Introduction

During the last decade fundamental research on smart structures using intelligent materials has raised industrial interest in applying these results to many problems found in commercial and civil life. The main objective of smart structure technology is noise and vibration reduction in civil engineering, machine tools, automobiles, trains, and aerospace engineering. Both strongly coupled phenomena limit the design of highly advanced and efficient lightweight structures, whereby nowadays noise is considered one of the worst forms of environmental pollution worldwide. As stated in the EC white paper "European Transport Policy for 2010" [COM(2000)468], over 100 million people in the European Community are seriously affected by noise, causing an estimated damage of 10 - 30 billion €/year. In addition to simply being annoying, day-to-day noise exposure may cause serious health problems such as sleep disturbance, stress, disturbance of mental activities, hardness of hearing, and even deafness as well as an increased risk of heart attacks. For example, the risk of a heart attack increases by 20% at noise levels above 65 dB(A) (outdoor Leq), and a child's learning ability significantly decreases with increased noise levels. Consequently, the political target of the EC must be the substantial reduction of the number of people regularly affected by long-term, average levels of noise. Taking into consideration only road and rail traffic, 32% of the population is seriously disturbed by an outdoor noise level of Leq > 55 dB(A) and 13% of the population has serious health problems as the result of outdoor noise levels above 65 dB(A). But, due to increasing traffic, noise exposure in Europe by road and rail has already reached its highest levels. In Germany, for instance, inner urban traffic reaches a noise level of 81 dB(A) during the day, 72 dB(A) at night, and freight rail traffic up to 79 dB(A) at night. With a further increase in traffic, an additional elevation of up to 5 dB(A) is to be expected in noise levels. The EU is defining new standards for the year 2010 to compensate for these noise emissions, targeting a reduction of 19 dB(A) for road traffic and an even higher required reduction of 21 - 26 dB(A) for freight rail traffic. Moreover, the WHO is striving for a more ambitious reduction of up to 29 dB(A) for road traffic and up to 34 dB(A) for railways. It is obvious that the EU and WHO goals cannot be achieved with advanced traffic management or political methods (e.g. traffic restriction) alone. An approach based on lightweight design and smart structure technology combined with traffic management concepts has to be pursued. Beyond exterior noise aspects, interior noise disturbance also has to be considered, particularly for the drivers of automotives. Noise exposure within vehicles significantly contributes to the physical fatigue of the driver and, as a consequence, accounts for significant number of accidents with fatal or serious injuries. Beyond their impact on noise, smart structure technology will for the first time allow for a concurrent lightweight design that enables the efficient use of natural resources in the product itself (less, fuel consumption, less exhaust emission,…). With the upcoming demand of highly efficient, emissionless lightweight structures and increased standards for any type of emission, new intelligent materials systems are needed that allow for both highly damped and controllable as well as light but durable structures for any type of high-tech application.

Up to present, many intelligent materials systems such as fiber composites with embedded piezo-ceramics or shape memory alloys are derived, characterized, and applied in smart structures on a laboratory scale without having an impact yet on the design rules for engineered structures or without their application in mass products. Although their potential could be demonstrated and realized to a certain extent in prototype structures, the performance of intelligent material systems is still insufficient. They require an unacceptable electronic periphery, data on their durability and reliability is lacking and, most importantly, are not yet included in standard design and manufacturing processes. These deficits should be overcame by the newly established Integrated Project "Intelligent Materials for Active Noise Reduction - InMAR". The objective of InMAR is the research and realization of intelligent, high-performance, adaptive material systems with integrated electronics for different individual applications. These are applicable for noise mitigation purposes - even in highly loaded structures as construction material - in the same manner that common passive or lightweight materials have been used up to now. Aside from the development of the materials or material systems themselves, this research also includes their characterization, simulation tools for the design process, handling and manufacturing techniques as well as the reliability of these material systems. According to common trends in engineering, the development has to be performed on an experimental as well as theoretical and numerical level.

