Contact Details:
Michael G. Ruppert
School of Electrical Engineering and Computing
The University of Newcastle
Callaghan, NSW 2308, Australia
+61 2 4921 7345
Michael(dot)Ruppert(at)newcastle.edu.au
Biography
Michael Ruppert received the Dipl.-Ing. Degree with excellence in automation technology in production, with a specialization in systems theory and automatic control, from the University of Stuttgart, Germany, in 2013. In 2017, he received the Ph.D. degree in electrical engineering from The University of Newcastle, Australia where he is now a Postdoctoral Research Associate with the School of Electrical Engineering and Computing. His research interests include the control, estimation and self-sensing of microelectromechanical (MEMS) systems such as piezoelectric microcantilever and nanopositioning systems for multifrequency and single-chip atomic force microscopy.
As a Visiting Researcher, he was with the Mechanical Engineering Department, University of Texas at Dallas, USA. During his research visit he worked on the fabrication of piezoelectric microcantilevers in the clean room and lead-authored the publication on the first silicon-on-insulator MEMS on-chip atomic force microscope, recently published and identified as a JMEMS RightNow paper in the IEEE Journal of Microelectromechanical Systems, and which was highlighted in the IEEE Spectrum magazine. During his visit, Dr. Ruppert also consulted to Zyvex LABS, Richardson, USA on the analysis of process stability of scanning tunneling microscope enabled nanolithography.
New Paradigm in Microscopy: Atomic Force Microscope on a Chip
Dr. Ruppert received the Academic Merit Scholarship from the University of Stuttgart, the Baden-Württemberg Scholarship, and held Postgraduate Research Scholarships with the University of Newcastle and with the CSIRO, Clayton, VIC, Australia. Dr. Ruppert’s research has been recognized with the 2013 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM) Best Conference Paper Finalist Award and with The University of Newcastle FEBE Postgraduate Research Prize in 2014 and 2016.
Professional Activities
- July 2017: Lead organizer and chair of invited session on “Design and Control of Micro and Nano Precision Mechatronic Systems” at the IEEE International Conference on Advanced Intelligent Mechatronics (AIM), Munich, Germany, 2017
- May 2017: IEEE Seminar at University of Western Australia on ‘Self-Sensing, Estimation and Control in Multifrequency Atomic Force Microscopy’
- 2013-present: Reviewer for Journals IEEE TNANO, IEEE TMEC, IEEE TCST, IEEE JMEMS, AJC
2017 | ||
| 20. |  | M. G. Ruppert, D. M. Harcombe, M. R. P. Ragazzon, S. O. R. Moheimani, A. J. Fleming A Review of Demodulation Techniques for Amplitude Modulation Atomic Force Microscopy (Journal Article) Bellstein Journal of Nanotechnology, In Press , 2017. @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}, url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/07/m11627988-1.pdf}, 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} } 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. |
| 19. |  | M. G. Ruppert, Y. K. Yong Note: Guaranteed collocated multimode control of an atomic force microscope cantilever using on-chip piezoelectric actuation and sensing (Journal Article) Review of Scientific Instruments, 88 (086109), 2017. @article{Ruppert2017b, title = {Note: Guaranteed collocated multimode control of an atomic force microscope cantilever using on-chip piezoelectric actuation and sensing}, author = {M. G. Ruppert and Y. K. Yong}, url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/08/2017_JNote_RSI_Vol88_086109-2.pdf}, doi = {10.1063/1.4990451}, year = {2017}, date = {2017-08-15}, journal = {Review of Scientific Instruments}, volume = {88}, number = {086109}, abstract = {The quality (Q) factor is an important parameter of the resonance of the microcantilever as it determines both imaging bandwidth and force sensitivity. The ability to control the Q factor of multiple modes is believed to be of great benefit for atomic force microscopy techniques involving multiple eigenmodes. In this paper, we propose a novel cantilever design employing multiple piezoelectric transducers which are used for separated actuation and sensing, leading to guaranteed collocation of the first eight eigenmodes up to 3 MHz. The design minimizes the feedthrough usually observed with these systems by incorporating a guard trace on the cantilever chip. As a result, a multimode Q controller is demonstrated to be able to modify the quality factor of the first two eigenmodes over up to four orders of magnitude without sacrificing robust stability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quality (Q) factor is an important parameter of the resonance of the microcantilever as it determines both imaging bandwidth and force sensitivity. The ability to control the Q factor of multiple modes is believed to be of great benefit for atomic force microscopy techniques involving multiple eigenmodes. In this paper, we propose a novel cantilever design employing multiple piezoelectric transducers which are used for separated actuation and sensing, leading to guaranteed collocation of the first eight eigenmodes up to 3 MHz. The design minimizes the feedthrough usually observed with these systems by incorporating a guard trace on the cantilever chip. As a result, a multimode Q controller is demonstrated to be able to modify the quality factor of the first two eigenmodes over up to four orders of magnitude without sacrificing robust stability. |
