Energy Harvesting Backpack Research Articles

Experimental Verification of a Magnetically Geared Generator for Backpack Energy Harvesting System

Experimental Verification of a Magnetically Geared Generator for Backpack Energy Harvesting System

Biomechanical modeling and experiments of energy harvesting backpacks

The energy harvesting backpack is a promising solution for powering wearable electronic devices by converting biomechanical energy from human motion into electricity. However, the majority of current energy harvesting backpack models primarily focus on harvester dynamics while neglecting the crucial role of humans as an energy source in the system. Some studies have utilized inverted pendulum models through active control torque and optimization-based methods to investigate human factors in bioenergy harvesting systems, but this is complex for the practical application of biomechanical models. To overcome these issues, a new biomechanical model of the energy harvesting backpack is proposed in this paper. The contribution of this study is not only modeling the cooperative dynamics between backpacks and humans which is easily solvable and comprehensible but also defining multi-indicators for model verification and backpack evaluation. The biomechanical model without load is established based on the D' Alembert principle and empirical gait phase division of 3:1 when it is assumed that the gait parameters remain constant regardless of the load being carried. Four sets of data from two distinct databases are utilized to analyze the dynamics of the bipedal walking model in both vertical and horizontal directions. The biomechanical model with energy harvesting backpacks is proposed to define four single direct indicators and two global indirect indicators for demonstrating the proposed model’s ability to predict the characteristics of backpacks. Finally, the foot-reaction force, the vibration of the center of mass, and the output power of three subjects are acquired in five experiments (i) with no backpack under variable walking speed; (ii) an ordinary backpack under variable walking speed; (iii) an ordinary backpack under variable loads; (iv) an energy harvesting backpack under variable walking speed; and (v) an energy harvesting backpack under variable loads. The comparison between the proposed model and experimental results demonstrates that the proposed model is easy to solve and comprehend, and can effectively capture the characteristics of both human and energy harvesting backpacks.

Human motion energy harvesting backpack using quasi-zero stiffness mechanism

In this study, a quasi-zero stiffness energy harvesting backpack (QZS-EHB) is proposed. The bistable quasi-zero stiffness mechanism is constructed by paralleling a pair of positive stiffness springs and a pair of negative stiffness springs to make the vibration system more easily excited by low-frequency human motion and generate snap-through action. The bidirectional vibration is mechanically modulated into unidirectional higher speed rotation, thus improving the electromechanical conversion efficiency. The theoretical model of the bistable system is established by using the Lagrange functional method to verify the bistable mechanism. A prototype is manufactured to validate the advantages of the design. The effects of spring stiffness, load weight, and motion speed on the performance of the harvester are investigated through a series of experiments. The results show that the peak voltage is 5.11 V and the peak power is 2.37 W, and the average power of the harvester is 0.77 W, with the load of 5 kg and the speed of 10 km/h. The QZS-EHB can light up a combination of LED lamps with a total power of 6 W, charge the cell phone, and enable self-powered localization and wireless information transmission, when people are jogging with the load of 2 kg. These tests verify that the proposed design can be used for emergency power consumption of people's outdoor activities.

An innovative energy harvesting backpack strategy through a flexible mechanical motion rectifier

This paper reports a fundamentally different strategy for realizing high-performance energy harvesting backpacks to effectively scavenge ultralow-frequency human body motions. The proposed backpack strategy is based on an innovative flexible mechanical motion rectifier (MMR) that consists of an inelastic strap, an elastic strap, a shaft with a double-layered plectrum, and a rotor. The flexible MMR first converts the human motion induced vibrations to the alternating spin of a shaft, and then enables the mono-directional spin of a rotor by a shaft through the stiffness self-adaptive plectrum. To examine the feasibility of the proposed strategy, an energy harvesting backpack was constructed with an array of the flexible MMR-based harvesters, and an electromechanical model of the backpack was also established and verified. Both simulations and experiments reveal the high output power of the backpack under various human travel velocities. Experiments show that, under a running velocity of 9 km/h, the backpack with a small payload of 3.6 kg can deliver high output power of 1.284 W. Under a walking velocity of 6 km/h, the electric energy generated by only one harvester of the backpack with a payload of 1.7 kg is sufficiently large for charging both a smart bracelet and a smart phone. This study demonstrates the feasibility of achieving high-performance energy harvesting backpacks with the flexible MMR for portable and wearable electronics.

