M. Amin Karami

Powering pacemakers from heartbeat vibrations using linear and nonlinear energy harvesters

Linear and nonlinear piezoelectric devices are introduced to continuously recharge the batteries of the pacemakers by converting the vibrations from the heartbeats to electrical energy. The power requirement of a pacemaker is very low. However, after few years, patients require another surgical operation just to replace their pacemaker battery. Linear low frequency and nonlinear mono-stable and bi-stable energy harvesters are designed according to the especial signature of heart vibrations. The proposed energy harvesters are robust to variation of heart rate and can meet the power requirement of pacemakers.

Electromechanical modeling of the low-frequency zigzag micro-energy harvester

An analytical electromechanical model is proposed to predict the deflection, voltage, and the power output of a proposed low-frequency micro-harvesting structure. The high natural frequencies of the existing designs of micro-scale vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this limitation. First, the natural frequencies and the mode shapes of the zigzag structure are calculated. The piezoelectric direct and reverse effect equations, together with the electrical equations, are used to relate the voltage output of the structure to the base vibrations magnitude and frequency. The closed-form solution of the continuous electromechanical vibrations gives the power output as a function of base acceleration spectrum. The usefulness of the design is proved by the significant increase of the power output from the same base accelerations, providing a method of designing a micro-scale harvester with low natural frequency. The optimal mechanical and electrical conditions for power generation are investigated through the case studies.

Modeling and experimental verification of a fan-folded vibration energy harvester for leadless pacemakers

This paper studies energy harvesting from heartbeat vibrations for powering leadless pacemakers. Unlike traditional pacemakers, leadless pacemakers are implanted inside the heart and the pacemaker is in direct contact with the myocardium. A leadless pacemaker is in the shape of a cylinder. Thus, in order to utilize the available 3-dimensional space for the energy harvester, we choose a fan-folded 3D energy harvester. The proposed device consists of several piezoelectric beams stacked on top of each other. The volume of the energy harvester is 1 cm3 and its dimensions are 2 cm × 0.5 cm × 1 cm. Although high natural frequency is generally a major concern with micro-scale energy harvesters, by utilizing the fan-folded geometry and adding tip mass and link mass to the configuration, we reduced the natural frequency to the desired range. This fan-folded design makes it possible to generate more than  10 μW of power per cubic centimeter. The proposed device is compatible with Magnetic Resonance Imaging. Although the proposed device is a linear energy harvester, it is relatively insensitive to the heart rate. The natural frequencies and the mode shapes of the device are calculated analytically. The accuracy of the analytical model is verified by experimental investigations. We use a closed loop shaker system to precisely replicate heartbeat vibrations in vitro.

ENERGY HARVESTING FROM CONSTRAINED BUCKLING OF PIEZOELECTRIC BEAMS

A piezoelectric vibration energy harvester is presented that can generate electricity from the weight of passing cars or crowds. The energy harvester consists of a piezoelectric beam, which buckles when the device is stepped on. The energy harvester can have a horizontal or vertical configuration. In the vertical (direct) configuration, the piezoelectric beam is vertical and directly sustains the weight of the vehicles or people. In the horizontal (indirect) configuration, the vertical weight is transferred to a horizontal axial force through a scissor-like mechanism. Buckling of the beam results in significant stresses and, thus, large power production. However, if the beam’s buckling is not controlled, the beam will fracture. To prevent this, the axial deformation is constrained to limit the deformations of the beam. In this paper, the energy harvester is analytically modeled. The considered piezoelectric beam is a general non-uniform beam. The natural frequencies, mode shapes, and the critical buckling force corresponding to each mode shape are calculated. The electro-mechanical coupling and the geometric nonlinearities are included in the model. The design criteria for the device are discussed. It is demonstrated that a device, realized with commonly used piezoelectric patches, can generate tens of milliwatts of power from passing car traffic. The proposed device could also be implemented in the sidewalks or integrated in shoe soles for energy generation. One of the key features of the device is its frequency up-conversion characteristics. The piezoelectric beam undergoes free vibrations each time the weight is applied to or removed from the energy harvester. The frequency of the free vibrations is orders of magnitude larger than the frequency of the load. The device is, thus, both efficient and insensitive to the frequency of the force excitations.

