Radiator with fin structure

Abstract

The radiator with the fin structure comprises a base located on the XY plane, the base supports a plurality of evenly-distributed vertical cooling fins, and the cooling fins are located on the YZ plane to form a first separation channel; the inner surface, facing the-Y vector direction, of each cooling fin is provided with a single fin, and the terminal of each cooling fin is provided with a protruding structure facing the + X direction. The invention aims to promote uniform distribution of heat on the surface of the heat sink by introducing the fins with airflow guiding features into the heat sink for redirecting buoyancy-driven airflow. By enhancing the interaction of rising hot air with areas of the fins that are not previously fully utilized, the fins improve the overall convective heat exchange efficiency, reduce the peak temperature of the fins, and improve thermal uniformity without significantly increasing the size or complexity of the heat sink.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of heat sinks, and particularly relates to a heat sink with a wing structure. BACKGROUND

[0002] In recent years, the progress of power electronics technology has enabled devices to have higher power density and higher switching frequency. Components such as metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), power diodes, and rectifiers are now required to operate reliably under high current loads while ensuring efficiency and minimizing heat loss. The heat generated by these devices is due to conduction loss, switching loss, and on-resistance. If not effectively dissipated, it will lead to thermal runaway, reduced efficiency, shortened service life, and even catastrophic failure.

[0003] Despite the progress in heat sink design, traditional solutions such as rectangular straight-fin aluminum heat sinks still have limitations in fully utilizing the overall volume of the fins. In particular, the upper region of the vertical fins, especially the top leading corner, usually has low heat flux and insufficient surface area utilization, resulting in uneven temperature distribution and reduced overall heat dissipation efficiency.

[0004] In addition, various strategies have been proposed in the prior art, including improving fin geometry, selecting appropriate materials, and optimizing airflow management. Techniques such as needle-shaped fins, louvered fins, and microchannel structures aim to increase the convective heat transfer coefficient and improve overall heat dissipation. However, these solutions often require significant modifications to the heat sink manufacturing process or involve complex geometries, thereby increasing costs, assembly difficulty, and reducing mechanical strength. SUMMARY

[0005] The present application aims to address the above limitations by innovatively improving the structure of traditional heat sinks. A heat sink with a wing structure is proposed, which introduces a wing-shaped extension wing on the inner surface of the vertical fins near the top leading corner to guide airflow, promote uniform distribution of heat within the fins, enhance convective heat dissipation, and alleviate local hot spots.

[0006] Specifically, the heat sink with a wing structure according to the present application defines the +Z vector as the upward direction and the -Z vector as the downward direction; the +X vector as the right direction and the -X vector as the left direction; the -Y vector as the front direction and the +Y vector as the rear direction. The heat sink comprises: a base on the XY plane, which supports a plurality of uniformly distributed vertical fins; the fins form a first separate channel on the YZ plane; each fin is equipped with a single wing on the inner surface facing the -Y vector direction; and the terminal of each fin is provided with a protruding structure facing the +X direction.

[0007] The present invention aims to alleviate this limitation by introducing a guided airflow feature, called a fin, into the fins. The fin is designed to redirect the buoyancy-driven airflow, thereby promoting uniform distribution of heat across the fin surface. By enhancing the interaction of the rising hot air with previously underutilized fin areas, the fin improves the overall convective heat transfer efficiency, reduces the fin peak temperature, and improves thermal uniformity, all without significantly increasing the size or complexity of the heat sink.

[0008] Preferably, the fin extends from the top corner on the +Z vector of the fin to the XZ plane, and the fin is set at a negative rotation angle relative to the +X vector, and when the forced cooling fluid flows in the +X direction, the airflow is guided by the fin to the base direction. Preferably, the negative rotation angle is set between -10° and -55° according to different heat sink sizes and airflow rates.

[0009] Preferably, the fin includes a guide groove and a baffle plate arranged on both sides of the guide groove.

[0010] Preferably, the baffle plate close to the fin side is fixedly attached to the fin.

[0011] Preferably, the length of the fin is set to be between 5-20mm according to the fin spacing and airflow requirements.

[0012] Preferably, the width of the protruding structure in the Y vector direction is 0.2-2.5 times the width of the fin to pressurize the forced cooling fluid.

