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Acoustic Noise and Vibration Research This report by MIT's Industrial Liaison Program identifies selected MIT research and faculty with expertise in the area of the acoustic noise reduction and vibration damping and related work, such as energy harvesting from vibration. This report captures information dated between 2008 and March 2010. For more information, please contact MIT’s Industrial Liaison Program at +1-617-253-2691.

NOISE/VIBRATION ....................................................................................................................................................4 DR. ANURADHA ANNASWAMY ....................................................................................................................................4

Active-Adaptive Control Laboratory (AACL) .........................................................................................................4 Supersonic Impinging Jets ......................................................................................................................................4 Blade Tonals in Underwater Vehicles ....................................................................................................................4 Publication: “Spark Ignition Engine Idle Speed Control: An Adaptive Control Approach” ...............................4

PROF. ANANTHA CHANDRAKASAN ..............................................................................................................................5 Digital Integrated Circuits and Systems Group at MIT ..........................................................................................5 MIT News Story: “Power from motion and vibrations: Forget about batteries. The ability to harness electricity from tiny vibrations could power a new generation of electronic devices.” .........................................5 An Efficient Piezoelectric Energy-Harvesting Interface Circuit ............................................................................6 Self-Powered Electronic Systems ............................................................................................................................6

PROF. JOEL L DAWSON ................................................................................................................................................7 Dawson Research Group ........................................................................................................................................7 Digitally-Assisted Analog Front-End for Biomedical Sensors ...............................................................................7 Digitally Assisted Subsampler for RF Power-Amplifier Linearization Systems .....................................................8 Transmitters for High Efficiency, 10 Gb/s Wireless Communications in the 60 GHz Band ..................................8

PROF. ZOLTAN S SPAKOVSZKY ....................................................................................................................................9 Gas Turbine Laboratory (GTL) ..............................................................................................................................9 Acoustic Shielding Prediction of a Hybrid Wing-Body Aircraft for NASA N+2 Goals .........................................9 Assessment of Inlet Distortion Noise in Highly Integrated Propulsion Systems ..................................................10 Assessment of Propfan Propulsion Systems for Reduced Environmental Impact ................................................10

PROF. KRIPA K. VARANASI .......................................................................................................................................10 Patent: Method and Apparatus for Damping Vibrations using Low-Wave-Speed Media, US 10/821344, 2004.......................................................................................................................................................................11 Hybrid Vibration Damping: Combined Viscous and Hysteretic Model ...............................................................11 Design of High-Performance Belt-Driven Positioning Systems ...........................................................................11 Design of a High-Speed, Low-Cost "Rack and Track" Linear Motion System .....................................................12 Dynamics of Pressurized Air Bearings at Low Fly Heights .................................................................................13

PROF. BRIAN L. WARDLE ..........................................................................................................................................13 Model-Based Design of MEMS Vibration-Energy-Harvesters .............................................................................14

PARTNER — THE PARTNERSHIP FOR AIR TRANSPORTATION NOISE AND EMISSIONS REDUCTION .........................14 New Web site offers aviation noise info, resources ..............................................................................................14 PARTNER Report: “Assessing Current Scientific Knowledge, Uncertainties and Gaps in Quantifying Climate Change, Noise and Air Quality Aviation Impacts” .................................................................................15 PARTNER Report: “Passive Sound Insulation” .................................................................................................15

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PARTNER Report: “Vibration and Rattle Mitigation” .......................................................................................15 MIT NEWS STORY: “MECHANICAL DEVICES STAMPED ON PLASTIC: TO TEST A NEW TECHNIQUE FOR CREATING MICROMACHINES… ...................................................................................................................................................15

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NOISE/VIBRATION

DR. ANURADHA ANNASWAMY Senior Research Scientist, http://meche.mit.edu/people/index.html?id=116 Research Interests: Adaptive Control Theory and Applications to Propulsion and Transportation; Control of Thermo-fluid Systems; Active Combustion Control; Active-adaptive Flow Control; Dynamic Instability; Control using Neural Networks

Active-Adaptive Control Laboratory (AACL) Director: Dr. Anuradha Annaswamy http://web.mit.edu/aaclab/index.html Research on Active-Adaptive Noise Control:

