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NASA NTRS2003

Carbon Nanotubes as Resonators for RF Spectrum Analyzers

Electromechanical resonators of a proposed type would comprise single carbon nanotubes suspended between electrodes (see Figure 1). Depending on the nanotube length, diameter, and tension, these devices will resonate at frequencies in a range from megahertz through gigahertz. Like the carbon-nanotube resonators described in the preceding article, these devices will exhibit high quality factors (Q values), will be compatible with integration with electronic circuits, and, unlike similar devices made from silicone and silicone carbide, will have tunable resonant frequencies as high as several GHz. An efficient electromechanical transduction method for the carbon nanotube resonators is provided by the previously observed variation of carbon nanotube length with charge injection. It was found that injection of electrons or holes, respectively, lengthens or shortens carbon nanotubes, by amounts of the order of a percent at bias levels of a few volts. The charge-dependent length change also enables a simple and direct means of tuning the resonant frequency by varying the DC bias and hence the tension along the tube, much like tuning a guitar string. In its basic form, the invention is a tunable high-Q resonator based on a suspended carbon nanotube bridge with attached electrodes (see Figure 1). An applied DC bias controls the tension and thus the frequency of resonance. If one were to superimpose a radio-frequency (RF) bias on the DC bias, then the resulting rapid variation in tension or length would set the tube into vibration. If, on the other hand, the carbon nanotube were to be set into vibration by interaction between an incident RF electric field and electric charges in the nanotube, then the vibration would give rise to an RF signal output that is proportional to the RF amplitude at the resonance frequency. Because the transduction mechanism is extremely sensitive and the active volume is only a few nanometers in diameter, this device is not well suited for use as a microwave power device. Instead, this carbon nanotube mechanical resonator would be useful primarily as part of a highly precise, sensitive, frequency-selective detector. An array of such devices featuring nanotubes of different lengths (and thus different frequencies) could be made to operate as a highspeed spectrum analyzer (see Figure 2)

Hunt, Brian↗

NASA NTRS2007

Development of a Tunable Electromechanical Acoustic Liner for Engine Nacelles

This report describes the development of a tunable electromechanical Helmholtz resonator (EMHR) for engine nacelles using smart materials technology. This effort addresses both near-term and long-term goals for tunable electromechanical acoustic liner technology for the Quiet Aircraft Technology (QAT) Program. Analytical models, i.e. lumped element model (LEM) and transfer matrix (TM) representation of the EMHR, have been developed to predict the acoustic behavior of the EMHR. The models have been implemented in a MATLAB program and used to compare with measurement results. Moreover, the prediction performance of models is further improved with the aid of parameter extraction of the piezoelectric backplate. The EMHR has been experimentally investigated using standard two-microphone method (TMM). The measurement results validated both the LEM and TM models of the EMHR. Good agreement between predicted and measured impedance is obtained. Short- and open circuit loads define the limits of the tuning range using resistive and capacitive loads. There is approximately a 9% tuning limit under these conditions for the non-optimized resonator configuration studied. Inductive shunt loads result in a 3 degree-of-freedom DOF) system and an enhanced tuning range of over 20% that is not restricted by the short- and open-circuit limits. Damping coefficient ' measurements for piezoelectric backplates in a vacuum chamber are also performed and indicate that the damping is dominated by the structural damping losses, such as compliant boundaries, and other intrinsic loss mechanisms. Based on models of the EMHR, a Pareto optimization design of the EMHR has been performed for the EMHR with non-inductive loads. The EMHR with non-inductive loads is a 2DOF system with two resonant fiequencies. The tuning ranges of the two resonant frequencies of the EMHR with non-inductive loads cannot be optimized simultaneously; a trade-off (i.e., a Pareto solution) must be reached. The Pareto solution provides the information for a designer that shows how design trade-offs can be used to satisfy specific design requirements. The optimization design of the EMHR with inductive loads aims at optimal tuning of these three resonant fiequencies. The results indicate that it is possible to keep the acoustic reactance of the resonator close to a constant over a given frequency range. An effort to mimic the second layer of the NASA 2DOF liner using a piezoelectric composite diaphragm has been made. The optimal acoustic reactance of the second layer of the NASA 2DOF liner is achieved using a thin PVDF composite diaphragm, but matching the acoustic resistance requires further investigation. Acoustic energy harvesting is achieved by connecting the EMHR to an energy reclamation circuit that converts the ac voltage signal across the piezoceramic to a conditioned dc signal. Energy harvesting experiment yields 16 m W continuous power for an incident SPL of 153 dB. Such a level is sufficient to power a variety of low power electronic devices. Finally, technology transfer has been achieved by converting the original NASA ZKTL FORTRAN code to a MATLAB code while incorporating the models of the EMHR. Initial studies indicate that the EMHR is a promising technology that may enable lowpower, light weight, tunable engine nacelle liners. This technology, however, is very immature, and additional developments are required. Recommendations for future work include testing of sample EMHR liner designs in NASA Langley s normal incidence dual-waveguide and the grazing-incidence flow facility to evaluating both the impedance characteristics as well as the energy reclamation abilities. Additional design work is required for more complex tuning circuits with greater performance. Poor electromechanical coupling limited the electromechanical tuning capabilities of the proof of concept EMHR. Different materials than those studies and perhaps novel composite material systems may dramatically improvehe electromechanical coupling. Such improvements are essential to improved mimicking of existing double layer liners.

