New generations of highly maneuverable aircraft, such as Uninhabited Combat Air Vehicles (UCAV) or Micro Air Vehicles (MAV) are likely to feature very flexible lifting surfaces. To enhance stealth properties and performance, the replacement of hinged control surfaces by smart wings and morphing airfoils is investigated. This requires a fundamental understanding of the interaction between aerodynamics, structures, and control systems. The goal is to build a model consistent with distributed control and to exercise this model to determine the progress possible in terms of flight control (lift, drag and maneuver performance) with an adaptive wing. Different modeling levels are examined and combined with a variety of distributed control approaches to determine what types of maneuvers and flight regimes may be possible. This paper describes the current progress of the project and highlights some recent findings.

Ongoing research in buffet loads alleviation has provided an application for recently developed piezoelectric actuators capable of higher force output than previously existing actuators could provide and that can be embedded within the vehicle's structure. These new actuators, having interdigitated electrodes, promise increased performance over previous piezoelectric actuators that were tested on the fin of an F/A-18 aircraft. Two new actuators being considered by the United States Air Force to reduce buffet loads on high performance aircraft were embedded into the fins of an F/A-18 wind-tunnel model and tested in the transonic Dynamics Tunnel at the NASA Langley Research Center. The purpose of this test program, called ENABLE (Evaluation of New Actuators in a Buffet Loads Environment), was to examine the performance of the new actuators in alleviating fin buffeting, leading to a systems-level study of a fin buffet loads alleviation system architecture being considered by the USAF, Boeing, and NASA for implementation on high performance aircraft. During this wind-tunnel test, the two actuators performed superbly in alleviating fin buffeting. Peak values of the power spectral density functions for tip acceleration were reduced by as much as 85%. RMS values of tip acceleration were reduced by as much as 40% while using less than 50% of the actuator's capacity. Details of the wind-tunnel model and results of the wind- tunnel test are provided herein.

ASSET (Applications for Smart Structures in Engineering and Technology) is a European Union thematic network set up to encourage the exploitation of smart technologies within the European framework. This paper describes the ASSET Membership, its activities and its objectives and finally attempts to assess its potential impact as one contributor to the process whereby members of the technology community interact with each other. Some of ASSET's activities will be open to the general community, most notably a demonstration seminar in May 2002. This will give the 50 members of the program an opportunity to display their achievements to a wide audience.

Within the framework of an idea competition for future-oriented key technologies and their industrial utilization, in 1997 BMBF called for project proposals from industries and research for so-called 'Leitprojekte'. An independent group of experts selected few project proposals from the many submitted, and proposed them to BMBF for promotion. One of these projects is the BMBF-Leitprojekt ADAPTRONIK which is introduced in this paper. Adaptronics describes the field of technology focusing on the development of a new class of so-called smart structures. The Leitprojekt ADAPTRONIK consists of 24 partners from industry and research institutes and is conducted under the responsibility of the German Aerospace Center (DLR). The project focuses on the development and structure-conforming integration of piezoelectric fibers and patches in structures for lightweight construction. It is aimed at active vibration and noise reduction, contour deformation and micro-positioning in the very sense of adaptronics in various industrial applications. The project targets are prototype assemblies from the fields of automotive industry, rail vehicles, mechanical engineering, medical engineering, and aerospace. In the paper the content, the status and an outlook will be presented.

The focus of this study is to evaluate the aeroelastic performance and control of adaptive wings. Ailerons and flaps have been designed and implemented into 3D wings for comparison with adaptive structures and active aerodynamic surface control methods. The adaptive structures concept, the experimental setup and the control design are presented. The wind-tunnel tests of the wing models are presented for the open- and closed-loop systems. The wind tunnel testing has allowed for quantifying the effectiveness of the piezoelectric vibration control of the wings, and also provided performance data for comparison with conventional aerodynamic control surfaces. The results indicate that a wing utilizing skins as active structural elements with embedded piezoelectric actuators can be effectively used to improve the aeroelastic response of aeronautical components. It was also observed that the control authority of adaptive wings is much greater than wings using conventional aerodynamic control surfaces.

Over the last decade, Northrop Grumman Corporation under internal and DoD funding, and others, have been working on integration of RF antennas into load-bearing aircraft structures. This multidisciplinary effort, collectively referred to as Conformal Load-bearing Antenna Structures (CLAS), requires concurrent consideration of structural and antenna performance issues and has involved a team consisting of avionics, structures, material, and manufacturing expertise. From the published articles to date it could be argued that the technology has had some spectacular success in its initial stages but not much has been published about the issues raised by CLAS that would still need to be addressed and solved for final technology inclusion in an operational air-vehicle. Presented are some key results from the Air Force Research Laboratory's (AFRL) Smart Skins Structures Technology Demonstrator (S³TD) program that while funded from the Air Vehicles Directorate looked at the total picture of integration from a multidisciplilnary standpoint. Issues related to airframe integration are also discussed that need further study and evaluation before CLAS can be sanctioned as a viable future DoD technology. Such topics, in no particular order of priority are 1) airframe CLAS panel location, 2) airframe configuration issues, 3) EMI/lightning issues, and 4) repair issues and supportability, 5) panel design enhancement, risks, and issues.

An effective structural health management (SHM) system can be a useful tool for making aircraft fleet management decisions ranging from individual aircraft maintenance scheduling and usage restrictions to fleet rotation strategies. This paper discusses the end-user requirements for the elements and architecture of an effective SHM system for application to both military and commercial aging aircraft fleets. The elements discussed include the sensor systems for monitoring and characterizing the health of the structure, data processing methods for interpreting sensor data and converting it into useable information, and automated methods for erroneous data detection, data archiving and information dissemination. Current and past SHM technology development/maturation efforts in these areas at the Boeing Company will be described. An evolutionary technology development strategy is developed in which the technologies needed will be matured, integrated into a vehicle health management system, and benefits established without requiring extensive changes to the end-user's existing operation and maintenance infrastructure. Issues regarding the end-user customer acceptance of SHM systems are discussed and summarized.

