arXiv subjects

S. O. Reza Moheimani

Publications and source records attributed to S. O. Reza Moheimani.

9 recordsLinked to original sources

arXiv2026

Digital Control of Negative Imaginary Systems Using Discrete-Time Multi-HIGS: Application to a Dual-Stage MEMS Force Sensor

In this paper, we propose a digital control approach for multi-input multi-output negative imaginary (NI) systems using discrete-time hybrid integrator-gain systems (HIGS) controllers. We show the NI property of the bimodal and trimodal discrete-time HIGS, as well as the parallel combinations of them, which are referred to as the multi-HIGS. Also, we demonstrate that linear NI systems can be asymptotically stabilized using discrete-time HIGS in digital control. We apply discrete-time bimodal and trimodal multi-HIGS controllers to a two-input two-output dual-stage force sensor with lightly damped resonant modes. To validate the theoretical findings, the closed-loop performance is evaluated in both time and frequency domains. Experimental results show that the discrete-time multi-HIGS effectively suppresses resonances while preserving favorable phase characteristics, which highlights its potential as a robust nonlinear NI controller for the digital control of NI systems.

eess.SY↗

arXiv2025

A three-axis Nanopositioner based on Near-Field Acoustic Levitation and Electromagnetic Actuation

Near-field acoustic levitation (NFAL) enables nanometer-scale positioning resolution and bandwidth exceeding several hundred hertz specifically along the vertical (Z) direction, owing to its high acoustic stiffness and squeeze film damping. However, its application to horizontal (XY) positioning is limited by significantly lower acoustic stiffness and insufficient damping in horizontal directions, resulting in reduced resolution and bandwidth. Moreover, NFAL-based positioning systems typically lack multi-axis actuation capabilities due to challenges in generating multi-directional acoustic forces. This work presents a hybrid positioning approach that overcomes the mentioned limitations by integrating NFAL with electromagnetic actuation. A planar magnetic platform is acoustically levitated, while a coplanar current-carrying coil provides horizontal trapping stiffness more than three orders of magnitude higher than that achievable with acoustic forces alone. Additionally, the coil generates three-dimensional electromagnetic forces, enabling multi-axis positioning capability. Eddy currents induced in a thin copper sheet integrated with the coil enhance horizontal damping by 52 times. We experimentally demonstrate precise 3-axis linear motion with a root mean square (RMS) positioning resolution better than 20 nm along all axes. The system achieves an in-plane motion range of 1.42 mm with a bandwidth of 16 Hz and a Z-axis motion range of 40 micrometers with a positioning bandwidth of 171 Hz.

physics.app-ph↗

arXiv2025

Roadmap on Atomic-scale Semiconductor Devices

Spin states in semiconductors provide exceptionally stable and noise-resistant environments for qubits, positioning them as optimal candidates for reliable quantum computing technologies. The proposal to use nuclear and electronic spins of donor atoms in silicon, introduced by Kane in 1998, sparked a new research field focused on the precise positioning of individual impurity atoms for quantum devices, utilising scanning tunnelling microscopy and ion implantation. This roadmap article reviews the advancements in the 25 years since Kane's proposal, the current challenges, and the future directions in atomic-scale semiconductor device fabrication and measurement. It covers the quest to create a silicon-based quantum computer and expands to include diverse material systems and fabrication techniques, highlighting the potential for a broad range of semiconductor quantum technological applications. Key developments include phosphorus in silicon devices such as single-atom transistors, arrayed few-donor devices, one- and two-qubit gates, three-dimensional architectures, and the development of a toolbox for future quantum integrated circuits. The roadmap also explores new impurity species like arsenic and antimony for enhanced scalability and higher-dimensional spin systems, new chemistry for dopant precursors and lithographic resists, and the potential for germanium-based devices. Emerging methods, such as photon-based lithography and electron beam manipulation, are discussed for their disruptive potential. This roadmap charts the path toward scalable quantum computing and advanced semiconductor quantum technologies, emphasising the critical intersections of experiment, technological development, and theory.

quant-ph↗

arXiv2025

Optimisation of design parameters to improve performance of a planar electromagnetic actuator

Planar electromagnetic actuators based on the principle of linear motors are widely employed for micro and nano positioning applications. These actuators usually employ a planar magnetic platform driven by a co-planar electromagnetic coil. While these actuators offer a large motion range and high positioning resolution, their actuation bandwidth is limited due to relatively small electromagnetic stiffness. We report optimization of the design parameters of the electromagnetic coil and the magnetic assembly to maximize the electromagnetic force and stiffness. Firstly, we derive closed-form expressions for the electromagnetic forces and stiffness, which enable us to express these quantities in terms of the design parameters of the actuator. Secondly, based on these derived expressions, we estimate the optimum values of the design parameters to maximize force and stiffness. Notably, for the optimum design parameters, the force and stiffness per unit volume can be increased by two and three orders of magnitude, respectively by reducing the pitch of the electromagnetic coil by a factor of 10. Lastly, we develop an electromagnetic actuator and evaluate its performance using a Microelectromechanical system (MEMS) based force sensor. By operating the force sensor in a feedback loop, we precisely measure the generated electromagnetic forces for different design parameters of the actuator. The experimental results obtained align closely with the analytical values, with an error of less than 15%.

