Ruppert, M G; Harcombe, D M; Fleming, A J Traditional and Novel Demodulators for Multifrequency Atomic Force Microscopy Conference 8th Multifrequency AFM Conference, Madrid, Spain, 2020. Abstract | BibTeX @conference{Ruppert2020b,
title = {Traditional and Novel Demodulators for Multifrequency Atomic Force Microscopy},
author = {M. G. Ruppert and D. M. Harcombe and A. J. Fleming},
year = {2020},
date = {2020-10-27},
booktitle = {8th Multifrequency AFM Conference},
address = {Madrid, Spain},
abstract = {A number of multifrequency atomic force microscopy (MF-AFM) methods make use of the excitation and detection of higher harmonics of the fundamental frequency, higher flexural eigenmodes or intermodulation products generated by the non-linear tip-sample force [1]. Schematically, these methods are depicted in Figure 1(a) where the main difference is the resulting spacing and amplitude of the frequency components in the generated spectrum shown in Figure 1(b). Regardless of which particular MF-AFM method is employed, each requires a demodulator to obtain amplitude and phase to form observables for the characterization of nanomechanical sample information. Since high-speed non-synchronous demodulators such as the peak-hold method, peak detector and RMS-to-DC converter are incompatible with MF-AFM [2], there is a need for high-bandwidth demodulation techniques capable of estimating multiple frequencies at once while maintaining robustness against unwanted frequency components [3]. In this talk, the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy is assessed experimentally. The compared methods include the lock-in amplifier, coherent demodulator, Kalman filter, Lyapunov filter, and direct-design demodulator. Each method is implemented on a field-programmable gate array (FPGA) with a sampling rate of 1.5 MHz. The metrics for comparison include implementation complexity, the sensitivity to other frequency components and the magnitude of demodulation artifacts for a range of demodulator bandwidths. Performance differences are demonstrated through higher harmonic atomic force microscopy imaging.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
A number of multifrequency atomic force microscopy (MF-AFM) methods make use of the excitation and detection of higher harmonics of the fundamental frequency, higher flexural eigenmodes or intermodulation products generated by the non-linear tip-sample force [1]. Schematically, these methods are depicted in Figure 1(a) where the main difference is the resulting spacing and amplitude of the frequency components in the generated spectrum shown in Figure 1(b). Regardless of which particular MF-AFM method is employed, each requires a demodulator to obtain amplitude and phase to form observables for the characterization of nanomechanical sample information. Since high-speed non-synchronous demodulators such as the peak-hold method, peak detector and RMS-to-DC converter are incompatible with MF-AFM [2], there is a need for high-bandwidth demodulation techniques capable of estimating multiple frequencies at once while maintaining robustness against unwanted frequency components [3]. In this talk, the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy is assessed experimentally. The compared methods include the lock-in amplifier, coherent demodulator, Kalman filter, Lyapunov filter, and direct-design demodulator. Each method is implemented on a field-programmable gate array (FPGA) with a sampling rate of 1.5 MHz. The metrics for comparison include implementation complexity, the sensitivity to other frequency components and the magnitude of demodulation artifacts for a range of demodulator bandwidths. Performance differences are demonstrated through higher harmonic atomic force microscopy imaging.  |
McCourt, L; Ruppert, M G; Routley, B S; Indirathankam, S; Fleming, A J A comparison of gold and silver nanocones and geometry optimisation for tip-enhanced microscopy Journal Article In: Journal of Raman Spectroscopy, pp. 1-9, 2020. Abstract | Links | BibTeX @article{McCourt2020,
title = {A comparison of gold and silver nanocones and geometry optimisation for tip-enhanced microscopy},
author = {L. McCourt and M. G. Ruppert and B. S. Routley and S. Indirathankam and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/J20e.pdf},
doi = {https://doi.org/10.1002/jrs.5987},
year = {2020},
date = {2020-08-24},
journal = {Journal of Raman Spectroscopy},
pages = {1-9},
abstract = {In this article, boundary element method simulations are used to optimise the
geometry of silver and gold nanocone probes to maximise the localised electric
field enhancement and tune the near-field resonance wavelength. These objectives
are expected to maximise the sensitivity of tip-enhanced Raman microscopes.
