Pablo A. Tarazaga

Control of a Space Rigidizable Inflatable Boom Using Macro-fiber Composite Actuators

An experimental investigation of vibration testing and active control of a space rigidizable inflatable composite boom containing embedded piezoelectric composite actuators was conducted. Inflatable deployable space structures offer reduced mass, higher packaging efficiency, lower life cycle cost, simpler design with fewer parts, and higher deployment reliability for many large deployable spacecraft structures applications. Enhancing deployed precision and repeatability for these structures is an ongoing research area, in particular for rigidizable inflatable material systems. In this study, in situ vibration testing and active damping using piezoelectric macro-fiber composite actuators embedded within a typical space-rigidizable deployable composite boom are investigated The embedded macro-fiber composites are shown to be capable of surviving integration, packaging, deployment and thermal rigidization in vacuum, and subsequently operating at their full actuation capability. Positive position feedback controllers using accelerometer, laser vibrometer, and strain gage feedback signals are designed and experimentally evaluated. Velocity-proportional and acceleration-proportional controllers are shown to be capable of attenuating fundamental bending response significantly using only modest control authority (—23dB with 10% of available voltage).

Frequency Range Selection for Impedance-Based Structural Health Monitoring

Impedance-based structural health monitoring uses collocated piezoelectric transducers to locally excite a structure at high frequencies. The response of the structure is measured by the same transducer. Changes in this response indicate damage. Frequency range selection for monitoring with impedance-based structural health monitoring has, in the past, been done by trial and error methods or has been selected after analysis by engineers familiar with the method. This study aims to determine if, in future applications, it is possible to automatically select preferred frequency ranges based on sensor characteristics, perhaps even before installing the system. In addition, the paper demonstrates a method for determining preferable frequency ranges for monitoring. The study examines the analysis of the measurement change through a damage metric and relates the results of the analysis to characteristics of the measurement. Specifically, outlier detection concepts were used to statistically evaluate the damage detection ability of the transducers at various frequency ranges. The variation in undamaged measurements is compared to the amount of change in the measurement upon various levels of damage. Testing was performed with both solid piezoceramic transducers and macrofiber composite piezoelectric devices of different sizes bonded to aluminum and fiber reinforced composite structures. The results indicate that characteristics of the structure, not the sensor alone, determine the optimal monitarine frequency ranges. the optimal monitoring frequency ranges.

Towards indoor localization of pedestrians via smart building vibration sensing

Indoor localization by means of GNSS or a cellular-based method is known to be difficult. Potentially, other wireless technologies could address the technical requirements, but they usually imply the end user must carry a device compatible with this additional technology too. In this paper we investigate the feasibility of collecting vibration sensor readings within a building to locate pedestrians by their footsteps. Vibration propagation in buildings is markedly different than radio wave propagation in free space, thus prompting one to question the suitability of conventional positioning algorithms for this task. We presents the results of experiments conducted with actual measurements from an instrumented, smart building. We expect such buildings to become more prevalent in the future thanks to the technical advances and cost reductions provided by the Internet-of-Things (IoT). The promising initial findings indicate that time-difference-of-arrival, within a limited spatial extent, could be a viable localization technique, and these results encourage further research into vibration-based indoor localization.

Vibration Event Localization in an Instrumented Building

In this paper, we present the preliminary results of an indoor location estimation campaign using real data collected from vibration sensors mounted throughout an instrumented smart building. The Virginia Tech Smart Infrastructure Laboratory house a unique testbed featuring a fully instrumented operational building with over 240 accelerometers permanently mounted to the steel structure. It is expected that in the future, more and more buildings will be constructed with sensors scattered about their infrastructures, in no small part due to the envisioned promises of such systems which include improved energy efficiency, health and safety monitoring, stronger security, improved construction practices, and improved earthquake resistance. One of the most promising uses of this smart infrastructure is for indoor localization, a scenario in which traditional radio-frequency based techniques often suffer. The detection and localization of indoor seismic events has many potential applications, including that of aiding in meeting indoor positioning requirements recently proposed by the FCC and expected to become law in the near future. The promising initial results of a simplistic time-difference-of-arrival based localization system presented in this paper motivate further study into the use of vibration data for indoor localization.

Theoretical and experimental correlation of mechanical wave formation on beams

Mechanical waves can be broadly categorized into traveling waves and standing waves. In this study, the nature of the waves in a finite solid medium is investigated to reveal the excitation parameters that influence their behavior. Theoretical and experimental analysis is conducted to find the conditions for generating traveling waves using piezoelectric ceramics as the actuation agent in piezo-structural-coupled systems. A continuous electromechanical model is developed in order to predict the structural dynamics and is validated through experiments. The results from this study provide the fundamental physics behind the generation of mechanical waves and their propagation through finite mediums.

