Method of detecting relative direction of motion of a radio frequency (RF) tag

• US 6,204,765 B1
• Filed: 03/13/1999
• Issued: 03/20/2001
• Est. Priority Date: 12/23/1997
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Inkrmec IP Corporation
• Inventors: Martinez, Rene D., Brady, Michael J., Moskowitz, Paul A.
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): PHAM, TOAN NGOC
• Application Number:
  US09/268,422
• Time in Patent Office: 738 Days
• Field of Search: 340/572.1, 340/572.2, 340/572.4, 340/825.49, 340/825.54, 340/825.71, 340/10.1, 340/10.51, 340/10.52, 342/42, 342/104, 342/107, 342/109, 342/147, 342/158, 342/357.01, 342/357.08, 342/450, 342/453, 342/114
• US Class Current: 340/572.1
• CPC Class Codes: G01S 11/06 using intensity measurements
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal

Abstract

A method of determining relative motion between a base station and an RF Tag is disclosed, wherein a property of the RF field at the position of the tag is determined at a first time and at a second time and is used to calculate the relative motion.

Claims

1. A method of determining the relative motion between a radio frequency (RF) transponder (tag) and a base station, wherein the base station produces an RF field at the position of the tag, comprising:

a) determining a property of the RF field at the position of the tag at a first time t₁;

b) determining the property of the RF field at the position of the tag at a second time t₂; and

c) determining the relative motion between the tag and the base station.

2. The method of claim 1, where the property of the RF field is the field strength of the RF field.

3. The method of claim 2, where the field strength of the RF field at the position of the tag is determined by determining the strength of the RF field backscattered from the tag to the base station.

4. The method of claim 2, where the field strength of the RF field at the position of the tag is determined by comparing a voltage induced in the tag with a comparison voltage.

5. The method of claim 4, where the comparison voltage is a comparison voltage used by the tag to determine if the tag may write to the tag non-volatile memory.

6. The method of claim 2, where the field strength of the RF field is asymmetric with respect to the base station.

7. The method of claim 6, where the field strength of the RF field at the position of the tag is determined by determining the strength of the RF field backscattered from the tag to the base station.

8. The method of claim 6, where the field strength of the RF field at the position of the tag is determined by comparing a voltage induced in the tag with a comparison voltage.

9. The method of claim 8, where the comparison voltage is a comparison voltage used by the tag to determine if the tag may write to the tag non-volatile memory.

10. The method of claim 1, where the property of the RF field is the phase of the RF field.