Supersonic Impinging Jets …We are developing novel closed-loop control strategies for articulating the microjet pressure is suggested, in order to maintain a uniform, reliable, and optimal reduction of these tones over the entire range of operating conditions. Experimental results from a STOVL supersonic jet facility at Mach 1.5 show that these strategies lead to 8-10 db reduction, compared to an open loop one, at the desired operating conditions. More recently, a pulsing microjet injection was used as a new control scheme to retain a uniform suppression of impinging jet noise. Through this method injection, a fairly good amount of noise reduction was achieved using 42% of the mass flow rate that led to the same level of noise reduction using steady microjet injection. As the duty cycle was increased, it was observed that the pulsed injection completely destroyed the distinct impinging tone for almost all heights. A systematic control design using these novel pulsing microjets is currently being explored. More at http://web.mit.edu/aaclab/research/supersonicjets/index.html

Blade Tonals in Underwater Vehicles The goal of this research is to use active control to modulate a control surface in order to suitably modify the tonal. In this case a biologically inspired method of tail articulation, consisting of a hinged stator trailing edge, is used to modify propeller inflow. The flapping stator induces a point circulation which convects downstream towards the propeller. Experimental work has been carried out at both low and high Reynold's number to observe the effect of tail articulation on the stator wake… More at http://web.mit.edu/aaclab/research/bladetonals/index.html

Publication: “Spark Ignition Engine Idle Speed Control: An Adaptive Control Approach” Y. Yildiz, A. M. Annaswamy, D. Yanakiev, I. Kolmanovsky, under review, 2009. http://web.mit.edu/aaclab/pdfs/Yildiray%20Yildiz%20TCST.pdf

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PROF. ANANTHA CHANDRAKASAN Joseph F. and Nancy P. Keithley Professor of Electrical Engineering, and Director, MIT Microsystems Technology Laboratories (MTL), http://www-mtl.mit.edu/~anantha/biography.html Research interests include micro-power digital and mixed-signal integrated circuit design, wireless microsensor system design, ultra-wideband radios, and emerging technologies.

Digital Integrated Circuits and Systems Group at MIT The Digital Integrated Circuits and Systems Group is involved with the design and implementation of various integrated systems ranging from ultra low-power wireless sensors and multimedia devices to high performance processors. The research spans across multiple levels of abstraction ranging from innovative new process technologies and circuit styles to architectures, algorithms, and software technologies. A key focus of this group is developing energy efficient integrated solutions for battery operated systems… More at http://mtlweb.mit.edu/researchgroups/icsystems/index.html and http://mtlweb.mit.edu/researchgroups/icsystems/gallery.html

MIT News Story: “Power from motion and vibrations: Forget about batteries. The ability to harness electricity from tiny vibrations could power a new generation of electronic devices.” David L. Chandler, MIT News Office, February 16, 2010 The Trans-Alaska Pipeline System, which traverses hundreds of miles of some of the most inhospitable terrain on Earth, must be monitored almost constantly for potential problems like corrosion or cracking. Humans do some of this work — surveying the pipeline from the air and inspecting it more closely in the areas that can be easily accessed by roads — but the bulk of it is done by mechanical “pigs,” sensor-laden robots that travel inside the pipeline looking for flaws. A simpler process might involve outfitting remote stretches of the pipeline with sensors that would automatically radio a warning of impending problems. But the need to periodically change the batteries on such sensors lessens the appeal of that option. For electronic devices in remote or inaccessible situations like this, including environmental or mechanical monitoring sensors as well as some kinds of biomedical monitors, it can be inconvenient or even impossible to replace batteries. But what if batteries weren’t necessary? Systems that could provide power for such sensors just by harvesting the normal vibrations of the pipeline (or bridges or industrial machinery and so on), eliminating or reducing the need for a battery, are being developed by Anantha Chandrakasan, MIT’s Joseph F. and Nancy P. Keithley professor of electrical engineering and director of the MIT Microsystems Technology Laboratories, and his former student Yogesh Ramadass SM ’06, PhD ’09. They have been working for years on the development of ways to harness small amounts of power from ambient vibrations… More at http://www.mit.edu/newsoffice/2010/power-from-motion-and-vibrations.html