| 18. |  | M. R. P. Ragazzon, M. G. Ruppert, D. M. Harcombe, A. J. Fleming, J. T. Gravdahl Lyapunov Estimator for High-Speed Demodulation in Dynamic Mode Atomic Force Microscopy (Journal Article) IEEE Transactions on Control Systems Technology, Accepted , 2017. @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} } 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. |
| 17. |  | D. M. Harcombe, M. G. Ruppert, A. J. Fleming Higher-harmonic AFM Imaging with a High-Bandwidth Multifrequency Lyapunov Filter (Inproceeding) Advanced Intelligent Mechatronics, Munich, Germany, 2017. @inproceedings{C17e, title = {Higher-harmonic AFM Imaging with a High-Bandwidth Multifrequency Lyapunov Filter}, author = {D. M. Harcombe and M. G. Ruppert and A. J. Fleming}, year = {2017}, date = {2017-07-03}, booktitle = {Advanced Intelligent Mechatronics}, address = {Munich, Germany}, abstract = {A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. Typically a lock-in amplifier is chosen as it is both narrowband and simple to implement. However, it inherently suffers drawbacks including a limited bandwidth due to post mixing low-pass filters and the necessity for multiple to be operated in parallel for MF-AFM. This paper proposes a multifrequency demodulator in the form of a modelbased Lyapunov filter implemented on a Field Programmable Gate Array (FPGA). System modelling and simulations are verified by experimental results demonstrating high tracking bandwidth and off-mode rejection at modelled frequencies. Additionally, AFM scans with a five-frequency-based system are presented wherein higher harmonic imaging is performed up to 1 MHz.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. Typically a lock-in amplifier is chosen as it is both narrowband and simple to implement. However, it inherently suffers drawbacks including a limited bandwidth due to post mixing low-pass filters and the necessity for multiple to be operated in parallel for MF-AFM. This paper proposes a multifrequency demodulator in the form of a modelbased Lyapunov filter implemented on a Field Programmable Gate Array (FPGA). System modelling and simulations are verified by experimental results demonstrating high tracking bandwidth and off-mode rejection at modelled frequencies. Additionally, AFM scans with a five-frequency-based system are presented wherein higher harmonic imaging is performed up to 1 MHz. |
| 16. |  | S. I. Moore, M. G. Ruppert, Y. K. Yong Design and Analysis of Piezoelectric Cantilevers with Enhanced Higher Eigenmodes for Atomic Force Microscopy (Invited Paper) (Inproceeding) Advanced Intelligent Mechatronics, Munich, Germany, 2017. @inproceedings{Moore2017b, title = {Design and Analysis of Piezoelectric Cantilevers with Enhanced Higher Eigenmodes for Atomic Force Microscopy (Invited Paper)}, author = {S. I. Moore and M. G. Ruppert and Y. K. Yong}, year = {2017}, date = {2017-07-02}, booktitle = {Advanced Intelligent Mechatronics}, address = {Munich, Germany}, abstract = {Atomic force microscope (AFM) cantilevers with integrated actuation and sensing provide several distinct advantages over conventional cantilever instrumentation such as clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. However, for multifrequency AFM techniques involving higher eigenmodes of the cantilever, optimization of the transducer location and layout has to be taken into account. This work proposes multiple integrated piezoelectric regions on the cantilever which maximize the deflection of the cantilever and the piezoelectric charge response for a given higher eigenmode based on the spatial strain distribution. Finite element analysis is performed to find the optimal transducer topology and experimental results are presented which highlight an actuation gain improvement up to 42 dB on the third mode and sensor sensitivity improvement up to 38 dB on the second mode.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Atomic force microscope (AFM) cantilevers with integrated actuation and sensing provide several distinct advantages over conventional cantilever instrumentation such as clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. However, for multifrequency AFM techniques involving higher eigenmodes of the cantilever, optimization of the transducer location and layout has to be taken into account. This work proposes multiple integrated piezoelectric regions on the cantilever which maximize the deflection of the cantilever and the piezoelectric charge response for a given higher eigenmode based on the spatial strain distribution. Finite element analysis is performed to find the optimal transducer topology and experimental results are presented which highlight an actuation gain improvement up to 42 dB on the third mode and sensor sensitivity improvement up to 38 dB on the second mode. |
