EP2039980B1 - Cryostat with stabilised outer vessel - Google Patents

Abstract

The cryostat (110) has an interior container (112) and an outer container (114), and a cavity (126) is arranged between the interior container and the outer container. The cavity is subjected with a negative pressure, and outer container has a base unit (130). The base unit has a thickness variation area with a concentrically varying base thickness. The base thickness for center of the base unit assumes a smaller value than external area. Independent claims are included for the following: (1) a biomagnetic measuring system, which has a biomagnetic sensor for detection of a magnetic field; and (2) a method for manufacturing a cryostat for insertion in a biomagnetic measuring system.

Description

Field of the invention

The invention relates to a cryostat, which is particularly suitable for use in a biomagnetic measuring system, as well as a biomagnetic measuring system comprising such a cryostat. The invention further relates to a method for producing a cryostat, which is particularly suitable for biomagnetic measurements. Such cryostats and measuring systems can be used in particular in the field of cardiology or in other medical fields, such as neurology. Other applications, such as non-medical applications, such as applications in materials research, are conceivable.

State of the art

In recent years, magnetic measurement systems, which until then were largely reserved for basic research, have found their way into many areas of biological and medical sciences. In particular, neurology and cardiology benefit from such biomagnetic measurement systems.

The basis of biomagnetic measurement systems is the fact that most cell activities in the human or animal body are associated with electrical signals, in particular electrical currents. The measurement of these electrical signals themselves, which are caused by the cell activity, is known for example from the field of electrocardiography. However, in addition to the purely electrical signals, the electrical currents are also connected to a corresponding magnetic field whose measurement is made use of the various known biomagnetic measurement methods.

While the electrical signals or their measurement outside the body are linked by various factors, such as the different electrical conductivities of the tissue types between the source and the body surface, magnetic signals penetrate these tissue areas almost undisturbed. The measurement of these magnetic fields and their changes thus allows conclusions about the currents flowing within the tissue, for example electrical currents within the heart muscle. A measurement of these magnetic fields with high time and / or spatial resolution over a certain range thus allows imaging methods which can reproduce, for example, a current situation of different areas of a human heart. Other known applications are, for example, in the field of neurology.

The measurement of magnetic fields of biological samples or patients, or the measurement of temporal changes of these magnetic fields, however, represents a metrological challenge. For example, the magnetic field changes in the human body, which are to be measured in the magnetocardiography, about one million times weaker than the magnetic field of the earth. The detection of these changes thus requires extremely sensitive magnetic sensors. In most cases, superconducting Quantum Interference Devices (SQUIDs) are therefore used in the field of biomagnetic measurements. Such sensors typically need to be cooled to 4 ° K (-269 ° C) to achieve the superconducting state, typically using liquid helium. The SQUIDs are therefore usually arranged individually or in a SQUID array in a so-called. Dewar vessel and are cooled there accordingly. Alternatively, laser-pumped magneto-optic sensors are currently being developed that can have approximately comparable sensitivity. Also in this case, the sensors are usually arranged in an array arrangement in a container for temperature stabilization.

Such containers for temperature stabilization, in particular containers for the cooling of magnetic sensors and so-called Dewar vessels are hereinafter generally referred to as "cryostat". In particular, these may be helium cryostats or other types of cryostat. Between the cryostat and the cryostat vessel, which is also referred to as dewar, is not distinguished below, even if the actual cryostat next to the cryostat vessel may include more parts.

The production of the cryostat for receiving biomagnetic sensor systems constructively presents a great challenge. The sensors are usually in one predetermined arrangement in these cryostats introduced, for example in the form of a hexagonal arrangement of SQUIDs or other magnetic sensors. In this case, usually the cryostat comprises an inner vessel, with sensors received therein, as well as an outer vessel. The space between inner vessel and outer vessel is evacuated. However, it is of considerable importance that the distance between the sensors housed in the inner cryostat vessel and the skin surface of the patient is kept as small as possible, since, for example, the signal strength decreases with a high power of the distance between sensor and skin surface. Accordingly, the distance between the bottoms of the inner and outer vessels must be kept small and extremely constant.

Numerous cryostats are known from the prior art, which can be used for magnetic measurements. For example, describes WO 94/03754 a cryostat vessel with an inner Dewar and an outer Dewar. The inner dewar is double-jacketed and features floor panels with curved bottoms. Furthermore, a number of radiation shields are provided.

Also DE 298 09 387 U1 describes a cryostat for radiomagnetic probing methods in which SQUIDs are preferably used. The cryostat has a high electromagnetic high-frequency transparency. In this case, a double vessel is again proposed, wherein a sensor is received at the bottom of an inner vessel. This inner vessel is formed in two parts and shows a bottom part with a raised edge which partially encloses a side wall.