Characterization and representation of mechanical waves generated in piezo-electric augmented beams

Mechanical waves are induced in solids due to the systems coupling with an external excitation. Depending upon the nature of the resulting displacement and phase difference between the vibrating particles at a particular frequency, the mechanical waves can be classified as standing waves, traveling waves or a combination of the two. This study focuses on the identification of these different forms of mechanical waves and discusses methods that can be suitably used for their classification. The Hilbert and Fourier methods of classification were validated using experimental results and then compared against each other. The experimental and theoretical analysis of mechanical waves was conducted on a beam with free-free boundary conditions excited by piezoelectric elements.

Gender Classification of Walkers via Underfloor Accelerometer Measurements

The ability to classify the gender of occupants in a building has far-reaching applications including security and retail sales. The authors demonstrate the success of machine learning techniques for gender classification. High-sensitivity accelerometers mounted noninvasively beneath an actual building floor provide the input for these machine learning methods. While other approaches using gait measurements, such as vision systems and wearable sensors, provide the potential for gender classification, they each face limitations. These limitations include an invasion of privacy, occupant compliance, required line of sight, and/or high sensor density. Underfloor mounted accelerometers overcome these limitations. The authors utilize the highly-instrumented Goodwin Hall smart building on the Virginia Tech campus to measure vibrations of the walking surface caused by walkers. In this paper, the gait of 15 individual walkers was recorded as they, alone, walked down the instrumented hallway. Fourteen accelerometers, mounted underneath the walking surface, recorded walking trials with the placement of the sensors unknown to the walker. This paper studies bagged decision trees, boosted decision trees, support vector machines, and neural networks as the machine learning techniques for their ability to classify gender. A tenfold-cross-validation method is used to comment on the validity of the algorithms ability to generalize to new walkers. This paper demonstrates that a gender classification accuracy of 88% is achievable using the underfloor vibration data from the Virginia Tech Goodwin Hall by using decision tree approaches.

Modal analysis of an ultra-flexible, self-rigidizing toroidal satellite component

Over the past few years, much research has been performed on understanding the dynamics of an ultra-large, flexible toroidal satellite component subject to an internal pressure. However, the harsh environment of space is no place for inflated, membrane-like materials for fear of micro meteorite bombardment and subsequent puncture. Addressing this issue directly, United Applied Technologies (Huntsville, AL) has developed a novel, thin film casting approach to create a self-rigidizing torus. Once inflated, the torus structure is able to support its own shape, thus eliminating the need for any internal pressure. The self-rigidizing torus is extremely flexible, much more so than its pressurized predecessors. Such compliancy makes modal testing extremely difficult. However, through careful application of traditional modal testing techniques (shaker and accelerometer testing), the damped natural frequencies and mode shapes of the self-rigidizing torus can be discerned in the frequencies and mode shapes of the self-rigidizing torus can be discerned in the frequency bandwidth of interest, 1–12 Hz.Copyright

Indoor positioning from vibration localization in smart buildings

Indoor localization by means of a global navigation satellite system (GNSS) remains a difficult problem due to GNSS signal impairments created by the buildings structure. This problem prompted the research community to devise many alternative techniques. Unfortunately, in order to locate persons indoors, these alternatives often require each person to carry some device to facilitate the localization process. This paper investigates the naturally-generated vibration signals from a persons footsteps as a potential source of information for indoor localization. Instrumenting a building with vibration sensors is a mature technology, but, historically, the role of the technology was measuring a buildings response to external events (e.g., earthquakes), not for measuring occupant-generated vibrations. Some prior work studied outdoor detection of footsteps near borders or within restricted areas, but that environment and the localization objectives differed sufficiently from the scope of this research to limit the relevance of prior results. This paper reports on measurements from an instrumented, public building and examines viability of conventional localization algorithms for locating persons moving within a building. Noting the sub-optimum performance of these algorithms in this localization task, this paper proposes an extension to existing techniques to accommodate signal distortions encountered by vibrations in building structures.

Mimicking the cochlear amplifier in a cantilever beam using nonlinear velocity feedback control

The mammalian cochlea exhibits a nonlinear amplification which allows mammals to detect a large range of sound pressure levels while maintaining high frequency sensitivity. This work seeks to mimic the cochlea?s nonlinear amplification in a mechanical system. A nonlinear, velocity-based feedback control law is applied to a cantilever beam with piezoelectric actuators. The control law reduces the linear viscous damping of the system while introducing a cubic damping term. The result is a system which is positioned close to a Hopf bifurcation. Modelling and experimental results show that the beam with this control law undergoes a one-third amplitude scaling near the resonance frequency and an amplitude-dependent bandwidth. Both behaviors are characteristic of data obtained from the mammalian cochlea. This work could provide insight on the biological cochlea while producing bio-inspired sensors with a large dynamic range and sharp frequency sensitivity.