An apparatus and a method for helium collection and reliquefaction in a magnetoencephalography measurement device
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Solution Overview
Problem
Magnetoencephalography (MEG) devices face challenges in helium re-liquefaction due to cryocooler-induced electromagnetic interference and mechanical vibrations, which complicate measurement analysis and reduce the reliability of magnetic field measurements.
Innovation Solution
A magnetoencephalography measurement device with a cryocooler apparatus suspended inside the Dewar vessel, a control unit that switches the cryocooler on or off based on scheduled activity periods, and a compressor for pumping helium gas between the Dewar vessel and storage tank, allowing for efficient re-liquefaction without interfering with measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cryocooler is used to re-liquefy helium directly into the Dewar vessel, then helium can be re-liquefied without long supply lines, but electromagnetic interference and mechanical vibrations are caused which disturb measurements
Solution Approach 1:
The cryocooler is extracted from the magnetically shielded room and placed outside, separating the re-liquefaction function from the measurement environment. This removes the source of electromagnetic interference and mechanical vibrations from the sensitive measurement zone while maintaining the ability to re-liquefy helium.
Solution Approach 2:
A transfer line system with shut-off valves acts as an intermediary between the external cryocooler and the Dewar vessel. The transfer line allows helium to be transported and re-liquefied outside the magnetically shielded room, then introduced into the vessel without introducing interference sources.
2Quantity of substance
If the cryocooler is operated continuously, then helium can be maintained at appropriate levels, but electromagnetic interference and vibrations continuously disturb measurements
Solution Approach 1:
The cryocooler operates periodically rather than continuously. It is activated only during scheduled inactivity periods when no measurements are being performed, allowing helium to be re-liquefied without causing continuous interference. The shut-off valves control the periodic operation by opening only during these inactivity windows.
Solution Approach 2:
The system proactively schedules cryocooler operation during known inactivity periods before measurements begin. This preliminary action ensures helium is re-liquefied in advance, maintaining appropriate levels without requiring the cryocooler to be present or active during measurement operations.
3Device complexity
If helium is allowed to boil off and vent to atmosphere, then the Dewar vessel remains simple in design, but helium is wasted which is a scarce and costly resource
Solution Approach 1:
Instead of discarding boiled-off helium to the atmosphere, the system recovers it using a compressor that collects the vapor and returns it to the storage tank. This recovery mechanism prevents helium loss while maintaining relative design simplicity by adding only a compressor and transfer line system.
4Quantity of substance
If long Liquid Helium supply lines are used to avoid re-liquefaction in the Dewar vessel, then helium can be supplied from external storage, but the supply lines become complicated and expensive
Solution Approach 1:
The re-liquefaction function is extracted from the internal Dewar vessel environment and performed externally. This eliminates the need for complex internal re-liquefaction equipment and long supply lines, as the cryocooler operates outside the magnetically shielded room and transfers helium only when needed.
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 solution reduces helium usage and improves MEG measurement quality by minimizing electromagnetic noise and mechanical disturbances, maintaining a stable helium level for continuous operation without the need for long helium supply lines.
Implementation Method 1
a cryocooler that liquefies helium directly into the Dewar vessel
Implementation Method 2
a compressor for pumping helium gas from the Dewar vessel to the storage tank
Implementation Method 3
Superconducting Quantum Interference Devices (SQUIDs), which are very sensitive magnetometers
Implementation Method 4
The SQUID magnetometers require a working temperature close to 4 Kelvins. To achieve this working temperature, in a Magnetoencephalography (MEG) measuring device the SQUID magnetometers are placed inside a specially designed vacuum insulated Dewar vessel containing Liquid Helium (LHe)
Implementation Method 5
vacuum insulated Dewar vessel
Data Source
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AI summary
The invention relates to a method and a magnetoencephalography (MEG) measurement device. In the method there is determined the ending of a scheduled inactivity period of the MEG device. At the ending of the inactivity period a cryocooler of the MEG device is switched off. Helium is allowed to boil in the Dewar vessel of the MEG device when the MEG device is active and used to perform patient measurements. The boiled helium is collected via a compressor to an external storage tank. When a new inactivity period for the MEG device commences, the cryocooler is started anew and helium is let from the external storage tank in- to the Dewar vessel, where it is re- liquefied by the cryocooler. The compressor may be switched off when the cryocooler is switched on.