A sensor to measure second sound waves in superfluid helium

Abstract

The present invention discloses a sensor for measuring the second sound wave in superfluid helium, comprising a top cover with a first through hole in the center and a base threaded with the top cover; a copper electrode with a polycarbonate porous membrane coated on the outside is embedded in the first through hole of the top cover; the non-gold-plated surface of the polycarbonate porous membrane is in close contact with the upper surface and side of the copper electrode, and the gold-plated surface on the upper side of the polycarbonate porous membrane is flush with the upper surface of the top cover; the lower end surface of the base is fixed to the external shell of the SMA radio frequency line male connector, and a vertical second through hole is provided in the center of the base; an opening is provided at the center position of the lower surface of the copper electrode, and the internal PIN needle of the SMA radio frequency line male connector passes through the second through hole and the polytetrafluoroethylene gasket and contacts the low-temperature conductive glue filled in the copper electrode opening. Compared with the existing sensor for measuring the second sound wave, the sensor of the present invention can be detached and reused, has no requirements on whether the material of the mounting surface is conductive, has a wide range of usage scenarios, and improves measurement precision and accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, in particular to a sensor for measuring a second sound wave in superfluid helium. Background Art

[0002] Superfluid helium has an extremely high thermal conductivity, approximately 800 times that of room-temperature copper, and an extremely low viscosity. Thanks to its excellent flow and heat transfer properties, superfluid helium cooling is widely used to cool large scientific devices such as accelerators and superconducting magnets. For example, Chinese patent publication No. CN107965940A discloses a superfluid helium cryogenic system, and Chinese patent publication No. CN114812095A discloses a superfluid helium refrigerator.

[0003] Superfluid helium is believed to consist of two components: a normal fluid and a superfluid, a phenomenon known as the two-fluid theory. In superfluid helium, the normal fluid has properties similar to those of a classical fluid; the superfluid has no viscosity and zero entropy; and the two components each have independent velocity fields.

[0004] Due to the unique properties of superfluid helium, a second type of sound wave exists in it. Unlike ordinary sound waves, this second type of sound wave is not a pressure wave, but a temperature wave, or what we call an entropy wave. This means that temperature propagates in superfluid helium as a wave.

[0005] The second acoustic wave in superfluid helium can be measured using a superleakage-type second acoustic wave sensor, which has been widely used in scientific research, superconducting defect detection and other fields.

[0006] Currently, conventional sensors for measuring the second acoustic wave in superfluids are typically integrated with the flow channel, pressing a coated membrane used to detect the signal against the inner or outer wall of the flow channel. This not only results in an uneven flow channel, affecting the accuracy of the measurement signal, but also imposes certain material requirements on the flow channel during use to ensure electrical continuity and proper grounding of the sensor, requiring the channel to be conductive. Furthermore, integrated sensors are inconvenient to reuse, increasing their cost. Summary of the Invention

[0007] In response to the above-mentioned problems existing in the prior art, the present invention provides a sensor for measuring the second acoustic wave in superfluid helium, which is easy to disassemble and install, has wide applicability, and improves measurement precision and accuracy.

[0008] A sensor for measuring the second acoustic wave in superfluid helium comprises a top cover with a first through hole at the center and a base threadedly engaged with the top cover;

[0009] A copper electrode coated with a polycarbonate porous membrane is embedded in the first through hole of the top cover; the polycarbonate porous membrane is a single-sided gold-plated structure, the non-gold-plated surface of the polycarbonate porous membrane is in close contact with the upper surface and side surface of the coated copper electrode, and the gold-plated surface on the upper side of the polycarbonate porous membrane is flush with the upper surface of the top cover;

[0010] The upper end surface of the base is provided with a groove for placing a polytetrafluoroethylene gasket, and the upper surface of the polytetrafluoroethylene gasket is against the copper electrode and the top cover; the lower end surface of the base is fixed to the outer shell of the SMA radio frequency line male connector, and a vertical second through hole is provided in the center of the base;

[0011] An opening is provided at the center of the lower surface of the copper electrode, and the internal PIN needle of the SMA radio frequency wire male connector passes through the second through hole and the polytetrafluoroethylene gasket and contacts the low-temperature conductive glue filled in the copper electrode opening; the SMA radio frequency wire male connector is connected to the analysis instrument through a test circuit.

