Control of microwave source efficiency in a microwave heating apparatus

Abstract

A microwave heating apparatus and a method of operating a microwave heating apparatus are provided. The microwave heating apparatus includes a microwave source for generating microwaves, a transmission line for transmitting the generated microwaves from the microwave source to a cavity, a measuring device that measures the power of microwaves transmitted from the microwave source and a receiving device that receives operational data indicative of the power supplied to the microwave source. The microwave heating apparatus further includes a control unit adapted to adjust the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line based on the measured power of the transmitted microwaves and the received operational data in order to control the efficiency of the microwave source. The microwave heating apparatus improves control of the microwave source efficiency.

1 . A method of operating a microwave heating apparatus comprising a microwave source adapted to feed microwaves to a cavity via a transmission line, the method comprising the steps of:
 measuring the power of microwaves transmitted from the microwave source to the cavity;   receiving operational data indicative of the power supplied to the microwave source; and   adjusting the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line based on the measured power of the transmitted microwaves and the received operational data in order to control the efficiency of the microwave source.   
     
     
         2 . The method of  claim 1  further comprising the step of measuring the power of microwaves reflected back towards the microwave source. 
     
     
         3 . The method of  claim 1 , wherein the step of adjusting of the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line comprises:
 moving, within the transmission line, at least one element of the group including a slug tuner, a motor driven slug tuner, a plunger and a motor driven plunger; or changing the geometry or length of the transmission line.   
     
     
         4 . The method of  claim 2 , wherein the step of adjusting of the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line comprises:
 moving, within the transmission line, at least one element of the group including a slug tuner, a motor driven slug tuner, a plunger and a motor driven plunger; or changing the geometry or length of the transmission line.   
     
     
         5 . The method of  claim 1 , wherein the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line is adjusted such that the efficiency of the microwave source is increased or maximized if the measured power of the reflected microwaves is below a predetermined threshold and such that the efficiency of the microwave source is decreased or minimized if the measured power of the reflected microwaves is above the predetermined threshold. 
     
     
         6 . The method of  claim 1 , wherein the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line is adjusted as a function of the ratio between the measured power of the transmitted microwaves and the power supplied to the microwave source. 
     
     
         7 . The method of  claim 1  further comprising the step of turning off the microwave source if the measured power of the reflected microwaves is above a security threshold. 
     
     
         8 . The method of  claim 2  further comprising the step of turning off the microwave source if the measured power of the reflected microwaves is above a security threshold. 
     
     
         9 . The method of  claim 3  further comprising the step of turning off the microwave source if the measured power of the reflected microwaves is above a security threshold. 
     
     
         10 . A microwave heating apparatus comprising:
 a microwave source for generating microwaves;   a transmission line for transmitting the generated microwaves from the microwave source to a cavity;   a measuring device capable of measuring the power of microwaves transmitted from the microwave source;   a receiving device capable of receiving operational data indicative of the power supplied to the microwave source; and   a control unit that adjusts the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line based on the measured power of the transmitted microwaves and the received operational data in order to control the efficiency of the microwave source.   
     
     
         11 . The microwave heating apparatus of  claim 10  further comprising an additional measuring device that measures the power of microwaves reflected back towards the microwave source. 
     
     
         12 . The microwave heating apparatus of  claim 10 , wherein, for adjusting the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line, the control unit is configured to:
 move, within the transmission line, an element being at least one of the group including a slug tuner, a motor driven slug tuner, a plunger and a motor driven plunger; or change the geometry or the length of the transmission line.   
     
     
         13 . The microwave heating apparatus of  claim 11 , wherein, for adjusting the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line, the control unit is configured to:
 move, within the transmission line, an element being at least one of the group including a slug tuner, a motor driven slug tuner, a plunger and a motor driven plunger; or change the geometry or the length of the transmission line.   
     
     
         14 . The microwave heating apparatus of  claim 12 , wherein the plunger is positioned proximate the microwave source. 
     
     
         15 . The microwave heating apparatus of  claim 11 , wherein the control unit is configured to adjust the impedance of the transmission line and/or the impedance matching between the microwave source and the transmission line such that the efficiency of the microwave source is increased or maximized if the measured power of the reflected microwaves is below a predetermined threshold and such that the efficiency of the microwave source is decreased or minimized if the measured power of the reflected microwaves is above the predetermined threshold. 
     
     
         16 . The microwave heating apparatus of  claim 11 , wherein the control unit is configured to turn off the microwave source if the measured power of the reflected microwaves is above a security threshold. 
     
     
         17 . The microwave heating apparatus of  claim 11 , wherein the control unit is configured to control the efficiency of the microwave source as a function of the ratio between the measured power of the transmitted microwaves and the power supplied to the microwave source. 
     
     
         18 . The microwave heating apparatus of  claim 14 , wherein the control unit is configured to control the efficiency of the microwave source as a function of the ratio between the measured power of the transmitted microwaves and the power supplied to the microwave source. 
     
     
         19 . The microwave heating apparatus of  claim 18  further comprising a directional coupler adapted to measure the power of the transmitted microwaves and the power of the reflected microwaves. 
     
     
         20 . The microwave heating apparatus of  claim 19 , wherein the microwave source is a magnetron and the operational data is the anode current of the magnetron.