阅读说明：本技术 低介电高损耗的氧化硅衰减陶瓷组合物、氧化硅衰减陶瓷及其制备方法和应用 (Low-dielectric high-loss silicon oxide attenuation ceramic composition, silicon oxide attenuation ceramic and preparation method and application thereof ) 是由 石明 林文雄 黄见洪 于 2021-08-05 设计创作，主要内容包括：本发明提供一种低介电高损耗的氧化硅衰减陶瓷组合物、氧化硅衰减陶瓷及其制备方法和应用。本发明的氧化硅衰减陶瓷由氧化硅衰减陶瓷组合物制备得到,所述氧化硅衰减陶瓷组合物,至少包括SiO-(2)、Al-(2)O-(3)、Fe-(2)O-(3)、MgO、K-(2)O和Na-(2)O。本发明的氧化硅衰减陶瓷,介电常数低,且损耗角正切值大。相比常用的衰减瓷,微波在陶瓷表面上产生的阻抗更小,并且通过大的电损耗,更有效地吸收微波,更适用于制成微波器件中的衰减器。(The invention provides a silicon oxide attenuation ceramic composition with low dielectric and high loss, silicon oxide attenuation ceramic and a preparation method and application thereof. The silica attenuating ceramic of the present invention is prepared from a silica attenuating ceramic composition comprising at least SiO 2 、Al 2 O 3 、Fe 2 O 3 、MgO、K 2 O and Na 2 And O. The silicon oxide attenuation ceramic has low dielectric constant and large loss tangent. Compared with the common attenuation porcelain, the microwave has smaller impedance generated on the surface of the porcelain, and the microwave is more effectively absorbed through large electric loss, so that the ceramic is more suitable forAnd (5) forming an attenuator in the microwave device.)

1. A silica attenuating ceramic composition comprising at least SiO₂、Al₂O₃、Fe₂O₃、MgO、K₂O and Na₂O；

The silicon oxide attenuation ceramic composition comprises the following components in parts by weight:

70-80 parts by weight of SiO₂12-15 parts by weight of Al₂O₃0.05 to 0.15 part by weight of Fe₂O₃0.3-0.8 weight part of MgO and 7.0-7.5 weight parts of K₂O, 3.0-4.0 weight portions of Na₂O。

2. The silica attenuating ceramic composition of claim 1, wherein the sum of the parts by weight of each component is 100 parts by weight.

3. A silica attenuating ceramic prepared from the silica attenuating ceramic composition of claim 1 or 2.

4. The silica attenuating ceramic of claim 3, wherein the carbon content in the silica attenuating ceramic is greater than 0 and not more than 40%.

Preferably, the silica attenuating ceramic has at least one of the following electromagnetic parameters:

(1) the dielectric constant is less than 55 in the range of 8.2GHz-12.4 GHz;

(2) a dielectric loss of less than 1.9;

(3) the magnetic conductivity approaches to 1;

(4) the magnetic loss is less than 0.1 and approaches to 0.

Preferably, the silica attenuating ceramic has a shaped ceramic body structure.

Preferably, the shaped ceramic body structure is selected from square, spike, cap, wedge, castellated or city wall.

5. The method of claim 3 or 4, comprising subjecting the silica attenuating ceramic composition to ball milling, molding, sintering, dipping, and carbon deposition pyrolysis to obtain the silica attenuating ceramic.

Preferably, the preparation method specifically comprises the following steps:

s1, ball milling: carrying out dry powder mixing, grinding and ball milling on the silicon oxide attenuation ceramic composition to obtain ceramic powder;

s2, bonding and forming: mixing the ceramic powder obtained in the step S1 with a binder to obtain slurry, and performing hot-press casting to obtain a blank body with a specific shape and structure;

s3, dewaxing: embedding the blank into a sagger filled with alumina powder, and performing heat treatment and dewaxing through a resistance furnace;

s4, sintering: sintering heat treatment is carried out on the dewaxed blank;

s5, dipping: and (5) placing the sintered blank body obtained in the step (S4) in a sugar solution for dipping, drying and cracking carbon deposition to obtain the silicon oxide attenuation ceramic.

6. The method of claim 5, wherein the ball milling in step S1 comprises: the silica attenuating ceramic composition is placed in a ball mill jar and milling balls are added.

