Energy harvesting from body motion using rotational micro-generation

Autonomous system applications are typically limited by the power supply operational lifetime when battery replacement is difficult or costly. A trade-off between battery size and battery life is usually calculated to determine the device capability and lifespan. As a result, energy harvesting research has gained importance as society searches for alternative energy sources for power generation. For instance, energy harvesting has been a proven alternative for powering solar-based calculators and self-winding wristwatches. Thus, the use of energy harvesting technology can make it possible to assist or replace batteries for portable, wearable, or surgically-implantable autonomous systems. Applications such as cardiac pacemakers or electrical stimulation applications can benefit from this approach since the number of surgeries for battery replacement can be reduced or eliminated. Research on energy scavenging from body motion has been investigated to evaluate the feasibility of powering wearable or implantable systems. Energy from walking has been previously extracted using generators placed on shoes, backpacks, and knee braces while producing power levels ranging from milliwatts to watts. The research presented in this paper examines the available power from walking and running at several body locations. The ankle, knee, hip, chest, wrist, elbow, upper arm, side of the head, and back of the head were the chosen target localizations. Joints were preferred since they experience the most drastic acceleration changes. For this, a motor-driven treadmill test was performed on 11 healthy individuals at several walking (1-4 mph) and running (2-5 mph) speeds. The treadmill test provided the acceleration magnitudes from the listed body locations. Power can be estimated from the treadmill evaluation since it is proportional to the acceleration and frequency of occurrence. Available power output from walking was determined to be greater than 1mW/cm³ for most body locations while being over 10mW/cm³ at the foot and ankle locations. Available power from running was found to be almost 10 times higher than that from walking. Most energy harvester topologies use linear generator approaches that are well suited to fixed-frequency vibrations with sub-millimeter amplitude oscillations. In contrast, body motion is characterized with a wide frequency spectrum and larger amplitudes. A generator prototype based on self-winding wristwatches is deemed to be appropriate for harvesting body motion since it is not limited to operate at fixed-frequencies or restricted displacements. Electromagnetic generation is typically favored because of its slightly higher power output per unit volume. Then, a nonharmonic oscillating rotational energy scavenger prototype is proposed to harness body motion. The electromagnetic generator follows the approach from small wind turbine designs that overcome the lack of a gearbox by using a larger number of coil and magnets arrangements. The device presented here is composed of a rotor with multiple-pole permanent magnets having an eccentric weight and a stator composed of stacked planar coils. The rotor oscillations induce a voltage on the planar coil due to the eccentric mass unbalance produced by body motion. A meso-scale prototype device was then built and evaluated for energy generation. The meso-scale casing and rotor were constructed on PMMA with the help of a CNC mill machine. Commercially available discrete magnets were encased in a 25mm rotor. Commercial copper-coated polyimide film was employed to manufacture the planar coils using MEMS fabrication processes. Jewel bearings were used to finalize the arrangement. The prototypes were also tested at the listed body locations. A meso-scale generator with a 2-layer coil was capable to extract up to 234 µW of power at the ankle while walking at 3mph with a 2cm³ prototype for a power density of 117 µW/cm³. This dissertation presents the analysis of available power from walking and running at different speeds and the development of an unobtrusive miniature energy harvesting generator for body motion. Power generation indicates the possibility of powering devices by extracting energy from body motion

Power Generation by Harvesting Ambient Energy with a Micro-Electromagnetic Generator

