Tuning techniques for a slot antenna

Abstract

A wireless communication device and method for identifying a container, or communication information about a container, using a slot in the container as an antenna. The device includes a wireless communication device for transmitting information regarding the container. The container includes an outer wall forming a rim and a slot between the rim edge and the outer wall that is circular and continues without boundaries. The wireless communication device is coupled to the slot to provide the slot antenna for communications. An impedance matching network is additionally provided to make the operating frequency of the slot substantially the same as the operating frequency of the wireless communication device. Alternatively, shorting posts may be placed in the slot to define boundaries of the slot to match the operating frequency of the slot to the operating frequency of the antenna. Variable impedance matching is provided between the wireless communication device and the slot.

1. A device for identifying a container having a slot, comprising:
 a wireless communication device mounted on the container to communicate remotely information associated with the container;  
 a slot antenna formed by electronically associating said wireless communication device to the slot; and  
 a variable reactance element including sub-elements whose proximity changes as a function of changes in a width associated with the slot, thereby changing reactance characteristics of said slot antenna.  
 
     
     
       2. The device of  claim 1 , wherein said variable reactance element is a variable capacitor. 
     
     
       3. The device of  claim 2 , wherein said variable capacitor's capacitance increases as the width associated with the slot decreases. 
     
     
       4. The device of  claim 2 , wherein the variable capacitor's capacitance decreases as the width associated with the slot decreases. 
     
     
       5. The device of  claim 2 , wherein said variable capacitor includes two parallel plates positioned on flanges. 
     
     
       6. The device of  claim 1 , wherein said variable reactance element is a variable inductor. 
     
     
       7. The device of  claim 6 , wherein said variable inductor includes a helical coil having loops, said loops comprising said sub-elements. 
     
     
       8. The device of  claim 6 , wherein the variable inductor's inductance increases as the width associated with the slot decreases. 
     
     
       9. The device of  claim 6 , wherein the variable inductor's inductance decreases as the width associated with the slot decreases. 
     
     
       10. The device of  claim 1 , wherein the slot is formed from a rim edge and an outer wall. 
     
     
       11. The device of  claim 10 , wherein said variable reactance element comprises a clip positioned between said rim edge and said outer wall. 
     
     
       12. A system for identifying a container, comprising:
 a container having a slot;  
 a wireless communication device mounted on the container to communicate remotely information associated with the container;  
 a slot antenna formed by electronically associating said wireless communication device to said slot, said slot antenna having a variable impedance as a function of a width associated with the slot; and  
 an impedance matching network including a variable reactance element associated with said wireless communication device, said impedance matching network matching impedances between said slot antenna and said wireless communication device.  
 
     
     
       13. The system of  claim 12 , wherein said variable reactance element comprises a variable capacitor. 
     
     
       14. The system of  claim 13 , wherein said variable capacitor increases capacitance as said width decreases. 
     
     
       15. The system of  claim 13 , wherein said variable capacitor decreases capacitance as said width decreases. 
     
     
       16. The system of  claim 12 , wherein said variable reactance element comprises a variable inductor. 
     
     
       17. The system of  claim 16 , wherein said variable inductor increases inductance as said width decreases. 
     
     
       18. The system of  claim 16 , wherein said variable inductor decreases inductance as said width decreases. 
     
     
       19. A method of monitoring a container comprising:
 associating a wireless communication device with the container;  
 moving the container through at least one interrogation point containing an interrogation reader;  
 communicating monitoring information associated with the container between said wireless communication device and said interrogation reader through a slot antenna formed by a slot within the container; and  
 matching impedances between said slot antenna and said wireless communication device with an impedance matching network.  
 
     
     
       20. The method of  claim 19 , wherein matching impedances comprises varying a variable reactance elements within said impedance matching network. 
     
     
       21. The method of  claim 20 , wherein varying a variable reactance element comprises varying a variable capacitor. 
     
     
       22. The method of  claim 21 , wherein varying a variable capacitor comprises compressing two parallel plates as a width associated with said slot decreases. 
     
     
       23. The method of  claim 21 , wherein varying a variable capacitor comprises moving two parallel plates from substantially overlapped positions to positions where said parallel plates have less overlapping areas as a width associated with said slot decreases. 
     
     
       24. The method of  claim 20 , wherein varying a variable reactance element comprises varying a variable inductor. 
     
     
       25. The method of  claim 24 , wherein varying a variable inductor comprises compressing a helical coil, as a width associated with said slot decreases. 
     
     
       26. The method of  claim 24 , wherein varying a variable inductor comprises spreading a helical coil, as a width associated with said slot decreases. 
     
     
       27. The method of  claim 19 , wherein matching impedances comprises varying at least one variable reactance element within said impedance matching network. 
     
     
       28. The method of  claim 19 , wherein matching impedances comprises varying a plurality of variable reactance elements within said impedance matching network. 
     
     
       29. A device for identifying a container having a slot, comprising:
   a wireless communication device mounted on the container to communicate remotely information associated with the container;        a slot antenna formed by electronically associating said wireless communication device to the slot; and        a variable reactance element to change reactance characteristics of said slot antenna.     
     
     
       30. The device of  claim 29 , wherein said variable reactance element is a variable capacitor. 
     
     
       31. The device of  claim 30 , wherein said variable capacitor's capacitance increases as a width associated with the slot decreases. 
     
     
       32. The device of  claim 30 , wherein the variable capacitor's capacitance decreases as a width associated with the slot decreases. 
     
     
       33. The device of  claim 30 , wherein said variable capacitor includes two parallel plates positioned on flanges. 
     
     
       34. The device of  claim 29 , wherein said variable reactance element is a variable inductor. 
     
     
       35. The device of  claim 34 , wherein said variable inductor includes a helical coil having loops. 
     
     
       36. The device of  claim 34 , wherein the variable inductor's inductance increases as a width associated with the slot decreases. 
     
     
       37. The device of  claim 34 , wherein the variable inductor's inductance decreases as a width associated with the slot decreases. 
     
     
       38. The device of  claim 34 , wherein the variable inductor's inductance changes based on a proximity of an element to said variable inductor. 
     
     
       39. The device of  claim 38 , wherein the variable inductor's inductance increases based on a proximity of a ferrite element to said variable inductor. 
     
     
       40. The device of  claim 38 , wherein the variable inductor's inductance decreases based on a proximity of an aluminum element to said variable inductor. 
     
     
       41. The device of  claim 40 , wherein the slot is formed from a rim edge and an outer wall. 
     
     
       42. The device of  claim 38 , wherein said variable reactance element comprises a clip positioned between said rim edge and said outer wall. 
     
     
       43. The system of  claim 29 , wherein said variable reactance element includes sub- elements whose proximity changes as a function of changes in a width associated with the slot to change reactance characteristics of said slot antenna.   
     
     
       44. The system of  claim 16 , wherein the variable inductor's inductance changes based on a proximity of an element to said variable inductor. 
     
     
       45. The system of  claim 44 , wherein the variable inductor's inductance increases based on a proximity of a ferrite element to said variable inductor. 
     
     
       46. The system of  claim 44 , wherein the variable inductor's inductance decreases based on a proximity of an aluminum element to said variable inductor. 
     
     
       47. The method of  claim 24 , wherein the variable inductor's inductance changes based on a proximity of an element to said variable inductor. 
     
     
       48. The system of  claim 47 , wherein the variable inductor's inductance increases based on a proximity of a ferrite element to said variable inductor. 
     
     
       49. The system of  claim 47 , wherein the variable inductor's inductance decreases based on a proximity of an aluminum element to said variable inductor.