Closed-Loop Multi-Turn Magnetic Sensor Domain Wall Initialization
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Solution Overview
Problem
Multi-turn magnetic sensors, particularly open-loop sensors, are limited in the number of revolutions they can count due to domain wall annihilation at the sensor's end, preventing further rotation measurements without power supply.
Innovation Solution
A closed-loop multi-turn magnetic sensor design featuring a nanowire with a bridge-type crossing, initialized by a circuit with varying metal trace spacings to propagate domain walls without annihilation, using TMR sensors for state measurement and current application to maintain the desired domain wall state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an open-loop sensor is used, then the sensor structure is simpler, but the number of revolutions that can be counted is limited due to domain wall annihilation at the sensor end
Solution Approach 1:
The sensor is divided into multiple loops (at least two loops) connected in series, with domain walls being injected at specific locations to propagate through each loop. This segmentation allows the sensor to count multiple revolutions by having domain walls traverse multiple loop segments, thereby extending the measurement range while maintaining a relatively simple overall structure.
Solution Approach 2:
An initialization circuit is provided that pre-injects domain walls into the sensor loops before measurement begins. This preliminary action ensures that domain walls are already in place to detect rotations from the start, eliminating the need for complex reset mechanisms and enabling continuous revolution counting without domain wall annihilation.
2Use of energy by moving object
If domain walls are injected without power supply, then the sensor operates passively, but the domain walls may annihilate at the sensor end preventing further measurement
Solution Approach 1:
A bridge structure is introduced as an intermediary element connecting the loops. This bridge acts as a protective mediator that prevents domain wall annihilation at the junction points between loops, allowing domain walls to propagate continuously through multiple loops without losing stability, thus maintaining reliable operation without external power supply.
3Reliability
If a closed-loop structure is implemented, then domain wall annihilation is prevented, but the sensor requires additional initialization circuitry to maintain domain wall state
Solution Approach 1:
The initialization circuit is designed to automatically inject domain walls at specific locations within the closed-loop structure without requiring external intervention or complex control systems. The circuit self-regulates by detecting when domain walls are needed and injecting them accordingly, thereby maintaining domain wall propagation stability with minimal additional complexity.
4Measurement precision
If metal traces with varying spacings are used in the initialization circuit, then domain walls can be precisely injected, but the manufacturing precision requirements increase
Solution Approach 1:
The metal traces are designed with different spacings at different locations within the initialization circuit. Specifically, traces are spaced closer together at locations where domain wall injection is required, and spaced farther apart at other locations. This local variation in quality allows precise domain wall injection at critical points while reducing manufacturing difficulty at non-critical areas.
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
Enables continuous rotation tracking of an external magnetic field without power, improving sensor reliability and robustness to stray fields by maintaining domain walls across the sensor loop.
Implementation Method 1
Multi-turn magnetic sensors can be used to detect the number of revolutions of a multi-turn sensor by measuring an external magnetic field
Implementation Method 2
a plurality of tunnel-magnetoresistance (TMR) sensors configured to measure a state of the sensor
Implementation Method 3
an initialization circuit configured to inject the pair of domain walls into the nanowire, wherein the initialization circuit comprises a first set of metal traces
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Aspects of this disclosure relate to a resettable closed-loop multi-turn magnetic sensor. In one aspect, the sensor includes a nanowire forming a plurality of loops, a plurality of domain orientation sensors configured to detect locations of a pair of domain walls within the nanowire, and an initialization circuit configured to inject the pair of domain walls into the nanowire. The nanowire forms a closed-loop via a bridge crossing connecting two of the loops.