This paper discusses the implementation of a single optical backbone interconnect that can accommodate the wide variety of information that must be exchanged within a typical avionics system. The building block elements of this common optical backbone are based on products that have been developed for the commercial telecommunications and cable TV industries. During the development of this architecture a subsystem interconnect domain analysis was performed. This analysis focused primarily on the three most demanding interconnect domains in an avionics system; 1) the Vehicle Management System (VMS), 2) the Integrated RF (IRF), and 3) the Integrated Core Processor (ICP). The results of this analysis were used to create an approach for a single fiber optic backbone connecting multiple systems and subsystems together. Each group of communication sources and destinations can use their native format (analog/digital), signaling rate (100KHz to 20GHz), protocol (Fibre Channel, ATM, Mil-Std-1553, etc.), and topology (linear ring, point- to-point). All of these communication types coexist on this single optical backbone. The interconnect media is generally topology, protocol, performance, and signaling format independent. A laboratory system has been developed and demonstrated using commercial off-the-shelf (COTS) components. This system can also be used to provide a common interconnect for a variety of fiber optic sensors used in the creation of smart structures. This can provide a single backbone, distributed throughout the platform, for sensors that exploit various optical properties. Some of the sensor types could be Fiber Bragg Gratings (FBGs), Extrinsic Fabry-Perot Interferometers (EFPIs), and Mach- Zehnder interferometers.

Recent satellites, growing in size and electrical power capacity, require sophisticated technology in terms of thermal and structural design. On the other hand, reducing their lifecycle cost while maintaining their reliability remains a definite necessity. From this point of view, a health monitoring system, designed to monitor the thermal and structural condition of a satellite during all its life stages, is expected to be a very useful tool. The authors are developing a health monitoring system for satellites utilizing a FBG (fiber Bragg grating) sensor. This paper first reports on a newly developed optical fiber connector that is used to install FBG sensors in satellite structures. Then, the assessment of a FBG sensor system in a space environment simulated in a thermal vacuum chamber is described. Finally, the results of an experimental study are presented in which damage due to thermal stress, that is typical in satellite structure, is detected by investigating the reflection spectrum from the embedded FBG sensor.

Reducing maintenance costs while keeping a constant level of safety is a major issue for Air Forces and airlines. The long term perspective is to implement condition based maintenance to guarantee a constant safety level while decreasing maintenance costs. On this purpose, the development of a generalized Structural Health Monitoring System (SHMS) is needed. The objective of such a system is to localize the damages and to assess their severity, with enough accuracy to allow low cost corrective actions. The present paper describes a SHMS based on acoustic emission technology. This choice was driven by its reliability and wide use in the aerospace industry. The described SHMS uses a new learning methodology which relies on the generation of artificial acoustic emission events on the structure and an acoustic emission sensor network. The calibrated acoustic emission events picked up by the sensors constitute the knowledge set that the system relies on. With this methodology, the anisotropy of composite structures is taken into account, thus avoiding the major cause of errors of classical localization methods. Moreover, it is adaptive to different structures as it does not rely on any particular model but on measured data. The acquired data is processed and the event's location and corrected amplitude are computed. The methodology has been demonstrated and experimental tests on elementary samples presented a degree of accuracy of 1cm.

Knowledge of integrity of in-service structures can greatly enhance their safety and reliability and lower structural maintenance cost. Current practices limit the extent of real-time knowledge that can be obtained from structures during inspection, are labor-intensive and thereby increase life-cycle costs. Utilization of distributed sensors integrated with the structure is a viable and cost-effective means of monitoring the structure and reducing inspection costs. Acellent Technologies is developing a novel system for actively and passively interrogating the health of a structure through an integrated network of sensors and actuators. Acellent's system comprises of SMART Layers, SMART Suitcase and diagnostic software. The patented SMART Layer is a thin dielectric film with an embedded network of distributed piezoelectric actuators/sensors that can be surface-mounted on metallic structures or embedded inside composite structures. The SMART Suitcase is a portable diagnostic unit designed with multiple sensor/actuator channels to interface with the SMART Layer, generate diagnostic signals from actuators and record measurements from the embedded sensors. With appropriate diagnostic software, Acellent's system can be used for monitoring structural condition and for detecting damage while the structures are in service. This paper enumerates on the SMART Layer and SMART Suitcase and their applicability to composite and metal structures.

Future military aircraft will be taking advantage of advances in optical information networks. Fly by Light will encompass not only using commercially based databus networks between processors but also incorporating purely optical sensors and transducers. Several types of optical transducers are available and have been demonstrated for feedback and health monitoring. Integration techniques that include optical tunable filters, high-speed switches, cross- connect switches, multiplexers and demultiplexers operating in the 1550-nm band have been demonstrated. This integrated approach shows the potential to reduce weight, increase bandwidth and improve supportability for production air vehicles.

This paper describes a smart monitoring system, incorporating optical fiber sensing techniques, capable of providing important structural information to designers and users alike. This technology has wide industrial and commercial application in areas including aerospace, civil, maritime and automotive engineering. In order to demonstrate the capability of the sensing system it has been installed in a 35m free-standing carbon fiber yacht mast, where a complete optical network of strain and temperature sensors were embedded into a composite mast and boom during lay-up. The system was able to monitor the behavior of the composite rig through a range of handling conditions. The resulting strain information can be used by engineers to improve the structural design process. Embedded fiber optic sensors have wide ranging application for structural load monitoring. Due to their small size, optical fiber sensors can be readily embedded into composite materials. Other advantages include their immediate multiplexing capability and immunity to electro-magnetic interference. The capability of this system has been demonstrated within the maritime and industrial environment, but can be adapted for any application.

Systems Planning and Analysis, Inc., under sponsorship from the Office of Naval Research (ONR), has developed a proprietary structural health monitoring system for large- scale structures based on optical fiber Bragg grating (FBG) sensors. This paper describes the operational capabilities of the health monitoring system and recent rest results on large-scale naval structures performed at Naval Surface Warfare Center, Carderock Division (NSWCCD). DSWDM technology developed under this effort is electro-optics based and has been shown to provide significantly higher sampling rates than comparative FBG interrogation technologies. The baseline system under development interrogates more than 120 sensors along five fiber channels. The prototype DSWDM system also possesses a number of advantages intrinsic to optical fiber sensors as compared to resistance strain gages (RSGs). These advantages include extremely low installed weight and volume, immunity to electromagnetic interference and corrosive environments, and low signal attenuation and drift. The LPD-17 propeller was retrofitted with 24 FBGs and strain and temperature data was recorded for direct comparison with conventional RSGs. Static and dynamic full- scale propeller operating loads were applied to the LPD-17 propeller. Sampling rates of approximately 1.7 kHz were demonstrated using the DSWDM system that provided good agreement in measured strain levels between FBGs and reference RSGs.