[0013] Preferably, the length of the protruding structure in the X vector direction is between one sixth and one eighth of the length of the fin.

[0014] Preferably, the protruding structures form a second separation channel between them, and the width of the second separation channel in the Y vector direction is between 0.1-0.5 times the width of the first separation channel.

[0015] Preferably, the protruding structure is connected to the fin at an inclined angle.

[0016] Preferably, fixed side walls are provided on both sides of the heat sink in the Y vector direction. Preferably, the fin is set as a rectangular sheet, a trapezoidal structure or an L-shaped structure.

[0017] The present invention strategically manages the natural buoyancy-driven airflow to maximize the effective surface area of each fin. This optimization enables the heat sink to dissipate heat more efficiently while taking advantage of the inherent physical properties of air buoyancy, thereby achieving a superior fin geometry and outstanding thermal performance with minimal modification to the traditional heat sink structure.

[0018] Compared with the prior art, the present application has the following beneficial effects: The present application effectively guides cooling air through the fins, maximizes the utilization rate of available airflow, and enhances convective heat transfer without increasing fan rotation speed or airflow speed, thereby maintaining system energy efficiency. Furthermore, the FEA results verify that the technical advantages of the present application's heat sink over the traditional rectangular design are lower and uniform working temperature, stable and optimized airflow distribution, which realizes the improvement of thermal management efficiency and material utilization rate. It is especially suitable for high-power electronic applications that are sensitive to reliability, efficiency and cost. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a schematic diagram of a heat sink with fin structure in this embodiment.

[0020] Figure 2 It is a schematic diagram of the heat sink fins and their different directions in this embodiment.

[0021] Figure 3 It is a simulation of a traditional heat sink with similar size in this embodiment.

[0022] Figure 4 It is a FEA result showing the temperature distribution effect of a traditional heat sink in this embodiment.

[0023] Figure 5 It is a FEA result showing the pressure distribution effect of a traditional heat sink in this embodiment.

[0024] Figure 6 It is a significant uniformity effect diagram of the temperature distribution of the heat sink of the present application in this embodiment.

[0025] Figure 7 It is a airflow pressure distribution effect diagram of the heat sink of the present application in this embodiment.

[0026] Among them, 10 is the heat sink base; 11 is the heat sink fin; 12 is the fin; 13 is the protruding structure; 14 is the separation channel. DETAILED DESCRIPTION

[0027] The following description is used to disclose the present application so that those skilled in the art can implement the present application. The preferred embodiments in the following description are only as examples, and other obvious modifications can be made by those skilled in the art.

[0028] In this embodiment, in order to more clearly describe the technical solution, in the three-dimensional Cartesian space, +Z vector represents the upward direction, -Z represents the downward direction; +X represents the right direction, -X represents the left direction; -Y represents the front direction, +Y represents the rear direction.

[0029] Specifically, as Figures 1-2As shown, the fin structure heat sink of the present application comprises: The base is located on the XY plane, and supports a plurality of uniformly distributed vertical fins, which form first separate channels on the YZ plane; the inner surface of each fin in the direction of the -Y vector is equipped with a single fin, and the terminal end of each fin is provided with a protruding structure in the +X direction.

[0030] In this embodiment, the fin is designed to redirect the buoyancy-driven air flow, thereby promoting the uniform distribution of heat on the fin surface. By enhancing the interaction of the rising hot air with the previously underutilized fin area, the fin improves the overall convective heat transfer efficiency, reduces the peak temperature of the fin, and improves the thermal uniformity, without significantly increasing the size or complexity of the heat sink.

[0031] It should be noted that in this embodiment, the fin can be designed as a rectangular sheet or other structural shape, such as a trapezoidal structure, an L-shaped structure, etc., which are not limited thereto. The different fin structures are consistent with the simulation results in terms of technology, which helps to maintain flexibility in the manufacturing process and can expand the scope of protection to cover different forms of fin structures.

[0032] It should be noted that as long as the fins are arranged vertically at the inlet of the working fluid, the fin structure can be applied to any vertical fin. On the other hand, the protruding structure on the fin should be arranged at the downstream end of the heat sink to forcibly cool and guide the working fluid after the air flow passes through the fin, thereby enhancing the overall heat dissipation effect.

