Multilayer backing layer structure, method of manufacture and medical ultrasound probe

Abstract

The application relates to the technical field of medical ultrasonic probes, in particular to a multilayer backing layer structure, a preparation method and a medical ultrasonic probe. The multilayer backing layer structure comprises a foam base layer, the foam base layer is composed of PMI foam, and the upper surface of the foam base layer is concave-convex; an epoxy resin layer, the epoxy resin layer is composed of a first epoxy resin mixture, and the epoxy resin layer is bonded to the upper surface of the foam base layer; and a sound transmission layer, the sound transmission layer is composed of a second epoxy resin mixture, and the sound transmission layer covers the epoxy resin layer. Under the action of the sound transmission layer, the transmission of ultrasonic waves is greater than the reflection, as many ultrasonic waves as possible enter the epoxy resin layer, and noise is avoided from being reflected back to the piezoelectric layer. When the ultrasonic waves pass through the epoxy resin mixture, the mechanical energy of the ultrasonic waves is converted into heat energy, so that the effect of sound attenuation is achieved.

Description

Technical Field

[0001] This invention relates to the field of medical ultrasound probe technology, specifically to a multi-layer backing structure, its preparation method, and a medical ultrasound probe. Background Technology

[0002] Medical ultrasound probes typically consist of a lens, a matching layer, a piezoelectric transducer, and a backing layer. The piezoelectric transducer serves to both transmit and receive ultrasound signals. It propagates ultrasound waves not only forward but also backward. Generally, the ultrasound waves propagated backward can cause signal noise, affecting the performance of the ultrasound probe. Therefore, a backing layer is usually placed behind the piezoelectric transducer to absorb the ultrasound waves propagated backward and reduce noise.

[0003] Current backing layers mostly use epoxy resin as the matrix, with metal powder, inorganic fillers, and rubber as fillers, which are physically mixed to obtain a uniform single-layer structure. This uniform single-layer backing layer has a uniform overall density and equal sound attenuation at every point. The mechanical energy of the ultrasound waves is converted into heat energy through the scattering effect of the tiny fillers and the viscous effect between the resin and rubber, thus achieving sound attenuation.

[0004] However, a uniform single-layer backing layer requires a large amount of filler to meet the design requirements for acoustic impedance and attenuation, inevitably resulting in a heavier and thicker backing layer. The uniform single-layer backing layer also has a low acoustic attenuation coefficient, leading to significant ultrasonic wave reflection, which can negatively impact medical ultrasound probes. Summary of the Invention

[0005] In view of this, the present invention provides a multi-layer backing structure, a preparation method, and a medical ultrasound probe to solve the problems of heavy mass and low sound attenuation coefficient of uniform single-layer backing structures.

[0006] In a first aspect, the present invention provides a multilayer backing structure, the multilayer backing structure comprising:

[0007] A foam base layer, wherein the foam base layer is composed of PMI foam and the upper surface of the foam base layer is uneven;

[0008] An epoxy resin layer, the epoxy resin layer being composed of a first epoxy resin mixture, and the epoxy resin layer being bonded to the upper surface of the foam base layer;

[0009] A sound-permeable layer, the sound-permeable layer being composed of a second epoxy resin mixture, and the sound-permeable layer covering the epoxy resin layer.

[0010] Beneficial effects: During ultrasonic wave transmission, when the ultrasound waves reach the acoustic layer, the transmission rate exceeds the reflection rate due to the acoustic layer's effect. This allows the ultrasound waves to penetrate the epoxy resin layer as much as possible, preventing reflection back to the piezoelectric layer and thus avoiding noise. After passing through the acoustic layer, the ultrasound waves continue to propagate through the epoxy resin mixture. Due to the scattering effect of the tiny fillers and the viscosity between the resin and rubber, the mechanical energy of the ultrasound waves is converted into heat energy, achieving sound attenuation. Furthermore, the porous structure of PMI foam not only reduces the overall mass of the backing layer but also causes continuous scattering of ultrasound waves within it, resulting in sound attenuation. Additionally, the difference in acoustic impedance between PMI foam and the epoxy resin mixture also causes some reflection. Therefore, this method solves the problem of heavy backing layers and low sound attenuation coefficients in uniform single-layer structures.

