Ronan Frizzell

A Vision for Thermally Integrated Photonics Systems

Thermal management has traditionally been relegated to the last step in the design process. However, with the exponential growth in data traffic leading to ever-greater levels of component integration and ever-higher levels of energy consumption, thermal management is rapidly becoming one of the most critical areas of research within the ICT industry. Given the vast use of optics for efficient transmission of high-speed data, this paper focuses on a new thermal solution for cooling the components within pluggable optical modules. Thermally Integrated Photonics Systems (TIPS) represents a new vision for the thermal building blocks required to enable exponential traffic growth in the global telecommunications network. In the TIPS program, existing thermal solutions cannot scale to meet the needs of exponential growth in data traffic. The main barriers to enabling further growth were identified and a research roadmap was developed around a scalable and efficient integrated thermal solution. In particular, the effects of replacing inefficient materials and large macroTECs with better thermal spreaders and μTECs are investidated. In addition, new forms of μChannel cooling into the package to more efficiently remove the heat generated by the lasers and the TECs are being studied which can lead to future photonic devices that can be deployed in a vastly more dense and integrated manner to address the requirements of future telecommunication networks.

Enhanced vibrational energy harvester based on velocity amplification

This article presents a fundamental investigation in which velocity amplification is employed in non-resonant structures to enhance the power harvested from ambient vibrations. Velocity amplification is achieved utilising sequential collisions between free-moving masses, and the final velocity is proportional to the number of masses and the mass ratios selected. The governing theory is discussed, particularly how the final velocity scales with the number of masses. This article examines n-mass velocity-amplified vibration energy harvesters and examines their performance relative to single-mass harvesters. Electromagnetic energy conversion is chosen as it is fundamental in allowing the free movement of the masses. Experimental results from two- and three-mass prototypes are presented that demonstrate a wider frequency response and a gain in power of 33 times compared to single-mass configurations under wideband random excitation. The volume of the devices was constrained, which resulted in the two-mass system outperforming the triple-mass system counter to expectations. This was caused by the triple-mass device experiencing an increased number of impact due to the volume constraint, leading to high losses in the system. It is recommended that in order to realise the full benefits of the triple-mass system, additional volume for mass actuation is required.

GaAs solar cells for Indoor Light Harvesting

GaAs solar cells are the highest efficiency single-junction photovoltaic technology. Their wide bandgap lends them to efficient conversion of indoor light. In this paper GaAs solar cells are experimentally compared to Dye Sensitised solar cells, traditionally used for indoor light harvesting. The power density of GaAs solar cells was found to be over 3× greater than DSSC modules under indoor light levels. A credit card sized GaAs cell can provide 0.67 mW or 4 mW to a wireless sensor node in a dimly lit corridor (~200 lux) or well-lit office space (~1000 lux) respectively. A near linear relationship is measured between the open-circuit and maximum power voltages of GaAs solar cells at low light levels allowing their use with power conditioning circuits (MPPT tracking) based on the fractional-voltage method.

A high figure of merit vibrational energy harvester for low frequency applications

Small-scale vibration energy harvesters that respond efficiently at low frequencies are challenging to realize. This paper describes the design and implementation of one such harvester, which achieves a high volumetric Figure of Merit (FoMv = 2.6% at 11.50 Hz) at the scale of a C-type battery and outperforms other state-of-the-art devices in the sub 20 Hz frequency range. The device employs a 2 Degree-of-Freedom velocity-amplified approach and electromagnetic transduction. The harvester comprises two masses oscillating one inside the other, between four sets of magnetic springs. Collisions between the two masses transfer momentum from the heavier to the lighter mass, exploiting velocity amplification. The paper first presents guidelines for designing and optimizing the transduction mechanism, before a nonlinear numerical model for the system dynamics is developed. Experimental characterisation of the harvester design is then presented to validate both the transducer optimization and the dynamics model. Th...

A Multiple Degree-of-Freedom Velocity-Amplified Vibrational Energy Harvester: Part B — Modelling

Vibrational energy harvesting has become relevant as a power source for the reduced power requirement of electronics used in wireless sensor networks (WSNs). Vibrational energy harvesters (VEHs) are devices that can convert ambient kinetic energy into electrical energy using three principal transduction mechanisms: piezoelectric, electromagnetic and electrostatic.In this paper, a macroscopic two degree-of-freedom (2Dof) nonlinear energy harvester, which employs velocity amplification to enhance the power scavenged from ambient vibrations, is presented. Velocity amplification is achieved through sequential collisions between free-moving masses, and the final velocity is proportional to the mass ratio and the number of masses. Electromagnetic induction is chosen as the transduction mechanism because it can be readily implemented in a device which uses velocity amplification.The experimental results are presented in Part A of this paper, while in Part B three theoretical models are presented: (1) a coupled model where the two masses of the non-linear oscillator are considered as a coupled harmonic oscillators system; (2) an uncoupled model where the two masses are not linked and collisions between masses can occur; (3) a model that considers both the previous cases. The first two models act as necessary building blocks for the accurate development of the third model.This final model is essential for a better understanding of the dynamics of the 2-Dof device because it can represent the real behaviour of the system and captures the velocity amplification effect which is a key requirement of modelling device of interest in this work. Moreover, this model is essential for a future optimization of geometric and magnetic parameters in order to develop a MEMS scale multi-degree-of-freedom device.Copyright

A Multiple-Degree-of-Freedom Velocity-Amplified Vibrational Energy Harvester: Part A — Experimental Analysis

