This paper provides a comprehensive review on transducer technologies for underwater communications. The popularly used communication transducers, such as piezoelectric acoustic transducers, electromagnetic acoustic transducers, and acousto-optic devices are reviewed in detail. The reasons that common air communication technologies are invalid die to the differences between the media of air and water are addresses. Because of the abilities to overcome challenges the complexity of marine environments, piezoelectric acoustic transducers are playing the major underwater communication roles for science, surveillance, and Naval missions. The configuration and material properties of piezoelectric transducers effects on signal output power, beamwidth, amplitude, and other properties are discussed. The methods of code and decode communication information signals into acoustic waves are also presented. Finally, several newly developed piezoelectric transducers are recommended for future studies.
KEYWORDS: Ferroelectric polymers, Solar cells, Finite element methods, Systems modeling, Data modeling, Acoustics, Transducers, Particles, Lithium niobate, Electrodes
A flexible transparent piezoelectric surface acoustic wave (SAW) transducer was recently developed based on ultrahigh transparent polyvinylidene fluoride (PVDF) piezoelectric film and Indium tin oxide (ITO) transparency interdigital electrode. The ITO electrode was configurated as a pair of interdigital electrode pattern with input and output terminals. On the surface of a solar cell panel, the measured visible light transparency efficiency of the PVDF film is 99.4%1 . When the input is a pulse voltage signal and the output is a receiver circuit, the SAW transducer is acting as a sensor to detect the variation of the mass, such dust on the surface. When a sinusoidal voltage is applied to the input terminal of the SAW transducer and the output connected with matched resistive load, a unique direction propagation acoustic wave is generated to remove fully covered dust in a few minutes. The transducer can be used for self-sensing and cleaning dust for solar panel, building windows, optical equipment. The transducer can also be used for structure health monitoring and bio detections, etc. In this paper, the finite element modeling results with different conditions for this SAW transducer are presented. These results will provide guidelines for a specific sensor design to match some practical application requirements.
With the rapid development of portable electrical devices, the demand for batteries to power these portable devices increases dramatically. However, the development of the battery technology is slow in energy storage capability and cannot meet such requirements. This paper proposed an optimal frame design for a kind of portable piezoelectric stack energy harvesters, with large force magnification ratio and high energy transmission ratio. Two kinds of design approaches have been studied and explored, i.e., flexure compliant mechanism math based and finite element analysis (FEA) based. Prototypes are fabricated and assembled. Experiments with both static test and dynamic test have been conducted to approve the effectiveness of the proposed design. The measured force magnification ratio of 6.13 times and 21.8 times for the first-stage harvester and the dual-stage harvester are close to the design objective of 7.17 times and 24.4 times. The designed single stage harvester can generate 20.7mW/g2 at resonance frequency of 160Hz with optimal resistance of 393Ω under 0.8g base excitation with 100gram top mass, and the dual stage harvester has power generation of 487mW/g2 at resonance frequency of 38.9Hz with optimal resistance of 818Ω under 1.94g base excitation with 100gram top mass. The proposed two-stage PZT energy harvester can be used to develop portable power regenerator to compensate the urgent battery needs in remote area for both civic and military application.
A carbon nanocomposite-based contact mode interdigitated center of pressure sensor (CMIPS) has been developed.
The experimental study demonstrated that the CMIPS has the capability to measure the overall pressure as well as
the center of pressure in one dimension, simultaneously. A theoretical model for the CMIPS is established here
based on the equivalent circuit of the CMIPS configuration as well as the material properties of the sensor. The
experimental results match well with the theoretical modeling predictions. This theoretical model will provide
guidelines for future advanced sensor development based on the CMIPS. A system mapped with two or more pieces
of the CMIPS can be used to obtain information from the pressure distribution in multi-dimensions. As an
intelligent system component, the inexpensive CMIPS can be used broadly for improving sensing and control
capabilities of aircraft and measurement capabilities of biomedical research as well as chemical industries.
Researchers at NASA-LaRC have developed a hybrid actuation system (HYBAS) that cooperatively employs an
electroactive polymer and an electrostrictive single crystal. Experimental measurements and theoretical model
predictions have been in good agreement thus far. To date, current research has only explored the usage of one
electroactive polymer and one electrostrictive single crystal. A computational model was created based on this
theoretical model. It implements the equations necessary to predict the actuator displacement profile and maximum
displacement. Among the model variables are the actuator material properties. Changing the actuator materials has
notable effects on actuator performance. As many viable materials as could be found were compiled into a database
which can serve as a building block upon which a larger database can be built. Using these materials, a trade study was
performed to determine which combination of materials demonstrates the best performance. As more electroactive
materials are compiled, more extensive trade studies can be performed. Thus, the work in this paper will serve as a
guideline for future HYBAS designs.
