Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Wideband vibration energy harvesting using electromagnetic transduction for powering internet of things

The ‘Internet of Things-(IoT)’ envisions a world scattered with physical sensors that collect and transmit data about almost anything and thereby enabling intelligent decision-making for a smart environment. While technological advancements have reduced the power consumption of such devices significantly, the problem of perpetual energy supply beyond the limited capability of batteries is a bottleneck to this vision which is yet to be resolved. This issue has surged the research to investigate the prospect of harvesting the energy out of ambient mechanical vibrations. However, limited applications of conventional resonant devices under most practical environments involving frequency varying inputs, has gushed the research on wideband transducers recently. To facilitate multi-frequency operation at low-frequency regime, design innovations of the Silicon-onInsulator based MEMS suspension systems are performed through multi-modal activation. For continuous bandwidth widening, the benefits of using nonlinear stiffness in the system dynamics are investigated. By topologically varying the spring architectures, dramatically improved operational bandwidth with large power-density is obtained, which is benchmarked using a novel figure-of-merit. However, the fundamental phenomenon of multi-stability limits many nonlinear oscillator based applications including energy harvesting. To address this, an electrical control mechanism is introduced which dramatically improves the energy conversion efficiency over a wide bandwidth in a frequencyamplitude varying environment using only a small energy budget. The underlying effects are independent of the device-scale and the transduction methods, and are explained using a modified Duffing oscillator model. One of the key requirements for fully integrated electromagnetic transducers is the CMOS compatible batch-fabrication of permanent magnets with large energy-product. In the final module of the works, nano-structured CoPtP hard-magnetic material with large coercivity is developed at room-temperature using a current modulated electro-deposition technique. The demagnetization fields of the magnetic structures are minimized through optimized micro-patterns which enable the full integration of high performance electromagnetic energy harvesters

Bifurcation scenarios, dynamical integrity and control of noncontact atomic force microscopes

The research focuses on the description of the global dynamical behavior of a reduced-order model of noncontact Atomic Force Microscope. Different numerical analyses and continuation techniques are carried out to investigate the evolution of the main system periodic solutions and relevant basins of attraction under variations of the most significant system parameters. Local bifurcations, stability boundaries and basin erosion processes around primary and subharmonic resonance regions are studied in presence of both the parametrical horizontal excitation and the external one, and the obtained behavior charts are used not only to compare the results with the literature ones, but also as practical instruments to characterize the operation ranges in terms of the selected parameters. With the same perspective, dynamical integrity concepts, such as detection of basins of attraction, and quantification of their erosion process via integrity measures, are applied to determine acceptable frequency-dependent thresholds associated with a priori safe design targets. Furthermore, an external feedback control is introduced with the aim to take the system response to a selected reference one, thus providing a simple and efficient method to avoid possible unstable motions. Upon checking the effectiveness of the procedure in the weakly nonlinear regime via a perturbation approach, several numerical analyses in the strongly nonlinear regime are accomplished to achieve a description of its dynamical behavior as a function of the newly inserted parameters, and to critically evaluate the effectiveness of the control actuation on the system dynamics, with also a view to the overall response scenario

Mathematical and Numerical Aspects of Dynamical System Analysis

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

Development of a single beam SERF magnetometer using caesium atoms for medical applications

This thesis describes the design and implementation of a compact zero-field optically pumped magnetometer for human biomagetic measurements. This project aimed to achieve lower operating temperatures and a higher sensor bandwidth than current commercial rubidium-based equivalent sensors. Through careful selection of the sensing alkali, caesium, and all constituent components of the sensor package design, both of these aims are achieved. All of the required systems and components for a single-beam zero-field magnetometer are discussed, including a high efficiency cell heating and monitoring system, multi-axis field control and the optical detection scheme. Through full understanding and development of these systems, miniaturised and microfabricated versions are developed that facilitate the construction of a sensor package with external dimensions of 25 × 25 × 50 mm3. A number of machine learning tools are developed and applied to directly optimise the sensor’s sensitivity through control of the appropriate operational parameters, yielding a factor of five improvement. These techniques also enabled the investigation of the effect of nitrogen buffer gas pressure on the sensor’s measured sensitivity, demonstrating a linear increase in sensitivity with increasing pressure. The prototype sensor demonstrated a significant advancement in terms of bandwidth achieving a linear frequency response up to ' 900 Hz. The external package temperature of the sensor for prolonged timescales (> 1 hour) maintained a skin-safe temperature (< 41 ◦C), with a biomagnetic field level sensitivity, 90 fT/√ Hz, and compact package footprint, less than a square inch. A practical measurement of the magnetic field of a cardiac signal successfully demonstrates the sensor as a suitable biomagnetic measurement tool.This thesis describes the design and implementation of a compact zero-field optically pumped magnetometer for human biomagetic measurements. This project aimed to achieve lower operating temperatures and a higher sensor bandwidth than current commercial rubidium-based equivalent sensors. Through careful selection of the sensing alkali, caesium, and all constituent components of the sensor package design, both of these aims are achieved. All of the required systems and components for a single-beam zero-field magnetometer are discussed, including a high efficiency cell heating and monitoring system, multi-axis field control and the optical detection scheme. Through full understanding and development of these systems, miniaturised and microfabricated versions are developed that facilitate the construction of a sensor package with external dimensions of 25 × 25 × 50 mm3. A number of machine learning tools are developed and applied to directly optimise the sensor’s sensitivity through control of the appropriate operational parameters, yielding a factor of five improvement. These techniques also enabled the investigation of the effect of nitrogen buffer gas pressure on the sensor’s measured sensitivity, demonstrating a linear increase in sensitivity with increasing pressure. The prototype sensor demonstrated a significant advancement in terms of bandwidth achieving a linear frequency response up to ' 900 Hz. The external package temperature of the sensor for prolonged timescales (> 1 hour) maintained a skin-safe temperature (< 41 ◦C), with a biomagnetic field level sensitivity, 90 fT/√ Hz, and compact package footprint, less than a square inch. A practical measurement of the magnetic field of a cardiac signal successfully demonstrates the sensor as a suitable biomagnetic measurement tool

