An oil-filled isolated piezoresistive pressure sensor suitable for high pressure environments

Abstract

The application relates to an oil-filled isolated piezoresistive pressure sensor suitable for a high-pressure environment, which comprises the following steps: one end of an alloy shell is sealedly connected with a metal corrugated diaphragm, the other end of the alloy shell is sealedly connected with a base, so that an enclosed mounting cavity is formed in the alloy shell; a pressing ring is fixedly connected with the alloy shell and the metal corrugated diaphragm outside the enclosed mounting cavity, so that the metal corrugated diaphragm is structurally reinforced and fixedly limited; a metal elastic body is mounted in the enclosed mounting cavity and comprises a relatively large-sized connecting part and a relatively small-sized sensing part; the connecting part is connected with the inner wall of the alloy shell; a closed cavity is formed in the metal elastic body and filled with silicon oil as a pressure transmission medium; the outer side of the sensing part and the inner wall of the alloy shell form a cavity, a metal strain gauge is deposited on the side wall of the sensing part and used as a strain detection circuit; and the metal strain gauge is electrically connected with a pressure-sensitive electronic device in the base through electric flying wires.

Description

Technical Field

[0001] This invention relates to the field of pressure sensor technology, and in particular to an oil-filled isolated piezoresistive pressure sensor suitable for high-pressure environments. Background Technology

[0002] Isolated pressure sensors are widely used in complex and harsh measurement environments such as aerospace, oil drilling, marine engineering and nuclear power plants. Their typical structure is to fill the space between an external metal diaphragm and an internal pressure-sensitive chip with silicone oil. The pressure is transmitted to the internal pressure-sensitive chip by the deformation of the diaphragm, so that the measured medium does not directly contact the sensitive element.

[0003] However, existing conventionally designed sensors have limited pressure resistance and often exhibit nonlinearity or even failure under ultra-high pressure (hundreds of MPa). Traditional thin-film pressure sensors produce severe nonlinearity under high pressure, requiring complex calibration to achieve linearized output. While existing miniaturized oil-filled sensors are small in size, their pressure resistance is only on the order of tens of MPa. Summary of the Invention

[0004] The technical problem this invention aims to solve is to achieve safe pressure measurement and protect the sensitive element from overload under high-pressure environments, while ensuring the sensitivity and linearity of the sensor output, as well as the reliability and ease of manufacture of the structure. Existing oil-filled pressure sensors still have significant shortcomings in practical applications. When external pressure experiences a sudden impact or exceeds the sensor's rated range, the deformation of the diaphragm is directly transmitted to the internal sensitive structure through the silicone oil medium. Since traditional structures are primarily used for medium isolation, they typically lack effective pressure buffering or pressure reduction mechanisms, resulting in high-pressure loads acting on the sensitive element with almost no attenuation. This makes the internal pressure-sensitive structure susceptible to excessive mechanical stress, leading to structural overload, plastic deformation, or even failure. Therefore, in high-pressure environments of hundreds of MPa or sudden overpressure, the pressure-bearing capacity and reliability of existing diaphragm-filled pressure sensors still cannot meet practical application requirements. Therefore, a new oil-filled isolated piezoresistive pressure sensor is needed, which can effectively reduce the pressure borne by the sensing element while maintaining signal output performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, this application provides an oil-filled isolated piezoresistive pressure sensor suitable for high-pressure environments, comprising: an alloy housing, a metal corrugated diaphragm, a pressure ring, a metal elastomer, a metal strain gauge, and a base; One end of the alloy shell is sealed to a metal corrugated diaphragm, and the other end is sealed to a base, forming a closed mounting cavity inside the alloy shell. The pressure ring is fixedly connected to the alloy shell and the metal corrugated diaphragm on the outside of the closed installation cavity, which strengthens the structure and limits the fixation of the metal corrugated diaphragm. The metal elastomer is installed in a closed mounting cavity, including a relatively large connecting part and a relatively small sensing part; wherein, the connecting part is connected to the inner wall of the alloy shell; a sealed cavity is formed inside the metal elastomer and filled with silicone oil as a pressure transmission medium; The outer side of the sensing part forms a cavity with the inner wall of the alloy shell. Metal strain gauges are deposited on the side wall of the sensing part as strain detection circuits. The metal strain gauge is electrically connected to the piezoresistive electronic device in the base via a flying wire.

[0006] In one implementation, an opening structure for mounting a corrugated metal diaphragm and an annular support step are provided; the outer peripheral edge of the corrugated metal diaphragm is disposed on the annular support step and is fixedly connected to the alloy shell by welding. The pressure ring is fixedly connected to the metal corrugated diaphragm and alloy shell by welding. The connecting part of the metal elastomer has its outer wall threaded into the internal thread of the alloy shell.