[0033] It should be noted that in this embodiment, taking a rectangular fin as an example, the size of the fin can be adjusted according to different demand parameters.

[0034] Preferably, the fin extends from the top corner on the +Z vector of the fin to the XZ plane, and the fin is negatively rotated by a preset angle relative to the +X vector, so that when the forced cooling fluid flows in the +X direction, it is guided to the base direction through the fin; it should be noted that there is no fin on the XZ plane in the +Y direction. The size of the fin and the negative rotation angle relative to the +X vector are precisely calculated to guide the incoming air downward, thereby alleviating the thermal buoyancy effect.

[0035] Preferably, the fin extends from the top corner on the +Z vector of the fin to the XZ plane, and the fin is negatively rotated by a preset angle relative to the +X vector, so that when the forced cooling fluid flows in the +X direction, it is guided to the base direction through the fin; it should be noted that there is no fin on the XZ plane in the +Y direction. The size of the fin and the negative rotation angle relative to the +X vector are precisely calculated to guide the incoming air downward, thereby alleviating the thermal buoyancy effect.

[0036] Preferably, the fin includes a rectangular guide groove and a baffle plate arranged on both sides of the guide groove.

[0037] Preferably, the baffle plate near the fin side is fixedly attached to the fin.

[0038] Preferably, the length of the fin is set to be between 5-20mm according to the fin pitch and air flow requirements.

[0039] Preferably, the width of the raised structure in the Y vector direction is 0.2-2.5 times the width of the fin, to pressurize the forced cooling fluid.

[0040] Preferably, the length of the raised structure in the X vector direction is between one sixth and one eighth of the length of the fin.

[0041] Preferably, the raised structures form a second separation channel between them, with a width in the Y vector direction of between 0.1-0.5 times the width of the first separation channel.

[0042] Preferably, the raised structure is at an angle to the fin at the connection.

[0043] Preferably, fixed side walls are set on both sides of the radiator in the Y vector direction. It should be noted that the fixed side walls on both sides of the radiator have a heat transfer coefficient of , on the one hand, to form a defined cooling air channel and ensure consistent air flow direction, and on the other hand, to prevent cooling fluid leakage and ensure the integrity of the cooling path. This design ensures that air passes evenly through the fin channel, optimizing the convective heat transfer of the radiator.

[0044] In order to better illustrate the technical solution, taking a light and thin consumer electronics as an example, the base of the radiator is set to have XY plane dimensions of 40mm x 30mm, a thickness of 2mm, and is made of 6063 aluminum alloy material, with a surface anodizing treatment and an oxide layer thickness of 6μm, and a bottom bonding surface roughness of Ra≤0.6μm, to facilitate close bonding with the consumer electronics chip. Vertical fins are set on the cover base, preferably 6 fins, evenly distributed on the base, with a fin height set to 10mm in the +Z direction, a fin thickness set to 1mm along the X direction, and a fin pitch set to 5mm along the Y direction, forming 5 first separation channels with a channel width of 5mm. The fins and the base are integrally die-cast, with the same material as the base.

[0045] A rectangular sheet structure is used, extending from the +Z vector top corner of the fin to the XZ plane, with a length of 8mm along the extension direction, a width of 3mm along the Y direction, and a thickness of 0.5mm. A negative rotation angle of -15° relative to the +X vector is preset, suitable for the low air flow rate environment in consumer electronics. The fin includes a guide groove, which can be set to have a width of 1mm, a depth of 0.2mm, and a height of 0.5mm on both sides of the baffle, with the baffle close to the fin being fixed and bonded to the fin by laser welding, with a welding strength of ≥40N.

[0046] Further, the convex structure is in the shape of a trapezoidal table, the width in the Y vector direction is 0.8 times the fin width, i.e. 2.4 mm, to achieve moderate pressurization of the forced cooling fluid; the length in the X vector direction is one-seventh of the length of the heat dissipation fin, about 4.3 mm; the connection with the heat dissipation fin is at an inclination angle of 30°; and four second separation channels are formed between the convex structures, with the width in the Y vector direction being 0.3 times the width of the first separation channel, i.e. 1.5 mm.

