Background Art A sterilizer utilizing microwaves is conventionally proposed in, for example, Publication of Japanese Patent Application 2001-145688.

In such the sterilizer, mercury in liquid state and/or vapor state is filled in a discharge bulb which is transparent with respect to ultraviolet rays. Vapor pressure of mercury in the discharge bulb is equal to or smaller than 10-1 kPa. When microwaves are irradiated to the discharge bulb, mercury in the discharge bulb is excited by the energy of the microwaves and mercury emits ultraviolet radiation.

The ultraviolet radiation emitted from mercury passes through a glass wall of the discharge bulb and irradiates an object to be sterilized such as water or a medical appliance. Such the sterilizer is used in a microwave oven serving as a microwave generator for home use.

In the sterilizer utilizing microwaves, the longer a term for irradiating the microwaves becomes, the higher a temperature of the sterilizer increases. For example, when the microwaves are irradiated in a term about 60 sec. , the temperature of the sterilizer reaches near to 100°C. Thus, the term for irradiating the microwaves or a term for setting a timer of the microwave oven is restricted less than a predetermined term, for example, 90 sec.

A user, however, occasionally sets the timer of the microwave oven at a term longer than the predetermined term mistakenly.

When the microwaves are irradiated in a long term, the temperatures of the discharge bulb, the object to be sterilized, and so on will be increased much higher, so that elements such as a container into which the object to be sterilized is contained and/or the object to be sterilized, which are, for example, made of resin, will be melted down.

Disclosure of Invention A purpose of the present invention is to solve the above-mentioned problem and to provide a safety sterilizer utilizing microwaves by which the temperature in the container of the sterilizer does not increase so high for preventing the melt down of the container and/or the object to be sterilized which are, for example, made of resin, even though the microwaves are irradiated in a long term.

For accomplishing the above-mentioned purpose, a sterilizer in accordance with an aspect of the present invention comprises a discharge bulb emitting ultraviolet radiation owing to sustenance of discharge while microwaves are irradiated and means for stopping the discharge in the discharge bulb passing a predetermined term sufficient to sterilization of an object to be sterilized, even though the irradiation of microwaves has been continued.

By such a configuration, even though the microwaves are irradiated to the discharge bulb in a term longer than the predetermined term, the sustenance of discharge is stopped when the predetermined term sufficient to sterilization of an object to be sterilized. Thus, the temperature in the vicinity of the discharge bulb is not increased so high. It is possible to prevent the melt down of a container of the sterilizer and/or an object to be sterilized, which are, for example, made of resin.

Several kinds of mechanisms can be used as the means for stopping the sustenance of discharge in the discharge bulb. For example, quantum mechanical characteristics of mercury vapor, which is a material for emitting the ultraviolet rays, can be utilized.

A temperature in the discharge bulb will increase corresponding to the increase of the term of irradiation of the microwaves. As is known, when the temperature in the discharge bulb increases too high, the discharge in the discharge bulb is adversely reduced. Thus, it is possible automatically to stop the discharge in the discharge bulb by selecting structural dimensions of the discharge bulb and a quantity of mercury vapor filled in the discharge bulb.

Alternatively, a mechanism for shielding the discharge bulb from the microwaves or a mechanism for moving the discharge bulb from a position irradiated by the microwaves can be utilized. For example, an actuator responding to variation of temperature such as a bimetal or a shape-memory alloy can be used for moving the mechanism.

Brief Description of Drawings FIG. 1 is a perspective view showing a condition that a sterilizer is put into a microwave oven for processing the sterilization in a first embodiment of the present invention; FIG. 2 is a perspective view showing a configuration of the sterilizer in the first embodiment; FIG. 3 is a perspective view showing a configuration of a base member of a container of the sterilizer in the first embodiment; FIG. 4 is a sectional view showing a configuration of a discharge bulb of the sterilizer in the first embodiment; FIG. 5 is a graph showing a relation between density of mercury"y"and the shortest slant distance"A"of the discharge bulb in the first embodiment; FIG. 6A is a graph showing a timing chart of intensity of ultraviolet radiation emitted from the discharge bulb in the first embodiment; FIG. 6B is a graph showing a timing chart of a temperature of the discharge bulb in the first embodiment; FIG. 7A is a perspective view showing a partial configuration of a sterilizer when a temperature of a discharge bulb is lower than a predetermined temperature in a second embodiment of the present invention; FIG. 7B is a side view showing a configuration of the discharge bulb in the second embodiment; FIG. 7C is a perspective view of the sterilizer when the temperature of the discharge bulb is higher than the predetermined temperature in the second embodiment; FIG. 8A is a sectional view showing a discharge bulb and a moving member of a sterilizer in a third embodiment of the present invention when a temperature of the discharge bulb is lower than a predetermined temperature; FIG. 8B is a sectional view showing the discharge bulb and the moving member of the sterilizer when the temperature of the discharge bulb is higher than the predetermined temperature; FIG. 9A is a partially broken perspective view showing a configuration of a sterilizer in a fourth embodiment of the present invention; FIG. 9B is a conceptual diagram showing a principle for starting discharge of discharge bulbs in the fourth embodiment; FIG. 10A is a partially broken perspective view showing a configuration of a sterilizer in a fifth embodiment of the present invention; FIG. lOB is a conceptual diagram showing positional relations of two discharge bulbs in the fifth embodiment; and FIG. 11 is a perspective view showing a configuration of a sterilizer in a sixth embodiment of the present invention.

