A great leap forward towards free energy
Author: Yu Jia, April 2013
"What I offer here, is what the world desires. I offer free energy."
Premises
Imagine a world where your mobile phone never warns you it is running out of battery, where your computer mouse, keyboards, tv remotes, switches on walls and all sorts of sensors are both wireless and battery-less and where countless tiny self powered and self sustaining electronic minions labour away in the background to clean your room, monitor your health, regulate traffic, rush to aid emergencies and accidents and makes sure our vast infrastructure are safe and sound. Imagine a world where everything is autonomous and powers itself.
We are surrounded by ambient energy. Look at a busy transit hub and the massive amounts of people moving around; the mechanical vibration emitted by cars, trains and airplanes; as well as heat fluctuations and kinetic energy wasted by industrial scale machinery and infrastructure. We are immersed in a pool of ambient energy. We "just" need to use it.
This research attempts to reinvent resonant-based kinetic energy harvesters to harness the power of the ambient vibration for realising self-sustaining and self-powered "everlasting" electronics; such as wireless sensor nodes for applications including structural health monitoring to keep our infrastructure safe or wearable medical sensors to make sure our bodies are healthy. This is an account of my research journey down to the very fundamental physics in an attempt to re-invent the technology from the very core of its mechanical principles.
Premises
Imagine a world where your mobile phone never warns you it is running out of battery, where your computer mouse, keyboards, tv remotes, switches on walls and all sorts of sensors are both wireless and battery-less and where countless tiny self powered and self sustaining electronic minions labour away in the background to clean your room, monitor your health, regulate traffic, rush to aid emergencies and accidents and makes sure our vast infrastructure are safe and sound. Imagine a world where everything is autonomous and powers itself.
We are surrounded by ambient energy. Look at a busy transit hub and the massive amounts of people moving around; the mechanical vibration emitted by cars, trains and airplanes; as well as heat fluctuations and kinetic energy wasted by industrial scale machinery and infrastructure. We are immersed in a pool of ambient energy. We "just" need to use it.
This research attempts to reinvent resonant-based kinetic energy harvesters to harness the power of the ambient vibration for realising self-sustaining and self-powered "everlasting" electronics; such as wireless sensor nodes for applications including structural health monitoring to keep our infrastructure safe or wearable medical sensors to make sure our bodies are healthy. This is an account of my research journey down to the very fundamental physics in an attempt to re-invent the technology from the very core of its mechanical principles.
Stagnation
It has almost become an unwritten rule that the word "resonance" describes the fundamental resonant mode observed from a directly excited vibratory system. The field of vibration energy harvesting, either the linear vibration camp or the nonlinear vibration folks; either the mono-stable approach or the bi-stable technique, have all unquestioningly adopted this "conventional" resonant phenomenon as the de facto fundamental physics of the technology.
The improvement in power performance index reported in the literature has more or less flattened off in the past half decade or so, with many research efforts moving towards wider system integration and optimization such as the Holistic project jointly undertaken by Imperial, Southampton and other partners. I attended and presented my paper at the PowerMEMS 2012 conference last year, which is like the Mecca for top energy harvesting researchers from around the world. The current trend and belief, I sensed from majority of the energy harvesting community, is that peak power density is not going to witness a disruptive jump in the foreseeable future and the burden is now thrust upon the wireless radio and micro-controller communities to minimize the power budget of the power consuming electronics.
Well, I personally don't believe we have squeezed nearly enough juice out of our ambient power. In fact, we have barely scratched the surface. The directly excited fundamental mode of resonance, or simply "resonance", constituents a very narrow and confined component of the entire available power spectrum. The energy is all out there, we "just" have to harvest it!
It has almost become an unwritten rule that the word "resonance" describes the fundamental resonant mode observed from a directly excited vibratory system. The field of vibration energy harvesting, either the linear vibration camp or the nonlinear vibration folks; either the mono-stable approach or the bi-stable technique, have all unquestioningly adopted this "conventional" resonant phenomenon as the de facto fundamental physics of the technology.
The improvement in power performance index reported in the literature has more or less flattened off in the past half decade or so, with many research efforts moving towards wider system integration and optimization such as the Holistic project jointly undertaken by Imperial, Southampton and other partners. I attended and presented my paper at the PowerMEMS 2012 conference last year, which is like the Mecca for top energy harvesting researchers from around the world. The current trend and belief, I sensed from majority of the energy harvesting community, is that peak power density is not going to witness a disruptive jump in the foreseeable future and the burden is now thrust upon the wireless radio and micro-controller communities to minimize the power budget of the power consuming electronics.
Well, I personally don't believe we have squeezed nearly enough juice out of our ambient power. In fact, we have barely scratched the surface. The directly excited fundamental mode of resonance, or simply "resonance", constituents a very narrow and confined component of the entire available power spectrum. The energy is all out there, we "just" have to harvest it!
