Stacked photo-plethysmography sensor package formed in free curved surface

Abstract

This stacked photo-plethysmography sensor package formed in a free curved surface can form a light-emitting unit and a light-receiving unit in a free curved surface shape to be applied to the miniaturization and thinning of an electronic device, and improve the positional relationship between a light-emitting element and a light-receiving element to improve the accuracy of photo-plethysmography. The stacked photo-plethysmography sensor can improve the accuracy of photo-plethysmography by improving the positional relationship between the light-emitting element and the light-receiving element. The stacked photo-plethysmography sensor according to the present invention improves the positional relationship between the light-emitting element and the light-receiving element to improve the light receiving effect, thereby greatly improving the accuracy of plethysmography. The present invention can be processed in various forms by using a flexible film, thereby having the effect of obtaining an accurate measurement result while minimizing wearing inconvenience for a user.

Description

Free-formed laminated photoplethysmography sensor package

[0001] The present invention relates to a laminated photoplethysmography sensor, and more particularly, to a laminated photoplethysmography sensor package formed as a free-form surface in which a light-emitting part and a light-receiving part are formed as a free-form surface in a curved shape, so that the sensor can be applied to miniaturization and thinning of electronic devices, and the positional relationship between the light-emitting element and the light-receiving element is improved, thereby improving the accuracy of photoplethysmography.

[0002] Photoplethysmography sensors are widely known as sensors that measure blood flow using light. Typically, photoplethysmography illuminates the skin or blood vessels and measures the intensity and distribution of the light reflected from the skin or blood vessels to determine blood flow.

[0003] Conventional photoplethysmography sensors typically have a single-layer, planar structure, with the light-emitting element and photodetector positioned on the same plane. However, this structure can result in measurement accuracy that varies depending on the installation location and target, and in some cases, can lead to inaccurate measurement results. Furthermore, crosstalk between the light-emitting element and photodetector can generate noise, lowering measurement accuracy.

[0004] Recently, with the miniaturization and thinning of hand health electronic devices or wearable electronic devices equipped with photoplethysmography sensors, photoplethysmography sensors are also required to be formed in a curved shape and miniaturized.

[0005] Accordingly, as the light-emitting and light-receiving portions of the photoplethysmography sensor are formed in a curved shape, the demand for a configuration and technology that can improve measurement accuracy is increasing.

[0006] The present invention aims to provide a laminated photoplethysmography sensor package formed as a free-form surface, which can be applied to miniaturization and thinning of electronic devices by forming a light-emitting unit and a light-receiving unit as a free-form surface in a curved shape, and which improves the positional relationship between the light-emitting element and the light-receiving element to enhance the accuracy of photoplethysmography.

[0007] The present invention aims to provide a laminated photoplethysmography sensor package that uses a flexible film to increase the flexibility of the sensor and to make it suitable for application targets of various shapes and sizes.

[0008] In order to achieve the above purpose, a laminated photoplethysmography sensor package formed as a free-form surface according to the features of the present invention is provided.

[0009] A support that forms a free-form surface on one side;

[0010] A light receiving unit located on the upper part of one side of the support unit and formed as a free curved surface corresponding to the curved shape of one side of the support unit;

[0011] A light-transmitting adhesive layer positioned on the upper portion of the light-receiving portion;

[0012] A light emitting portion laminated on top of the light receiving portion with the light-transmitting adhesive layer in between, and formed into a free curve corresponding to the curved shape of the light receiving portion;

[0013] a cover window covering the above light-emitting portion; and

[0014] Including a substrate electrically connected to the light-receiving unit and the light-emitting unit,

[0015] The above cover window,

[0016] A cover portion positioned above the light-emitting portion and formed as a free-form surface corresponding to the curved shape of the light-emitting portion; and

[0017] Including a side portion extending downward from the above cover portion,

[0018] The substrate extends into the space between the support and the cover window.

[0019] It further includes an adhesive film positioned between the light-emitting portion and the cover window.

[0020]

[0021] It further includes a cushion layer formed of a flexible material and positioned between the support and the light receiving portion.