Best Mode for Carrying Out the Invention First Embodiment A first embodiment of the present invention is described. FIG.

1 shows a condition that a sterilizer 1 is put into a heat chamber 101 of a microwave oven 100 for processing the sterilization. FIG. 2 shows a configuration of the sterilizer 1 in the first embodiment.

FIG. 3 shows a configuration of a base member 2b of a container 2 of the sterilizer 1.

As shown in the figures, the container 2 of the sterilizer 1 has an egg shaped cross section in a longitudinal direction and a circular cross section in a lateral direction. The container 2 is dividable into a cover member 2a and the base member 2b. A first discharge bulb 3a and a second discharge bulb 3b are respectively provided in an inside of the container 2.

The first discharge bulb 3a is provided substantially at the center of the cover member 2a. The second discharge bulb 3b is provided substantially at the center of the base member 2b, and a holder 5 for holding an object 4 to be sterilized is formed around the second discharge bulb 3b on the base member 2b. The base member 2b has mounting legs 2c on outer face thereof. The first and second discharge bulbs 3a and 3b are detachable from the cover member 2a and the base member 2b, since they can be interchanged when the life of the discharge bulb is expired. Thus, the cover member 2a and the base member 2b respectively have mounting structures 9a and 9b by which the first and second discharge bulbs 3a and 3b can easily be positioned precisely for taking a predetermined positional relation.

In the figure, a teat of a baby's bottle fixed on a screw of the bottle is illustrated as an example of the object 4. The object 4, however, is not limited to the illustration, and various goods which need the sterilization by the ultraviolet radiation can be sterilized.

Furthermore, the shapes of the container 2 are not limited to the illustration on the same score. When there is no need for distinguishing the first discharge bulb 3 a with the second discharge bulb 3b, they are abbreviated as"discharge bulbs 3a and 3b"in the following description.

At least a part of the container 2 is made of a material such as polycarbonate, soda glass, or the like, which has transparency with respect to visible rays having wavelengths from 380 nm to 780 nm and microwaves, but ultraviolet rays. It is possible that a fluorescent material is spread on at least a part of inner faces of the container 2, or at least a part of the container 2 is made of a material including a fluorescent material.

The discharge bulbs 3a and 3b are respectively formed circular cylindrical shape having an inner hollow space into which a material emitting ultraviolet radiation such as mercury vapor is filled in airtight. At least a part of the discharge bulbs 3a and 3b are made of a material such as quartz glass which has transparency with respect to the ultraviolet radiation. The discharge bulbs 3a and 3b are respectively formed by sealing both ends of quartz glass tubes having, for example, a wall of 1 mm in thickness, a diameter of 0.8 cm at both ends and a length of 2 cm in longitudinal direction. A quantity of 30 mg of mercury and argon gas having a pressure of 10 Torr which serves as a buffer gas are filled in the inner hollow spaces of the discharge bulbs 3a and 3b. The discharge bulbs 3a and 3b are respectively disposed on the cover member 2a and the base member 2b of the container 2 in a manner so that cylindrical faces of the discharge bulbs 3a and 3b, from which ultraviolet radiation is emitted, face the object 4 to be sterilized.

The microwave oven 100 serves as a microwave generator for home use. The microwave oven 100 generates and irradiates microwaves having a frequency of 2.45 GHz. For sterilizing the object 4, the object 4 is mounted on the holder 5 of the base member 2b, and the cover member 2a is engaged with the base member 2b so that the object 4 is contained in the container 2 and disposed between the discharge bulbs 3a and 3b. Subsequently, the container 2 of the sterilizer 1 is put into the heat chamber 101 of the microwave oven 100.

When the microwave oven 100 is activated, the microwaves having a wavelength of 12 cm are irradiated to the container 2 of the sterilizer 1. The microwaves passes through the container 2 and reaches to the discharge bulbs 3a and 3b. When the microwaves reach to the discharge bulbs 3a and 3b, electrons in the inner hollow spaces of the discharge bulbs 3a and 3b receive kinetic energy from electric fields owing to the microwaves, so that the electrons will bombard mercury atoms and the mercury atoms bombarded by the electrons will be ionized.