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An Efficient Piezoelectric Energy-Harvesting Interface Circuit Principal Investigator: Dr. Anantha P Chandrakasan Date: 10/19/09 Energy harvesting is an emerging technology with applications to handheld, portable, and implantable electronics. Harvesting ambient vibration energy through piezoelectric (PE) means is a popular energy-harvesting technique that can potentially supply 10’s-100’s of W of available power. One of the limitations of existing PE-harvesters is in their interface circuitry. Commonly used full-bridge rectifiers and voltage doublers severely limit the electrical power extractable from a PE- harvesting element. Further, the power consumed in the control circuits of these harvesters reduces the amount of usable electrical power. This work presents a bias-flip rectifier that can improve upon the power extraction capability of existing full-bridge rectifiers by greater than 4X. An efficient control circuit with embedded DC-DC converters that can share their filter inductor with the bias-flip rectifier, thereby reducing the volume and component count of the overall solution, is demonstrated. We show a conventional full-bridge rectifier circuit together with the implemented bias-flip rectifier circuit. The main limitation of the full-bridge rectifier is that, even when ideal diodes are considered, most of the current available from the harvester does not go into charging the output capacitor CRECT at high values of VRECT. The shaded portion of the current waveform in We also show the time spent in charging or discharging CP every half-cycle. This loss in charge limits the amount of electrical power that can be extracted using the full-bridge rectifier. The bias-flip rectifier consists of an inductor LSHARE that is connected in parallel with the PE-harvester. When switches M1 and M2 of the bias-flip rectifier are turned ON, the inductor helps in flipping the voltage VBF across CP. After the switches close, the PE current IP needs to supply a smaller amount of charge to CP to bring it up to ±VRECT. This reduction in charge lost significantly improves the amount of power extractable from the harvester. The inductor used in the rectifier is shared efficiently with other DC-DC converters in the system. The entire chip was fabricated in a 0.35-µm CMOS process. We show the measured power obtained at the output of the rectifier for the different rectifier scenarios with off-chip diodes. The effectiveness of the bias-flip rectifier improves as the inductance is increased. An 820µH inductor provides a 4.2X improvement in power extracted compared to the full-bridge rectifier. This power improvement increases to above 7X when on-chip diodes are used. The DC-DC converters employed in the system achieve greater than 85% efficiency with shared inductors, in the micro-watt power levels output by the piezoelectric energy-harvester.

Self-Powered Electronic Systems Principal Investigator: Dr. Anantha P Chandrakasan Depts/Labs/Centers: MIT Energy Initiative Date: 09/19/08 A micro energy processor that could harvest energy from vibrations, temperature differences, solar panels, and radio waves could wirelessly provide the power to run Bluetooth headsets or implanted medical devices. This project will try to develop control systems for "self-powered" devices, such as biomedical sensors or therapeutic devices that generate their own electricity from the user's movements or body heat so that they never require battery replacement.

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PROF. JOEL L DAWSON Mark Hyman, Jr Career Development Associate Professor of Electrical Engineering, http://www-mtl.mit.edu/~jldawson/

Dawson Research Group The Dawson research group designs RF and mixed-signal CMOS ICs for communications systems and medical applications. Our research approach centers on the idea that we work in an extremely interesting era for such circuits. Economic forces favor a heavily digital chip, and it is often not profitable to make device and process concessions for the analog circuits. Given that we have millions of digital gates at our disposal, together with analog devices that are fast but otherwise far from ideal, what is the new optimal division of functionality between the analog and digital domains? We seek answers to this question in part by exercising architectural creativity. In addition, we explore the application of mathematical optimization techniques to allocate resources between analog and digital subsystems. http://www-mtl.mit.edu/~jldawson/research_group/group_projects.html

Digitally-Assisted Analog Front-End for Biomedical Sensors Principal Investigator: Prof. Joel l Dawson Other Investigator: Dr. Anantha P Chandrakasan Depts/Labs/Centers: Microsystems Technology Laboratories Date: 10/19/09 Biomedical sensors are used to measure a myriad of biopotential signals including electroencephalogram (EEG), electrocardiogram (EKG), electromyogram (EMG), and neural field potential (NFP) signals. Most of the useful information in these signals resides in the frequency range of 0.5 Hz to 1 kHz, allowing ultra-low power circuits to be used when processing them. This is critical for systems that are implanted, since energy is extremely scarce, and the lifetime of the device must be on the order of 10 years. Unfortunately, these signals are often as small as 10 µVs, and their low frequency location make them vulnerable to aggressors such as DC offset, powerline noise, and flicker noise. DC offset can result from charge accumulation at the interface between the metal electrodes and the skin, and also from amplifier offsets caused by random mismatches. While chopper stabilization has proved effective at mitigating the effects of amplifier DC offset and flicker noise, electrode DC offset cannot be removed through chopping and must be high-pass filtered at the front end of the system to prevent saturation. Powerline noise, typically at 50 or 60 Hz, is mostly a common-mode signal that requires adequate common-mode rejection. However, if there are mismatches or inductive loops in the electrodes, these aggressors can become differential-mode signals, corrupting the desired signal, and potentially saturating the system. In closed-loop deep brain stimulation systems, another aggressor arises from stimulation artifacts. In that case, the NFPs can be much smaller than stimulation artifacts placing stringent requirements on the dynamic range of the system and potentially leading to signal corruption. We propose a mixed-signal sensor interface that mitigates the effects of all of the aforementioned aggressors in an area efficient manner. Area efficiency is particularly compelling in implantable devices that use tens or hundreds of electrodes, such as neural recording systems. The proposed system uses a chopper stabilized operational amplifier with capacitive feedback to achieve

