Chalcogenide Glass-on-Graphene Photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators

Built-In test of MEMS capacitive accelerometers for field failures and aging degradation.

Postprint (published version

Built-In Self-Test Solution for CMOS MEMS Sensors

This thesis presents a new readout circuit with integrated Built-in Self-Test (BIST) structure for capacitive Micro-Electro-Mechanical Systems (MEMS). In the proposed solution instead of commonly used voltage control signals to test the device, charge control stimuli are employed to cover a wider range of structural defects. The proposed test solution eliminates the risk of MEMS structural collapse in the test phase. Measurement results using a prototype fabricated in TSMC 65nm CMOS technology indicate that the proposed BIST scheme can successfully detect minor structural defects altering MEMS nominal capacitance

Piezoelectric based energy harvesting on low frequency vibrations of civil infrastructures

Piezoelectric-based energy harvesting is an efficient way to convert ambient vibration energy into usable electric energy. The piezoelectric harvester can work as a sustainable and green power source for different electric devices such as sensors and implanted medical devices. However, its application on civil infrastructures has not been fully studied yet. This dissertation aimed to study and improve the piezoelectric-based energy harvesting on civil infrastructures, especially on bridge structures. To reach the objective, a more accurate model for piezoelectric composite beams was built first, which can be adopted for the modeling of different kinds of energy harvesters. The model includes both direct and inverse piezoelectric effects and can provide a better prediction for the dynamic response and energy output of a harvester. Secondly, to examine the piezoelectric-based energy harvesting on civil infrastructures, four concrete slab-on-girder bridges that represent the majority of bridges in the United States were modeled and used as the platforms for the energy harvesting. Piezoelectric cantilever–based harvesters were adopted for the energy harvesting performance simulation considering their wide usage. Different parameters of the bridges and the harvester were studied regarding to the harvesting performance. Two major problems for energy harvesting on civil infrastructures were identified, namely their low frequency vibrations and wide frequency ranges. Then, a multi-impact energy harvester was proposed to improve the harvesting performance under the vibration of low frequencies. The multi-impact was first introduced and theoretically proven. Theoretical and experimental studies for the multi-impact energy harvester were conducted. Both the results show an increased energy output power than the one from the conventional cantilever-based energy harvester. A parametric study was also presented which can serve as a guideline for the design and manufacture for the proposed harvester. Finally, a nonlinear energy harvester was proposed utilizing the magnet levitation. A larger band width was expected due to the stiffness non-linearity of the system. A theoretical model was built for the harvester and its energy output was simulated under the excitation of sinusoidal vibrations and bridge vibrations. The simulation results show a promising way to apply energy harvesting in the field of civil engineering

Design, modelling and testing of a novel energy harvesting device

This work is a feasibility study to develop a novel energy harvesting device. Energy harvesting devices capture energy in various forms from the surrounding and transform it into usable electrical energy. These devices do not require any refuelling or recharging and are virtually a never ending source of energy. The energy harvesting devices rely on di erent mechanisms of energy conversion, depending on the energy source. This work focuses on conversion of mechanical energy from vibrations into electric energy using piezoelectric materials. Most of the existing devices are shaped like a cantilever beam, thus limiting the tunability to a single resonance frequency. It is believed that by modifying the geometry of the energy harvesting device and applying a pre-load to the active material (piezoelectric), a variable tunability can be achieved. Also, the application of an axial compressive pre-load helps to further increase the power output of the device. Therefore, in this present work, the performance of a simply supported beam shaped energy harvesting device is investigated both numerically and experimentally. For the numerical analyses nite element simulations are carried out using ANSYS. An electro-mechanical model of the simply supported beam has been developed through a series of approaching models with increasing complexity, starting from an analytical solution. The nal three-dimensional model was used as a base to create a model of the beam that has been used during the experimental tests. Shape optimization studies were carried out on this nite element model to analyse the power output of the device. It has been observed, through pre-stressed modal analyses, that the axial pre-load decreases the resonance frequency of the beam, thereby giving the beam the ability to be tuned. Also,it has been observed that an optimisation of the beam footprint shape can increase the power output by almost 40%.The experimental work focussed on the investigation of the harmonic behaviour of the simply supported beam under di erent pre-load conditions. It was observed that the experimental results were in disagreement with the nite element simulations and also with the reference literature. The disagreement was identi ed to be due to the hinge design that does not ensure the alignment of the two tips of the beam and therefore the application of a perfectly axial pre-load. From the work presented here it emerges that the possibility to develop a simply supported beam shaped energy harvesting device that rely on the application of an axial pre-load to obtain tunability and an higher power output is promising. The nite element simulations gave good results on the beam behaviour and on the possibility to further increase its output by optimising the shape of its footprint. The experimental work allowed to identify the hinge design as a problem area to design a pro table device

Micromachined in-plane acoustic pressure gradient sensors

textThis work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz.Electrical and Computer Engineerin

Harvesting traffic-induced vibrations for structural health monitoring of bridges

This paper discusses the development and testing of a renewable energy source for powering wireless sensors used to monitor the structural health of bridges. Traditional power cables or battery replacement are excessively expensive or infeasible in this type of application. An inertial power generator has been developed that can harvest traffic-induced bridge vibrations. Vibrations on bridges have very low acceleration (0.1–0.5 m s _2 ), low frequency (2–30 Hz), and they are non-periodic. A novel parametric frequency-increased generator (PFIG) is developed to address these challenges. The fabricated device can generate a peak power of 57 µW and an average power of 2.3 µW from an input acceleration of 0.54 m s _2 at only 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration (0.54–9.8 m s _2 ) and frequency range (up to 30 Hz) without any modifications or tuning. Its performance was tested along the length of a suspension bridge and it generated 0.5–0.75 µW of average power without manipulation during installation or tuning at each bridge location. A preliminary power conversion system has also been developed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90794/1/0960-1317_21_10_104005.pd

A Belleville-spring-based electromagnetic energy harvester

Energy harvesting from kinetic ambient energy is particularly effective to power autonomous sensors. This work proposes an innovative energy converter based on two counteracting Belleville springs and exploiting their peculiarity, for a height to thickness ratio equal to 1.414, of nearly zero stiffness over a wide deflection range. After analytical and numerical modelling a prototype is developed and experimentally investigated. The sub-optimal geometry of the commercial springs used in the prototype, together with a non-ideal response, makes the operating frequency for the prototype higher than in analytical and numerical predictions. Nevertheless, the harvester exhibits a significantly large bandwidth, together with a high output power, compared to similar solutions in the literature, for all the examined configurations and input excitations