As mentioned above, not only mercury, but also argon gas are filled into the inner hollow spaces of the discharge bulbs 3a and 3b.

Since the energy level of the excited argon atom is near to the energy level of ionized mercury, the mercury atoms can easily be ionized.

When a number of electrons reaches to a predetermined degree, the electrons directly receive the energy from the microwaves, so that the discharge state of mercury in the discharge bulbs 3a and 3b is maintained. While the discharge state is maintained, the electrons are accelerated by the electric field owing to the microwaves and bombard the mercury atoms, so that the mercury atoms are ionized or excited. When the excited mercury atom returns to normal state, it emits rays corresponding to energy gap between the excited state and the normal state. A main wavelength of the rays is 254 nm, and the ultraviolet rays having the wavelength of 254 nm have strong bactericidal action. Such the ultraviolet rays are irradiated to the object 4 for processing sterilization. The discharge bulbs 3a and 3b emit visible rays having wavelengths of 436 nm and 546 nm further to the ultraviolet rays.

In case that the fluorescent material is spread on the inner face of the container 2 or the material of the container 2 includes the fluorescent material, the fluorescent material converts the ultraviolet rays to the visible rays, and the visible rays can pass trough the container 2 and a window of a front door of the microwave oven 100.

Thus, the user can confirm that the sterilization owing to the ultraviolet radiation has been processed.

Furthermore, ozone is generated in the container 2 owing to the emission of the ultraviolet radiation. The object 4 can be sterilized not only by the ultraviolet radiation but also ozone gas.

Generally, the microwave oven 100 is designed such that the electric field owing to the microwaves become the highest at a position several centimeters above the bottom of the heat chamber 101, since food is generally disposed on a saucer in the heat chamber 101. As shown in FIG. 1, the container 2 of the sterilizer 1 is directly put into the heat chamber 101 of the microwave oven 100.

Thus, the second discharge bulb 3b is mounted on the base member 2b of the container 2 so that it is positioned several centimeters above the bottom of the heat chamber 101 where the intensity of the electric field owing to the microwaves is the highest.

Furthermore, there are several positions at an interval of 1/2 ( ; L is a wavelength of the microwaves) in the heat chamber 101 of the microwave oven 100 where the intensity of the electric field owing to the microwaves is higher. Thus, when the position of the first discharge bulb 3a provided on the cover member 2a in the container 2 is higher an integral multiple of a half of the wavelength of the microwaves { (/L/2) X n (n is an integer)} than the position of the second discharge bulb 3b provided on the base member 2b, both on the first and second discharge bulbs 3a and 3b can receive the energy of the electric fields owing to the microwaves, effectively.

In the first embodiment, the discharge bulbs 3a and 3b respectively serve as means for stopping the discharge themselves when the temperatures of the discharge bulbs 3a and 3b reach to a predetermined temperature. Such the discharge stopping function can be achieved by structural dimensions of the inner hollow spaces of the discharge bulbs 3a and 3b and quantities of mercury vapor filled in the inner hollow spaces of the discharge bulbs 3a and 3b.

Subsequently, the specific dimensions of the discharge bulbs 3a and 3b are described with reference to FIGS. 4 and 5. FIG. 4 shows a sectional view of the discharge bulbs 3a and 3b. The longest slant distance (diagonal line) binding between two points on the inner faces of the inner hollow space of the discharge bulb 3a or 3b is designated by a symbol"D". The smallest distance (diameter) binding two points in a direction perpendicular to an inner face of the inner hollow space of the discharge bulb 3a or 3b is designated by a symbol"A" (cm).

The longest slant distance"D"is made shorter than a half of the wavelength 1 of the microwaves. More specifically, the length of the longest slant distance"D"becomes about 2.15 cm corresponding to the above-mentioned dimensions of the discharge bulb 3a or 3b. Since the wavelength of the microwaves is 12 cm, the discharge bulb 3a or 3b satisfies this requirement.

If the longest slant distance"D"is longer than a half of the wavelength ; L of the microwaves, the discharge bulbs 3a and 3b can respectively serve as antennas for receiving the microwaves, so that the largest magnetic field will be applied to the discharge bulbs 3a and 3b. The energy which is supplied to mercury in the discharge bulbs 3a and 3b from the microwaves becomes too large, so that the temperature of the discharge bulbs 3a and 3b will extremely be increased, for example, above 500°C. Thus, the container 2 and the object 4 will be melted down when they are made of, for example, resin.