Out DE 195 44 593 A1 a vacuum-insulated cryocontainer is known which can be used for the storage of low-boiling liquefied gases, in particular for combustible cryofuel. This has an outer container and a stored in the outer container, the gases receiving inner container and means for securing the outer container against pressure increase in the space provided between the containers isolation space. On the inner container, a device for overpressure protection is arranged, which releases an opening between the inner container and the insulation space at a predetermined failure pressure.

The conventional cryostat used for magnetic measurements, however, in practice have a number of disadvantages and difficulties which can affect the reliability and reproducibility of the measurements. A problem There is, for example, that in particular in transition areas between bottom parts and the side walls of the cryostat vessels tensions can easily occur, which can lead to cracks, which in turn can have a strong negative impact on the quality of the cryostat.

Furthermore, deformations may occur, for example, when pumping the gap between the inner and outer vessel, which can lead to the formation of thermal bridges between the bottoms of the vessels. Thus, there is a conflict of objectives in the construction of the cryostat to the extent that on the one hand, a distance between the two plates should be designed as large as possible to such deformation-te To avoid thermal bridges, but on the other hand, this distance should be kept as small as possible in order to achieve a high signal quality for the sensor signals.

This conflict of objectives is aggravated in particular by the fact that in biomagnetic measuring systems, the dimensions of the cryostat usually exceed the dimensions of cryostats known from the laboratory field. This is due in particular to the fact that most modern biomagnetic measuring systems are imaging systems which not only record measured values at one point, but rather measure them simultaneously over a larger surface area or spatial area as far as possible. For example, in magnetocardiography, it is usually measured by means of a sensor array over an approximately circular region of, for example, 300 mm to 400 mm in diameter, which corresponds approximately to the dimensions of a human breast. However, these large dimensions cause even the smallest deflections of the vessels, for example deflections in the percentage range (that is to say curvature relative to lateral expansion), in particular in the center region of the cryostat vessels, can cause the described problems with the formation of thermal bridges.

Object of the invention

The object of the present invention is thus to provide a cryostat which avoids the above-described disadvantages of known cryostats. In particular, the cryostat on the one hand to ensure high signal quality and on the other hand allow reliable evacuation of a cavity between an inner vessel and an outer vessel.

Description of the invention

This object is achieved by a cryostat and a method for producing a cryostat having the features of the independent claims. Advantageous developments of the invention, which can be implemented individually or in combination, are shown in subclaims. The wording of all claims is hereby incorporated by reference into the content of the description.

It is proposed a cryostat for use in a biomagnetic measuring system, which has at least one inner vessel and at least one outer vessel, and at least one arranged between the inner vessel and the outer vessel cavity. Analogously, a plurality of such inner and / or outer vessels and / or a plurality of cavities may be provided. The cavity is supposed to be under vacuum be acted upon, so should be able to be sealed in order to be evacuated. For this purpose, inner and outer vessel may, for example, corresponding seals (for example, separate sealing rings and / or sealing adhesions at joints or similar types of seals), a pump connection for connection to a device for generating a vacuum (eg a vacuum pump) or the like.

The outer vessel and the inner vessel can be made of a variety of possible materials, which ensure the required mechanical stability of these vessels. It is particularly preferred if these vessels are wholly or partly made of a fiber composite material, ie a composite of a fiber material and a matrix material made of a plastic. Alternatively or additionally, however, a variety of other materials can be used, such as metals, plastics, ceramics or a combination of these materials.

The outer vessel has a bottom part. This bottom part can be constructed in one piece with the remaining components of the outer vessel, but can also be supplemented in a modular design by other components of the outer vessel, for example - as described below - a side wall and / or other parts, such as lid parts. As described above, this bottom part is particularly critical and should, if possible, have no appreciable deflection when the cavity is pumped out. Typical pressures after pumping off may be in the range from 10 ^-3 mbar to 10 ^-4 mbar at room temperature, for example.

For this purpose, the invention proposes to make the bottom part of the outer vessel analogous to a bridge construction. In such a bridge construction, a load is met by the bridge having a corresponding arcuate curvature. Similarly, it is proposed that the bottom part has a thickness variation region which preferably extends over a large area of the bottom part. For example, this thickness variation range can extend over a range between 50 and 100% of the lateral extent of the bottom part. In this thickness variation region, the bottom part has a concentrically varying bottom thickness, wherein the bottom thickness decreases towards the middle of the thickness variation region and assumes a lower value there than in an outside region of the thickness variation region. However, a "thickness" should always be understood to mean an averaged value over a small area, so that, for example, local unevennesses in the thickness (for example a starting point) can be disregarded.

The thickness variation range over the lateral extent of the bottom part or of the thickness variation range can be, for example, between 0.1% and 5%, preferably between 0.5% and 2% and particularly preferably in the range from 0.75% to 1%. The thickness variation can for example be continuous, for example in the form of a parabolic surface profile and / or thickness profile of the bottom thickness. Alternatively or additionally, however, a continuous or stepwise variation of the floor thickness can also take place.

