External Load Resistance Research Articles

Distributed Parameter Model for Assorted Piezoelectric Harvester to Prevent Charge Cancellation

Charge cancellation initiated by strain change of a continuous piezoelectric layer can significantly impact the performance. The proposed analytical model presents a cantilever with tip mass segmented bimorph piezoelectric for higher modes of vibration considering the effect of strain nodes. The bimorph piezoelectric segments are connected in parallel with an external resistive load. The electromechanical coupling factors and electric circuit equations are derived under the distributed-parameter extended Hamilton beam assumptions along with harmonic base translation without rotatory motion. These computed solutions are in good agreement with simulation using finite element method COMSOL software, as well as experimental data, which are mentioned in the literature.

Piezoelectric Pre-Stressed Bending Mechanism for Impact-Driven Energy Harvester

This paper experimentally demonstrates and evaluates a piezoelectric power generator bending mechanism based on pre-stressed condition whereby the piezoelectric transducer being bended and remained in the stressed condition before applying a force on the piezoelectric bending structure, which increase the stress on the piezoelectric surface and hence increase the generated electrical charges. An impact force is being exerted onto bending the piezoelectric beam and hence generating electrical power across an external resistive load. The proposed bending mechanism prototype has been manufactured by employing 3D printer technology in order to conduct the evaluation. A free fall test has been conducted as the evaluation method with varying force using a series of different masses and different fall heights. A rectangular piezoelectric harvester beam with the size of 32mm in width, 70mm in length, and 0.55mm in thickness is used to demonstrate the experiment. It can be seen from the experiment that the instantaneous peak to peak AC volt output measured at open-circuit is increasing and saturated at about of 70V when an impact force of about 80N is being applied. It is also found that a maximum power of about 53mW is generated at an impact force of 50N when it is connected to an external resistive load of 0.7KΩ. The reported mechanism is a promising candidate in the application of energy harvesting for powering various wireless sensor nodes (WSN) which is the core of Internet of Things (IoT).

Performance of a thermoelectric generator intensified by temperature oscillation

The present study aims to investigate the performance of a thermoelectric generator (TEG) under the influence of sinusoidal temperature distribution at the hot side or cold side surface. The impacts of the period and amplitude of the periodic temperature, the temperature difference between the two surfaces, and the external load resistance on the power output and efficiency of the TEG are studied. The numerical simulations indicate that the period of temperature fluctuation plays no part on the TEG performance, whereas the power output of the TEG is significantly affected by the oscillating temperature. The higher the temperature amplitude, the larger the power output. With the temperature amplitude of 75 K at the hot side surface, the power output can be intensified up to 18%. In contrast, the maximum improvement in the power output is less than 1% when the oscillating temperature is excited at the cold side surface with the temperature amplitude of 15 K. The predictions also suggest that the optimal external load resistance is not affected by the boundary conditions of oscillating temperature, and the TEG performance is identical when the temperature difference between the two surfaces is fixed.

Sex difference in the heat shock response to high external load resistance training in older humans