[0022] The light-receiving portion includes one or more first lead wires transmitting an electrical signal, the light-emitting portion includes one or more second lead wires transmitting an electrical signal, and the substrate includes a connecting portion coupled to the first and second lead wires between a side portion of the cover window of the support portion and a side portion of the support portion; and an extension portion extending from the connecting portion to the outside of the cover window.

[0023] The substrate further includes a signal processing unit mounted on the extension unit and processing a signal received from the light receiving unit.

[0024] By the above-described configuration, the present invention has the effect of forming a light emitting unit and a light receiving unit in a curved free-form surface in a laminated photoplethysmography sensor package, thereby enabling application to miniaturization and thinning of electronic devices.

[0025] The present invention improves the positional relationship between the light-emitting element and the light-receiving element, thereby enhancing the light-receiving effect and greatly improving the accuracy of blood flow measurement.

[0026] The present invention can be processed into various shapes using a flexible film, thereby minimizing discomfort to the user while obtaining accurate measurement results.

[0027] FIG. 1 and FIG. 2 are drawings showing the external appearance of a laminated photoplethysmography sensor package formed as a free-form surface according to an embodiment of the present invention.

[0028] FIG. 3 is a drawing showing an exploded view of a laminated photoplethysmography sensor package formed as a free-form surface according to an embodiment of the present invention.

[0029] FIG. 4 is a drawing showing the configuration of a laminated photoplethysmography sensor package with a separated cover window according to an embodiment of the present invention.

[0030] FIG. 5 is an enlarged view showing a cushion layer, a light-receiving portion, a light-transmitting adhesive layer, a light-emitting portion, and an adhesive film according to an embodiment of the present invention.

[0031] Fig. 6 is a drawing showing an enlarged view of a support according to an embodiment of the present invention.

[0032] Figure 7 is a drawing showing an enlarged view of a substrate according to an embodiment of the present invention.

[0033] FIG. 8 is a drawing showing a cushion layer according to an embodiment of the present invention formed so as not to cover an outer portion of one side of a support portion facing a portion where a first lead line extends from a light-receiving portion.

[0034] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Regardless of the drawing reference numerals, identical or similar components will be assigned the same reference numerals, and redundant descriptions thereof will be omitted. Furthermore, when describing embodiments disclosed in this specification, if a detailed description of a related known technology is judged to obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted.

[0035] Terms that include ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms are used solely to distinguish one component from another.

[0036] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0037] In this application, each step described may be performed regardless of the listed order, except in cases where a special causal relationship requires that the steps be performed in the listed order.

[0038] In this application, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0039]

[0040] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0041] FIG. 1 and FIG. 2 are drawings showing the external appearance of a laminated photoplethysmography sensor package formed as a free-form surface according to an embodiment of the present invention.

[0042] A laminated photoplethysmography sensor package (100) formed as a free-form surface according to an embodiment of the present invention includes a support portion (110), a light-receiving portion (120), a light-transmitting adhesive layer (130), a light-emitting portion (140), a cover window (150), and a substrate (160).

[0043] A free-form surface is formed on one side of the support member (110). The support member (110) provides a support function for other components. A light receiving member (120) is positioned on the upper side of one side of the support member (110).

[0044] The light receiving portion (120) is formed as a free curved surface and is aligned with the curved shape of the support portion (110).

[0045] A light-transmitting adhesive layer (130) is formed on the upper portion of the light-receiving portion (120). Through this configuration, the light-emitting portion (140) can be laminated on the upper portion of the light-receiving portion (120). The light-emitting portion (140) is formed as a free-form surface following the curved shape of the light-receiving portion (120). A cover window (150) is positioned on the upper portion of the light-emitting portion (140).

[0046] This cover window (150) protects the light emitting portion (140) and is formed as a free curved surface to match the curved shape of the light emitting portion (140).

[0047] The substrate serves to electrically connect the light-receiving portion (120) and the light-emitting portion (140).

[0048] Hereinafter, each component included in the laminated photoplethysmography sensor package (100) of the present invention will be described in detail.