An Efficient Design of an Energy Harvesting Backpack for Remote Applications

During past couple of decades, energy harvesting from human body motion has been explored extensively to provide electricity needed for energizing cell phones and other gadgets. In this paper, an optimized design of a suspended-load backpack with a mechanical motion rectifier (MMR) is presented. The Genetic Algorithm (GA) is used to optimize the system parameters for producing maximum output power with an 8-kg backpack, which is the lightest proposed in previous studies. A prototype of the backpack is fabricated based on the obtained optimal parameters, and experimental results for a normal walking speed show instant power of 11.57 Watts and average power of 4.37 Watts, which are one of the highest among all models in previous works. Finally, a modified dynamic model of the backpack is proposed based on an experimental model of the human shoulders displacement during walking to minimize the output power error between numerical simulation data and experimental test results.

Bistable energy harvesting backpack: Design, modeling, and experiments

Inspired by the dynamics of the noninertial systems, a novel bistable energy harvesting backpack is proposed that improves biomechanical energy harvesting performance. In contrast to traditional bistable energy harvesters that use an oblique compressed spring, a new bistable backpack is developed that uses the change of a spring torque direction located on a pinion. A detailed nondimensionalized model of the novel bistable energy harvesting backpack is developed and analyzed. Based on the dynamic bistable model, the influence of the carried backpack mass on the symmetry and the bifurcation frequency and amplitude of oscillation is examined to determine the ideal design parameters of the bistable backpack for experimental analysis and prototype manufacture. A comparison is made between the new bistable backpack and a traditional linear backpack under both harmonic and human walking excitation. The new bistable backpack design exhibits an improved frequency bandwidth from 1 Hz to 1.65 Hz at the base harmonic excitation of 2 m/s2 and the harvesting performance is enhanced from 2.34 W to 3.32 W when the walking speed is 5.6 km/h. The bench and treadmill tests verify the theoretical analysis and demonstrate the ability of the bistable energy harvesting backpack for broadband and performance enhancement.

A piezoelectric vibration energy harvester based on the reverse-rhombus double-bridge force amplification frame

In recent years, the use of wearable and portable electronic devices has steadily increased. These devices are becoming more and more powerful. However, advances in device performance have resulted in the need for significantly higher power to operate electronic devices. The power supply problem of these electronic devices has become one of the factors hindering their development. In order to solve the power supply problem of these electronic devices, researchers have begun to study methods of generating energy from the ambient sources. This study presents the design, modeling and experimental tests of a novel piezoelectric energy harvester with the reverse-rhombus double-bridge force amplification frame, which can harvest energy from human motion. The double-bridge structure of the energy harvester can effectively amplify the force acting on the piezoelectric stack and improve the output performance of the energy harvester. A lumped parameter model for the vibration energy harvester based on the piezoelectric stack is presented and the analytical formulations for the electromechanical coupling are derived. The non-linear model is simulated to study the effects of the parameters, such as preload, external excitation frequency and load resistance, on the output performance. The prototype of the vibration energy harvester based on piezoelectric stack was fabricated. The shaker experiment and the backpack energy harvesting experiment were performed. The theoretical model is validated through comparisons with simulation and experimental results. The piezoelectric energy harvester developed in this paper can be used to harvest the mechanical energy of the human motion, as well as the vibration energy of the surrounding environment. The presented theoretical model can be utilized to model other types of piezoelectric energy harvester and predict their output performance.

Backpack Energy Harvesting System With Maximum Power Point Tracking Capability

A backpack energy harvester converts mechanical energy associated with the oscillation of the backpack during human walking, into electric energy. It can be a very promising solution for supplying portable devices, especially in outdoor activities, disaster relief, and military applications. In this article, a backpack energy harvesting system that is able to self-adapt its operating condition to maximize the extracted power while supplying a dc load is presented and studied, analytically and experimentally. It is based on a mechanical motion rectifier that converts the up-and-down oscillation of the backpack into a unidirectional rotation of a dc generator. The generator output voltage is regulated by a power electronic interface implementing a maximum power point tracking technique to maximize the extracted power. Experimental results confirm the tracking ability of the proposed system and show the advantages with respect to other wearable energy harvesting systems published in the literature.