The bottom part has for example a round or a polygonal cross-section. Accordingly, the term "concentrically varying" should be understood to mean that this term includes only a decrease in bottom thickness toward the center of the thickness variation range, but not necessarily a round shape of the thickness variation range and / or an axis symmetry of thickness variation, even if a round shape and an axial symmetry about an axis of the cryostat represent a preferred embodiment.

The concentrically varying bottom thickness offers the advantage that the overall structure of the bottom part is considerably stabilized, similar to the construction of a bridge arch. In this way, thermal bridges between the outer vessel and the inner vessel are avoided, and even after several Abpumpvorgängen the cryostat and the cryostat comprehensive biomagnetic measuring system can reproducibly and reliably put into operational readiness.

The distance between the bottom part of the outer vessel and an inner bottom part of the inner vessel may for example be between 3 mm and 30 mm, in particular between 10 mm and 25 mm and particularly preferably about 20 mm. The bottom part itself or the thickness variation region may have a diameter of, for example, at least 200 mm, preferably a diameter of about 400 mm. The bottom part may have an outwardly facing outside and an inwardly facing inside, wherein the outside at normal pressure in the cavity (ie, when not evacuated cavity) preferably has a substantially planar course. The inside, however, may have a curved surface at normal pressure in the cavity. This further development offers the advantage that in this way it can be achieved that, in the pumped-down state, by means of an appropriate choice of the curvature of the curved surface, a flat surface is created which assigns the inner vessel. In this way, an approximately constant distance in the pumped-out state can preferably be set anywhere in the cavity between the bottom part of the outer vessel and the inner bottom part.

The bottom part may in particular comprise a fiber material, for example a glass fiber material and / or a carbon fiber material and / or a mineral fiber material. Through this fiber reinforcement, the stability of the cryostat, in particular in the region of the bottom part, additionally increased. In addition to the fiber material, a curable matrix material can then be used, for example - as described above - a matrix material with an epoxy resin or a similar curable matrix material, which together with the fiber material can form a fiber composite material.

The outer vessel may further comprise a side wall connected in a circumferential connection region with the bottom part. As described above, this side wall may, for example, have a round or polygonal cross-section, but in principle any cross-sections can be realized. The bottom part may preferably have a raised edge, along which the bottom part is connected to the side wall of the outer vessel. In this case, it is particularly preferred if the raised edge has a step surface, wherein the side wall is seated on this step surface. The step surface may additionally comprise a collar which is arranged concentrically with the side wall, so that the side wall can be supported inwardly on this collar of the step surface. Examples of this construction will be further explained below.

In addition to the cryostat a biomagnetic measuring system, in particular a biomagnetic measuring system according to one or more of the initially described, known from the prior art embodiments, proposed. The biomagnetic measuring system comprises at least one cryostat according to one of the embodiments described above. Furthermore, the biomagnetic measuring system comprises at least one biomagnetic sensor, preferably an array of biomagnetic sensors, which are set up for the detection of a magnetic field. As described above, these biomagnetic sensors may include, for example, SQUIDs and / or magneto-optical sensors.

In addition to the cryostat and the biomagnetic measuring system, a method for producing a cryostat for use in a biomagnetic measuring system is furthermore proposed, in particular a cryostat according to one of the embodiments described above. The cryostat should comprise at least one inner vessel and at least one outer vessel and at least one cavity arranged between the inner vessel and the outer vessel, which can be subjected to a negative pressure. The outer vessel has a bottom part which has a thickness variation area comprising a concentrically varying floor thickness. The floor thickness assumes a lower value in the area of the middle of the thickness variation area than in an outdoor area. For further possible details of the configuration of the cryostat, reference may be made, for example, to the above description.

• mindestens ein aushärtbarer Werkstoff (beispielsweise das oben beschriebene Matrixmaterial des Faserverbundwerkstoffes) wird in eine Form eingebracht. Zusätzlich können weitere Werkstoffe in diese Form eingebracht werden, oder der aushärtbare Werkstoff kann weitere Werkstoffe umfassen, beispielsweise die oben beschriebenen Faserwerkstoffe. Die Form weist mindestens ein Formnest, d.h. eine entsprechend gestaltete Öffnung auf, wobei dieses Formnest vorzugsweise vollständig ein Negativ des herzustellenden Bodenteils bildet. Weiterhin umfasst die Form mindestens ein erstes Stempelteil, welches eine in das Formnest hinein gekrümmte Oberfläche aufweist.
• Nach dem Einbringen des aushärtbaren Werkstoffes in das Formnest der Form wird der aushärtbare Werkstoff ausgehärtet, beispielsweise durch einfaches Abwarten, durch thermisches Aushärten, durch chemisches Aushärten (zum Beispiel durch Zugabe eines Starters), durch photochemisches Aushärten oder durch andere Aushärtverfahren oder Kombinationen der genannten und/oder anderer Aushärtverfahren. Nach dem Aushärten kann das Bodenteil anschließend der Form entnommen werden. Auf diese Weise wird unter Verwendung des besagten ersten Stempels, welcher beispielsweise eine konvexe parabolisch gekrümmte Oberfläche aufweisen kann, die konzentrisch variierende Bodendicke des Dickenvariationsbereichs des Bodenteils erzeugt.