This paper describes the use of a fiber optic system to measure strain at thousands of locations along optical fibers where weakly reflecting Bragg gratings have been photoetched. The optical fibers were applied to an advanced composite transport wing long with conventional foil strain gages. A comparison of the fiber optic and foil gage systems used for this test will be presented including: a brief description of both strain data systems; a discussion of the process used for installation of the optical fiber; comparative data from the composite wing test; the processes used for the location and display of the high density fiber optic data. Calibration data demonstrating the potential accuracy of the fiber optic system will also be presented. The opportunities for industrial and commercial applications will be discussed. The fiber optic technique is shown to be a valuable augmentation to foil strain gages providing insight to structural behavior previously requiring reliance on modeling.

Composite propellers are subject to stringent quality control, extensive developmental testing, and ongoing health assessment. The feasibility of embedded fiber-optic smart instrumentation was examined for use in the commercial manufacture and testing processes used by Hartzell Propeller. Embedded extrinsic Fabry-Perot interferometric (EFPI) fiber-optic strain sensors were used for cure monitoring and material testing of a carbon-graphite plate. Strain was measured during the hot press cure of the four- ply 90/0/0/90 test article. Next, directional strain dependence on temperature and pressure was determined through controlled surveys. Finally, the fiber-optic strain readings were compared to surface resistive strain gage measurements during a tensile test. The cure strain data showed the effects of thermal mismatch between composite, resin, and the press platens. The temperature and pressure surveys validated the use of the sensors over a wide-range of environmental conditions, and the tensile test showed good correlation between embedded and surface strain measurements. Hence, the embedded sensors can provide information on internal strain that was extrapolated form external measurements previously. Experimental implementation of the sensors for cure monitoring and for developmental testing of propellers is ongoing.

A clear milestone has been reached in the development and demonstration of smart structures technologies for space applications. The success of recent space experiments not only demonstrates the feasibility of several new technologies, but also provides a glimpse of the various future opportunities available for research and development in the smart structures area. Three missions are discussed herein, as well as the role of the Air Force Research Laboratory (AFRL) and its government, industry, and academic partners in bringing them to fruition. The currently operating Vibration Isolation, Suppression, and Steering (VISS) space experiment and the Middeck Active Control Experiment Reflight (MACE-II), as well as the upcoming Satellite Ultra-quiet Isolation Technology Experiment (SUITE) are discussed in terms of notable achievements and lessons learned over the course of their execution. Directions for future research revealed by these experiments are also discussed, along with technology needs and transition opportunities for future operational systems.

In recent years, there has been a significant interest in, and move towards using highly sensitive, precision payloads on space vehicles. In order to perform tasks such as communicating at extremely high data rates between satellites using laser cross-links, or searching for new planets in distant solar systems using sparse aperture optical elements, a satellite bus and its payload must remain relatively motionless. The ability to hold a precision payload steady is complicated by disturbances from reaction wheels, control moment gyroscopes, solar array drives, stepper motors, and other devices. Because every satellite is essentially unique in its construction, isolating or damping unwanted vibrations usually requires a robust system over a wide bandwidth. The disadvantage of these systems is that they typically are not retrofittable and not tunable to changes in payload size or inertias. Previous work, funded by AFRL, DARPA, BMDO and others, developed technology building blocks that provide new methods to control vibrations of spacecraft. The technology of smart materials enables an unprecedented level of integration of sensors, actuators, and structures; this integration provides the opportunity for new structural designs that can adaptively influence their surrounding environment. To date, several demonstrations have been conducted to mature these technologies. Making use of recent advances in smart materials, microelectronics, Micro-Electro Mechanical Systems (MEMS) sensors, and Multi-Functional Structures (MFS), the Air Force Research Laboratory along with its partner DARPA, have initiated an aggressive program to develop a Miniature Vibration Isolation System (MVIS) (patent pending) for space applications. The MVIS program is a systems-level demonstration of the application of advanced smart materials and structures technology that will enable programmable and retrofittable vibration control of spacecraft precision payloads. The current effort has been awarded to Honeywell Space Systems Operation. AFRL is providing in-house research and testing in support of the program as well. The MVIS program will culminate in a flight demonstration that shows the benefits of applying smart materials for vibration isolation in space and precision payload control.

A high-performance vibration isolation system has been developed to isolate large-sensitive payloads from aircraft disturbances. The isolation system senses and adjusts for low frequency aircraft maneuvers and changes in the aircraft's flight angle of attack. Additionally, the isolation system passively filters higher frequency disturbances from aircraft to payload. Six pneumatic struts configured as a hexapod or Stewart Platform make up the primary portion of the isolation system and accomplish vibration isolation and payload support. Each isolator strut is a unique Patented design that takes advantage of gas (the ultimate smart material), because it has a capacity for large energy storage and it possesses a near linear viscosity over a broad temperature range. Any gas that exhibits a somewhat perfect-gas characteristic can be used inside the strut with similar performance results. For our application, gaseous nitrogen (GN2) was used. The pneumatic strut has shown an ideal isolator roll-off quality that is tunable for a variety of payloads and linear over a large dynamic range. Tunability stems from a dual chamber design that allows air-spring-rate changes while maintaining constant support of the load. The strut performance trait combined with the deterministic nature of the hexapod affords predictability and controllability. The system design enables a soft floating support of large payloads with accurate knowledge of their orientation with respect to the aircraft. Another distinctive feature of the isolation system design is a servo-controlled leveling system that senses a set point from an integrally mounted LVDT and fills or exhausts gas, as necessary, maintaining strut position during the rigors of flight. A combination of Commercial Off The Shelf (COTS) and control cards with custom plumbing provides the leveling function. All tolled, the isolation system has functioned flawlessly in service, and has raised the bar for vibration isolator performance. In this paper the isolation system design will be detailed, and its performance measurements will be presented.