In order to gap the bridge between fundamental research and applied technology the consortium of the IP InMAR consists of all leading research institutions in Europe (8 research organizations, 11 universities) in the field of smart structures and intelligent material systems as well as most of the major industries of the intended applications (23 companies), 8 of which are considered SMEs. The consortium combines researchers from various, complementary specialties and enables the cross-frontier cooperation of partners beyond their traditional target markets by providing S&T excellence and by ensuring the quality of the consortium.. Thus, the IP InMAR compromises a vertical integration of the "full-chain" of stake-holders involved in knowledge production, development and manufacture, knowledge transfer as well as potential users. Horizontal integration is achieved by the multi-disciplinary character of the proposed research activities. The IP InMAR has a duration of 4 years and a total budget of 27 Mio. € of which almost 50% is provided by the industry.

Since the requirements for intelligent material systems - in contrast to those for conventional light-weight materials - greatly depend on the intended application and operational conditions, these material systems can only be developed in a concurrent approach that simultaneously considers the application. From manifold application possibilities, noise problems in land-based traffic and related infrastructure such as buildings, bridges, and tunnels are chosen for application purposes. The newly designed intelligent material systems will be applied to active noise reduction concepts based on Active Structural Acoustic Control (ASAC) or Active Noise Control (ANC) for Sound Quality Design. It is expected that for automotives, trains, and in civil engineering reduced noise radiation and emission will increasingly become more of a design aspect which cannot be achieved by conventional materials and concepts. In a broader perspective, advanced intelligent material systems can be introduced to noise and vibration-related design aspects in all fields of industrial and civil applications.

Scientific and Technological Objectives of InMAR

Since research on intelligent materials, control strategies for active noise reduction and the simulation of both is highly interdisciplinary and each subject is highly dependent on the others, the fundamental research on these subjects has always be considered together with the technological development of active noise reduction systems. Technology development will be performed exemplarily for applications in automotives, trains and infrastructure. As underlying principle for noise reduction concepts, Active Structural Acoustic Control (ASAC) will primarily be considered. Since the noise radiation will be controlled either by controlling the structural vibration of the radiating structure or by interrupting the structure borne sound path, special focus has to be given to intelligent material systems as construction material. However, especially when internal noise problems are dealt with, the Active Noise Control with new acoustic actuators and materials, and possibly combined with ASAC approach, may prove to be more feasible, and will also be studied here.

Research on intelligent material systems addresses the design of intelligent materials, the embedding of electronics and the design of control strategies for broadband noise. For a technological breakthrough of active noise reduction, the sensing and actuation capabilities as well as the load-carrying characteristics of intelligent materials, defined as composites consisting of transducer materials and conventional materials, have to be enhanced. These intelligent materials, together with the necessary power electronics, electronics for data management and the control, form a system where the individual components interact in a complex manner. The electronics can either be embedded in the composite or be stand-alone in a miniaturized form. When designing the structure of the intelligent material and the control strategy the highly stochastic, broadband excitation of noise has to be taken into account. Although major research work already has been carried out, aspects such as characterization, handling, manufacturing, reliability and recycling were not addressed so far. Research on intelligent material systems includes the numerical as well as the experimental simulation. Output of this work-package will be fully qualified and characterized material systems for the application in the following fields. According to the different research aspects on intelligent material systems, the fundamental research is divided into the three technology areas intelligent material systems, system integration and life-cycle of these materials and systems. The trisection also reflects the evolutionary progress in the development of intelligent material systems. Within these technology areas intelligent material systems will be designed and characterized, simulation and manufacturing technologies developed according to the problems defined in the application scenarios.