On the other hand, the longest slant distance"D"is made shorter than a half of the wavelength A of the microwaves, the energy which is applied to mercury in the discharge bulbs 3a and 3b from the microwaves become smaller, so that the extreme increase of the temperatures of the discharge bulbs 3 a and 3b can be prevented. It, however, is necessary to make the longest slant distance"D"equal to or longer than 1/10 of the wavelength ; L of the microwaves so as to receive a sufficient energy from the microwaves for emitting a sufficient quantity of ultraviolet radiation used for sterilizing the object 4. Hereupon, the power of the microwave oven 1 is assumed in a region from 500 W to 700 W.

When the microwaves are irradiated to the discharge bulbs 3a and 3b, discharge occurs in the discharge bulbs 3a and 3b, so that the temperatures of the discharge bulbs 3a and 3b will be increased. The pressure of mercury vapor in the discharge bulbs 3 a and 3b will increase corresponding to the increase of the temperatures of the discharge bulbs 3a and 3b. A relation between the temperature of the discharge bulb and the pressure of mercury vapor is shown in table 1.

(Table 1) Temperature of discharge bulb (°C) Pressure of mercury vapor (mmHg) 0 0. 000185 50 0. 01267 100 0. 2729 150 2. 807 200 17. 287 250 74. 375 300 246. 8 350 672. 69 It is found from the table 1 that ratios of increase of the pressure of mercury vapor are gradually reduced corresponding to the increase of the temperature of the discharge bulb. The reason of this phenomenon is considered. When the microwaves are irradiated to the discharge bulb, electrons in the discharge bulb receive kinetic energy from the electric field owing to the microwaves, and the electrons bombard mercury atoms. The temperature of the discharge bulb will increase due to bombarding of the electrons and the mercury atoms, so that mercury in liquid state is evaporated corresponding to the increase of the temperature of the discharge bulb. Thus, the pressure of mercury vapor in the discharge bulb also increases corresponding to the increase of the temperature of the discharge bulb, and the number of mercury atoms in the discharge bulb also increases.

When the number of the mercury atoms in the discharge bulb becomes larger than a predetermined level, kinetic energy of the electrons becomes insufficient to ionize mercury atoms. Thus, it becomes difficult to maintain the discharge of mercury atoms in the discharge bulb. In other words, it is possible to stop the discharge in the discharge bulb by selecting a density of mercury when the temperature of the discharge bulb becomes higher than a predetermined value. The density of mercury is defined as a division of a quantity of mercury in vapor state by a capacity of the inner hollow space of the discharge bulb.

It is found from experiments that a proper density of mercury, by which the discharge in the discharge bulb can be stopped, depends on the shortest slant distance"A"of the discharge bulb (see FIG. 4).

In our experiment, when the shortest slant distance"A"of the discharge bulb was 0. 8 cm, the discharge in the discharge bulb was stopped at 200°C of the temperature of the discharge bulb. The density of mercury at that time was 1. 178 X 10-4 g/cm3. With respect to the cylindrical shaped discharge bulb having a diameter of 0.8 cm, a quantity of mercury, by which the density of mercury becomes 1.178 X 10-4 g/cm3, should be filled on the discharge bulb.

Specifically, the quantity of mercury filled in the discharge bulb was 30 mg. Similarly, when the shortest slant distance"A"of the discharge bulb was 1 cm, the density of mercury when the discharge was stopped was 4. 58 X 10-4 g/cm3. Results of the experiments are plotted on a graph shown in FIG. 5. A characteristic curve designated by solid line in FIG. 5 shows a relation between the density of mercury"y"and the shortest slant distance"A"of the discharge bulb. The characteristic curve is shown by the equation y=2.2407 X 10-'ex (7.6822A).

FIG. 6A shows a time chart of an intensity of ultraviolet radiation emitted from the discharge bulb 3a or 3b in the first embodiment. FIG. 6B shows a time chart of the temperature of the discharge bulb 3a or 3b. As can be seen from FIGS. 6A and 6B, when the temperature of the discharge bulb reached to a predetermined temperature (the highest increased temperature), the discharge of the mercury was stopped and the emission of ultraviolet was stopped. While the discharge was stopped, the temperature of the discharge bulb gradually decreased, even though the microwaves had been irradiated. When the temperature of the discharge bulb decreased to a predetermined temperature (the lowest decreased temperature), the density of mercury also decreased and the discharge of mercury atoms in the discharge bulb restarted again.

Since the discharge bulb in the first embodiment repeats the startup of the discharge and the stop of the discharge, it is possible to prevent the melt down of the container 2 and the object 4, even though the microwaves has been irradiated in a long term due to erroneous setting of the timer of the microwave oven 100.