This paper describes the development and capabilities of ELITE-3, a product that incorporates piezoelectric actuators to provide ultrastable work surfaces for very high resolution wafer production, metrology, microscopy, and other applications. The electromechanical, electronic, and software/firmware parts of the ELITE-3 active workstation are described, with an emphasis on considerations relating to the piezoelectric transducers. Performance of the system and its relation to the smart materials is discussed. As the floor beneath a vibration-sensitive instrument supported by ELITE-3 moves, piezoelectrics are controlled to minimize the motion of the instrument. A digital signal processor (DSP) determines the appropriate signals to apply to the actuators. A PC-based interface allows reprogramming of control algorithms and resetting of other parameters within the firmware. The modular product allows incorporation of vibration isolator, actuator and sensor modules into original equipment manufacturer (OEM) products. Alternatively, a workstation can be integrated as an integrated standalone system. The paper describes the system architecture, overall approach to vibration isolation, and various system components, and summarizes motivations for key design approaches.

The demand in the automobile sector for greater comfort in the vehicle is of a high importance alongside the requirements for a low emission of pollutants. With regard to a higher comfort the reduction of the interior noise level is mostly associated with a higher structural weight. It is for this reason that the application of so-called intelligent materials is appropriate since these can be used to realize an overall adaptive system. The materials under discussion are pizeceramic foils and fibers which can easily be fitted to thin-walled structures like a roof panel or a dash-board. Investigations have shown that the knowledge of the dynamic structural behavior is vital at the design of an adaptive system. Mostly this knowledge can only be gained by using sophisticated numerical models associated with a great effort of computing time. In order not to expand the computing time a model has been developed which allows a fast assessment of the dynamic behavior of a structure with integrated smart materials. The results of this model are presented for a flat steel plate with bonded piezoceramic foils. The accuracy of this model is being proved by the presentation of experimental results.

The possibility of using active control to reduce the sound radiated from a thin automotive panel between 30 and 250 Hz was explored. A steel panel representing a typical automotive application was selected, and QuickPack piezoceramic actuators were bonded on one side of the panel as a disturbance source, with inputs ranging from single-frequency sine wave to broadband band-limited white noise. A finite element model was created to determine the best sound radiating modes within the frequency band of interest, calculate mode shapes and determine the optimal location and size of the control actuators and sensors. Custom QuickPack devices were selected and bonded based on the results of the FEM. Optimal control laws were determined, using system models based on control and disturbance transfer functions. For narrowband control an inductive shunt was designed, where the kinetic energy generated when the plate moves is dissipated in a resonant RLC electric circuit. Also, both narrowband and broadband multiple input - multiple output (MIMO) control algorithms with two sensor and two actuator channels were designed and implemented on a digital signal processor (DSP). The overall sound radiated from the plate was reduced by 3dB RMS between 30-250Hz, while the peak sound reduction obtained at the target mode was 24dB.

There is significant human-system interaction in an automotive cockpit, and for particular components this interaction can be ever-present while being transient in nature. It is envisioned that environmentally responsive materials can be used in some components to accommodate personal and transient differences in the desired human-system interaction. Systems containing responsive gels have been developed to provide user activation and adjustment of the physical properties of a particular interior automotive component. Proprietary reverse viscosification gel formulations were developed that are thermally responsive. Formulations were modified to adjust the dynamic modulus and viscosity in terms of magnitude, amount of change over the viscosification transition, and the temperature over which the transition occurs. Changes in the physical properties of two orders of magnitude and more were achieved over a narrow transition region. Preliminary human factors assessment indicates that this order of magnitude of change is desirable. As the system of responsive gel, encapsulating material and activation mechanism is developed further, additional human factors studies will refine the desired physical properties and thermal activation mechanism. Ultimately, this system will have to perform over the broad range of temperatures imposed on interior automotive components and exhibit long-term durability chemically, physically and mechanically.

In several fields (optics, space, aircraft, fluid control, biomedical, and manufacturing) there is a strong need for compact, robust and efficient positioning mechanisms that also offer high precision, short response times, low power consumption, low electromagnetic interference and multiple degrees of freedom. Piezoelectric actuators are generally good candidates for building such mechanisms. The products manufactured by Cedrat Recherche SA are piezoelectric actuators offering compact size, high deformation (up to 1%) and high stiffness. These actuators have successfully passed different qualification tests (air and space qualification, lifetime tests). They can easily be integrated in applications, as shown by examples of mechanisms taken from various fields: a super amplified actuator for a MRI biomedical device, a tip-tilt for mirrors, a chopper for X-ray diffraction, a helicopter flap mechanism and an XYZ stage for the AFM microscope of the MIDAS instrument of the ESA ROSETTA space mission.

Numerous industrial applications that currently utilize expensive solenoids or slow wax motors are good candidates for smart material actuation. Many of these applications require millimeter-scale displacement and low cost; thereby, eliminating piezoelectric technologies. Fortunately, there is a subset of these applications that can tolerate the slower response of shape memory alloys. This paper details a proof-of-concept study of a novel SMA cage actuator intended for proportional braking in commercial appliances. The chosen actuator architecture consists of a SMA wire cage enclosing a return spring. To develop an understanding of the influences of key design parameters on the actuator response time and displacement amplitude, a half-factorial 2⁵ Design of Experiment (DOE) study was conducted utilizing eight differently configured prototypes. The DOE results guided the selection of the design parameters for the final proof-of-concept actuator. This actuator was built and experimentally characterized for stroke, proportional control and response time.

A piezohydraulic pump making use of the step and repeat capability of piezoelectric actuators has been developed for actuation of aircraft control surfaces. The piezohydraulic pump utilizes a piezoelectric stack actuator to drive a piston in a cylinder. The cylinder is fitted with two check valves. On the compression stroke, oil is forced out of the cylinder. On the intake stroke, oil is drawn into the cylinder. The oil is used to drive a linear actuator. The actuator was driven at 7cm/sec with a 271N (61lb) blocking force. To achieve this, the piezoelectric stack actuator was driven at 60Hz with a switching power supply. The system utilizes an accumulator to eliminate cavitation. This work discusses piezohydraulic pumping theory, pump design, and pump performance. Consideration of pump performance includes the effects of varying accumulator pressure, hydraulic oil viscosity, and load imposed on the linear actuator.