[0007] In one implementation, the sensing part of the metal elastomer is not in contact with the base.

[0008] In one implementation, the corrugated metal diaphragm is a circular thin-walled metal diaphragm structure with concentric annular corrugations on its surface.

[0009] In one implementation, the sensing part of the metallic elastomer has its outer wall formed into a non-complete cylindrical structure by locally cutting material, so that its outer contour forms a variable cross-section irregular cylindrical structure with a planar region and bilateral symmetrical thinning. Metal strain gauges are deposited on the planar area.

[0010] In one implementation, metal strain gauges are deposited using magnetron sputtering micro-nano fabrication technology and connected in the form of a Wheatstone bridge to form a strain detection circuit.

[0011] In one implementation, a U-shaped lead groove is provided on the outer wall of the metal elastomer for embedding electrical wires; and rubber is filled and cured inside the U-shaped lead groove.

[0012] In one implementation, the electric flywire is connected to the varistor via conductive pins on the inner surface of the base.

[0013] In one implementation, the base uses electrical vias on its outer surface to extract internal electrical signals from the varistor.

[0014] In a second aspect, a manufacturing method is provided, applicable to the oil-filled isolated piezoresistive pressure sensor of the first aspect, comprising: The first step is to process the alloy shell; The second step is to process the metal elastomer; The third step is surface pretreatment of the metal elastomer; Step 4: Deposition of the insulating layer; Step 5: Deposition of strain-sensitive metal thin films; Step 6: Strain gauge pattern formation; Step 7: Install the metal elastomer; Step 8: Electrical signal connection and potting reinforcement; Step 9: Silicone oil filling; Step 10: Install the metal corrugated diaphragm; Step 11: Base installation and overall encapsulation.

[0015] The present invention has the following advantages due to the adoption of the above technical solutions: The structure of this invention effectively isolates the measured high-pressure medium from the sensitive structure through a metal corrugated diaphragm and a silicone oil pressure transmission structure, thereby improving the reliability of the sensor in high-pressure and corrosive environments. It utilizes the pressure buffering mechanism formed by the compressibility of silicone oil and the stiffness of the corrugated diaphragm structure to achieve effective pressure reduction protection against high pressures of hundreds of megapascals. By designing the metal elastomer as a variable cross-section irregular column structure with symmetrical thinning on both sides, the strain is concentrated in the sensitive area, thereby significantly improving the sensor sensitivity. Attached Figure Description

[0016] Figure 1 This is an exploded assembly diagram of an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of the assembly according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a metal elastomer according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a metal elastic variable cross-section structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the flying wire layout of the metal elastomer according to an embodiment of the present invention; Figure 6 This is a flowchart of the metal elastomer processing technology according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0018] In this embodiment of the application, an oil-filled isolated piezoresistive pressure sensor suitable for high-pressure environments is provided, comprising: an alloy shell, a metal corrugated diaphragm, a pressure ring, a metal elastomer, a metal strain gauge, and a base; One end of the alloy shell is sealed to a metal corrugated diaphragm, and the other end is sealed to a base, forming a closed mounting cavity inside the alloy shell. The pressure ring is fixedly connected to the alloy shell and the metal corrugated diaphragm on the outside of the closed installation cavity, which strengthens the structure and limits the fixation of the metal corrugated diaphragm. The metal elastomer is installed in a closed mounting cavity, including a relatively large connecting part and a relatively small sensing part; wherein, the connecting part is connected to the inner wall of the alloy shell; a sealed cavity is formed inside the metal elastomer and filled with silicone oil as a pressure transmission medium; The outer side of the sensing part forms a cavity with the inner wall of the alloy shell. Metal strain gauges are deposited on the side wall of the sensing part as strain detection circuits. The metal strain gauge is electrically connected to the piezoresistive electronic device in the base via a flying wire.

[0019] The sensor and its manufacturing method are described below with reference to more accompanying drawings, in one or more detailed embodiments, and their advantages are explained.

[0020] Detailed Implementation Examples based on Figures 1 to 6 ,in Figure 1 This diagram illustrates the exploded structure of an oil-filled, isolated piezoresistive pressure sensor suitable for high-pressure environments. Figure 2 This is a schematic diagram of the assembly cross-section. Figure 3 This is a schematic diagram of the overall structure of a metallic elastomer. Figure 4 This is a partial structural diagram of a metal elastomer variable cross-section sensing unit. Figure 5 This is a schematic diagram of the electrical wire layout and reinforcement structure on the surface of a metallic elastomer. Figure 6 This is a process flow diagram of the metal elastomer surface film and strain gauge in an embodiment of the present invention.