Furthermore, since the material, which has transparency with respect to visible rays, is used at least a part of the container 2, the visible rays having the wavelengths of 436 nm and 546 nm emitted from the discharge bulbs 3a and 3b can be irradiated to outside of the container 2. Thus, the user can visually check the operation of the sterilizer 1.

Still furthermore, the power of the microwave oven 100 is selected in a range from 500 W to 700 W, a sufficient quantity of ultraviolet radiation which is necessary for sterilizing the object 4 can be emitted, and the temperatures of the discharge bulbs 3a and 3b do not increase so high.

Still furthermore, the discharge bulbs 3a and 3b are provided in the container 2 such that the cylindrical faces of the discharge bulbs 3a and 3b, from which the ultraviolet radiation is emitted, face the object 4. Thus, the relative positions of the emitting faces of the ultraviolet radiation and the faces to be sterilized can be held stably, so that the object 4 can be sterilized effectively and surely.

Second Embodiment A second embodiment of the present invention is described.

FIG. 7A shows a base member 2b of a container of a sterilizer 1 when a temperature of a discharge bulb 3b is lower than a predetermined temperature. FIG. 7B shows a side view of the discharge bulb 3b.

FIG. 7C shows the base member 2b of the container 2 of the sterilizer 1 when the temperature of the discharge bulb 3b is higher than the predetermined temperature.

In the figures, only a second discharge bulb 3b provided on the base member 2b is illustrated. A first discharge bulb 3a provided on a cover member 2a (not illustrated), however, has substantially the same configuration. Furthermore, elements designated by the same numerals are the same as those in the first embodiment, so that the descriptions of them are omitted.

In the second embodiment, the means for stopping the discharge in the discharge bulb is a mechanism for shielding a surface of the discharge bulb corresponding to the variation of the temperature of the discharge bulb. As can be seen from figures, a plurality of sets of shielding members 7 are provided on a cylindrical surface of the discharge bulb 3b. The shielding member 7 is made of a material which reflects or absorbs the microwaves. The shielding member 7 varies between a first state shown in FIGS. 7A and 7B, and a second state shown in FIG. 7C.

In the first state shown in FIGS. 7A and 7B, each shielding member 7 is outwardly protruded in longitudinal direction of the discharge bulb 3b from both ends of the discharge bulb 3b. While the temperature of the discharge bulb 3b is lower than a predetermined temperature, each shielding member 7 takes the first state. When the temperature of the discharge bulb 3b becomes higher than the predetermined temperature, the shielding member 7 takes the second state. In the second state shown in FIG. 7C, each shielding member 7 is inwardly turned along the cylindrical surface of the discharge bulb 3b. Since most of the cylindrical surface of the discharge bulb 3b is covered by the shielding members 7, most of the microwaves irradiated to the discharge bulb 3b are reflected or absorbed by the shielding members 7. Thus, energy of the microwaves reaching to the inner hollow space of the discharge bulb 3b becomes much smaller, so that the discharge of mercury atom in the discharge bulb 3b will be stopped. While the discharge in the discharge bulb 3b has been stopped, the temperature of the discharge bulb 3b gradually decreases. When the temperature of the discharge bulb 3b becomes lower than the predetermined temperature, the shielding member 7 returns to the first state.

Since the discharge bulb 3b in the second embodiment repeats the startup of the discharge and the stop of the discharge, the temperature of the discharge bulb 3b do not increase higher than the predetermined temperature. Thus, it is possible to prevent the melt down of the container 2 and/or the object 4, even though the microwaves have been irradiated in a long term.

For varying the shielding member 7 between the first state and the second state, a bimetal can be used as an actuator for rotating the shielding member 7. Specifically, a hinge rotatably supporting the shielding member (thin plate) 7 is formed by a bimetal, for example, a combination of an alloy of nickel and iron and an alloy of nickel, iron and chromium, the shielding member 7 can be rotated owing to the difference between thermal expansion coefficients of the materials constituting the bimetal corresponding to the variation of the temperature of the discharge bulb 3b.

Alternatively, the shielding member 7 can be made of a shape-memory alloy. In such the case, the shielding member 7 can serve as an actuator itself owing to the variation of the temperature of the discharge bulb 3b.

Furthermore, it is possible to use a meshed metal plate or thin plate of resin or ceramics including metal powder as the shielding member 7 instead of metal thin plate.

In the heat chamber of the microwave oven, the elements made of metal will be discharged corresponding to the potential thereof.

Thus, it is preferable to provide a resin coating on the surfaces of the shielding member 7 for preventing the sustenance of the discharge from the shielding member 7.

Third Embodiment A third embodiment of the present invention is described.