A low-mass sound generator with particularly good performance at low audio frequencies (i.e. 30 to 300 Hz) has been developed. The actuation component is a Thunder actuator (Face Int. Corp.). This actuator is coupled to a resonant compliant diaphragm to increase output in the low frequency band. The modal response of various 28 cm diameter prototypes was monitored using laser Doppler vibrometry and nearfield acoustic holography. The first mode appears near 40 Hz, with a maximum displacement of 3.4 microns per volt. Sound pressure levels measured in the farfield using 200 volts peak drive found nominal levels of 74+/- 6 dB(at 25 cm) over the band from 38 to 330 Hz. Near 45 and 100 Hz the SPL reaches 80 dB. (Above 330 Hz the output is higher, but remains well behaved to at least 2 kHz.) Higher outputs can be obtained by using a higher drive voltage and multiple devices. Because of its low mass, this device is particularly interesting for aerospace applications. This work was developed in the NRL/ONR Smart Blanket program, which is exploring the use of active controlled surface covers for reducing sound levels in payload fairing regions.

A new packaging technique for piezoceramic wafers is presented in which encapsulation of the piezoceramic incorporates the electrical leads. This technique for encapsulation produces a hermetically sealed package that also is flexible. The resulting product is called Flex-Patch because of the high flexibility. Micro-graphs of the flexed piezoceramic show that despite micro-cracking within the ceramic there is little, if any, loss in performance. Flex-Patch may be surface mounted or embedded into composites.

Small, autonomous mobile robots are needed for applications such as reconnaissance over difficult terrain or internal inspection of large industrial systems. Previous work in experimental biology and with legged robots has revealed the advantages of using leg actuators with inherent compliance for robust, autonomous locomotion over uneven terrain. Recently developed field-effect electroactive elastomer artificial muscle actuators offer such compliance as well as attractive performance parameters such as force/weight and efficiency, so we developed a small (670 g) six-legged robot, FLEX, using AM actuators. Electrically, AM actuators are a capacitive, high-impedance load similar to piezoelectrics, which makes them difficult to rive optimally with conventional circuitry. Still, we were able to devise a modular, microprocessor-based control system capable of driving 12 muscles with up to 5,000 V, operating form an on- board battery. The artificial muscle actuators had excellent compliance and peak performance, but suffered from poor uniformity and degradation over time. FLEX is the first robot of its kind. While there is room for improvement in some of the robot systems such as actuators and their drivers, this work has validated the idea of using artificial muscle actuators in biologically inspired walking robots.

The power requirements imposed on the amplifier by piezoelectric actuators in both open and closed loop vibration suppression control systems is discussed. We consider a two-degree-of-freedom mechanical system driven by a piezoelectric stack for the purpose of analyzing power flow and power dissipation. A state space model for this system that includes the electrical input and output variables of the piezoelectric actuator is developed. The power requirements of the open loop system are measured and compared to simulations performed with the state-space model. Results show that the simulations correlate well with the measured data. We then investigate the power requirements for two closed-loop vibration suppression control schemes. We show that the closed-loop power flow and power dissipation is a function of the type of feedback control law implemented. In our simulations, a feedback controller that introduces significant damping (approximately 70% critical) increases the frequency range in which real power is flowing between the actuator and the mechanical system. A controller that introduces only light damping is primarily reactive over the frequency range studied but exhibits a narrowband region of real power flow. Linear amplifier analysis demonstrates that the closed-loop control system must be considered in determining the power dissipation requirements for the control system.

As technologies for magnetorheological (MR) fluid hardware further evolve towards commercial adoption, the appeal for simpler, more cost-effective solutions becomes evident. While the skills involved in methods of manufacturing and cost-reduction efforts for mass production lie with the manufacturing community, practical and cost-effective MR technologies must first exist. As part of a 'whole approach' MR solution, the MR damper technology presented in this paper illustrates the development of a fast-response, low-power, cost-effective solution. Fundamentally, a competitive 'whole approach' active or semi-active MR solution can be viewed as system of separate components: parameter sensing, intelligent control, power delivery, and MR hardware technology. The development of any one single component should not successfully evolve without the addressing the cost efficiency and commercialization concerns of the other three. The MR hardware component should be predictable in performance behavior, capable of high damping force at minimal power, and fast in time response to complement simplified control schemes. The design effort is further challenged to meet these requirements within a simple, cost-effective package that holds commercial development appeal. This research includes the characterization of a new prototype MR damper including a description of the device technology, characterization test results and current work. It is evident by these results that this MR technology, comprising simple, commercial-off-the-shelf (COTS) components where possible, presents an attractive, practical and cost effective component of the 'whole approach' MR solution.

A new concept for pneumatic motion control is discussed that is enabled by magnetorheological (MR) technology. This concept involves placing MR braking devices functionally in parallel with pneumatic actuators. Through closed-loop feedback of a position sensor, accurate and robust motion control is achieved. Furthermore, these systems address many of the problematic issues associated with other pneumatic motion control systems such as: complexity, compliance and sensitivity to air quality. The basic system structure is presented as well as several concepts for MR-pneumatic actuators. A general control structure is proposed that can implicitly accommodate the inherent tradeoff between speed and accuracy in motion control systems. Some laboratory data is presented that explores the behavior of these systems and the nature of this tradeoff. Ideally, this technology will fill a niche between unsophisticated directional control and complex servo control systems.

One of the most exciting new applications for magnetorheological fluid technology is that of real-time controlled dampers for use in advanced prosthetic devices. In such systems a small magnetorheological fluid damper is used to control, in real-time, the motion of an artificial limb based on inputs from a group of sensors. A 'smart' prosthetic knee system based on a controllable magnetorheological fluid damper was commercially introduced to the orthopedics and prosthetics market in 2000. The benefit of such an artificial knee is a more natural gait that automatically adapts to changing gait conditions.

The Boeing Active Flow Control (AFC) System (BAFCS) is a DARPA sponsored program to develop AFC technology to achieve a significant increase in payload for rotorcraft applications such as the V-22 tiltrotor vehicle. The program includes Computational Fluid Dynamics (CFD) analysis, wind tunnel testing and development of smart material based AFC actuators. This paper will provide an overview of the program, concentrating on the development of the AFC actuators, and is an update of reference 1,2.

