Magnetic Field Detection Device With Impedance Matching
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Solution Overview
Problem
Existing magnetic field detection devices face challenges in enhancing sensitivity for weak magnetic fields, particularly in applications like capsule endoscopes, where increasing the number of turns and detection surface area of the coil leads to increased thermal noise, compromising signal-to-noise ratio.
Innovation Solution
A magnetic field detection device is designed with a resonance circuit and a capacitor connected in parallel to the coil, along with a low noise amplifier, where the capacitor's reactance opposes the imaginary part of the resonance circuit's impedance, reducing the combined impedance and thermal noise, thereby enhancing sensitivity while maintaining a high signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of turns and detection surface area of the coil are increased to enhance sensitivity, then the sensitivity is improved, but the thermal noise increases
Solution Approach 1:
The patent changes the electrical parameters of the detection circuit by introducing a capacitor with specific reactance value. The capacitor's reactance is set to oppose the imaginary part of the resonance circuit's impedance, transforming the circuit's impedance characteristics and reducing thermal noise while maintaining sensitivity.
Solution Approach 2:
The capacitor acts as an intermediary element between the coil and the low noise amplifier. It mediates the impedance mismatch and thermal noise issues by providing a reactance that counteracts the inductive reactance of the coil, thereby reducing the overall thermal noise without compromising the detection sensitivity.
2Measurement precision
If self-excitation is used to increase sensitivity, then the detection sensitivity is improved, but the circuit configuration becomes complicated
Solution Approach 1:
The patent extracts and eliminates the self-excitation mechanism from the circuit configuration. By removing this complex feature, the circuit becomes simpler while still achieving high detection sensitivity through the alternative approach of using a capacitor with opposing reactance in conjunction with a low noise amplifier.
3Measurement precision
If the alternating magnetic field strength is increased to improve detection accuracy, then the position detection accuracy is improved, but the device may detect stronger interfering magnetic fields
Solution Approach 1:
The patent substitutes the mechanical approach of increasing magnetic field strength with an electrical approach. Instead of boosting the alternating magnetic field, the invention uses electrical circuit elements (capacitor and low noise amplifier) to enhance the detection sensitivity, thereby avoiding the detection of stronger interfering magnetic fields while still achieving high position detection 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
This configuration effectively reduces noise levels and maintains high sensitivity, allowing for accurate detection of weak magnetic fields even with increased coil turns and surface area, thereby improving the signal-to-noise ratio for precise position detection.
Implementation Method 1
a winding coil for converting a magnetic field signal of an alternating magnetic field into a voltage signal
Implementation Method 2
having a capacitor connected in parallel to the coil; an element connected in series to an output stage of the resonance circuit. The element has a reactance whose sign is opposite to that of an imaginary part of an impedance of the resonance circuit
Data Source
AI summary
A magnetic field detection device includes: a resonance circuit having a winding coil for converting a magnetic field signal of an alternating magnetic field into a voltage signal and having a capacitor connected in parallel to the coil; an element connected in series to an output stage of the resonance circuit; and a low noise amplifier connected to an output stage of the element. The element has a reactance whose sign is opposite to that of an imaginary part of an impedance of the resonance circuit at a detected frequency of the alternating magnetic field. An absolute value of a combined impedance of the resonance circuit and the element is smaller than an internal resistance of the coil.