physics.app-ph↗

arXiv2024

Constant di/dz Scanning Tunneling Microscopy: Atomic Precision Imaging and Hydrogen Depassivation Lithography on a Si(100) - 2 x 1 : H Surface

We introduce a novel control mode for Scanning Tunneling Microscopy (STM) that leverages di/dz feedback. By superimposing a high-frequency sinusoidal modulation on the control signal, we extract the amplitude of the resulting tunneling current to obtain a di/dz measurement as the tip is scanned over the surface. A feedback control loop is then closed to maintain a constant di/dz, enhancing the sensitivity of the tip to subtle surface variations throughout a scan. This approach offers distinct advantages over conventional constant-current imaging. We demonstrate the effectiveness of this technique through high-resolution imaging and lithographic experiments on several Si(100)-2x1:H surfaces. Our findings, validated across multiple STM systems and imaging conditions, pave the way for a new paradigm in STM control, imaging, and lithography.

eess.SY↗

arXiv2024

Discrete-time Integral Resonant Control of Negative Imaginary Systems: Application to a High-speed Nanopositioner

We propose a discrete-time integral resonant control (IRC) approach for negative imaginary (NI) systems, which overcomes several limitations of continuous-time IRC. We show that a discrete-time IRC has a step-advanced negative imaginary property. A zero-order hold-sampled NI system can be asymptotically stabilized using a discrete-time IRC with suitable parameters. A hardware experiment is conducted where a high-speed flexure-guided nanopositioner is efficiently damped using the proposed discrete-time IRC with the discrete-time controller being implemented in FPGA hardware at the sampling rate of 1.25 MHz.

eess.SY↗

arXiv2023

Model-based Control of the Scanning Tunneling Microscope: Enabling New Modes of Imaging, Spectroscopy, and Lithography

The invention of scanning tunneling microscope (STM) dates back to the work of Binnig and Rohrer in the early 1980s, whose seminal contribution was rewarded by the 1986 Nobel Prize in Physics for the design of the scanning tunneling microscope. Forty years later, the STM remains the best existing tool for studying electronic, chemical, and physical properties of conducting and semiconducting surfaces with atomic precision. It has opened entirely new fields of research, enabling scientists to gain invaluable insight into properties and structure of matter at the atomic scale. Recent breakthroughs in STM-based automated hydrogen depassivation lithography (HDL) on silicon have resulted in the STM being considered a viable tool for fabrication of error-free silicon-based quantum-electronic devices. Despite the STM's unique ability to interrogate and manipulate matter with atomic precision, it remains a challenging tool to use. It turns out that many issues can be traced back to the STM's feedback control system, which has remained essentially unchanged since its invention about 40 years ago. This article explains the role of feedback control system of the STM and reviews some of the recent progress made possible in imaging, spectroscopy, and lithography by making appropriate changes to the STM's feedback control loop. We believe that the full potential of the STM is yet to be realized, and the key to new innovations will be the application of advanced model-based control and estimation techniques to this system.

eess.SY↗

arXiv2023

Negative Imaginary Control Using Hybrid Integrator-Gain Systems: Application to MEMS Nanopositioner

In this paper, we propose a new approach to address the control problem for negative imaginary (NI) systems by using hybrid integrator-gain systems (HIGS). We investigate the single HIGS of its original form and its two variations, including a multi-HIGS and the serial cascade of two HIGS. A single HIGS is shown to be a nonlinear negative imaginary system, and so is the multi-HIGS and the cascade of two HIGS. We show that these three types of HIGS can be used as controllers to asymptotically stabilize linear NI systems. The results of this paper are then illustrated in a real-world experiment where a 2-DOF microelectromechanical system nanopositioner is stabilized by a multi-HIGS.

eess.SY↗

arXiv2023

A negative imaginary approach to hybrid integrator-gain system control

In this paper, we show that a hybrid integrator-gain system (HIGS) is a nonlinear negative imaginary (NNI) system. We prove that the positive feedback interconnection of a linear negative imaginary (NI) system and a HIGS is asymptotically stable. We apply the HIGS to a MEMS nanopositioner, as an example of a linear NI system, in a single-input single-output framework. We analyze the stability and the performance of the closed-loop interconnection in both time and frequency domains through simulations and demonstrate the applicability of HIGS as an NNI controller to a linear NI system.

eess.SY↗