Parametric resonance
By going through the dust covered books of the grand Cambridge library, I fetched out a less famous cousin of our well known Mr Resonance. This shy and relatively unheard physical phenomenon is known as parametric resonance and is induced by parametric excitation, which involves a time dependent modulation in at least one of the system parameters. In terms of the generic equations of motion, a damped Mathieu equation is typically used to describe this special and exotic resonance, with a time domain coefficient in one of its homogenous terms.
My personal scientific hero, Michael Faraday, was amongst the earliest to have observed this peculiar resonance and Lord Rayleigh initiated one of the first experimental investigations. The Russians extensively studied this phenomenon in the early to mid twentieth century, but these research efforts at the time appeared to be fuelled purely by academic curiosity. Aeronautic, ship science, vibrational dynamic and civil engineers might have had to study and occasionally deal with parametric resonance due to its devastating ability to store much more energy and attain significantly greater vibrational amplitude than its "conventional" resonant cousin. This is because unlike directly excited resonance, the resonance build up deriving from parametric excitation is not bound by linear damping and can only be saturated with the onset of nonlinear damping at high amplitudes or with the constraints of physical limits.
By going through the dust covered books of the grand Cambridge library, I fetched out a less famous cousin of our well known Mr Resonance. This shy and relatively unheard physical phenomenon is known as parametric resonance and is induced by parametric excitation, which involves a time dependent modulation in at least one of the system parameters. In terms of the generic equations of motion, a damped Mathieu equation is typically used to describe this special and exotic resonance, with a time domain coefficient in one of its homogenous terms.
My personal scientific hero, Michael Faraday, was amongst the earliest to have observed this peculiar resonance and Lord Rayleigh initiated one of the first experimental investigations. The Russians extensively studied this phenomenon in the early to mid twentieth century, but these research efforts at the time appeared to be fuelled purely by academic curiosity. Aeronautic, ship science, vibrational dynamic and civil engineers might have had to study and occasionally deal with parametric resonance due to its devastating ability to store much more energy and attain significantly greater vibrational amplitude than its "conventional" resonant cousin. This is because unlike directly excited resonance, the resonance build up deriving from parametric excitation is not bound by linear damping and can only be saturated with the onset of nonlinear damping at high amplitudes or with the constraints of physical limits.
While this is devastating for infrastructures such as bridges or transports such as airplanes, this is great news for vibration energy harvesting. Before I continue, I just want to say one of my most joyful moments in the lab was when my parametrically excited vibration harvester prototype generated so much instantaneous power, it literally sparked and set fire to my power conditioning circuitry. Therefore, when employed appropriately, this resonant phenomenon can harness a much greater region of the available power spectrum. When combined with ordinary resonance, they can complement each other and greatly maximize the mechanical-to-electrical power conversion efficiency, improving upon the very fundamental mechanism of this technology.
So if it is so great, then how come no one has used it yet? Although relatively less known, parametric resonance is by no means a secret to the experts of the vibration community. In fact, extensive research interest exists in parametric resonance due to its alternative and interesting behaviour. Sensors such as gyroscopes have already explored the incorporation of prametric resonance as a means of mechanical amplification. However, there is a catch. |
The problem
At best, it is less straightforward to activate. At worst, I would describe it as the Higgs Boson of the vibrational resonances in terms of its elusiveness. In the absence of an active parametric driving force, it is almost a Hercules labour trying to activate and access the parametric resonant regime. However, it is utterly counter-intuitive to waste additional power draining actuators for energy harvesting applications. Either by your multi-physics eigenfrequency or frequency sweep simulations, or an experimental frequency scan by laser vibrometers or electrical measurement apparatus, you will find little luck to unveil this stubbornly hidden resonance.
This is because parametric resonance has a long list of strict boundary conditions to fulfil prior to its activation. In other words, it is not that "direct" to excite. One of the most limiting conditions is a critical damping dependent intiation threshold amplitude, which acts as an activation barrier. Direct resonance is immune from any such activation barrier and will offer some sort of response no matter how small the excitation is. For parametric resonance, below a certain excitation amplitude, the output response will converge to zero. With higher damping (energy harvesting relies on electrical damping to extract energy), this activation barrier also becomes higher. Real world ambient vibration on the other hand, is generally modest to begin with. Therefore, despite its promising potentials to outperform direct resonance, it is almost impossible to passively activate it in the first place.
At best, it is less straightforward to activate. At worst, I would describe it as the Higgs Boson of the vibrational resonances in terms of its elusiveness. In the absence of an active parametric driving force, it is almost a Hercules labour trying to activate and access the parametric resonant regime. However, it is utterly counter-intuitive to waste additional power draining actuators for energy harvesting applications. Either by your multi-physics eigenfrequency or frequency sweep simulations, or an experimental frequency scan by laser vibrometers or electrical measurement apparatus, you will find little luck to unveil this stubbornly hidden resonance.
