Atomic Force Microscope Resonant Frequency Shift Detection
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Solution Overview
Problem
Conventional atomic force microscopes using Phase-Locked Loop (PLL) circuits for resonant frequency shift detection suffer from low detection speed and reduced sensitivity, making it difficult to achieve high-speed imaging and sensitive detection of biologic molecules' functional dynamics.
Innovation Solution
An atomic force microscope configuration that includes a displacement sensor, a resonant frequency shift detecting section with a reference signal extracting band pass filter and a phase shift signal extracting band pass filter, and a phase detecting section to determine the phase difference between reference and phase shift signals, allowing for quick and sensitive detection of resonant frequency shifts without relying on PLL circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Phase-Locked Loop (PLL) circuit is used for resonant frequency shift detection, then the detection system can track frequency changes, but the detection speed becomes slow and sensitivity is reduced
Solution Approach 1:
The patent extracts only the essential frequency information from the cantilever oscillation signal by detecting zero-crossing points, eliminating the need for complex PLL circuits. This extraction approach achieves both high detection speed and sensitivity by focusing only on the critical timing information rather than processing the entire signal through a slow feedback loop.
Solution Approach 2:
The patent replaces the mechanical feedback-based PLL system with an electronic timing measurement system that directly measures the period of oscillation by detecting zero-crossing points. This substitution eliminates the inherent speed limitations of PLL circuits while maintaining frequency detection capability.
2Productivity
If conventional PLL-based detection is used, then frequency tracking is possible, but high-speed imaging and sensitive detection of biologic molecules cannot be achieved
Solution Approach 1:
The patent performs preliminary detection of zero-crossing points at each oscillation cycle, allowing immediate calculation of frequency shifts without waiting for PLL lock-in time. This preliminary action enables high-speed imaging while maintaining sensitivity by capturing frequency information at every oscillation cycle rather than averaging over multiple cycles.
3Loss of information
If the cantilever oscillation period changes due to resonant frequency shift, then sample information can be obtained, but the detection system requires complex circuitry to track these changes
Solution Approach 1:
The patent creates a simplified temporal copy of the oscillation signal by detecting only the zero-crossing points, which preserves the essential frequency information needed for sample characterization. This copying approach reduces circuit complexity while maintaining the ability to accurately detect sample shape information through frequency shifts.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and sensitive detection of resonant frequency shifts, improving imaging speed and sensitivity, particularly suitable for observing biologic molecules by detecting frequency shifts in each cycle of cantilever oscillation.
Implementation Method 1
A displacement sensor 105 is generally based on an optical lever and monitors the displacement of the cantilever 101
Implementation Method 2
The actuator 111 is, for example, a piezo element
Implementation Method 3
The amplitudes thermally induced around the resonant frequency are larger than those at the other frequencies... This sharply increases the oscillation amplitude in the vicinity of the resonant frequency (increased Q value)
Implementation Method 4
The cantilever 101 is thermally fluctuated
Implementation Method 5
The interaction between the probe of the self-excitedly oscillating cantilever 101 and the sample (they need not necessarily contact) apparently changes the spring constant of the cantilever 101 from the original value owing to the interaction force gradient between the probe and the sample. This shifts (changes) the resonant frequency of the cantilever 101
Data Source
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AI summary
There is provided an atomic force microscope (AFM) with increase the speed and sensitivity of detection of the resonant frequency shift in a cantilever. An AFM (1) extracts a reference signal and a phase shift signal from a detection signal from a displacement sensor of the cantilever. The reference signal is restrained from a phase change in accordance with the resonant frequency shift. The phase shift signal has a phase shifted in accordance with the resonant frequency shift. The AFM (1) determines the phase difference of the phase shift signal from the reference signal, as the resonant frequency shift. The AFM (1) may detect the phase difference between a plus-minus inversion point on the reference signal and a corresponding plus-minus inversion point on the phase shift signal. The AFM (1) may adjust phase before phase detection. The phase adjustment may move the detection point for the resonant frequency shift defined on the oscillation waveforms to the plus-minus inversion point. The detection point is set at a position where the cantilever and a sample are closest to each other on the oscillation waveform.