[0049] FIG. 3 is an exploded view of a stacked photoplethysmography sensor package formed as a free-form surface according to an embodiment of the present invention, FIG. 4 is a view showing the configuration of a stacked photoplethysmography sensor package with a cover window separated according to an embodiment of the present invention, FIG. 5 is an enlarged view of a cushion layer, a light-receiving unit, a light-transmitting adhesive layer, a light-emitting unit, and an adhesive film according to an embodiment of the present invention, FIG. 6 is an enlarged view of a support unit according to an embodiment of the present invention, FIG. 7 is an enlarged view of a substrate according to an embodiment of the present invention, and FIG. 8 is a view showing a cushion layer according to an embodiment of the present invention formed so as not to cover an outer portion of one surface of the support unit opposite to a portion where a first lead line extends from the light-receiving unit.

[0050] As shown in FIGS. 3 and 6, the support (110) is one of the basic components of the laminated photoplethysmography sensor package (100).

[0051] The support member (110) can form a free-form surface on one side. This surface shape can be adjusted according to various applications and purposes.

[0052] A light receiving portion (120) is positioned on one side of the support portion (110). The shape of the light receiving portion (120) can be formed as a free curved surface to match the curved shape of the support portion (110).

[0053] The other side of the support (110), i.e. the other side, can be coupled with a signal processing unit (163), and this side faces in the opposite direction to one side of the support (110).

[0054] The support member (110) serves to support and protect other components in a fixed position.

[0055] The support member (110) forms a free-form surface on one side in a roughly hexahedral shape, forms a side surface extending downward from the upper surface, and forms a second border surface (111) extending outward along the border from the lower side on the side surface of the support member (110).

[0056] The second edge surface (111) can be combined with at least a portion of the first edge surface of the cover window (150).

[0057] The support member (110) can be formed of various materials, and among them, a material that is both strong and flexible can be selected.

[0058] The second border surface (111) forms a passage (112) through which the substrate (160) passes.

[0059] The second border surface (111) is the side of the support (110) that faces the substrate (160).

[0060] The shape of the support member (110) may be formed into a curved surface, a flat surface, or various other shapes. The specific shape may be determined according to the application field or design conditions.

[0061] As illustrated in FIGS. 3 and 8, a cushion layer (113) formed of a flexible material may be positioned between the support member (110) and the light receiving member (120). This cushion layer (113) may be formed so as not to cover an outer portion of one surface of the support member (110) that faces the portion from which the first lead line extends from the light receiving member (120).

[0062] In other words, the cushion layer (113) can be formed so that the length of the cushion layer (113) is shorter than the length of the upper surface of the support part (110) so that the first lead wire of the light receiving part (120) does not come into contact with it.

[0063] As shown in FIGS. 3 and 5, the light receiving unit (120) is located at the bottom of the stacked photoplethysmography sensor package (100), and the light emitted by the light emitting unit (140) can be measured and converted into an electrical signal by reflecting the reflected light reflected by the measurement unit.

[0064] The light receiving unit (120) includes a light receiving unit film (121) and a light receiving element formed on the light receiving unit film (121).

[0065] The light receiving portion (120) is located on the upper side of one side of the support portion (110) and can be formed as a free curved surface corresponding to the curved shape of one side of the support portion (110).

[0066] The light-receiving film (121) may be formed of a flexible film. The light-receiving film (121) may be formed of a material that is transparent and can be deformed by an external force, such as a PET film.

[0067] The photodetector can be formed using elements such as organic photodiodes (OPDs). Technology has been developed for OPDs to detect objects even under strong light. OPDs are optical sensors that convert light energy into electrical energy to detect color and brightness.

[0068] Specifically, the light-receiving element can be formed by being deposited on the upper or lower surface of the light-receiving film (121). The light-receiving element can be formed of an organic element so that durability can be maintained even if the light-receiving film (121) is bent by an external force.

[0069] The light receiving element may include an internal light receiving element (122) and an external light receiving element (123).

[0070] The internal light-receiving element (122) may be formed to be surrounded by an external light-receiving element (123). Specifically, the internal light-receiving element (122) may be formed in a square or circular shape, and the external light-receiving element (123) may be formed to surround the internal light-receiving element (122).

[0071] The external light receiving element (123) may be formed in a form in which an opening is formed inside and the internal light receiving element (122) is accommodated in the opening. Specifically, the external light receiving element (123) may be formed in a frame shape.