[0021] In this detailed embodiment, the alloy shell is exemplified as a cylindrical structure.

[0022] exist Figure 1The diagram illustrates a pressure ring 1, a corrugated metal diaphragm 2, a metal elastomer 3, a metal strain gauge 4, an alloy housing 5, conductive leads 6, an electrical via 7, and a base 8. In a more specific implementation, the base 8 and housing 5 are made of 316 stainless steel; the corrugated diaphragm 2 and the metal elastomer 3 are made of 60Si2CrVA spring steel; the strain gauge 4 is a NiCr metal thin-film resistor; the conductive leads 6 are made of copper alloy gold-plated leads; the electrical via 7 is encapsulated with ceramic pins; and high-voltage silicone oil is used.

[0023] In the detailed embodiments of this application, the pressure ring 1 is an annular metal structural component, the outer diameter of which matches the outer diameter of the metal corrugated diaphragm 2, used for axial positioning and structural reinforcement of the metal corrugated diaphragm 2. The metal corrugated diaphragm 2 is a circular thin-walled metal diaphragm structure, with a concentric annular corrugated structure formed on its surface to improve the elastic deformation capacity of the diaphragm and reduce the axial structural stiffness. The alloy shell 5 is an integral cylindrical metal structural component, with an opening structure and an annular support step at its top for mounting the metal corrugated diaphragm 2. The outer peripheral edge of the metal corrugated diaphragm 2 is disposed on the annular support step and is fixedly connected to the alloy shell 5 by welding. Preferably, laser welding is used to form a continuous annular weld between the outer peripheral edge of the metal corrugated diaphragm 2 and the alloy shell 5 to achieve a high-pressure sealing connection. The pressure ring 1 is positioned above the outer edge of the corrugated metal diaphragm 2 and is fixedly connected to the corrugated metal diaphragm 2 and the alloy shell 5 by welding. Preferably, laser welding is used to form a ring-shaped welded structure between the pressure ring 1, the corrugated metal diaphragm 2, and the alloy shell 5, thereby reinforcing and limiting the outer periphery of the corrugated metal diaphragm 2 to ensure good structural stability and sealing reliability under high pressure environments above 210 MPa. The alloy shell 5 contains a closed mounting cavity for installing the metal elastomer 3. The base 8 is located at the bottom of the alloy shell 5. The base 8 is a cylindrical support structure with a threaded structure on its outer side, and is connected and sealed to the alloy shell 5 by threads, thus forming the overall sensor encapsulation structure. The electrical through-hole 7 is located inside the base 8 and is an insulated and sealed through-hole structure used to extract the internal electrical signals of the sensor. The conductive pin 6 is installed in the electrical through-hole 7 and connected to an external circuit to output the sensor's electrical signals.

[0024] The corrugated metal diaphragm 2 is disposed at the top opening of the alloy housing 5 and is in direct contact with the measured medium. The pressure ring 1 is a ring-shaped structural component. The corrugated metal diaphragm 2 is fixedly installed on the top end face of the alloy housing 5 by laser welding, thereby forming a sealed isolation structure so that the pressure of the external measured medium only acts on the corrugated metal diaphragm 2 and does not enter the sensor.

[0025] The metal elastomer 3 is installed inside the alloy housing 5, and the outer wall of its connecting part is connected by a metric M10. The 1.0 thread engages with the internal thread of the alloy shell 5 for secure installation, thus achieving reliable mechanical installation; the metal elastomer 3 forms a cylindrical sealed cavity inside, which is filled with silicone oil as a pressure transmission medium.

[0026] A serpentine metal strain gauge 4 is formed on the outer wall of the metal elastomer 3 by magnetron sputtering deposition using micro-nano fabrication technology. The metal strain gauge 4 is connected in the form of a Wheatstone bridge to form a strain detection circuit. At the same time, metal pads are deposited on the outer wall of the metal elastomer 3 for electrical connection.