A new configuration of an electroactive polymer, ceramic-based micro hybrid actuation system (μHYBAS) is proposed in this paper. The μHYBAS is a device concept to utilize different electroactive materials in a cooperative and efficient method for optimized electromechanical performance. A theoretical model has been developed, based on the elastic and electromechanical properties of the materials and on the configuration of the device. The μHYBASs investigated use piezoelectric polyvinylidene fluoride (PVDF) as the electroactive polymer (EAP) element combined with the electroactive ceramic (EAC) elements, which are piezoelectric hard lead zirconate titanate (PZT), soft PZT, or Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 single crystal (PZN-PT single crystal). The μHYBAS demonstrates significantly enhanced electromechanical performance by utilizing advantages of synergistic contributions of the electromechanical responses of an electroactive polymer and an electroactive ceramic. The modeled results provide guidelines for future developments of high performance μHYBASs to meet various applications.
An electroactive polymer (EAP)-ceramic hybrid actuation system (HYBAS) was developed recently at NASA Langley Research Center. This paper focuses on the effect of the bending stiffness of the EAP component on the performance of a HYBAS, in which the actuation of the EAP element can match the theoretical prediction at various length/thickness ratios for a constant elastic modulus of the EAP component. The effects on the bending stiffness of the elastic modulus and length/thickness ratio of the EAP component were studied. A critical bending stiffness to keep the actuation of the EAP element suitable for a rigid beam theory-based modeling was found for electron irradiated P(VDF-TrFE) copolymer. For example, the agreement of experimental data and theoretical modeling for a HYBAS with the length/thickness ratio of EAP element at 375 times is demonstrated. However, the beam based theoretical modeling becomes invalid (i.e., the profile of the HYBAS movement does not follow the prediction of theoretical modeling) when the bending stiffness is lower than a critical value.
As previously reported, a NASA Langley-developed electroactive polymer-ceramic hybrid system (HYBAS) has demonstrated significant enhancement in actuating displacement. The displacement of the system is derived from both the electrostrictive polymer and from single crystal elements. The electroactive elements are driven by a single power source. Recently, a modification of HYBAS has been made to increase the capability of air driving for synthetic jet devices (SJ) used in aerodynamic control technologies. The dependence of the air driving capability of the modified HYBAS on the configuration of the actuating device has been investigated. For this particular application, the modified HYBAS demonstrated a 50% increase in the volume change in the synthetic jet air chamber, as compared with that of the HYBAS without the modification.
An electroactive polymer (EAP), high energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer, based actuation micropump diaphragm (PAMPD) has been developed for air flow control. The displacement strokes and profiles as a function of amplifier and frequency of electric field have been characterized. The volume stroke rates (volume rate) as function of electric field, driving frequency have been theoretically evaluated, too. The PAMPD exhibits high volume rate. It is easily tuned with varying of either amplitude or frequency of the applied electric field. In addition, the performance of the diaphragms were modeled and the agreement between the modeling results and experimental data confirms that the response of the diaphragms follow the design parameters. The results demonstrated that the diaphragm can fit some future aerospace applications to replace the traditional complex mechanical systems, increase the control capability and reduce the weight of the future air dynamic control systems.
A hybrid actuation system (HYBAS) utilizing advantages of a combination of electromechanical responses of an electroative polymer (EAP), an electrostrictive copolymer, and an electroactive ceramic single crystal, PZN-PT single crystal, has been developed. The system employs the contribution of the actuation elements cooperatively and exhibits a significantly enhanced electromechanical performance compared to the performances of the device made of each constituting material, the electroactive polymer or the ceramic single crystal, individually. The theoretical modeling of the performances of the HYBAS is in good agreement with experimental observation. The consistence between the theoretical modeling and experimental test make the design concept an effective route for the development of high performance actuating devices for many applications. The theoretical modeling, fabrication of the HYBAS and the initial experimental results will be presented and discussed.
The electrostrictive graft elastomer is a new type of electromechanically active polymer developed by NASA. The material has demonstrated promising electromechanical properties including large electrical field induced strain, high electromechanical output, and a relatively high mechanical modulus. As a two-component system, the elastomer contains flexible backbone chains and electro-responsive polar grafted crystal domains. The two-component material system enables optimization of the electrostriction by controlling the relative fraction of the two components and the molecular morphology. The present work is a systematic study on the effects of the relative fraction of the two components and morphology on the electrical field induced strain. The results show that the elastomer containing more polar grafted domains and higher crystallinity yields higher electric field-induced strains.