BackgroundLiterature reports on the effects of resistance training on heat shock protein70 (Hsp70) adaptation in older subjects are scarce. Moreover, the optimum training load required to obtain a beneficial adaptation profile is lacking. Therefore, the aim of this study was to determine the effects of resistance training at various external loads on extracellular Hsp70 (eHsp70) resting levels in older humans. MethodsFifty-six community-dwelling older (68±5years) volunteers were randomized to 12weeks of resistance training (3×/week) at either high-resistance (HIGH, 8 males, 10 females, 2×10–15 repetitions at 80% 1RM), low resistance (LOW, 9 Males, 10 Females, 1×80–100 repetitions at 20% 1RM), or mixed low resistance (LOW+, 9 Males, 10 Females, 1×60 repetitions at 20% 1RM followed by 1×10–20 repetitions at 40% 1RM). Serum was available from 48 out of the 56 participants at baseline and after 12weeks for determination of eHsp70. Mid-thigh muscle volume (computed tomography), muscle strength (1RM & Biodex dynamometer) and physical functioning (including 6min walk distance [6MWD]) were assessed. ResultsThere was a sex-related dichotomy in the heat shock response to high external load training. We observed a significant decrease in eHsp70 concentration in the HIGH group for female, but not male, subjects. At baseline, men had a larger muscle volume, leg press and leg extension 1RM compared to women (all p<0.001). Also, the 6MWD was significantly higher in men compared to women at baseline. However, this difference disappeared when correcting for height. Moreover, the overall functional performance and physical activity scores were similar in men and women. None of the participants' characteristics nor any of the outcome variables differed between groups at baseline. There was a significant increase in the strength and physical performance parameters in both men and women post-exercise (all p<0.05). Females in the HIGH group clearly demonstrated a larger gain in leg press 1RM and the isometric knee extensor strength compared to females in the LOW group (p=0.036 and p=0.044, respectively). More so, we found an inverse association between the change in eHsp70 levels and improvement in isometric knee extensor strength and 6MWD (r=−0.443, p=0.002 and r=−0.428, p=0.002; respectively) post exercise. ConclusionsOur results show that resistance training at high external load decreases the resting levels of eHsp70 in older females. Whether this reflects a better health status requires further investigation.

Coupled magneto-electro-mechanical lumped parameter model for a novel vibration-based magneto-electro-elastic energy harvesting systems

The objective of this paper is to present a coupled magneto-electro-mechanical (MEM) lumped parameter model for the response of the proposed magneto-electro-elastic (MEE) energy harvesting systems under base excitation. The proposed model can be used to create self-powering systems, which are not limited to a finite battery energy. As a novel approach, the MEE composites are used instead of the conventional piezoelectric materials in order to enhance the harvested electrical power. The considered structure consists of a MEE layer deposited on a layer of non-MEE material, in the framework of unimorph cantilever bars (longitudinal displacement) and beams (transverse displacement). To use the generated electrical potential, two electrodes are connected to the top and bottom surfaces of the MEE layer. Additionally, a stationary external coil is wrapped around the vibrating structure to induce a voltage in the coil by the magnetic field generated in the MEE layer. In order to simplify the design procedure of the proposed energy harvester and obtain closed form solutions, a lumped parameter model is prepared. As a first step in modeling process, the governing constitutive equations, Gauss's and Faraday's laws, are used to derive the coupled MEM differential equations. The derived equations are then solved analytically to obtain the dynamic behavior and the harvested voltages and powers of the proposed energy harvesting systems. Finally, the influences of the parameters that affect the performance of the MEE energy harvesters such as excitation frequency, external resistive loads and number of coil turns are discussed in detail. The results clearly show the benefit of the coil circuit implementation, whereby significant increases in the total useful harvested power as much as 38% and 36% are obtained for the beam and bar systems, respectively.

Enhanced performance of ZnO microballoon arrays for a triboelectric nanogenerator

In recent years, triboelectric nanogenerators (TENGs), harvesting energy from the environment as a sustainable power source, have attracted great attention. Currently, many reports focus on the effect of surface modification on the electrical output performance of the TENG. In this work, we have fabricated vertically grown ZnO microballoon (ZnOMB) arrays on top of pyramid-featured PDMS patterned film, contacted with PTFE film to construct the TENG. The electrical output performances of the designed TENG are presented under external forces with different frequencies. The corresponding output open-circuit voltage with ZnOMBs could reach about 57 V the current density about 59 mA m−2 at 100 Hz, which was about 2.3 times higher than without any ZnO. The global maximum of the instantaneous peak power could reach 1.1 W m−2 when the external load resistance was about 2 MΩ. Furthermore, the electrical output of the fabricated device could light 30 commercial LED bulbs without any rectifier circuits or energy-storage elements. This clearly suggests that this kind of surface modification can dramatically enhance the output performance of the TENG. Moreover, the design of TENG demonstrated here can be applied to various energy harvesting applications.