Liu, Fei↗

NASA NTRS2017

A Piezoelectric Passive Wireless Sensor for Monitoring Strain

Interest in passive wireless sensing has grown over the past few decades to meet demands in structural health monitoring.(Deivasigamani et al., 2013; Wilson and Juarez, 2014) This work describes a passive wireless sensor for monitoring strain, which does not have an embedded battery or chip. Without an embedded battery, the passive wireless sensor has the potential to maintain its functionality over long periods in remote/harsh environments. This work also focuses on monitoring small strain (less than 1000 micro-ɛ). The wireless sensing system includes a reader unit, a coil-like transponder, and a sensing unit. It operates in the Megahertz (MHz) frequency range, which allows for a few centimeters of separation between the reader and sensing unit during measurements. The sensing unit is a strain-sensitive piezoelectric resonator that maximizes the energy efficiency at the resonance frequency, so it converts nanoscale mechanical variations to detectable differences in electrical signal. In response to an external loading, the piezoelectric sensor breaks from its original electromechanical equilibrium, and the resonant frequency shifts as the system reaches a new balanced equilibrium. In this work, the fixture of the sensing unit is a small, sticker-like package that converts the surface strain of a test material to measurable shifts in resonant frequencies. Furthermore, electromechanical modeling provides a lumped-parameter model of the system to describe and predict the measured wireless signals of the sensor. Detailed characterization demonstrates how this wireless sensor has resolution comparable to that of conventional wired strain sensors for monitoring small strain.

Zou, Xiyue↗

NASA NTRS2007

Electromechanical acoustic liner

A multi-resonator-based system responsive to acoustic waves includes at least two resonators, each including a bottom plate, side walls secured to the bottom plate, and a top plate disposed on top of the side walls. The top plate includes an orifice so that a portion of an incident acoustical wave compresses gas in the resonators. The bottom plate or the side walls include at least one compliant portion. A reciprocal electromechanical transducer coupled to the compliant portion of each of the resonators forms a first and second transducer/compliant composite. An electrical network is disposed between the reciprocal electromechanical transducer of the first and second resonator.

Sheplak, Mark↗

NASA NTRS1992

Electromechanical systems with transient high power response operating from a resonant AC link

The combination of an inherently robust asynchronous (induction) electrical machine with the rapid control of energy provided by a high frequency resonant AC link enables the efficient management of higher power levels with greater versatility. This could have a variety of applications from launch vehicles to all-electric automobiles. These types of systems utilize a machine which is operated by independent control of both the voltage and frequency. This is made possible by using an indirect field-oriented control method which allows instantaneous torque control in all four operating quadrants. Incorporating the AC link allows the converter in these systems to switch at the zero crossing of every half cycle of the AC waveform. This zero loss switching of the link allows rapid energy variations to be achieved without the usual frequency proportional switching loss. Several field-oriented control systems were developed by LeRC and General Dynamics Space Systems Division under contract to NASA. A description of a single motor, electromechanical actuation system is presented. Then, focus is on a conceptual design for an AC electric vehicle. This design incorporates an induction motor/generator together with a flywheel for peak energy storage. System operation and implications along with the associated circuitry are addressed. Such a system would greatly improve all-electric vehicle ranges over the Federal Urban Driving Cycle (FUD).

