Table of contents

The design and development of a smart wireless system for remote reading of a passive surface acoustic wave (SAW) sensor is presented in this paper. The SAW sensor is a lithium niobate wafer with an inter-digital transducer (IDT) with reflectors, which is inductively coupled to a microstrip meander antenna (ICMA). The reading system is a special FM radar, which transmits and receives FM electromagnetic signals. The transmitted FM signal is picked up by the ICMA which subsequently, converts into a SAW in the LiNbO₃ wafer through the IDTs. These SAWs are reflected back to the IDTs by the reflectors, converted back to an electromagnetic wave and returned to the FM radar by the ICMA. The acoustic velocity varies as a function of the propagation characteristics of the SAW in the substrate and results in varying time delay of the echoes, which is detected by the system. The resolution and accuracy of such a system are investigated theoretically and experimentally. The operating principle is evaluated for a remote temperature measurement system. The salient feature of this system is that no power source is required at the sensor and thus is applicable for remote temperature sensing of propellant in barrel-launched adaptive munitions (BLAM), tank rounds and other munitions and missiles. This is also suitable for other remote reading SAW sensors such as indentity tags, wireless pressure sensors, wireless gas sensors, strain sensors, hospital sterilizer sensors, etc.

Cement-matrix composites for smart structures are reviewed. The functions include strain sensing, damage sensing, temperature sensing, thermoelectricity, vibration reduction and radio wave reflection. The functions are rendered by the use of admixtures, such as short carbon fibers, short steel fibers and silica fume.

Smart structural systems require the electronic control systems which are integrated into the structures to be small, light weight and power-efficient. The field programmable gate array (FPGA) is a good platform to implement such controllers. In our previous work, FPGA-based digital controllers were built and tested on a simple structural system. In order to implement multivariable controllers, the hardware resources for FPGA-based architecture need to be further reduced. Distributed arithmetic (DA) has long been proven to be a very efficient means to mechanize computations that are dominated by inner products involving constant multiplicand. The computational requirements of the smart structural controllers match this type very well. In this paper various DA structure controllers are designed and results are compared with multiply-and-accumulate structure controllers. Single- and multi-variable controllers are implemented and tested on a cantilevered beam.

Nano- and micro-coiled carbon fibers find applications in electronic devices, electromagnetic absorbers and filters. Smart devices can be conceived using tunable films on these fibers and tunable host materials. A new method of producing helical carbon fibers with dimensions in the order of less than a micrometer has been developed using microwaves. The microwave CVD system presented here eliminates the use of the toxic impurity gas, which is required in the conventional method. Both methods involve gas phase reactions over a substrate seeded with an appropriate catalyst. Micro-coiled carbon fiber (MCCF) was grown by the catalytic pyrolysis of acetylene on a silicon carbide substrate on which nickel metal powder was dispersed as a catalyst. Various factors, for example flow rate of the gas, particle size of the catalyst, effect of reaction temperature and time, were studied in order to understand the growth of the microwave synthesis of MCCF. MCCFs were also synthesized by a conventional method in the presence of thiophene as an impurity gas so that a comparison can be made with the materials obtained by the microwave system. The morphology of the final products were investigated by scanning electron microscopy. The carbon products obtained by traditional and microwave methods were investigated with the help of x-ray diffraction. The effect of various reaction conditions on the morphological development of a MCCF were examined in detail. Furthermore, a brief study was made on the microwave absorbing property of the MCCF.

A new type of remote query sensor for monitoring pressure, relative humidity, and phase-transitions is presented. The sensor consists of a planar inductor-capacitor resonant circuit, the resonant frequency of which changes in response to different environmental parameters. The sensor does not require an internal power source, rather it responds to the interrogation field. A loop antenna is used to monitor the sensor.

Delamination damage in composite rotorcraft flexbeams caused by excessive vibratory and fatigue loads can lead to degradation in flapwise and lagwise performance of the rotor blade. In addition, delaminations can result in rapid fatigue failure of these tailored composite elements leading to catastrophic results. A novel damage detection strategy is evaluated in this work which attempts to exploit the dereverberated transfer function response of beams with tapered geometries. This approach avoids high fidelity finite element models of damaged one-dimensional beams with non-uniform geometries. To obtain the dereverberated transfer function response, a virtual control force is applied to the reverberated transfer function response to remove resonant and anti-resonant dynamics associated with the beam's boundary conditions. Magnitude and phase characteristics between each actuator and sensor can then be used to infer changing structural properties. Analytical and experimental results suggest that this approach can be used to quantitatively and qualitatively infer delamination damage in non-uniform beams. Experimental results are displayed for beams with varying thickness and width tapers.

Vibrations of a non-uniform circular cylindrical ceramic piezoelectric shell rotating about its axis are studied. It is shown that the shell can be used as a rotation sensor to measure the angular rate of a rotating body. Two-dimensional equations for a piezoelectric shell are employed. The sensitivity of the sensor and its dependence on various physical and geometric parameters are examined.