A prototype DC triboelectric generator for harvesting energy from natural environment

A prototype direct current Triboelectric Generator (DC-TEG) has been demonstrated to generate dc voltages by converting rotational mechanical energy into electrical energy. The generator primarily consists of four rotating wheels (two copper electrodes and two triboelectric wheels) utilizing polytetrafluoroethylene (PTFE) tape and nylon fabric as the triboelectric materials in its design. Once subjected to mechanical rotation, the interaction between the two triboelectric materials generates equal, but opposite charges and deposits them on the copper electrodes resulting in a dc voltage across an external load resistor. The power performance of the generator, with changes in angular frequency, has been measured. The DC-TEG can generate a dc voltage of about 1.5 mV across an external load of 15.14 kΩ at a rotational speed of 10 rev/sec. The dependences of current and power on the angular frequency have also been measured. Preliminary results suggest that the relationship between the dc voltage and angular frequency of rotation is quadratic, however further measurements at relatively higher angular frequencies are needed before a proper mathematical model may be established. The work here presents a new, cost-effective DC-TEG design for power scavenging from any naturally or artificially occurring rotational mechanical motion facilitated by either wind or flowing water for self-powered systems.

Broadband energy harvesting using nonlinear vibrations of a magnetopiezoelastic cantilever beam

This paper investigates the mechanical behavior of a unimorph piezoelectric cantilever beam with a tip magnet and nonlinear boundary conditions imposed by repelling permanent two external magnets, subjected to a harmonic base excitation for broadband energy harvesting. The energy harvester is modeled as an in-extensional beam with Euler-Bernoulli assumptions. The curvature and inertia terms are assumed to be nonlinear due to large amplitude vibrations. The governing equations of motion are derived using the Euler-Lagrange equations. The reduced-order model equations (ROMs) are obtained based on the Galerkin method. A numerical study is performed to reveal the influence of different parameters such as tip magnet, presence and absence of the external magnets, gap distance between magnets, mechanical damping ratio and external resistance load on the scavenged power from the nonlinear energy harvester. It is shown that the addition of two external magnets and a sufficient tip magnet, and proper gap distance between magnets significantly increases the power and the voltage. In addition, it is shown that considering geometric nonlinearity, for both in the absence and presence of the two external magnets, affect and broaden the frequency range. It is observed that gap distance between beams significantly affect the frequency range and hysteresis region of the broadband energy harvester. Energy conservation is examined in the absence of the mechanical damping ratio, and it is shown that energy harvesting annihilates the vibrations. In addition, the effect of the external resistance load on the average power is discussed in the presence and absence of the external magnets for different value of the tip magnet and gap distance and the optimum value of the resistance load is obtained for each system.

Innovative design of a thermoelectric generator with extended and segmented pin configurations

A thermoelectric generator is one of the key candidates for the renewable energy devices, which directly converts waste heat into electricity. The wide applications of the device are suppressed because of the device low efficiency. In this paper, a new innovative design of the thermoelectric generator incorporating the extended pin with segmented pin configuration is introduced. The new design allows the device operating at two different cold junction temperatures. The maximum efficiency and the output power for the innovative design of thermoelectric device are formulated. The performance of the thermoelectric device is evaluated using the operating parameters such as the hot and cold junction temperatures in terms of temperature ratio, and external load resistance ratio. The reveals that the innovative design improves the maximum efficiency and output power of the thermoelectric generator. Increasing the cold junction temperature difference increases the device maximum efficiency by 3.5–6.2%. The maximum device output power and maximum thermal efficiency occur at different values of external load parameter. However, the reduction in the efficiency is considerably small for the external load parameter maximizing the device output work.

Electrokinetic streaming power generation using squeezing liquid flows in slit channels with wall slip

Electrical power generation via squeezing liquid motion is theoretically analyzed. Instead of squeezing discrete liquid droplets as extensively investigated in recent literature, we consider extracting the electrokinetic energy resulting from the streaming potential/current phenomenon by squeezing continuous liquid flows in an arbitrary number of slit channels arranged in parallel with an external load resistance and subjected to wall boundary slip. Analytical solutions to the instantaneous energy conversion efficiency, load current, and squeezing force and speed are derived assuming quasi-static, unidirectional flow conditions for the two squeezing modes of constant squeezing speed and force. Electrokinetic energy conversion efficiencies predicted by our present linear analysis for the two squeezing modes are found to be mathematically the same despite the drastic differences found in the load current and squeezing force-speed responses between the two modes. Parametric studies reveal that energy conversion efficiencies above 30% can be attained by introducing boundary slip, and that the value of the external load resistance at which the energy conversion efficiency approaches to maximum varies with respect to variations in the slip length, number of slit channels, and the slit channel geometry. Depending on the parametric conditions given, the electrokinetic energy conversion efficiency can either be increased or decreased as the separation distance between the slit channel parallel plates is reduced over the duration of the squeezing motion. Conversion efficiencies are also discussed in terms of the Debye parameter, liquid conductivity, and surface conductance for the electrokinetic power generator considered herein.