This is because parametric resonance has a long list of strict boundary conditions to fulfil prior to its activation. In other words, it is not that "direct" to excite. One of the most limiting conditions is a critical damping dependent intiation threshold amplitude, which acts as an activation barrier. Direct resonance is immune from any such activation barrier and will offer some sort of response no matter how small the excitation is. For parametric resonance, below a certain excitation amplitude, the output response will converge to zero. With higher damping (energy harvesting relies on electrical damping to extract energy), this activation barrier also becomes higher. Real world ambient vibration on the other hand, is generally modest to begin with. Therefore, despite its promising potentials to outperform direct resonance, it is almost impossible to passively activate it in the first place.
The solution
Here is where I come in with my patent pending research contribution where I have devised a comprehensive design approach to fundamentally and passively (without the need to actively invest actuating power) reduce the intiation threshold amplitude by a significant margin in order to realistically call upon and employ this superior resonance. One of the design approaches is to utilize auto-parametric resonance, which is a subset of parametric resonance where energy captured by direct excitation is internally transferred to a subsidiary osscilatory system as parametric resonance due to a specific integer ratio relationship in the natural frequencies of the various coupled subsystems.
An analogy I like to use is: direct resonance is like a mediocre conference level footballer who would play for you at low wages (vibration excitation) and his performance (power output) will steadily improve with higher incentives. Whereas, parametric resonance is a Premier league superstar who will refuse your employment offer below a certain fat wage and perhaps a complimentary spa in his backyard. However, when the superstar does play for you, his performance is going to rapidly outrace the ordinary player. I, sirs, am the master negotiator who has devised an ingenious plan to employ the superstar at minimum wage.
The result so far
My experimental prototypes, both device level macro-scale and MEMS (micro-electro-mechanical system) devices, have shown over an order of magnitude higher power output when driven in parametric resonance than direct resonance, and have demonstrated over an order of magnitude lower initiation threshold amplitude for the threshold-aided designs. The aim is not to replace direct resonance, but rather for the two resonant cousins to simutaneously complement and complete each other. With further incorporation of nonlinearity, bi-stability and all other exoctic vibrational phenomena, a much wider region of the power spectrum can be harvested.
Related academic publications:
Y. Jia et al., Parametriclly excited MEMS vibration energy harvester, Proceedings in PowerMEMS 2012, Atlanta, USA, 2-5 December, 2012, pp. 215-218.
Y. Jia et al., A parametrically excited vibration energy harvester, J. Intel. Mat. Struc. Syst., 2013, DOI: 10.1177/1045389X13491637
Y. Jia et al., Parametrically excited MEMS vibration energy harvester with design approaches to overcome the intiation threshold amplitude, J. Micromech. Microeng., 2013 (special issue invited paper, in press)
Y. Jia et al., Directly and parametrically excited bi-stable vibration energy harvesters, Proceedings in IEEE Transducers and EuroSensors 2013, Barcelona, Spain, 16-20 June, 2013, pp. 454-457.
Here is where I come in with my patent pending research contribution where I have devised a comprehensive design approach to fundamentally and passively (without the need to actively invest actuating power) reduce the intiation threshold amplitude by a significant margin in order to realistically call upon and employ this superior resonance. One of the design approaches is to utilize auto-parametric resonance, which is a subset of parametric resonance where energy captured by direct excitation is internally transferred to a subsidiary osscilatory system as parametric resonance due to a specific integer ratio relationship in the natural frequencies of the various coupled subsystems.
An analogy I like to use is: direct resonance is like a mediocre conference level footballer who would play for you at low wages (vibration excitation) and his performance (power output) will steadily improve with higher incentives. Whereas, parametric resonance is a Premier league superstar who will refuse your employment offer below a certain fat wage and perhaps a complimentary spa in his backyard. However, when the superstar does play for you, his performance is going to rapidly outrace the ordinary player. I, sirs, am the master negotiator who has devised an ingenious plan to employ the superstar at minimum wage.
The result so far
My experimental prototypes, both device level macro-scale and MEMS (micro-electro-mechanical system) devices, have shown over an order of magnitude higher power output when driven in parametric resonance than direct resonance, and have demonstrated over an order of magnitude lower initiation threshold amplitude for the threshold-aided designs. The aim is not to replace direct resonance, but rather for the two resonant cousins to simutaneously complement and complete each other. With further incorporation of nonlinearity, bi-stability and all other exoctic vibrational phenomena, a much wider region of the power spectrum can be harvested.
Related academic publications:
Y. Jia et al., Parametriclly excited MEMS vibration energy harvester, Proceedings in PowerMEMS 2012, Atlanta, USA, 2-5 December, 2012, pp. 215-218.
Y. Jia et al., A parametrically excited vibration energy harvester, J. Intel. Mat. Struc. Syst., 2013, DOI: 10.1177/1045389X13491637
Y. Jia et al., Parametrically excited MEMS vibration energy harvester with design approaches to overcome the intiation threshold amplitude, J. Micromech. Microeng., 2013 (special issue invited paper, in press)
Y. Jia et al., Directly and parametrically excited bi-stable vibration energy harvesters, Proceedings in IEEE Transducers and EuroSensors 2013, Barcelona, Spain, 16-20 June, 2013, pp. 454-457.