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accurate gain (The system is shown as single-ended for simplicity, but is implemented in a fully differential manner). We show a simplified schematic of the amplifier, including a novel input chopper that creates a switched capacitor resistance between its inputs and a reference voltage. This resistance is shown as Rp and is used to create a high-pass filter with a corner frequency well below 1 Hz, while setting the common-mode voltage of the input to a desired level. The pole frequency is actually set by the Miller-multiplied feedback capacitor Cf and is inversely proportional to the amplifier’s gain AV, allowing a reduction of many orders of magnitude in component sizes. An additional feedback path is introduced that includes the filter, ADC, DSP, and a feedback DAC. This path can be used to notch out unwanted signals such as powerline noise or stimulation artifacts before they can saturate the system.

Digitally Assisted Subsampler for RF Power-Amplifier Linearization Systems Principal Investigator: Prof. Joel l Dawson Depts/Labs/Centers: Microsystems Technology Laboratories Date: 10/19/09 Subsampling is recognized as an energy-efficient signal processing technique for highly digital transceivers. However, subsamplers are notorious for low SNR performance due to noise folding and for stringent requirements for anti-aliasing prefilters. This combination of faults has largely undermined their use in high-performance receivers. In transmitters, however, the situation is fundamentally different. The signal environment has fewer extreme aggressors, such as blockers, and the transmitted data is often known in advance of actual transmission. This last fact enables the use of averaging and other signal processing techniques to overcome the noise-folding problem. We show a digitally assisted subsampler, which is designed to serve as a downconversion path in adaptive predistortion transmitters with 800MHz-5.8GHz RF power amplifiers. We use digital averaging to overcome the noise-folding problems of subsampling, obtaining a final SNDR of 73.1dB for signals centered around a 2.4GHz carrier. Using quadrature subsampling, we obtain both I and Q samples from the same physical path and thereby eliminate the IQ gain mismatch. When used as part of an adaptive predistortion system, the subsampler enables an EVM improvement of 3.2% and distortion products suppression of up to 7.6dB for 802.11g signals. The subsampler IC, designed in a 90-nm CMOS process, consumes 6.0mW from a 1.2V supply.

Transmitters for High Efficiency, 10 Gb/s Wireless Communications in the 60 GHz Band Principal Investigator: Prof. Joel l Dawson Depts/Labs/Centers: Lincoln Laboratory, Microsystems Technology Laboratories Date: 10/19/09 The purpose of this project is to design an RF transmitter architecture that achieves 10 Gb/s data transfer over a 60 GHz wireless link with high power efficiency. With the availability of 7 GHz of unlicensed bandwidth centered at 60 GHz, this space has emerged as an active area of research. A number of challenges will be faced in the process of bringing this project to completion. Strong atmospheric absorption at 60 GHz lowers the signal-to-noise ratio (SNR) available at the receiver. The low SNR limits the complexity of the constellations that can be used and thus reduces the number of bits per symbol that can be encoded with the modulation strategy. Extremely fast

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baseband modulators will therefore be required for high data rate transmission because more symbols per second will have to be transmitted. The fundamental challenge of simultaneously obtaining good linearity and high efficiency in power amplifiers is further exacerbated at this carrier frequency, complicating transceiver design. Delivering significant power at 60 GHz requires very fast devices with high fmax and fT. This technological hurdle has been lowered with recent advances in SiGe, III-V semiconductor technology and deeply scaled CMOS. The technical approach of this project is to exploit complete co-design of the modulation strategy with a new power amplifier concept: Asymmetric Multilevel Outphasing (AMO). This architecture combines the best properties of polar transmitters and outphasing (LINC) transmitters. The power amplifier’s efficiency is improved without significantly degrading its linearity by using the combination of drain voltage modulation and rapid outphasing. A key aspect of this project will be the investigation of energy recovery as a means of further improving the transmitter’s efficiency. The use of resistance compression networks as a means of recovering the energy normally lost during outphasing will be critical. To achieve these goals, the most significant research challenges are: (1) achieving baseband modulation commensurate with 10 Gb/s transmission with the new AMO architecture, and (2) designing a symbol constellation and modulation strategy that maximally exploits the architecture.