Multi-parameter theoretical analysis of wearable energy harvesting backpacks for performance enhancement

Wearable energy harvesting technologies show a promising potential in IoT (Internet of Things) and human daily life because of their continuous power supply in place of traditional chemical batteries. However, the coupling effects between mechanical and electrical parameters, as well as human motion features, significantly complicate the performance of wearable energy harvesters. To address this issue, a multi-parameter theoretical analysis is conducted in this paper to improve the performance of an energy harvesting backpack composed of a spring, mass, electromagnetic motor, and rack-pinion-based power takeoff. The analytical equation of the average output power of the energy harvesting backpack is derived as a function of spring stiffness, external resistance, and structural and electrical damping. A comprehensive analytical analysis and numerical simulation are performed based on the average power equation to study the influence of carried mass and walking speed on the energy conversion performance. Experimental tests are implemented for different human subjects, various carried mass, spring stiffness, and electrical resistances to verify the analytical analysis. Theoretical and experimental results demonstrate that the optimal carried mass and external resistance for generating the maximum power output are determined by the total damping of the mechanical system and electrical circuit instead of resonance. Moreover, the sensitivity of power output to the human walking frequency and the carried mass can be reduced by sacrificing the peak output power. The results show that the optimal backpack with a carried mass of 12.95 kg can generate 4 W power at the walking speed of 5.6 km/h.

Design, modelling, and testing of a vibration energy harvester using a novel half-wave mechanical rectification

Portable and wearable electric devices are an important part of our life and the energy supply is critical for their functions. Energy harvesting from human motion is a promising solution to provide the energy supply. This paper presents the design, modeling and testing of a vibration energy harvester using a novel half-wave mechanical rectification to enhance the performance of suspended energy harvesting backpack. The proposed half-wave mechanical rectification mechanism uses one set of rack-pinion and a one-way clutch that converts bidirectional vertical oscillation into unidirectional rotation of the generator with nonlinear inertia. As validated by both modelling and bench tests, the proposed half-wave mechanical rectification-based energy harvesting system can obtain about twofold average output power as the previous full-wave mechanical rectification system in the desired dominant excitation frequency and also maintains larger output power in the target frequency range. The influences of external resistance, human walking speed, and payload mass are also studied to comprehensively characterize the performance and robustness of the proposed design. Treadmill tests on different human subjects demonstrate an average power range of 3.3–5.1 W under a walking speed of 4.8 km/h (3 mph) with a 13.6 kg (30 lbs.) payload. Experimental results indicate that the proposed suspended energy harvesting backpack could continuously generate an amount of electricity suitable for powering portable and wearable electronic devices, which can be applied to the military, field workers, outdoor enthusiasts and disaster relief scenarios.

Comparison of Control Strategies and Electromechanical Devices for the Backpack Energy Harvesting System

This article provides a general overview on the control strategies and their implications for the backpack energy harvesting system. The control strategies include reactive control and resistive damping. The study is performed for three cases of electric generator: the direct drive linear generator, the rotary machine integrated with the trans-rotary magnetic gear (MITROMAG), and the rotary machine coupled with a mechanical rack and pinion (MRP). Equivalent circuits based upon electrical–mechanical analogies are employed to help understand the system dynamics under the two control strategies. It is shown that in all cases, upon reactive control, more power can be harvested; however, it comes at the cost of a higher velocity, peak power, and force requirement. Moreover, it is shown that for most of the operating points considered, the direct drive linear generator outperforms the geared electromechanical devices in terms of the harvested power. Furthermore, it is revealed that the low stiffness of the MITROMAG slightly increases its harvested power compared to the MRP under the resistive damping strategy.