[0072] The light-transmitting adhesive layer (130) is positioned on top of the light-receiving portion (120). The light-transmitting adhesive layer (130) primarily has a function of transmitting light, and may be, for example, OCA (Optical Clear Adhesive). The light emitted from the light-emitting portion (140) is irradiated to the measurement portion (skin, etc.) and then reflected, and the reflected light passes through the light-transmitting adhesive layer (130) and is irradiated to the light-receiving portion (120).

[0073] The thickness of the light-transmitting adhesive layer (130) is greater than the thickness of the light-receiving portion (120), but less than the combined thickness of the light-receiving portion (120) and the light-emitting portion (140). This may be a design consideration to improve the performance and efficiency of the sensor.

[0074] The thickness of the light-transmitting adhesive layer (130) is 40 μm, the thickness of the light-receiving portion (120) is 25 μm, and the thickness of the light-emitting portion (140) is 20 μm.

[0075] As shown in FIGS. 3 and 5, the light emitting portion (140) is laminated on top of the light receiving portion (120) with a light-transmitting adhesive layer (130) interposed therebetween, and can be formed into a free curved surface corresponding to the curved shape of the light receiving portion (120).

[0076] The light-emitting part (140) is composed of a light-emitting part film (141) formed of a flexible film and a light-emitting element (142) formed on the film (141). The light-emitting element (142) serves to emit light.

[0077] The light-emitting film (141) is flexible and can be bent by an external force, and can also form a free-form surface in a curved shape. The light-receiving film (121) can be formed of a material that is light-transmitting and can be deformed by an external force, such as, for example, a PET film. In particular, since the light-emitting film (141) is positioned on the upper portion of the light-receiving portion (120), it is necessary to have a light-transmittance level higher than a predetermined level.

[0078] The light-emitting element (142) is positioned between the internal light-receiving element (122) and the external light-receiving element (123) when viewed from the top of the light-emitting portion (140). In particular, the light-emitting element (142) can be formed in a frame shape and includes a hollow portion that penetrates forward and backward.

[0079] Some forms of the light-emitting portion (140) may include a partition wall made of a light-shielding material, which extends vertically from the light-emitting portion film (141). Additionally, the partition wall may be partially inserted into a groove formed in the light-emitting portion film (141).

[0080] The partition wall is formed along both edges of the light emitting element (142), and can be formed by being inserted into the groove of the light emitting film (141) and extending vertically from the light emitting film (141) to a certain height.

[0081] The light-emitting element (142) can improve the light-receiving effect by minimizing light scattering due to the partition wall.

[0082] An adhesive film (144) may be positioned between the light emitting portion (140) and the cover window (150).

[0083] The adhesive film (144) helps to increase the stability and durability of the laminated photoplethysmography sensor package (100).

[0084] The stacked photoplethysmography sensor package (100) can improve the accuracy of photoplethysmography by improving the positional relationship between the light-emitting element (122) and the light-receiving element (122, 123) by positioning the light-emitting element (142) higher than the light-receiving element (122, 123).

[0085] The light-receiving portion (120) and the light-emitting portion (140) are each formed using a flexible film as a support base. The flexible film is made of a light-transmitting material, such as PET, and can be bent or curved by an external force.

[0086] The light-receiving portion (120) and the light-emitting portion (140) are formed of a transparent organic insulator or an inorganic insulator, and the organic insulator may include polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), etc.

[0087] The light-receiving unit (120) includes a light-receiving unit film (121) formed of a flexible film. An internal light-receiving element (122) and an external light-receiving element (123) are formed on the light-receiving unit film (121). The internal light-receiving element (122) has, for example, a rectangular shape, and the external light-receiving element (123) is positioned to surround the internal light-receiving element (122).

[0088] The light-emitting portion (140) includes a light-emitting portion film (121) formed of a flexible film, and a light-emitting element (122) is formed on the film (121). The light-emitting element (122) is positioned between the internal light-receiving element (122) and the external light-receiving element (123) when viewed from the top of the light-receiving portion film (121).

[0089] The external light-receiving element (123) is formed in a form that surrounds the internal light-receiving element (122), and can be formed in the shape of a frame, specifically. This frame includes a hollow portion in the center, and the internal light-receiving element (122) can be accommodated in this hollow portion.