A summary of current research topics in active flow control at NASA Langley Research Center is presented. These topics are predominantly part of the Morphing Project, but closely related research topics form other projects are also included. A multi-disciplinary approach to technology development is being attempted that includes researchers from the more historical disciplines of fluid mechanics, acoustics, material science, structural mechanics, and control theory. The overall goals of the topics presented are focused on advancing the state of knowledge and understanding of controllable fundamental mechanisms in fluids rather than on specific engineering problems. The term micro used in the title indicates that the topics discussed are problems where a small, low-cost fluidic or shape-change input can create a large controllable output though the use of unsteady and nonlinear aerodynamics at receptive sties. Accompanying these fluid mechanics problems is the associated research in innovative actuators, sensors and control strategies including the development of design tools and system integration aids. The products of this research are to be demonstrated either in bench-top experiments, wind-tunnel tests, or in flight as part of the fundamental NASA R&D program and then transferred to more applied research programs within NASA, DOD< and U.S. industry.

Aircraft Manufactures are always searching for ways of improving aircraft performance. The aircraft engine inlet, or air induction system, has a major impact on the vehicle flight performance, mission effectiveness, and life cycle cost of the vehicle. Smart Materials technology applied to the aircraft engine inlet is a way to improve aircraft performance and enable new missions. The Smart Materials technology enables an unprecedented level of integration of sensors, actuators, and structures. Sater and et assess the status of the Smart Materials technology applications and demonstrations. This technology broadens the structural design envelope by increasing the adaptability of the structure to its surrounding flowfield. These new designs were not previously possible or practical with conventional structural materials and actuators due to their stiffness, weight, and size. With tools and processes now established, this technology can be integrated effectively into large- and full-scale Department of Defense (DoD) platforms, enabling new, high payoff mission capabilities. The Smart Aircraft and Marine Project System Demonstration (SAMPSON) program, a Defense Advanced Research Projects Agency (DARPA) funded, three-year, phased effort, managed by NASA Langley Research Center (NASA LaRC) and the Navy' s Office of Naval Research (ONR), will accomplish the first step towards this platform integration in two system level demonstrations of the application of Smart Materials and Structures technology in aircraft and marine vehicles. The aircraft demonstration will validate control of tactical aircraft inlet geometry and internal flows to provide improved range and survivability. The aircraft demonstration will consist of two wind-tunnel tests at NASA LaRC exhibiting physical shape change concepts on a full-scale F-15 fighter engine inlet.2 The primary focus of the SAMPSON marine effort is to develop and demonstrate smart applications for a large-scale marine systems. The marine demonstrations are documented separately. Both the aircraft and marine demonstrations provide significant risk reduction for transition of smart technologies to other applications by virtue of their scale (both structural and loading). Concurrently with the system demonstrations, the SAMPSON Consortium (consisting of Boeing, Electric Boat, and Pennsylvania State University) will establish the second step of the transition process by developing plans with the DoD to define in-flight and at-sea test programs for selected platforms. This will ensure a smooth transition from DARPA to the DoD users at the end of the program. The benefit of this program to the DoD is substantial risk reduction for transition of the technology to other platforms. This risk reduction will be accomplished through the demonstration of key smart materials and structures technologies in both aircraft inlets and marine systems. The validation of these key technologies in large-scale demonstrations will facilitate their application in production vehicles to enable new, high payoff mission capabilities at an affordable cost. This paper documents the first wind-tunnel test of the SAMPSON Smart Inlet in the NASA LaRC l6Foot Transonic Tunnel. The test was completed in the spring of 2000.

A compact high-torque rotary motor was developed for use in large-displacement structural shape control applications. The main principle underlying its operation is rectification and accumulation of small resonant displacement of piezoelectric bimorphs using roller clutches as mechanical diodes. On the driving half of each cycle, the forward motion of the bimorph is converted to rotation of the shaft when the hub drive torque exceeds that of the load. On the recovery half of each cycle, a second, fixed, roller clutch prevents the load from backdriving the shaft. This approach substantially increased the output mechanical power relative to that of previous inchworm-type motor designs. Experiments to date, conducted under conditions of continuous operation at a 90 Vrms drive level, have demonstrated a stall torque of about 0.4 N-m, a no-load speed of about 750 RPM, peak power output greater than 1 W, and power density of about 5 W/kg. While not yet competitive with conventional motor technologies, this motor may also be fabricated in unusual (i.e., non-cylindrical) form factors, enabling greater geometric conformability than that of typical motors. The use of commercial roller clutches, piezoelectric bimorphs, and single frequency drive signals also results in a simple, inexpensive design.

In late 1997 under ONR and DARPA funding members of the SAMPSON Marine Naval Team (Naval Surface Warfare Center, Lockeed Martin and General Dynamics Electric Boat) began investigating the benefits of the tab assisted control (TAC) concept for underwater control surfaces. Results of water tunnel tests conducted in 1998 indicated that the addition of a small trailing-edge tab, typically 10% of the mean chord of the entire control surface structure, vastly enhances the versatility of the control surface system. Depending on the orientation of the tab with respect to the primary control surface (flap) this tab may be used to significantly modify lift, reduce torque, and increase maneuvering capabilities. In 1999 a plan was established to actuate the tab with Shape Memory Alloy (SMA) actuators as a first step towards development of a continuously compliant or flexible control surface similar to that demonstrated in the DARPA Smart Vortex Leveraging Tab (SVLT) program. Testing of a SMA-actuated TAC device occurred late summer 2000. This paper presents a summary of these activities as well as current plant to test and evaluate the FlexTAC (Flexible Tab Assisted Control) concept, which replaces the tab with a continuously compliant trailing edge.

The ability to control fan nozzle exit area is an enabling technology for next generation high-bypass-ratio turbofan engines. Performance benefits for such designs are estimated at up to 9% in thrust specific fuel consumption (TSFC) relative to current fixed-geometry engines. Conventionally actuated variable area fan nozzle (VAN) concepts tend to be heavy and complicated, with significant aircraft integration, reliability and packaging issues. The goal of this effort was to eliminate these undesirable features and formulate a design that meets or exceeds leakage, durability, reliability, maintenance and manufacturing cost goals. A Shape Memory Alloy (SMA) bundled cable actuator acting to move an array of flaps around the fan nozzle annulus is a concept that meets these requirements. The SMA bundled cable actuator developed by the United Technologies Corporation (Patents Pending) provides significant work output (greater than 2200 in-lb per flap, through the range of motion) in a compact package and minimizes system complexity. Results of a detailed design study indicate substantial engine performance, weight, and range benefits. The SMA- based actuation system is roughly two times lighter than a conventional mechanical system, with significant aircraft direct operating cost savings (2-3%) and range improvements (5-6%) relative to a fixed-geometry nozzle geared turbofan. A full-scale sector model of this VAN system was built and then tested at the Jet Exit Test Facility at NASA Langley to demonstrate the system's ability to achieve 20% area variation of the nozzle under full scale aerodynamic loads. The actuator exceeded requirements, achieving repeated actuation against full-scale loads representative of typical cruise as well as greater than worst-case (ultimate) aerodynamic conditions. Based on these encouraging results, work is continuing with the goal of a flight test on a C-17 transport aircraft.