Energy Harvesting Backpacks for Human Load Carriage: Modelling and Performance Evaluation

In recent years, there has been an increasing demand for portable power sources as people are required to carry more equipment for occupational, military, or recreational purposes. The energy harvesting backpack that moves relative to the human body, could capture kinetic energy from human walking and convert vertical oscillation into the rotational motion of the generators to generate electricity. In our previous work, a light-weight tube-like energy harvester (TL harvester) and a traditional frequency-tuneable backpack-based energy harvester (FT harvester) were proposed. In this paper, we discuss the power generation performance of the two types of energy harvesters and the energy performance of human loaded walking, while carrying energy harvesting backpacks, based on two different spring-mass-damper models. Testing revealed that the electrical power in the experiments showed similar trends to the simulation results, but the calculated electrical power and the net metabolic power were higher than that of the experiments. Moreover, the total cost of harvesting (TCOH), defined as additional metabolic power in watt required to generate 1 W of electrical power, could be negative, which indicated that there is a chance to generate 6.11 W of electricity without increasing the metabolic cost while carrying energy harvesting backpacks.

Vibration energy-harvesting using inerter-based two-degrees-of-freedom system

Rotary electromagnetic generators that have high power density, large power output, and large rotational inertia are increasingly used in vibration energy-harvesting systems. When applied to single-degree-of-freedom (SDOF) systems, it is found that the inertance reduces the system frequency bandwidth. Furthermore, the maximum power output of SDOF systems is limited by the mechanical damping and the maximum allowable stroke. Two-degrees-of-freedom (2DOF) energy-harvesting systems have been proposed in recent years and demonstrated to have larger power output and wider bandwidth compared with SDOF systems. However, a considerable additional physical mass has to be added to an SDOF system to create a 2DOF energy-harvesting system, which may increase the total weight and requires more space. By utilizing the rotational inertia of the electromagnetic generator and a line-to-rotation mechanism as inerter, an inerter-based 2DOF system that requires neglectable additional physical mass is proposed, in which a spring and an inerter are connected in series between the primary mass and the vibration base. Parameters including the mass ratio, the frequency tuning ratio, the spring ratio, and the damping ratio, were optimized for the inerter-based 2DOF system. Optimal specific power with stroke limitation was obtained. A benchmark test using an energy harvesting backpack was done to validate the analysis results. Both analyses and experimental tests show that the inerter-based 2DOF can have larger specific power and larger power-to-stroke ratio compared with its SDOF counterpart. The energy conversion efficiency is also improved. Compared with the conventional 2DOF system, the inerter-based 2DOF system is not only lightweight but also less sensitive to parameter changes.

Design, model, and performance evaluation of a biomechanical energy harvesting backpack

Abstract Introducing compliant elements to backpack structures has been shown to reduce both the peak forces experienced by the user and the metabolic cost of walking. In previous work, we developed a novel load carriage system that allowed weight carried in a backpack to oscillate in the medial-lateral direction. In this paper, we introduce a new energy harvesting module, to be added to the load carriage module, that generates electricity from the movement of the carried mass. The energy harvesting module is implemented for two outcomes: to generate electricity for powering portable electronics and to effectively modulate oscillation amplitude and phase of the carried mass in the load carriage system. This paper outlines the design, model, and performance evaluation of our novel energy harvesting device. First, a model was developed so that we may determine device parameters that result in desired device behaviour. Then, the model was evaluated using a combination of bench top experiments and human walking experiments to validate its predictive capabilities. Testing revealed that the model can be used to predict general device behaviour, but could be further developed to improve accuracy. Lastly, we evaluated device performance in human walking experiments. The energy harvesting device generated up to 0.22 ± 0.08 W of electrical power while walking. Walking with the device while generating electricity did not significantly increase user effort, compared to walking with the weight rigidly fixed.

Leakage Flux of the Trans-Rotary Magnetic Gear

This paper investigates the leakage flux of the trans-rotary magnetic gear (TROMAG). TROMAG is a magnetic gear that converts a high-force low-speed linear motion to a low-torque high-speed rotation and vice versa. TROMAG is tailored to force-intensive linear motion applications such as backpack energy harvesting and artificial heart in which the gear is positioned close to the human body and/or electronic devices. In such applications, it is critical to ensure the TROMAG’s magnetic field penetrating the surrounding environment (referred to as the leakage flux hereafter) is below the limits permitted by standards. This paper employs 3-D finite-element analysis (FEA) to study spatial distribution and magnitude of the leakage flux. The FEA calculations of magnetic field are verified by experimental measurements. Both radial and quasi-Halbach configurations are investigated, and it is revealed that the quasi-Halbach configuration exhibits less leakage flux. Moreover, it is shown that the use of a thin iron shield surrounding the TROMAG can effectively reduce the leakage down to permissible values.