[0027] An annular cavity is formed between the outer side of the sensing part of the metal elastomer 3 and the inner wall of the alloy shell 5, and electrical connection lines are arranged in the cavity. The pads on the outer wall of the metal elastomer 3 are electrically connected to the conductive pins 6 on the base 8 through flying wires, thereby realizing the transmission of strain signals to external circuits. In order to improve the reliability of electrical connection under severe vibration environment and effectively release the concentrated stress generated by the flying wires at the pads, four U-shaped lead grooves 3a are formed along the axial direction on the surface of the lower planar section of the metal elastomer 3. In terms of structure and process, firstly, a strain relaxation wiring design is adopted. The flying wires are embedded in the lead grooves 3a with a slight arc. This arc margin can effectively absorb the thermal expansion and contraction stress caused by extreme high temperature gradient and buffer the static pulling force of the radial expansion and contraction of the elastomer on the solder joint under ultra-high pressure environment. Secondly, at the root of the pads and the solder joint of the flying wires on the outer wall of the metal elastomer 3, a micron-level tough polymer protective material (fluorosilicone rubber) is locally coated. The high viscoelasticity of the material is used to flexibly transfer and diffuse the concentrated mechanical stress of the solder joint to a larger area of ​​the elastomer surface. Furthermore, the lead groove 3a is filled and cured with fluorosilicone rubber to physically fix the main body of the flying wire and provide impact-resistant buffer. The above-mentioned multi-level protection mechanism together avoids the risk of weld root fracture under alternating vibration.

[0028] To improve the strain sensitivity of the sensor, the outer wall of the metallic elastomer 3 is formed into a non-perfect cylindrical structure by locally reducing material, resulting in a variable cross-section irregular cylindrical structure with a planar region on both sides and symmetrical thinning. A metallic strain gauge 4 is deposited in the planar region. Because the wall thickness in this region is relatively thin, the strain generated under the same pressure is greater, thereby improving the measurement sensitivity of the pressure sensor.

[0029] When external pressure is applied to the corrugated metal diaphragm 2, the diaphragm undergoes elastic deformation, transmitting the pressure to the silicone oil medium inside. Due to the low compressibility of silicone oil, its volume change is negligible under normal pressure conditions. However, in extremely high-pressure environments above 210 MPa and under conditions requiring high sensitivity for small strain detection, this characteristic may still affect the accuracy of pressure transmission. This structure addresses this by coupling the corrugated metal diaphragm 2 with a metal elastomer 3 and filling the sealed cavity with silicone oil as the pressure transmission medium. The metal elastomer 3 includes a threaded connection at the top and a variable cross-section sensing part at the bottom. The threaded connection is fixed to the alloy shell 5 via external threads, ensuring the high-pressure sealing reliability of the cavity. The variable cross-section sensing part is formed by locally reducing material to create a variable cross-section irregular column structure with symmetrical thinning on both sides. Its internal cylindrical cavity communicates with the inner cavity of the threaded part. External pressure is transmitted to the silicone oil through the elastic deformation of the corrugated diaphragm. The silicone oil pressure then acts directly on the internal cavity wall of the variable cross-section sensing part of the metal elastomer 3, causing it to undergo elastic deformation. Due to the low structural stiffness at the variable cross-section, the strain is concentrated in the outer wall plane area of ​​the sensing part. The metal strain gauge 4 deposited on the outer wall then generates a change in resistance, which is converted into a voltage signal by a Wheatstone bridge circuit. This voltage signal is then output to the external signal processing circuit via a flying wire and conductive pin 6 to achieve pressure signal measurement. For 210 MPa high pressure and complex vibration conditions, to ensure the reliability of the electrical connection, this embodiment adopts process reinforcement measures without changing the main mechanical structure. First, a strain relaxation wiring process is used, where the conductive filament forms a naturally drooping arc compensation between the pad and the conductive pin 6 during flying wire connection. The arc design is used to absorb the stress caused by the thermal expansion and contraction of the material due to temperature gradients, and to buffer the static tensile force generated by the radial expansion and contraction of the elastomer on the solder joint under high pressure. Secondly, the solder joint elastic encapsulation technology involves locally coating a layer of micron-sized tough polymer protective material (fluorosilicone rubber) at the root of the solder pad and the connection point of the flying wire of the metal strain gauge 4. This protective layer not only serves as insulation, but also utilizes its high viscoelasticity to diffuse the concentrated stress of the solder joint to a larger area of ​​the elastomer surface, preventing the solder root from breaking under alternating vibration.

[0030] The theoretical model for the pressure drop and strain response caused by external pressure through corrugated diaphragms, silicone oil media, and metallic elastomer structures can be analyzed by establishing a pressure transfer equation and a structural elasticity model. The specific derivation process is as follows: Let the uniform pressure exerted by the external force on the upper surface of the diaphragm be... The uniform back pressure of the silicone oil inside the cavity on the lower surface of the diaphragm is The net uniform pressure exerted on the diaphragm is then...

