1. An ignition system comprising:
a spark plug;
a discharge power supply for applying voltage to the spark plug to generate a spark discharge; and
an AC power supply for supplying AC power to a spark generated by the spark discharge, wherein
the spark plug includes
an insulator having an axial hole extending in an axis direction thereof,
an electrode disposed in the axial hole and having a tip end located frontward of a tip end of the insulator in the axis direction,
a metal shell arranged on a periphery of the insulator, and
a ground electrode fixed to an end portion of the metal shell and forming a gap between the tip end portion of the electrode and the ground electrode,
voltage from the discharge power supply and AC power from the AC power supply are supplied to the gap through the electrode, and
the AC power from the AC power supply is applied to a spark generated by the voltage from the discharge power supply in the gap.
2. The ignition system according to claim 1, wherein, with a wavelength of the AC power set to \u03bb(m), a protruding length of the tip end of the electrode from the tip end of the metal shell along the axis is set to \u03bb8 (m) or less.
3. The ignition system according to claims 1 or 2, wherein an average value of the AC power to be applied to a spark at one spark discharge is set to 50 W or more and 500 W or less.
4. The ignition system according to claims 1 or 2, wherein a size of the gap is set to 1.3 mm or less.
5. The ignition system according to claims 1 or 2, wherein the insulator does not exist in an area with a radius of 1 mm from the center of the gap.
6. The ignition system according to claims 1 or 2, wherein an oscillation frequency of the AC power is set to 5 MHz or more and 100 MHz or less.
7. The ignition system according to claims 1 or 2, wherein electrostatic capacity of a portion of the spark plug, the portion being located frontward of the tip end of the metal shell in the axis direction, is set equal to or less than one hundredth of electrostatic capacity of the whole spark plug.
8. The ignition system according to claims 1 or 2, wherein total volume of portions of the electrode, the ground electrode, and the insulator, the portions being located in an area with a radius of 2.5 mm from the center of the gap, is set to 20 mm3 or less.
9. The ignition system according to claim 8, wherein on a projection plane upon projecting the ground electrode and the center of the gap on a surface orthogonal to a line segment linking the electrode and the ground electrode and forming the shortest distance of the gap with respect to a direction in which the line segment extends,
an area of a projection region of the ground electrode, which is located in an area with a radius of 2 mm from a projection point at the center of the gap, is set to 7.6 mm2 or less.
10. The ignition system according to claim 8, wherein
the ground electrode includes a gap corresponding portion corresponding to the gap in the axis direction, and
a minimum width of the gap corresponding portion is set to 3.0 mm or less.
11. The ignition system according to claim 8, wherein, when viewed from the tip end side in the axis direction, at least part of a tip end surface of the electrode is configured to be visually identifiable.
12. The ignition system according to claim 8, wherein
at least the tip end portion of the electrode forms a circular column, and
an outside diameter of the tip end portion of the electrode is set to 3.0 mm or less.
13. The ignition system according to claim 8, wherein a protruding length of the ground electrode from the end of the metal shell along the axis is set to 10 mm or less.
14. A spark plug used for the ignition system according to claim 1.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. Ceramics having excellent high-frequency characteristics which contain SiO2, Al2O3, MgO, ZnO and B2O3 as constituent components, said ceramics comprising:
30 to 50% by weight of a crystal phase containing ZnO and Al2O3;
5 to 15% by weight of a crystal phase containing SiO2 and MgO; and
40 to 60% by weight of an amorphous phase comprising substantially SiO2 or SiO2 and B2O3;
wherein the content of an SiO2 crystal phase is suppressed to be not larger than 6% by weight, and the dielectric loss at 60 GHz is not larger than 15104.
2. Ceramics according to claim 1, wherein the content of B2O3 in said amorphous phase is not larger than 100 ppm.
3. Ceramics according to claim 1, wherein the content of a willemite crystal phase containing SiO2 and ZnO is suppressed to be not larger than 6% by weight.
4. Ceramics according to claim 1, wherein the content of carbon is not larger than 100 ppm.
5. Ceramics according to claim 1, wherein Co is contained in an amount of from 0.05 to 5% by weight calculated as CoO.
6. Ceramics according to claim 5, wherein Co is contained at least in the crystal phase that contains ZnO and Al2O3 and in the amorphous phase.
7. Ceramics according to claim 5, wherein the color position is such that the brightness L* is lower than 80 and the chroma C* is higher than 20 in the L*a*b color display system.
8. A method of producing ceramics having excellent high-frequency characteristics, comprising:
preparing a mixture of starting materials of 65 to 85% by weight of a crystallized glass containing SiO2, Al2O3, MgO, ZnO and B2O3, 5 to 20% by weight of a ZnO powder, and 1 to 20% by weight of an amorphous silica powder containing not larger than 500 ppm of impurities calculated as metals;
preparing a slurry by adding an organic binder to said mixture;
molding said slurry; and
removing the binder from the obtained molded article, followed by firing at 800 to 1000 C.
9. The method of producing ceramics according to claim 8, wherein said amorphous silica powder has an average particle diameter of from 1.2 to 6 m, and contains particles having particle diameters of not smaller than 2 m in an amount of not larger than 15% by weight.
10. The method of producing ceramics according to claim 8, wherein the binder is removed by the heat treatment conducted in two stages at 650 to 710 C. and at 720 to 770 C.
11. The method of producing ceramics according to claim 10, wherein the heat treatment is conducted at 650 to 710 C. for not shorter than one hour and at 720 to 800 C. for not shorter than one hour.
12. The method of producing ceramics according to claim 8, wherein said starting material mixture contains the Co3O4 powder having a specific surface area of not smaller than 10 m2g in an amount of from 0.05 to 5% by weight calculated as CoO.
13. A high-frequency wiring board comprising an insulating substrate formed of ceramics of claim 1, and a wiring layer which is formed on the surface of andor inside of said insulating substrate and is capable of transmitting signals of high frequencies of not lower than 1 GHz.
14. The high-frequency wiring board according to claim 13, wherein said wiring layer is constituted by at least one kind of a strip line, a microstrip line, a coplanar line and a dielectric waveguide line, and is formed by the co-firing with said insulating substrate.
15. The high-frequency wiring board according to claim 14, wherein said wiring layer contains at least one kind of element selected from copper, silver and gold.
16. The high-frequency wiring board according to claim 13, wherein the wiring layer formed on the surface of said insulating substrate contains copper, and an Au layer is plated maintaining a thickness of 1 m on said copper-containing wiring layer.