[0012] In the present invention, the sensor measures the second sound wave in superfluid helium by converting the vibration signal of the superfluid passing through a polycarbonate porous membrane into an electrical signal. Compared with existing sensors for measuring the second sound wave, this sensor can be disassembled and reused, has no requirements on whether the material of the mounting surface is conductive, and has a wide range of usage scenarios.

[0013] Furthermore, a first mounting hole is provided on the outer edge of the base for fixing the base on the superfluid helium flow channel to be measured.

[0014] Furthermore, the pore size of the polycarbonate porous membrane is 0.1 to 0.5 μm, and the thickness of the gold layer on the gold-plated surface is 20 to 100 nm.

[0015] Furthermore, low-temperature glue is filled between the SMA radio frequency line male connector and the inner wall of the second through hole.

[0016] Furthermore, the opening on the lower surface of the copper electrode has a diameter of 0.8 to 3 mm and a depth of 0.3 to 3 mm.

[0017] Furthermore, the top cover and the base are both made of conductive metal.

[0018] Furthermore, a first indium wire sealing ring is provided between the lower end surface of the base and the male connector of the SMA radio frequency cable, and a second indium wire sealing ring is provided between the lower end surface of the top cover and the base. The first indium wire sealing ring and the second indium wire sealing ring play a sealing role to prevent leakage.

[0019] Furthermore, the copper electrode, low-temperature conductive glue, and the internal PIN needle of the SMA radio frequency cable male connector serve as the positive electrode of the sensor;

[0020] The gold-plated surface of the polycarbonate porous membrane, the top cover, the second indium wire sealing ring, the base, the first indium wire sealing ring and the outer shell of the SMA radio frequency cable male connector serve as the negative electrode of the sensor;

[0021] The positive and negative electrodes of the sensor are separated by the non-gold-plated surface of the polycarbonate porous membrane and a polytetrafluoroethylene gasket to avoid short circuit.

[0022] During formal use, the sensor is first mounted through the first mounting hole on the superfluid helium flow path to be measured, and the male SMA RF cable connector is connected to the test circuit. While the normal fluid components in the superfluid helium are blocked by the polycarbonate porous membrane, the superfluid components pass through the pores of the polycarbonate porous membrane and cause the membrane to vibrate, generating a signal from the sensor. This signal is then transmitted to the corresponding analytical instrument via the male SMA RF cable connector, completing the measurement of the second sound wave in the superfluid helium.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The sensor provided by the present invention for measuring the second acoustic wave in superfluid helium meets the electrical continuity requirements and has no requirements on the material of the flow channel to be measured, and is therefore versatile.

[0025] 2. All components of the sensor provided by the present invention are integrated into a module and can be disassembled from the flow channel for reuse.

[0026] 3. The single-sided gold-plated polycarbonate porous membrane of the sensor provided by the present invention can be manually adjusted to be flush with the surface of the top cover, ensuring the smooth continuity of the surface and improving the measurement precision and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of a sensor for measuring the second acoustic wave in superfluid helium according to the present invention;

[0028] Figure 2 for Figure 1 sectional view of .

[0029] In the figure: 1- low-temperature conductive adhesive; 2- polycarbonate porous membrane; 3- top cover; 4- base; 5- SMA RF cable male connector; 6- first indium wire sealing ring; 7- low-temperature adhesive; 8- second indium wire sealing ring; 9- polytetrafluoroethylene gasket; 10- copper electrode; 11- first mounting hole; 12- second mounting hole. DETAILED DESCRIPTION

[0030] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0031] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words “include” or “comprise” and the like used in the present invention mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as “connect” or “connected” and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Up”, “down”, “left”, “right” and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0032] Example

[0033] like Figure 1 and Figure 2 As shown, a sensor for measuring the second sound wave in superfluid helium includes a copper electrode 10, a polycarbonate porous membrane 2, a top cover 3, a base 4, an SMA radio frequency cable male connector 5, a low-temperature conductive glue 1, a low-temperature glue 7, a polytetrafluoroethylene gasket 9, a first indium wire sealing ring 6 and a second indium wire sealing ring 8.