Experimental Study of the Nonlinear Hybrid Energy Harvesting System

This paper focuses on experimental nonlinear vibration analysis of the proposed hybrid energy harvester. A nonlinear energy harvesting structure is proposed to convert ambient vibrations to the electrical energy using the piezoelectric and electromagnetic mechanisms. A repelling magnetic force is introduced to the system to both reduce the resonant frequency of the system and increase the frequency bandwidth by making the vibrations nonlinear. The paper is the continuation of a previous work by the authors in which the vibrations of the harvester was analytically characterized. Both mono-stable and bi-stable situations are studied. Depending on the level of excitations the bi-stable system can exhibit oscillations about each of its equilibriums, chaotic vibrations or the limit cycle oscillations (LCO) over both of the equilibriums. The proper design of the harvester allows the system to perform Limit Cycle Oscillations in response to moderate base excitations. The paper discusses the experimental results on electro-mechanical vibrations and the energy generation of the nonlinear hybrid harvester at different magnetic force levels, excitation frequencies and excitation levels.

Controlled buckling of piezoelectric beams for direct energy harvesting from passing vehicles

A piezoelectric device is introduced and modeled to directly interact with the tires of passing vehicles and generate electrical power for roadside applications. Piezoelectric beams are vertically placed on the surface of the road to generate energy from the load of passing vehices. A metal cap is connected to the top end of the bimorphs. The vertical motion of the metal cap is limited by the containing fixture of the device. Tires of the passing vehicles pass over the metal cap and force the bimorph into buckling. The buckling of the piezoelectric beam generates significant amount of power. By controlling the extent of deformation of the beam we make sure that the beam is not damaged by the buckling. To this end, the amount of axial recession of the metal cap (equal to axial deformation of the beam) is precision controlled by the containing fixture. When the beam deflects it axially shrinks due to geometric nonlinearities. This lowers the metal cap. After a certain amount of deformation the metal cap rests on the containing fixture and the tire load is no more transmitted to the piezoelectric beam.In this paper the performance of the proposed energy harvesting device is analytically modeled. Geometric nonlinearities and piezoelectric couplings have been included in the model. The vibrations of the device are transient. Power is generated when the tire pushes down the metal cap and when the metal cap springs back after the tire has passed. The design criteria for the device are discussed. It is demonstrated that the device can be realized with commonly used piezoelectric patches and can generate hundreds of milliwatts from the moving traffic. The device is not prone to resonance and generates notable amounts of power from passing of each tire. It therefore can be used as a self-sufficient sensor for traffic control.Copyright

Experimental investigation of fan-folded piezoelectric energy harvesters for powering pacemakers

This paper studies the fabrication and testing of a magnet free piezoelectric energy harvester (EH) for powering biomedical devices and sensors inside the body. The design for the EH is a fan-folded structure consisting of bimorph piezoelectric beams folding on top of each other. An actual size experimental prototype is fabricated to verify the developed analytical models. The model is verified by matching the analytical results of the tip acceleration frequency response functions (FRF) and voltage FRF with the experimental results. The generated electricity is measured when the EH is excited by the heartbeat. A closed loop shaker system is utilized to reproduce the heartbeat vibrations. Achieving low fundamental natural frequency is a key factor to generate sufficient energy for pacemakers using heartbeat vibrations. It is shown that the natural frequency of the small-scale device is less than 20 Hz due to its unique fan-folded design. The experimental results show that the small-scale EH generates sufficient power for state of the art pacemakers. The 1 cm3 EH with18.4 gr tip mass generates more than16 μW of power from a normal heartbeat waveform. The robustness of the device to the heart rate is also studied by measuring the relation between the power output and the heart rate.