FIG. 8A shows a discharge bulb 3 in a container of a sterilizer when a temperature of the discharge bulb 3 is lower than a predetermined temperature. FIG. 8B shows the discharge bulb 3 of the sterilizer when the temperature of the discharge bulb 3 is higher than the predetermined temperature.

In the figures, only the discharge bulb 3 and a moving member 8 are illustrated. The discharge bulb 3 and the moving member 8 can be provided on both of the cover member 2a and the base member 2b (not illustrated). Elements designated by the same numerals are the same as those in the first or second embodiment, so that the descriptions of them are omitted.

In the third embodiment, the means for stopping the discharge in the discharge bulb is a mechanism for moving the discharge bulb corresponding to the variation of the temperature of the discharge bulb. As can be seen from figures, the discharge bulb 3 is held on the moving member 8. The moving member 8 varies between a first state shown in FIG. 8A and a second state shown in FIG. 8B.

In the first state shown in FIG. 8A, two arms 8a and 8b of the moving member 8 is tightly folded, and the cylindrical surface 31 of the discharge bulb 3 supported on the arm 8a is substantially parallel with, for example, a bottom 21 of a container 2 of the sterilizer 1.

While the temperature of the discharge bulb 3 is lower than a predetermined temperature, the moving member 8 takes the first state.

When the temperature of the discharge bulb 3 becomes higher than the predetermined temperature, the moving member 8 takes the second state. In the second state shown in FIG. 8B, the arm 8a supporting the discharge bulb 3 stands substantially at right angle with respect to another arm 8b which is fixed on, for example the bottom 21 of the container 2.

For varying the moving member 8 between the first state and the second state, a bimetal can be used as an actuator for rotating the arm 8a around a hinge portion 8c. Specifically, a hinge portion 8c rotatably supporting the arm 8a with respect to the arm 8b is formed by a bimetal, for example, a combination of an alloy of nickel and iron and an alloy of nickel, iron and chromium, the arm 8a of the moving member 8 can be rotated owing to the difference between thermal expansion coefficients of the materials constituting the bimetal corresponding to the variation of the temperature of the discharge bulb 3.

Alternatively, the moving member 8 can be made of a shape-memory alloy. In such the case, the moving member 8 can serve as an actuator itself owing to the variation of the temperature of the discharge bulb 3.

As mentioned above, the wavelength A of the microwaves is 12 cm, so that there are several positions at an interval of 6 cm in the heat chamber of the microwave oven where the electric field owing to the microwaves is higher. As mentioned above, the microwave oven is generally designed such that the electric field owing to the microwaves become the highest at a position several centimeters above the bottom of the heat chamber, since food is generally disposed on a saucer in the heat chamber. As shown in FIG. 1, the container 2 of the sterilizer 1 is directly put into the heat chamber 101 of the microwave oven 100. Thus, the discharge bulb 3 in the first state is mounted on the base member 2b of the container 2 such that it is positioned several centimeters above the bottom of the heat chamber 101 where the electric field owing to the microwaves is the highest. When the temperature of the discharge bulb 3 increases higher than the predetermined temperature, the moving member 8 is varied to take the second state. The discharge bulb 3 supported on the arm 8a of the moving member 8 is moved above with a rotation, as shown FIG. 8B.

Since the intensity of the electric field owing to the microwaves becomes the smallest at a position above, for example, 3 cm from the position where the intensity of the electric field is the highest, it is preferable to move the discharge bulb 3 to the position about 3 cm in the second state above the position in the first state.

The length of the arm 8a is selected with consideration of the length of the discharge bulb 3.

When the discharge bulb 3 is moved to the position where the intensity of the electric field is the smallest, the discharge in the discharge bulb 3 will be stopped. Thus, the temperature of the discharge bulb 3 gradually decreases. When the temperature of the discharge bulb 3 decreases lower than the predetermined temperature, the moving member 8 returns to the first state shown in FIG. 8A from the second state shown in FIG. 8B. The discharge bulb 3 is positioned at the position where the intensity of the electric field owing to the microwaves is the highest, and the discharge in the discharge bulb is restarted.

By such the configuration in the third embodiment, the temperature of the discharge bulb 3 do not increase so high, and the melt down of the container of the sterilizer and/or the object to be sterilized can be prevented even though the microwaves are continuously irradiated to the discharge bulb 3 in a long term.

Similar to the second embodiment, it is preferable to provide a resin coating on the surfaces of the moving member 8 for preventing the sustenance of the discharge from the moving member 8.

Fourth Embodiment A fourth embodiment of the present invention is described.

FIG. 9A shows a configuration of a sterilizer 1 in the fourth embodiment. FIG. 9B shows a concept of the fourth embodiment.

The fourth embodiment relates to an improvement of startup characteristics of the discharge bulbs.

