Current Sensor With Opposing Bias Fields For Disturbing Field Cancellation
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Solution Overview
Problem
Current sensors using magneto-resistive elements face challenges in suppressing disturbing magnetic fields both along the magneto-sensitive axis and the sensitivity-influencing axis directions, leading to sensitivity variations and output changes, and require magnetic shields that result in sensor upsizing.
Innovation Solution
A current sensor design incorporating two magneto-sensitive portions with different magnetic field strengths, where a first bias magnetic field is applied to one portion and an opposing bias magnetic field is applied to the other, allowing for cancellation of disturbing fields in both axis directions without the need for a magnetic shield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a magnetic shield is used to suppress disturbing magnetic fields, then the influence of disturbing magnetic fields is reduced, but the sensor size increases
Solution Approach 1:
The sensor is divided into two separate magnetic sensing elements positioned at different locations relative to the bus bar. Each element detects magnetic field components in specific directions, and their outputs are combined through differential processing to cancel out disturbing magnetic fields while maintaining compact dimensions without requiring external magnetic shields
Solution Approach 2:
Each magneto-sensitive portion is configured with specific orientation and positioning to detect particular components of the magnetic field. The first element detects fields in one direction while the second element detects fields in a perpendicular direction, allowing selective suppression of disturbing fields in specific spatial zones without requiring omnidirectional magnetic shielding
2Device complexity
If magneto-resistive elements are used without a core, then the sensor structure is simplified, but the sensor becomes more susceptible to disturbing magnetic fields
Solution Approach 1:
The patent converts the susceptibility of coreless magneto-resistive elements to magnetic fields into a benefit by using differential measurement. Two elements are positioned to experience different magnetic field components, and by subtracting their outputs, the system cancels out disturbing fields while maintaining the structural simplicity of coreless design
Solution Approach 2:
The two magneto-sensitive portions are positioned asymmetrically relative to the bus bar, with different orientations and locations. This asymmetric arrangement ensures that each element experiences a unique combination of magnetic field components, enabling the differential output to selectively cancel disturbing fields while preserving the coreless simple structure
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 design effectively suppresses disturbing magnetic fields in both axis directions, stabilizing sensor output and eliminating the need for a magnetic shield, thereby maintaining sensitivity and reducing sensor size.
Implementation Method 1
a magneto-resistive element (MR element) such as GMR element is used as a magnetic sensing element
Implementation Method 2
a first bias magnetic field is applied to the first magneto-sensitive portion and a second bias magnetic field in a direction opposite to a direction of the first bias magnetic field is applied to the second magneto-sensitive portion
Data Source
AI summary
A current sensor includes a bus bar through which an electric current to be measured flows, a first magnetic sensing element including a first magneto-sensitive portion including a magneto-resistive element, and a second magnetic sensing element including a second magneto-sensitive portion including a magneto-resistive element. Strength of a magnetic field generated by the electric current sensed by the first magneto-sensitive portion is different from a strength of the magnetic field sensed by the second magneto-sensitive portion. A first bias magnetic field is applied to the first magneto-sensitive portion and a second bias magnetic field in a direction opposite to a direction of the first bias magnetic field is applied to the second magneto-sensitive portion.