This thesis investigated the potential power output of a micro-electromagnetic generator fabricated using typical microfabrication materials and techniques. The design was based on a desire to free bio-implanted or remote electronic devices from batteries and their finite power supplies. A micro-electromagnetic generator could harvest energy from the ambient environment and power such devices indefinitely. Designs for the stator coil and rotor magnet components of the generator were optimized to produce maximum current density based upon electromagnetic theory. The relative orientation of the coil to the rotor and material selection for each component were considered. Coils were fabricated using low-resistance gold. A method for overlaying two evaporated gold wires was devised and successfully fabricated in order to avoid side-wall thinning of the coils which has been shown to lead to high resistivities. Rotors were made with nickel, a ferromagnetic material. The required parameters for reduced stress plating using a nickel electroplating bath were investigated in order to pattern and deposit nickel for the rotors. Once fabricated, the rotors were magnetized through the use of an electromagnet. In addition, a testing apparatus that provided precise alignment, a method of rotation to simulate operational functionality, and power measurement capabilities was designed and assembled. Testing of the magnets showed that the nickel rotors were able to be highly magnetized when placed near a strong field. However, upon removal from the field the magnetization quickly dissipated. It was determined that the coercivity, or magnetic hardness, of electroplated nickel was too low for the rotor magnets to retain a field for any appreciable amount of time. Testing of the micro-generator revealed that power output did not exceed 2 nA, which was expected given that the magnetic rotors did not retain their flux density. It was shown that nickel does not maintain the flux density required for a micro-electromagnetic generator and different materials should be investigated

Recent Advances in Energy Harvesting from the Human Body for Biomedical Applications

Energy harvesters serve as continuous and long-lasting sources of energy that can be integrated into wearable and implantable sensors and biomedical devices. This review paper presents the current progress, the challenges, the advantages, the disadvantages and the future trends of energy harvesters which can harvest energy from various sources from the human body. The most used types of energy are chemical; thermal and biomechanical and each group is represented by several nano-generators. Chemical energy can be harvested with a help of microbial and enzymatic biofuel cells, thermal energy is collected via thermal and pyroelectric nano-generators, biomechanical energy can be scavenged with piezoelectric and triboelectric materials, electromagnetic and electrostatic generators and photovoltaic effect allows scavenging of light energy. Their operating principles, power ratings, features, materials, and designs are presented. There are different ways of extracting the maximum energy and current trends and approaches in nanogenerator designs are discussed. The ever-growing interest in this field is linked to a larger role of wearable electronics in the future. Possible directions of future development are outlined; and practical biomedical applications of energy harvesters for glucose sensors, oximeters and pacemakers are presented. Based on the increasingly accumulated literature, there are continuous promising improvements which are anticipated to lead to portable and implantable devices without the requirement for batteries

Development of Electromagnetic Micro-Energy Harvesting Device

The use of energy harvesting devices has generated much research interests in recent years. There are numerous energy harvesters available in the market that are piezoelectric, electromagnetic, electrostatic or combination of piezoelectric and electromagnetic. Many of the harvesters have shown great potential but are either severely limited in power generation since they are actually never optimized to its potential. One of the goals of this thesis is to develop an electromagnetic micro-energy harvester that is capable of working at low frequencies (5-30 Hz) and is capable of producing electrical power for small devices. Generally, batteries have been used to power low voltage electronics, however the need for self-sustaining and reliable power source have always been a major issue. This project aims to make a harvester of size AA battery that can be used as a reliable and continuous source of power for bio-medical as well as industrial applications. Firstly, a linear harvester is developed for applications where there is no set natural frequency. The linear harvester consists of a stator and a mover. The stator includes copper coils, outer iron case and delrin holder for the coils while the mover consists of permanent magnets, iron pole and cylindrical rod. The working principles developed are used to optimize and improve the efficiency of energy harvesting system. The linear harvesting system is tested with the permanent magnet to iron pole ratio of 1.25 and permanent magnet to coil ratio of 0.73. The power density of the linear harvester is determined to be 4.44e-4 W/cm3. Thereafter, optimization is done in comsol to improve the performance of the energy harvesting system. The optimized magnet to iron ratio is determined to be 3.175 and permanent magnet to coil ratio of 0.7938. The optimized ratios are used to develop an inertial type non-linear energy harvesting device. The structure of the non-linear harvester is same as the linear one except two stationary magnets are added at the top and bottom of the harvester that act as a non-linear spring. The non-linear harvesting device is tested and the power density of the system is determined to be 2.738e-2 W/cm3. The non-linear harvester was tested at acceleration level of 1g and it was determined that the harvester worked best at natural frequency of 8.66 Hz. The maximum power produced was 38.1 mW. The non-linear type of harvester is easy to assemble and optimize to match ambient natural frequency of numerous vibrating systems. Two frequency tuning methods are looked at for the non-linear energy harvesting system. One is by changing the magnetic air gap and the second is by changing the thickness of the stationary top and bottom magnets. It is determined that changing magnetic air gap is more effective at tuning for a range of natural frequencies. For applications where the natural frequency of the system doesn't exist, such as buoys and beacons at sea, the linear energy harvester works best. For applications where the system vibrates at a certain natural frequency, the non-linear harvester should be used. Finally, this thesis is concluded with a discussion on the electromagnetic micro-harvester and some suggestions for further research on how to optimize and extend the functionality of the energy harvesting system