[0034] A 1.2mm diameter, 1mm deep opening is located at the center of the lower surface of the copper electrode 10, serving as the sensor's positive electrode. The polycarbonate porous membrane 2 is gold-plated on one side, with the non-gold-plated surface of the polycarbonate porous membrane 2 closely covering the upper and side surfaces of the copper electrode 10. The gold-plated surface of the polycarbonate porous membrane 2 is flush with the upper surface of the top cover 3.

[0035] The polycarbonate porous membrane 2, with a pore size of 0.2 μm and a 50 nm thick gold layer on one side, serves as the sensor's negative electrode. The non-gold-plated surface of the polycarbonate porous membrane 2 is placed against the non-perforated surface of the copper electrode 10, forming the sensor's electrode assembly. The top cover 3 is sanded to the desired size, and the entire sensor electrode assembly is inserted through the upper through-hole of the top cover 3 until the gold-plated surface of the polycarbonate porous membrane 2 is flush with the top surface of the top cover 3.

[0036] The top cover 3 is made of aluminum, with a deep inner thread on its lower end. The upper outer surface of the base 4 is also threaded to a certain depth, screwing the top cover 3 and base 4 together to secure them. The base 4 is also made of aluminum, with a second mounting hole 12 of a specific size at the bottom and a second through-hole with a diameter of 5mm in the center for mounting the SMA male connector 5 for the RF cable.

[0037] The internal PIN needle of the SMA radio frequency line male connector 5 passes through the second through hole and the polytetrafluoroethylene gasket 9 and contacts the low-temperature conductive glue 1 filled in the opening of the copper electrode 10. The SMA radio frequency line male connector 5 is connected to the analysis instrument through the test circuit.

[0038] As a preferred embodiment of the present invention, a second indium wire sealing ring 8 is provided between the top cover 3 and the base 4 to perform a sealing function and prevent leakage.

[0039] As a preferred embodiment of the present invention, a polytetrafluoroethylene gasket 9 is provided between the copper electrode 10 and the base 4 for sealing and insulation. The size of the polytetrafluoroethylene gasket 9 can be 22mm*5mm and the thickness can be 3mm.

[0040] As a preferred embodiment of the present invention, a first indium wire sealing ring 6 is provided between the SMA radio frequency cable male connector 5 and the base 4 to perform a sealing function and prevent leakage.

[0041] As a preferred embodiment of the present invention, the cavity in the middle of the base 4 and the SMA radio frequency line male connector 5 are filled with low-temperature glue 7 to play a fixing and sealing role.

[0042] As a preferred embodiment of the present invention, a low-temperature conductive glue 1 is filled between the opening at the bottom end of the copper electrode 10 and the PIN of the SMA radio frequency line male connector 5 to play a role of fixing and conducting electricity.

[0043] As a preferred embodiment of the present invention, a first mounting hole 11 is reserved on the outer ring of the base 4 for fixing it on the superfluid helium flow channel to be measured.

[0044] Since the copper electrode 10 is conductive and the low-temperature conductive adhesive 1 is conductive and contacts the internal PIN of the SMA radio frequency cable male connector 5 , the electrical continuity of the positive electrode of the sensor is ensured.

[0045] Since aluminum is conductive, the gold-plated surface of the polycarbonate porous membrane 2 is also conductive and is in contact with the top cover 3, thereby ensuring the electrical continuity of the negative electrode of the sensor.

[0046] Since the first indium wire sealing ring 6 and the second indium wire sealing ring 8 are conductive, and the base 4 is made of metal and connected to the outer shell of the SMA radio frequency cable male connector 5, the electrical continuity of the sensor negative electrode is guaranteed.

