Force Amplifier Research Articles

A Frequency Up-Conversion Piezoelectric Energy Harvester Shunted to a Synchronous Electric Charge Extraction Circuit.

A frequency up-conversion piezoelectric energy harvester (FUC-PEH) consists of a force amplifier, a piezoelectric stack, a low-frequency oscillator (LFO), and a stop limiter. The force amplifier generates the amplification of stress on the piezoelectric stack. The LFO, comprising a spring and a mass block, impacts the stop limiter during vibration to induce high-frequency oscillations within the piezoelectric stack. In this paper, we represent and simplify the FUC-PEH as a lumped-parameter model based on piezoelectric material constitutive equations and structural dynamic theories. Using the electromechanical analogy, we developed an equivalent circuit model (ECM) of the FUC-PEH. A parametric study was performed to investigate the impact of system parameters, such as spring stiffness and concentrated mass, on the FUC-PEH performance. The collision-induced amplitude truncation (AT) effect enlarges the operation bandwidth. ECM simulations show that low-frequency input excitation is converted into a high-frequency output response, enhancing the energy conversion efficiency. Furthermore, we aimed to improve the FUC-PEH's performance using a synchronous electric charge extraction (SECE) circuit. Using the ECM approach, we established a system-level model that considers the electromechanical coupling behavior. The simulation results provide insights into the performance of FUC harvesters with SECE circuits and offer valuable design guidance.

Man-Power-Amplifying Exoskeleton with Pneumatic Actuator

This study describes the activity of developing a force amplifier exoskeleton with one degree of freedom. The system was developed as a research prototype to conduct control system studies. The device consists of an arm with a pneumatic cylinder actuator controlled by a pressure regulator. As for the human–machine interface, the system has a force sensor. The idea is to verify the possibility of developing a simple system from the sensor system’s point of view and the control system’s architecture while simultaneously obtaining an effective, economical, and reliable device. The idea developed in this project is to use the user’s available ability to control movements in unknown environments. The user constitutes the central part of the entire control system: he defines the references for the speeds and forces to be applied to the environment and observes the rates of the controlled robotic system through his own sight and proprioceptive system. On the other hand, the machine produces and controls the forces applied to the environment by the actuator. In this way, the device shows an increased admittance. A mathematical system model was created to verify the idea’s feasibility. Following the results of the simulations, a prototype was built on which experimental tests were carried out. As stated above, it was possible to obtain the described behavior with the use of a force sensor, one-axis type, interposed between the machine and the user, to constitute the human–machine interface; using a pressure regulator, it was possible to avoid the sensors for the force feedback by the environment. The result is a simple architecture for the sensors and the control algorithm. Specific test protocols were proposed to test the performance of the human–machine “system”, and a test bench was developed that allows the tracking of variable signals represented on a monitor, which the user must follow. The system is intuitive to use, with a rapid learning curve, and the user can handle high loads according to the different signals to be followed with good precision, even at high speeds.

Investigation of nonlinear magnetic stiffness based thin-layer stacked piezoelectric generators with a force-amplification structure

This paper investigates a nonlinear piezoelectric stack energy harvester incorporating a magnetic spring (NPEH) that utilizes impact-induced frequency modulation to augment the harvested power. The proposed configuration comprises a force amplifier, a piezoelectric stack, a spring-mass system, and a limiter. We formulate a two-degree-of-freedom (2DoF) theoretical model that accounts for the nonlinear characteristics of the system and corroborate it with experimental data. We examine the effects of system parameters on the output performance of the NPEH and demonstrate that the nonlinear magnetic spring facilitates a wideband energy harvesting. For instance, when the surface magnetic field intensities of the upper and lower magnets are 156 mT and 256 mT, respectively, the operational bandwidth reaches 5.23 Hz, which is 154 % greater than that of a linear spring system. Additionally, the nonlinear magnetic spring mitigates the voltage decay during the collision period due to its hysteresis response, thereby increasing the average power. At an excitation frequency of 9 Hz and with surface field strengths of the upper and lower magnets set at 156 mT and 256 mT respectively, the NPEH generates an RMS power of 2.2 mW (with an instantaneous power peak of 1.20 W). We provide design guidelines for optimizing the energy harvesting performance based on the parametric analysis.