[0031]

[0032] The diaphragm satisfies the theoretical conditions for thin plates. The diaphragm material is an isotropic linear elastic material, and the deformation is characterized by small deflection and small rotation. The external load is a static or quasi-static load. The diaphragm edge is fixed and without slippage. The normal load acting on the diaphragm surface is a uniformly distributed pressure. Under these conditions, the deflection distribution of a fixed circular thin plate under uniformly distributed pressure is as follows:

[0033] in

[0034] In the formula: For the diaphragm in radius Deflection at the point; The net uniform pressure (Pa) borne by the diaphragm. The effective radius of the diaphragm (m); Young's modulus (Pa) of the diaphragm material; Poisson's ratio; The thickness of the diaphragm is (h). This refers to the bending stiffness of the thin plate.

[0035] At the center of the diaphragm At this point, the deflection reaches its maximum value:

[0036] Substituting into equation (3), we get:

[0037] Define the diaphragm flexibility factor:

[0038] Therefore, the maximum deflection of the diaphragm can be expressed as:

[0039] The physical meaning of the diaphragm flexibility coefficient C is specifically expressed as a characterizing index of the diaphragm's pressure response sensitivity and structural stiffness. The flexibility coefficient C defines the maximum central deflection of the diaphragm under a unit uniformly distributed pressure load (i.e., The larger the C value, the easier it is for the diaphragm to deform under the same pressure, meaning the higher the diaphragm's "mechanical sensitivity." This coefficient integrates the diaphragm's geometric dimensions (radius a, thickness h) and material mechanical properties (Young's modulus E, Poisson's ratio μ). It reflects the diaphragm's overall ability to resist bending deformation and is inversely proportional to the bending stiffness D.

[0040] The change in oil cavity volume is caused by diaphragm deformation; the sidewalls and bottom of the oil cavity are rigid structures. The change in oil cavity volume mainly originates from diaphragm deformation. The amount of change in oil cavity volume is:

[0041] Substituting equation (2) into the integral, we get:

[0042] The silicone oil compression model assumes a small compression rate; the bulk modulus of the silicone oil can be considered constant; the oil cavity is a closed structure with no leakage; and the effects of dissolved gases and bubbles are ignored. The bulk modulus is defined as:

[0043] Under low compression conditions, it can be approximated as:

[0044] in: The bulk modulus of silicone oil (Pa); The initial volume of silicone oil (m³); This represents the change in oil cavity volume (m³). The back pressure of the silicone oil is (Pa).

[0045] The diaphragm-silicone oil coupling relationship results in a uniform pressure distribution inside the oil cavity. Substituting equations (7) and (9) into equation (11) yields:

[0046] Substituting equation (12) into equation (1) yields:

[0047] Therefore, the net pressure borne by the diaphragm is:

[0048] Definition of dimensionless coupling coefficient:

[0049] Then equation (14) can be written as:

[0050] in The coefficient represents the coupling effect between the diaphragm elasticity and the compressibility of the silicone oil. The larger the coefficient, the stronger the coupling effect between the silicone oil compression and the diaphragm flexibility, and the smaller the pressure transmitted to the internal structure, thus achieving a more significant pressure reduction effect.

[0051] The diaphragm strength was checked. The diaphragm experiences primarily bending stress with relatively small deflection, and the load is uniformly distributed pressure. The approximate engineering formula for the maximum bending stress of a circular plate is:

[0052] in: The maximum bending stress of the diaphragm, Net pressure, For the diaphragm radius, Given the diaphragm thickness, an external pressure of 210 MPa, and the diaphragm material being 60Si2CrVA spring steel with a yield strength of [missing value], [missing value].

[0053] To ensure structural safety, it is necessary to meet the following requirements.

[0054] Substituting the yield strength of spring steel (1665 MPa) and the compressive strength (210 MPa) into equations (17) and (19), we obtain the following:

[0055] This embodiment addresses the ultra-high pressure measurement environment of 210 MPa in oil drilling. Considering the space constraints of small sensor size and high integration required by downhole measurement tools, key structural parameters were selected and verified. Given the limitations of the downhole drilling tool's mounting hole diameter, the overall outer diameter of the sensor needs strict control. Based on this, the effective radius of the metal corrugated diaphragm 2 was selected. This size satisfies the requirements for miniaturized packaging while ensuring sufficient pressure-bearing area to generate effective deflection. To ensure no plastic deformation occurs under extremely high pressure of 210 MPa, the diaphragm thickness was selected. ,at this time This is much smaller than the critical failure ratio, providing sufficient strength margin. Simultaneously, the internal cavity length of the metallic elastomer 3 is set... To obtain a suitable initial oil cavity volume V, substitute the final dimensions and material parameters to obtain: , Substituting the values, we get:

[0056] Based on theoretical calculations, the pressure reduction structure of this invention reduces the external high pressure of 210MPa to 1.51MPa.