A study of a piezoelectric energy harvesting system using magnetorheological fluids

This thesis reports the study of a piezoelectric energy harvesting system using a thin layer of magnetorheological fluid as a soft impact mechanism to enhance the frequency of the energy generator. Currently, the major bottleneck of vibration energy harvesting is the dynamic nature of vibrations in the environment which necessitates that vibration energy harvesters change their frequency to match that of the source. This work used the variable rheological properties of magnetorheological fluids to tune the frequency of a piezoelectric energy harvester. The study employed both numerical and experimental studies to investigate the effect of using the fluid in vibration energy harvesting. The results obtained show an increase in the output voltage and frequency of the device by 9.7% and 36%, respectively. For the first time, a soft impact frequency-increased piezoelectric energy harvesting system using magnetorheological fluid is studied in this thesis

New Formulation for Finite Element Modeling Electrostatically DrivenMicroelectromechanical Systems

The increased complexity and precision requirements of microelectromechanical systems(MEMS) have brought about the need to develop more reliable and accurate MEMS simulation tools. To better capture the physical behavior encountered, several finite elementanalysis techniques for modeling electrostatic and structural coupling in MEMS devices havebeen developed in this project. Using the principle of virtual work and an approximationfor capacitance, a new 2-D lumped transducer element for the static analysis of MEMS hasbeen developed. This new transducer element is compatible to 2-D structural and beamelements. A novel strongly coupled 3-D transducer formulation has also been developed tomodel MEMS devices with dominant fringing electrostatic fields. The transducer is compatible with both structural and electrostatic solid elements, which allows for modeling complexdevices. Through innovative internal morphing capabilities and exact element integrationthe 3-D transducer element is one of the most powerful coupled field FE analysis tools available. To verify the accuracy and effectiveness of both the 2-D and 3-D transducer elements a series of benchmark analyses were conducted. More specifically, the numerically predicted results for the misalignment of lateral combdrive fingers were compared to available analytical and modeling techniques. Electrostatic uncoupled 2-D and 3-D finite element models werealso used to perform energy computations during misalignment. Finally, a stability analysisof misaligned combdrive was performed using a coupled 2-D finite element approach. Theanalytical and numerical results were compared and found to vary due to fringing fields

Exploiting the Principal Parametric Resonance of an RLC Circuit for Vibratory Energy Harvesting