Hybrid Energy Cell with Hierarchical Nano/Micro-Architectured Polymer Film to Harvest Mechanical, Solar, and Wind Energies Individually/Simultaneously.

We report the creation of hybrid energy cells based on hierarchical nano/micro-architectured polydimethylsiloxane (HNMA-PDMS) films with multifunctionality to simultaneously harvest mechanical, solar, and wind energies. These films consist of nano/micro dual-scale architectures (i.e., nanonipples on inverted micropyramidal arrays) on the PDMS surface. The HNMA-PDMS is replicable by facile and cost-effective soft imprint lithography using a nanoporous anodic alumina oxide film formed on the micropyramidal-structured silicon substrate. The HNMA-PDMS film plays multifunctional roles as a triboelectric layer in nanogenerators and an antireflection layer for dye-sensitized solar cells (DSSCs), as well as a self-cleaning surface. This film is employed in triboelectric nanogenerator (TENG) devices, fabricated by laminating it on indium-tin oxide-coated polyethylene terephthalate (ITO/PET) as a bottom electrode. The large effective contact area that emerged from the densely packed hierarchical nano/micro-architectures of the PDMS film leads to the enhancement of TENG device performance. Moreover, the HNMA-PDMS/ITO/PET, with a high transmittance of >90%, also results in highly transparent TENG devices. By placing the HNMA-PDMS/ITO/PET, where the ITO/PET is coated with zinc oxide nanowires, as the top glass substrate of DSSCs, the device is able to add the functionality of TENG devices, thus creating a hybrid energy cell. The hybrid energy cell can successfully convert mechanical, solar, and wind energies into electricity, simultaneously or independently. To specify the device performance, the effects of external pushing frequency and load resistance on the output of TENG devices are also analyzed, including the photovoltaic performance of the hybrid energy cells.

Triboelectric and Piezoelectric Effects in a Combined Tribo‐Piezoelectric Nanogenerator Based on an Interfacial ZnO Nanostructure

In this contribution, combined triboelectric and piezoelectric generators (TPEG) with a sandwich structure of aluminum‐polydimethylsiloxane/polyvinylidene fluoride composite‐carbon (Al‐PPCF‐Carbon) are fabricated for the purpose of mechanical energy harvesting. Improved by the surface modification of PPCF with zinc oxide (ZnO) nanorods through a hydrothermal method, the TPEG generates an open‐circuit voltage (Voc) of ≈40 V, a short‐circuit current (Isc) of 0.28 μA with maximum power density of ≈70 mWm−2, and maximum conversion efficiency of 34.56%. Subsequently, in order to understand the transduction mechanism of the triboelectric and piezoelectric effects, analyses focusing on the potential composition ratio in the final output and the impact of ZnO interfacial nanostructure are carried out. The observed potential ratio between triboelectric and piezoelectric effects is 12.75:1 and the highest potential improvement by ZnO nanorods of 21.8 V is achieved by the TPEG fabricated with spacer. Finally, the relationships between the voltage, power density, conversion efficiency, and the external load resistances are also discussed. Overall, the fabricated TPEG is proved to be a simple and effective nanogenerator in mechanical energy conversion with enhanced output potential and conversion efficiency.