PROF. ZOLTAN S SPAKOVSZKY Associate Professor of Aeronautics and Astronautics, and Director, Gas Turbine Laboratory (GTL), http://web.mit.edu/aeroastro/people/spakovszky.html Specialization and Research Interests: Internal flows, turbomachinery, propulsion systems and control, aeroengine dynamic system modeling, aero-acoustics.

Gas Turbine Laboratory (GTL) Research at the GTL is focused on advanced propulsion systems and turbomachinery with activities in computational, theoretical, and experimental study of: (1) loss mechanisms and unsteady flows in turbomachines, (2) compression system stability and active control, (3) heat transfer in turbine blading, (4) gas turbine engine noise reduction and aero-acoustics, (5) pollutant emissions and community noise, and (6) MEMS-based high-power-density engines… More at http://web.mit.edu/aeroastro/labs/gtl/index.html

Acoustic Shielding Prediction of a Hybrid Wing-Body Aircraft for NASA N+2 Goals Leo Ng, Phil Weed, Advisor: Prof. Spakovszky Reducing the environmental impact of air travel is a major focus in aeronautical research today. The hybrid wing-body aircraft, in which the lifting fuselage is blended with the wings, has the potential to burn less fuel, produce fewer emissions, and generate less noise. Building upon previous work from the Silent Aircraft Initiative, this project aims to develop a set of advanced predictive methods that will enable the design of a hybrid wing-body aircraft to meet NASA’s N+2 goals: (i) 25% less fuel burn, (ii) 80% less emissions, and (iii) 52 dB less noise compared to current aircrafts in service… More at http://web.mit.edu/aeroastro/labs/gtl/MIT_GTL_curr_research.html

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Assessment of Inlet Distortion Noise in Highly Integrated Propulsion Systems Jeff Defoe, Alex Narkaj, Advisor: Prof. Spakovszky Among the Silent Aircraft Initiative SAX40’s many unique characteristics are engines which are highly integrated into the airframe. S-shaped inlet ducts deliver air to the engines, but these ducts ingest the boundary layer over the wing and thus the flow through the duct is highly non-uniform. Predicting noise propagation through non-uniform flow fields is a complex task, as most classical acoustics formulations deal with uniform flow fields. This research project deals with the numerical simulation of the noise source caused by the engine fan in the duct, in particular multiple-pure-tone (MPT) noise caused by blade-to-blade variations, and with its propagation upstream through the duct and to far-field receivers. The acoustic waves involved are nonlinear and the propagation is through a highly non-uniform flow field… More at http://web.mit.edu/aeroastro/labs/gtl/MIT_GTL_curr_research.html

Assessment of Propfan Propulsion Systems for Reduced Environmental Impact Andreas Peters, Advisor: Prof. Spakovszky … Taking into account the stringent noise certification requirements, the level of potential propfan overall noise reduction using advanced technologies in conjunction with a design strategy for both low noise and reduced fuel burn / emissions is investigated within the scope of this research effort. The goal of the project is to define the optimum propfan engine configuration and airframe integration concept with respect to improved performance and reduced noise and fuel burn. More at http://web.mit.edu/aeroastro/labs/gtl/MIT_GTL_curr_research.html

PROF. KRIPA K. VARANASI d'Arbeloff Assistant Professor of Mechanical Engineering, http://meche.mit.edu/people/?id=372 Research Interests: Nanoengineered Surfaces and their applications to Energy, Water, Oil & Gas, Agriculture, Aviation, Electronics Cooling Systems; and Fluid-Surface and Thermal-Fluid-Surface Interactions; Superhydrophobic, Superhydrophilic, Oleophobic/Oleophilic Surfaces; Biomimetics; Phase-Change Phenomena (Condensation, Boiling, Freezing and Ice formation) on nanoengineered surfaces; Nucleation and Growth; Micro and Nanoscale Heat Transfer; Heat Pipes and Thermal Interfaces; Harsh Environment Coatings and Surface Technologies (Ceramics and Metals); Subsea Separation (fluid-fluid and fluid-gas) and Flow Assurance; Quantum Dots, Plasmonics and Bandgap Engineering; Nanomanufacturing (Ceramics and Metals)

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Patent: Method and Apparatus for Damping Vibrations using Low-Wave-Speed Media, US 10/821344, 2004 More at http://web.mit.edu/kripa/www/patents.htm

