An Umbrella-Shaped Topology for Broadband MEMS Piezoelectric Vibration Energy Harvesting

While cantilever topologies offer high power responsiveness for MEMS vibration energy harvesting (VEH), they are less robust than multiply clamped or membrane topologies. This paper attempts to address this topological optimisation dilemma by attempting to achieve both high power density and robustness. The proposed umbrella-shaped topology constituents of a single central anchor while the membrane area extends outwards and is further enclosed by a ring of proof mass. Implemented on a 0.5 μm AlN on 10 μm doped Si process, a fabricated device (121 mm2 die area) recorded a peak power of 173 μW (1798 Hz and 0.56 g). The normalised power density compares favourably against the state-of-the-art cantilever piezoelectric MEMS VEH, while not sacrificing robustness. Furthermore, this device offers a broadband response, and it has experimentally demonstrated over 3 times higher band-limited noise induced power density than a cantilevered harvester fabricated using the same process

On the partial connection between random matrices and interacting particle systems

In the last decade there has been increasing interest in the fields of random matrices, interacting particle systems, stochastic growth models, and the connections between these areas. For instance, several objects appearing in the limit of large matrices arise also in the long time limit for interacting particles and growth models. Examples of these are the famous Tracy-Widom distribution functions and the Airy_2 process. The link is however sometimes fragile. For example, the connection between the eigenvalues in the Gaussian Orthogonal Ensembles (GOE) and growth on a flat substrate is restricted to one-point distribution, and the connection breaks down if we consider the joint distributions. In this paper we first discuss known relations between random matrices and the asymmetric exclusion process (and a 2+1 dimensional extension). Then, we show that the correlation functions of the eigenvalues of the matrix minors for beta=2 Dyson's Brownian motion have, when restricted to increasing times and decreasing matrix dimensions, the same correlation kernel as in the 2+1 dimensional interacting particle system under diffusion scaling limit. Finally, we analyze the analogous question for a diffusion on (complex) sample covariance matrices.Comment: 31 pages, LaTeX; Added a section concerning the Markov property on space-like path

Laws of large numbers for eigenvectors and eigenvalues associated to random subspaces in a tensor product

Given two positive integers $n$ and $k$ and a parameter $t\in (0,1)$, we choose at random a vector subspace $V_{n}\subset \mathbb{C}^{k}\otimes\mathbb{C}^{n}$ of dimension $N\sim tnk$. We show that the set of $k$-tuples of singular values of all unit vectors in $V_n$ fills asymptotically (as $n$ tends to infinity) a deterministic convex set $K_{k,t}$ that we describe using a new norm in $\R^k$. Our proof relies on free probability, random matrix theory, complex analysis and matrix analysis techniques. The main result result comes together with a law of large numbers for the singular value decomposition of the eigenvectors corresponding to large eigenvalues of a random truncation of a matrix with high eigenvalue degeneracy.Comment: v3 changes: minor typographic improvements; accepted versio

MEMS Vibration Energy Harvesting Devices With Passive Resonance Frequency Adaptation Capability

International audienceFurther advancement of ambient mechanical vibration energy harvesting depends on finding a simple yet efficient method of tuning the resonance frequency of the harvester to match the one dominant in the environment. We propose an innovative approach to achieve a completely passive, wideband adaptive system by employing mechanical nonlinear strain stiffening. We present analytical analysis of the underlying idea as well as experimental results obtained with custom fabricated MEMS devices. Nonlinear behavior is obtained through high built-in stresses between layers in these devices. We report experimentally verified frequency adaptability of over 36% for a clamped-clamped beam device at 2 g input acceleration. We believe that the proposed solution is perfectly suited for autonomous industrial machinery surveillance systems, where high amplitude vibrations that are necessary for enabling this solution, are abundant

Comparison of different beam shapes for piezoelectric vibration energy harvesting

International audienceThis paper reports the comparison of different beam shapes of piezoelectric vibration energy harvesters in regards to their stress level and power harvestable. We proved that trapezoidal and circular shapes allow to reduce the stress level in the material for a low decrease of the power harvested at a given resonance frequency, which increases the reliability of the device. The reliability of the piezoelectric harvesters and in particular their tolerance to high accelerations are an important problematic. We are also developing a process to fabricate home made MEMS piezoelectric harvesters, and the first devices have been fabricated

Design, fabrication and characterization of wideband piezoelectric energy harvesters

International audienceThere is nowadays a huge interest for piezoelectric vibration energy harvesters, in order to power wireless sensor networks’ nodes in industrial or natural environment. However, there are still several issues for these devices. First, as these scavengers are resonant, their resonance frequency has to match the dominant frequency in the surroundings to be efficient. As a consequence, an energy harvesting device with adaptable resonance frequency is needed to make this energy scavenging method more efficient [1]. Then, another problem of these scavengers is micro-fabrication: the ultimate goal is to have a system on chip with the sensors, the RF transceiver, the energy harvesters, low power electronics and a microcontroller. To be able to obtain such a chip, the fabrication process of the harvesters has to be CMOS compatible, to allow integration and batch fabrication of the harvesters and electronics.In this work, an innovative passive way of resonance frequency automatic tracking will be presented. We propose a new approach using mechanical non-linear behaviour of the system, so that the nonlinear system tracks the vibration frequency peak [2]. An experimentally verified frequency adaptability of over 36% for a clamped-clamped beam device at 2g (1g=9.81m.s-2) input acceleration is reported. We believe that the proposed solution is perfectly suited for piezoelectric energy harvesters.Moreover, new results of fabrication and characterization of piezoelectric micro- harvesters designed for a frequency of 200Hz and low input accelerations will be presented. We developed a process fully CMOS compatible for AlN (Aluminum Nitride) piezoelectric harvesters. A device of 3 mm3, fabricated with this process, harvests 620nW at 214 Hz for a low input acceleration of 0,17g. Under vacuum the figure of merit of this device is the best figure of merit published up to now. We are now waiting to characterize nonlinear devices fabricated with this process