[0047] Since the non-gold-plated surface of the polycarbonate porous membrane 2 and the polytetrafluoroethylene gasket 9 are not conductive, the positive and negative electrodes of the sensor are separated to avoid short circuit.

[0048] During formal use, the sensor is first mounted through first mounting hole 11 on the superfluid helium flow path to be measured, and the male SMA RF cable connector 5 is connected to the test circuit. While the normal fluid components in the superfluid helium are blocked by the polycarbonate porous membrane 2, the superfluid components pass through the pores of the polycarbonate porous membrane 2 and cause the membrane to vibrate, generating a signal from the sensor. This signal is then transmitted to the corresponding analytical instrument via the male SMA RF cable connector 5, completing the measurement of the second sound wave in the superfluid helium.

[0049] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sensor for measuring the second acoustic wave in superfluid helium, characterized in that It comprises a top cover (3) with a first through hole at the center and a base (4) threadedly engaged with the top cover (3); a first mounting hole (11) is provided on the outer edge of the base (4) for fixing the base (4) on a superfluid helium flow channel to be measured; A copper electrode (10) coated with a polycarbonate porous membrane (2) is embedded in the first through hole of the top cover (3); the polycarbonate porous membrane (2) is a single-sided gold-plated structure, the non-gold-plated surface of the polycarbonate porous membrane (2) is in close contact with the upper surface and side surface of the coated copper electrode (10), and the gold-plated surface on the upper side of the polycarbonate porous membrane (2) is flush with the upper surface of the top cover (3); The upper end surface of the base (4) is provided with a groove for placing a polytetrafluoroethylene gasket (9), and the upper surface of the polytetrafluoroethylene gasket (9) is against the copper electrode and the top cover; the lower end surface of the base (4) is fixed to the outer shell of the SMA radio frequency line male connector (5), and a vertical second through hole is provided in the center of the base (4); An opening is provided at the center of the lower surface of the copper electrode (10); the internal PIN pin of the SMA radio frequency line male connector (5) passes through the second through hole and the polytetrafluoroethylene gasket (9) and contacts the low-temperature conductive glue (1) filled in the opening of the copper electrode (10); the SMA radio frequency line male connector (5) is connected to the analysis instrument through the test circuit.

2. The sensor for measuring the second acoustic wave in superfluid helium according to claim 1, characterized in that: The pore size of the polycarbonate porous membrane (2) is 0.1-0.5 μm, and the thickness of the gold layer on the gold-plated surface is 20-100 nm.

3. The sensor for measuring the second acoustic wave in superfluid helium according to claim 1, characterized in that: Low-temperature glue (7) is filled between the SMA radio frequency line male connector (5) and the inner wall of the second through hole.

4. The sensor for measuring the second acoustic wave in superfluid helium according to claim 1, characterized in that The opening on the lower surface of the copper electrode (10) has a diameter of 0.8-3 mm and a depth of 0.3-3 mm.

5. The sensor for measuring the second acoustic wave in superfluid helium according to claim 1, characterized in that: The top cover (3) and the base (4) are both made of conductive metal.

6. The sensor for measuring the second acoustic wave in superfluid helium according to claim 5, characterized in that: A first indium wire sealing ring (6) is provided between the lower end surface of the base (4) and the SMA radio frequency line male connector (5), and a second indium wire sealing ring (8) is provided between the lower end surface of the top cover (3) and the base (4).

7. The sensor for measuring the second acoustic wave in superfluid helium according to claim 6, characterized in that: The copper electrode (10), the low-temperature conductive glue (1) and the internal PIN pin of the SMA radio frequency line male connector (5) serve as the positive electrode of the sensor; The gold-plated surface of the polycarbonate porous membrane (2), the top cover (3), the second indium wire sealing ring (8), the base (4), the first indium wire sealing ring (6) and the outer shell of the SMA radio frequency line male connector (5) serve as the negative electrode of the sensor; The positive and negative electrodes of the sensor are separated by the non-gold-plated surface of the polycarbonate porous membrane (2) and a polytetrafluoroethylene gasket to avoid short circuit.

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