The method comprises the following steps for producing the bottom part:

• at least one curable material (for example the above-described matrix material of the fiber composite material) is introduced into a mold. In addition, other materials can be introduced into this mold, or the curable material may include other materials, such as the fiber materials described above. The mold has at least one mold cavity, ie a correspondingly shaped opening, wherein this mold cavity preferably forms completely a negative of the base part to be produced. Furthermore, the mold comprises at least one first stamp part, which has a surface curved into the mold cavity.
• After the hardenable material has been introduced into the mold cavity of the mold, the curable material is cured, for example, simply by waiting, by thermal curing, by chemical curing (for example, by adding a starter), by photochemical curing, or by other curing techniques or combinations of the above and others / or other curing process. After curing, the bottom part can then be removed from the mold. In this way, using the said first punch, which may for example have a convex parabolically curved surface, the concentrically varying bottom thickness of the thickness variation region of the bottom part is produced.

The method according to the invention can also be developed in various ways. Thus, for example, the mold may furthermore have at least one second stamp part, wherein the second stamp part has a curvature which is substantially opposite to the first stamp part. If, for example, the curved surface of the first stamping part projects convexly into the mold cavity, then the second stamping part can, for example, have a curved surface which is concavely curved in such a way that the curvature points out of the interior of the mold cavity. In this case, for example, the two curved surfaces of the stamp parts can then be curved in such a way that the formed intermediate of the bottom part assumes the shape of a curved shell after hardening. Subsequently, after hardening of the hardenable material, the bottom part can be removed from the mold cavity and be subjected to a subsequent cutting process and / or grinding process. By means of this cutting method and / or grinding method, the convex surface of the bottom part can then be leveled, for example, in the region of the thickness variation region, and thus a substantially flat underside of the bottom part or the thickness variation region can be produced.

embodiments

Further details and features of the invention will become apparent from the following description of preferred embodiments in conjunction with the subclaims. In this case, the respective features can be implemented on their own or in combination with one another. The invention is not limited to the embodiments. The embodiments are shown schematically in the figures. The same reference numerals in the individual figures designate the same or functionally identical or with respect to their functions corresponding elements.

In detail shows:

FIG. 1

an embodiment of a cryostat for use in a biomagnetic measuring system in a sectional view;

FIG. 2

a section of the representation according to FIG. 1 in the region of a transition between an inner bottom part and an inner side wall of an inner vessel;

FIG. 3

a section of the representation according to FIG. 1 in the region of a transition between a bottom part and a side wall of an outer vessel;

FIG. 4

the bottom part of the cryostat according to FIG. 1 in a detailed representation;

FIGS. 5A and 5B

a schematic example of a conventional bottom part in the uncurved and curved state;

Figures 6A and 6B

a schematic example of a bottom part according to the invention in the uncurved and curved state;

FIGS. 7A and 7B

two further possible embodiments of inventive floor parts;

FIG. 8

a first embodiment of a method according to the invention for producing a cryostat; and

FIG. 9

A second embodiment of a method for producing a cryostat according to the invention.

In FIG. 1 is a possible embodiment of a cryostat 110 according to the invention shown in a sectional view. The cryostat 110 has an inner vessel 112 and an outer vessel 114 enclosing the inner vessel 112. The outer vessel 114 is configured substantially cylindrical and has various flanges 116 and 118. While the lower of these flanges 116 substantially performs support functions, the upper flange 118 serves to receive a lid 120 of the outer vessel 114. Through this cover 120 projects a neck 122 of the inner vessel 112. Through this neck 122, biomagnetic sensors (shown in FIG FIG. 1 not shown) into the interior of a (also substantially cylindrical) main vessel 124 of the inner vessel 112 are introduced. In addition, leads to these sensors can be led through the neck 122 to the outside and connected to a corresponding electronics, so that measurement signals of these sensors can be queried.

Between the inner vessel 112 and the outer vessel 114, a cavity 126 is formed. This cavity 126 may, for example, by means of a in FIG. 1 Vacuum socket not shown are evacuated. By this evacuation and formation of a negative pressure in this cavity 126, an insulating effect of the cryostat 110 is increased. In this way, the interior of the main vessel 124 of the inner vessel 112 can be cooled, for example, by means of liquid helium, without requiring a replacement or replacement of this liquid helium at short intervals.

Both the inner vessel 112 and the outer vessel 114 have substantially continuous fiber composite materials as materials. Furthermore, both the inner vessel 112 and the outer vessel 114 are modular. Thus, for example, the outer vessel 114 next to the lid 120 has a side wall 128 and a bottom part 130. The inner vessel 112 has, in addition to the neck 122 in the region of the main vessel 124, a circular ring 132, which seals the neck 122 relative to the main vessel 124. Furthermore, the inner vessel 112 has an inner side wall 134 and an inner bottom part 136. In this embodiment, the side walls 128, 134 are provided with a cylindrical shape, which is not absolutely necessary. Thus, for example, polygonal cross sections or irregular cross sections can be used.

