V. V. N. Sriram Malladi

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.

Traveling Wave Phenomenon Through Piezoelectric Actuation of a Free-Free Cylindrical Tube

Previous work has demonstrated that piezoceramics are capable of generating net wave propagation without reflections in one-dimensional structures. The investigation into cylindrical traveling waves provides insight into unique dynamics (i.e., symmetric and non-symmetric modes) that have yet to be fully defined for two and three dimensional systems. The work herein will focus on the generation and characterization of traveling waves that propagate along the circumferential direction. The coupled system, given by a free-free cylinder with multiple piezoelectric actuator (PZT) patches, is used to evaluate several traveling wave modes in the cylinder. The use of structurally integrated piezoelectric patches as actuators has many advantages over the conventional shakers. Apart from the small, low weight, low cost and the size of these ceramic plates, PZTs can also generate waves over a wide frequency range. The use of multiple PZTs can be leveraged to excite the systems at a given frequency with a defined phase difference between them in order to generate highly controlled directional traveling waves in the cylindrical structure without reflections. Finite Element Modeling (FEM), in conjunction with experiments, were conducted to provide a comprehensive understanding of the generation and propagation behavior of the traveling wave modes in a thin walled cylinder.Copyright

Vehicle Propulsion by Solid State Motion

Traveling waves have shown the potential to transport material and are thus investigated as a propulsion mechanism. Through the use of piezoelectric actuators (PZTs), traveling waves were produced in beams with both free-free and fixed-free boundary conditions. It is shown that traveling waves can be generated by exciting two PZTs at a common frequency with a phase difference between the PZT signals. Experimentation showed the signal that creates the best traveling wave occurs at a driving frequency halfway between adjacent bending resonance frequencies and a phase difference of 90° between both PZTs signals. This has produced traveling waves in fixed-free beams and free-free beams in both air and water as well as for an underwater vehicle. These traveling waves generated useful propulsion in both the fixed-free and free-free beams.Copyright

Reduced Plate Model Used for 2D Traveling Wave Propagation

The focus of this study is to understand traveling wave generation and propagation in reduced order 2D plate models. A plate with all clamped (C-C-C-C) boundary conditions was selected to be the medium through which the wave propagation occurs. The plate is excited at multiple locations by point forces which generates controlled oscillations resulting in net traveling waves. A finite element model is developed and the traveling wave response is simulated. The numerical model is complex with a large number of degrees-of-freedom making a parametric study computationally intensive. In order to overcome this computational burden, balanced truncation based and interpolation-based model reduction techniques are employed to reduce the total number of degrees-of-freedom. The capabilities of these reduction techniques to capture the steady-state frequency-domain characteristics and the steady-state time-domain response have been compared in this paper.Copyright

Travelling Wave Phenomenon Through a Piezoelectric Actuation on a Free-Free Beam

A mechanical wave is generated as a result of an oscillating body interacting with the well-defined medium and it propagates through that medium transferring energy from one location to another. The ability to generate and control the motion of the mechanical waves through the finite medium opens up the opportunities for creating novel actuation mechanisms. The focus of this study is on understanding the traveling wave generation and propagation by establishing the relationships that illustrate the role of structural and electromechanical parameters. A brass beam with free-free boundary conditions was selected to be the medium through which the wave propagation occurs. Two piezoelectric elements were bonded on the opposite ends of the beam and were used to generate the controlled oscillations. Excitation of the piezoelectrics results in coupled system dynamics that can be translated into generation of the waves with desired characteristics. Theoretical analysis based on the distributed parameter model and experiments were conducted to provide the comprehensive understanding of the wave generation and propagation behavior.Copyright

Generation of Traveling Waves in a 2D Plate for Future Drag Reduction Manipulation

In most systems, friction drag is an obstacle to be hurdled and is a large source of energy inefficiency in airplanes, ships, pipes, etc. By reducing the amount of friction drag between a fluid and a surface, large energy savings are possible. This study investigates the generation of traveling surface waves propagating in the spanwise direction (perpendicular to flow) that can later be applied to decrease the friction drag in turbulent flow. A thin plate with C-F-C-F boundary conditions is excited by two piezoelectric actuators at the same frequency but with a phase difference between them. The operational deflection shapes are captured at five different frequencies where one to four regions of traveling waves exist in the plate at each frequency, with some moving in opposing directions. The traveling waves have standing waves superimposed, where the form of the standing waves are determined by the participation of nearby modes. This work provides initial assessment on the generation of traveling waves in 2D structures that can potentially be used for drag reduction in the future.

Investigation into the superposition of multiple mode shape composed traveling waves

Structural traveling waves have potential applications in numerous areas such as propulsion and skin friction drag reduction. Recent research has shown that via the two-mode excitation method, traveling waves can be generated in both one- and two-dimensional structures via the use of low-profile piezoelectric actuators. Traveling waves on a one-dimensional beam propagate in a single direction, while those on a two-dimensional structure, such as a plate, do not necessarily propagate uniformly across the surface. The propagation patterns can include unidirectional traveling waves with spatial phase shifts, wave fronts moving in opposing directions, or even rotationally moving waves. These propagation patterns depend on the participating modes and vary based on the excitation frequency, thus if multiple frequency traveling waves are generated on a plate, multiple propagation patterns are superimposed. In this study, traveling waves were generated in a plate at two different frequencies. Those frequencies were then simultaneously excited on the plate to generate a propagation pattern containing traveling waves at both frequencies. The superimposed propagation pattern was then analyzed by comparing it with a numerical combination of the individual frequency patterns. The experimentally superimposed traveling waves were found to be a linear combination of the individual frequency waves. In addition, by combining multiple frequency waves, the percentage of the plate containing traveling waves increased.

ANFIS Driven Strain Control of Thin-Shape Memory Alloy Wires Using Seebeck Voltage of a Shape Memory Alloy–Constantan Thermocouple

Shape memory alloy (SMA) actuators exhibit considerable hysteresis between the supply voltage (conventionally used in resistive heating) and strain characteristics of the SMA. Hence, it is not easy to control the strain of a thin-SMA wire, unless a model is developed that can match the actuator’s nonlinearities for predicting the supply voltage required by the SMA system accurately. The work presented in this paper proposes the use of a blackbox technique called the adaptive neurofuzzy inference system (ANFIS) to study the hysteretic behavior of SMAs. The input parameters for such an ANFIS model would be a physical variable at time t and at a time tþ n, where n is a time shift. The present work studies the effect of a time shift on the actuator nonlinearities for two ANFIS models. One of the models studies the relationship between the desired displacement of an SMA and the supply voltage across the SMA, while the other model predicts the actual displacement of an SMA from the feedback temperature. A novel SMA–Constantan thermocouple records the feedback temperature. [DOI: 10.1115/1.4028455]