Similar studies have used limited parameter sets or used a performance
metric other than localised electric field enhancement. In this article, the optical
responses for a range of nanocone geometries are simulated for excitation
wavelengths ranging from 400 to 1000 nm. Performance is evaluated by measuring
the electric field enhancement at the sample surface with a resonant
illumination wavelength. These results are then used to determine empirical
models and derive optimal nanocone geometries for a particular illumination
wavelength and tip material. This article concludes that gold nanocones are
expected to provide similar performance to silver nanocones at red and nearinfrared
wavelengths, which is consistent with other results in the literature.
In this article, 633 nm is determined to be the shortest usable illumination
wavelength for gold nanocones. Below this limit, silver nanocones will provide
superior enhancement. The use of gold nanocone probes is expected to dramatically
improve probe lifetime, which is currently measured in hours for silver
coated probes. Furthermore, the elimination of passivation coatings is expected
to enable smaller probe radii and improved topographical resolution.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this article, boundary element method simulations are used to optimise the
geometry of silver and gold nanocone probes to maximise the localised electric
field enhancement and tune the near-field resonance wavelength. These objectives
are expected to maximise the sensitivity of tip-enhanced Raman microscopes.
Similar studies have used limited parameter sets or used a performance
metric other than localised electric field enhancement. In this article, the optical
responses for a range of nanocone geometries are simulated for excitation
wavelengths ranging from 400 to 1000 nm. Performance is evaluated by measuring
the electric field enhancement at the sample surface with a resonant
illumination wavelength. These results are then used to determine empirical
models and derive optimal nanocone geometries for a particular illumination
wavelength and tip material. This article concludes that gold nanocones are
expected to provide similar performance to silver nanocones at red and nearinfrared
wavelengths, which is consistent with other results in the literature.
In this article, 633 nm is determined to be the shortest usable illumination
wavelength for gold nanocones. Below this limit, silver nanocones will provide
superior enhancement. The use of gold nanocone probes is expected to dramatically
improve probe lifetime, which is currently measured in hours for silver
coated probes. Furthermore, the elimination of passivation coatings is expected
to enable smaller probe radii and improved topographical resolution. |
Omidbeike, M; Yong, Y K; Fleming, A J Sensing and Decentralized Control of a Five-Axis Monolithic Nanopositioning Stage Inproceedings In: IFAC World Congress, 2020. Abstract | Links | BibTeX @inproceedings{C20a,
title = {Sensing and Decentralized Control of a Five-Axis Monolithic Nanopositioning Stage},
author = {M. Omidbeike and Y. K. Yong and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2021/02/C20a.pdf},
year = {2020},
date = {2020-07-11},
booktitle = {IFAC World Congress},
abstract = {This article describes the design and calibration of a five degree-of-freedom linearand angular displacement sensor utilizing piezoresistive strain gages. A simple decentralized controller is then implemented to follow linear and angular reference signals. The foremost difficulty with piezoresistive sensors is their high-temperature sensitivity. In addition, they are sensitive to motion in multiple degrees of freedom, which must be decoupled before use as a displacement sensor. A new sensing design is proposed which provides decoupled measurements of linear and angular displacements in multi-axis monolithic nanopositioning stages. The proposed method employs system identification and feedforward techniques to calibrate each axis and minimize cross-coupling. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
This article describes the design and calibration of a five degree-of-freedom linearand angular displacement sensor utilizing piezoresistive strain gages. A simple decentralized controller is then implemented to follow linear and angular reference signals. The foremost difficulty with piezoresistive sensors is their high-temperature sensitivity. In addition, they are sensitive to motion in multiple degrees of freedom, which must be decoupled before use as a displacement sensor. A new sensing design is proposed which provides decoupled measurements of linear and angular displacements in multi-axis monolithic nanopositioning stages. The proposed method employs system identification and feedforward techniques to calibrate each axis and minimize cross-coupling. |
Xavier, M S; Fleming, A J; Yong, Y K Modelling and Simulation of Pneumatic Sources for Soft Robotic Applications Inproceedings In: IEEE/ASME International Conference on Advanced Intelligent Mechatronics, Boston, MA, 2020. Abstract | Links | BibTeX @inproceedings{C20b,
title = {Modelling and Simulation of Pneumatic Sources for Soft Robotic Applications},
