Chopped Bias Magnetic Field Solid-State Spin Sensor
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Solution Overview
Problem
Solid-state spin sensors face challenges in maintaining a constant bias magnetic field over time due to non-idealities in materials and environmental factors, leading to drift that degrades their performance, especially at lower frequencies, making it difficult to distinguish between changes in the bias magnetic field and the physical quantity being measured.
Innovation Solution
Implementing a time-varying or chopped bias magnetic field that reverses polarity at known intervals, allowing the sensor to cancel out slow drift and improve sensitivity for low-frequency measurements by alternating between two bias magnetic fields with opposite polarities, thereby reducing noise and spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a constant bias magnetic field is applied to the solid-state spin sensor, then the quantum energy levels can be distinguished and individually interrogated, but drift in the bias magnetic field degrades measurement performance especially at lower frequencies
Solution Approach 1:
The patent applies periodic reversal of the bias magnetic field polarity at a frequency higher than the measurement frequency but lower than the sensor bandwidth. This periodic action transforms the low-frequency 1/f noise into high-frequency noise that can be filtered out, while maintaining the ability to distinguish quantum energy levels through the alternating field. The sensor measures the difference between measurements taken during positive and negative bias field phases, effectively canceling out drift components.
2Measurement precision
If the bias magnetic field is reversed periodically, then slow drift and 1/f noise are canceled out improving low-frequency sensitivity, but the system complexity increases due to field switching requirements
Solution Approach 1:
The patent implements self-service by using the sensor's own measurement capability to detect and cancel drift. The alternating bias field method allows the sensor to perform differential measurements where the drift affects both positive and negative phases equally, and the difference measurement automatically rejects this common-mode drift without requiring external reference sensors or complex compensation systems.
3Measurement precision
If the bias magnetic field reversal frequency is increased, then drift cancellation is improved, but noise from the switching process may interfere with measurements
Solution Approach 1:
The patent carefully selects the bias field reversal frequency to be higher than the measurement frequency of interest but lower than the sensor's bandwidth. This creates a separation where the periodic switching noise falls into a frequency gap that can be filtered out, while the measurement signal remains in the passband. The periodic modulation transfers the measurement signal to a higher frequency where 1/f noise is reduced, and the switching frequency is chosen to minimize interference with the measurement band.
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 approach enhances the sensitivity of solid-state spin sensors to 1 nT/√Hz or less, enabling accurate low-frequency measurements by effectively nullifying slow drift in the bias magnetic field and reducing 1/f noise, thereby improving the device's performance for applications requiring stability at mHz frequencies.
Implementation Method 1
The time-varying bias magnetic field splits the resonances of the color center defects
Implementation Method 2
The color center defects emit fluorescent light in response to the optical excitation radiation and the microwave radiation
Implementation Method 3
the microwave radiation manipulates the quantum spin states of the color center defects in order to make a measurement of the physical quantity to be measured
Data Source
AI summary
Applying a bias magnetic field to a solid-state spin sensor enables vector magnetic field measurements with the solid-state spin sensor. Unfortunately, if the bias magnetic field drifts slowly, it creates noise that confounds low-frequency field measurements. Fortunately, the undesired slow drift of the magnitude of the bias magnetic field can be removed, nullified, or cancelled by reversing the direction (polarity) of the bias magnetic field at known intervals. This makes the resulting solid-state spin sensor system suitable for detecting low-frequency (mHz, for example) changes in magnetic field or other physical parameters.