Burrows, Linda M.↗

NASA NTRS1992

Electromechanical systems with transient high power response operating from a resonant ac link

The combination of an inherently robust asynchronous (induction) electrical machine with the rapid control of energy provided by a high frequency resonant ac link enables the efficient management of higher power levels with greater versatility. This could have a variety of applications from launch vehicles to all-electric automobiles. These types of systems utilize a machine which is operated by independent control of both the voltage and frequency. This is made possible by using an indirect field-oriented control method which allows instantaneous torque control all four operating quadrants. Incorporating the ac link allows the converter in these systems to switch at the zero crossing of every half cycle of the ac waveform. This zero loss switching of the link allows rapid energy variations to be achieved without the usual frequency proportional switching loss. Several field-oriented control systems were developed under contract to NASA.

Burrows, Linda M.↗

NASA NTRS2004

Development of Electronic Load Controllers for Free-Piston Stirling Convertors Aided by Stirling Simulation Model

The free-piston Stirling convertor end-to-end modeling effort at the NASA Glenn Research Center has produced a software-based test bed in which free-piston Stirling convertors can be simulated and evaluated. The simulation model includes all the components of the convertor: the Stirling cycle engine, heat source, linear alternator, controller, and load. So far, it has been used in evaluating the performance of electronic controller designs. Three different controller design concepts were simulated using the model: 1) Controllers with parasitic direct current loading. 2) Controllers with parasitic alternating current loading. 3) Controllers that maintain a reference current. The free-piston Stirling convertor is an electromechanical device that operates at resonance. It is the function of the electronic load controller to ensure that the electrical load seen by the machine is always great enough to keep the amplitude of the piston and alternator oscillation at the rated value. This is done by regulating the load on the output bus. The controller monitors the instantaneous voltage, regulating it by switching loads called parasitic loads onto the bus whenever the bus voltage is too high and removing them whenever the voltage is too low. In the first type of controller, the monitor-ing and switching are done on the direct-current (dc) bus. In the second type, the alternating current bus is used. The model allows designers to test a controller concept before investing time in hardware. The simulation code used to develop the model also offers detailed models of digital and analog electronic components so that the resulting designs are realistic enough to translate directly into hardware circuits.

Regan, Timothy F.↗

NASA NTRS2007

High-Temperature Properties of Piezoelectric Langatate Single Crystals

Langasite type crystals belong to non-polar point group of 32 and do not show any phase transformations up to the melting temperature. Langatate (La3Ga(5.5)Ta(0.5)O14) demonstrates piezoelectric activity better than quartz and possesses attractive properties for high temperature sensors, resonators and filter applications. High-quality and colorless langatate crystals were grown by the Czochralski technique. The electromechanical and electrical properties of langatate crystals in different crystallographic directions were characterized at elevated temperature. The piezoelectric coefficient along x-axis was 7 pC/N as measured by a Berlincourt meter for a plate geometry with an aspect ratio of 10:1. The dielectric constant did not exhibit any significant temperature dependence (K33 approx. 21 at 30 C and K33 approx. 23 at 600 C). Loss tangent at 100 kHz remained <0.003 up to 300 C and <0.65 at 600 C. The dielectric properties along the y-axis were similar and its temperature dependence was analogous to the x-axis. Electromechanically, the inactive z-axis exhibited no resonance with K33 approx. 84 at room temperature, decreasing down to approx. 49 at 600 C. Resistivity of these crystals along x-axis decreased from approx. 6x10(exp 11) omega-cm at room temperature, to approx. 1.6x10(exp 6) omega-cm at 600 C.