[0090] The light-emitting element (122) can be formed in a frame shape, and the hollow portion in the center accommodates the internal light-receiving element (122). The external light-receiving element (123) formed in this way includes a frame-shaped hollow portion that surrounds both the light-emitting element (122) and the internal light-receiving element (122).

[0091] The light-emitting element (122) and the internal light-receiving element (122) and the external light-receiving element (123) are positioned spaced apart from each other. The degree of separation between the light-emitting element (122) and the internal light-receiving element (122) and the external light-receiving element (123) can be adjusted at a certain level for optical interference and measurement accuracy of the sensor. Specifically, the degree of separation between the light-emitting element (122) and the internal light-receiving element (122) and the external light-receiving element (123) can be determined between 0.3 times and 0.6 times the width of the light-emitting element (122) and the internal light-receiving element (122) and the external light-receiving element (123).

[0092] The distance between the light-emitting element (122) and the internal light-receiving element (122) and the external light-receiving element (123) is 0.2 mm, the width of the light-emitting element (122) is 0.4 mm, the length of one side of the internal light-receiving element (122) is 2 mm, the length of one side of the light-emitting element (122) is 3.6 mm, and the length of one side of the external light-receiving element (123) is 4.7 mm.

[0093] The light receiving unit (120) includes one or more first lead wires (124) that transmit electrical signals.

[0094] The light emitting portion (140) includes one or more second lead wires (143) that transmit electrical signals.

[0095] The cover window (150) is formed of a light-transmitting material and is positioned above the light-emitting portion (140), and can form a free-form surface on one side corresponding to the curved shapes of the light-receiving portion (120) and the light-emitting portion (140).

[0096] As shown in FIG. 3, the cover window (150) includes a cover portion (151), a side portion (152), and a first border surface (153).

[0097] The cover part (151) is located on the upper part of the light emitting part (140) and can be formed into a free curved surface corresponding to the curved shape of the light emitting part (140).

[0098] The side portion (152) can extend downward from the cover portion (151).

[0099] The substrate (160) can extend into the space between the support (110) and the cover window (150).

[0100] As illustrated in FIG. 7, the substrate (160) includes a connecting portion (161) that is connected to the first lead wire (124) and the second lead wire (143) between the side portion (152) of the cover window (150) of the support portion (110) and the side portion of the support portion (110), and an extension portion (162) that extends from the connecting portion (161) to the outside of the cover window (150) and is connected to the lower surface of the support portion (110).

[0101] The substrate (160) is mounted on the extension portion (162) and further includes a signal processing portion (163) that processes a signal received from the light receiving portion (120).

[0102] The signal processing unit (163) receives a PPG signal from the first lead wire (124) of the light receiving unit (120) and measures the intensity or distribution of light reflected from the skin or blood vessels to calculate the amount of blood flow.

[0103] The signal processing unit (163) can transmit a power supply signal to the light emitting unit (140) through the second lead wire (143).

[0104] The part of the extension (162) where the signal processing unit (163) is mounted is connected to the other surface of the support unit (110). The other surface of the support unit (110) may be a surface facing one surface of the support unit (110).

[0105] The substrate (160) is a flexible printed circuit board (FPCB), and the extension portion (162) extends from the connection portion (161) to a certain length, is bent 180 degrees, and is joined to the other surface of the support portion (110). The other surface of the support portion (110) may be a surface facing one surface of the support portion (110).

[0106] The passageway (112) of the support (110) may have an extension (162) portion where one side of the second edge surface (111) is opened and bent 180 degrees, and a connection portion (161) may be located.

[0107] The passage (112) is formed by opening one side of the second edge surface (111) so that one side of the substrate (160) is formed in a part that extends beyond the second edge surface (111).

[0108] At least a portion of the first edge surface (153) is secured to and joined to the upper surface of the second edge surface (111), and a waterproof connection can be formed between the first edge surface (153) and the second edge surface (111).

[0109]

[0110] Hereinafter, embodiments of the laminated photoplethysmography sensor package formed as a free-form surface of the present invention have been described. The technical features disclosed in each embodiment of the present invention are not limited to that embodiment, and, unless mutually incompatible, the technical features disclosed in each embodiment may be combined and applied to other embodiments.