Experimental research of a dual-beam compressive-mode piezoelectric energy harvester

In this article, we present a dual-beam compressive-mode piezoelectric energy harvester (DC-PEH). The DC-PEH is made up of a force amplifier, a piezoelectric stack, and a pair of symmetrically arranged cantilever-mass systems, supported by a base that is fixed on a rod. A two-stage force amplification mechanism of the DC-PEH is realized by coupling the elastic beams with the force amplifier. We first established a force analysis to describe the two-stage force amplification effect of the DC-PEH. Furthermore, a prototype has been fabricated and we carried out a series of experiments. We examined the open-circuit voltage and working bandwidth of the DC-PEH to verify the two-stage force amplification effect under different accelerations. Moreover, a parametric study was performed to investigate the influence of structure parameters on the output performance of the DC-PEH. We conducted the frequency sweep response and power output comparisons with different lengths of beams and different masses.

Magnetostrictive biomechanical energy harvester with a hybrid force amplifier

Vibrating energy harvesters, capable of converting mechanical energy into electrical energy, have attracted unprecedented interest in both academia and industry because of their great potential for harvesting energy induced by human activity and energy around the body, and to drive low-power wearable biosensors and electronics, micro-robots, and implantable biomedical devices. In this paper, based on the magnetostrictive inverse effect, we propose a magnetostrictive vibration harvester using Terfenol-D, which generates electrical energy when subjected to human movement. A hybrid force amplification frame is integrated in this harvester to amplify weak biological movements. The detailed mathematical model of the multi-stage force amplification process is established, the hybrid force amplifier is also designed in detail, and its structural dimensions are optimized. The position and form of the bias magnetic field arrangement based on the Terfenol-D harvester is systematically analyzed. The experiment shows that 4.13 V peak voltage and 426.4 mW peak power are generated when the harvester is fully compressed. The output power is 213.16 mW and 371.43 mW at an average acceleration of 2.5 g for slow walking and 4 g for jogging, respectively. The results of this study suggest that the combination of rod Terfenol-D and force amplification mechanisms can be used to design bio-vibrational energy harvester with excellent performance, which is especially suitable for self-powered wearable electronic devices.

Towards real-time self-powered sensing with ample redundant charges by a piezostack-based frequency-converted generator from human motions

This paper presents a piezostack-based frequency up-converting generator for scavenging ultra-low frequency (lower than 5 Hz) vibration energy associated with human motion. The generator, consisting of a force amplifier, a piezoelectric stack, a spring-mass system, and a spring limiter, realizes ultra-low frequency conversion mainly through the impact-induced frequency conversion effect. To estimate the output voltage of the generator numerically, we built a two-degree-of-freedom (2DOF) equivalent model based on the mechanical structure of the harvester. Moreover, we conducted five series of experiments to investigate the output performance of a fabricated prototype. The prototype generates an instantaneous peak-peak output power of 5.56 W (averaged power of 0.93 mW) excited by human running motions. A 'SHU' LED array was lighted up in real-time successfully. We then tested the performance of the prototype in a real-time self-powered system. The generator is able to power a watch and a thermometer in real-time. More importantly, when the excitation stops, they are powered by redundant charges for approximately 50 minutes and 1 minute, respectively. This research can make an essential contribution to ultra-low frequency vibration energy harvesting and the realization of real-time self-powered wearable devices.

Design, modeling and testing of a vibration absorption device with energy harvesting based on force amplifier and piezoelectric stack

This article presents the design, modeling and testing of a novel vibration absorption device with energy harvest based on compliant mechanism and piezoelectric stack. The vibration absorption device can absorb external vibration with high bandwidth through a hybrid compliant mechanism. Meanwhile, the mechanical energy of the vibration can be converted into electrical energy by piezoelectric stack. The hybrid compliant mechanism contains a bridge type force amplifier and a lever type force amplifier both based on flexure hinges. The analytical model is established for predicting the force amplification ratio and the output electricity power. Also, the dimensions of the device are optimized. A prototype is fabricated and tested with input vibration at different frequencies. The experimental results are well identical with the analytical model. In addition, the proposed vibration absorption device has better performance by comparing with existing designs.

