Hyun Jeong Song

Energy Harvesting Devices Using Macro-fiber Composite Materials

This study addresses the experimental validation of a design methodology for an energy harvesting device utilizing macro-fiber composite (MFC) materials. The energy harvesting device is composed of a cantilever beam with MFC elements, a tip mass, a rectifier, and an electrical resistance. A theoretical model of the energy harvesting device was developed for the estimation of generated power, voltage, and current under sinusoidal base excitation at its first natural frequency, and its performance verified via experiment. A parametric study was performed to gain insight into methods to maximize generated power and current based on perturbations to beam thickness, length, width, and density. Performance characteristics of the energy harvesting device utilizing two types of MFC patches (d31- and d33-types) were experimentally evaluated under different acceleration levels. In addition, the effects of beam thickness, natural frequency, and electrical resistance were experimentally investigated.

Stiffness and Damping in Fe, Co, and Ni Nanowire-Based Magnetorheological Elastomeric Composites

The stiffness and damping properties of the aligned magnetorheological (MR) elastomer composites filled with 10 wt% Fe, Co, and Ni nanowires were investigated under normalized strain amplitude of 1, 2, and 3%, cyclic deformation frequency of 1 Hz, and magnetic flux density of 0, 0.1, and 0.2 T. The highest values of the dynamic stiffness are observed for the Ni- and the lowest for the Fe-based composites within the whole range of strain amplitude and magnetic flux density. The MR effect on the dynamic stiffness is the most significant for 1% strain amplitude and it almost completely disappears for 3% amplitude for all composites. The equivalent damping coefficient values have maxima for 1% strain amplitude for all composites. These values abruptly drop with an increase of strain amplitude to 2% and only slightly change as strain amplitude is further increased to 3%. The MR effect on the equivalent damping coefficient is high for all composites and strain amplitudes.

Energy Harvesting Utilizing Single Crystal PMN-PT Material and Application to a Self-Powered Accelerometer

This study investigates the performance of an energy harvester (EH) utilizing a single crystal lead magnesium niobate-lead titanate (PMN-PT) material via analysis and experiment. The EH, intended to convert mechanical energy at a harmonic frequency such as from a fixed revolutions per minute (RPM) rotating machine, was composed of a cantilever beam having a single crystal PMN-PT patch, a tip mass, a rectifier, and an electric load. The fundamental frequency of the EH was finely adjusted via moving a tip mass spanwise. The analysis was used to select an optimal EH configuration based on a weight constraint (less than 200 g) and a narrow band frequency range (nominally 60 Hz). The analysis and performance were validated experimentally for different excitation levels. The harvested dc power was measured for low acceleration levels of 0.05-0.2 g (where 1 g=9.81 m/s 2 ) typical of rotating machinery. The maximum dc power generated was 19 mW for an excitation of 0.2 g. The measured power density (i.e., maximum dc power over total device volume) and measured specific power (i.e., maximum dc power over total device mass) of the energy harvester were 0.73 mW/cc and 0.096 mW/g, respectively. The EH developed in this study was compared with other configurations and types via metrics of mean square acceleration weighted power (MSAP) and MSAP density. Charging performance of the single crystal PMN-PT based EH was evaluated by recharging a battery. In addition, the effect of the capacitance of the rectifier circuit on charging time was also investigated. Finally, the EH was also used to drive an accelerometer using only energy that was harvested from ambient vibration. The accelerometer was continuously and successfully operated when the persistent excitation level exceeded 0.1 g.

PERFORMANCE EVALUATION OF MULTI-TIER ENERGY HARVESTERS USING MACRO-FIBER COMPOSITE PATCHES

This study presents the performance evaluation of a vibration-based energy harvester using macro-fiber composite (MFC) elements, which can harvest power from environmental or ambient vibration and shock. An innovative multi-tier energy harvester (MTEH), comprised of a small number of vibrating beam elements with same fundamental frequencies, is developed in this study to overcome the harvested power limitations of single-tier energy harvesters (STEHs) with only a single vibrating beam element. First, the governing equations of motion of an MTEH were theoretically obtained for series and parallel connections of pairs of MFC patches on each tier surface. Based on the theoretical model, a vibration-based MTEH, having three tiers with MFC patches adhered to the bottom and top of each tier surface, was designed and fabricated. MTEH performance, which included generated voltage, current, and power, was experimentally and theoretically evaluated in the frequency domain and compared with that of a similar STEH.

Field dependent response of magnetorheological elastomers utilizing spherical Fe particles versus Fe nanowires

This study compares the dynamic response of nanowire-based magnetorheological elastomers (MREs), to those containing conventional spherical particles. MRE samples were fabricated by curing the iron particle laden elastomeric material in a magnetic field. Material characteristics of the MRE samples were evaluated using a material test machine that was modified to measure static and frequency dependent characteristics of these samples under different magnetic fields. The MRE samples consisted of a silicone rubber matrix containing various weight fractions of iron particles of differing morphology. Nanowires were used to enhance the interaction forces and contact area between particles. The static and dynamic properties of the MREs were evaluated under a compressive load for the various compositions and weight fractions. The stress vs. strain characteristics were measured for each sample. The equivalent damping coefficient of the MRE samples was measured and characterized under magnetic fields of differing intensities. The dynamic characteristic (dynamic stiffness) was measured under sinusoidal excitation in the frequency domain.