Theoretical Approaches in Non-Linear Dynamical Systems

From Preface: The 15th International Conference „Dynamical Systems - Theory and Applications” (DSTA 2019, 2-5 December, 2019, Lodz, Poland) gathered a numerous group of outstanding scientists and engineers who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without great effort of the staff of the Department of Automation, Biomechanics and Mechatronics of the Lodz University of Technology. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our event was attended by over 180 researchers from 35 countries all over the world, who decided to share the results of their research and experience in different fields related to dynamical systems. This year, the DSTA Conference Proceedings were split into two volumes entitled „Theoretical Approaches in Non-Linear Dynamical Systems” and „Applicable Solutions in Non-Linear Dynamical Systems”. In addition, DSTA 2019 resulted in three volumes of Springer Proceedings in Mathematics and Statistics entitled „Control and Stability of Dynamical Systems”, „Mathematical and Numerical Approaches in Dynamical Systems” and „Dynamical Systems in Mechatronics and Life Sciences”. Also, many outstanding papers will be recommended to special issues of renowned scientific journals.Cover design: Kaźmierczak, MarekTechnical editor: Kaźmierczak, Mare

Femtosecond Laser Ablation with Single and Two-Photon Excitation for MEMS

There is an increasing interest in femtosecond laser micromachining of materials because of the femtosecond laser\u27s unique high peak power, ultrashort pulse width, negligible heat conductivity process during the laser pulse, and the minimal heat affected zone, which is in the same order of magnitude of the ablated submicron spot. There are some obstacles in reaching optimal and reliable micromachining parameters. One of these obstacles is the lack of understanding of the nature of the interaction and related physical processes. These processes include amorphization, melting, re-crystallization, nucleated-vaporization, and ablation. The focus of this Dissertation was to study the laser-matter interaction with single and two-photon excitation for optical micro-electro-mechanical system (OMEMS) applications. The laser pulse interaction mechanism was studied by performing a series of experiments including self-imaging experiments, two-photon absorption measurements, and micromachining processes characterizations. As a result of the self-imaging experiment, it was found for both Si and GaP that the material surface reflectivity increased twice as much during the action of the laser pulse. The generation of electron-hole plasma of 1022 cm-3 density was assigned to be responsible for the reflectivity jump. The Drude damping time of the generated plasma was determined to be 0.35 fs for silicon and 0.27 fs for gallium phosphate. Additionally, a precise measurement of the two-photon absorption (TPA) coefficient (β) was done. The TPA coefficient was found to be 0.2 cm/GW. Experimental results were in good agreement with the theoretical expectations up to a point at which the ablation started kicking off and the plasma absorption took place. In case of a single pulse interaction with silicon, self-assembled nano-filaments of a few tens of microns\u27 length and about 100 nm width were observed for the first time with the femtosecond single pulse interaction. The filaments were characterized using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Femtosecond micromachining parameters of silicon were then characterized. The laser beam was first cleaned up using two optical techniques: spatial filtering and expanding. Both cleaning-up techniques gave a clean beam profile; however, with spatial filtering, it was hard to maintain the laser beam quality for a long time as the pinhole in the telescope was destroyed in a matter of hours, so the second technique was used instead. One- and two-dimensional amplitude gratings were written on the Si surface using the characterized micromachining parameters. The properties of one-dimensional machined grating depended on laser polarization orientation with respect to laser scanning direction and pulse energy. 1-D diffraction patterns were obtained from parallel machined samples, while 2-D diffraction patterns were obtained from a perpendicular machined sample at laser energy density \u3c 0.6 J/cm2. The 2-D diffraction patterns resulted from secondary periodical ripples along the polarization direction. During parallel writing directions, these ripples smoothed out; in perpendicular directions, they remained and gave rise to 2-D diffraction pattern. These ripples had large periods (3-5 microns) and were perpendicular to the small periods that have been reported. The investigations presented in this Dissertation increase the understanding of the ablation mechanism under a single laser pulse, the semiconductor materials\u27 behavior on the femtosecond time scale, and the associated self-assemble structure process. The feasibility of short-pulse laser micromachining of semiconductor materials for the micro-electro-mechanical systems (MEMS) was also shown along with the process characterization, which provided guidelines that could help in explaining and advancing the currently existing laser materials processes