[0011] In one alternative embodiment, the multilayer backing structure further includes:

[0012] A reflective layer for reflecting ultrasonic waves passing through the foam base layer and the epoxy resin layer, the reflective layer covering the lower surface of the foam base layer and being composed of metal foil.

[0013] Beneficial effects: The reflective layer primarily reflects unabsorbed ultrasonic waves, while also possessing a high sound attenuation coefficient. This allows the reflected ultrasonic waves to be continuously scattered within the PMI foam, resulting in sound attenuation. Furthermore, upon passing through the epoxy resin mixture, the mechanical energy of the ultrasonic waves is converted back into heat energy, further attenuating the sound.

[0014] In one alternative embodiment, the metal foil comprises copper foil or aluminum foil.

[0015] In one alternative embodiment, the surface of the foam base layer has a serrated texture.

[0016] Beneficial effects: By setting the uneven surface of the foam base layer to a specific sawtooth structure, compared with other uneven structures, the reflection path of ultrasonic waves can be deflected, increasing the propagation path, thereby further achieving the effect of sound attenuation.

[0017] In one alternative embodiment, the acoustic layer is used to allow ultrasonic waves to be transmitted into the epoxy resin layer and the foam base layer, the foam base layer and the epoxy resin layer respectively being used to attenuate the transmitted ultrasonic waves.

[0018] The first epoxy resin mixture includes at least epoxy resin, rubber, and metal powder, and the second epoxy resin mixture includes at least epoxy resin, ceramic sheet, and polyamide.

[0019] Beneficial effects: During the transmission of ultrasound, since the acoustic impedance of the sound-transmitting layer is similar to that of the piezoelectric vibrator, when the ultrasound is transmitted to the sound-transmitting layer, the transmission of ultrasound is greater than the reflection. As much of the ultrasound will enter the epoxy resin layer as possible, it will avoid being reflected back to the piezoelectric layer and forming noise.

[0020] Secondly, the present invention also provides a method for preparing a multilayer backing structure as described in any of the above embodiments, the method comprising:

[0021] PMI foam is poured into a pre-made mold and the PMI foam is subjected to a first curing operation to form a foam base layer, wherein the upper surface of the foam base layer is uneven.

[0022] A first epoxy resin mixture is poured into the upper surface of the foam base layer, and a second curing operation is performed on the first epoxy resin mixture to form the epoxy resin layer and make the epoxy resin layer adhere to the upper surface of the foam base layer.

[0023] A third curing operation is performed on the upper surface of the acoustic layer and the epoxy resin layer, wherein the upper surface of the epoxy resin layer is the side away from the upper surface of the foam base layer.

[0024] In an optional implementation, the method further includes:

[0025] The third curing operation is performed on the lower surface of the reflective layer and the foam base layer, wherein the reflective layer is used to reflect ultrasonic waves passing through the foam base layer and the epoxy resin layer, and the reflective layer is composed of a metal foil, including copper foil or aluminum foil.

[0026] In an optional embodiment, prior to the second curing operation on the first epoxy resin mixture, the method further includes:

[0027] The first epoxy resin mixture poured onto the uneven upper surface of the foam base layer is subjected to degassing treatment to obtain the treated first epoxy resin mixture; wherein the unevenness of the upper surface of the foam base layer is serrated.

[0028] In one optional embodiment, the second curing operation on the first epoxy resin mixture includes:

[0029] A second curing operation is performed on the treated first epoxy resin mixture.