In FIG 9A, the container 2 of the sterilizer 1 has a cylindrical shape, and the discharge bulb 3a and 3b respectively have a cylindrical shape. The shapes of the container and the discharge bulb in the sterilizer in accordance with the present invention are not limited to those. The shapes of them can be modified corresponding to the use or the shapes of the object to be sterilized. In other words, the height of the container 2 can be varied corresponding to the object 4. Thus, the discharge bulb 3a provided on the cover member 2a is not necessarily disposed at a position where the intensity of the electric field owing to the microwaves is higher.

In the above-mentioned first embodiment, the smaller the size of the discharge bulb becomes, the lower the temperature of the discharge bulb increases. However, when the size of the discharge bulb becomes smaller, it is difficult to induce the discharge in the discharge bulb. As shown in FIGS. 9A and 9B, the first and second discharge bulbs 3a and 3b are disposed in the container 2 such that ultraviolet radiation emitted from the second discharge bulb 3b can reach to the first discharge bulb 3a, and vice versa. The object 4 to be sterilized is positioned between the discharge bulbs 3a and 3b.

Inner surfaces of the container 2 can reflect the ultraviolet radiation.

By such the configuration, one of the first and second discharge bulbs 3a and 3b is induced to be discharged earlier, the ultraviolet radiation emitted from the discharge bulb 3a or 3b discharged earlier can contribute to the discharge of the other discharge bulb 3b or 3a. As a result, both of the discharge bulbs 3a and 3b can be discharged earlier from the start of the irradiation of the microwaves.

Specifically, it is assumed that the second discharge bulb 3b provided on the base member 2b is disposed at a position where the intensity of the electric field owing to the microwaves is higher, and the first discharge bulb 3 a provided on the cover member 2a is disposed at a position where the intensity of the electric field is lower.

When the microwaves are irradiated to the first and second discharge bulbs 3a and 3b, the second discharge bulb 3b provided on the base member 2b can start the discharge earlier than the first discharge bulb 3a, since the second discharge bulb 3b receives higher energy of the electric field than the first discharge bulb 3a. The first discharge bulb 3a, however, is irradiated by the ultraviolet radiation emitted from the second discharge bulb 3b, so that the discharge bulb 3a can start the discharge momentarily. As a result, the object 4 can be sterilized effectively and surely in a short time, with no relation to the size and/or shape of the object 4.

Fifth Embodiment A fifth embodiment of the present invention is described. FIG.

10A shows a configuration of a sterilizer 1 in the fifth embodiment.

FIG. 10B shows a concept of the fifth embodiment. The fifth embodiment relates to an improvement of startup characteristics of the discharge bulbs, too.

As mentioned above, there are several positions at an interval off/2 (1 is the wavelength of the microwaves) in the heat chamber of the microwave oven where the electric field owing to the microwaves is higher. In other words, the discharge bulbs are not necessarily disposed at positions where the electric field owing to the microwaves is higher. In the fifth embodiment, two discharge bulbs are regarded as a system serving as an antenna for receiving the microwaves.

As shown in FIG. 10A, first, second and third discharge bulbs 3 a, 3b and 3c are provided in the container 2, and the first and third discharge bulbs 3a and 3c are provided on the cover member 2a of the container 2. The first and third discharge bulbs 3a and 3c take a relation shown in FIG. 10B with respect to the positions thereof.

Shapes of the discharge bulbs 3a and 3c are projected on an optional line"L"so as not to overlap shadows of the discharge bulbs 3a and 3c. A distance between points"b"and"c"on the line"L" which corresponds to the shortest distance between surfaces of the discharge bulbs 3a and 3c opposing each other is designated by a symbol"X". A distance between a point"a"on the line"L"which is a shadow of the farthermost point of the discharge bulb 3a from the other discharge bulb 3c and the point"c"which is a shadow of the nearest point of the discharge bulb 3c to the discharge bulb 3 a is designated by a symbol"Y1". Similarly, a distance between a point "d"which is a shadow of the farthermost point of the discharge bulb 3c from the discharge bulb 3a and the point"b"which is a shadow of the nearest point of the discharge bulb 3a to the discharge bulb 3c is designated by a symbol"Y2". It is necessary to satisfy the following conditions.

X< X/2, and Y 1/2 Hereupon, the symbol"Y"designates the larger one of the distances designated by the symbols"Y1"and"Y2".

When two discharge bulbs 3a and 3c are regarded as a system, a length of the system is longer than a half of the wavelength 1 of the microwaves. When the microwave oven is used as a microwave generator, a half of the wavelength ; L is 6 cm. By satisfying the above-mentioned conditions, the discharge bulbs 3a and 3c can serve as an antenna, so that it can receive the energy of the electric field owing to the microwaves effectively.