[0057] In another aspect of the present invention, a method for manufacturing a sensor is provided: The first step involves machining the alloy shell 5, which is made of 316 stainless steel. An internal thread structure for mounting the metal elastomer 3 is machined inside the alloy shell 5, and a mounting end face for mounting the metal corrugated isolation diaphragm 2 is machined on the top of the alloy shell. The bottom of the alloy shell 5 has a threaded connection structure that mates with the base 8, thus facilitating subsequent overall assembly and sealing. After machining, the alloy shell is deburred, cleaned, and dried to ensure the cleanliness of the internal cavity.

[0058] The second step involves processing the metallic elastomer 3. This metallic elastomer is formed from 60Si2CrVA spring steel, with an internal cylindrical cavity created using electrical discharge machining (EDM) for subsequent filling with silicone oil as a pressure transmission medium. An external mounting thread is machined onto the outer wall of the metallic elastomer 3, and an annular positioning boss (flange limiting platform) is provided at the root of this thread. This external thread connects to the internal thread inside the alloy housing 5, and the annular positioning boss provides end-face sealing and axial limiting with the bearing step surface inside the alloy housing 5, thereby achieving precise spatial positioning and reliable fixation of the metallic elastomer 3 within the alloy housing 5. Furthermore, in the sensing area on the outer wall of the metallic elastomer 3, a symmetrically thinned, variable cross-section irregular column structure is formed by locally removing material to create a strain concentration area for subsequent deposition of metal strain gauges. This variable cross-section structure is axially independent of the aforementioned mounting thread portion, ensuring that installation stress does not affect the strain distribution in the sensing area. Furthermore, in the sensing region on the outer wall of the metallic elastomer 3, a variable cross-section irregular column structure with bilateral symmetrical thinning is formed by locally removing material to create a strain concentration area for subsequent deposition of metal strain gauges. Simultaneously, below the variable cross-section sensing region, four U-shaped lead grooves 3a are uniformly machined axially using a micro-milling process, with smooth chamfered edges to prevent damage to the leads. After machining, the metallic elastomer undergoes precision cleaning and drying.

[0059] The third step is surface pretreatment of the metal elastomer. To ensure adhesion for subsequent film deposition, the surface of the metal elastomer 3 needs to be pretreated. First, the outer surface of the metal elastomer is mechanically polished to reduce surface roughness and improve film deposition uniformity, reducing the surface roughness Ra to 0.1 μm. Subsequently, it undergoes ultrasonic cleaning sequentially in acetone, anhydrous ethanol, and deionized water to remove surface oil and particulate contaminants. After cleaning, it is dried using nitrogen blowing or an oven drying method. If necessary, plasma cleaning can be further used to remove residual organic contaminants and improve substrate surface activity. After the above treatment, a clean metal substrate surface with good adhesion properties is obtained.

[0060] Step 4, Insulating Layer Deposition: Since the metal elastomer 3 is a conductive material, to avoid electrical short circuits between the strain resistor and the metal substrate, an insulating layer needs to be deposited on the outer surface of the metal elastomer 3 first. In this embodiment, an aluminum oxide (Al2O3) insulating film is deposited on the outer surface of the metal elastomer 3. Magnetron sputtering is preferably used for deposition: the metal elastomer is placed in the vacuum chamber of the magnetron sputtering equipment, and the chamber is evacuated to approximately 10... 3 10 5Pa, then argon gas is introduced as the working gas, and alumina target is used as the sputtering target. Under the action of plasma, the target atoms are sputtered and deposited on the surface of the metal elastomer, thereby forming an Al2O3 insulating film with a thickness of tens to hundreds of nanometers.

[0061] Step 5, Strain-Sensitive Metal Thin Film Deposition: After the insulating layer is formed, a strain-sensitive metal material layer is deposited on its surface. In this embodiment, the strain-sensitive material is a NiCr alloy. Magnetron sputtering is preferably used for deposition to ensure uniform deposition of the strain-sensitive metal material on the surface of the insulating layer, forming a metal thin film layer with a thickness of tens of nanometers.

[0062] Step 6, Strain Gauge Pattern Formation: The deposited metal film is a continuous overlay structure, requiring micro-nano patterning to form a strain gauge resistor structure. First, photoresist is spin-coated onto the surface of the metal film and soft-baking is performed to remove the solvent. Then, a photomask is used for alignment, and ultraviolet exposure is used to form a predetermined pattern on the photoresist. The strain gauge pattern is obtained through a development process. Afterward, wet etching is used to remove the areas of the metal film not protected by the photoresist, thereby forming a serpentine structure metal strain gauge resistor. After etching, residual photoresist is removed by acetone or oxygen plasma process, and the surface is cleaned. After completing the above steps, the metal strain gauge 4 can be formed by thinning the area outside the metal elastomer (3).