In order to bring advances in intelligent materials to the level of industrial use in integrated applications, the material design process has to become part of the complete product creation process. This demands that the product's functional performance and respective simulation models, which are the cornerstone of today's design process, be capable of supporting the specific aspects related to advanced materials, active systems, actuators, sensors, and control, and that these be integrated into system-level and virtual prototype models. An essential requirement for this is the coupling of various physical disciplines such as structural mechanics, acoustics, electro-magnetism, or durability with control algorithms within one simulation. Moreover, effects on very a different scale need to be interconnected, ranging from the microstructure of the active materials to the acoustic far-field enclosing the structure under consideration, which, in turn, will be the controlling variable for the intelligent material. This level of bi-directional integration is not known in other engineering disciplines and requires a new class of models and tools. Finally, proper parameterization , a reduction of the applicable models, and the fast recalculation of various design alternatives will be key elements in deriving an optimal system and material design. Such a modeling approach will be established in the InMAR project. Based on this approach, the simulation of full-system behavior can be performed, taking into account the characteristics of the innovative material as well as multi-attribute performance goals. This then allows for the proper target setting on the level of the materials and material systems (essential for "materials by design") as well as for the development of optimization procedures for the material parameters and material system configuration.

The largest gains in weight reduction, size reduction and probably cost reduction are obtained when all functional components are fully integrated. Even stronger, it is unlikely that such systems will be introduced if they are not fully integrated. In order to realize these objectives, some of the components could be given multiple functions, such as thin active layers which are used for mounting the electronic components, for the interconnections, and for example the face layers in sandwich constructions. The design of such systems should be done in an interdisciplinary manner and with constraints given by the industrial partners. The design of the system is complicated by the fact that the control of multichannel systems for broadband noise reductions is computationally rather demanding, and usually requires heavy signal processing hardware because fully programmable systems like a Personal Computer or Digital Signal Processor are used. So reduction of computational complexity and hardware implementation of certain parts of the algorithm have a direct influence on the possibility to achieve the desired goals and should be taken into account in the overall design process. In addition, for relatively high sound pressure levels and vibration levels, also the weight and size of the power amplifiers should be reduced. The combination of detailed simulation models is needed to optimize overall system performance. However, the availability of simpler design rules is important from a practical point of view. These simple design rules can be on the component level but also at a subsystem level or even system level

The main objectives of the technology areas are to understand, to design and to develop: •   new complex multifunctional passive, semi-active and active materials and material structures, •   actuator and sensor systems based on the developed materials, fully operational under harsh environment, high and broad-band load and under large deformation •   their manufacturing technologies, and •   novel, miniaturized control and electronics systems for the multifunctional materials, and for the actuator and sensor systems •   simulation and optimization tools for the design of intelligent systems •   technologies to integrate intelligent material systems in structural components and •   methods and procedures to assess their reliability, environmental impact and life-cycle including condition monitoring to be used in the macro-scale application of active noise reduction. The expected innovations on intelligent material systems in total will increase the acceptance of smart structure technology and the industrial applications in order to replace classical, ineffective methods of noise and vibration suppression.

Beside the fact that the automotive industry is a driving factor in the economy, automotives are to be considered as one of the major contributor to noise emission. Beyond the aspect of exterior noise, major effort is undertaken to improve or design the interior noise of automotives. Most concepts are based on absorption and state a contradiction to light weight design. Therefore, automotives are an ideal application for active noise reduction concepts. The major noise sources of automotives are power train and the tire-road contact noise (rolling noise) and consequently considered here. In the overall view of the vehicle, any kind of attenuation (rolling noise, engine, aerodynamics, etc.) of the vehicle body (not only body-in-white) and their effect on radiated noise to the exterior as well to the interior has to be investigated. Depending on the attenuation, structural borne sound within the body or the vibration of panel-like components such as sheet metal panels or windows has to be controlled for an efficient noise reduction. All problems have in common the need for advanced concepts for active noise reduction based on intelligent materials. Current state-of-the-art based on passive approaches are insufficient to meet the future requirements. The objective will be development of advanced noise reduction systems requiring high-temperature, highly flexible, highly loaded or transparent intelligent material systems.