The DARPA/AFRL/NASA Smart Wing program, conducted by a team led by Northrop Grumman Corporation (NGC) under the DARPA Smart Materials and Structures initiative, addresses the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. This paper presents an overview of the smart wing program. The program is divided into two phases. Under Phase 1, (1995 - 1999) the NGC team developed adaptive wing structures with integrated actuation mechanisms to replace standard hinged control surfaces and provide variable, optimal aerodynamic shapes for a variety of flight regimes. Two half-span 16% scale wind tunnel models, representative of an advanced military aircraft wing, one with conventional control surfaces and the other with shape memory alloy (SMA) actuated smart control surfaces, were fabricated and tested in the NASA Langley Research Center (LaRC) Transonic Dynamics Tunnel (TDT) wind tunnel during two series of tests, conducted in May 1996 and June 1998, respectively. Details of the Phase 1 effort are documented in several papers. The on-going Phase 2 effort discussed here was started in January 1997 and includes several significant improvements over Phase 1: 1) a much larger, full-span model; 2) both leading edge (LE) and trailing edge (TE) smart control surfaces; 3) high-band width actuation systems; and 4) wind tunnel tests at transonic Mach numbers and high dynamic pressures (up to 300 psf.) representative of operational flight regimes. Phase 2 includes two wind tunnel tests, both at the NASA LaRC TDT - the first one was completed in March 2000 and the second (and final) test is scheduled for April 2001. The first test-demonstrated roll-effectiveness over a wide range of Mach numbers achieved using a combination of hingeless, smoothly contoured, SMA actuated, LE and TE control surfaces. The second test addresses the development and demonstration of high bandwidth actuation. An overview of the Phase 2 effort is presented here; detailed discussions of the wind tunnel testing, model design and fabrication, and actuation system development are given in companion papers.

A wind tunnel demonstration was conducted on a scale model of an unmanned combat air vehicle (UCAV). The model was configured with traditional hinged control surfaces and control surfaces manufactured with embedded shape memory alloys. Control surfaces constructed with SMA wires enable a smooth and continuous deformation in both the spanwise and cordwise directions. This continuous shape results in some unique aerodynamic effects. Additionally, the stiffness distribution of the model was selected to understand the aeroelastic behavior of a wing designed with these control surfaces. The wind tunnel experiments showed that the aerodynamic performance of a wing constructed with these control surfaces is significantly improved. However, care must be taken when aeroelastic effects are considered since the wing will show a more rapid reduction in the roll moment due to increased moment arm about the elastic axis. It is shown, experimentally, that this adverse effect is easily counteracted using leading edge control surfaces.

Building on the research performed during the DARPA / AFRL Smart Wing Phase 1 program to improve vehicle aerodynamic efficiency using control surfaces actuated by smart materials, the goal of the Phase 2, Test 1 effort was to increase the size of the model and the control surfaces and conduct wind tunnel tests at higher dynamic pressure and Mach number. This paper describes 1) model design for required safety and increased aileron effectiveness at high dynamic pressure; 2) model instrumentation; 3) SMA actuator control system design and implementation and 4) wind tunnel test results. Pictured below (Figure 1) is the model installed in the NASA Langley's Transonic Dynamic Tunnel (TDT).

A key objective of the Smart Wing Phase 2, Test 2 is to demonstrate high-rate actuation of hingeless control surfaces using smart material-based actuators. Actuation rates resulting in a minimum of 20 degree(s) flap deflection in 0.33 sec, producing a sweep rate of at least 60 degree(s)/sec, are desired. This sweep rate is similar to those specified for many of the existing military platforms with hinged control surfaces. The ability to deploy control surfaces without discrete hingeline would, however, enhance platform mission by reducing radar cross section and improving aerodynamic performance. Studies on numerous actuation concepts and flexible structures were executed during the early and mid phase of the program in an effort to satisfy these goals. In the first study, several actuation concepts with different transducers were modeled and analyzed. These concepts included distributed piezoelectric stack actuators with and without hydraulic amplifiers and pumps, antagonistic tendon actuation, and eccentuation. The transducers selected for the trade studies included piezoelectric ultrasonic motors, actively cooled SMA, ferromagnetic SMA, and stacks made from piezoelectric ceramic wafer, piezoelectric single crystal wafer, irradiated PVDF-TrFE film, and dielectric elastomer film. Although many of the technologies are not fully mature, they provide a glimpse of what improvements could be possible with their successful development. The studies showed that distributed polymer stacks provided the most elegant solution, but eccentuation was deemed the most realistic and lowest risk approach to attaining the program goals. A common issue to all the concepts was the structural stiffness that the actuators worked against. This was resolved in the second study by developing a flexcore- elastomeric skin trailing edge structure with eccentuation using high power ultrasonic motors. This paper describes the two studies and the final concept in detail.

Due to its simple and predictable molecular recognition chemistry, DNA is a versatile self-assembly molecule. Two strands of DNA most strongly bind together to form a double helix only when their base sequences are complementary. Here we show how this construction rule can be used to induce nanoscale motion. In particular, we have devised two DNA-based molecular motors powered by DNA. Both consist of two double-stranded arms held together at one end by a single-stranded flexible hinge. One motor, referred to as molecular tweezers, has two single-stranded extensions at the ends of the arms, which serve as handles used to pull the tweezers shut. The tweezers are closed when a particular piece of single-stranded DNA, called the fuel strand, hybridizes with the handles. In the other motor, referred to as an actuator, the single-stranded extensions are joined together so that the motor forms a loop-like structure. The fuel strand hybridizing with the actuator pushes the two arms apart. Both motors are returned to their original configuration by a removal strand which binds to a single-stranded overhang of the fuel strand and then removes the fuel strand from the motor strand by the process of branch migration.