Design and Treadmill Test of a Broadband Energy Harvesting Backpack With a Mechanical Motion Rectifier

The energy harvesting backpack that converts the kinetic energy produced by the vertical oscillatory motion of suspended loads to electricity during normal walking is a promising solution to fulfill the ever-rising need of electrical power for the use of electronic devices in civilians and military. An energy harvesting backpack that is based on mechanical motion rectification (MMR) is developed in this paper. Unlike the conventional rack-pinion mechanism used in the conventional energy harvesting backpacks, the rack-pinion mechanism used in the MMR backpack has two pinions that are mounted on a generator shaft via two one-way bearings in a way that the bidirectional oscillatory motion of the suspended load is converted into unidirectional rotation of the generator. Due to engagement and disengagement between the pinions and the generator shaft, the MMR backpack has broader bandwidths than the conventional energy harvesting backpacks; thus, the electrical power generated is less sensitive to change in walking speed. Two male subjects were recruited to test the MMR backpack and its non-MMR counterpart at three different walking speeds. For both subjects, the MMR backpack for most of the time generated more power than the non-MMR counterpart. When compared with literature, the MMR backpack had nearly sixfold improvement in bandwidth. Finally, the MMR backpack generated nearly 3.3 W of electrical power with a 13.6 kg load and showed nearly two- to tenfold increases in specific power when compared with a conventional energy harvesting backpack.

Wearable energy harvesting technologies: Physiological cost and operational readiness

Introduction: Two wearable energy harvesting systems – an Energy Harvesting Backpack (EHB) and a Knee Energy Harvester (KEH) – were evaluated to determine the effects on Soldier metabolics and the efficiencies of harvesting electrical energy during steady-state movement.

Effects of Carrying a Loaded Energy Harvesting Backpack on Trunk Lean

Soldiers are fielded with a wide range of loads to carry including battery powered electronic devices. An energy harvesting backpack (EHB) was developed to convert gait kinetic energy into electrical power, providing a power source to recharge batteries and reduce the load of extra batteries carried in standard backpacks. Little is known about the kinematic effects of carrying the EHB compared to the military standard assault pack (AP). PURPOSE: To determine if trunk lean changes when carrying the EHB compared to the AP and whether these changes are affected by pack, load, and speed. METHODS: Sixteen subjects (28.6±4.7 years; 173.9±10.1 cm; 76.9±16.1 kg) walked on an instrumented treadmill under 8 combinations of pack, load, and speed conditions each for 5 minutes. Conditions included 1) pack: AP and EHB, 2) load: 7.9 kg (light) and 15.9 kg (heavy), and 3) speed: 1.34 m/s and a self-selected faster speed. Due to its design, the empty EHB mass was 4.4 kg greater than the AP. Kinematic data were collected to calculate trunk lean relative to the vertical axis (degrees). A 3-way repeated measures ANOVA was used to determine effects of pack, load, and speed on trunk lean with an alpha level set a priori at p<0.05. Post-hoc pairwise comparisons were performed with Bonferroni corrections. RESULTS: A significant main effect of speed on trunk lean (F1,13=44.1, p<0.001) was observed where forward lean was greater at faster speeds (Slow: 3.8±0.6; Fast: 7.5±0.7, F1,13=44.1, p<0.001). There was a significant pack x load interaction on trunk lean (AP-Light: 1.4±2.1; AP-Heavy: 4.6±2.3; EHB-Light: 5.5±2.9; EHB-Heavy: 10.9±3.4; F1,13=15.5, p=0.002). Subjects using the EHB walked with greater increase in forward lean when carrying the heavy load. CONCLUSION: Walking with heavy loads and carrying the EHB produced greater increase in forward lean when compared to the AP. This suggests a potential nonlinear effect of pack and load on trunk lean. The weight cost or oscillation of the EHB may also contribute to these changes in gait. Phase relationships between the user and EHB centers-of-mass could be examined in future research to study the effects on gait biomechanics. Further analysis is also warranted to determine tradeoffs in power generated from the EHB and Soldier biomechanics while walking with the system.

