Magnetocardiography SQUID Sensor Cooling With Coil-in-Vacuum Isolation
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Solution Overview
Problem
Existing magnetocardiography systems face challenges in maintaining high sensitivity and reducing thermal noise and vibration due to the use of liquid refrigerants, which can lead to evaporation and physical damage to SQUID sensors, and require efficient cooling methods to enhance signal-to-noise ratio.
Innovation Solution
A magnetic field measuring apparatus with a coil-in-vacuum (CIV) design that includes a double-wall structure for the neck portion, a coaxial dual-tube refrigerant system, and a triaxial gradiometer configuration to minimize thermal noise and vibration, while facilitating easy replacement of SQUID sensor modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a SQUID sensor is directly immersed in liquid helium for cooling, then cooling efficiency is improved, but rapid contraction stress and physical damage to the sensor occur
Solution Approach 1:
A vacuum unit is introduced as an intermediary between the liquid helium refrigerant and the SQUID sensor. The pick-up coil and SQUID sensor are mounted on the outer surface of the vacuum unit, which is cooled by liquid helium filling the inner space. This intermediary structure allows efficient cooling while preventing direct contact between the sensor and liquid helium, thus avoiding rapid contraction stress and physical damage.
2Temperature
If air or other gases flow into the internal helium storage container, then heat transfer is improved, but adsorption and condensation damage the SQUID sensor surface
Solution Approach 1:
The internal space of the vacuum unit is filled with liquid helium, creating an inert refrigerant environment. This prevents air or other gases from contacting the SQUID sensor surface, eliminating adsorption and condensation damage while maintaining efficient heat transfer through the vacuum unit wall.
3Loss of energy
If the neck portion diameter is decreased to reduce heat flow, then evaporation rate is reduced, but structural stability deteriorates
Solution Approach 1:
The vacuum unit is constructed using composite materials, specifically glass fiber reinforced plastic, which provides high strength and structural stability even with a reduced neck portion diameter. This allows the neck to be made smaller to reduce heat flow and evaporation rate while maintaining the necessary mechanical strength through the use of high-strength composite materials.
4Measurement precision
If a pick-up coil is mounted inside the internal helium storage container, then distance to signal source is reduced, but vibration from boiling liquid helium increases
Solution Approach 1:
The vacuum unit serves as an intermediary structure that allows the pick-up coil to be mounted on its outer surface, close to the signal source for high measurement precision, while isolating the coil from the vibration caused by boiling liquid helium inside the vacuum unit. The vacuum unit wall acts as a vibration barrier, separating the coil from the harmful vibration environment.
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 apparatus enhances measurement sensitivity and reliability by reducing evaporation rates, minimizing thermal noise, and improving the signal-to-noise ratio, while allowing for efficient cooling and maintenance of SQUID sensors.
Implementation Method 1
a vacuum unit (120) comprising an internal container (160) storing a liquid refrigerant (30), and an external container (110) surrounding the internal container (160), wherein a space between the internal container (160) and the external container (110) is maintained in a vacuum state
Implementation Method 2
As heat enters the internal helium storage container, liquid helium is evaporated while boiling
Implementation Method 3
A superconducting quantum interference device (SQUID) is an ultra-sensitive sensor, capable of measuring ultra-low magnetic fields generated in biological activities of heart, brain, nerves and the like
Data Source
AI summary
A magnetic field measuring apparatus according to an example embodiment includes: an external container; an internal container storing a liquid refrigerant, disposed inside the external container, and including a neck portion having a first diameter and a body portion having a second diameter greater than the first diameter, wherein a space between the internal container and the external container is maintained in a vacuum state; a SQUID sensor module mounting plate disposed below the internal container; a plurality of SQUID sensor modules mounted below the SQUID sensor module mounting plate; and a 4K heat shielding portion formed of a conductive mesh disposed to surround the SQUID sensor module mounting plate and the plurality of SQUID sensor modules.