Preferably, after the dry powder ball milling, the powder is sieved by 160-200 meshes to obtain uniform fine porcelain powder.

Preferably, in step S2, the mass ratio of the porcelain powder to the binder is 100 (10-15). Preferably, the binder is paraffin wax.

Preferably, in step S2, the ceramic powder and the binder are mixed by heating and cooking to obtain the slurry.

Preferably, the slurry is also vacuum degassed prior to hot-press molding.

Preferably, in step S3, the dewaxing conditions include: the temperature is 900 ℃ and 1000 ℃, and the time is 5-15 hours.

7. The method according to claim 5 or 6, wherein in step S4, the sintering temperature is 1250-. Preferably, the sintering time is 10 to 12 hours.

Preferably, in step S5, the saccharide solution has a mass concentration of 5-40 wt%. Preferably, the time of the impregnation is 10 to 60 hours.

Preferably, the saccharide solution is selected from at least one of an aqueous sucrose solution, an aqueous lactose solution and an aqueous glucose solution. Preferably, in step S5, the carbon deposition cracking specifically includes performing carbon deposition heat treatment on the dipped and dried embryo body. Preferably, the carbon deposition heat treatment conditions are as follows: 900 ℃ and 1000 ℃, and preserving the heat for 20-40 minutes.

8. Use of the silica attenuating ceramic of claim 3 or 4 in an attenuator.

9. An attenuator comprising the silicon oxide attenuating ceramic according to claim 3 or 4.

10. Use of the attenuator of claim 9 in a microwave device.

Preferably, the microwave device is a microwave vacuum electronic device.

Preferably, the microwave vacuum electronic device is selected from a traveling wave tube, a backward wave tube, a gyrotron, a forward wave amplifier, a coaxial magnetron, and the like.

Technical Field

The invention belongs to the technical field of material preparation, and particularly relates to a low-dielectric high-loss silicon oxide ceramic composition, silicon oxide attenuation ceramic, and a preparation method and application thereof.

Background

In many microwave vacuum electronic devices (traveling wave tubes, return wave tubes, gyrotrons, forward wave amplifiers, coaxial magnetrons, etc.), it is often necessary to place attenuators to provide matched electromagnetic terminations, to suppress band-edge oscillations and oscillations in higher order or spurious modes, and to eliminate other off-design modes. The attenuator generally has two structural forms: firstly, a thin film structure; the second is a body structure. Known as membrane attenuators and body attenuators. The power that body attenuator can bear is bigger than the thin film attenuator, and body attenuation materials are mostly adopted for high-power microwave devices.

At present, commonly used body attenuation materials for microwave tubes at home and abroad mainly comprise aluminum oxide-based composite attenuation porcelain, aluminum nitride-based composite attenuation porcelain, beryllium oxide-based composite attenuation porcelain and the like, wherein the attenuation porcelain is basically relatively compact porcelain, the dielectric constants of the attenuation porcelain are relatively large (generally larger than 12), and the microwave impedance is relatively large, so that most of preset microwaves to be designed and absorbed are often reflected on the surface of the porcelain and cannot enter the porcelain body to be absorbed and converted when the microwave attenuation porcelain is used; and their dielectric losses are not large enough (typically less than 0.4). If the dielectric constant of the attenuating ceramic can be made small, the impedance can be made small, and the loss tangent can be made larger, the attenuation ceramic is beneficial to absorbing and attenuating microwaves and the use and design of the attenuator.

Patent document No. 200910185822.0 discloses a TiO-containing film for microwave electrovacuum devices₂The attenuation porcelain and the preparation method thereof have larger dielectric constant which is more than 20, and dry pressing is adopted, so that more complex parts cannot be pressed; patent document No. 201310586401.5 discloses a high thermal conductivity TiO-containing material₂The attenuation porcelain and the preparation method thereof are mainly characterized in that BeO is adopted as a substrate, the thermal conductivity is higher, but the BeO material is toxic and limited in use, and the dielectric property parameters of the attenuation porcelain are not disclosed; patent document No. 201711345906.7 discloses a TiO compound₂Attenuating porcelainThe preparation process adopts a hot-pressing sintering process, so that the process cost is high, the formed structure is single, the subsequent required processing cost is high, and the patent document does not disclose the dielectric property parameters of the attenuation ceramic.