This paper introduces a phenomenological algorithm for simulation of rate independent hysteretic responses of shape memory alloys (SMAs) in cyclic uniaxial thermomechanical loads. The algorithm is proposed in a compact differential form that uses only seven well-defined material parameters and is adjustable to a particular alloy by fitting a single experimental pseudoelastic loop. It has been developed as a tool for predictions of history dependent uniaxial σ-ε-T responses of SMA elements to be embedded into the smart structures and composites. Simulated model responses to a variety of thermomechanical loading paths, including partial internal loop behaviours, are demonstrated. The computer program with a numerically implemented algorithm is available on the Internet.

A smart structure is one that senses its internal state and external environment, and based on the information gained responds in a manner that fulfils its functional requirements. The primary advantage of moving towards smart structures technology is the potential cost benefit of condition-based maintenance strategies and the prospective life extension that may be achieved through in situ health monitoring. The monitoring of operational health and performance, and diagnosis of any faults as they occur, is a relatively new concept that is being developed globally to provide advantages of safer , more reliable and affordable structures. Health monitoring can be achieved by positioning (embedded or surface mounted) sensor systems on a structure to measure those physical parameters that are informative with respect to the state of the structural health. Information relating to the severity and location of damage, as well as to the nature of the loading is of obvious importance to this endeavour.

In the aerospace industry bonded composite patches are increasingly being used to extend the operational life of ageing aircraft. The application of bonded composite patches to repair or reinforce defective metallic structures is widely acknowledged as an effective and versatile procedure. Such patches have been successfully applied to the repair of cracked structures, to the reinforcement of components subject to material loss due to corrosion damage and as a general means of stress reduction through the provision of a supplementary load path. However, certification requirements mandate the need for a methodology for monitoring the damage state of both the defective underlying structure and of the repair. In this case the concept of smart structures can be used to detect damage in the repair itself as well as monitor damage growth in the parent structure.

This paper reports on the development of a `perceptive repair' or `smart' system which will provide information on the in-service performance of the repair and the associated structure. In this respect, this paper focuses on the detection of disbond in the adhesive layer between adhered and the metallic parent structure. One of the criteria of this smart system is that it must be economical, reliable and, preferably, self-powered. To this end, it was proposed that piezoceramic of piezoelectric material be utilized because of their ease of application. These materials were chosen because they can be used both as a actuator and as a sensor. This paper presents a set of numerical investigations performed to highlight the viability of using this material system, and the associated signal analysis that can be employed to detect the presence or the development of disbonds in the adhesive in a bonded repair situation.

The piezoelectric induced bending and twisting deformation of laminated shallow shells has been presented in this report. A simple and efficient method has been developed for the static analysis of shallow shells under mechanical, thermal, and piezoelectric fields. The governing equations are based on the linear theory of piezoelectricity and the classical thin shallow shell assumptions. Approximate solutions have been obtained using the conventional Ritz analysis for different boundary conditions. Comparisons of degenerate cases with published analytical and experimental results show good agreement. Several cases have been reported here, investigating the effects of material stiffness coupling, shell shallowness, and actuator geometric parameters on the bending and twisting deformation of piezoelectric laminated structures. It is shown that the desired shape could be better controlled by a proper selection of the lay-up configuration and geometric characteristics of the structure such as the thickness, size, and location of the piezoelectric actuators.

This paper studies the optimal design of piezoelectric actuators for suppressing noise transmission of a vibration plate. The optimal placement of the actuators to reduce the global noise levels is still a significant design problem, especially placement limited to discrete locations. With the increase of the alternative locations and number of actuators, a large number of placement possibilities exist. These multi-dimensional nonlinear problems are very difficult for traditional optimization methods. In this paper, genetic algorithms have introduced to solve the problem of optimal discrete placement of piezoelectric patches. In order to improve the diversity of the population, a new selection factor is presented that is based on immune diversity, which is dependent on the string denseness and its function value. The survivor probability of the string with higher denseness will be reduced. Several cases for a simple supported plate under different load conditions show that the improved algorithms are efficient.

The problem of an arbitrarily varying axial strain field's transfer from material host to embedded fiber-optic sensor is studied. A derivation is proposed by which the axial in-fiber strain field is predicted given an arbitrary, axially varying, strain field at some distance in the material host. The spatial fields are considered in terms of spatial wavelength content and a spatial wavelength-dependent transfer function is outlined, to assist in the solution of the transfer problem. Results from the proposed approach are plotted against conventional finite-element results for the same physical problem.

A new multi-function microsensor with a barium lanthanum titanate (Ba_1-xLa_xTiO₃) thin film is developed for the fabrication of a thin-film resistor and a metal-insulator-semiconductor (MIS) capacitor on a SiO₂/Si substrate. The results reveal that the thin-film resistor has good sensitivity to visible light and good thermal sensitivity within the temperature range of 28-400 °C. The MIS capacitor is sensitive to changes in the relative humidity (RH), with a 130% change of the current for a humidity change from 12 to 92% RH at a test frequency of 500 Hz, and with short response times of 5 and 4.5 s for the adsorption and desorption of water vapor, respectively. The effects of the test frequency on the photo, thermal and humidity sensitivity performances are also investigated. Since the lifetime of charge carriers of Ba_1-xLa_xTiO₃ thin films is only 16 ms, about half that of Sr_1-xLa_xTiO₃ thin films, the device can detect light modulation at higher frequencies.

