Magnetic Sensor Bias Field Cancellation via Feedback
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Solution Overview
Problem
Existing magnetic sensors are affected by bias magnetic fields, leading to reduced sensitivity and inability to detect target magnetic fields when the bias magnetic field intensity exceeds a certain value, as it changes the operating point of magneto-resistive elements and results in decreased resistance value changes with respect to magnetic field changes.
Innovation Solution
A magnetic sensor design that includes a magnetic detecting unit with first and second magnetic detecting elements, a differential amplifier for generating a negative feedback current to cancel out detected magnetic fields, a bias magnetic field detecting means to identify and output a correcting current, and a second magnetic field generating conductor to apply a correcting magnetic field, ensuring the total magnetic field components at the detecting elements are substantially constant, thereby canceling out the bias field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magneto-resistive elements are used to detect magnetic fields, then magnetic field detection capability is achieved, but sensitivity decreases when bias magnetic field intensity exceeds a certain value
Solution Approach 1:
The patent implements a feedback mechanism where the output of the bridge circuit is fed back through an operational amplifier to generate a feedback current that flows through the magnetic field generating conductor. This feedback current creates a magnetic field that opposes and cancels the bias magnetic field, thereby stabilizing the operating point of the magneto-resistive elements and maintaining detection sensitivity even in the presence of strong bias magnetic fields.
Solution Approach 2:
The patent changes the operating parameters of the magneto-resistive elements by dynamically adjusting the magnetic field environment through the feedback mechanism. By varying the feedback current based on the detected magnetic field strength, the system maintains the magneto-resistive elements within their optimal sensitivity range, effectively counteracting the parameter degradation caused by bias magnetic fields.
2Reliability
If bias magnetic field is present, then the operating point of magneto-resistive elements changes, but detection accuracy deteriorates
Solution Approach 1:
The feedback circuit continuously monitors the output of the bridge circuit and adjusts the feedback current to maintain a stable operating point. When a bias magnetic field shifts the operating point, the feedback mechanism detects this change and generates a compensating magnetic field that restores the operating point to its optimal position, thereby maintaining detection accuracy.
Solution Approach 2:
The system takes preliminary anti-action by proactively generating a counteracting magnetic field before the bias magnetic field can significantly degrade detection accuracy. The feedback mechanism anticipates operating point shifts and applies corrective magnetic field in real-time, preventing accuracy deterioration rather than merely responding to it.
3Measurement precision
If bridge circuit is used with four magneto-resistive elements, then magnetic field detection is achieved, but output does not match assumed output when bias magnetic field is large
Solution Approach 1:
The feedback mechanism ensures that the bridge circuit output accurately reflects only the detection target magnetic field by canceling out bias magnetic field effects. The operational amplifier adjusts the feedback current to maintain the bridge circuit in a state where bias fields do not influence the differential output, thereby ensuring output accuracy matches assumed output even in the presence of large bias magnetic fields.
Solution Approach 2:
The patent converts the harmful effect of bias magnetic fields into a beneficial feedback signal. The bias field's influence on the magneto-resistive elements is detected by the bridge circuit and fed back through the operational amplifier, which then generates a compensating signal. This transforms the originally harmful bias field effect into an opportunity for active compensation and improved output accuracy.
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 solution effectively suppresses the effects of bias magnetic fields, maintaining high sensitivity and accuracy in detecting target magnetic fields by stabilizing the operating points of magneto-resistive elements, even in the presence of bias fields, and enhancing magnetic field detection resolution.
Implementation Method 1
four magneto-resistive elements constituting a bridge circuit
Implementation Method 2
a magnetic field generating conductor, by means of an applied current, generates a magnetic field
Data Source
AI summary
A magnetic sensor suppressing bias magnetic field effects includes a magnetic detecting unit including first to fourth magneto-resistive elements to which a first magnetic field to be detected is applied, a differential amplifier into which the output voltage of the magnetic detecting unit is input, a first magnetic field generating conductor which, by a first feedback current output by the differential amplifier, applies to the magnetic detecting unit a second magnetic field to cancel the first magnetic field detected by the magnetic detecting unit, a bias magnetic field detector which detects a bias magnetic field applied to the magnetic detecting unit and outputs a second feedback current corresponding to the bias magnetic field, and a second magnetic field generating conductor which, by the second negative feedback current, applies to the magnetic detecting unit a correcting magnetic field to cancel the bias magnetic field detected by the magnetic detecting unit.