Hybrid Vibration Damping: Combined Viscous and Hysteretic Model Date: 05/04/09 In acoustics and vibration literature there are essentially two important models for damping: viscous and hysteretic damping models. A system in which the damping force at any instant is proportional to the velocity of motion is said to possess viscous damping. In such systems the energy dissipated varies linearly with frequency. However, in most materials and structures the damping properties vary slowly with frequency. Hence using viscous damping to model energy dissipation in such materials leads to underestimating and overestimating damping at low and high frequencies, respectively. Therefore, a complex modulus approach which directly uses the properties of the energy dissipation in the damping medium as a function of frequency is usually employed to describe the steady-state dynamics of the system. Among the several models using the complex modulus approach, the simplest is the so-called frequency-independent hysteretic damping model (e.g., Nashif; Crandall), in which the modulus and loss factor of the material are assumed to be constant with frequency. Although the hysteretic model is very convenient to predict the response under steady harmonic motion, it suffers from the disadvantage of defying causality under transient excitations, and hence cannot be used in Laplace domain (in which most of the control design is performed). On the other hand, the viscous damping model does not suffer such problems with transient response and can therefore be used in the Laplace domain. Moreover, many machines consist of both hysteretic and viscous elements. A common example is the case of an isolation system in which the isolation table behaves more or less as a hysteretic element whereas the air legs on which the table stands is nearly viscous. Another example is that of the damped screw discussed above in which the damping element is hysteretic where as the damping in the bearing races, motor is nearly viscous. Hence, it is important to provide a framework to handle this mixed viscous and hysteretic damping. A search of literature reveals no so such studies on this problem.

Design of High-Performance Belt-Driven Positioning Systems Date: 05/04/09 Flat steel belt drives provide smooth power transmission between offset rotors or between a rotor and a linear stage. But because of belt "creep" or "microslip," it is almost always necessary to employ a feedback sensor located on the "driven" or "output" component of the system. This makes the system susceptible to instabilities at high feedback gains. Two types of instability in belt drives are by now well-understood: In the first, the longitudinal (axial) compliance of the belt gives rise to a resonance in which the driving and driven components of the system oscillate with different phases; at high gains this resonance leads to instability. In the second, if the belt travels at speeds approaching that of bending waves, the belt diverges from its nominally straight shape between pulleys.

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In this research, we develop a model for the axial resonance of a belt-driven linear stage and verify it with experiments on the stage shown below. Next, we model and measure the error motions and instabilities that arise from lateral (i.e., transverse bending) vibration of the belt. This vibration can arise either from "external" disturbances acting transverse to the belt, or from "parametric" excitation of the belt due to the time varying tension within the belt when the system is commanded to accelerate. Although the simplest linear models predict that lateral belt vibration is decoupled from motion of its endpoints, we show when this vibration is sufficiently large it can cause significant error motion of the driven pulley. We perform a set of experiments on a simple belt drive (shown below) to measure this effect and document the effects of various controllers on the response. Next, we show analytically that the large axial forces that are necessary to produce high accelerations can cause a parametric excitation large enough to cause instability. This effect is again demonstrated in our experiment, and the results are compared with the predictions from the model. As in the case of a lead-screws, we find that the performance of the belt-driven stage can be improved significantly if we can introduce predictable damping into the system. We have demonstrated that such damping can be introduced in a very cost-effective and robust manner by using low-wave-speed materials. The method employed is found to provide significant damping in the axial and transverse modes of the belt. http://web.mit.edu/kripa/www/publications/leadscrew%20drives_jdsmc04.pdf

Design of a High-Speed, Low-Cost "Rack and Track" Linear Motion System Date: 05/04/09 This project is in building and testing a novel linear drive. The main objective was to build a low-cost stage which can achieve very rapid motion with reasonable precision. The drive consists of a toothed belt simultaneously engaging a sprocket and a linear rack with mating tooth forms. The sprocket moves relative to the rack along the length of the rack. Rotary motion of a sprocket mated to the belt results in linear motion of the belt as it disengages the sprocket. This linear motion is transmitted to the linear rack immediately opposite, or very close to, where the belt disengages the sprocket. The belt is engaged with the rack for a number of pitches to transmit force between rack and the belt. This drive has several advantages over traditional linear drives. Firstly, the close proximity of where the belt disengages the sprocket and engages the rack minimizes the effective length of the belt undergoing stretching between the drive and driven sides of the mechanism. This increases the resonant frequency in which the carriage and the motor oscillate as the belt undergoes longitudinal stretching, thereby increasing the system bandwidth under non-collocated control. Next it also results in low wind up of the drive. Secondly, multiple tooth engagement between the belt and rack and belt and sprocket results in averaging out manufacturing errors. This yields smoother and more precise motion. This elastic averaging improves damping in the system which is very advantageous for closed-loop control. Thirdly, as the sprocket moves along the rack the stiffness of the drive is constant with position and is not affected by the length of travel. Finally, toothed belt drives can run without lubrication. Hence maintenance is minimized and there is no contamination from lubricants.