A particularly critical area in the production of the cryostat 110 is the in FIG. 1 The region of the transition between the base parts 130, 136 and the sidewalls 128, 134 of the outer vessel 114 or of the inner vessel 112, designated by the reference numeral 138, in this region. The forces acting on the evacuation of the cavity 126 affect the inner vessel 112 (in FIG FIG. 1 labeled with F ₁ ) and on the outer vessel 114 (in FIG. 1 denoted by F ₂ ) particularly critical and can lead to damage of the cryostat 110.

When evacuating the cavity 126 in FIG FIG. 1 acts on the side wall 134 of the inner vessel 112, the outwardly directed, to the cavity 126 through force _f1. This force results in a circumferential connection region 140, which in FIG. 2 shown in detail, between the inner bottom portion 136 and the inner side wall 134 of the inner vessel 112 to tension. In order to avoid cracking due to these distortions in this connecting region 140, the connecting region 140 has a circumferential reinforcing element 142, which in this exemplary embodiment is formed integrally with the inner bottom part 136. However, non-one-piece embodiments are also conceivable, for example with a separately formed reinforcing element 142. The inner bottom part 136 has a raised, annular edge 144, which is formed in its upper region as a step 146. This step 146 has a lower step surface 148 on which the lower edge of the inner side wall 134 of the inner vessel 112 rests. Furthermore, the step 146 includes a collar 150 which annularly surrounds the lower edge of the side wall 134.

The reinforcing element 142 differs from the remaining inner bottom part 136 essentially by its structural properties. Thus, preferably, the entire inner bottom part 136 is made of a fiber composite material, which preferably comprises an epoxy resin as a matrix material and, for example, glass fibers as a fiber material. In addition, other additives may be included. In the region of the reinforcing element 142, this fiber material, which in FIG. 2 is not shown, oriented in the circumferential direction and thus has in FIG. 2 into the drawing plane. In the rest of the bottom part 136, however, the fiber orientation of the fiber material is substantially radially extending, ie in FIG. 2 parallel to the drawing plane.

Furthermore, in the FIGS. 1 and 2 it can be seen that the inner bottom part 136 has a series of recesses 152. These recesses 152 are used to hold biomagnetic sensors, which are not shown in the figures. For example, can be used for this purpose SQUIDs, for example, at one through the neck 122 of the inner vessel 112 are mounted in the main vessel 124 introduced linkage. The biomagnetic sensors may, for example, be accommodated in a hexagonal arrangement in the base part 136 so that they can receive measurement signals over a surface area and thus for example map a chest area of a patient. The depressions 152 serve, for example, for the purpose of fixing the biomagnetic sensors and, moreover, shortening the distance between the sensor and the skin surface of the patient in that the effective bottom thickness of the inner bottom part 136 from the original D to the distance d in FIG FIG. 2 is reduced. Furthermore, in the inner bottom part 136 threaded holes 154 to which, for example, a linkage for holding the biomagnetic sensors can be fixed.

Similarly, the bottom portion 130 of the outer vessel 114 also has a raised edge 156. This one is in FIG. 3 shown in detail. In this case, since the force F ₂ acting on the side wall 128 of the outer vessel 114 is directed inward, ie opposite to the force F ₁ in FIG FIG. 2 , to reinforce the transition region between the side wall 128 and the bottom part 130, a step 158 is again provided in the raised edge 156 of the bottom part 130. Again, this step 158 has a step surface 160 on which the side wall 128 rests. Again, a collar 162 is provided, which, however, in contrast to the collar 150 in FIG. 2 , Due to the opposite force acting on the force F ₁ F _{2 is arranged} in this case on the inside of the side wall 128 and the transition region between the side wall 128 and the bottom part 130 reinforced.

Between the inner bottom part 136 of the inner vessel 112 and the bottom part 130 of the outer vessel 114, as shown FIG. 1 it can be seen, in a region in which both bottom parts 130, 136 run flat, a distance a, which is typically only between 10 and 25 mm. This preferred distance results in a high signal quality, as magnetic fields generally decrease with a high power of the distance between source and detector. By the in FIG. 1 illustrated construction with the recesses 152, in which the sensors are accommodated, and the small distance a between inner bottom portion 136 and bottom portion 130, the distance between, for example, a patient's breast and the biomagnetic sensors received in the recesses 152 is reduced to a minimum.