| 15. |  | M. G. Ruppert, M. Maroufi, A. Bazaei, S. O. R. Moheimani Kalman Filter Enabled High-Speed Control of a MEMS Nanopositioner (Inproceeding) 20th IFAC World Congress, 2017, (accepted). @inproceedings{Ruppert2017b, title = {Kalman Filter Enabled High-Speed Control of a MEMS Nanopositioner}, author = {M. G. Ruppert and M. Maroufi and A. Bazaei and S. O. R. Moheimani}, year = {2017}, date = {2017-07-01}, booktitle = {20th IFAC World Congress}, abstract = {We demonstrate a novel tracking controller formulation based on a linear time-varying Kalman Filter to regulate amplitude and phase of a reference signal independently. The method is applicable to sinusoidal references such as spiral, cycloid and Lissajous trajectories which are commonly used for imaging in high-speed Atomic Force Microscopy (AFM). A Microelectromechanical Systems (MEMS) based nanopositioner, whose fundamental resonance frequency is dampened with an additional damping feedback loop, is employed. For a scan range of 2um, we demonstrate experimental tracking of sinusoids with frequencies as high as 5kHz, well beyond the open-loop fundamental resonance, with a tracking error of only 4.6nm.}, note = {accepted}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } We demonstrate a novel tracking controller formulation based on a linear time-varying Kalman Filter to regulate amplitude and phase of a reference signal independently. The method is applicable to sinusoidal references such as spiral, cycloid and Lissajous trajectories which are commonly used for imaging in high-speed Atomic Force Microscopy (AFM). A Microelectromechanical Systems (MEMS) based nanopositioner, whose fundamental resonance frequency is dampened with an additional damping feedback loop, is employed. For a scan range of 2um, we demonstrate experimental tracking of sinusoids with frequencies as high as 5kHz, well beyond the open-loop fundamental resonance, with a tracking error of only 4.6nm. |
| 14. |  | M. G. Ruppert, D. M. Harcombe, M. R. P. Ragazzon, S. O. R. Moheimani, A. J. Fleming Frequency Domain Analysis of Robust Demodulators for High-Speed Atomic Force Microscopy (Inproceeding) American Control Conference, Seattle, WA, 2017. @inproceedings{C17b, title = {Frequency Domain Analysis of Robust Demodulators for High-Speed 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 = {2017-05-01}, booktitle = {American Control Conference}, address = {Seattle, WA}, abstract = {A fundamental but often overlooked component in the z-axis feedback loop of the atomic force microscope (AFM) operated in dynamic mode is the demodulator. It’s purpose is to obtain a preferably fast and low-noise estimate of amplitude and phase of the cantilever deflection signal in the presence of sensor noise and additional distinct frequency components. In this paper, we implement both traditional and recently developed robust methods on a labVIEW digital processing system and rigorously compare these techniques experimentally in terms of measurement bandwidth, implementation complexity and robustness to noise. We conclude with showing high-speed tapping-mode AFM images in constant height, highlighting the significance of an adequate demodulator bandwidth.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } A fundamental but often overlooked component in the z-axis feedback loop of the atomic force microscope (AFM) operated in dynamic mode is the demodulator. It’s purpose is to obtain a preferably fast and low-noise estimate of amplitude and phase of the cantilever deflection signal in the presence of sensor noise and additional distinct frequency components. In this paper, we implement both traditional and recently developed robust methods on a labVIEW digital processing system and rigorously compare these techniques experimentally in terms of measurement bandwidth, implementation complexity and robustness to noise. We conclude with showing high-speed tapping-mode AFM images in constant height, highlighting the significance of an adequate demodulator bandwidth. |
| 13. |  | M. Maroufi, M. G. Ruppert, A. G. Fowler, S. O. R. Moheimani Design and Control of a Single-chip SOI-MEMS Atomic Force Microscope (Inproceeding) American Control Conference, 2017, (accepted). @inproceedings{Maroufi2017, title = {Design and Control of a Single-chip SOI-MEMS Atomic Force Microscope}, author = {M. Maroufi and M. G. Ruppert and A. G. Fowler and S. O. R. Moheimani}, year = {2017}, date = {2017-05-01}, booktitle = {American Control Conference}, abstract = {This paper presents a novel microelectromechanical systems (MEMS) implementation of an on-chip atomic force microscope (AFM), fabricated using a silicon-on-insulator process. The device features an XY scanner with electrostatic actuators and electrothermal sensors, as well as an integrated silicon microcantilever. A single AlN piezoelectric electrode is used for simultaneous actuation and deflection sensing of the cantilever via a charge sensing technique. With the device being operated in closed loop, the probe scanner is successfully used to obtain 8mmx8mm tapping-mode AFM images of a calibration grating.}, note = {accepted}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } This paper presents a novel microelectromechanical systems (MEMS) implementation of an on-chip atomic force microscope (AFM), fabricated using a silicon-on-insulator process. The device features an XY scanner with electrostatic actuators and electrothermal sensors, as well as an integrated silicon microcantilever. A single AlN piezoelectric electrode is used for simultaneous actuation and deflection sensing of the cantilever via a charge sensing technique. With the device being operated in closed loop, the probe scanner is successfully used to obtain 8mmx8mm tapping-mode AFM images of a calibration grating. |