[0047] Side walls are arranged on both sides of the heat sink in the Y vector direction, with a height of 10 mm consistent with the heat dissipation fin and a thickness of 1 mm, and are integrally formed with the base and the heat dissipation fin to serve as a fixing and airflow guiding function.

[0048] The overall size of the specification heat sink is 40 mm x 30 mm x 12 mm, and the weight is 22 g, which is suitable for CPU / GPU heat dissipation of ultra-thin notebook computers, tablet computers and other consumer electronic devices. Under natural convection conditions, the heat dissipation power can reach 10 W, and the thermal resistance ; when matched with a built-in micro fan of the device, the air volume , the heat dissipation power is increased to 15 W, and the thermal resistance is reduced to 2.0 ℃ / W. In this embodiment, the fin negative rotation angle of –15° can effectively guide the buoyancy-driven airflow, and the combination of the trapezoidal table convex structure and the second separation channel optimizes the flow path of the forced airflow, balancing thinness and heat dissipation efficiency.

[0049] In another preferred embodiment, in order to better illustrate the technical solution, taking a heat sink for industrial equipment as an example, preferably, the XY plane size of the base is 100 mm x 50 mm, the thickness is 4 mm, the ADC12 die-cast aluminum alloy material is adopted, the surface is sprayed with high-temperature resistant insulating paint with a temperature resistance of ≥120 ℃, four M3 mounting holes are reserved at the bottom to adapt to the installation standard of the industrial control module. The number of vertical heat dissipation fins is 15, the fin height is 18 mm, the fin thickness is 1.5 mm, and the fin spacing is 6 mm, forming 14 first separation channels with a channel width of 6 mm; the heat dissipation fins are connected to the base by brazing, the brazing layer thickness is 0.15 mm, and the interface thermal resistance . Preferably, the fin adopts an L-shaped structure, extends from the +Z vector top corner of the heat dissipation fin to the XZ plane, with a length of 12 mm, a width of 4 mm, and a thickness of 0.8 mm; the negative rotation preset angle relative to the +X vector is –30°, which is suitable for medium airflow rate in industrial equipment; the fin flow guide groove width is 1.5 mm, the depth is 0.3 mm, and the height of the two side baffles is 0.8 mm; the side baffle close to the heat dissipation fin is riveted and fixed with the heat dissipation fin, and the number of riveting points is 2 per fin.

[0050] In this application scenario, the protruding structure is designed as a semi-cylindrical shape, with a Y-direction width of 1.5 times the width of the fin, or 6mm, to enhance the pressurization effect; its X-direction length is one-sixth the length of the heatsink, approximately 8.3mm; and it is inclined at a 45° angle to the heatsink. The width of the second separation channel in the Y-direction is 0.2 times the width of the first separation channel, or 1.2mm. Fixed sidewalls are designed on both sides in the Y-direction, with a height of 18mm and a thickness of 2mm, and are welded to the base. The inner side of the sidewalls has guide patterns to further optimize airflow distribution.

[0051] It should be noted that this heat sink has dimensions of 100mm × 50mm × 22mm and weighs 180g. It is suitable for industrial control equipment such as PLC modules and industrial power supplies. Its heat dissipation power is 25W under natural convection, and its thermal resistance is... In terms of air volume The forced air cooling power is increased to 70W, and the thermal resistance is reduced to 1.1℃ / W. The L-shaped fins combined with a -30° negative rotation angle enhance the interaction between airflow and the heat sink surface; the semi-cylindrical protrusion structure has a significant pressurizing effect, and together with the side wall guide pattern, it can achieve efficient heat dissipation in the compact space of industrial equipment, meeting the heat dissipation requirements of medium power devices.

[0052] In another preferred embodiment, to better illustrate this technical solution, taking a high-power automotive electronic heat sink as an example, the preferred design features a base with XY plane dimensions of 200mm × 80mm and a thickness of 6mm, made of 1070 pure aluminum with a surface micro-arc oxidation treatment and a thickness of 12μm. The bottom is covered with thermally conductive gel, resulting in a thermal conductivity coefficient of... It is fitted to the automotive electronic power module and has sealing grooves around its perimeter. There are 30 vertical heat sinks, each 30mm high and 2.5mm thick, with a 7mm spacing, forming 29 first separation channels, each 7mm wide. The heat sinks are manufactured using an extrusion molding process and connected to the base via friction stir welding, ensuring strong welds. In this embodiment, the optional winglet adopts a trapezoidal structure, extending from the apex of the +Z vector of the heat sink to the XZ surface, with an upper base of 5mm, a lower base of 8mm, a length of 18mm, and a thickness of 1.2mm; the preset negative rotation angle relative to the +X vector is -50°, which is suitable for the higher airflow rate in automotive electronics; the winglet guide groove is 2mm wide and 0.4mm deep, and the baffles on both sides are 1.2mm high, with the baffles near the heat sink being vacuum brazed to the heat sink.