Disclosure of Invention

The invention aims to provide a silicon oxide ceramic composition with low dielectric and high loss, a silicon oxide attenuation ceramic, and a preparation method and application thereof.

The invention provides a silicon oxide attenuation ceramic composition, which at least comprises SiO₂、Al₂O₃、Fe₂O₃、MgO、K₂O and Na₂O。

According to an embodiment of the present invention, the silica attenuating ceramic composition comprises the following components in parts by weight:

70-80 parts by weight of SiO₂12-15 parts by weight of Al₂O₃0.05 to 0.15 part by weight of Fe₂O₃0.3-0.8 weight part of MgO and 7.0-7.5 weight parts of K₂O, 3.0-4.0 weight portions of Na₂O。

Preferably, the sum of the parts by weight of the above components is 100 parts by weight.

Illustratively, SiO₂Can be 72, 74, 74.5, 75, 76, 78, 80 parts by weight;

Al₂O₃the weight parts of the components can be 12 parts, 13 parts, 14 parts and 15 parts;

Fe₂O₃the weight portion of the (B) can be 0.1 portion, 0.12 portion, 0.13 portion, 0.14 portion and 0.15 portion;

MgO can be 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part and 0.8 part by weight;

K₂the weight portion of O can be 7.0 portions, 7.1 portions, 7.2 portions, 7.3 portions, 7.4 portions and 7.5 portions;

Na₂the amount of O may be 3.0 parts, 3.1 parts, 3.2 parts, 3.3 parts, 3.4 parts, 3.5 parts, 3.7 parts or 4.0 parts by weight.

Preferably, the silica attenuating ceramic composition comprises the following components: 74.5 parts by weight of SiO₂14 parts by weight ofAl₂O₃0.1 part by weight of Fe₂O₃0.7 parts by weight of MgO, 7.2 parts by weight of K₂O, 3.5 parts by weight of Na₂O。

The invention also provides a silicon oxide attenuation ceramic prepared from the silicon oxide attenuation ceramic composition.

According to an embodiment of the invention, the carbon content in the silica attenuating ceramic is more than 0 and not more than 40 wt%, such as from 1 to 30 wt%, such as from 5 to 20 wt%.

Preferably, the silica attenuating ceramic has at least one of the following electromagnetic parameters:

(1) the dielectric constant is less than 55 in the range of 8.2GHz-12.4 GHz;

(2) a dielectric loss of less than 1.9;

(3) the magnetic permeability approaches 1, such as 0.99;

(4) the magnetic loss is less than 0.1 and approaches to 0.

According to an embodiment of the present invention, the silica attenuating ceramic has a shaped ceramic body structure. Preferably, the shaped ceramic body structure is selected from square, spike, hat, wedge, castellated or castellated, as shown in fig. 4.

The invention also provides a preparation method of the silicon oxide attenuation ceramic, which comprises the steps of carrying out ball milling, forming, sintering, dipping and carbon deposition cracking treatment on the silicon oxide attenuation ceramic composition to prepare the silicon oxide attenuation ceramic.

According to an embodiment of the invention, the preparation method specifically comprises the following steps:

s1, ball milling: carrying out dry powder mixing, grinding and ball milling on the silicon oxide attenuation ceramic composition to obtain ceramic powder;

s2, bonding and forming: mixing the ceramic powder obtained in the step S1 with a binder to obtain slurry, and performing hot-press casting to obtain a blank body with a specific shape and structure;

s3, dewaxing: embedding the blank into a sagger filled with alumina powder, and performing heat treatment and dewaxing through a resistance furnace;

s4, sintering: sintering heat treatment is carried out on the dewaxed blank;

s5, dipping: and (5) placing the sintered blank body obtained in the step (S4) in a sugar solution for dipping, drying and cracking carbon deposition to obtain the silicon oxide attenuation ceramic.

According to an embodiment of the present invention, in step S1, the ball milling includes: the silica attenuating ceramic composition is placed in a ball mill jar and milling balls are added.