[0030] Thirdly, the present invention also provides a medical ultrasound probe, which is composed of a lens, a matching layer, a piezoelectric vibrator and the aforementioned multilayer backing structure. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the backing layer structure in an embodiment of the present invention;

[0033] Figure 2 A schematic diagram illustrating the effect of PMI sawtooth foam;

[0034] Figure 3 This is a schematic diagram of the fabrication process of a multilayer backing structure;

[0035] Figure 4 This is a schematic diagram of the overall process for preparing a multilayer backing structure.

[0036] Figure 5 This is a schematic diagram of the process for preparing a multilayer backing structure, after refining step S3. Detailed Implementation

[0037] 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 embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Medical ultrasound probes typically consist of a lens, a matching layer, a piezoelectric transducer, and a backing layer. The piezoelectric transducer serves to both transmit and receive ultrasound signals. It propagates ultrasound waves not only forward but also backward. Generally, the ultrasound waves propagated backward can cause signal noise, affecting the performance of the ultrasound probe. Therefore, a backing layer is usually placed behind the piezoelectric transducer to absorb the ultrasound waves propagated backward and reduce noise.

[0042] Current backing layers are mostly made of epoxy resin as the matrix, with metal powder, inorganic fillers and rubber as fillers, and a uniform single-layer structure is obtained through physical mixing.

[0043] The backing layer has a uniform single-layer structure with uniform overall density and equal sound attenuation at every point.

[0044] The mechanical energy of ultrasound is converted into heat energy through the scattering effect of microfillers and the viscous effect between resin and rubber, thereby achieving the effect of sound attenuation.

[0045] In terms of materials, a uniform single-layer backing layer requires a large amount of filler to meet design requirements for acoustic impedance and attenuation, inevitably resulting in a heavier and thicker backing layer. In terms of manufacturing processes, the excessive filler during the mixing and molding of a uniform single-layer structure leads to a sharp increase in viscosity, which is detrimental to molding. Structurally, the lack of sound-transmitting material on the surface of the uniform single-layer backing layer results in a significant difference in acoustic impedance between the backing layer and the piezoelectric vibrator, leading to considerable ultrasonic wave reflection. Based on these drawbacks, a multi-layer, multi-functional backing layer structure needs to be designed to replace the uniform single-layer structure to meet the requirements of high-performance ultrasonic probes.

[0046] The following is combined Figures 1 to 2 The following describes embodiments of the present invention.

[0047] According to an embodiment of the present invention, in one aspect, the present invention provides a multi-layer backing structure, the multi-layer backing structure comprising: a foam base layer, an epoxy resin layer, and a sound-permeable layer.

[0048] Specifically, the foam base layer is composed of PMI foam, and the upper surface of the foam base layer is uneven. For example, the unevenness can be a wavy structure, a spherical protrusion or spherical groove structure, a rectangular depression or rectangular protrusion, a hemispherical depression or hemispherical protrusion, or other types of structures. Of course, this embodiment is merely an example of specific types of unevenness, but it is not a limitation. Those skilled in the art can make changes according to actual conditions, as long as the same technical effect is achieved.

[0049] Furthermore, in this embodiment of the invention, the epoxy resin layer is composed of a first epoxy resin mixture, and the epoxy resin layer is bonded to the upper surface of the foam base layer. The first epoxy resin mixture can be composed of epoxy resin, rubber, and other substances, or it can be composed of epoxy resin, metal powder, and other substances. Those skilled in the art can modify the weight ratios of the various substances according to actual conditions; this embodiment does not limit this, as long as the same technical effect is achieved.

[0050] Furthermore, in this embodiment of the invention, the sound-permeable layer is composed of a second epoxy resin mixture, and the sound-permeable layer covers the epoxy resin layer, that is, the sound-permeable layer covers the upper surface of the epoxy resin layer. The second epoxy resin mixture can be composed of epoxy resin, ceramic sheets, and other substances, or it can be composed of epoxy resin, polyamide, and other substances. Similarly, those skilled in the art can change the weight ratio between the various substances according to the actual situation, and this embodiment does not limit this, as long as the same technical effect is achieved.

