2020 |
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| 5. |  | M. G. Ruppert; D. M. Harcombe; A. J. Fleming Traditional and Novel Demodulators for Multifrequency Atomic Force Microscopy Conference 8th Multifrequency AFM Conference, Madrid, Spain, 2020. Abstract | BibTeX | Tags: AFM, Demodulation, Multifrequency AFM @conference{Ruppert2020b,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. |
| 4. |  | M. G. Ruppert; N. J. Bartlett; Y. K. Yong; A. J. Fleming Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements Journal Article In: Sensors and Actuators A: Physical, vol. 312, pp. 112092, 2020, (This work was supported by the Australian Research Council Discovery Project DP170101813). Abstract | Links | BibTeX | Tags: AFM, Cantilever, Demodulation, DP170101813, MEMS, System Identification @article{Ruppert2020,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. |
| 3. |  | D. M. Harcombe; M. G. Ruppert; A. J. Fleming A review of demodulation techniques for multifrequency atomic force microscopy Journal Article In: Beilstein Journal of Nanotechnology, vol. 11, pp. 76-97, 2020, ISSN: 21904286. Abstract | Links | BibTeX | Tags: AFM, Demodulation, Multifrequency AFM, SPM @article{Harcombe2020,This article compares the performance of traditional and recently proposed demodulators for multifrequency atomic force microscopy. 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 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. |
2019 |
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| 2. |  | M. R. P. Ragazzon; S. Messineo; J. T. Gravdahl; D. M. Harcombe; M. G. Ruppert Generalized Lyapunov Demodulator for Amplitude and Phase Estimation by the Internal Model Principle Proceedings Article In: 8th IFAC Symposium on Mechatronic Systems, 2019, (accepted for publication). Abstract | BibTeX | Tags: AFM, Cantilever, Demodulation, SPM @inproceedings{Ragazzon2019,Effective demodulation of amplitude and phase is a requirement in a wide array of applications. Recent efforts have increased the demodulation performance, in particular, the Lyapunov demodulator allows bandwidths up to the carrier frequency of the signal. However, being inherently restricted to a single order filtering of the input signal, signal components outside its passband are not sufficiently attenuated for all applications, such as in multifrequency atomic force microscopy. In this article, the structure of the Lyapunov demodulator is transformed to an equivalent form, taking advantage of the internal model representation of the sinusoid to be tracked. A generalization of this formulation allows the application of standard filtering techniques in order to shape the characteristics of the demodulator, while retaining the perfect tracking condition provided by the internal model. Guidelines for the filter design are provided in order to achieve the desired characteristics, such as filtering order, tracking bandwidth, and transient performance. The resulting generalized Lyapunov demodulator structure is highly flexible, allows for direct employment of any standard filter type, is computationally simple, and easy to implement requiring only a bandpass filter, a single integrator, and two nonlinear transformations. Numerical results demonstrate the effectiveness of the approach, and provide a comparison of the various filters considered. |
| 1. |  | S. I. Moore; M. G. Ruppert; D. M. Harcombe; A. J. Fleming; Y. K. Yong Design and Analysis of Low-Distortion Demodulators for Modulated Sensors Journal Article In: IEEE/ASME Transactions on Mechatronics, vol. 24, no. 4, pp. 1861-1870, 2019, ISSN: 10834435, (This work was supported by the Australian Research Council Discovery Project DP170101813). Abstract | Links | BibTeX | Tags: Demodulation, DP170101813, Multifrequency AFM, Nanopositioning, SPM @article{Moore2019,System-based demodulators in the form of a Kalman and Lyapunov filter have been demonstrated to significantly outperform traditional demodulators, such as the lock-in amplifier, in bandwidth sensitive applications, for example high-speed atomic force microscopy. Building on their closed loop architecture, this article describes a broader class of high-speed closed-loop demodulators. The generic structure provides greater flexibility to independently control the bandwidth and sensitivity to out-of-band frequencies. A linear time-invariant description is derived which allows the utilization of linear control theory to design the demodulator. Experimental results on a nanopositioner with capacitive sensors demonstrate the realization of arbitrary demodulator dynamics while achieving excellent noise rejection. |
2020 |
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| 5. | | Traditional and Novel Demodulators for Multifrequency Atomic Force Microscopy Conference 8th Multifrequency AFM Conference, Madrid, Spain, 2020. |
| 4. | | Amplitude Noise Spectrum of a Lock-in Amplifier: Application to Microcantilever Noise Measurements Journal Article In: Sensors and Actuators A: Physical, vol. 312, pp. 112092, 2020, (This work was supported by the Australian Research Council Discovery Project DP170101813). |
| 3. | | A review of demodulation techniques for multifrequency atomic force microscopy Journal Article In: Beilstein Journal of Nanotechnology, vol. 11, pp. 76-97, 2020, ISSN: 21904286. |
2019 |
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| 2. | | Generalized Lyapunov Demodulator for Amplitude and Phase Estimation by the Internal Model Principle Proceedings Article In: 8th IFAC Symposium on Mechatronic Systems, 2019, (accepted for publication). |
| 1. | | Design and Analysis of Low-Distortion Demodulators for Modulated Sensors Journal Article In: IEEE/ASME Transactions on Mechatronics, vol. 24, no. 4, pp. 1861-1870, 2019, ISSN: 10834435, (This work was supported by the Australian Research Council Discovery Project DP170101813). |