By this reduction of the distance a, however, the problems mentioned above with deformations of the bottom part 130 of the outer vessel 114 occur. The bottom part 130 is in FIG. 4 shown in detail without the inner vessel 112. The bottom part 130, like the entire cryostat 110, may be, for example, a round cross-section or a polygonal one Have cross-section. Out FIG. 4 For example, in the non-limiting embodiment shown, the bottom portion 130 is basically divided into three sections and has an annular bevelled area 164 and a circular, substantially planar, thick variation area 166, in addition to the aforementioned raised edge 156. The substantially flat thickness variation region 166 is preferably the region in which, as shown in FIG FIG. 1 it can be seen that the inner vessel 112 has the smallest distance to the outer vessel 114. This area thus represents the area in which the risk of contact between inner vessel 112 and outer vessel 114 and thus the formation of thermal bridges is particularly high when the force F ₁ , which occurs when the cavity 126 is pumped out.

To solve this problem, it is proposed to design this thickness variation region 166 with a concentrically varying ground thickness. In this case, the thickness of the bottom part 130 in the thickness variation region 166 decreases from a thickness B ₁ in the edge region, ie in the region of the transition of the thickness variation region 166 to the tapered region 164, to a value B ₂ in the middle of the thickness variation region 166. This decrease is typically about 1%. If the thickness variation region 166 thus has a diameter of approximately 400 mm, then the value B ₁ -B ₂ is approximately 3 to 4 mm. In this case, the thickness variation region 166 has an outwardly facing inner side 168 and an outwardly facing surface 170. While the inner surface 168 in a state in which the cavity 126 is not pumped, has a slightly curved course, the outer surface 170 is preferably designed flat. Alternatively, however, this outer surface 170 may be adapted, for example, to other geometries, such as a patient's head surface or breast surface, depending on the field of application of the cryostat 110.

In the FIGS. 5A to 6B the effect of the concentrically varying thickness of the bottom part 130 is illustrated schematically. The show FIGS. 5A and 5B a conventional bottom portion 130 of constant thickness, whereas the Figures 6A and 6B show a bottom part 130 according to the invention with concentrically varying thickness. The thickness variation and the curvature are shown greatly exaggerated in the figures.

In FIG. 5A a bottom part 130 is shown with a constant, that is not varying thickness, as in the prior art and is used in conventional cryostat. It shows FIG. 5A the unloaded case, so a case in which the cavity 126 has no pressure difference to the area outside of the cryostat 110, so a non-pumped case. FIG. 5B on the other hand shows the case that the cavity 126 of the cryostat 110 is evacuated. In this case acts inwards, ie towards the cavity 126, a force F ₂ on the bottom part 130. Since the bottom part 130 is firmly anchored in its edge region (the raised edge 156 and the tapered portion 164 are neglected in this and subsequent figures), the bottom part 130 curves in the middle up. The resulting deflection is in FIG. 5B denoted by Δ. This deflection Δ can be at normal suppression in the range of 10 ^-2 to 10 ^-3 mbar up to a few millimeters. As a result, thermal bridges to the overlying, not shown in the figures inner vessel 112 can form, which greatly reduce the insulating effect of the cryostat 110.

In the Figures 6A and 6B an example of a bottom portion 130 is shown, which is designed according to the invention. Again, the raised edge 156 and the tapered portion 164 are not shown, and the curves are greatly exaggerated to illustrate the principle. Thus, for example, a part of the thickness variation range 166 is shown. Again, FIG FIG. 6A the non-pumped-down case in which, for example, in the cavity 126 normal pressure prevails, whereas FIG. 6B represents the case of the pumped state. In this pumped-down state, a force F ₂ directed toward the cavity 126 acts on the bottom part 130.

How out FIG. 6B can be seen causes in this case, in which the bottom part 130 is configured according to the invention, the force F _2, a deformation of the bottom part 130. However, this deformation is on the one hand slightly smaller than in the above in FIG. 5B in the prior art case, due to the "bridge arch effect" described above. On the other hand, the concave curvature of the inwardly facing surface 168 of the bottom portion 130, that even in the deformed state, the bottom portion 130 can not bulge upwards, ie toward the inner vessel 112, or that such a bulge compared to the prior art strong is reduced. In this way, the risk of bridge formation in this particularly critical region of the cryostat 110 is greatly reduced.

In the FIGS. 7A and 7B Further possible embodiments of the bottom part 130 are shown (again only the thickness variation region 166 of the bottom part 130 being shown in each case), which show that also other embodiments of the curvature of the surfaces in the thickness variation region 166 than those in FIG FIG. 6A shown curvature are possible.

So is in FIG. 6A only the inwardly facing surface 168 curves, whereas the outwardly facing surface 170 is preferably in the uninflated state just designed. However, as discussed above, other configurations of the outer surface 170 are possible, such as anatomical shapes or curved shapes, for example, similar to the inner surface 168.

Furthermore, in FIG. 6A the curvature of the inner surface 168 is continuous and, for example, parabolic, with a concave, parabolic curvature. That this need not necessarily be the case is, for example, in FIG. 7 shown in a very schematic way. Here, it is shown that the curved surface 168 may also have, for example, a non-continuous thickness variation with steps 172. Since the bottom part 130 is preferably round or polyhedral, these steps can be, for example, ring steps 172. The effect of this stepped embodiment is basically the same as in Figs Figures 6A and 6B shown.