The train industry is facing similar problems. The major noise source of trains is the rolling noise. Having in mind that the system wheel-axis-bogie is a high-loaded structure, highly damped, intelligent materials must de developed to reduce the radiated noise of wheels. Those highly damped materials may function with no external energy, or by generating their own energy or with distributed but independently working units with actuators and sensors. Since ANC or ASAC concepts based on intelligent materials are only demonstrated for low-loaded structures, the design of an intelligent material system for high-loaded structures will state a major breakthrough in this technology. Beside the rolling noise, aerodynamically induced noise should be considered. In particular high-speed trains are emitting noise from the aerodynamically excited large, almost flat side panels of the wagon. These panels will even more contribute to the overall radiated noise of trains when passive and active noise optimized wheels are used. Smart panels with embedded actuators, sensors and electronics will be developed. Furthermore, the ventilation systems of trains significantly contribute to the noise radiation when the train is in the station. Facing similar requirements, research results obtained on train ventilation systems can easily be adopted to those for automotives and buildings.

Research performed for infrastructure such as buildings or bridges has to been seen in context with an overall reduction of noise affection of the population. Although within this Integrated Project concepts are considered to reduce the noise at the source, a significant noise level will remain to affect people. Particularly for buildings at inner urban roads or close to rails or airports the remaining noise level will still exceed the tolerable limits for people. Therefore, as an accompanying measure the transmitted noise through windows and facades should actively be controlled. Discussing active windows and facades it is important to keep in mind, that for the well-being not a total noise reduction but a frequency selective reduction is required for the well-being of the people. The sound of birds, for instance, should be still heard. Within buildings, interior noise and sound quality is also determined by heath, ventilation, air condition systems (HVAC) and elevators becoming even more significant, when the noise emission from outside is controlled. Again active concepts based on intelligent materials will be developed applicable in the state-of-the-art civil engineering technology. Bridges and tunnels are the place of important noise and vibration sources generated mainly by railway and highway traffic. The negative impact of this noise pollution and these vibrations on the environment is usually increased by the proximity of bridges and tunnels towards urban areas. Passive solutions for noise and vibration mitigation have demonstrated a good efficiency but the performance of such solutions shows some limitations.

Noise reduction in all above fields can find great benefits from new intelligent material systems, new components and devices and new noise control systems as derived in the technology areas. Of course, the cost aspects are quite relevant when the balance benefit/cost is taken into account to decide if a technical solution is ready for production. Beside, also innovative simulation tools can help to better understand phenomena and problems, so that new applications of existing technologies or technologies derived are envisaged. The main objectives of the application scenarios are to design and develop advanced active noise reduction concepts for •   exterior noise of automotive and trains, •   interior noise in automotive, trains and buildings •   and sound quality design of interiors as cost-effective solutions for a broad-band noise reduction up to 10 db(A) or higher for exterior and interior noise.

The scientific and technological objectives are reflected in the structure of the IP as shown in Figure below. According to these objectives, the IP InMAR is structured in three complementary technology areas (sub-projects) dealing with intelligent material systems and their integration, simulation, and life-cycle aspects. These technology areas strictly concentrate on providing the enabling technology required for the application scenarios but at the same time strongly rely on the system definitions and requirements provided by them. The applications scenarios again are divided into three sub-projects for application, integration, and verification in automotives, trains, and infrastructure.

Cluster 1: Technology Area	Enabling Technology →	Cluster 2: Application Scenarios
	← System Requirements

Sub-Project	Work Areas	Sub-Project	Work Areas
TA 1 Intelligent Material Systems	Material Systems	AS 1 Noise Reduction by Automotives	Tire & Breaks
	Actuator & Sensor Systems		Power Train
	Manufactoring		Sheet Metal Parts
	Control		Car & Truck Bodies
	Electronics		Sound Quality of Interior Noise
			Noise Transmission of Windows
TA 2 System Integration	Simulation & Optimization	AS 2 Noise Reduction by Trains	Wheels & Breaks
	Electronic & Control Systems		Power Train & Bogie
	System Integration		Ventilation
	Characterization & Validation
TA 3 Life-Cycle	Reliability	AS 3 Noise Reduction by Infrastructure	Windows & Facades
	Condition Monitoring		Bridges & Tunnels
			Elevators