[0111] Therefore, although each embodiment focuses on its own technical features, each technical feature can be applied in combination with each other as long as they are not mutually incompatible.

[0112] The present invention is not limited to the above-described embodiments and the attached drawings, and various modifications and variations are possible within the scope of those skilled in the art. Therefore, the scope of the present invention should be defined not only by the claims of this specification but also by equivalents thereof.

Claims

1. A support that forms a free curved surface on one side; A light receiving unit located on the upper part of one side of the support unit and formed as a free curved surface corresponding to the curved shape of one side of the support unit; A light-transmitting adhesive layer positioned on the upper portion of the light-receiving portion; A light emitting portion laminated on top of the light receiving portion with the light-transmitting adhesive layer in between, and formed into a free curve corresponding to the curved shape of the light receiving portion; a cover window covering the above light-emitting portion; and Including a substrate electrically connected to the light-receiving unit and the light-emitting unit, The above cover window, A cover portion positioned above the light-emitting portion and formed as a free-form surface corresponding to the curved shape of the light-emitting portion; and Including a side portion extending downward from the above cover portion, The substrate extends into the space between the support and the cover window. A laminated photoplethysmography sensor package formed as a free-form surface.

2. In paragraph 1, Further comprising an adhesive film positioned between the light emitting portion and the cover window. A laminated photoplethysmography sensor package formed as a free-form surface.

3. In paragraph 1, Further comprising a cushion layer formed of a flexible material and positioned between the support member and the light receiving member. A laminated photoplethysmography sensor package formed as a free-form surface.

4. In paragraph 1, The above light-receiving unit includes one or more first lead wires transmitting an electrical signal, The light emitting portion includes one or more second lead wires for transmitting an electrical signal, The above substrate is, A connecting portion connected to the first and second lead wires between the side portion of the cover window of the support portion and the side portion of the support portion; and Including an extension extending from the above connecting portion to the outside of the cover window; A laminated photoplethysmography sensor package formed as a free-form surface.

5. In paragraph 4, The above substrate is, It is mounted on the extension portion and further includes a signal processing portion that processes a signal received from the light receiving portion. A laminated photoplethysmography sensor package formed as a free-form surface.

6. In paragraph 5, Among the above extensions, the part where the signal processing unit is mounted is connected to the other side of the support part—the other side of the support part is a surface facing one side of the support part. A laminated photoplethysmography sensor package formed as a free-form surface.

7. In paragraph 4, The above substrate is a flexible printed circuit board (FPCB), The above extension extends from the above connecting portion to a certain length, is bent 180 degrees, and is joined to the other side of the support portion, which is a side facing one side of the support portion. A laminated photoplethysmography sensor package formed as a free-form surface.

8. In paragraph 4, Further comprising a cushion layer formed of a flexible material and positioned between the support member and the light receiving member, The above cushion layer is formed so as not to cover the outer portion of one side of the support portion opposite to the portion where the first lead line extends from the light receiving portion. A laminated photoplethysmography sensor package formed as a free-form surface.

9. In paragraph 1, One side of the above support and the above cover are formed as free-form surfaces of the same shape. A laminated photoplethysmography sensor package formed as a free-form surface.

10. In paragraph 1, The above cover window, Further comprising a first border surface extending outward from the lower end of the above side portion, The above support part, A second edge surface extending outward from the lower end of the side surface of the support portion and coupled to at least a portion of the first edge surface. A laminated photoplethysmography sensor package formed as a free-form surface.

11. In paragraph 10, The above second border surface forms a passage through which the substrate passes. A laminated photoplethysmography sensor package formed as a free-form surface.

12. In paragraph 11, The above passageway, One side of the second edge surface is opened so that one side of the substrate is formed in a part that extends beyond the second edge surface. A laminated photoplethysmography sensor package formed as a free-form surface.

13. In paragraph 1, At least a portion of the first edge surface is secured to and joined to the upper surface of the second edge surface, The first edge surface and the second edge surface are waterproof bonded. A laminated photoplethysmography sensor package formed as a free-form surface.

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