[0051] With this configuration, during ultrasonic wave transmission, when the ultrasound reaches the sound-permeable layer, the transmission rate exceeds the reflection rate due to the layer's effect. This allows the ultrasound to penetrate the epoxy resin layer as much as possible, preventing reflection back to the piezoelectric layer and thus avoiding noise. After passing through the sound-permeable layer, the ultrasound continues its transmission through the epoxy resin mixture. Due to the scattering effect of the tiny fillers and the viscosity between the resin and rubber, the mechanical energy of the ultrasound is converted into heat energy, achieving sound attenuation. Furthermore, the porous structure of PMI foam not only reduces the overall mass of the backing layer but also causes continuous scattering of ultrasound within it, resulting in sound attenuation. Additionally, the difference in acoustic impedance between the PMI foam and the epoxy resin mixture also causes some reflection. Therefore, this design effectively solves the problem of heavy, low-attenuation coefficients in uniform single-layer backing layers.

[0052] Furthermore, in an optional embodiment, the multilayer backing structure further includes a reflective layer for reflecting ultrasonic waves passing through the foam base layer and the epoxy resin layer. The reflective layer covers the lower surface of the foam base layer and is composed of metal foil.

[0053] Of course, this embodiment is merely an example of the type of reflective layer, but it is not intended to limit it. Those skilled in the art can make changes according to the actual situation, such as using other methods that can achieve the same technical effect.

[0054] With this configuration, the reflective layer primarily functions to reflect unabsorbed ultrasonic waves, while also possessing a high sound attenuation coefficient. This allows the reflected ultrasonic waves to be continuously scattered within the PMI foam, resulting in sound attenuation. Furthermore, upon passing through the epoxy resin mixture, the mechanical energy of the ultrasonic waves is converted back into heat energy, further attenuating the sound.

[0055] Furthermore, in an alternative embodiment, the metal foil includes copper foil or aluminum foil.

[0056] Furthermore, in an optional embodiment, the surface of the foam base layer has a serrated texture.

[0057] This design, which sets the surface of the foam base layer to a serrated structure, deflects the ultrasonic wave reflection path compared to other serrated structures, increasing the propagation path and thus further achieving the effect of sound attenuation.

[0058] Furthermore, in an optional embodiment, the acoustically transparent layer is used to allow ultrasonic waves to be transmitted into the epoxy resin layer and the foam base layer, the foam base layer and the epoxy resin layer respectively serving to attenuate the transmitted ultrasonic waves.

[0059] As a preferred embodiment, the acoustic layer can be a sandwich structure and is composed of multiple layers of materials.

[0060] The first epoxy resin mixture comprises at least epoxy resin, rubber, and metal powder, and the ratio of epoxy resin, rubber, and metal powder can be 10:3:20. The metal powder can be tungsten powder, alumina, iron oxide, etc.

[0061] Furthermore, the second epoxy resin mixture includes at least epoxy resin, ceramic sheets, and polyamide. The material distribution of the second epoxy resin mixture from top to bottom is ceramic sheets, polyurethane sheets, and epoxy resin sheets.

[0062] With this setup, during the transmission of ultrasound, since the acoustic impedance of the sound-transmitting layer is similar to that of the piezoelectric vibrator, when the ultrasound is transmitted to the sound-transmitting layer, the transmission of the ultrasound is greater than the reflection. As much of the ultrasound will enter the epoxy resin layer as possible, it will avoid being reflected back to the piezoelectric layer and forming noise.

[0063] Acoustic tests were conducted on the multi-layered backing layer with a sawtooth structure, and the results were compared with those of a uniform single-layer backing layer with the same proportions and dimensions.

[0064] name thickness quality Sound attenuation coefficient Multi-layer sawtooth foam structure 5cm 10.53g 23.8 dB / mm Uniform single-layer structure 5cm 23.17g 10.3 dB / mm

[0065] Clearly, multi-layer serrated foam structures have advantages over uniform single-layer structures in terms of lighter weight and higher sound attenuation coefficient.