In FIG. 7B Another example of non-continuous thickness variation is shown. In this example, the inwardly facing surface 168 has a generally flat central portion 174 and an adjoining annular curvature portion 176.

Numerous other embodiments that do not depart from the spirit of the invention are possible and readily apparent to those skilled in the art in light of the above description. Thus, for example, local variations in thickness may occur, which deviate from the course with a generally inwardly decreasing thickness of the bottom part 130. For example, local imperfections which are negligible may be disregarded for thermal bridge formation when considering the thickness profile. Numerous other embodiments are also conceivable, for example embodiments in which additional depressions, bores, grooves or the like are introduced into one or both of the surfaces 168, 170, but the overall course of the curvature of these surfaces does not deviate from the above concept of the invention.

Based on FIGS. 8 and 9 In the following, two possible methods for producing a bottom part 130, for example a bottom part with the features of the above-described bottom parts 130, will be described.

In both cases, a manufacturing method is used in which the bottom part 130 is produced by means of a mold 178. This mold 178 has an upper punch 180 and a lower punch 182, which together form a mold cavity 184. This mold nest 184 is in the FIGS. 8 and 9 shown in a simplified way, so for example Again, the beveled portion 164 and / or a raised edge 156 of the bottom portion 130 are disregarded. A "stamp" is not necessarily a movable part of the mold 178 to understand, but it may, for example, to be rigid components of this form 178, wherein the stamp 180, 182 to mold cavity 184 indicative surfaces 186, 188 have. The two punches 180, 182 are along a parting line 190, which in the FIGS. 8 and 9 also shown only schematically, separable. A "dividing line" is not necessarily to be understood as meaning a line, but also, for example, a dividing surface or the like. Also, the punches 180, 182 may include other, for example, movable or exchangeable mold parts to impart further contours to the bottom portion 130.

In both methods, ie both in the FIG. 8 represented methods, as well as in the FIG. 9 1, a fiber material 192 is introduced into the mold cavity 184. This fibrous material 192 can be designed, for example, in the form of fiber mats, for example in the form of glass fiber, carbon fiber or mineral fiber mats or mixtures of different fiber materials. The fiber material 192 is in the FIGS. 8 and 9 only schematically indicated and is preferably introduced into the mold cavities 184 so that they are substantially filled. Subsequently, a non-cured matrix material 194 (in the FIGS. 8 and 9 indicated by a puncture) introduced into the mold cavities 184, which in the FIGS. 8 and 9 is also shown only slightly. Preferably, this matrix material 194 is poured into the mold cavities 184 such that the fiber material 192 is completely impregnated with the uncured matrix material 194. For example, this matrix material 194 may be an epoxy resin. However, other types of matrix materials 194 are also conceivable, for example other types of thermosetting plastics, thermoplastics or other hardenable matrix materials 194.

Subsequently, in both figures, the matrix material 194 is cured, which can be done for example by simple waiting, thermal initialization, addition of a starter, photochemical activation or other types of activation. In this way, in each case an at least partially cured bottom part 130 is formed in the mold cavities 184.

The two in the FIGS. 8 and 9 The methods shown differ essentially in how, in these methods, the concentrically varying bottom thickness of the bottom part 130 is generated. At the in FIG. 8 As already shown, the mold cavity 184 is already designed by appropriate design of the dies 180, 182 in such a way that the bottom part 130 removed from the mold cavity 184 already approximates, for example, the Shape of in FIG. 6A has bottom part 130 shown. This means that even after casting and curing the inwardly facing inside 168 of the bottom part 130 (see FIG. 6A ) has a curvature, whereas the outwardly facing outer side 170 shows, for example, a substantially planar course.

At the in FIG. 9 In contrast, the concentrically varying ground thickness is subsequently produced by a cutting process. Here, the two surfaces 186, 188 of the dies 180, 182 have a substantially constant curvature, so that the bottom part 130 removed from the mold cavity 184 after curing initially has a substantially constant bottom thickness, but is curved overall. Also, different curvatures of the surfaces 186, 188 are possible in principle. The concentrically varying ground thickness is subsequently produced by cutting this bottom part along a cutting line 196 (which, in turn, can also be a cut surface). This can be done for example by a simple sawing. Alternatively or additionally, instead of a cutting method, a grinding method can be used in which the bottom part 130 in FIG. 9 from below by means of a preferably flat grinding tool to the cutting line 196 is ground. Also in this way, for example, the in FIG. 6A produce illustrated bottom portion 130 with the concentrically varying floor thickness.

Finally, it should be noted that in the FIGS. 8 and 9 are only examples of a variety of possible manufacturing processes for producing a bottom part. These examples, especially those in FIG. 9 illustrated cutting or grinding process, but are characterized by a high process reliability, high reproducibility of the generated bottom parts 130 and by comparatively low production costs for the molds 178.