A simple design study is conducted to investigate the feasibility of using piezoelectric materials in a power supply for an in vivo MEMS application. An analysis is presented comparing the 33- and 31- modes of operation for a piezoelectric generator. It will be shown that a transversely loaded membrane (31-mode) or thin plate element has a mechanical advantage in converting applied pressure to working stress for piezoelectric conversion. A design study is carried out using a square PZT-5A membrane driven by a fluctuating pressure source (blood pressure). The expected power output from a 1cm 2 plate is calculated for a range of thicknesses, along with the power output from a 9micrometers thick plate for a range of areas. Additionally, the feasibility of providing intermittent power instead of continuous power or increased excitation frequency will be shown. The primary conclusion of this analysis is that an in vivo piezoelectric generator on a size scale of 1cm ²may be able to power a MEMS application in the (mu) W power range continuously, and up to the (mu) W range intermittently.

At present the ability to control the properties of polymeric materials through manipulation of microstructure is limited due to synthetic procedures that usually afford materials with considerable heterogeneity of molecular architecture. Although conventional polymer synthesis has enabled the preparation of wide variety of materials for diverse technological applications, the next generation of advanced materials will likely encompass design concepts from natural systems, such as tissues and bone, in which complex hierarchical structures are synthesized with very high specificity. Emulation of these natural systems requires the precise specification of intermolecular interactions between materials components, which necessitates the near-absolute control of molecular structure that is currently inaccessible via conventional materials synthesis. However, protein-based materials can be synthesized with near absolute uniformity of macromolecular architecture using in vivo biosynthesis, and may be considered model uniform polymers capable of forming hierarchically ordered systems with multiple levels of interactive structure. By utilizing the principles of protein structure and the concepts of polymer materials science, non-natural protein-based polymers can be designed that are capable of being elaborated into materials targets with unique properties that arise as a consequence of their structural specificity (Scheme 1). Novel methods for the facile construction of concatameric genes that encode precisely defined, repeating peptide blocks have been developed,1 which have enabled the preparation of protein polymers with near-absolute control of size, composition, sequence, and stereochemistry. Using this approach, protein polymers have been designed on the basis of structural features programmed into the polypeptide at the molecular level that self-assemble into lamellar crystallites,2 lyotropic smectic mesophases,3 and thermo-reversible nanoparticles.4 Study of these materials is essential for understanding the elements of structure-based design in materials research, but the design principles elucidated in these studies may have potential for applications in medicine and nanotechnology.

Significant opportunities exist for the processing of synthetic and biological polymers using electric field (electroprocessing). We review casting of multi-component films and the spinning of fibers in electric fields, and indicate opportunities for the creation of smart polymer systems using these approaches. Applications include 2D substrates for cell growth and diagnostics, scaffolds for tissue engineering and repair, and electromechanically active biosystems.

Significant reduction of helicopter blade-vortex interaction (BVI) noise is currently one of the most advanced research topics in the helicopter industry. This is due to the complex flow, the close aerodynamic and structural coupling, and the interaction of the blades with the trailing edge vortices. Analytical and numerical modeling techniques are therefore currently still far from a sufficient degree of accuracy to obtain satisfactory results using classical model based control concepts. Neural networks with a proven potential to learn nonlinear relationships implicitly encoded in a training data set are therefore an appropriate and complementary technique for the alternative design of a nonlinear controller for BVI noise reduction. For nonlinear and adaptive control different neural control strategies have been proposed. Two possible approaches, a direct and an indirect neural controller are described. In indirect neural control, the plant has to be identified first by training a network with measured data. The plant network is then used to train the controller network. On the other hand the direct control approach does not rely on an explicit plant model, instead a specific training algorithm (like reinforcement learning) uses the information gathered from interactions with the environment. In the investigation of the BVI noise phenomena, helicopter developers have undertaken substantial efforts in full scale flight tests and wind tunnel experiments. Data obtained in these experiments have been adequately preprocessed using wavelet analysis and filtering techniques and are then used in the design of a neural controller. Neural open-loop control and neural closed-loop control concepts for the BVI noise reduction problem are conceived, simulated and compared against each other in this work in the above mentioned framework.

The hysteresis between transformation to martensite and austenite in a SMA is discussed here as an intrinsic material property to be used to enhance damping. Initially the SMA constitutive modeling is described on a thermomechanical basis before considering the coupling of the SMA with a host structure targeting in the long term to a composite. The different parameters influencing damping with regard to the applied loads is discussed and conclusions are drawn with regard to how these parameters have to be set such that damping of a SMA-composite can be optimized.

This paper explains how a piezoelectric bimorph actuator may be used as a multifunction device in a handheld electronics product - replacing traditional buzzers, rotary motors, and voice coil speakers to supply tone alert, vibrating alert and loudspeaker functions in a single device. The first development hurdle was to establish performance metrics which could be used to compare the piezoelectric device to traditional technologies. Subjective user testing was combined with mathematical modeling to create design specifications. The next challenge was to establish design guidelines, since the device performance is integrally tied to the OEM housing design. Finally, new production testing methodologies were developed that would correlate stand-alone component performance with final system performance.

For some structural components conventional methods of loads and usage monitoring, supplemented by on ground NDT measurements to detect damages can be unsatisfying due to various reasons: low reliability of sensing technique or low accessibility and sometimes high cost of dismantling for regular NDT. Sensor methodologies having evolved form conventional ultrasonic inspection in principle have the potential to detect damages in various types of structures: 2D, 3D, metal, composite - provided significant interaction of ultrasonic waves with local damage is given. SWISS (Smart Wide-area Imaging Sensor System) requires a physical interaction model of ultrasonic excitation with structure and its potential damage and merges sensor data to determine spatial distribution of impedance by imaging which performs localization and sizing of damage in one. Second: use of signal and image processing techniques to alert when damage becomes critical. SWISS has been designed by EADS to image various types of damage from considerate distance by means of permanently installed piezo-elements. SWISS features a sensor minimization to achieve low weight and still high reliability and the use of cheap electronics but clever testing and analyzing to achieve low cost for in-service application. SIEMENS NDT has been able to demonstrate SWISS functionality on complex components by appropriate use of Phased Arrays.