author = {M. S. Xavier and A. J. Fleming and Y. K. Yong},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/AIM2020_Published.pdf},
doi = {10.1109/aim43001.2020.9158802},
year = {2020},
date = {2020-07-01},
booktitle = {IEEE/ASME International Conference on Advanced Intelligent Mechatronics},
address = {Boston, MA},
abstract = {The mathematical models for two widely used pneumatic systems in the soft robotics community are presented: syringe pumps and compressed air systems. These models enable prediction and optimisation of performance of soft actuators under pressurisation, allowing the user to select pneumatic components for a desired behaviour. Analytical models are confirmed with simulations developed using SimScape Fluids and SimScape Electrical within Simulink/MATLAB. By using a polytropic law, the models show agreement with the simulations with less than 10% discrepancy for the typical pressures used with soft actuators. Syringe pumps are shown to be much slower compared to the compressed air systems. In the latter, the addition of an air receiver allows very short actuation time.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The mathematical models for two widely used pneumatic systems in the soft robotics community are presented: syringe pumps and compressed air systems. These models enable prediction and optimisation of performance of soft actuators under pressurisation, allowing the user to select pneumatic components for a desired behaviour. Analytical models are confirmed with simulations developed using SimScape Fluids and SimScape Electrical within Simulink/MATLAB. By using a polytropic law, the models show agreement with the simulations with less than 10% discrepancy for the typical pressures used with soft actuators. Syringe pumps are shown to be much slower compared to the compressed air systems. In the latter, the addition of an air receiver allows very short actuation time. |
Raghunvanshi, D S; Moore, S I; Fleming, A J; Yong, Y K Electrode Configurations for Piezoelectric Tube Actuators With Improved Scan Range and Reduced Cross-Coupling Journal Article In: IEEE/ASME Transactions on Mechatronics, 25 (3), pp. 1479-1486, 2020, ISSN: 00346748. Abstract | Links | BibTeX @article{J20d,
title = {Electrode Configurations for Piezoelectric Tube Actuators With Improved Scan Range and Reduced Cross-Coupling},
author = {D. S. Raghunvanshi and S. I. Moore and A. J. Fleming and Y. K. Yong},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/J20d.pdf},
doi = {10.1109/TMECH.2020.2978241},
issn = {00346748},
year = {2020},
date = {2020-06-01},
journal = {IEEE/ASME Transactions on Mechatronics},
volume = {25},
number = {3},
pages = {1479-1486},
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}
}
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. |
Ruppert, M G; Bartlett, N J; Yong, Y K; Fleming, A J Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements Journal Article In: Sensors and Actuators A: Physical, 312 , pp. 112092, 2020. Abstract | Links | BibTeX @article{Ruppert2020,
title = {Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements},
author = {M. G. Ruppert and N. J. Bartlett and Y. K. Yong and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2020/09/J20f.pdf},
doi = {10.1016/j.sna.2020.112092},
year = {2020},
date = {2020-05-29},
journal = {Sensors and Actuators A: Physical},
volume = {312},
pages = {112092},
abstract = {The lock-in amplifier is a crucial component in many applications requiring high-resolution displacement sensing; it's purpose is to estimate the amplitude and phase of a periodic signal, potentially corrupted by noise, at a frequency determined by a reference signal. Where the noise can be approximated by a stationary Gaussian process, such as thermal force noise and electronic sensor noise, this article derives the amplitude noise spectral density of the lock-in-amplifier output. The proposed method is demonstrated by predicting the demodulated noise spectrum of a microcantilever for dynamic-mode atomic force microscopy to determine the cantilever on-resonance thermal noise, the cantilever tracking bandwidth and the electronic noise floor. The estimates are shown to closely match experimental results over a wide range of operating conditions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The lock-in amplifier is a crucial component in many applications requiring high-resolution displacement sensing; it's purpose is to estimate the amplitude and phase of a periodic signal, potentially corrupted by noise, at a frequency determined by a reference signal. Where the noise can be approximated by a stationary Gaussian process, such as thermal force noise and electronic sensor noise, this article derives the amplitude noise spectral density of the lock-in-amplifier output. The proposed method is demonstrated by predicting the demodulated noise spectrum of a microcantilever for dynamic-mode atomic force microscopy to determine the cantilever on-resonance thermal noise, the cantilever tracking bandwidth and the electronic noise floor. The estimates are shown to closely match experimental results over a wide range of operating conditions. |
