Orthogonal Fluxgate Sensor Thermal Stress Reduction
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Solution Overview
Problem
Current orthogonal fluxgate sensors face issues with mechanical stresses, vibrations, and thermal inhomogeneities due to the method of placing the ferromagnetic core in the holder, leading to increased low-frequency noise, especially when using unipolar excitation or multiple windings, which are undesirable for measuring magnetic field gradients.
Innovation Solution
The ferromagnetic core is embedded in a filler material with good thermal conductivity and low hardness, covering at least 50% of its surface and length, and placed within a dimensionally stable holder to reduce thermal and mechanical stresses, ensuring a secure and vibration-resistant attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ferromagnetic core is tightly placed in the holder or fixed in points, then the core is securely attached, but mechanical stresses are exerted on the core due to thermal expansions and vibrations increase
Solution Approach 1:
A filler material is introduced as an intermediary substance between the ferromagnetic core and the holder. This filler material simultaneously provides mechanical support, absorbs thermal expansion stresses, and dampens vibrations, thereby securing the core while eliminating harmful mechanical stresses and vibrations that would occur with direct rigid mounting.
2Reliability
If the core is coated by epoxide or placed tightly in the holder, then the core is protected from oxidation, but thermal inhomogeneities increase due to poor thermal contact
Solution Approach 1:
The filler material serves as a thermal intermediary that improves heat transfer between the core and the holder. Unlike epoxide coatings that create thermal barriers, the filler material maintains intimate thermal contact while still providing mechanical compliance, thereby protecting the core from oxidation through the holder structure while ensuring homogeneous temperature distribution.
Solution Approach 2:
The thermal conductivity parameter of the interface between core and holder is optimized by selecting a filler material with appropriate thermal properties. This changes the thermal contact parameters to achieve both protection and thermal homogeneity, unlike rigid tight fitting that creates thermal contact resistance.
3Object-affected harmful factors
If unipolar excitation is used to achieve low magnetic noise, then magnetic noise is reduced to ∼1pT/√Hz@1Hz, but temperature gradients increase along the core due to Peltier's effect
Solution Approach 1:
The filler material acts as a thermal mediator that conducts heat away from regions of the core where Peltier heating occurs during unipolar excitation. By providing a low-thermal-resistance path through the filler material to the holder, temperature gradients along the core are reduced while allowing the unipolar excitation to continue operating at its low magnetic noise level.
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 configuration significantly reduces low-frequency noise by minimizing temperature gradients and mechanical effects, achieving improved thermal and mechanical contact, and enhancing the sensor's performance in measuring magnetic fields with reduced ultra-low frequency noise below 1 Hz.
Implementation Method 1
The ferromagnetic core is at least on 50 % of its surface and 50 % of its length embedded with filler material with good thermal conductivity
Implementation Method 2
embedded with filler material with good thermal conductivity and low hardness, resulting in a significant reduction of thermal inhomogeneities of the core and an increase in its thermal inertia. Unwanted mechanical stresses do not act on the core
Implementation Method 3
If the sensor operates with unipolar excitation flowing directly through the sensor's core, another significant disadvantage is the Peltier's effect causing a temperature gradient along the core through which the electric current with the DC component flows
Implementation Method 4
The principle of the fluxgate sensor activity is based on the alternating excitation of the ferromagnetic core by the so-called excitation field, for example, from the excitation coil, and on the detection of the flux changes caused by external, i.e. measured magnetic field induced in the sensing coil
Data Source
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AI summary
The invention relates to an orthogonal fluxgate sensor with a ferromagnetic core (11, 11.1, 11.2) placed inside a sensing coil (23, 23.1, 23.2). The ferromagnetic core (11, 11.1, 11.2) is at least partially embedded in a filler material (22) so that at least 50 % of the surface of the ferromagnetic core is in direct contact with the filler material (22) whose final coefficient of thermal conductivity at 25°C is greater than 0.1 Wm-1K-1 and whose final Shore A hardness at 25 °C is from 5 to 70. The layer of the filler material has to be sufficiently massive to ensure the temperature homogenization of the core and minimization of mechanical stresses acting on the core; both of these problems increase the noise of the sensor in the existing solutions. In addition, the space filled with the filler material (22) is, in a length section equal to at least 50 % of the longitudinal core dimension, bounded in directions perpendicular to the longitudinal core dimension by at least one hollow object, which guarantees the maintenance of vibration resistance and the dimensional stability of the low hardness filler material.