| 12. |  | S. I. Moore, M. G. Ruppert, Y. K. Yong Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement (Journal Article) Beilstein Journal of Nanotechnology, 8 , pp. 358–371, 2017. @article{Moore2017b, title = {Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement}, author = {S. I. Moore and M. G. Ruppert and Y. K. Yong}, url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/02/2190-4286-8-38.pdf}, year = {2017}, date = {2017-02-06}, journal = {Beilstein Journal of Nanotechnology}, volume = {8}, pages = {358--371}, abstract = {Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes. |
| 11. |  | M. G. Ruppert, A. G. Fowler, M. Maroufi, S. O. R. Moheimani On-chip Dynamic Mode Atomic Force Microscopy: A silicon-on-insulator MEMS approach (Journal Article) IEEE Journal of Microelectromechanical Systems, 26 (1), pp. 215-225, 2017. @article{Ruppert2017, title = {On-chip Dynamic Mode Atomic Force Microscopy: A silicon-on-insulator MEMS approach}, author = {M. G. Ruppert and A. G. Fowler and M. Maroufi and S. O. R. Moheimani}, doi = {10.1109/JMEMS.2016.2628890}, year = {2017}, date = {2017-02-01}, journal = {IEEE Journal of Microelectromechanical Systems}, volume = {26}, number = {1}, pages = {215-225}, abstract = {The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm x 8μm in closed loop.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm x 8μm in closed loop. |
2016 | ||
| 10. |  | M. G. Ruppert, D. M. Harcombe, S. O. R. Moheimani High-Bandwidth Demodulation in MF-AFM: A Kalman Filtering Approach (Journal Article) IEEE/ASME Transactions on Mechatronics, 21 (6), pp. 2705-2715, 2016. @article{Ruppert2016, title = {High-Bandwidth Demodulation in MF-AFM: A Kalman Filtering Approach}, author = {M. G. Ruppert and D. M. Harcombe and S. O. R. Moheimani}, doi = {10.1109/TMECH.2016.2574640}, year = {2016}, date = {2016-12-01}, journal = {IEEE/ASME Transactions on Mechatronics}, volume = {21}, number = {6}, pages = {2705-2715}, abstract = {Emerging multifrequency atomic force microscopy (MF-AFM) methods rely on coherent demodulation of the cantilever deflection signal at multiple frequencies. These measurements are needed in order to close the z-axis feedback loop and to acquire complementary information on the tip-sample interaction. While the common method is to use a lock-in amplifier capable of recovering low-level signals from noisy backgrounds, its performance is ultimately bounded by the bandwidth of the low-pass filters. In light of the demand for constantly increasing imaging speeds while providing multifrequency flexibility, we propose to estimate the in-phase and quadrature components with a linear time-varying Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field Programmable Gate Array (FPGA). Tracking bandwidth and noise performance are verified experimentally and trimodal AFM results on a two-component polymer sample highlight the applicability of the proposed method for MF-AFM.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Emerging multifrequency atomic force microscopy (MF-AFM) methods rely on coherent demodulation of the cantilever deflection signal at multiple frequencies. These measurements are needed in order to close the z-axis feedback loop and to acquire complementary information on the tip-sample interaction. While the common method is to use a lock-in amplifier capable of recovering low-level signals from noisy backgrounds, its performance is ultimately bounded by the bandwidth of the low-pass filters. In light of the demand for constantly increasing imaging speeds while providing multifrequency flexibility, we propose to estimate the in-phase and quadrature components with a linear time-varying Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field Programmable Gate Array (FPGA). Tracking bandwidth and noise performance are verified experimentally and trimodal AFM results on a two-component polymer sample highlight the applicability of the proposed method for MF-AFM. |
| 9. |  | M. G. Ruppert, S. O. R. Moheimani Multimode Q Control in Tapping-Mode AFM: Enabling Imaging on Higher Flexural Eigenmodes (Journal Article) IEEE Transactions on Control Systems Technology, 24 (4), pp. 1149-1159, 2016. @article{Ruppert2016b, title = {Multimode Q Control in Tapping-Mode AFM: Enabling Imaging on Higher Flexural Eigenmodes}, author = {M. G. Ruppert and S. O. R. Moheimani}, doi = {10.1109/TCST.2015.2478077}, year = {2016}, date = {2016-07-01}, journal = {IEEE Transactions on Control Systems Technology}, volume = {24}, number = {4}, pages = {1149-1159}, abstract = {Numerous dynamic Atomic Force Microscopy (AFM) methods have appeared in recent years, which make use of the excitation and detection of higher order eigenmodes of the microcantilever. The ability to control these modes and their responses to excitation is believed to be the key to unraveling the true potential of these methods. In this work, we highlight a multi-mode Q control method that exhibits remarkable damping performance and stability robustness. The experimental results obtained in ambient conditions demonstrate improved imaging stability by damping non-driven resonant modes when scanning is performed at a higher eigenmode of the cantilever. Higher scan speeds are shown to result from a decrease in transient response time. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Numerous dynamic Atomic Force Microscopy (AFM) methods have appeared in recent years, which make use of the excitation and detection of higher order eigenmodes of the microcantilever. The ability to control these modes and their responses to excitation is believed to be the key to unraveling the true potential of these methods. In this work, we highlight a multi-mode Q control method that exhibits remarkable damping performance and stability robustness. The experimental results obtained in ambient conditions demonstrate improved imaging stability by damping non-driven resonant modes when scanning is performed at a higher eigenmode of the cantilever. Higher scan speeds are shown to result from a decrease in transient response time. |
| 8. |  | M. G. Ruppert, D. M. Harcombe, S. O. R. Moheimani State estimation for high-speed multifrequency atomic force microscopy (Inproceeding) American Control Conference, pp. 2617-2622, Boston, MA, USA, 2016. @inproceedings{Ruppert2016b, title = {State estimation for high-speed multifrequency atomic force microscopy}, author = {M. G. Ruppert and D. M. Harcombe and S. O. R. Moheimani}, doi = {10.1109/ACC.2016.7525311}, year = {2016}, date = {2016-07-01}, booktitle = {American Control Conference}, pages = {2617-2622}, address = {Boston, MA, USA}, abstract = {A fundamental component in the z-axis feedback loop of an atomic force microscope (AFM) operated in dynamic mode is the lock-in amplifier to obtain amplitude and phase of the high-frequency cantilever deflection signal. While this narrowband demodulation technique is capable of filtering noise far away from the carrier and modulation frequency, its performance is ultimately bounded by the bandwidth of its low-pass filter which is employed to suppress the frequency component at twice the carrier frequency. Moreover, multiple eigenmodes and higher harmonics are used for imaging in modern multifrequency AFMs, which necessitates multiple lock-in amplifiers to recover the respective amplitude and phase information. We propose to estimate amplitude and phase of multiple frequency components with a linear time-varying Kalman filter which allows for an efficient implementation on a Field Programmable Gate Array (FPGA). While experimental results for the single mode case have already proven to increase the imaging bandwidth in tapping-mode AFM, multifrequency simulations promise further improvement in imaging flexibility. }, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } A fundamental component in the z-axis feedback loop of an atomic force microscope (AFM) operated in dynamic mode is the lock-in amplifier to obtain amplitude and phase of the high-frequency cantilever deflection signal. While this narrowband demodulation technique is capable of filtering noise far away from the carrier and modulation frequency, its performance is ultimately bounded by the bandwidth of its low-pass filter which is employed to suppress the frequency component at twice the carrier frequency. Moreover, multiple eigenmodes and higher harmonics are used for imaging in modern multifrequency AFMs, which necessitates multiple lock-in amplifiers to recover the respective amplitude and phase information. We propose to estimate amplitude and phase of multiple frequency components with a linear time-varying Kalman filter which allows for an efficient implementation on a Field Programmable Gate Array (FPGA). While experimental results for the single mode case have already proven to increase the imaging bandwidth in tapping-mode AFM, multifrequency simulations promise further improvement in imaging flexibility. |
| 7. |  | M. G. Ruppert, S. O. R. Moheimani High-bandwidth Multimode Self-sensing in Bimodal Atomic Force Microscopy (Journal Article) Beilstein Journal of Nanotechnology, 7 , pp. 284-295, 2016. @article{Ruppert2016b, title = {High-bandwidth Multimode Self-sensing in Bimodal Atomic Force Microscopy}, author = {M. G. Ruppert and S. O. R. Moheimani}, doi = {10.3762/bjnano.7.26}, year = {2016}, date = {2016-02-24}, journal = {Beilstein Journal of Nanotechnology}, volume = {7}, pages = {284-295}, abstract = {Using standard microelectromechanical system (MEMS) processes to coat a microcantilever with a piezoelectric layer results in a versatile transducer with inherent self-sensing capabilities. For applications in multifrequency atomic force microscopy (MF-AFM), we illustrate that a single piezoelectric layer can be simultaneously used for multimode excitation and detection of the cantilever deflection. This is achieved by a charge sensor with a bandwidth of 10 MHz and dual feedthrough cancellation to recover the resonant modes that are heavily buried in feedthrough originating from the piezoelectric capacitance. The setup enables the omission of the commonly used piezoelectric stack actuator and optical beam deflection sensor, alleviating limitations due to distorted frequency responses and instrumentation cost, respectively. The proposed method benefits from a more than two orders of magnitude increase in deflection to strain sensitivity on the fifth eigenmode leading to a remarkable signal-to-noise ratio. Experimental results