TEM Dual Objective Lens Stray Field Cancellation
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Solution Overview
Problem
Transmission electron microscopes (TEMs) face challenges in observing magnetic samples due to stray magnetic fields generated by the objective lens, which can alter the intrinsic state of the sample, especially when using ferromagnetic substances with high magnetic permeability.
Innovation Solution
A TEM design that includes a first and second objective lens, with a controller to manage the magnetic fields, allowing for the cancellation of stray magnetic fields at the sample position by adjusting the excitation currents of the lenses and incorporating a magnetic field sensor for external field detection, ensuring minimal disruption to the sample's magnetic state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic objective lens is used to focus and image the electron beam, then the electron beam can be properly focused and imaged, but the magnetic field produced by the objective lens affects the magnetic properties of the sample
Solution Approach 1:
A magnetic shield (yoke) is introduced as an intermediary component between the objective lens and the sample. The yoke provides a low-reluctance path that guides and confines the magnetic flux, preventing it from reaching the sample while still allowing the lens to function for electron beam focusing and imaging.
Solution Approach 2:
The harmful magnetic field effect is extracted and separated from the useful imaging function. By using the yoke to confine the magnetic flux within its structure, the harmful magnetic field influence on the sample is removed while the useful electron beam focusing function is preserved.
2Adaptability or versatility
If the excitation of the imaging lens system is varied to change magnification, then the magnification can be adjusted, but the varying magnetic field reaches the sample via the magnetic circuit and affects the sample
Solution Approach 1:
The magnetic shield (yoke) acts as an intermediary that decouples the imaging lens system from the sample. When the excitation of the imaging lens system is varied to adjust magnification, the yoke confines the resulting magnetic field variations within its structure, preventing them from reaching and affecting the sample.
3Object-affected harmful factors
If a magnetic shield (yoke) is used to reduce stray magnetic fields at the sample position, then the magnetic field effects on the sample are reduced, but the overall device complexity increases
Solution Approach 1:
The magnetic shield (yoke) is merged with the existing magnetic circuit components of the objective lens assembly. By integrating the shield into the pole pieces and magnetic circuit structure, the design reduces stray fields while minimizing the increase in overall device complexity through unified construction.
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
This configuration enables precise control of magnetic fields, allowing for accurate observation of magnetic samples without altering their state, even when external or internal magnetic fields vary, thereby reducing the effects of stray magnetic fields and enabling desired magnetic field applications.
Implementation Method 1
the controller performs an operation for controlling the first objective lens according to imaging conditions to produce a magnetic field that cancels out stray magnetic fields at a position where the sample is placed
Implementation Method 2
the controller performs an operation for controlling the second objective lens to construct a transmission electron microscope image of the sample from the electron beam transmitted through the sample
Data Source
AI summary
A transmission electron microscope (100) capable of reducing the effects of stray magnetic fields includes an electron beam source (2), an illumination lens system (4) for causing the electron beam to impinge on a sample (S), a sample stage (6) for holding the sample (S), a first objective lens (8), a second objective lens (10) disposed behind the first objective lens (8), an imaging lens system (16) disposed behind the second objective lens (10), and a controller (22) configured or programmed for controlling the first objective lens (8) and the second objective lens (10). The first objective lens (8) has upper and lower polepieces disposed on opposite sides of the sample (S). The upper and lower polepieces together produce a magnetic field. The controller (22) performs an operation for controlling the second objective lens (10) to construct a TEM (transmission electron microscope) image of the sample (S) out of the electron beam transmitted through the sample (S). Furthermore, the controller performs an operation for controlling the first objective lens (8) according to imaging conditions to produce a magnetic field that cancels out stray magnetic fields at the position where the sample (S) is placed.