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The system was reliably able to produce moves with trapezoidal velocity profile with stage accelerations of 15 m/s^2 and a max velocity of 12.5 m/s. The motor settled to within one motor count in less than 100 ms. The positional resolution of the stage was less than 20 microns. The details of the design can be found in Perry’s thesis entitled, "Linear Drive with High Stiffness and Low Inertia." See http://web.mit.edu/kripa/www/publications/leadscrew%20drives_jdsmc04.pdf

Dynamics of Pressurized Air Bearings at Low Fly Heights Pressurized air bearings find wide application in precision motion systems where smooth motion and fine positioning are required. But the absence of friction and their relatively low stiffness and damping (especially when coupled to a direct-drive) make them susceptible to vibratory disturbances and instabilities. The stiffness of such bearings is known to increase as the fly height is decreased, but very small fly heights require very accurate manufacture and (in traditional designs) often lead to pressure instabilities. In this project, the aim is to characterize the stiffness, damping, and stability of air bearing systems at very low fly heights, to develop techniques for the suppression of the instabilities, and to reduce the cost of manufacturing air bearing systems with very low fly heights. Experiments to Characterize Stiffness and Damping of Porous Graphite Air Bearings at very Low Fly Heights (nearly 1micron) -- The experimental set up consists of a porous graphite air bearing that is preloaded against a flat surface. A photograph of the test set up is also shown. The bearing is excited using an electromagnetic shaker via a force transducer (PCB208B) and the gap between the graphite pad and the flat surface is measured using capacitance gauges. A sine sweep excitation is generated by a signal analyzer (HP35670A) and supplied to the shaker via a voltage amplifier. As the bearing undergoes harmonic motion, we measure the force to position transfer function from which we deduce the dynamic stiffness and loss factor of the bearing. The preload force between the bearing and the flat surface is measured by a tensioning mechanism. By measuring the tension force using a strain-gauge load cell (which I built myself), we monitor the preload between the bearing and the flat surface as the bearing undergoes harmonic excitation. We perform these experiments at various values of supply pressure. For each supply pressure, we measure the stiffness and damping at various levels of preload.

PROF. BRIAN L. WARDLE Charles Stark Draper Associate Professor of Aeronautics and Astronautics, and Director, Nano-Engineered Composite aerospace STructures (NECST) Consortium, http://web.mit.edu/aeroastro/www/people/wardle/index.html Professor Wardle's research interests are in the area of structures and materials, primarily focusing on aerospace applications. Current research areas are composite systems, active materials, structural health monitoring (SHM), and power-conversion devices at the MEMS scale. Topics of interest to him include: structural mechanics, durability, advanced material systems, safety/reliability and performance of structural systems, microelectromechanical systems (MEMS), structural health monitoring and nanocomposites. Professor Wardle's educational activities cover experimentation and modeling of materials and structures.

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Model-Based Design of MEMS Vibration-Energy-Harvesters Principal Investigator: Prof. Brian L Wardle Depts/Labs/Centers: Microsystems Technology Laboratories Date: 10/09/09 The recent development of “low power” (10s-100s of µW) sensing and data transmission devices, as well as protocols with which to connect them efficiently into large, dispersed networks of individual wireless nodes, has created a need for a new kind of power source. Embeddable, non-life-limiting power sources are being developed to harvest ambient environmental energy available as mechanical vibrations, fluid motion, radiation, or temperature gradients. While potential applications range from building climate control to homeland security, the application pursued most recently has been that of structural health monitoring (SHM), particularly for aircraft. This SHM application and the power levels required favor the piezoelectric harvesting of ambient vibration energy. Current work focuses on harvesting this energy with MEMS resonant structures of various geometries. Coupled electromechanical models for uniform beam structures have been developed to predict the electrical and mechanical performance obtainable from ambient vibration sources. The optimized models have been verified by comparison to tests on a macro-scale device both without and with a proof mass at the end of the structure. A non-optimized, uni-morph beam prototype has been designed and fabricated. Design tools to allow device optimization for a given vibration environment have been under detailed investigation considering various geometries of the device structures and fabrication constraints, especially in microfabrication. Future work will focus on fabrication and testing of optimized uni-morph and proof-of-concept bi-morph prototype beams. System integration and development, including modeling the power electronics, will be included.