The use of a piezoelectric force sensor in the magnetic force microscopy of thin permalloy films

A piezoelectric force sensor is suggested for magnetic force microscopy (MFM) purposes. Added between the piezoelectric resonator and the magnetic probe is a mechanical force amplifier in the form of a thin, long resonant arm with an integral micro-rod whereby the amplitude of the force acting on the probe is amplified by a factor of 20 to 40 at a low noise level. When the sensor was operated in air, its noise floor was found to be 1.4 pN (RMS) at a bandwidth of 100 Hz. The piezoelectric sensor requires no repeated calibration; and it is capable of operating in a vacuum, and at cryogenic temperatures. By using this sensor we carried out the MFM of ultrathin (1.5- and 3-nm-thick) Ni79Fe21 permalloy films. The 1.5-nm-thick permalloy films studied have a nanoisland structure, whereas 3-nm-thick ones are contiouous. Domain structures were found in both. The MFM image was found to suffer substantial changes when the external magnetic field was altered by 1 Oe. The structures under study featured both “elastic” and “viscous” magnetic force components.

Harnessing energy from spring suspension systems with a compressive-mode high-power-density piezoelectric transducer

In this paper, we present a compressive-mode high-power-density piezoelectric transducer for harvesting vibration energy from spring suspension systems. This device is comprised of a piezoelectric stack and a force amplifier. The piezoelectric stack is mainly composed of multiple PZT-5H piezoelectric units. The force amplifier strengthens the force on the piezoelectric stack to increase the generated energy. We propose an electromechanical conversion relation for the transducer. In this paper, we studied the output capabilities of a prototype though a series of experiments. The experimental results verify the proposed relation and show that the prototype can reach an average output power of 13.63 mW at the resonant frequency of 46.3 Hz under the 0.3 g harmonic excitation with the 1.975 kΩ matched impedance. The prototype has an excellent charge performance with microfarad level capacitors. For instance, the prototype charged a 1000 μF capacitor to saturation (7.5 V) within 18.1 s. The maximum 420 LED diodes were successfully lit by the prototype. Furthermore, the prototype charged a 3 V, 25 mAh lithium battery by 0.017 V in 300 s. This research can be of great significance for piezoelectric energy harvesting and powering wireless sensors in spring suspension systems.

Design and performance enhancement of a force-amplified piezoelectric stack energy harvester under pressure fluctuations in hydraulic pipeline systems

Pipelines are a safe and environmentally friendly way to convey fluids over a long distance. Pressure fluctuations generated by unsteady flows are a common phenomenon in hydraulic pipeline systems. In this paper, a piezoelectric stack energy harvester is designed to scavenge the vibration energy of pressure fluctuations in pipeline systems, where a force amplifier is introduced as an auxiliary booster to enhance the energy conversion efficiency under low-frequency excitation levels. The device can be integrated with health monitoring sensors to eliminate the needs of batteries or wired power supplies to individual sensors. The working principle of the force amplifier is analyzed by investigating the magnification coefficient based on a dynamic model. The optimized structural parameters are also investigated by theoretical studies. Besides, the finite element model of the force amplifier is also constructed to analyze the magnification coefficient and to validate the theoretical results. Experimental studies are also carried out to identify the effect of the force amplifier on the proposed energy harvester. The results show that there is great potential to realize a self-powered wireless sensor network technology for pipeline monitoring.

Design and Development of a Novel Two-Directional Energy Harvester With Single Piezoelectric Stack

This article presents the design, fabrication, and testing of a novel piezoelectric energy harvester. Its unique feature is that a single piezoelectric stack is used for harvesting the energy from two-directional excitation in vertical directions. To accept the input forces in two directions, a flexure-based two-stage force amplifier is integrated with a conical transmission mechanism and a sliding guiding mechanism. An analytical model is established to predict the force amplification ratio of the proposed energy harvester. In order to maximize the output performance of the energy harvester, the dominant parameters of the mechanism are determined, which are optimally designed by resorting to a genetic algorithm. A prototype energy harvester is fabricated for experimental testing. Experimental results indicate that the developed harvester exhibits the advantages of high safety factor, large force amplification ratio, and compact size. It can provide the maximum average output power density of over 286.70 kW · m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> from 10-N force excitation in two directions.