Sehirlioglu, Alp↗

NASA NTRS2008

Controller for Driving a Piezoelectric Actuator at Resonance

A digital control system based partly on an extremum-seeking control algorithm tracks the changing resonance frequency of a piezoelectric actuator or an electrically similar electromechanical device that is driven by a sinusoidal excitation signal and is required to be maintained at or near resonance in the presence of uncertain, changing external loads and disturbances. Somewhat more specifically, on the basis of measurements of the performance of the actuator, this system repeatedly estimates the resonance frequency and alters the excitation frequency as needed to keep it at or near the resonance frequency. In the original application for which this controller was developed, the piezoelectric actuator is part of an ultrasonic/sonic drill/corer. Going beyond this application, the underlying principles of design and operation are generally applicable to tracking changing resonance frequencies of heavily perturbed harmonic oscillators. Resonance-frequency-tracking analog electronic circuits are commercially available, but are not adequate for the present purpose for several reasons: The input/output characteristics of analog circuits tend to drift, often necessitating recalibration, especially whenever the same controller is used in driving a different resonator. In the case of an actuator in a system that has multiple modes characterized by different resonance frequencies, an analog controller can tune erroneously to one of the higher-frequency modes. The lack of programmability of analog controllers is problematic when faults occur, and is especially problematic for preventing tuning to a higher-frequency mode. In contrast, a digital controller can be programmed to restrict itself to a specified frequency range and to maintain stability even when the affected resonator is driven at high power and subjected to uncertain disturbances and variable loads. The present digital control system (see figure) is implemented by means of an algorithm that comprises three main subalgorithms: a hill-climbing control algorithm, an estimation-based extremum-seeking control (ESC) algorithm, and a supervisory algorithm. The hill-climbing algorithm is useful for coarse tracking to find and remain within the vicinity of the resonance. The ESC algorithm is not capable of coarse resonance tracking, but is capable of fine resonance tracking once the estimates of parameters generated by the hill-climbing algorithm have converged sufficiently. On the basis of the parameter-estimation errors, the supervisory algorithm switches operation to whichever of the other two algorithms performs best at a given time.

Aldrich, Jack↗

NASA NTRS1989

Experimental investigation into passive damping enhancement for space structures

This work presents experiments which were conducted to verify kinetic and strain energy damping enhancement schemes for large/precision space structures. Two types of damping mechanisms were applied to a 5 meter long, 10 bay aluminum box truss with a quasi free-free three-dimensional suspension. Tuneable proof mass dampers (PMDs) were implemented with space realizable linear electromechanical drivers. Tuneable piezoelectric truss members were designed and constructed for the demonstration of resonant shunted piezoelectric damping concepts. The truss damping was measured and compared to analytical predictions obtained from a frequency domain system modeling technique. The proof mass damper implementation was found to increase first mode damping from 0.6 percent of critical to 6.4 percent of critical with a system mass increase of 2.7 percent. The resonant shunted piezoelectrics increased first mode damping to 6.0 percent with a similar mass penalty.

Hagood, Nesbitt W.↗

NASA NTRS1990

Electromechanical actuation for thrust vector control applications

The advanced launch system (ALS), is a launch vehicle that is designed to be cost-effective, highly reliable, and operationally efficient with a goal of reducing the cost per pound to orbit. An electromechanical actuation (EMA) system is being developed as an attractive alternative to the hydraulic systems. The controller will integrate 20 kHz resonant link power management and distribution (PMAD) technology and pulse population modulation (PPM) techniques to implement field-oriented vector control (FOVC) of a new advanced induction motor. The driver and the FOVC will be microprocessor controlled. For increased system reliability, a built-in test (BITE) capability will be included. This involves introducing testability into the design of a system such that testing is calibrated and exercised during the design, manufacturing, maintenance, and prelaunch activities. An actuator will be integrated with the motor controller for performance testing of the EMA thrust vector control (TVC) system. The EMA system and work proposed for the future are discussed.