PARTNER — THE PARTNERSHIP FOR AIR TRANSPORTATION NOISE AND EMISSIONS REDUCTION Director: Prof. Ian Waitz, Jerome C. Hunsaker Professor of Aeronautics and Astronautics, and Department Head, Department of Aeronautics and Astronautics, http://web.mit.edu/aeroastro/people/waitz.html PARTNER — the Partnership for AiR Transportation Noise and Emissions Reduction — is a leading aviation cooperative research organization, and an FAA/NASA/Transport Canada-sponsored Center of Excellence. PARTNER fosters breakthrough technological, operational, policy, and workforce advances for the betterment of mobility, economy, national security, and the environment. PARTNER is an academic, industry, and government collaborative that researches solutions for existing and anticipated aviation-related noise and emissions problems. We conduct basic research and engineering development, and prototype solutions. See: http://mit.edu/aeroastro/partner/index.html and http://web.mit.edu/aeroastro/partner/projects/index.html

New Web site offers aviation noise info, resources MARCH 11, 2009 — Community members, civic leaders, homebuyers, and others concerned about aviation noise have a new Web site to help them understand noise sources and effects, explore options for dealing with noise, and access noise-related resources. PARTNER's NoiseQuest site, developed by Penn State, includes information about aviation noise sources,

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what to do about noise, land use planning. reducing noise in homes, guidance for homebuyers, ongoing research and more. See http://www.noisequest.psu.edu/

PARTNER Report: “Assessing Current Scientific Knowledge, Uncertainties and Gaps in Quantifying Climate Change, Noise and Air Quality Aviation Impacts” Final Report of the International Civil Aviation Organization Committee on Aviation and Environmental Protection Workshop L. Q. Maurice and D. S. Lee, editors, 2009 http://web.mit.edu/aeroastro/partner/reports/caepimpactreport.pdf

PARTNER Report: “Passive Sound Insulation” PARTNER Project 1.5 Report Daniel H. Robinson, Robert J. Bernhard, Luc G. Mongeau. January 2008. Report No. PARTNER-COE-2008-003. http://web.mit.edu/aeroastro/partner/reports/proj1/proj1.5report.pdf

PARTNER Report: “Vibration and Rattle Mitigation” PARTNER Project 1.6 Report Daniel H. Robinson, Robert J. Bernhard, Luc G. Mongeau. January 2008. Report No. PARTNER-COE-2008-004 http://web.mit.edu/aeroastro/partner/reports/proj1/proj1.6report.pdf

MIT NEWS STORY: “MECHANICAL DEVICES STAMPED ON PLASTIC: TO TEST A NEW TECHNIQUE FOR CREATING MICROMACHINES… MIT researchers deposited films of gold on a sheet of plastic; grooves in the plastic are visible as a series of horizontal lines” Larry Hardesty, MIT News Office, February 26, 2010 Microelectromechanical devices — tiny machines with moving parts — are everywhere these days: they monitor air pressure in car tires, register the gestures of video game players, and reflect light onto screens in movie theaters. But they’re manufactured the same way computer chips are, in facilities that can cost billions of dollars, and their rigidity makes them hard to wrap around curved surfaces. MIT researchers have discovered a way to make microelectromechanical devices, or MEMS, by stamping them onto a plastic film. That should significantly reduce their cost, but it also opens up the possibility of large sheets of sensors that could, say, cover the wings of an airplane to gauge their structural integrity. The printed MEMS are also flexible, so they could be used to make sensors with irregular shapes. And since the stamping process dispenses with the harsh chemicals and high temperatures ordinarily required for the fabrication of MEMS, it could allow MEMS to incorporate a wider range of materials… … Because the researchers hadn’t set out to make MEMS, and because, to their knowledge, their films constitute the first stamped MEMS devices, they’re still trying to determine the ideal application of the technology. Sheets of sensors to gauge the structural integrity of aircraft and

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bridges are one possibility; but the MEMS could also change the physical texture of the surfaces they’re applied to, altering the airflow over a wing, or modifying the reflective properties of a building’s walls or windows. A sheet of thousands of tiny microphones could determine, from the difference in the time at which sound waves arrive at different points, where a particular sound originated. Such a system could filter out extraneous sounds in a noisy room, or even perform echolocation, the way bats do. The same type of sheet could constitute a paper-thin loudspeaker; the vibrations of different MEMS might even be designed to interfere with each other, so that transmitted sounds would be perfectly audible at some location but inaudible a few feet away. The technology could also lead to large digital displays that could be rolled up when not in use… More at http://www.mit.edu/newsoffice/2010/printable-mems-0226.html and http://www.rle.mit.edu/organic/research.htm