Martin R. Cacan

Metamaterial-inspired structures and concepts for elastoacoustic wave energy harvesting

Enhancement of structure-borne wave energy harvesting is investigated by exploiting metamaterial-based and metamaterial-inspired electroelastic systems. The concepts of wave focusing, localization, and funneling are leveraged to establish novel metamaterial energy harvester (MEH) configurations. The MEH systems transform the incoming structure-borne wave energy into electrical energy by coupling the metamaterial and electroelastic domains. The energy harvesting component of the work employs piezoelectric transduction due to the high power density and ease of application offered by piezoelectric materials. Therefore, in all MEH configurations studied in this work, the metamaterial system is combined with piezoelectric energy harvesting for enhanced electricity generation from waves propagating in elastic structures. Experiments are conducted to validate the dramatic performance enhancement in MEH systems as compared to using the same volume of piezoelectric patch in the absence of the metamaterial component. It is shown that MEH systems can be used for both broadband and tuned wave energy harvesting. The MEH concepts covered in this paper are (1) wave focusing using a metamaterial-inspired parabolic acoustic mirror (for broadband energy harvesting), (2) energy localization using an imperfection in a 2D lattice structure (for tuned energy harvesting), and (3) wave guiding using an acoustic funnel (for narrow-to-broadband energy harvesting). It is shown that MEH systems can boost the harvested power by more than an order of magnitude. (Some figures may appear in colour only in the online journal)

Energy harvesting from hydraulic pressure fluctuations

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring to avoid catastrophic failures. Energy harvesting in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is the dynamic pressure ripple, which is caused by the action of pumps and actuators. Pressure ripple is a deterministic source with a periodic time-domain behavior conducive to energy harvesting. An energy harvester prototype was designed for generating low-power electricity from pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining a mechanical coupling allowing for dynamic-pressure-induced deflection of the stack. The prototype exhibited an off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack was much higher than the frequency content of the pressure ripple. The prototype was designed to provide a suitable power output for powering sensors with a maximum output of 1.2 mW. This work also presents electromechanical model simulations and experimental characterization of the piezoelectric power output from the pressure ripple in terms of the force transmitted into the harvester. (Some figures may appear in colour only in the online journal)

Dramatic enhancement of structure-borne wave energy harvesting using an elliptical acoustic mirror

Broadband structure-borne wave energy harvesting is reported by wave focusing using an elliptical acoustic mirror (EAM). The EAM is formed by an array of cylindrical stubs mounted along a semi-elliptical path on the surface of a plate. The array back-scatters incoming guided waves and focuses them at the focal location where a piezoelectric energy harvester is located. Multiple scattering simulations and experiments illustrate the broadband focusing characteristics of the EAM. More than an order of magnitude improvement in piezoelectric power generation is documented for an EAM-based energy harvester with respect to a free harvester over the 30–70 kHz frequency range.

Autonomous Airdrop Systems Employing Ground Wind Measurements for Improved Landing Accuracy

Aerial cargo delivery, also known as airdrop, systems are heavily affected by atmospheric wind conditions. Guided airdrop systems typically employ onboard wind velocity estimation methods to predict the wind in real time as the systems descend, but these methods provide no foresight of the winds near the ground. Unexpected ground winds can result in large errors in landing location, and they can even lead to damage or complete loss of the cargo if the system impacts the ground while traveling downwind. This paper reports on a ground-based mechatronic system consisting of a cup and vane anemometer coupled to a guided airdrop system through a wireless transceiver. The guidance logic running on the airdrop systems onboard autopilot is modified to integrate the anemometer measurements at ground level near the intended landing zone with onboard wind estimates to provide an improved, real-time estimate of the wind profile. The concept was first developed in the framework of a rigorous simulation model and then validated in the flight test. Both simulation and subsequent flight tests with the prototype system demonstrate reductions in the landing position error by more than 30% as well as a complete elimination of potentially dangerous downwind landings.

Combined Lateral and Longitudinal Control of Parafoils Using Upper-Surface Canopy Spoilers

Precision placement of guided airdrop systems necessarily requires some mechanism enabling effective directional control of the vehicle. Often this mechanism is realized through asymmetric deflection of the parafoil canopy trailing-edge brakes. In contrast to conventional trailing-edge deflection used primarily for lateral steering, upper-surface bleed air spoilers have been shown to be extremely effective for both lateral and longitudinal (i.e., glide slope) control of parafoil and payload systems. Bleed air spoilers operate by opening and closing several spanwise slits in the upper surface of the parafoil canopy, thus creating a virtual spoiler from the stream of expelled ram air. The work reported here considers the autonomous landing performance of a small-scale parafoil and payload system using upper-surface bleed air spoilers exclusively for both lateral steering and glide slope control. Landing accuracy statistics computed from a series of Monte Carlo simulations in a variety of atmospheric conditi...