[0053] It should be noted that this specification of radiator measures 200mm × 80mm × 36mm and weighs 1.2kg. It is suitable for high-power automotive electronic devices such as DC / DC converters and on-board chargers in new energy vehicles. When used in conjunction with automotive cooling systems, such as airflow... Coolant flow rate At this time, the heat dissipation power can reach 200W, and the peak temperature of the power module can be reduced by 15-20℃, and the heat uniformity can be improved by 25%. The trapezoidal fin is designed with a negative rotation angle of -50°, which effectively meets the heat exchange demand under high air flow rate; the strong boosting effect of the rectangular block-shaped protruding structure and the wide second separation channel ensure the efficient flow of a large amount of cooling fluid, and the side wall reinforcing rib enhances the reliability of the radiator in the vibration environment of automobile driving.

[0054] The protruding structure is rectangular block-shaped, the Y-direction width is 2.2 times the fin width, i.e. 17.6mm, which maximizes the boosting effect; the X-direction length is one-eighth of the length of the fin, about 25mm; the connection with the fin is inclined at an angle of 60°; the Y-direction width of the second separation channel is 0.4 times the width of the first separation channel, i.e. 2.8mm. The fixed side wall is provided on both sides in the Y-direction, with a height of 30mm and a thickness of 3mm, and is integrally extruded with the base and the fin, and the outer side of the side wall is provided with a reinforcing rib to improve the vibration resistance of the structure.

[0055] The fin structure of the present application increases along the negative rotation angle as the air flow rate increases, ensuring the directional guiding effect of the air flow under different flow rates; the fin length is in the range of 5-20mm, combined with the adjustment of the fin spacing, to avoid air flow blockage; the present application further balances the boosting effect and air flow resistance through the multiple relationship between the width and length of the protruding structure; the second separation channel width multiple is controlled in the range of 0.1-0.5, to realize the secondary distribution of air flow while avoiding excessive pressure loss; on this basis, in order to further strengthen the control of air flow, the fixed side wall is designed to consider the reliability requirements of air flow guiding and installation environment.

[0056] In order to verify the efficiency of the embodiment, Figure 3 A conventional radiator with similar size is shown, which is strategically placed on a 60W heat block along the XY plane to ensure efficient heat conduction. The thermal performance under specific working conditions is simulated by FEA. Air is chosen as the cooling fluid, maintaining room temperature and standard atmospheric pressure, and the flow rate is controlled at 2 m / s. This speed can establish a laminar flow state, reducing turbulence and improving thermal transfer stability. The laminar flow flows in the +X direction, ensuring that the cooling air effectively acts on the surface of the radiator. In addition, fixed side walls are provided on both sides of the radiator, and the heat transfer coefficient is On the one hand, it forms a defined cooling air channel to ensure consistent airflow direction; on the other hand, it prevents cooling fluid leakage to ensure the integrity of the cooling path. This design ensures that air flows uniformly through the fin channels, optimizing the convective heat transfer of the radiator.

[0057] Figure 4 The FEA results show that the temperature distribution of the conventional radiator is uneven, with lower temperature in some areas and significantly higher temperature in some areas, proving that the conventional design cannot achieve the best temperature distribution.Figure 5 The pressure profile shows that the buoyancy effect actually affects the cooling fluid flow, reducing the heat dissipation efficiency and leading to material waste.

[0058] To evaluate the thermal and fluid dynamic performance of the heat sink of the present invention, a detailed FEA was performed under the same conditions as the conventional heat sink. Figure 6 It is shown that the temperature distribution of the heat sink of the present invention is significantly uniform, with a significant improvement compared to the conventional design. The improved fin geometry, especially the winglets provided on the inner surface, effectively enhances the air flow effect and avoids stagnant areas. As a result, the hot spots that occur in the conventional heat sink are almost completely eliminated.