Electroactive polymers (EAP) demonstrate advantages over some traditional electroactive materials such as electro-ceramics and magneostrictive materials for electromechanical device applications due to their high strain, light weight, flexibility, and low cost. Electroactive polymer-based microelectromechanical systems (EAP-MEMS) are increasingly demanded in many aerospace and medical applications. This paper will briefly review recent progress in the developments and applications of EAP- MEMS. In the past few years, several new configurations of micromachined actuators/transducers have been developed using electroactive polymers. The performance of these micromachined EAP-based devices has been evaluated for both fluid and air conditions. The performance of EAP-MEMS has also been theoretically modeled based on material properties and device configurations. In general, the results obtained from modeling agree with the experimental measurements. Critical process issues, including patterned micro-scale electrodes, molded micro/nano electroactive polymer structures, polymer to electrode adhesion and the development of conductive polymers for electrodes will be discussed. The challenges to develop complete polymer MEMS will also be addressed.
KEYWORDS: Polymers, Actuators, Data modeling, Silicon, Electrodes, Selenium, Solids, Digital video recorders, Performance modeling, Microelectromechanical systems
We report on the performance of micromachined unimorph actuators (PMAT) based on the electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymer. Because of the high electrostrictive strain and high elastic energy density of the active polymer, the PMAT exhibits a very high stroke level with high load capability and high displacement voltage ratio. In addition, the experimental data also demonstrate that the PMAT is capable of operating over a broad frequency range. The PMAT performance was modeled and the agreement between the modeling results and experimental data confirms that the response of the PMAT indeed follows the design parameters.
Micromachined unimorph actuators based on the electrostrictive P(VDF-TrFE) copolymer have been fabricated. The performance of the devices has been modeled and characterized. The experimental results on the device responses are very close to the prediction of the model, indicating a high actuator displacement and voltage sensitivity. For a typical unimorph device with 1 mm length, the displacement at the center of the device can reach 30 micrometers , and the ratio of the displacement/applied voltage is more than 30nm/V. Furthermore, over more than 3 frequency decades, the dispersion of the displacement is less than 20%, which indicates the high frequency capability of this polymer based MEMS. To demonstrate the high force capability of the device, the displacement response of the device was evaluated at 200 Hz ina fluid medium and there is no observable change in the displacement response in fluid medium when compared with that measured in air. Due to the large field induced electrostrictive strain and high frequency capability of the electrostrictive P(VDF-TfFE), the device is capable of operating at no-resonance model with high displacement and force output, and over a broad frequency range (DC to >10 kHz). The observed performance of the device indicates that this type of electrostrictive P(VDF-TrFE) based MEMS is attractive for micro-pump, values, and air coupled ultrasonic transducer array, etc.
Peizoelectric and electrostrictive polymers are widely used in many areas of electromechanical actuation and transduction. This paper summarizes the current status and recent works in this class of polymers. For the piezoelectric polymers, the electromechanical properties of poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), which possess the best piezoelectric performance among the known piezopolymers, are presented. In order to improve the strain capability and other electromechanical properties, the large electrostrictive response and high electromechanical conversion efficient near a first order ferroelectric-paraelectric transition of P(VDF-TrFE) copolymer were exploited. It is shown that the copolymer, treated with high energy electron irradiation, exhibits high electrostrictive strains (-5% longitudinal strain under 150 MV/m and 3.5% transverse starin under 100 MV/m) with high strain energy density, high load capability and improved electromechanical coupling factor. For the comparison, the works related to the Maxwell stress induced strain response in soft polymers are also discussed.
In order to characterize the electromechanical properties of newly developed electrostrictive poly(vinylidene fluoride- trifluorethylene) copolymers for practical device applications, the following results are presented: 1) The driving field amplitude dependence of the material response. It was found that M(S = ME2) exhibits the driving field amplitude dependence and that the apparent piezoelectric coefficient for the material under DC bias depends on both the driving field amplitude and DC field. 2) Load capability. The copolymer film has a high mechanical load capability. For example, the transverse strain remains 0.6% at 47MV/m under a tensile load of 45 MPA. The load dependence of the material response prove that the electric field induced strain in the copolymer films mainly originates from the electric field induced phase transition in the crystal regions. 3) Frequency dependence of the material response. Although the strain response decreases with increasing frequency, it is found that the strain response at 1 kHz can reach more than 80% of the response at 1Hz.
An exceptionally high electrostrictive response was observed in electron irradiate polyvinelidene fluoride- trifluoroethylene [P(VDF-TrFE)] copolymer. Moreover, the transverse strain of the material can be tuned over a large range by different sample treatment conditions. For example, in films uniaxially stretched, the strain can be comparable or even larger than the longitudinal strain, while in films unstretched, the transverse strain is quite small. In addition, when the films are completely clamped mechanically in the lateral directions, the films can still generate large longitudinal strains. Due to relatively high elastic modulus of the films, high elastic strain energy densities, which are much higher than those in conventional piezo and electrostrictive ceramics and magnetostrictive materials.
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