The Effect of an Energy Harvesting Backpack on Perceived Exertion during Locomotion

Biomechanical energy harvesting from elastically-suspended load carriage is a promising source of power for Soldiers, who often march with heavy loads at varying speeds on various terrains. An energy harvesting backpack (EHB) has been developed which generates power from vertical oscillations during locomotion. Ideally, the EHB should not increase psycho-physiological burden compared to the standard military assault pack (AP). PURPOSE: To compare ratings of perceived exertion (RPE) while walking with an EHB and an AP at different speeds on different grades. METHODS: 16 subjects (M±SD; 28.6±4.9 years; 173.4±10.6 cm; 78.7±16.4 kg) walked on a treadmill with each pack for 5 minutes at each of three grades (+5%, 0%, and -5%) and each of two speeds (1.34 m/s and self-selected faster speed). Both the AP and EHB contained a 15.9 kg load, but the design of the EHB made it 4.4 kg heavier than the AP. A Borg RPE score was taken during the last 10 seconds of walking at each grade and speed. A within-subjects ANOVA was used to determine effects of pack, grade, and speed on log-transformed RPE. Alpha level was set a priori at p<0.05. Post-hoc comparisons were explored using Bonferroni corrections. RESULTS: There were main effects for pack, speed, and grade (F1,152=14.3, F1,152=100.1, and F1,152=346.3, respectively; p<0.001) with no interaction effects. Subjects reported a greater sense of exertion with the EHB (11.9±2.8) than with the AP (11.2±2.6) regardless of speed and grade. Faster speeds elicited higher RPE scores than slower speeds (13.1±2.4 and 10.1±2.1, respectively), while the incline grade produced higher RPE scores (13.1±2.5) than decline and level grades (10.3±2.3 and 11.2±2.5, respectively). CONCLUSIONS: The EHB caused greater levels of perceived exertion that were not altered by walking speed or grade. This may be due to the extra stabilization required or the extra weight cost of the EHB. Kinematic variables (trunk lean) related to this research suggest potential non-linear effects of EHB use, which may also be related to the increased perceptions of exertion found here. This may affect trade-offs between power generation, perceived exertion, and metabolic cost that warrants further research and may ultimately affect user-acceptance of suspended-load energy harvesting systems in the field.

Energy harvesting through a backpack employing a mechanically amplified piezoelectric stack

Over the past few decades, the use of portable and wearable electronics has grown steadily. These devices are becoming increasingly more powerful, however, the gains that have been made in the device performance has resulted in the need for significantly higher power to operate the electronics. This issue has been further complicated due to the stagnate growth of battery technology over the past decade. In order to increase the life of these electronics, researchers have begun investigating methods of generating energy from ambient sources such that the life of the electronics can be prolonged. Recent developments in the field have led to the design of a number of mechanisms that can be used to generate electrical energy, from a variety of sources including thermal, solar, strain, inertia, etc. Many of these energy sources are available for use with humans, but their use must be carefully considered such that parasitic effects that could disrupt the user's gait or endurance are avoided. This study develops a novel energy harvesting backpack that can generate electrical energy from the differential forces between the wearer and the pack. The goal of this system is to make the energy harvesting device transparent to the wearer such that his or her endurance and dexterity is not compromised. This will be accomplished by replacing the strap buckle with a mechanically amplified piezoelectric stack actuator. Piezoelectric stack actuators have found little use in energy harvesting applications due to their high stiffness which makes straining the material difficult. This issue will be alleviated using a mechanically amplified stack which allows the relatively low forces generated by the pack to be transformed to high forces on the piezoelectric stack. This paper will develop a theoretical model of the piezoelectric buckle and perform experimental testing to validate the model accuracy and energy harvesting performance.