Energy harvesting using rattleback: Theoretical analysis and simulations of spin resonance

This paper investigates the spin resonance of a rattleback subjected to base oscillations which is able to transduce vibrations into continuous rotary motion and, therefore, is ideal for applications in Energy harvesting and Vibration sensing. The rattleback is a toy with some curious properties. When placed on a surface with reasonable friction, the rattleback has a preferred direction of spin. If rotated anti to it, longitudinal vibrations are set up and spin direction is reversed. In this paper, the dynamics of a rattleback placed on a sinusoidally vibrating platform are simulated. We can expect base vibrations to excite the pitch motion of the rattleback, which, because of the coupling between pitch and spin motion, should cause the rattleback to spin. Results are presented which show that this indeed is the casethe rattleback has a mono-peak spin resonance with respect to base vibrations. The dynamic response of the rattleback was found to be composed of two principal frequencies that appeared in the pitch and rolling motions. One of the frequencies was found to have a large coupling with the spin of the rattleback. Spin resonance was found to occur when the base oscillatory frequency was twice the value of the coupled frequency. A linearized model is developed which can predict the values of the two frequencies accurately and analytical expressions for the same in terms of the parameters of the rattleback have been derived. The analysis, thus, forms an effective and easy method for obtaining the spin resonant frequency of a given rattleback. Novel ideas for applications utilizing the phenomenon of spin resonance, for example, an energy harvester composed of a magnetized rattleback surrounded by ferromagnetic walls and a small scale vibration sensor comprising an array of several magnetized rattlebacks, are included.

MODELING OF A BEAM WITH A MASS IN THE MIDDLE FOR HEART BEAT VIBRATION ENERGY HARVESTING

This work presents a model for energy harvesting characterization of a simply supported beam with a mass in the middle to be used for powering pacemakers from heartbeat vibrations. The required power for a typical pacemaker is about 1.0 microwatts. A uniform cross-section beam, bimorph structures, employing double piezoelectric layers is used. PSI-5H4E piezoelectric and brass substrate is used in this study. Different configurations are utilized to identify the optimal design for lightweight energy harvesting devices with low-power applications to tune the natural frequencies of the energy harvester towards the operating ambient vibration source. In this paper, the exact analytical solution of the piezoelectric beam energy harvester with Euler–Bernoulli beam assumptions is presented. The energy harvester is intended to generate power from heartbeat induced vibrations to power implantable cardiac devices. The base excitations are thus heartbeat induced tissue vibrations. The proposed configuration harvests energy from the reverberation of heartbeats and converts it to electricity and could generate about 0.22 microwatts of power. Using the Fourier transform, the frequency response function for the voltage; current and power of the harvester are obtained. The power output for a range of values for the resistive load connected to the bimorph PZT layers is investigated to determine the optimized value of the resistive load that gives the maximum power output for the corresponding configuration of the beam. Stress analysis is performed for the substrate and PZT layer to make sure that the stress are within the permissible values to avoid breaking or failing of the beam. Results show that the use of mid mass is capable of harvesting a significant power with the proposed configurations.© 2014 ASME

Energy harvesting from arterial blood pressure for powering embedded micro sensors in human brain

This manuscript investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the human brain. One of the major hurdles in recording and measuring electrical data in the human nervous system is the lack of implantable and long term interfaces that record neural activity for extended periods of time. Recently, some authors have proposed micro sensors implanted deep in the brain that measure local electrical and physiological data which are then communicated to an external interrogator. This paper proposes a way of powering such interfaces. The geometry of the proposed harvester consists of a piezoelectric, circular, curved bimorph that fits into the blood vessel (specifically, the Carotid artery) and undergoes bending motion because of blood pressure variation. In addition, the harvester thickness is constrained such that it does not modify arterial wall dynamics. This transforms the problem into a known strain problem and the...