[0063] Step 7, Installation of the Metal Elastomer: After the strain gauge is prepared, the metal elastomer 3 is screwed into the alloy housing 5. Specifically, the metric thread on the outside of the metal elastomer is engaged with the internal thread inside the alloy housing to secure it firmly inside. At this point, an annular space is formed between the outer wall of the metal elastomer and the inner wall of the alloy housing for arranging electrical connection lines.

[0064] Step 8, Electrical Signal Connection and Encapsulation Reinforcement: Flying wire connections are made at the strain gauge pads on the outer wall of the metal elastomer 3 using metal wires. One end of the flying wire is soldered to the strain gauge pad, and the other end is connected to the conductive pin 6 on the base 8, thus enabling the transmission of strain signals to the external circuit. During wiring, the wires are inserted into the pre-processed lead groove 3a with a slight arc (allowing for thermal expansion). Subsequently, room temperature vulcanizing (RTV) high-temperature fluorosilicone rubber is injected into the groove using a dispensing device, and the groove is placed in a vacuum environment for degassing, followed by stepped heating curing. The wires are arranged in the annular space between the metal elastomer and the alloy shell, and are firmly encapsulated in the groove by the polymer elastomer, effectively eliminating the pulling effect of alternating stress on the wire bundle.

[0065] Step 9, Silicone Oil Filling: Silicone oil is filled into the internal cavity of the metal elastomer 3 as a pressure transmission medium. The filling process is carried out under vacuum to avoid air residue, thus ensuring sufficient silicone oil filling and preventing bubble formation. After silicone oil filling is completed, the internal cavity forms a sealed pressure transmission structure.

[0066] Step 10, Install the corrugated diaphragm: Install the metal corrugated isolation diaphragm 2 at the top opening of the alloy housing 5. Then, install the pressure ring 1 above the diaphragm and fix the corrugated isolation diaphragm to the end face of the alloy housing by laser welding, thereby forming a sealed structure so that the external measured medium only acts on the surface of the corrugated isolation diaphragm and does not directly enter the sensor.

[0067] Step 11, Base Installation and Overall Encapsulation: Finally, the base 8 is installed onto the bottom of the alloy housing 5, and sealed and fixed using a threaded connection. The conductive pins 6 are led out through the electrical through-holes 7 on the base, thereby enabling the connection between the internal electrical signals of the sensor and the external circuitry.

[0068] After completing the assembly steps described above, the oil-filled isolated piezoresistive pressure sensor described in this embodiment can be used for pressure measurement.

[0069] In this embodiment, the sensor works as follows: When the sensor is operating, the outer surface of the corrugated metal diaphragm 2 is in direct contact with the measured medium. When an external pressure P is applied to the surface of the corrugated metal diaphragm 2, the diaphragm undergoes elastic deformation under pressure and experiences a slight axial flexural displacement. Since the inner side of the corrugated metal diaphragm 2 is in contact with the silicone oil medium inside the cavity of the metal elastomer 3, the deformation of the diaphragm causes the silicone oil to compress, thus creating a pressure change within the silicone oil. This pressure is uniformly transmitted to the inner cavity wall of the metal elastomer 3 through the silicone oil medium.

[0070] Silicone oil, as a pressure transmission medium, possesses good fluidity and a certain degree of volume compressibility. When external high pressure is applied to the corrugated diaphragm, the silicone oil undergoes slight volume compression while transmitting pressure, thus buffering pressure changes and making the pressure changes acting on the metallic elastomer more stable. Under the pressure of the silicone oil, the inner wall of the metallic elastomer 3 is subjected to a uniform internal pressure load, causing the metallic elastomer to undergo elastic deformation. Because the outer wall of the metallic elastomer is locally thinned to form a symmetrically thinned variable cross-section irregular column structure, the structural stiffness of this thinned area is relatively low. Therefore, under the same internal pressure conditions, this area will generate a large strain, thus forming a significant strain concentration zone.

[0071] Metal strain gauges 4, deposited on the surface of the thinned region, are tightly bonded to the surface of the metal elastomer. When the metal elastomer undergoes elastic deformation, the strain gauges also experience the same strain change. Due to the piezoresistive effect, the resistance value of the metal strain gauges changes with the strain. The metal strain gauges are connected in a Wheatstone bridge configuration to form a strain detection circuit. When the metal elastomer deforms, the resistance value of each strain gauge changes, resulting in a change in the bridge output voltage. This voltage signal is transmitted through a flying wire to the conductive pin 6 on the base 8, and then output to an external signal conditioning circuit. After amplification, filtering, and conversion of the bridge output signal by the external signal processing circuit, an electrical signal corresponding to the external pressure is obtained, thereby realizing the measurement of pressure.