Preferably, ball milling may be performed by a ball milling method known in the art as long as porcelain powder is obtained. For example, the ball milling is carried out by using agate balls, and the diameter of the agate balls is 20 mm.

Preferably, after the dry powder ball milling, the powder is sieved by 160-200 meshes to obtain uniform fine porcelain powder.

According to the embodiment of the invention, in the step S2, the mass ratio of the porcelain powder to the binder is 100 (10-15). Preferably, the binder is paraffin wax.

According to the embodiment of the present invention, in step S2, the ceramic powder and the binder are mixed by heating and cooking to obtain the slurry. Preferably, the heating temperature is 120-. Preferably, mixing and stirring is performed for 100-.

According to an embodiment of the present invention, in step S2, the hot press molding may be performed in a hot press molding apparatus known in the art as long as a desired shape structure of the green body is obtained. Illustratively, during hot-press casting, the temperature of the slurry is adjusted to 70 ℃, and the grouting pressure is 0.3 Mpa.

Preferably, the shape structure of the embryo body can be any structure. Illustratively, the structure is selected from a square, spike, cap, wedge, castellated, or castellated shape, and the like.

Preferably, the slurry is also vacuum degassed prior to hot-press molding. Illustratively, the vacuum degassing time is 25-35 minutes.

According to an embodiment of the present invention, in step S3, the dewaxing conditions include: the temperature is 900 ℃ and 1000 ℃, and the time is 5-15 hours.

According to the embodiment of the present invention, in step S4, the sintering temperature is 1250-. Preferably, the sintering time is 10 to 12 hours.

Preferably, after sintering, the blank can be ground according to the size requirement.

According to an embodiment of the present invention, in step S5, the saccharide solution has a mass concentration of 5 to 40 wt%, preferably 5 to 30 wt%, exemplary 5 wt%, 20 wt%, 30 wt%. Preferably, the time of the impregnation is 10 to 60 hours, such as 10 hours, 24 hours, 48 hours.

Preferably, the saccharide solution is selected from at least one of an aqueous sucrose solution, an aqueous lactose solution and an aqueous glucose solution.

According to an embodiment of the present invention, in step S5, the drying specifically includes a heating process. Preferably, the drying is carried out at 200 ℃ for 10-30 minutes. Illustratively, the heat treatment is performed in an oven.

According to the embodiment of the invention, in step S5, the carbon deposition cracking specifically includes performing carbon deposition heat treatment on the dipped and dried embryo body. Preferably, the carbon deposition heat treatment conditions are as follows: 900 ℃ and 1000 ℃, and preserving the heat for 20-40 minutes.

Preferably, the carbon deposit heat treatment is performed in a hydrogen furnace. The invention does not make specific requirements on the hydrogen furnace, and can select the hydrogen furnace commonly used by the personnel in the field to carry out carbon deposition heat treatment as long as the silicon oxide attenuation ceramic can be obtained.

The invention also provides the application of the silicon oxide attenuation ceramic in an attenuator.

The invention provides an attenuator, which contains the silicon oxide attenuation ceramic.

The invention also provides an application of the attenuator in a microwave device.

According to an embodiment of the invention, the microwave device is a microwave vacuum electronic device.

Preferably, the microwave vacuum electronic device is selected from a traveling wave tube, a backward wave tube, a gyrotron, a forward wave amplifier, a coaxial magnetron, and the like.

The invention has the beneficial effects that:

the invention provides a silicon oxide attenuation ceramic with low dielectric and high loss, when in microwave attenuation use, because the dielectric constant is low, the microwave impedance on the surface of the ceramic is small, so that more microwave signals enter the ceramic body, and the signals are absorbed and converted into heat energy in the high-loss ceramic body.

The silicon oxide attenuation ceramic with low dielectric constant and high loss is low in manufacturing raw material cost and process cost, and the dielectric constant and the loss of the ceramic can be conveniently adjusted by adjusting the concentration of the saccharide solution in the cracked carbon deposit. The special-shaped ceramic body structure is formed by hot-press casting, and the special-shaped structure design requirement of the microwave attenuator ceramic can be met. In the preparation method of the invention, the carbon content in the final ceramic body can be adjusted by adjusting the concentration of the saccharide solution, thereby facilitating the adjustment of dielectric parameters and meeting the requirements of different dielectric parameters of the attenuation ceramic.

