Adjustable Compensation Ratio Feedback for Magnetic Shielding
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Solution Overview
Problem
Conventional closed-loop negative-feedback systems for controlling or compensating physical fields, such as in MRI instruments, face limitations due to the presence of an Interacting Medium (IM) between the sensor and the Protected Volume (PV), leading to inaccurate field cancellation and compensation, especially when the sensor is located outside the PV, and fail to account for spatial and temporal variations in the IM's effect on the fields.
Innovation Solution
The Adjustable Compensation Ratio (ACR) system introduces a secondary feedback loop with ratiometric offset processing and frequency-dependent transfer functions to accurately compensate for the effects of the IM, allowing for precise cancellation of fields within the PV by incorporating parametric coefficients that account for the IM's anisotropic and frequency-dependent interactions, even when the sensor is external to the PV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional closed-loop negative-feedback system is used with the sensor located outside the PV, then the system structure is simple and easy to implement, but the field cancellation accuracy within the PV deteriorates due to the IM effect
Solution Approach 1:
The patent introduces an intermediary transfer function that mathematically models the IM's effect on field transmission. This transfer function acts as a mediator between the external sensor measurements and the actual field conditions within the PV, allowing accurate field cancellation despite the sensor being located outside the protected volume.
Solution Approach 2:
The system dynamically adjusts the compensation ratio parameter based on the characterized IM transfer function. By changing this parameter according to the IM's frequency-dependent and anisotropic properties, the system maintains high field cancellation accuracy across different operating conditions while keeping the sensor external to the PV.
2Measurement precision
If the sensor is placed within or immediately adjacent to the PV, then the field cancellation accuracy is improved, but the system cannot operate in high static field environments such as MRI instruments
Solution Approach 1:
The transfer function serves as an intermediary that bridges the gap between external sensor placement and internal field control. It enables the system to achieve accuracy equivalent to internal sensing while maintaining the practical advantage of external sensor placement in high static field environments.
Solution Approach 2:
The patent replaces the mechanical approach of physically placing the sensor inside the PV with a mathematical model-based approach. The transfer function model substitutes for direct physical measurement, allowing the system to operate in environments where physical sensor placement would be impossible or impractical.
3Productivity
If the compensating field is made constant throughout the volume for optimum system performance, then the system performance is optimized at the sensor location, but differential error increases with distance from the sensor when field gradients are present
Solution Approach 1:
The patent makes the compensation ratio dynamic by introducing an adjustable parameter that can be tuned based on the IM characteristics and operating conditions. This dynamic adjustment allows the system to optimize performance across the entire PV volume rather than at a single sensor location, compensating for field gradients while maintaining overall system effectiveness.
4Device complexity
If the IM effect on traversing fields is not compensated for, then the system structure remains simple, but temporal degradation of control accuracy occurs due to frequency-dependent and direction-dependent interactive effects
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the IM's transfer function properties (frequency-dependent and anisotropic effects) before operation. This pre-characterization allows the system to compensate for IM effects in advance, maintaining reliable and stable control accuracy across varying operating conditions without requiring complex real-time adjustments.
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
The ACR system achieves high levels of field interference cancellation and control within the PV, maintaining a high attenuation factor and minimizing the need for periodic adjustments, even with moderate environmental changes, by using empirically determined or analytically derived parameters that account for the IM's influence on the fields.
Implementation Method 1
a magnetic field sensor external to the PV but within the OV to generate a feedback signal representative of a superposition of the interfering field and the compensating field
Implementation Method 2
compensating magnetic field generated within a Protected Volume (PV) that is partially shielded from the compensating magnetic field by an intervening, Interacting Medium (IM)
Data Source
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AI summary
Apparatus for implementing Adjustable Compensation Ratio (ACR) active shielding or control of physical fields (magnetic, electric, electromagnetic, acoustic, etc.), comprising the addition of a secondary internal feedback loop within a conventional primary closed feedback loop topology. Compensation-ratio transfer function order and coefficients adjustment permits accommodating frequency-dependent and frequency- independent effects within a Protected Volume when a system field sensor or sensor array is not at the exact location where external field interference must be optimally canceled. A Laplace polynomial term precisely sets this parameter in a supplementary feedback link by modeling the frequency-dependent characteristic of an Interacting Medium without deleterious effect on other desirable primary closed-loop characteristics. The inventive ACR can be used in advanced active cancellation for magnetic shielding purposes.