The last two decades have seen evolution of smart materials and structures technologies from theoretical concepts to physical realization in many engineering fields. These include smart sensors and actuators, active damping and vibration control, biomimetics, and structural health monitoring. Recently, additive manufacturing technologies such as 3D printing and printed electronics have received attention as methods to produce 3D objects or electronic components for prototyping or distributed manufacturing purposes. In this paper, the viability of manufacturing all-printed smart structures, with embedded sensors and actuators, will be investigated. To this end, the current 3D printing and printed electronics technologies will be reviewed first. Then, the plausibility of combining these two different additive manufacturing technologies to create all-printed smart structures will be discussed. Potential applications for this type of all-printed smart structures include most of the traditional smart structures where sensors and actuators are embedded or bonded to the structures to measure structural response and cause desired static and dynamic changes in the structure.
In recent years, wireless strain sensors have received attention as an efficient method to measure response of a structure
in a remote location. Wireless sensors developed for remote measurement include RF wireless sensor modules and
microstrip antenna-based sensors. In this paper, a simple wireless vibration sensor based on a piezoelectric sensor and
the Frequency Modulation (FM) technique is developed for remote measurement of vibrating structures. The
piezoelectric sensor can generate a voltage signal proportional to dynamic strain of the host structure. The voltage signal
is then frequency modulated and transmitted wirelessly to a remote station by a simple FM transmitter circuit. Finally,
the received signal is demodulated by a conventional FM radio circuit, and the vibration measurement data can be
recovered. Since this type of wireless sensor employs a simple FM circuit, they do not require any wireless data
transmission protocols allowing a low-cost wireless sensor in compact format. The proposed concept of the wireless
vibration measurement is experimentally verified by measuring vibration of an aluminum cantilever beam. The proposed
sensor could potentially be an efficient and cost effective method for measuring vibration of remote structures for
dynamic testing or structural health monitoring.
In recent years, printed electronics have received attention as a method to produce low-cost macro electronics on flexible
substrates. In this regard, inkjet and aerosol printing have been the primary printing methods for producing passive
electrical components, transistors, and a number of sensors. In this research, a custom aerosol printer was utilized to
create a strain sensor capable of measuring static and dynamic strain. The proposed sensor was created by aerosol
printing a multiwall carbon nanotube solution onto an aluminum beam covered with an insulating layer. After printing
the carbon nanotube-based sensor, the sensor was tested under quasi-static and vibration strain conditions, and the results
are presented. The results show that the printed sensor could potentially serve as an effective method for measuring
dynamic strain of structural components.
Recently, printed electronics have received growing attention as a new method to produce low-cost large-area
electronics on flexible substrates. Much of the current research relies mainly on an inkjet printing technique to deposit
electrically functional material solutions onto plastic substrates in order to fabricate various electronic components such
as resistors, capacitors and transistors. In this paper, we propose to apply the printed electronics technology to the
development of strain sensors for the purpose of measuring structural vibration. To accomplish this, we have developed
an aerosol printing system that exhibits better performance in printing on various types of substrates. The system
consists of a moving platform, an ultrasonic atomizer, and a shutter to control the flow of the aerosol. Using the system,
we demonstrate that a functional strain sensor can be printed directly on the surface of a nonmetallic structure. To form a
strain sensor, a water-based conductive polymer, PEDOT-PSS, was deposited on a plastic substrate using the aerosol
printer. Then, the piezoresistive response of the printed strain sensor was measured for three different low frequency
dynamic strain loadings. The results showed that this type of printed strain sensor can be used to measure the vibration
of the host structure. The result of this research will serve as a critical step toward the fabrication of self-sensing
structures with printed sensors and accompanying electronics.
Recently, a new design concept for multifunctional fasteners using smart materials was proposed by the authors. These
piezoelectric devices, named 'smart fasteners,' can be fabricated by modifying the design of ordinary fasteners such that
they have a piezoelectric transducer and a control unit embedded in their body. These smart fasteners can not only clamp
structural members like ordinary fasteners but also induce or detect structural responses. In this paper, the capability of
the smart fasteners to excite and detect Lamb waves in the clamped structure for structural health monitoring is
presented. For this purpose, a mathematical model for the Lamb wave excitation with the smart fasteners is derived first
using the potential function method. By applying the space domain Fourier transform, the model is transformed into the
wave number domain where the boundary conditions are applied to get the solution. The obtained solution is then
converted back into the physical space using the inverse Fourier transform. Finally, closed-form solutions for the surface
displacements are obtained using the residue theorem in the complex plane. With the analytic solutions, mode tuning capabilities of the smart fasteners are analyzed and then experimentally verified.
In this paper, a new design concept for multifunctional fasteners using smart materials is presented. The proposed
piezoelectric devices, named 'smart fasteners,' can be fabricated by modifying the design of ordinary fasteners such that
they have a piezoelectric element and a control unit embedded in their body. These smart fasteners can not only clamp
structural members like ordinary fasteners but also measure the response of the structure and generate forces to enhance
the dynamic performance of the structure. Due to their fastener-type design, they are more convenient to install onto or
remove from structures compared to conventional piezoceramic patch actuators for which a bonding epoxy layer needs
to be applied. In order to demonstrate their applicability in active vibration controls, a simulation study was conducted
on a fixed-fixed beam structure. Since the control force is applied at the boundary of the structure where the smart
fasteners are attached, a new control algorithm called Active Boundary Control (ABC) was developed using the
Lyapunov's direct method. The simulation results show that smart fasteners can be used to suppress vibration of the
beam by applying the Lyapunov-based Active Boundary Control algorithm.