Comparison of monolithic and composite piezoelectric material–based energy harvesting devices

This study presents a comparison of the energy harvesting capacity of monolithic and composite piezoelectric materials, especially in the same energy harvesting configuration. The energy harvesting device was composed of a cantilever beam with active piezoelectric materials, a full-bridge rectifier circuit and an electrical load (resistance). Two energy harvesting devices were fabricated, both of which had piezoelectric patches mounted on top and bottom of the cantilever vibrating element. The first energy harvesting device utilized PZT-5H patches as a monolithic piezoelectric material, and the second energy harvesting device used macro-fiber composite patches as a composite piezoelectric material. The vibrating element used in this study was a stainless steel cantilevered beam with the same dimension as the patch. Characteristics of the energy harvesting devices, including generated power, current, and voltage, were compared in frequency domain and evaluated with respect to the electrical load under different excitation levels. In addition, the effects of the natural frequencies of the energy harvesting devices to the harvesting performance were evaluated. The power density (i.e. power over volume) and specific power (i.e. power over mass) of the energy harvesting devices were compared. In addition, the current density (i.e. current over volume) and specific current (i.e. current over mass) were also presented. Finally, the charging and discharging performances of the energy harvesting devices were also evaluated using a polymer Li-ion battery as the electrical load.

Impact of Nanowire Versus Spherical Microparticles in Magnetorheological Elastomer Composites

This study presents static and dynamic characterization of nanowire-based magnetorheological elastomer (MRE) composites. MRE composites were synthesized using a silicone rubber filled with magnetizable particles. Fe and Co particles of varying weight fraction (10, 30, and 50 wt%) were dispersed in the elastomeric matrix. To assess particle morphology, nanowire-based MRE composites were compared with spherical microparticle- based MRE composites. Under static and sinusoidal compressive loads, the field-dependent properties of the MRE composites such as static and dynamic stiffness, elastic modulus, yield stress, and equivalent damping were measured using a modified material testing machine. To investigate particle alignment effects in nanowire-based MRE composites, samples were cured in the presence of a magnetic field (aligned nanowires) and in the absence of a field (unaligned nanowires).

Semi-Active Isolation System Using Self-Powered Magnetorheological Dampers

This study addresses experimental evaluation of a semi-active vibration isolation system using a self-powered magnetorheological (MR) damper. To this end, a self-powered MR damper was constructed by electronically connecting an MR damper with a power harvesting dynamic vibration absorber (DVA) that can convert mechanical energy due to vibration and shock into electrical energy by means of electromagnetic induction. In this study, an MR damper for seat suspensions of the Expeditionary Fighting Vehicle (EFV) was chosen for the application of the self-powered MR damper. The generated voltage, current, and power of the power harvesting DVA were experimentally measured in frequency domain under various acceleration levels of 0.3–1.2 g (where one g = 9.81 m/s2 ). In addition, damper force testing of the self-powered MR damper (i.e., in this study, a prototype EFV MR damper with the power harvesting DVA) was experimentally conducted in time and frequency domains. To evaluate vibration isolation performance of a semi-active isolation system using the self-powered MR damper, an EFV seat suspension mockup using the self-powered MR damper was constructed. Under eight different representative random excitation accelerations, the vibration isolation performance of the EFV seat suspension mockup using the self-powered MR damper was experimentally evaluated.Copyright

Analysis of Energy Harvesting Devices Using Macro-Fiber Composite Materials

This paper addresses modeling, design, theoretical and experimental characteristics of an energy harvesting device utilizing macro-fiber composite (MFC) materials. The energy harvesting device is composed of a cantilever beam with MFC materials, a tip mass, a rectifier, and an electrical resistance. An theoretical model of the energy harvesting device is established for estimation of generated power, voltage, and current under sinusoidal base excitation at its first natural frequency. Parametric studies are achieved to maximize generated power and current with variation of beam thickness, natural frequency, type of MFC and electrical resistance. Also, performance characteristics of the energy harvesting device with two MFC patches are theoretically and experimentally evaluated under different acceleration levels.Copyright

Energy Harvesting Utilizing Single Crystal PMN-PT Material

This study compares the measured and predicted characteristics of an energy harvester utilizing single crystal lead magnesium niobate-lead titanate (PMN-PT) material. The energy harvester is composed of a cantilever beam with a single crystal PMN-PT patch, a tip mass, a rectifier and an electric load. Characteristics of the energy harvester were studied via both analysis and experiment. A theoretical model was established and experimentally validated. Natural frequency of energy harvester was fixed with tip mass. The generated power was also experimentally obtained for different levels of acceleration. The energy harvester was also used to drive an accelerometer using only energy harvested from ambient vibration.Copyright