[0059] Quantitative analysis shows that the average operating temperature of the heat sink of the present invention is reduced by about 2.4°C compared to the conventional heat sink. In power electronics applications, this temperature reduction can significantly improve system reliability, prolong the service life of semiconductor devices, and reduce the risk of thermal runaway. In addition, the uniform temperature distribution ensures that there is no local stress concentration, reducing the risk of material fatigue or deformation.

[0060] The FEA also analyzed the air flow pressure profile ( Figure 7 ). The results show that the design of the present invention achieves a more uniform pressure distribution, with a maximum pressure of Although slightly higher than the maximum pressure of the conventional heat sink of 4.297 , the key difference lies in the uniform distribution: the present invention maintains a stable and uniform pressure field within the fin channels, eliminating the disturbance caused by buoyancy and the unnecessary backflow effect, ensuring the stability of the cooling process and achieving consistent convective heat transfer.

[0061] It should be noted that the slight increase in pressure is not a disadvantage, but rather indicates that the air is in more complete contact with the surface of the fins. By effectively guiding the cooling air through the winglets, the heat sink of the present invention maximizes the utilization rate of available air flow, achieving enhanced convective heat transfer without the need to increase fan speed or air flow speed, thereby maintaining system energy efficiency.

[0062] In summary, the FEA results verify the technical advantages of the heat sink of the present invention compared to the conventional rectangular design: lower and more uniform operating temperature, stable and optimized air flow distribution, achieving improved thermal management efficiency and increased material utilization. This embodiment is particularly suitable for high- demand power electronics applications that are sensitive to reliability, efficiency, and cost.

[0063] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only the principles of the present invention. Without departing from the spirit and scope of the present invention, various changes and improvements can be made to the present invention, and these changes and improvements fall within the scope of the claimed present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A heat sink with a fin structure, characterized by, The +Z vector represents the upward direction, and the -Z vector represents the downward direction. The +X vector represents the right direction, and the -X vector represents the left direction; the -Y vector represents the front direction, and the +Y vector represents the rear direction. The heat sink comprises: a base on the XY plane, which supports a plurality of uniformly distributed vertical fins, the fins being located on the YZ plane to form a first separation channel; each fin is equipped with a single fin on the inner surface in the direction of the -Y vector, and the terminal of each fin is provided with a protruding structure in the +X direction.

2. The heat sink with fin structure according to claim 1, wherein the fin extends from the top corner of the fin in the +Z vector direction to the XZ plane, and the fin is rotated at a negative angle relative to the +X vector, and when the forced cooling fluid flows in the +X direction, the fin guides the flow to the base direction; wherein the negative rotation angle is set between -10° and -55° according to different heat sink sizes and air flow rates.

3. The heat sink with fin structure according to claim 2, wherein the fin comprises a flow guide groove and a baffle plate arranged on both sides of the flow guide groove.

4. The heat sink with fin structure according to claim 3, wherein the baffle plate close to the fin side is fixedly attached to the fin.

5. The heat sink with fin structure according to claim 4, wherein the length of the fin is set to be between 5-20 mm according to the fin spacing and air flow requirements.

6. The heat sink with fin structure according to claim 4, wherein the width of the protruding structure in the Y vector direction is 0.2-2.5 times the width of the fin to increase the pressure of the forced cooling fluid.

7. The heat sink with fin structure according to claim 6, wherein the length of the protruding structure in the X vector direction is between one-sixth and one-eighth of the length of the fin.

8. The heat sink with fin structure according to claim 7, wherein the second separation channel is formed between the protruding structures, and the width of the second separation channel in the Y vector direction is between 0.1-0.5 times the width of the first separation channel.

9. The heat sink with fin structure according to claim 8, wherein the connection between the protruding structure and the fin is at an inclined angle.

10. The heat sink with fin structure according to any one of claims 1-9, wherein fixed side walls are provided on both sides of the heat sink in the Y vector direction; the fin is provided in the form of a rectangular sheet, a trapezoidal structure, or an L-shaped structure.

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