Vibrational energy harvesters (VEHs) are devices which convert ambient vibrational energy into electrical power, offering an alternative to batteries for powering wireless sensors. Detailed experimental characterisation of a 2-degree-of-freedom (2-Dof) VEH is presented in Part A of this paper, while a theoretical analysis is completed in Part B. This design employs velocity amplification to enhance the power harvested from ambient vibrations, while also seeking to increase the bandwidth over which power can be harvested. Velocity amplification is achieved through sequential collisions between free-moving masses. Electromagnetic induction was chosen as the transduction mechanism as it can be readily implemented in a velocity amplified system, although other transduction mechanisms can also be used.The VEH prototype was tested experimentally under both sinusoidal excitation and exponentially correlated Gaussian noise, with different VEH geometries. The maximum power generated under a sinusoidal excitation of arms = 0.6 g was 12.95 mW for a resistive load of 13.5 Ω at 12 Hz, while the maximum power under exponentially correlated Gaussian noise with σ = 0.8 grms, autocorrelation time τ = 0.01s and resistive load 13.5 Ω was 5.3 mW. Maximum bandwidths of 54% and 66%, relative to the central frequency, were achieved under sinusoidal and noise excitation, respectively. The device shows resonant peaks at approximately 15 and 30 Hz, while significant power is also generated in the 17–20 Hz range due to non-linear effects. The VEH component dynamics were analysed using a laser Doppler vibrometer (LDV), while Lab VIEW was used to control the electromagnetic shaker, read the LDV signal and record the VEH output voltage. The aim of this investigation is to achieve a more complete understanding of the dynamics of velocity-amplified systems to aid the optimization of velocity amplified VEH designs.Copyright

The influence of mass configurations on velocity amplified vibrational energy harvesters

Vibrational energy harvesters scavenge ambient vibrational energy, offering an alternative to batteries for the autonomous operation of low power electronics. Velocity amplified electromagnetic generators (VAEGs) utilize the velocity amplification effect to increase power output and operational bandwidth, compared to linear resonators. A detailed experimental analysis of the influence of mass ratio and number of degrees-of-freedom (dofs) on the dynamic behaviour and power output of a macro-scale VAEG is presented. Various mass configurations are tested under drop-test and sinusoidal forced excitation, and the system performances are compared. For the drop-test, increasing mass ratio and number of dofs increases velocity amplification. Under forced excitation, the impacts between the masses are more complex, inducing greater energy losses. This results in the 2-dof systems achieving the highest velocities and, hence, highest output voltages. With fixed transducer size, higher mass ratios achieve higher voltage output due to the superior velocity amplification. Changing the magnet size to a fixed percentage of the final mass showed the increase in velocity of the systems with higher mass ratios is not significant enough to overcome the reduction in transducer size. Consequently, the 3:1 mass ratio systems achieved the highest output voltage. These findings are significant for the design of future reduced-scale VAEGs.

Experimental characterisation of dual-mass vibration energy harvesters employing velocity amplification:

Vibration energy harvesting extracts energy from the environment and can mitigate reliance on battery technology in wireless sensor networks. This article presents the nonlinear responses of two multi-mass vibration energy harvesters that employ a velocity amplification effect. This amplification is achieved by momentum transfer from larger to smaller masses following impact between masses. Two systems are presented that show the evolution of multi-mass vibration energy harvester designs: (1) a simplified prototype that effectively demonstrates the basic principles of the approach and (2) an enhanced design that achieves higher power densities and a wider frequency response. Various configurations are investigated to better understand the nonlinear dynamics and how best to realise future velocity-amplified vibration energy harvesters. The frequency responses of the multi-mass harvesters show that these devices have the potential to reduce risks associated with deploying vibration energy harvester devices in wireless sensor network applications; the wide frequency response reduces the need to re-tune the harvesters following frequency variations of the source vibrations.

Optimization of coil parameters for a nonlinear two Degree-of-Freedom (2DOF) velocity-amplified electromagnetic vibrational energy harvester

A 2DOF velocity amplified electromagnetic vibrational energy harvester is analyzed. The system consists of two masses, one larger than the other, oscillating relative to each other in response to external excitation. The large mass is designed with a centrally located cavity into which a second smaller mass is placed. This configuration allows the larger mass to impart momentum to the smaller mass during impact, which significantly amplifies the velocity of the smaller mass. By coupling high strength magnets (placed on the larger mass) and a coil (embedded in the smaller mass), an electric current is induced in the coil through the relative motion of the two masses. To intensify the magnetic field, the magnets are arranged with alternating polarity within the soft-iron body of the larger mass. Between the two masses, and between the larger mass and the support, four springs are placed. The smaller mass is designed to disconnect from the larger mass, when input vibrations of sufficient magnitude are present, and this leads to significant nonlinearity in the system response, which is well described by its transfer function. The nonlinearity leads to an increased bandwidth over which the system can harvest energy. As a further improvement, the energy harvester is optimized by changing the properties of the coil. Four different coils are compared in terms of their voltage and power output. Finally, a theoretical model is proposed in order to predict the optimal configuration.

A wideband 2-DOF resonator for electromagnetic energy harvesting systems

In this work, a novel resonator consisting of two detachable mass-springs has been developed. Fitting analysis shows that a corresponding mathematical model exhibits quantitative similarity between the simulation results and experimental data. Simulation results show that an electromagnetic energy harvester using the proposed resonator also has a improved electromechanical conversion efficiency compared to both a conventional 1-DOF resonator and a fully attached 2-DOF resonator.