Use of Ground-Based Wind Measurements for Improved Guided Airdrop Accuracy

Uncertainty in atmospheric winds represents one of the primary sources of landing error in airdrop systems. While guided airdrop systems can compensate for uncertainties in the wind profile, unexpected winds in the drop zone can still result in large errors in landing location, and they can even lead to damage or complete loss of the cargo if the system hits the ground while traveling downwind. This work examines the impact of real-time knowledge of the winds in the drop zone on guided aidrop landing accuracy and landing quality. Measurements of the horizontal wind profile at multiple altitudes above the target provided by a ground-based LIDAR are considered in addition to a simple ground wind measurement. The guidance logic running on the airdrop system’s onboard autopilot is modified to integrate the wind measurements near the intended landing zone with onboard wind estimates to provide an improved, real-time estimate of the wind profile. The strategy is first developed in the framework of a rigorous simulation model and then validated in flight test. In both simulated and actual flight tests, knowledge of the wind profile near the target provided from the LIDAR unit improved landing accuracy by 40%. Knowledge of the ground winds alone provided by a low-cost, lightweight, highly portable device, again in both simulated and actual flight tests, is enough to improve landing accuracy by 33% and completely eliminate potentially dangerous downwind landings.

Shared Control of a Guided Parafoil and Payload System

The direct inclusion of human pilots into airdrop operations has a strong potential to increase the landing accuracy of conventionally autonomous guided airdrop systems. Human pilots have significant mental flexibility and an innate ability to prioritize requirements to aid safe and accurate landings. Autonomous algorithms on the other hand, are generally rigid in nature and cannot handle situations not directly programmed into the software. This paper outlines the work done to develop an integrated human-machine interface that combines the flexibility of human control decisions with the powerful ability of autonomous systems to measure data on the aircraft and generate key estimates. Two interfaces are presented melding a first person view camera mounted to the payload of the airdrop system and a birds eye GPS based map of the drop zone with relevant system estimates overlaid. Flight testing of these digital feedback methods to the pilot are studied to identify the ability of human operators to successfully and accurately control an airdrop system to the ground. Results indicated that a trained human operator has the ability to improve landing accuracy over a conventionally autonomous system by 36%.

Energy Harvesting From Hydraulic Pressure Fluctuations

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring in order to avoid catastrophic failures. These systems lend themselves to energy harvesting for powering sensor nodes. The foremost reason is that the power intensity of hydraulic systems is orders of magnitude higher than typical energy harvesting sources considered to date, such as wind turbulence, water flow, or vibrations of civil structures. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is what is termed dynamic pressure ripple caused by the action of pumps and actuators. Pressure ripple is conducive to energy harvesting as it is a deterministic source with an almost periodic time domain behavior. Pressure ripple generally increases in magnitude with the mean pressure of the system, which in turn increases the power that can be harvested. The harvested energy in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. An energy harvester prototype was designed for generating low-power electricity from dynamic pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining mechanical coupling to the system to allow for dynamic pressure induced deflection of the stack. The system exhibits an attractive off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack is much higher than the frequency content of ripple. Although the energy harvester is not excited at resonance, the high energy intensity of the ripple results in significant electrical power output. The prototype provided a maximum output of 1.2 mW at 120Ω. With these results, it is clear that the energy harvester provides non-negligible power output suitable for powering sensors and other low power components. This work also presents electromechanical model simulations for predicting the piezoelectric power output in terms of the force transmitted from the pressure ripple as well as experimental characterization of the power output as a function of the force from the ripple.Copyright

Comparative Investigation of the Electroelastic Dynamics of Piezoceramics With Interdigitated and Uniform Electrodes

Piezoelectric systems and structures have been used for decades in a variety of applications ranging from vibration control and sensing to morphing and energy harvesting. Conventional piezoelectric ceramics with uniform electrodes typically employ the 31-mode of piezoelectricity in bending, where the 3- and 1-directions are the directions of poling and strain, respectively. In order to employ the more effective 33-mode of piezoelectricity, Interdigitated Electrodes (IDEs) have been used recently in the design of the Macro-Fiber Composite (MFC). In this paper, an investigation into the two-way electroelastic coupling in bimorph cantilevers (in the sense of direct and converse piezoelectric effects) that employ IDEs for 33-mode operation is conducted. To this end, distributed-parameter electroelastic models are developed for the dynamic scenarios that involve two-way coupling, namely piezoelectric power generation and shunt damping as well as the problem of dynamic actuation. Various interdigitated MFC bimorph cantilevers are tested against the model under dynamic actuation, power generation, and shunt damping to identify their modal electromechanical coupling terms. Detailed investigations are conducted by decoupling the system dynamics to keep the direct and converse effects separately pronounced for parameter identification. Additionally, this work sheds light on the literature comparing the electrical power generation performances of 33-mode (interdigitated electrodes) and 31-mode (uniform electrodes) piezoelectric bimorphs of the same volume based on extensive experiments and distributed-parameter electroelastic modeling.Copyright

Adaptive Control of Precision Guided Airdrop Systems with Highly Uncertain Dynamics

The bulk of research in the field of precision guided airdrop systems has focused on improving landing accuracy in the presence of atmospheric winds that can exceed vehicle airspeed. One important challenge of parafoil systems is their highly uncertain flight dynamic behavior and control response, which can result from canopy degradation or an offnominal inflation event. This significantly impacts the ability to reach the target and can often lead to very large miss distances. This work addresses guided airdrop system model uncertainty with a novel combined direct and indirect adaptive control strategy to quickly characterize vehicle dynamics and lateral control sensitivity in flight. Extensive simulation and experimental flight testing indicate that the proposed adaptive algorithm is capable of high-accuracy landing in a large variety of degraded conditions, including unknown nonlinear changes in control sensitivity as well as control reversals. In comparison, current industry standard algorithms experie...