Roth, Mary Ellen↗

NASA NTRS1999

Hybrid Active-Passive Systems for Control of Aircraft Interior Noise

Previous work has demonstrated the large potential for hybrid active-passive systems for attenuating interior noise in aircraft fuselages. The main advantage of an active-passive system is, by utilizing the natural dynamics of the actuator system, the control actuator power and weight is markedly reduced and stability/robustness is enhanced. Three different active-passive approaches were studied in the past year. The first technique utilizes multiple tunable vibration absorbers (ATVA) for reducing narrow band sound radiated from panels and transmitted through fuselage structures. The focus is on reducing interior noise due to propeller or turbo fan harmonic excitation. Two types of tunable vibration absorbers were investigated; a solid state system based upon a piezoelectric mechanical exciter and an electromechanical system based upon a Motran shaker. Both of these systems utilize a mass-spring dynamic effect to maximize tile output force near resonance of the shaker system and so can also be used as vibration absorbers. The dynamic properties of the absorbers (i.e. resonance frequency) were modified using a feedback signal from an accelerometer mounted on the active mass, passed through a compensator and fed into the drive component of the shaker system (piezoelectric element or voice coil respectively). The feedback loop consisted of a two coefficient FIR filter, implemented on a DSP, where the input is acceleration of tile ATVA mass and the output is a force acting in parallel with the stiffness of the absorber. By separating the feedback signal into real and imaginary components, the effective natural frequency and damping of the ATVA can be altered independently. This approach gave control of the resonance frequencies while also allowing the simultaneous removal of damping from the ATVA, thus increasing the ease of controllability and effectiveness. In order to obtain a "tuned" vibration absorber the chosen resonant frequency was set to the excitation frequency. In order to minimize sound radiation a gradient descent algorithm was developed which globally adapted the resonance frequencies of multiple ATVA's while minimizing a cost based upon the radiated sound power or sound energy obtained from an array of microphones.

Fuller, Chris R.↗

NASA NTRS1987

On the glitches in the force transmitted by an electrodynamic exciter to a structure

Around resonance, the force transmitted by an exciter into a structure will be smaller or greater than a reference force generated by its coils due to electromechanical interaction. A simple analysis is presented which reveals how this phenomenon of force drop-off is controlled by three factors. The first factor, called Armature Mass Factor, describes a purely mechanical interaction between the structure and the exciter. The electromechanical energy conversion and its interaction with the structure yields two additional factors, called Electrical Resistance and Electrical Inductance Factors. They describe the effects of coil resistance, inductance and magnetic field strength relative to structural damping and stiffness. Present analysis indicates that, under proper circumstances, more than 90 percent of the force drop-off can be eliminated if armature-to-structure mass ratio is smaller or equal to half of modal loss factor.

Rao, Dantam K.↗

NASA NTRS2003

The computation of the k factor for lossy materials around resonance

An important property of a piezoelectric material for practical applications is its ability to generate and to detect stress waves, i.e. to convert electrical energy into mechanical energy and vice versa. As it is well known, the electromechanical coupling factor k fully characterize this energy conversion under static conditions. In this work we show that the definition of kw as ratio of energies can also be extended to lossy materials (kw); the losses are accounted by considering comlex quantities for the elastic, dielectric and piezoelectric material constants.

coupling coefficients↗

NASA NTRS2015

2D Electrostatic Actuation of Microshutter Arrays

An electrostatically actuated microshutter array consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutter arrays demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.

Multiobject Imaging↗

NASA NTRS2015

2D Electrostatic Actuation of Microshutter Arrays

Electrostatically actuated microshutter arrays consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutters demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.

Multiobject Imaging↗

NASA NTRS1991

A synchronous chopper mechanism for use at cryogenic temperature

A mechanically resonant synchronous chopper mechanism is described for use at cryogenic temperatures. The mechanism is a critical optical component of the Diffuse Infrared Background Experiment (DIRBE) and has been operating on orbit without incident since Nov. 1989. The requirements, electromechanical design, and testing of the mechanism are described. A description of the problems encountered and solutions implemented during the development of the mechanism is provided. Finally, a modified chopper design, which incorporated lessons learned and that has several advantages over the flight chopper design, is offered.

Hakun, Claef↗

NASA NTRS2010

Temperature-Dependent Electrical and Micromechanical Properties of Lanthanum Titanate with Additions of Yttria

Temperature-dependent elastic properties were determined by establishing continuous flexural vibrations in the material at its lowest resonance frequency of 31tHz. The imaginary part of the complex impedance plotted as a function of frequency and temperature reveals a thermally activated peak, which decreases in magnitude as the temperature increases. Additions of yttria do not degrade the electromechanical in particularly the elastic and anelastic properties of lanthanum titanate. Y2O3/La2Ti2O7 exhibits extremely low internal friction and hence may be more mechanical fatigue-resistant at low strains.

Goldsby, Jon C.↗