The use of ambient energy sources to independently power small electronic devices, a process commonly known as energy harvesting, has recently become a focus of research due to advances in low-power electronic applications. A particular class of energy harvesting devices, known as vibratory energy harvesters (VEHs), utilizes low-level vibrations present in numerous natural and man-made environments to generate electrical energy for electronic devices. This work investigates the use of a new technique to harvest energy from ambient vibrations by parametrically exciting a resonance condition of the electric current in a nonlinear oscillating circuit. To accomplish this parametric resonance phenomenon, we consider an electromechanical coupling device, an oscillating cantilever beam with a ferromagnetic tip mass, which changes the permeability of an iron-alloy cored inductor coil to produce a harmonically-varying modulation of the inductance. Such a type of harvester possesses the potential to generate large amplitude System response that is not limited by the linear damping of the system, as is the case with directly-excited systems, but rather whose behavior is governed by the nonlinearity of the system. In order to study the ability of such an energy harvesting system to generate electricity when subject to external vibrations, we develop a second-order differential equation to model the theoretical dynamic behavior of a parametrically-driven nonlinear circuit. Due to the complexity of the nonlinear and harmonically-varying components of the governing equation, we use the Method of Multiple Scales to derive an approximate analytical solution for the steady-state current response and output power of the circuit near the principal parametric resonant frequency. We show that the relationship of parameter modulation depth and load resistance characterize the bandwidth of the response and define a critical forcing threshold, below which no energy is harvested. The harvested power is maximized when the load resistance is half of the maximum load resistance at which the critical threshold is still achieved for a given forcing level. We also demonstrate the need for nonlinear damping in the system to attenuate the growth of the response to a physically attainable level. We show the dependence of the natural frequency of the circuit on the parametric forcing parameter, which can lead detuning of the system at different forcing levels. An experimental set up is developed to test the assertions presented by the analytical model. Numerous parameter constraints are balanced in the experimental design in order to be able to achieve the critical forcing threshold necessary for exciting the parametric resonance condition. The frequency response behavior of the electrical current and load power in the circuit is observed by varying the natural frequency of the system, which is compared against the variation of forcing frequency presented in the theoretical section. The beam is excited at its natural frequency of 85.8 Hz across input accelerations ranging from 1:1g – 1:5g. A maximum output power of 28.67 mW across an 8 Ω resistance is achieved at an input acceleration of 1:5g. The behavior of the experimental data is in good agreement with the findings of the theoretical model with respect to the bandwidth, nonlinear behavior, and sensitivity to forcing and damping parameters. The analytical model under predicts the peak power measured experimentally, but the general trend is well modeled. Furthermore, several key observations are noted during the experimental procedures, notably the effects of eddy current damping on the behavior of the response and the development of quasiperiodic solutions near the saddle node bifurcation point

Towards Touch-to-Access Device Authentication Using Induced Body Electric Potentials

This paper presents TouchAuth, a new touch-to-access device authentication approach using induced body electric potentials (iBEPs) caused by the indoor ambient electric field that is mainly emitted from the building's electrical cabling. The design of TouchAuth is based on the electrostatics of iBEP generation and a resulting property, i.e., the iBEPs at two close locations on the same human body are similar, whereas those from different human bodies are distinct. Extensive experiments verify the above property and show that TouchAuth achieves high-profile receiver operating characteristics in implementing the touch-to-access policy. Our experiments also show that a range of possible interfering sources including appliances' electromagnetic emanations and noise injections into the power network do not affect the performance of TouchAuth. A key advantage of TouchAuth is that the iBEP sensing requires a simple analog-to-digital converter only, which is widely available on microcontrollers. Compared with existing approaches including intra-body communication and physiological sensing, TouchAuth is a low-cost, lightweight, and convenient approach for authorized users to access the smart objects found in indoor environments.Comment: 16 pages, accepted to the 25th Annual International Conference on Mobile Computing and Networking (MobiCom 2019), October 21-25, 2019, Los Cabos, Mexic

A three-axis accelerometer for measuring heart wall motion

This thesis presents the work carried out in the design, simulation, fabrication and testing of miniaturised three-axis accelerometers. The work was carried out at the Faculty of Science and Engineering at Vestfold University College (Tønsberg, Norway), the MIcroSystems Engineering Centre (MISEC) at Heriot-Watt University and in collaboration with the Interventional Centre at Rikshospitalet University Hospital (Oslo, Norway). The accelerometers presented in this thesis were produced to be stitched to the surface of human hearts. In doing so they are used to measure the heart wall motion of patients that have just undergone heart bypass surgery. Results from studies carried out are presented and prove the concept of using such sensors for the detection of problems that can lead to the failure of heart bypasses. These studies were made possible using commercially available MEMS (MicroElectroMechanical Systems) three-axis accelerometers. However, the overall size of these sensors does not meet the requirements deemed necessary by the medical team (2(W) 2(H) 5(L) mm3) and fabrication activities were necessary to produce custom-made sensors. Design verification and performance modelling were carried out using Finite Element Analysis (FEA) and these results are presented alongside relevant analytical calculations. For fabrication, accelerometer designs were submitted to three foundry processes during the course of the work. The designs utilise the piezoresistive effect for the acceleration sensing and fabrication was carried out by bulk micromachining. Results of the characterisaton of the sensors are presente