[0072] Through the above structural design, the pressure sensor described in this embodiment can achieve the following functions: First, the measured medium is isolated from the internal structure of the sensor by a metal corrugated diaphragm, thereby preventing the measured medium from directly entering the sensor and improving the reliability of the sensor in corrosive or high-pressure environments.

[0073] Secondly, the pressure is stably transmitted through the silicone oil medium, so that the pressure can be applied evenly inside the metal elastomer. At the same time, the compressibility of the silicone oil is used to buffer pressure changes, thereby improving measurement stability.

[0074] Furthermore, by locally thinning the outer wall of the metal elastomer, the strain is concentrated in the area where the strain gauge is located, thereby improving the strain response sensitivity of the sensor.

[0075] Finally, a metal strain gauge structure is formed on the surface of the metal elastomer through a thin film deposition process, enabling the sensor to convert the minute deformation of the metal elastomer into a measurable electrical signal, thereby achieving high-precision pressure measurement.

[0076] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An oil-filled, isolated piezoresistive pressure sensor suitable for high-pressure environments, characterized in that, include: Alloy shell, metal corrugated diaphragm, pressure ring, metal elastomer, metal strain gauge and base; One end of the alloy shell is sealed to a metal corrugated diaphragm, and the other end is sealed to a base, forming a closed mounting cavity inside the alloy shell. The pressure ring is fixedly connected to the alloy shell and the metal corrugated diaphragm on the outside of the closed installation cavity, which strengthens the structure and limits the fixation of the metal corrugated diaphragm. The metal elastomer is installed in a closed mounting cavity, including a relatively large connecting part and a relatively small sensing part; wherein, the connecting part is connected to the inner wall of the alloy shell; a sealed cavity is formed inside the metal elastomer and filled with silicone oil as a pressure transmission medium; The outer side of the sensing part forms a cavity with the inner wall of the alloy shell. Metal strain gauges are deposited on the side wall of the sensing part as strain detection circuits. The metal strain gauge is electrically connected to the piezoresistive electronic device in the base via a wire; The alloy shell is provided with an opening structure for installing a metal corrugated diaphragm and an annular support step; the outer peripheral edge of the metal corrugated diaphragm is provided on the annular support step and is fixedly connected to the alloy shell by welding; the pressure ring is fixedly connected to the metal corrugated diaphragm and the alloy shell by welding; the connecting part of the metal elastomer has its outer side wall engaged with the internal thread of the alloy shell by threads. The sensing part of the metallic elastomer is not in contact with the base; the sensing part of the metallic elastomer has an outer wall that is partially cylindrical by locally cutting material, so that its outer contour forms a variable cross-section irregular column structure with a planar region and bilateral symmetrical thinning; wherein, a metallic strain gauge is deposited on the planar region. The corrugated metal diaphragm is a circular, thin-walled metal diaphragm structure with concentric annular corrugations on its surface. The ratio of the radius to the thickness of the corrugated metal diaphragm is less than or equal to 4.38, where the units for both the radius and the thickness are mm. Metal strain gauges are deposited using magnetron sputtering micro-nano fabrication technology and connected in the form of a Wheatstone bridge to form a strain detection circuit. The outer wall of the metal elastomer is provided with a U-shaped lead groove for embedding electrical wires; and the U-shaped lead groove is filled and cured with rubber.

2. The oil-filled isolated piezoresistive pressure sensor suitable for high-pressure environments according to claim 1, characterized in that, The electric fly wire is connected to the varistor electronic device through conductive pins on the inner surface of the base.

3. The oil-filled isolated piezoresistive pressure sensor suitable for high-pressure environments according to claim 2, characterized in that, The base allows for the extraction of internal electrical signals from the varistor through electrical vias on its outer surface.

4. A manufacturing method applicable to the oil-filled isolated piezoresistive pressure sensor according to claim 1, characterized in that, include: The first step is to process the alloy shell; The second step is to process the metal elastomer; The third step is surface pretreatment of the metal elastomer; Step 4: Deposition of the insulating layer; Step 5: Deposition of strain-sensitive metal thin films; Step 6: Strain gauge pattern formation; Step 7: Install the metal elastomer; Step 8: Electrical signal connection and potting reinforcement; Step 9: Silicone oil filling; Step 10: Install the metal corrugated diaphragm; Step 11: Base installation and overall encapsulation.

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