using bimodal AFM imaging on a two component polymer sample validate that the self-sensing scheme can therefore be used to provide both the feedback signal, for topography imaging on the fundamental mode, and phase imaging on the higher eigenmode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using standard microelectromechanical system (MEMS) processes to coat a microcantilever with a piezoelectric layer results in a versatile transducer with inherent self-sensing capabilities. For applications in multifrequency atomic force microscopy (MF-AFM), we illustrate that a single piezoelectric layer can be simultaneously used for multimode excitation and detection of the cantilever deflection. This is achieved by a charge sensor with a bandwidth of 10 MHz and dual feedthrough cancellation to recover the resonant modes that are heavily buried in feedthrough originating from the piezoelectric capacitance. The setup enables the omission of the commonly used piezoelectric stack actuator and optical beam deflection sensor, alleviating limitations due to distorted frequency responses and instrumentation cost, respectively. The proposed method benefits from a more than two orders of magnitude increase in deflection to strain sensitivity on the fifth eigenmode leading to a remarkable signal-to-noise ratio. Experimental results using bimodal AFM imaging on a two component polymer sample validate that the self-sensing scheme can therefore be used to provide both the feedback signal, for topography imaging on the fundamental mode, and phase imaging on the higher eigenmode. |
| 6. |  | M. G. Ruppert, K. S. Karvinen, S. L. Wiggins, S. O. R. Moheimani A Kalman Filter for Amplitude Estimation in High-Speed Dynamic Mode Atomic Force Microscopy (Journal Article) IEEE Transactions on Control Systems Technology, 24 (1), pp. 276-284, 2016. @article{Ruppert2016b, title = {A Kalman Filter for Amplitude Estimation in High-Speed Dynamic Mode Atomic Force Microscopy}, author = {M. G. Ruppert and K. S. Karvinen and S. L. Wiggins and S. O. R. Moheimani}, doi = {10.1109/TCST.2015.2435654}, year = {2016}, date = {2016-01-01}, journal = {IEEE Transactions on Control Systems Technology}, volume = {24}, number = {1}, pages = {276-284}, abstract = {A fundamental challenge in dynamic mode atomic force microscopy (AFM) is the estimation of the cantilever oscillation amplitude from the deflection signal which might be distorted by noise and/or high-frequency components. When the cantilever is excited at resonance, its deflection is typically obtained via narrowband demodulation using a lock-in amplifier. However, the bandwidth of this measurement technique is ultimately bounded by the low-pass filter which must be employed after demodulation to attenuate the component at twice the carrier frequency. Furthermore, to measure the amplitude of multiple frequency components such as higher eigenmodes and/or higher harmonics in multifrequency AFM, multiple lock-in amplifiers must be employed. In this work, the authors propose the estimation of amplitude and phase using a linear time-varying Kalman filter which is easily extended to multiple frequencies. Experimental results are obtained using square-modulated sine waves and closed-loop AFM scans, verifying the performance of the proposed Kalman filter.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A fundamental challenge in dynamic mode atomic force microscopy (AFM) is the estimation of the cantilever oscillation amplitude from the deflection signal which might be distorted by noise and/or high-frequency components. When the cantilever is excited at resonance, its deflection is typically obtained via narrowband demodulation using a lock-in amplifier. However, the bandwidth of this measurement technique is ultimately bounded by the low-pass filter which must be employed after demodulation to attenuate the component at twice the carrier frequency. Furthermore, to measure the amplitude of multiple frequency components such as higher eigenmodes and/or higher harmonics in multifrequency AFM, multiple lock-in amplifiers must be employed. In this work, the authors propose the estimation of amplitude and phase using a linear time-varying Kalman filter which is easily extended to multiple frequencies. Experimental results are obtained using square-modulated sine waves and closed-loop AFM scans, verifying the performance of the proposed Kalman filter. |
2015 | ||
| 5. |  | M. G. Ruppert, S. O. R. Moheimani Multi-Mode Q Control in Multifrequency Atomic Force Microscopy (Inproceeding) ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, pp. V004T09A009, Boston, Massachusetts, USA, 2015. @inproceedings{Ruppert2015, title = {Multi-Mode Q Control in Multifrequency Atomic Force Microscopy}, author = {M. G. Ruppert and S. O. R. Moheimani}, doi = {10.1115/DETC2015-46989}, year = {2015}, date = {2015-08-01}, booktitle = {ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference}, pages = {V004T09A009}, address = {Boston, Massachusetts, USA}, abstract = {Various Atomic Force Microscopy (AFM) modes have emerged which rely on the excitation and detection of multiple eigenmodes of the microcantilever. The conventional control loops employed in multifrequency AFM (MF-AFM) such as bimodal imaging where the fundamental mode is used to map the topography and a higher