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al₂O₃ ceramic thin film, the in situ measurement of humidity levels.

In the present work, a simplified mathematical model of ultrasonic elastic fin micromotors has been developed. According to the operating principle of this type of motor, the motions of a rotor in each cycle of the stator vibration are divided into several stages based on whether the fin tip and the stator are in contact with slip, contact without slip or separation. The equations of motion of the rotor in each stage are derived. The valid range of the model has been discussed through numerical examples. This work provides an initial effort to construct a model for the elastic fin motor by considering the dynamical deformation of the rotor as well as the intermittent contacts.

The use of a special type of smart material, known as segmented constrained layer (SCL) damping, is investigated for improved rotor aeromechanical stability. The rotor blade load-carrying member is modeled using a composite box beam with arbitrary wall thickness. The SCLs are bonded to the upper and lower surfaces of the box beam to provide passive damping. A finite-element model based on a hybrid displacement theory is used to accurately capture the transverse shear effects in the composite primary structure and the viscoelastic and the piezoelectric layers within the SCL. Detailed numerical studies are presented to assess the influence of the number of actuators and their locations for improved aeromechanical stability. Ground and air resonance analysis models are implemented in the rotor blade built around the composite box beam with segmented SCLs. A classic ground resonance model and an air resonance model are used in the rotor-body coupled stability analysis. The Pitt dynamic inflow model is used in the air resonance analysis under hover condition. Results indicate that the surface bonded SCLs significantly increase rotor lead-lag regressive modal damping in the coupled rotor-body system.

This paper presents the results of a health monitoring study, carried out during the destructive load testing of a prototype reinforced concrete (RC) bridge. The bridge was made up of cement-concrete reinforced with steel rods, and represented a popular class of road bridges in which regular health monitoring is a very important issue during the service life. The bridge was instrumented with piezoceramic transducer (PZT) patches, which were electrically excited at high frequencies, of the order of kHz, and the real part of admittance (conductance) was extracted as a function of the exciting frequency. The patches were scanned for the acquisition of this signature at various stages during the loading process. The signatures of the patches located in the vicinity of the damage were found to have undergone drastic changes, while those farther away were less affected. Damage was quantified in non-parametric terms using the root mean square of the deviation in signatures with respect to the baseline signature of the healthy state. This non-parametric index was found to correlate well with the damage progression in the structure.

Reported in this study are the effects of the surface-electrode resistance on the performance of ionic polymer-metal composite (IPMC) artificial muscles. The IPMC artificial muscles manufactured in this study is composed of a perfluorinated ion-exchange membrane, platinum composited by using a chemical processing technique that employs a platinum salt and appropriate reducing agents. Furthermore, the IPMC artificial muscles were optimized for producing improved forces by changing multiple process parameters including the time-dependent concentrations of the salt and reducing agents. However, the analytical results confirmed that the platinum electrode is successfully deposited on the surface of the material where platinum particles stay in a dense form that appears to introduce a significant level of surface-electrode resistance. In order to address this problem, a thin layer of silver (or copper) was electrochemically deposited on top of the platinum electrode to reduce the surface-electrode resistance. Actuation tests were performed for such IPMC artificial muscles under a low voltage. The test results show that the lower surface-electrode resistance generates higher actuation capability in the IPMC artificial muscles. This observation is briefly discussed based on the role that the equivalent circuit for the IPMC plays and a possible electrophoretic cation-transport phenomenon under the influence of an electric field.

This paper presents a novel float-encoded genetic algorithm and applies it to the optimal control of flexible smart structures bonded with piezoelectric actuators and sensors. A performance function is initially developed, based on the maximization of dissipation energy due to a control action. Then, according to this characteristic, a float-encoded genetic algorithm is presented which is capable of solving this optimization problem reliably and efficiently. The optimization algorithm that is developed for the control of flexible systems allows an integrated determination of actuator and sensor locations and feedback gains. The paper demonstrates the suitability of the proposed technique through its application to three standard benchmark test functions and a collocated cantilever beam.

This paper is concerned with the optimal design of a collocated pair of piezoelectric patch actuators that are surface bonded onto beams. The design involves selecting the optimal locations and sizes (or lengths) of the piezoelectric actuators based on a controllability perspective. The objective function is referred to as the controllability index, which is the singular value of a control matrix. The index measures the input energy required to achieve a desired structural control by the piezoelectric actuators. The controllability index is dependent on the placement and size of the piezoelectric patches, and thus by maximizing the index the designer can obtain the optimal design of the piezoelectric actuator. As illustrations, various beam examples with a pair of piezoelectric patch actuators are solved and the optimal design characteristics of the actuators are examined.