[0066] Secondly, the present invention also provides a method for preparing a multilayer backing structure as described in any of the above embodiments, such as... Figure 3 As shown, the method includes:

[0067] S1. PMI foam is poured into a pre-made mold, and the PMI foam is subjected to a first curing operation to form a foam base layer; wherein the upper surface of the foam base layer is uneven.

[0068] In this embodiment of the invention, a mold for the backing layer structure needs to be prefabricated. After the mold is made, PMI foam needs to be poured into the mold, and then the PMI foam is subjected to a first curing operation. Specifically, the requirements for the first curing operation are: a curing time of 12 hours and a curing temperature of 25°C.

[0069] After the first curing process, a foam base layer is formed. The upper surface of the foam base layer is uneven.

[0070] S2. The first epoxy resin mixture is poured into the upper surface of the foam base layer.

[0071] After the components of the first epoxy resin mixture are mixed evenly, it is directly poured into the upper surface of the foam base layer.

[0072] S3. Perform a second curing operation on the first epoxy resin mixture to form the epoxy resin layer and make the epoxy resin layer adhere to the upper surface of the foam base layer.

[0073] In this embodiment of the invention, after the first epoxy resin mixture is poured onto the upper surface of the foam base layer, a second curing operation is performed on the first epoxy resin mixture. The specific requirements for the second curing operation are: a curing time of 12 hours and a curing temperature of 25°C. After curing, due to the high roughness of the PMI foam and the adhesiveness of the epoxy resin, the two easily bond together.

[0074] S4. Perform a third curing operation on the upper surface of the sound-permeable layer and the epoxy resin layer, wherein the upper surface of the epoxy resin layer is the side away from the upper surface of the foam base layer.

[0075] In this embodiment of the invention, the sound-permeable layer needs to be placed over the epoxy resin layer, and then a third curing operation is performed on the upper surfaces of the sound-permeable layer and the epoxy resin layer. The specific process of the third curing operation is as follows:

[0076] A uniform layer of adhesive needs to be applied to each of the sound-permeable layer, epoxy resin layer, and reflective layer. Then, the sound-permeable layer, epoxy resin layer, and reflective layer are stacked in sequence, and a rectangular weight of about 6 kg is placed on top of the sound-permeable layer. The mixture is then pressurized and cured at room temperature for 48 hours.

[0077] Furthermore, in an alternative implementation, such as Figure 4 As shown, the method further includes:

[0078] S5. Perform the third curing operation on the reflective layer and the lower surface of the foam base layer, wherein the reflective layer is used to reflect ultrasonic waves passing through the foam base layer and the epoxy resin layer, and the reflective layer is composed of metal foil, including copper foil or aluminum foil.

[0079] Furthermore, in an alternative implementation, such as Figure 5 As shown, prior to the second curing operation on the first epoxy resin mixture, the method further includes:

[0080] S6. Degas the first epoxy resin mixture poured onto the uneven upper surface of the foam base layer to obtain the treated first epoxy resin mixture; wherein the unevenness of the upper surface of the foam base layer is serrated.

[0081] Specifically, the degassing process is as follows:

[0082] The mixed epoxy resin mixture needs to be placed into the mixing tank of a dedicated planetary mixer. Through the rotation and self-rotation of the planetary mixing head, the epoxy resin mixture is continuously subjected to shearing, compression, and friction forces in three-dimensional space, enabling it to achieve high-speed mixing in a short time. Simultaneously, the high vacuum of the equipment also removes air bubbles from the epoxy resin mixture.

[0083] Furthermore, in an alternative implementation, such as Figure 5 As shown, the second curing operation on the first epoxy resin mixture includes:

[0084] S7. Perform a second curing operation on the treated first epoxy resin mixture.

[0085] This involves a second curing operation on the first epoxy resin mixture that has undergone degassing treatment.

