With my advisors, Dr. Alex Slocum and Dr. Themis Sapsis, I used nonlinear mechanisms to increase the electricity generated from ambient vibrations. Please click on the image or read below to learn about the project. My master thesis and a journal article listed on the Publications page further describe this project.
Challenge
 Ambient vibrations are stochastic multifrequency, and timevarying.
 Traditional linear oscillators can only absorb ambient energy at one frequency.
 Example scenarios:

 Ambient vibration energy harvesting

 Cell phones carried by people.
 Ocean wave utilityscale generators.
 Small electroincs in remote locations.
 MEMs sensors implanted in the body.
 Shock absorption

 Protect offshore platforms from water wave impacts.
Solution
 Nonlinear oscillators are more robut to vibration signal changes than linear systems

 Many studies have shown that energy absorption by a nonlinear system depends more on the energy level of the ecxitation signal than the frequency of the excitation signal.
 Traditional linear oscillators can only absorb ambient energy at one frequency.

 This is a pasive solution which may be more robust and energyefficient than using controls.
Design a nonlinear spring
 We design an essentially nonlinear spring (i.e. its entire forceversusdeflection behavior is nonlinear), which many studies have shown to be critical for generating power over a large range of excitation signals.
 The chosen design has low friction and only one moving part (which increases device lifetime).
 The spring stiffness increases as the cantilever wraps around the rigid surface and shorter length of the cantilever is able to bend.

 The stiffness of a cantilever is 3EI/L^3. Here, L decreases as additional force is appled.
Case study: Power a cell phone from a person walking
 We study the electricity generated by an energy harvester that is excited by the motion of a person's hip while walking, walking quickly, and running.
 These different excitation signals represent how a person walks differently thorughout the day
 We restrict all of the systems to have a total mass of 60g (for the 2DOF systems, each mass is 30 g), and allowable peakpeak displacement of 6.8 cm. This displacement constraint represents the device outer casing.
 We simulate the generation of electricity by adding electromagnetic damping to the system.
 As shown below, only the nonlinear systems have a set of parameters that can generate a significant (>0.01 W) power for both walking and running.
Times series and FFTs of the human motion signals 
System 
Power Generated while Walking versus Parameters 
Power Generated while Running versus Parameters 
1DOF linear 

1DOF nonlinear 

2DOF linear 

2DOF nonlinear 
Conclusions
Nonlinearity makes the system more robust to environmental vibration specturm changes and the presence of parasitic damping.Power harvested by the optimized systems 
Effect of parasitic damping 
Future Work
 Build and test full prototypes with electromagnetic system
 Modify contactsurface stiffeningspring effect to be more volumecompact
 Analytically study stochastic nonlinear dynamics to predict maximum power and robustness
 Apply concepts to utilityscale oceanwave electricity generation
Ocean wave spectra of different sea states, from Hasselmann?et al., (1973) 