Configuration of segmented leg for the enhanced performance of segmented thermoelectric generator

Thermal analysis of a segmented thermoelectric generator is performed, and the segmented leg configurations maximizing the efficiency and the output power are formulated. The effect of operating conditions such as external load resistance, the temperatures of hot and cold junctions, on the device performance is studied. The segmented thermoelectric generator has the leg configuration consisting of the combination of modified lead telluride and modified bismuth telluride. The segmented thermoelectric generator performance, such as device efficiency and output power, is compared with those corresponding to a single material leg configuration (modified lead telluride or modified bismuth telluride) for various operating conditions. It is found that a unique value of the segmented leg combination maximizes the efficiency and the output power for each operating condition. The variation in the operating conditions changed the locus points of the maximum efficiency and the maximum output power. The segmented thermoelectric generator gives rise to the higher device efficiency and the output power than those of the single material leg configuration, especially for the low external load resistance. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous degradation of refractory organic pesticide and bioelectricity generation in a soil microbial fuel cell with different conditions

ABSTRACTIn this study, the soil microbial fuel cells (MFCs) were constructed based on sandy soil to remove the refractory organic pesticide hexachlorobenzene (HCB) in topsoil by a simple method. The construction of membraneless single-chamber soil MFCs by setting up the cathode- and the anode-activated carbon, inoculating the sludge and adding the co-substrates can promote HCB removal significantly. The results showed that HCB removal efficiencies in the soils contaminated with 40, 80 and 200 mg/kg were 71.14%, 62.15% and 50.06%, respectively, which were 18.65%, 18.46% and 19.17% higher than the control, respectively. The electricity generation of soil MFCs in different HCB concentrations was analyzed. The highest power density reached was 70.8 mW/m2, and an internal resistance of approximately 960 Ω was obtained when an external resistance loading of 1000 Ω was connected. Meanwhile, the influences of temperature, substrate species and substrate concentrations on soil MFCs initial electricity production were investigated. The addition of the anionic surfactant sodium dodecyl sulfate (SDS) into the soil MFCs system contributed to the improvement in HCB removal efficiency.

Nonlinear performances of an autoparametric vibration-based piezoelastic energy harvester

Nonlinear characterizations of an autoparametric vibration-based energy harvester are investigated. The harvester consists of a base structure subjected to an external excitation and a cantilever beam with a tip mass. Two piezoelectric sheets bounded to both sides of the cantilever beam are used to harvest the energy. The governing equations accounting for the coupled effects of the base vibration, the response of the cantilever beam and the generated power are derived. Approximate analysis of the simplified governing equations is then performed by the method of multiple scales. The usefulness of this approach is demonstrated by deriving analytical expressions for the global frequency and damping ratio of the cantilever beam. Their dependence on the electrical load resistance is quantified. Analytical expressions for the amplitudes of the base displacement and the displacement of the tip mass are derived. An expression that relates the output power to the load resistance, global damping, and displacement of the tip mass is derived. The effects of the external force and electric load resistance on the nonlinear responses of the system are determined. The results show different responses for different operational electric loads. The broadening of the excitation regime over which energy can be harvested is analyzed. The effects of the load resistance on the types of bifurcations near resonance are determined.

Performance Analysis of a Mini-Thermoelectric Engine for the Generation of Electricity

In this research work a small thermal engine was utilized for generation of electrical energy and its operation was analyzed in terms of the output performance with various external load resistances and different flywheel rotations. It was seen from the results that with increase of the external load there is a less considerable increase in voltage. It has been observed that by an increasing the external load from 100 Ω to about 2000 Ω, a rapid decrease in the output power is occurred. However, beyond a specific value of about 2000 Ω the decrease in the electrical power is relatively small. It was obvious from the results of output voltage, current and power with respect to the increase in hot air temperature (T1) that these physical quantities are increased at a constant rate for specific range of temperatures, from 185 °C to about 240 °C. It was worth mentioning that at higher temperatures the rate of increase in output voltage was reduced, implying that the expansion rate of hot air is getting saturated and the rotating speed of the flywheel reached its maximum capability to generate electricity.

