Rmc Rob Mestrom

Phase Feedback for Nonlinear MEM Resonators in Oscillator Circuits

In this paper, a phase feedback approach for using nonlinear microelectromechanical (MEM) resonators in oscillator circuits is investigated. Phase feedback makes use of the oscillation phase condition for oscillator circuits and enables fine-tuning of the frequency at which the resonator oscillates by means of setting the phase in the feedback amplifier. The principle of the approach is illustrated for a nonlinear Duffing resonator, which is representative of many types of MEM resonators. Next, the approach is applied to an electrostatically actuated nonlinear clamped-clamped beam MEM resonator, on simulation level. Phase feedback allows for operation of the resonator in its nonlinear regime. The closed-loop technique enables control of both the frequency of oscillation and the output power of the signal. Additionally, optimal operation points for oscillator circuits incorporating a nonlinear resonator can be defined. Application of phase feedback results in more robustness with respect to dynamic pull in than in open-loop case, however, at the cost of a deteriorated phase noise response.

Technical aspects of neurostimulation: Focus on equipment, electric field modeling, and stimulation protocols

Neuromodulation is a field of science, medicine, and bioengineering that encompasses implantable and non-implantable technologies for the purpose of improving quality of life and functioning of humans. Brain neuromodulation involves different neurostimulation techniques: transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS), which are being used both to study their effects on cognitive brain functions and to treat neuropsychiatric disorders. The mechanisms of action of neurostimulation remain incompletely understood. Insight into the technical basis of neurostimulation might be a first step towards a more profound understanding of these mechanisms, which might lead to improved clinical outcome and therapeutic potential. This review provides an overview of the technical basis of neurostimulation focusing on the equipment, the present understanding of induced electric fields, and the stimulation protocols. The review is written from a technical perspective aimed at supporting the use of neurostimulation in clinical practice.

On phase feedback for nonlinear MEMS resonators

In oscillator circuits, a resonator acts as a frequency selective network. Nonlinearities in the resonator may influence oscillator performance and may limit the signal to noise ratio. In this paper, a phase feedback approach for increasing the signal to noise ratio in MEMS resonators is investigated. The approach consists of fine-tuning the frequency at which the resonator oscillates by means of setting the oscillation phase condition in the amplifier of the oscillator circuit. The approach is explained for a nonlinear Duffing resonator, which is representative for certain types of MEMS resonators. Here, this approach is applied to a nonlinear clamped-clamped beam MEMS resonator. On simulation level, closed-loop phase feedback yields an increase in S/N-ratio of several decades compared to the open-loop system. Furthermore, optimal operation points for oscillator circuits incorporating a nonlinear resonator can be defined.

Modeling the common mode impedance of motor drive systems using the antenna wire concept

To describe radiated emission from cables in motor drive systems, a radiating (thin) wire antenna can be used. This equivalence allows the common mode impedance of the cable in such a system to be modeled as the input impedance of the antenna. Using a method of moments implementation for solving Pocklingtons equation for a vertical wire antenna above a perfectly conducting ground plane, a fast and flexible numerical model for the input impedance of the antenna is presented. Validation with measurements shows that the model captures the relevant behaviour, thus allowing it to be used effectively as a first step in the design process of motor drive systems.

A combined semi-analytical and experimental approach for multiphysical nonlinear MEMS resonators

A combined semi-analytical and experimental approach is proposed for predictive modelling of the nonlinear dynamic behaviour of microelectromechanical resonators. The approach is demonstrated for a clamped-clamped beam resonator, for which the mechanical, electrical, and thermal domains are relevant. Multiphysics modelling is applied, based on first principles, to derive a reduced-order model of the resonator. A qualitative correspondence between numerical and experimental steady-state responses has been obtained. Depending on the excitation values, both simulations and experiments show hardening and softening nonlinear dynamic behaviour. Since the model captures the observed experimental behaviour, it can be used to optimize the resonator behaviour with respect to nonlinear dynamic effects.