LIST OF REFERENCE NUMBERS

110

cryostat

112

inner vessel

114

outer vessel

116

flange

118

flange

120

cover

122

Neck of the inner vessel

124

main vessel

126

cavity

128

Sidewall outer vessel

130

Bottom part outer vessel

132

annulus

134

Inside wall

136

Inner base part

138

Critical area

140

connecting area

142

reinforcing element

144

Raised edge of the inner vessel

146

Level inner vessel

148

step surface

150

collar

152

wells

154

threaded holes

156

Raised edge of the bottom part

158

Stage outside vessel

160

step surface

162

collar

164

bevelled area

166

Region of varying thickness

168

inside

170

outside

172

annular steps

174

level central area

176

annular curvature area

178

shape

180

upper stamp

182

lower stamp

184

cavity

186

Surface of upper punch

188

Surface lower punch

190

parting line

192

Fiber material

194

matrix material

196

intersection

Claims (15)

1. Cryostat (110) for use in a biomagnetic measurement system, comprising at least one inner vessel (112) and at least one outer vessel (114), and at least one cavity (126) arranged between the inner vessel (112) and the outer vessel (114), in which negative pressure can be applied to the cavity (126), with the outer vessel (114) having a base part (130), characterized in that the base part (130) has a region of varying thickness (166) with a concentrically varying base thickness, with the base thickness assuming a smaller value towards the centre of the base part (130) than in an outer region.
2. Cryostat (110) according to the preceding claim, in which the base thickness is between 0.1% and 5%, preferably between 0.5% and 2%, and particularly preferably between 0.75% and 1%, over the lateral extent of the base part (130).
3. Cryostat (110) according to one of the two preceding claims, in which the variation in the base thickness is continuous or stepwise.
4. Cryostat (110) according to one of the preceding claims, in which the variation in the base thickness has at least approximately a parabolic profile.
5. Cryostat (110) according to one of the preceding claims, in which the region of varying thickness (166) extends over 50% to 100% of the lateral extent of the base part (130).
6. Cryostat (110) according to one of the preceding claims, in which the spacing between the base part (130) of the outer vessel (114) and an inner base part (136) of the inner vessel (112) is between 3 mm and 30 mm, preferably between 10 mm and 25 mm, and particularly preferably 20 mm.
7. Cryostat (110) according to one of the preceding claims, in which the base part (130) has a diameter of at least 200 mm and preferably has a diameter of 400 mm.
8. Cryostat (110) according to one of the preceding claims, in which the base part (130) has an outer side (170) facing outwards and an inner side (168) facing inwards, in which the outer side (170) has a substantially planar profile in the case of normal pressure in the cavity (126), with the inner side (168) having a curved surface in the case of normal pressure in the cavity (126).
9. Cryostat (110) according to one of the preceding claims, in which the base part (130) has a fibrous material (192), in particular a glass fibre material and/or a carbon fibre material and/or a mineral fibre material.
10. Cryostat (110) according to one of the preceding claims, in which the outer vessel (114) furthermore has a side wall (128) connected to the base part (130) in a circumferential connection region.
11. Cryostat (110) according to the preceding claim, in which the base part (130) has an elevated edge (156), in which the elevated edge (156) has a step surface (160), with the side wall (128) sitting on the step surface (160).
12. Biomagnetic measurement system, comprising at least one cryostat (110) according to one of the preceding claims, furthermore comprising at least one biomagnetic sensor for detecting a magnetic field.
13. Method for producing a cryostat (110) for use in a biomagnetic measurement system, particularly a cryostat (110) according to one of the preceding claims directed at a cryostat (110), in which the cryostat (110) comprises at least one inner vessel (112) and at least one outer vessel (114), and at least one cavity (126) arranged between the inner vessel (112) and the outer vessel (114), in which negative pressure can be applied to the cavity (126), with the outer vessel (114) having a base part (130), in which the base part (130) has a region of varying thickness (166) with a concentrically varying base thickness, with the base thickness assuming a smaller value towards the centre of the base part (130) than in an outer region, in which the method comprises the following steps for producing the base part (130):

    - at least one curable material (194) is introduced into a mould (178), in which the mould (178) has at least one mould cavity (184) and at least one first stamp part (180), with the first stamp part (180) having a surface (186) which curves into the mould cavity (184);

    - the curable material (192, 194) is cured.
14. Method according to the preceding claim, in which at least one fibrous material (192) is introduced into the mould cavity (184) during the introduction of the curable material (192, 194), with furthermore at least one curable matrix material (194) being introduced into the mould cavity (184).
15. Method according to one of the two preceding claims, in which the mould (178) furthermore has at least a second stamp part (188), in which the second stamp part (188) has a substantially opposite curvature compared to the first stamp part (186), with the base part (130) being removed from the mould cavity (184) once the curable material has cured and with a substantially planar underside (170) of the base part (130) being produced in a subsequent cutting method and/or grinding method.

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