Projects

@article{J17h,
title = {A Review of Demodulation Techniques for Amplitude Modulation Atomic Force Microscopy},
author = {M. G. Ruppert and D. M. Harcombe and M. R. P. Ragazzon and S. O. R. Moheimani and A. J. Fleming},
year = {2017},
date = {2017-09-01},
journal = {Bellstein Journal of Nanotechnology},
volume = {In Press},
abstract = {In this review paper, traditional and novel demodulation methods applicable to amplitude modulation atomic force microscopy are implemented on a widely used digital processing system. As a crucial bandwidth-limiting component in the z-axis feedback loop of an atomic force microscope, the purpose of the demodulator is to obtain estimates of amplitude and phase of the cantilever deflection signal in the presence of sensor noise or additional distinct frequency components. Specifically for modern multifrequency techniques, where higher harmonic and/or higher eigenmode contributions are present in the oscillation signal, the fidelity of the estimates obtained from some demodulation techniques is not guaranteed. To enable a rigorous comparison, the performance metrics tracking bandwidth, implementation complexity and sensitivity to other frequency components are experimentally evaluated for each method. Finally, the significance of an adequate demodulator bandwidth is highlighted during high-speed tapping-mode AFM experiments in constant height mode.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{J17g,
title = {An Algorithm for Transmitter Optimization in Electromagnetic Tracking Systems},
author = {M. N. Islam and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/05/07926412.pdf},
year = {2017},
date = {2017-08-30},
journal = {IEEE Transactions on Magnetics},
volume = {Accepted},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{J17f,
title = {A New Low-frequency Correction Technique for Piezoelectric Force Sensors in High-speed Nanopositioning Systems},
author = {Y. K. Yong and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/04/J17f-Preprint.pdf},
year = {2017},
date = {2017-08-02},
journal = {Review of Scientific Instruments},
volume = {88},
number = {046105},
pages = {1-3},
abstract = {Piezoelectric force and position sensors provide high sensitivity but are limited at low frequencies due to their high-pass response which complicates the direct application of integral control. To overcome this issue, an additional sensor or low-frequency correction method is typically employed. However, these approaches introduce an additional first-order response that must be higher than the high-pass response of the piezo and interface electronics. This article describes a simplified method for low-frequency correction that uses the piezoelectric sensor as an electrical component in a filter circuit. The resulting response is first-order, rather than second-order, with a cut-off frequency equal to that of a buffer circuit with the same input resistance. The proposed method is demonstrated to allow simultaneous damping and tracking control of a high-speed vertical nanopositioning stage},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{J17e,
title = {Lyapunov Estimator for High-Speed Demodulation in Dynamic Mode Atomic Force Microscopy},
author = {M. R. P. Ragazzon and M. G. Ruppert and D. M. Harcombe and A. J. Fleming and J. T. Gravdahl},
year = {2017},
date = {2017-08-01},
journal = {IEEE Transactions on Control Systems Technology},
volume = {Accepted},
abstract = {In dynamic mode atomic force microscopy (AFM), the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever and demodulator. While the common demodulation method is to use a lock-in amplifier (LIA), its performance is ultimately bounded by the bandwidth of the post-mixing low-pass filters. This article proposes an amplitude and phase estimation method based on a strictly positive real Lyapunov design approach. The estimator is designed to be of low complexity while allowing for high bandwidth. Additionally, suitable gains for high performance are suggested such that no tuning is necessary. The Lyapunov estimator is experimentally implemented for amplitude demodulation and shown to surpass the LIA in terms of tracking bandwidth and noise performance. High-speed AFM images are presented to corroborate the results.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@inproceedings{C17d,
title = {Monolithic Piezoelectric Nanopositioning Stage using an Integrated Sensor},
author = {M. Omidbeike and Y. R. Teo and Y. K. Yong and A. J. Fleming},
year = {2017},
date = {2017-07-09},
booktitle = {IFAC World Congress},
address = {Toulouse, France},
abstract = {This article describes a method for tracking control of monolithic nanopositioning systems using integrated piezoelectric sensors. The monolithic nanopositioner is constructed from a single sheet of piezoelectric material where a set of flexures are used for actuation and guidance, and another set are used for position sensing. This arrangement is shown to be highly sensitive to in-plane motion (in the x- and y-axis) and insensitive to vertical motion, which is ideal for position tracking control.

The foremost difficulty with piezoelectric sensors is their low-frequency high-pass response. In this article, a simple estimator circuit is used to allow the direct application of integral tracking control. Although the system operates in open-loop at DC, dynamic command signals such as scanning trajectories are accurately tracked. Experimental results show significant improvements in linearity and positioning error. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}

@inproceedings{C17c,
title = {Experimental Scanning Laser Lithography with Exposure Optimization},
author = {A. J. Fleming and O. T. Ghalehbeygi and B. S. Routley and A. G. Wills},
year = {2017},
date = {2017-07-09},
booktitle = {IFAC World Congress},
address = {Toulouse, France},
abstract = {Laser scanning lithography is a maskless method for exposing films of photoresist during semiconductor manufacturing. In this method a focused beam is scanned over a surface with varying intensity to create features in the photoresist. Given the shape of a desired feature, an exposure pattern must be found that approximates this shape in the developed photoresist. This can be cast as an optimization problem, which is complicated by the non-negative nature of the exposure function and the non-linear photochemistry of the film. In this article, a nonlinear programming approach is described that results in a tractable optimization problem which accounts for all of the practical constraints encountered in laser scanning lithography. This method is demonstrated to create a sub-wavelength feature which is verified by optical finite element simulation with a resolution of 20nm. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}