[0086] Thirdly, the present invention also provides a medical ultrasound probe, which is composed of a lens, a matching layer, a piezoelectric vibrator and the aforementioned multilayer backing structure.

[0087] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for preparing a multilayer backing structure for a medical ultrasound probe, characterized in that, The method includes: PMI foam is poured into a pre-made mold and the PMI foam is subjected to a first curing operation to form a foam base layer, wherein the upper surface of the foam base layer is uneven and the unevenness of the upper surface of the foam base layer is serrated. A first epoxy resin mixture is poured into the upper surface of the foam base layer, and a second curing operation is performed on the first epoxy resin mixture to form an epoxy resin layer and make the epoxy resin layer adhere to the upper surface of the foam base layer. The first epoxy resin mixture includes at least epoxy resin, rubber and metal powder, and the ratio of epoxy resin, rubber and metal powder is 10:3:

20. The acoustic layer and the upper surface of the epoxy resin layer are subjected to a third curing operation. The upper surface of the epoxy resin layer is the side away from the upper surface of the foam base layer. The acoustic layer is composed of a second epoxy resin mixture, which includes at least epoxy resin, ceramic sheet and polyamide. Since the acoustic impedance of the acoustic layer is similar to that of the piezoelectric vibrator, when the ultrasonic wave is transmitted to the acoustic layer, the transmission of the ultrasonic wave is greater than the reflection. The third curing operation is performed on the lower surface of the reflective layer and the foam base layer, wherein the reflective layer is used to reflect ultrasonic waves passing through the foam base layer and the epoxy resin layer, and the reflective layer is composed of a metal foil, including copper foil or aluminum foil.

2. The method for preparing the multilayer backing structure for a medical ultrasound probe according to claim 1, characterized in that, Prior to the second curing operation on the first epoxy resin mixture, the method further includes: The first epoxy resin mixture poured onto the uneven upper surface of the foam base layer is subjected to degassing treatment to obtain the treated first epoxy resin mixture.

3. The method for preparing the multilayer backing structure for a medical ultrasound probe according to claim 2, characterized in that, The second curing operation on the first epoxy resin mixture includes: A second curing operation is performed on the treated first epoxy resin mixture.

4. A multi-layer backing structure for a medical ultrasound probe, characterized in that, The multilayer backing structure is suitable for preparation using the preparation method described in any one of claims 1-3, wherein the multilayer backing structure comprises: A foam base layer, wherein the foam base layer is composed of PMI foam, and the upper surface of the foam base layer is uneven, wherein the unevenness of the upper surface of the foam base layer is serrated; An epoxy resin layer, the epoxy resin layer being composed of a first epoxy resin mixture, and the epoxy resin layer being bonded to the upper surface of the foam base layer; A sound-permeable layer, the sound-permeable layer being composed of a second epoxy resin mixture, and the sound-permeable layer covering the epoxy resin layer.

5. The multi-layer backing structure for a medical ultrasound probe according to claim 4, characterized in that, Also includes: A reflective layer for reflecting ultrasonic waves passing through the foam base layer and the epoxy resin layer, the reflective layer covering the lower surface of the foam base layer and being composed of metal foil.

6. The multi-layer backing structure for a medical ultrasound probe according to claim 5, characterized in that, The metal foil includes copper foil or aluminum foil.

7. The multilayer backing structure for a medical ultrasound probe according to any one of claims 4-6, characterized in that, The acoustic layer is used to allow ultrasonic waves to be transmitted into the epoxy resin layer and the foam base layer, and the foam base layer and the epoxy resin layer are respectively used to attenuate the transmitted ultrasonic waves. The first epoxy resin mixture includes at least epoxy resin, rubber, and metal powder, and the second epoxy resin mixture includes at least epoxy resin, ceramic sheet, and polyamide.

8. A medical ultrasound probe, characterized in that, The medical ultrasound probe includes a lens, a matching layer, a piezoelectric vibrator, and a multi-layer backing structure as described in any one of claims 4 to 7.

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