Proc. SPIE. 6173, Smart Structures and Materials 2006: Smart Structures and Integrated Systems
KEYWORDS: Actuators, Computational fluid dynamics, Ferroelectric materials, Control systems, Computer simulations, Kinematics, Finite element methods, Microsoft Foundation Class Library, Aerodynamics, Smart materials
A novel Morphing Flight Control Surface (MFCS) system has been developed. The distinction of this research effort is that the SenAnTech team has incorporated our innovative Highly Deformable Mechanism (HDM) into our MFCS. The feasibility of this novel technology for deformable wing structures, such as airfoil shaping, warping or twisting with a flexure-based high displacement PZT actuator has been demonstrated via computational simulations such as Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD). CFD was implemented to verify the accuracy of the complex potential flow theory for this application. Then, complex potential flow theory, kinematics, geometry, and static force analysis were incorporated into a multidisciplinary GUI simulation tool. This tool has been used to aid the design of the MFCS. The results show that we can achieve up to five degrees of wing twisting with our proposed system, while using minimal volume within the wing and adding little weight.
A new Sensor Validity Monitoring, Verification, and Accommodation (SVMVA) technique based on an artificial neural network is developed for a self-repairing Flight Control System (FCS). For the proposed system, the Learning Vector Quantization (LVQ) method is employed as the on-line, real time learning, monitoring, and estimation tool. In order to conduct a feasibility study, we applied the developed algorithm to a flight vehicle simulator. The simulation results show that the proposed SVMVA with LVQ can instantly detect the failure of physical sensors and accommodate them for more than 30 minutes. By employing this type of analytical sensor redundancy, a flight vehicle can save power, weight, and space, which are required for installing redundant physical sensors.
A vibration confinement is the act of restricting the vibration of a structure to a certain region on the structure. Confinement or restriction of vibrations to relatively unimportant areas helps in isolating vibration-sensitive components from vibratory disturbances and mitigating the damage of the components. In this research, an active vibration confinement technique based on full state feedback strategy, which was proposed by previous authors, is experimentally implemented and verified. The algorithm constructs a square matrix of the closed-loop eigenvectors and a rectangular matrix of the corresponding control vectors. Then, the control gain is uniquely determined by right-multiplying the inverse of the eigenvector matrix to the control vector matrix. The experiment is conducted for a pinned-pinned aluminum beam with two piezoelectric film sensors and two piezoceramic actuators bonded symmetrically along the beam. The vibration of the beam is estimated using an observer and the control actuation is realized using two piezoceramic patch actuators. Experimental results show that active vibration confinement can actually be realized for a lightly damped system with piezoceramic patch actuators.
The work in this study develops the framework for placement and actuation of novel mechanically reconfigurable dual-offset contour beam reflector antennas (DCBRA). Towards that end the methodology for the antennas' design is defined. The antenna designed in this study employs piezoelectrically driven ball screw actuators. These actuators are attached to a flexible sub reflector surface and are used to vary radiation pattern. In addition, two separate optimization problems are stated and solved: Actuator position optimization and actuation value optimization. For the former, a method termed as Greatest Error Suppression method is proposed where the position of each actuator is decided one by one after each evaluation of the error between the desired subreflector shape and the actual subreflector shape. For the second problem, a mathematical analysis shows that there exists only one optimal configuration. Two optimization techniques are used for the second problem: the Simulated Annealing algorithm and a simple univariate optimization technique. The univariate technique always generates the same optimal configuration for different initial configurations and it gives the low bound in the evaluation of the error. The Simulated Annealing algorithm is a stochastic technique used to search for global optimum point. Finally, as an example, the results of the proposed optimization techniques are presented for the generation of a subreflector shape for the geographical outline of Brazil.
A novel way to design, synthesize and adjust the reconfigurable dual offset contour beam reflector antenna employing an adjustable subreflector is presented. The work also presents a graphical user interface based computer code that connects the electro-magnetic effects to the mechanical surface deflections. The subreflector surface is described by using the finite element method and the far-field radiation pattern is calculated by reflector diffraction synthesis. The reflector surface shape is adjusted using a set of linear piezoelectric point actuators attached to its back surface, from which the diffraction synthesis code calculates the radiation pattern. An example of this method applied to the contiguous US is also presented. As a future work, a software package will be built where the finite element code and the diffraction synthesis code are combined, and it will be used for advanced actuator placement and reflector design problem.
Recently, singly curved smart antennas that have the ability of changing their reflector shape through the use of piezoelectric actuators have been studied. The results show that those antennas have the ability to steer and shape radiation patterns in the far-field. As an extension of the previous work, this study examines the use of `doubly curved'--spherical--antenna structures to achieve better performance in controlling an antenna's coverage area. The spherical antenna is made of a thin plastic shell with a small hole at the apex for base mounting. As actuators, four PZT strip patches are attached along the meridians separated by 90 degrees respectively. The antenna structure is modeled following Reissner's shallow spherical shell theory, and the forces developed by the PZT actuators are applied as the boundary conditions at the outer edge. The deformed shape of the antenna is calculated with respect to the applied voltage and the far-field radiation pattern for the shape is simulated on the computer. Based on the theoretical work, an actual working model of the doubly curved antenna is built. Several experiments with the model verify that the beam steering and beam shaping mode can be achieved in the real situation.
Recently, it has been demonstrated that aperture antennas can have their performance improved by utilizing PVDF as a shape controlling actuator. Since PVDF is a polymer with limited control authority, these antennas can only be employed in space based applications. This study examines more robust antenna structures devised of a thick metalized substrate with surface bonded piezoceramic (PZT) actuators. In this work, PZT-actuated adaptive antennas of cylindrical- cut shape are studied. First, the PZT-actuated antenna surface is modeled based on the classical curved beam theory and Newton's method. Second the Voltage vs. Deflection relationship is experimentally verified. Third, the resulting far field radiation pattern is simulated on computer.