator technologies for automatic control of conditions within buildings for comfort and energy savings, tagging for food packaging and for crime prevention application of sensors or smart materials in components Robustness of the smart system, e.g. interfacial issues relating to external connections to smart structures Device fabrication and manufacturability, e.g. electro-rheological fluids in active suspension systems, applications in telematics and traffic management Structural health monitoring, control and lifetime extension (including self-repair) of structures operating in hostile environments, e.g. vibration control in Aerospace and Construction applications. Projects can be based on any material format (e.g. speciality polymers, fibres and textiles, coatings, adhesives, composites, metals, and inorganic materials), which incorporate sensors or active functional materials such as: piezoelectrics, photochromics, thermochromics, electro and magneto rheological fluids, shape memory alloys, aeroelastictailored and other auxetic materials [10]-[1 1]. The potential application areas of smart materials and structures are very widespread and include energy - conservation, expensive systems with high potential for operational savings, e.g. transportation systems
such as aircraft or automobiles, aerospace structures, civil infrastructure, structural health monitoring, intelligent highways, high-speed railways, active noise suppression, robotics. In order to increase the speed of the railway vehicle and reduce the energy consumption, the vehicle body needs to be designed as light as possible, for heavy bodies result in limitations in the operating speed and requires actuators of increased size and power, so the flexibility of the structure becomes an important issue.