The silicon oxide attenuation ceramic has low dielectric constant and large loss tangent. Compared with the commonly used attenuating porcelain, the microwave has smaller impedance generated on the surface of the porcelain, and the microwave is more effectively absorbed through large electric loss, so that the ceramic is more suitable for being made into an attenuator in a microwave device.

The silicon oxide attenuating ceramic of the present invention can be used in microwave devices as an attenuator for matched electromagnetic termination, suppression of band-edge oscillations and oscillations of higher order or spurious modes, and elimination of other off-design modes, among others.

Drawings

FIG. 1 is a flow chart of a process for preparing a silica attenuating ceramic according to an example;

FIG. 2 is a test curve of real part of complex dielectric constant in a 3cm band for ceramics of examples 1, 2, 3 and comparative example 1;

FIG. 3 is a graph showing the dielectric loss tangent test curves of the ceramics of examples 1, 2 and 3 and comparative example 1 in a 3cm wavelength band;

FIG. 4 is a schematic diagram of the shape structure of a silica attenuating ceramic of the present invention.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

Example 1

The preparation method of the silicon oxide attenuation ceramic of the embodiment is as follows:

s101, batching: the materials are prepared according to the following mass percentages:

SiO₂:Al₂O₃:Fe₂O₃:MgO:K₂O:Na₂o74.5: 14:0.1:0.7:7.2:3.5 to obtain a silica-attenuated ceramic composition (total 100% by weight);

s102, ball milling: putting the prepared silicon oxide attenuation ceramic composition powder into a ball milling tank, adding grinding balls for dry powder mixing and ball milling, wherein the ball milling is carried out on agate balls with the ball diameter of 20mm, and sieving the mixture for 160-mesh and 200-mesh after ball milling for 24 hours to obtain ceramic powder;

s103, adding wax: mixing the porcelain powder and the paraffin wax in the steps, wherein the mass ratio of the porcelain powder to the paraffin wax is 100: 12, mixing and then placing in a slurry barrel, heating and boiling materials by using an electric heating furnace, controlling the temperature at 120 ℃, and simultaneously stirring for 140 minutes by a wax combining machine;

s104, forming: pouring the slurry into a bin in a hot-die casting machine, performing vacuum degassing for 30 minutes, and then performing part molding through the hot-die casting machine and a mold to obtain a blank with a certain shape structure, wherein a cuboid (with the size of 25 × 4, unit cm) is formed by pressing in the example, the temperature of the slurry is adjusted to 70 ℃, and the grouting pressure is 0.3 Mpa;

s105, dewaxing: embedding the parts into a sagger filled with alumina powder, and performing heat treatment dewaxing through a resistance furnace, wherein the dewaxing temperature is 960 ℃, and the dewaxing time is 15 hours;

s106, sintering: cooling, taking out and cleaning the parts, putting the parts into a resistance furnace for heat treatment and sintering, wherein the sintering temperature is 1250 ℃, and sintering and heat preservation are carried out for 12 hours to obtain a water-permeable porous material;

s107, grinding: after the temperature is reduced and the product is taken out of the furnace, grinding can be carried out according to the size requirement of the product. In this example, to test the dielectric parameters of a 3cm wave band material, the sample size was processed to 22.86 x 10.16 x 2.00 (in cm);

s108, dipping: putting the processed parts into a 20 wt% sucrose solution, soaking for 24 hours, taking out and airing;

s109, drying: after being dried, the mixture is thermally treated in an oven, and the temperature is kept at 200 ℃ for 30 minutes;

s110, carbon deposition cracking: the parts were heat treated in a hydrogen furnace and held at 960 ℃ for 30 minutes. The silicon oxide attenuation ceramic of the embodiment is obtained after the temperature is reduced and the ceramic is taken out of the furnace.

The silicon oxide attenuation ceramic prepared in the embodiment is subjected to an HP-8722ES network analyzer and an electronic industry military standard 'microwave high-loss solid material complex dielectric constant and complex permeability test method' (SJ20512-1995) to test the electromagnetic parameters of the material of the embodiment under a wave band of 3cm, and the test results are shown in Table 1.