Performance Analysis of a Mini-Thermoelectric Engine for the Generation of Electricity

In this research work a small thermal engine was utilized for generation of electrical energy and its operation was analyzed in terms of the output performance with various external load resistances and different flywheel rotations. It was seen from the results that with increase of the external load there is a less considerable increase in voltage. It has been observed that by an increasing the external load from 100 Ω to about 2000 Ω, a rapid decrease in the output power is occurred. However, beyond a specific value of about 2000 Ω the decrease in the electrical power is relatively small. It was obvious from the results of output voltage, current and power with respect to the increase in hot air temperature (T1) that these physical quantities are increased at a constant rate for specific range of temperatures, from 185 °C to about 240 °C. It was worth mentioning that at higher temperatures the rate of increase in output voltage was reduced, implying that the expansion rate of hot air is getting saturated and the rotating speed of the flywheel reached its maximum capability to generate electricity.

One-dimensional InGaZnO field-effect transistor on a polyimide wire substrate for an electronic textile

Amorphous InGaZnO (IGZO) is a promising semiconducting material to replace amorphous and polycrystalline Si. IGZO-based field-effect transistors (FET) can be versatile platforms for various electronic or optoelectronic applications. Here, we report on a one-dimensional (1-D) IGZO FET fabricated on a flexible polyimide wire substrate for electronic textiles (e-textiles). This flexible 1-D IGZO FET shows a high mobility of 18.18 cm2/Vs with a relatively good on/off current ratio of 104 at operating voltages below 5 V. Furthermore, a resistive-load inverter is implemented by connecting the 1-D IGZO FET to an external load resistor. Such an inverter exhibits obvious voltage switching characteristics, verifying the potential it is being a basic building block for an e-textile circuit system.

Thermal characteristics of a skutterudite thermoelectric generator: influence of device pin length on efficiency and output power

Thermodynamic analysis is presented in terms of dimensionless operating parameters, which includes temperature and load resistance ratios, and dimensionless device pin length for a skutterudite thermoelectric generator. To obtain the device geometric configuration maximising the thermal efficiency, the device characteristics are computed for various values of operating and pin geometric parameters. It is found that the device maximum efficiency does not coincide with the optimum dimensionless device pin length corresponding to the maximum thermal efficiency. Altering load resistance from its optimum value lowers the thermal efficiency considerably and the thermal efficiency variation becomes gradual for the reduced external load resistance. In addition, electrical resistance of the thermoelectric generator beyond its optimum value has an adverse effect on the thermal efficiency.

Nonlinear dynamics and comparative analysis of hybrid piezoelectric-inductive energy harvesters subjected to galloping vibrations

Modeling and comparative analysis of galloping-based hybrid piezoelectric-inductive energy harvesting systems are investigated. Both piezoelectric and electromagnetic transducers are attached to the transverse degree of freedom of the prismatic structure in order to harvest energy from two possible sources. A fully-coupled electroaeroelastic model is developed which takes into account the coupling between the generated voltage from the piezoelectric transducer, the induced current from the electromagnetic transducer, and the transverse displacement of the bluff body. A nonlinear quasi-steady approximation is employed to model the galloping force. To determine the influences of the external load resistances that are connected to the piezoelectric and electromagnetic circuits on the onset speed of galloping, a deep linear analysis is performed. It is found that the external load resistances in these two circuits have significant effects on the onset speed of galloping of the harvester with the presence of optimum values. To investigate the effects of these transduction mechanisms on the performance of the galloping energy harvester, a nonlinear analysis is performed. Using the normal form of the Hopf bifurcation, it is demonstrated that the hybrid energy harvester has a supercritical instability for different values of the external load resistances. For well-defined wind speed and external load resistance in the electromagnetic circuit, the results showed that there is a range of external load resistances in the piezoelectric circuit at which the output power generated by the electromagnetic induction is very small. On the other hand, there are two optimal load resistances at which the output power by the piezoelectric transducer is maximum. Based on a comparative study, it is demonstrated the hybrid piezoelectric-inductive energy harvester is very beneficial in terms of having two sources of energy. However, compared to the classical piezoelectric and electromagnetic energy harvesters, the results show that, considering a hybrid energy harvester leads to an increase in the onset speed of galloping and a decrease in the levels of the harvested power in both the piezoelectric and electromagnetic circuits which is explained by the additional resistive shunt damping effects in the hybrid energy harvester.