SQUID Sensor Flux Biasing for Mobile Magnetic Field Measurement
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Solution Overview
Problem
SQUID sensors face challenges in maintaining functionality while moving due to changes in the Earth's magnetic field, which affects their ability to accurately measure time-variable magnetic fields and gradients in mobile applications.
Innovation Solution
A magnetic sensor comprising a SQUID, a superconducting flux transformer with a pickup and input coil, a resistive element acting as a high pass filter, and a flux bias circuit, which provides a DC flux bias and impedes DC bias current below a threshold, allowing the sensor to function effectively in mobile applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a SQUID sensor is used to measure magnetic fields in mobile applications, then the sensor can detect minute magnetic fields with high sensitivity, but the sensor becomes affected by changes in the Earth's magnetic field due to movement
Solution Approach 1:
The magnetic field measurement function is segmented into two independent parts: a DC SQUID sensor for measuring time-variable magnetic fields and a separate flux biasing circuit for compensating Earth's magnetic field changes. This segmentation allows each component to specialize in one aspect, improving overall measurement reliability during mobile operations.
Solution Approach 2:
A flux biasing circuit is introduced as an intermediary component between the SQUID sensor and the Earth's magnetic field variations. This circuit generates a compensating magnetic flux that counteracts the effects of Earth's field changes, thereby maintaining measurement stability without affecting the sensor's sensitivity to target magnetic fields.
2Ease of operation
If DC bias current is allowed to flow through the input coil, then the SQUID can operate, but low-frequency drift and DC offset affect measurement accuracy
Solution Approach 1:
The harmful DC bias current component is extracted and separated from the useful AC signal. A high-pass filter is implemented to remove the DC offset and low-frequency drift components while preserving the higher frequency measurement signals, thereby improving measurement accuracy without completely disabling the SQUID's operational capability.
Solution Approach 2:
The electrical parameters of the input coil circuit are modified by introducing a high-pass filter configuration. This changes the frequency response characteristics of the circuit, allowing DC and low-frequency components to be blocked while permitting higher frequency measurement signals to pass through, thus resolving the contradiction between operational capability and measurement accuracy.
3Adaptability or versatility
If the sensor operates in mobile applications, then the sensor can be deployed in diverse locations, but the changing Earth's magnetic field interferes with accurate measurement
Solution Approach 1:
The flux biasing circuit performs preliminary counter-action by generating a compensating magnetic flux before the Earth's magnetic field changes can significantly affect the measurement. This proactive compensation mechanism continuously counteracts the harmful effects of Earth's field variations, enabling accurate measurements in mobile applications across diverse locations.
Solution Approach 2:
A feedback mechanism is implemented where the flux biasing circuit continuously monitors and compensates for Earth's magnetic field changes. The circuit adjusts the compensating flux in real-time based on the detected field variations, maintaining measurement accuracy despite the sensor's movement through different magnetic field environments.
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 accurate measurement of time-variable magnetic fields and gradients in mobile settings by mitigating the impact of Earth's magnetic field changes, with enhanced sensitivity and dynamic range, suitable for applications like magnetocardiography and geophysics.
Implementation Method 1
The superconducting flux transformer has a pickup coil comprising a base material, which has a phase transition to the superconducting state, for converting a time-variable magnetic flux, or flux gradient, into an electric current.
Implementation Method 2
The superconducting flux transformer also has an input coil that is fed by the pickup coil for converting the electric current into an auxiliary magnetic field.
Implementation Method 3
A Josephson junction is a region of material that provides a weak link between two fully superconducting regions. The direct current (DC) SQUID has two symmetrical Josephson junctions. They are able to sense extremely small magnetic fields.
Data Source
AI summary
A superconducting quantum interference device (SQUID) for mobile applications comprising: a superconducting flux transformer having a pickup coil and an input coil, wherein the input coil is inductively coupled to a Josephson junction; a resistive element connected in series between the pickup coil and the input coil so as to function as a high pass filter such that direct current (DC) bias current is prevented from flowing through the input coil; and a flux bias circuit electrically connected in parallel to the superconducting flux transformer between the pickup coil and the input coil so as to reduce motion-induced noise.