eigenmode is used to map sample material properties only focus on maintaining low bandwidth signals such as amplitude and/ or frequency shift. However, the ability to perform additional high bandwidth control of the quality (Q) factor of the participating modes is believed to be imperative to unfolding the full potential of these methods. This can be achieved by employing a multi-mode Q control approach utilizing positive position feedback. The controller exhibits remarkable performance in arbitrarily modifying the Q factor of multiple eigenmodes as well as guaranteed stability properties when used on flexible structures with collocated actuators and sensors. A controller design method based on pole placement optimization is proposed for setting an arbitrary on-resonance Q factor of the participating eigenmodes. Experimental results using bimodal AFM imaging on a two component polymer sample are presented.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Various Atomic Force Microscopy (AFM) modes have emerged which rely on the excitation and detection of multiple eigenmodes of the microcantilever. The conventional control loops employed in multifrequency AFM (MF-AFM) such as bimodal imaging where the fundamental mode is used to map the topography and a higher eigenmode is used to map sample material properties only focus on maintaining low bandwidth signals such as amplitude and/ or frequency shift. However, the ability to perform additional high bandwidth control of the quality (Q) factor of the participating modes is believed to be imperative to unfolding the full potential of these methods. This can be achieved by employing a multi-mode Q control approach utilizing positive position feedback. The controller exhibits remarkable performance in arbitrarily modifying the Q factor of multiple eigenmodes as well as guaranteed stability properties when used on flexible structures with collocated actuators and sensors. A controller design method based on pole placement optimization is proposed for setting an arbitrary on-resonance Q factor of the participating eigenmodes. Experimental results using bimodal AFM imaging on a two component polymer sample are presented. |
2014 | ||
| 4. |  | K. S. Karvinen, M. G. Ruppert, K. Mahata, S. O. R. Moheimani Direct Tip-Sample Force Estimation for High-Speed Dynamic Mode Atomic Force Microscopy (Journal Article) IEEE Transactions on Nanotechnology, 13 (6), pp. 1257-1265, 2014. @article{Karvinen2014, title = {Direct Tip-Sample Force Estimation for High-Speed Dynamic Mode Atomic Force Microscopy}, author = {K. S. Karvinen and M. G. Ruppert and K. Mahata and S. O. R. Moheimani}, doi = {10.1109/TNANO.2014.2360878}, year = {2014}, date = {2014-11-01}, journal = {IEEE Transactions on Nanotechnology}, volume = {13}, number = {6}, pages = {1257-1265}, abstract = {We present new insights into the modeling of the microcantilever in dynamic mode atomic force microscopy and outline a novel high-bandwidth tip-sample force estimation technique for the development of high-bandwidth z-axis control. Fundamental to the proposed technique is the assumption that in tapping mode atomic force microscopy, the tip-sample force takes the form of an impulse train. Formulating the estimation problem as a Kalman filter, the tip-sample force is estimated directly; thus, potentially enabling high-bandwidth z-axis control by eliminating the dependence of the control technique on microcantilever dynamics and the amplitude demodulation technique. Application of this technique requires accurate knowledge of the models of the microcantilever; a novel identification method is proposed. Experimental data are used in an offline analysis for verification.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present new insights into the modeling of the microcantilever in dynamic mode atomic force microscopy and outline a novel high-bandwidth tip-sample force estimation technique for the development of high-bandwidth z-axis control. Fundamental to the proposed technique is the assumption that in tapping mode atomic force microscopy, the tip-sample force takes the form of an impulse train. Formulating the estimation problem as a Kalman filter, the tip-sample force is estimated directly; thus, potentially enabling high-bandwidth z-axis control by eliminating the dependence of the control technique on microcantilever dynamics and the amplitude demodulation technique. Application of this technique requires accurate knowledge of the models of the microcantilever; a novel identification method is proposed. Experimental data are used in an offline analysis for verification. |
