Magnetic Field Compensation Using Virtual Sensor Signals
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Solution Overview
Problem
Existing magnetic field compensation methods for particle-optical systems, such as electron microscopes or ion-beam exposure apparatus, face challenges in accurately compensating low-frequency and static magnetic fields within the operating region due to the inability to place magnetic field sensors directly in the region, leading to deviations in measured fields and obstructed particle beam paths.
Innovation Solution
The method involves using at least two magnetic field sensors positioned outside the operating region to generate superposed feedback signals, which are then converted to drive compensation coils, with an additional feedback branch to account for spatial differences and field gradients, effectively simulating a virtual sensor within the region to enhance compensation of static and low-frequency fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If magnetic field sensors are positioned outside the operating region, then the particle beam path is not obstructed, but the measured magnetic field deviates from the actual field in the operating region due to spatial non-uniformity
Solution Approach 1:
The patent creates a virtual sensor signal that copies what a real sensor would measure if positioned at the particle beam location. This is achieved by mathematically processing signals from external sensors to reconstruct the magnetic field conditions at the operating region, allowing accurate field compensation without physically placing sensors in the beam path
Solution Approach 2:
The patent introduces an intermediate computational process that mediates between the external sensor measurements and the required field compensation. The processing unit acts as an intermediary, transforming external field measurements into corrected signals that represent the internal field conditions, enabling accurate compensation without direct internal sensing
2Device complexity
If a single magnetic sensor is used outside the operating region, then the device complexity is reduced, but the compensation accuracy deteriorates due to inability to account for field gradients and spatial variations
Solution Approach 1:
The patent segments the magnetic field measurement task by using multiple external sensors positioned at different locations. Each sensor measures the field at its specific position, and the processing unit segments the correction task by applying position-dependent correction factors to each sensor signal, enabling accurate reconstruction of the internal field distribution
Solution Approach 2:
The patent adds a computational dimension to the physical sensor arrangement. By introducing mathematical processing that accounts for spatial coordinates and field gradients, the system transforms limited physical sensor data into comprehensive field information, effectively adding a virtual measurement dimension without physical sensors at every location
3Measurement precision
If multiple sensors are positioned at different locations outside the operating region, then the compensation accuracy is improved, but the device complexity increases due to multiple feedback loops
Solution Approach 1:
The patent merges multiple sensor signals and their corresponding feedback loops into a unified processing framework. The processing unit combines the signals from multiple sensors, applies coordinated correction based on their respective positions, and generates unified compensation currents for the Helmholtz coils, reducing the effective complexity while maintaining multi-sensor accuracy benefits
Solution Approach 2:
The processing unit serves multiple functions: it processes signals from multiple sensors, applies position-dependent corrections, accounts for field gradients, and generates compensation signals. This multi-functional approach consolidates what would otherwise require separate dedicated circuits for each sensor, reducing overall system complexity
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 approach significantly improves the stability of magnetic field compensation, reducing deviations by a factor of 17 in the ion projection system, allowing for effective compensation of static field gradients and zero-point offsets, even when sensors cannot be placed within the operating region.
Implementation Method 1
the magnetic field is measured by at least two sensors located at different positions outside the operating region, generating respective sensor signals
Implementation Method 2
the coils are fed electric currents chosen such that the magnetic fields induced in the coils compensate the external magnetic field
Data Source
AI summary
For compensation of a magnetic field in an operating region a number of magnetic field sensors (S1, S2) and an arrangement of compensation coils (Hh) surrounding said operating region is used. The magnetic field is measured by at least two sensors (S1, S2) located at different positions outside the operating region, preferably at opposing positions with respect to a symmetry axis of the operating region, generating respective sensor signals (s1, s2), the sensor signals of said sensors are superposed to a feedback signal (ms, fs), which is converted by a controlling means to a driving signal (d1), and the driving signal is used to steer at least one compensation coil (Hh). To further enhance the compensation, the driving signal is also used to derive an additional input signal (cs) for the superposing step to generate the feedback signal (fs).