SQUID Bootstrap Circuit Signal Amplification
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Solution Overview
Problem
Existing SQUID sensors face challenges in amplifying small output signals without introducing significant noise from preamplifiers, particularly due to bulky or complex designs and high thermal losses in current noise reduction methods.
Innovation Solution
A SQUID Bootstrap Circuit (SBC) is introduced, combining additional positive feedback and noise cancellation techniques, featuring a mutually coupled dc-SQUID and feedback coil in series, which alters the dynamic resistance and current-to-flux characteristics to enhance signal amplification while reducing preamplifier noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If preamplifier is used to amplify SQUID output signals, then signal amplification is improved, but noise contribution from preamplifier increases
Solution Approach 1:
The patent applies negative feedback by connecting a feedback coil inductively coupled to the SQUID loop. The feedback coil generates a compensating magnetic flux that counteracts the external magnetic flux, enabling flux-locked loop operation. This feedback mechanism stabilizes the operating point and improves signal amplification while maintaining low noise performance through proper feedback coil design and positioning.
Solution Approach 2:
The feedback coil acts as an intermediary element between the SQUID sensor and the readout electronics. It converts the magnetic flux changes detected by the SQUID into compensating flux signals, enabling indirect measurement that avoids direct coupling of noisy electronics to the sensitive SQUID junctions.
2Object-affected harmful factors
If transformer and flux modulation are used to suppress preamplifier noise, then noise suppression is improved, but device complexity increases
Solution Approach 1:
The patent implements a feedback-based flux-locked loop that eliminates the need for complex transformer coupling and flux modulation circuits. The direct feedback coil connection simplifies the circuit topology while achieving effective noise suppression through stable operating point control and improved signal transfer characteristics.
Solution Approach 2:
The invention extracts and eliminates unnecessary intermediate components (transformers, modulation flux circuits) from the traditional SQUID readout system. By using direct feedback coil coupling, the design removes complex elements while retaining essential noise suppression functionality.
3Power
If series SQUID arrays are used to amplify signals, then signal amplification is improved, but parasitic resonances and manufacturing variations increase
Solution Approach 1:
The feedback coil configuration provides signal amplification through constructive feedback without requiring multiple SQUID devices in series. This single-SQUID approach with optimized feedback coupling achieves high signal transfer coefficients while avoiding parasitic resonances and manufacturing variations that plague array-based solutions.
4Power
If feedback coil is inductively coupled to SQUID, then signal transfer is improved, but mutual inductance optimization becomes difficult
Solution Approach 1:
The feedback coil is designed to exploit the SQUID's own magnetic field and inductance characteristics. By positioning the feedback coil to couple with the SQUID loop and using the SQUID's intrinsic properties, the system achieves optimal mutual inductance through self-adjusting field interactions rather than requiring complex external optimization procedures.
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
The SBC design significantly improves the signal-to-noise ratio by increasing the current-to-flux transfer coefficient and reducing preamplifier noise, achieving better signal amplification with reduced thermal noise and complexity.
Implementation Method 1
a feedback coil which is inductively coupled to the SQUID via a mutual inductance
Implementation Method 2
A 'dc-SQUID', which is biased to a direct current power supply, consists of a superconducting loop that is interrupted by two (identical) Josephson junctions
Implementation Method 3
a superconducting loop that is interrupted by two (identical) Josephson junctions
Data Source
Figure 1a~3b
Figure 4a~5b
Figure 6a~7d
AI summary
The SQUID Bootstrap Circuit (SBC) consists of a mutually coupled dc-SQUID and a feedback coil. The SQUID and the coil are connected in series. The feedback coil, which can be made of a superconductor or of a normal metal, can be either integrated on the SQUID chip, or be placed separately next to the SQUID. Together, both SQUID and coil form a novel two-terminal device, which will be named SBC. The invention combines the advantages of both, APF and NC and avoids certain drawbacks thereof. With the help of this new design, the current or voltage -Phi characteristics of SQUID will be asymmetric and the equivalent dynamic resistance will be changed.