| 3. |  | M. G. Ruppert, S. O. R. Moheimani Novel Reciprocal Self-Sensing Techniques for Tapping-Mode Atomic Force Microscopy (Inproceeding) 19th IFAC World Congress, Cape Town, South Africa, 2014. @inproceedings{Ruppert2014, title = {Novel Reciprocal Self-Sensing Techniques for Tapping-Mode Atomic Force Microscopy}, author = {M. G. Ruppert and S. O. R. Moheimani}, doi = {https://doi.org/10.3182/20140824-6-ZA-1003.00376}, year = {2014}, date = {2014-08-24}, booktitle = {19th IFAC World Congress}, address = {Cape Town, South Africa}, abstract = {We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively. A microcantilever, which can be batch fabricated through a standard microelectromechanical system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for actuation and deflection sensing. The setup enables the elimination of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. The voltage to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough which degrades the dynamic range of the sensors significantly. A feedforward control technique is employed to cancel the feedthrough and increase the dynamic range from less than 1 dB to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for TM-AFM imaging.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively. A microcantilever, which can be batch fabricated through a standard microelectromechanical system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for actuation and deflection sensing. The setup enables the elimination of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. The voltage to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough which degrades the dynamic range of the sensors significantly. A feedforward control technique is employed to cancel the feedthrough and increase the dynamic range from less than 1 dB to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for TM-AFM imaging. |
2013 | ||
| 2. |  | M. G. Ruppert, S. O. R. Moheimani A novel self-sensing technique for tapping-mode atomic force microscopy (Journal Article) Review of Scientific Instruments, 84 (12), pp. 125006, 2013. @article{Ruppert2013b, title = {A novel self-sensing technique for tapping-mode atomic force microscopy}, author = {M. G. Ruppert and S. O. R. Moheimani}, doi = {http://dx.doi.org/10.1063/1.4841855}, year = {2013}, date = {2013-12-01}, journal = {Review of Scientific Instruments}, volume = {84}, number = {12}, pages = {125006}, abstract = {This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing Micro Electro Mechanical System processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1dB to approximately 35dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for AFM imaging.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing Micro Electro Mechanical System processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1dB to approximately 35dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for AFM imaging. |
| 1. |  | M. G. Ruppert, M. Fairbairn, S. O. R. Moheimani Multi-Mode Resonant Control of a Microcantilever for Atomic Force Microscopy (Inproceeding) IEEE/ASME International Conference on Advanced Intelligent Mechatronics, pp. 77-82, Wollongong, Australia, 2013. @inproceedings{Ruppert2013, title = {Multi-Mode Resonant Control of a Microcantilever for Atomic Force Microscopy}, author = {M. G. Ruppert and M. Fairbairn and S. O. R. Moheimani}, doi = {10.1109/AIM.2013.6584071}, year = {2013}, date = {2013-07-09}, booktitle = {IEEE/ASME International Conference on Advanced Intelligent Mechatronics}, pages = {77-82}, address = {Wollongong, Australia}, abstract = {When operating the Atomic Force Microscope in tapping mode it is possible to decrease the quality factor of the microcantilever to enhance scan speed. %Standard Q Control techniques involve velocity feedback with the disadvantage of additional sensor equipment, or time-delay position feedback which may lead to instabilities of out-of-bandwidth modes.Various resonance controllers have been proposed which do not rely on expensive velocity sensors and guarantee stability of the closed loop system even in the presence of unmodeled dynamics. A new field of Atomic Force Microscopy is evolving, which makes use of multiple frequency excitation and detection of the cantilever modes making it necessary to be able to control these modes and their response to excitation. This work proposes a multi-mode Q control approach utilizing positive position feedback, offering full control over the first two flexural modes of the cantilever. By completely damping the first mode and adjusting the quality factor of the second mode, it is possible to scan and obtain images at the second resonance frequency which improves image quality at high scan speeds due to the increased bandwidth of the z-axis feedback loop.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } When operating the Atomic Force Microscope in tapping mode it is possible to decrease the quality factor of the microcantilever to enhance scan speed. %Standard Q Control techniques involve velocity feedback with the disadvantage of additional sensor equipment, or time-delay position feedback which may lead to instabilities of out-of-bandwidth modes.Various resonance controllers have been proposed which do not rely on expensive velocity sensors and guarantee stability of the closed loop system even in the presence of unmodeled dynamics. A new field of Atomic Force Microscopy is evolving, which makes use of multiple frequency excitation and detection of the cantilever modes making it necessary to be able to control these modes and their response to excitation. This work proposes a multi-mode Q control approach utilizing positive position feedback, offering full control over the first two flexural modes of the cantilever. By completely damping the first mode and adjusting the quality factor of the second mode, it is possible to scan and obtain images at the second resonance frequency which improves image quality at high scan speeds due to the increased bandwidth of the z-axis feedback loop. |