Design and testing of a new dual-axial underfloor piezoelectric energy harvester

This paper presents the design, fabrication, and testing of a dual-axial underfloor piezoelectric energy harvester based on piezoelectric stack. Usually, an underfloor energy harvester can only scavenge the energy from vertical force excitation. In addition to vertical pressure, the floor also suffers from lateral friction force during human walking. One uniqueness of the designed underfloor energy harvester lies in that it can collect energy from both vertical and horizontal excitation forces. To amplify the input force to get a larger output power, a flexure-based two-stage force amplifier is introduced and optimally designed. In order to transmit the two-directional (2-D) input force into the single direction that can be received by the force amplifier, the conical transmission mechanisms and slider mechanisms are introduced. Position limiters are adopted to protect the proposed mechanism. A prototype has been fabricated and tested. Experimental results indicate that the fabricated dual-axial piezoelectric energy harvester can provide an average output power up to 1.25 mW with a load resistance of 12 kΩ from 5 Hz force excitation of 100 N in two directions. With a load resistance of 26 kΩ, the harvested energy per walking footstep is derived as 7.00 mJ for the underfloor energy harvester.

Design of a Novel Two-Directional Piezoelectric Energy Harvester With Permanent Magnets and Multistage Force Amplifier.

This article presents the design and testing of a novel two-directional (2-D) piezoelectric stack-based energy harvester for capturing the mechanical energy from the human footstep. The uniqueness of the harvester lies in the fact that the energy of 2-D excitation is scavenged by a single piezoelectric stack transducer, which can reduce the loss of harvestable energy. The harvester is constructed by the integration of permanent magnets, position protection plates, and multistage force amplification frame. The input force and input displacement are restricted to guarantee the device's safety. The reported multistage force amplification frame with leverage mechanism and bridge-type amplifier enlarges the force acting on the piezoelectric stack, which further improves the power output. A linear guiding mechanism based on leaf flexure is applied to minimize the impact of input forces in other than moving directions. Through analytical modeling, the main architectural parameters of the device are determined. Simulation study with finite-element analysis is conducted to optimize the device parameters for achieving the largest force amplification ratio with a high safety factor. A prototype harvester is fabricated for experimental study. Results demonstrate the feasibility of the developed 2-D piezoelectric stack-based energy harvester.

Design, Fabrication, and Testing of a Novel 3-DOF Energy Harvester With Single Piezoelectric Stack

Abstract This paper presents the design, fabrication, and testing of a novel single stack-based piezoelectric energy harvester (PEH) for harvesting energy from three-degree-of-freedom (3-DOF) force excitation. One uniqueness lies in that the 3-DOF energy harvesting is implemented by using one piezoelectric stack. To scavenge energy from the 3-DOF input force, the proposed PEH is constructed with several force transmission mechanisms and slider mechanisms. The direction of the input force is first changed by the force transmission mechanisms, and the redundant force components are eliminated by the slider mechanisms. The transmitted force is then amplified by a two-stage force amplifier mechanism to improve the electric power output. The key parameters were found by establishing an analytical model of the proposed PEH. The best output performance of the PEH is achieved by selecting and optimally designing the key parameters. A prototype harvester was fabricated, and several experimental studies were conducted to verify the device performance. Results show the effectiveness of the developed 3-DOF PEH under the input force applied in x-axis, y-axis or z-axis. Furthermore, the issues that affect the practical application are discussed.

Design of a Novel Piezoelectric Energy Harvester Based on Integrated Multistage Force Amplification Frame

This paper proposes a novel integrated multistage energy harvester to scavenge the mechanical energy from human footstep during walking. The device involves a four-stage force amplification using wedge mechanism, leverage mechanism, half-bridge mechanism, and bridge-type force amplifier. It is devised to magnify the input force exerted on a piezoelectric stack so as to enhance the power output. By fully exploiting the characteristics of the force amplification frame, the harvester also provides the function of position protection, which enables the bearing of large load and thereby protecting the piezoelectric stack. By this, the maximum displacement input is restricted to a certain range to ensure the walking comfort. A static analytical model of the energy harvester is established through the force analysis based on the stiffness matrix method. The main architectural parameters of the device are optimized by adopting a multiobjective genetic algorithm with ANSYS software. Moreover, a prototype is fabricated for experimental investigation. Experimental results show that the harvester exhibits a large force amplification ratio of 17.9 and high-peak power output of 50.8 mW across a matched resistor.