In the illustration of FIG. 10B, error component of the positioning of the discharge bulbs 3a and 3c are magnified. The discharge bulbs 3a and 3c, however, are generally arranged substantially in parallel with each other. Specifically, center axes of the discharge bulbs 3a and 3c are arranged at an interval of a half of the wavelength of the microwaves, for example, 6 cm.

It is preferable that positional relations between the discharge bulbs 3 a and 3b, and the discharge bulbs 3c and 3b further satisfy the above-mentioned conditions. By such the configuration, the energy of the electric field owing to the microwaves can be received more effectively.

Furthermore, it is preferable that the discharge bulbs 3a, 3b and 3c are disposed in a manner so that the ultraviolet radiation emitted from one of the discharge bulbs 3a, 3b and 3c can reach to other discharge bulbs. The ultraviolet radiation emitted from the discharge bulb 3a, 3b or 3c discharged earlier can contribute to the discharge of the other discharge bulbs.

Sixth Embodiment A sixth embodiment of the present invention is described.

The sixth embodiment relates to the positioning of the container 2 in the heat chamber 101 of the microwave oven 100. As shown in FIG.

11, the sterilizer 1 in the sixth embodiment further comprises a positioning sheet 10, which is laid on a table in the heat chamber 101 of the microwave oven 100. When the microwave oven 100 has no table, the positioning sheet 10 is directly laid on the bottom of the heat chamber 101.

The positioning sheet 10 has a plurality of marks 10a which are positioned at an interval of integral multiple of a half of wavelength of the microwaves (1/2) in a horizontal direction. The marks 10a are, for example, recesses into which the containers 2 can easily be positioned. Specifically, the marks 10a are provided at an interval of 6 cm, 12 cm, 18 cm- , since the wavelength ; L of the microwaves in the microwave oven 100 is 12 cm.

The microwave oven 100 is generally designed in a manner so that the intensity of the electric field owing to the microwaves at the center of the bottom is the highest. Thus, the marks 10a are arranged at the center of the positioning sheet 10 and positions on a circle having a diameter of integral multiple of the wavelength 1 of the microwaves.

By using the positioning sheet 10, the user can precisely dispose the container 2 of the sterilizer 1 at a position where the intensity of the electric field owing to the microwaves is higher or the highest. As a result, the object 4 to be sterilized can effectively and surely be sterilized in a short period, even though the sizes of the discharge bulbs 3a and 3b are downsized for preventing the melt down of the container 2 and/or the object 4.

Furthermore, it is possible to put a plurality of containers 2 into the heat chamber 101 of the microwave oven 100, since the positioning sheet 10 has a plurality of marks 10a respectively showing the positions where the intensity of the electric field owing to the microwaves is higher. By such a configuration, a plurality of objects 4 can be sterilized, effectively and surely in a short time.

Other Modifications In the above-mentioned description, the microwave oven is used as a microwave generator for home use. The use of the sterilizer in accordance with the present invention is not limited for home use. An exclusive microwave generator can be used, and the frequency and the wavelength of the microwaves are not limited to 2.45 GHz and 12 cm.

Furthermore, in the above-description, mercury and argon gas are filled in the discharge bulbs. It, however, is possible to fill xenon gas, deuterium, halogenated iron, sulfur, or the like.

Furthermore, it is possible to fill a mixed gas of argon and neon instead of argon gas.

Still furthermore, the discharge bulbs are not limited to the cylindrical shape. It, however, is possible to take another optional shape when it satisfies the above-mentioned structural dimensions of the inner hollow space of the discharge bulb and quantities of mercury vapor filled in the inner hollow space of the discharge bulb.

Still furthermore, a teat of a baby's bottle and a screw for fixing the teat on the bottle are illustrated, for example, in FIG. 2, as examples of the objects to be sterilized. The sterilizer can be used for any goods which need the sterilization, so that the kind of the object is not limited.

Still furthermore, a plurality of discharge bulbs is provided in the container of the sterilizer for sterilizing the object evenly. It, however, is possible to use only one discharge bulb for sterilizing the object when a portion to be sterilized is disposed on a side of the object or when a high effective in the sterilization is not required.

Still furthermore, the object to be sterilized and the discharge bulbs are contained in the container in the above-mentioned embodiments. It, however, is possible to dispose the object and the discharge bulbs directly in the heat chamber of the microwave oven or an exclusive microwave generator.

This application is based on Japanese patent applications 2002-324636,2002-325996 and 2002-326058 filed in Japan, the contents of which are hereby incorporated by references.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.

Industrial Applicability As mentioned above, the sterilizer in accordance with the present invention can process the sterilization of the object owing to the ultraviolet radiation with using the microwave generator such as the microwave oven for home use.