As can be seen from the data in Table 1, the real part (μ') of magnetic permeability is 0.99 and is close to 1, and the imaginary part (μ ") of magnetic permeability is 0.06, and is lower, so that the material is known to be less magnetic; the real part of the dielectric constant (. epsilon. ') ranges from 10.48 to 9.25 in the range of 8.2GHz to 12.4GHz, and the imaginary part of the dielectric constant (. epsilon. ') ranges from 7.68 to 5.84 in the range of 8.2GHz to 12.4GHz, i.e., the dielectric loss (tan. delta. '. epsilon. '/. epsilon. ') 0.73 to 0.63. The dielectric properties of the silica-attenuated ceramic prepared in this example are shown in fig. 2 and 3.

TABLE 1

Example 2

The preparation method of the silica-attenuated ceramic of this example is the same as that of example 1, except that: the concentration of the sucrose solution was adjusted to 5 wt%. The dielectric properties of the silica-attenuated ceramics prepared in this example were measured as shown in FIGS. 2 and 3.

Example 3

The preparation method of the silica-attenuated ceramic of this example is the same as that of example 1, except that: the concentration of the sucrose solution was adjusted to 40 wt%. The dielectric properties of the silica-attenuated ceramics prepared in this example were measured as shown in FIGS. 2 and 3.

Example 4

The preparation method of the silica-attenuated ceramic of this example is the same as that of example 1, except that: in step S108, the immersion time was 10 hours. The dielectric properties of the silica-attenuated ceramic prepared in this example were substantially similar to those of example 1.

Example 5

The preparation method of the silica-attenuated ceramic of this example is the same as that of example 1, except that: in step S108, the immersion time was 48 hours. The dielectric properties of the silica-attenuated ceramic prepared in this example were substantially similar to those of example 1.

Comparative example 1

The preparation method of the silica attenuating ceramic of this comparative example is the same as that of example 1, except that: the present comparative example does not perform steps S108 to S110, and the silica-attenuated ceramic of the present comparative example is obtained after completion of the sintering. The dielectric properties of the silica-attenuated ceramic prepared by this comparative example were measured as shown by the curve C0 in fig. 2 and 3.

From the test results of fig. 2 and fig. 3, in example 1, epsilon' is 10.48 to 9.25, tan delta is 0.73 to 0.63, the dielectric constant is lower than that of the conventional attenuating porcelain, the dielectric loss is higher, and the method is more suitable for the design of the body attenuator commonly used in the microwave tube; in the embodiment 2, the concentration of the sucrose solution is reduced, the final carbon content is reduced, the dielectric constant and the loss are correspondingly reduced, the epsilon' is 4.39-4.19, and the tan delta is 0.15-0.14; in example 3, the concentration of sucrose solution was increased, the final carbon content was increased, the dielectric constant and the loss were increased, ε' was 53 to 27, and tan δ was 1.03 to 1.78. As is clear from the test results of comparative example 1, since comparative example 1 was not impregnated, the dielectric constant was small, ε' was 3.42 to 3.40, and tan. delta. was about 0.01. And after the sucrose solution is soaked and carbon deposition is cracked, the ceramic is endowed with loss performance, the dielectric constant is increased, and the loss is increased. The greater the concentration of the impregnating solution, the greater the resulting dielectric constant and losses.

Therefore, the final carbon content of the porcelain body can be adjusted by adjusting the concentration of the dipping solution, so that the dielectric property of the porcelain body can be adjusted. Therefore, the dielectric parameters can be customized in a certain range to meet the design requirements of the microwave tube attenuator.

Comparative example 2

The preparation method of the silica attenuating ceramic of this comparative example is the same as that of example 1, except that: in step S108, the immersion time was 1 hour. By testing the dielectric properties, the dielectric constant of the silicon oxide attenuation ceramic prepared by the comparative example is reduced to about 7, and the loss is reduced to about 0.3. The interior of the porcelain piece appears grey black through section dissection observation, and has color difference with the black on the surface of the porcelain piece, which indicates that the impregnation is incomplete, and uniform carbon content and attenuation performance are not formed, and the performance is not uniform, so the porcelain piece is not suitable for being used in a microwave attenuator.

The exemplary embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement and the like made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.