Design of a New Piezoelectric Energy Harvesting Handrail With Vibration and Force Excitations

This paper presents the design, fabrication and testing of a new type of energy harvesting handrail. One uniqueness of the handrail energy harvester is that it has two working modes for collecting the energy excited by both vibration and pulling force during the operation. In order to enable good stability and anti-jamming ability for the energy harvester, a compound bridge-type compliant force amplifier is adopted and its parameters are optimized based on multi-objective genetic algorithm with finite-element analysis simulation. Analytical dynamic model is established for the piezoelectric device and the output power is calculated. A prototype harvester is fabricated for experimental investigation. Experimental results verify the effectiveness of the derived analytical model. Moreover, results show that the maximum power output is up to 150 μW under vibration excitation and 15 mW under random pulling force input. A series of the designed energy harvesters can be used to scavenge the energy generated by passengers in a bus or subway under different motion states.

Design and testing of a novel bidirectional energy harvester with single piezoelectric stack

Abstract This paper presents the design, fabrication and testing of a novel piezoelectric energy harvester with a single piezo-stack for harvesting energy from excitations with bidirectional motion. A rhombus-type force amplifier is combined with a selectivity lever to utilize both pull and push inputs. Analytical model is established to predict the force amplification ratio of the proposed energy harvester under different directions of input force. In order to maximize the output performance of the energy harvester, the mechanism parameters are optimally designed. A prototype energy harvester is fabricated for experimental testing. Results indicate that the developed harvester has the merits of high safety factor and compact size, which can be adopted to harvest the mechanical energy for excitations with both pull and push inputs in bidirectional directions.

Dynamic simulation and optimization of clamping mechanism of online tension testing machine for wire ropes

Abstract This study analyzes the slipping and crushing behaviors of a steel wire rope during a tensile test using a curve-type clamping mechanism to realize safe and reliable clamping during safety testing. Then the dynamic simulation analysis of the clamping and stretching processes is performed using the finite element method. The reasons for the damage caused to the wire rope by clamping force are investigated. The clamping mechanism of the tensile testing machine is improved using a force amplifier and the optimization design of its jaws. The experimental results show that the improved clamping mechanism can effectively clamp the wire rope for tensile testing and meet test requirements.

Design of a New Piezoelectric Energy Harvester Based on Compound Two-Stage Force Amplification Frame

This paper presents the design and verification of a piezoelectric energy harvester with compound two-stage force amplification frame and compact footprint size to achieve high power output for a piezoelectric stack. An improved design of the conventional bridge-type force amplification frame is proposed with compound beam, which is able to maintain the large force amplification ratio while bearing a large loading force. Analytical model is developed based on Euler-Bernoulli beam theory to predict the force amplification ratio of the compound two-stage force amplifier. The architectural parameters are optimally tuned to achieve the largest force amplification ratio, so as to obtain the maximum power output for the piezoelectric stack under other constraints. Simulation study is carried out by finite element analysis to demonstrate the advantage of the proposed compound two-stage force amplifier over conventional design. Moreover, a prototype harvester is fabricated for experimental testing. Results indicate that the proposed harvester features high safety factor, large amplification ratio, and compact size, which can be adopted in practical application for scavenging energy induced by human footstep during walking.

Nationalism and war for territory: from ‘divisible’ territories to inviolable homelands

How did the rise of nationalism affect patterns of interstate wars? The conventional wisdom in mainstream security studies tends to treat the rise of nationalism as a ‘force amplifier’ that allowed states to wage war on an unprecedented scale, leading to deadlier—and, consequently, less frequent—wars. By building on emerging interdisciplinary research on territory and territoriality, this essay suggests that there was a second mechanism—complementary to the ‘force amplifier’ logic—through which the rise of nationalism affected the patterns of interstate war: nationalism changed the ‘character’ of territories in the modern state system, which, in turn, transformed state preferences over their territorial belongings. Before the rise of nationalism, state elites viewed their territories more as ‘divisible’ goods, which created strong incentives for states to wage frequent yet limited wars. The rise of nationalism, in this context, rendered territory controlled by a state more of an ‘inviolable homeland’, which then contributed to the increasing severity and decreasing frequency of interstate wars. The arguments presented in this essay have implications for not only the study of nationalism and war, but also bargaining models of war and the so-called ‘border fixity’ norm.