Method and device for remote sensing of objects

• US 5,576,693 A
• Filed: 09/06/1994
• Issued: 11/19/1996
• Est. Priority Date: 01/20/1992
• Status: Expired due to Term

• Current Assignee: Demodulation Incorporated
• Original Assignee: RSO Corporation N.V.
• Inventors: Persson, Leif, Tyren, Carl
• Primary Examiner(s): SWANN III, GLEN R
• Application Number:
  US08/256,483
• Time in Patent Office: 805 Days
• Field of Search: 340/572, 340/551
• US Class Current: 340/572.4
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01D 5/14 influencing the magnitude of a current or voltage
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10059 transponder driven
• CPC Class Codes: G08B 13/2408 using ferromagnetic tags
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2485 Simultaneous detection of multiple EAS tags

Abstract

The invention relates to a method and a device for remote sensing of objects, said method including the steps of marking said objects with at least one label (10) comprising at least one electrical resonant circuit (14) having an induction means (11) and a capacitor means (12), exciting said resonant circuit (14) to resonance at a resonant frequency, and detecting said resonant frequency of said resonant circuit (14) by the electromagnetic energy transmitted from said resonant circuit (14). An element (13) of a magnetic material having a varying permeability is coupled inductively to said induction element (11). The resonant frequency of said resonant circuit (14) is affected by the permeability of said element (13) of magnetic material, and said element (13) of magnetic material is exposed to an external and spatially heterogenous magnetic bias field through which the permeability of said element (13) of magnetic material is controlled. The invention relates also to methods for coding labels and for noise suppression of signals received from said labels.

Claims

1. Method of remote sensing of objects comprising the steps of:

marking said objects with at least one label including at least one electrical resonance circuit having an inductive element and a capacitive element;

exciting said resonance circuit to oscillate at a resonance frequency within a radio frequency spectrum; and

detecting the resonance frequency of the resonance circuit through the electromagnetic energy transmitted from said resonance circuit, the detecting step including the steps of

inductively coupling an element of magnetic material having a varying permeability to said inductive element,

affecting the resonance frequency of the resonance circuit through the permeability of the element of magnetic material, and

exposing said element of magnetic material to an external and spatially heterogeneous magnetic bias field to control the permeability of said element of magnetic material.

2. Method according to claim 1 wherein the permeability of said element of magnetic material controls the resonance frequency of a plurality of resonance circuits.

3. Method according to claim 1 wherein one element of magnetic material is inductively coupled to inductive elements of at least two electrical resonance circuits.

4. A device for remote sensing of objects, each object being marked with at least one label including at least one electric resonant circuit having an inductive element and a capacitive element, said resonant circuit being formed to be excited to oscillation at a resonant frequency within the radio frequency spectrum, the device comprising:

an electrical excitation means for producing an electromagnetic signal exciting said resonant circuit;

a detecting means, sensitive to electromagnetic radiation, for detecting electromagnetic radiation from said resonant circuit, said resonant circuit including at least one element inductively coupled to said inductive element, said at least one element being formed of a magnetic material having a varying permeability for affecting the resonant frequency of said resonant circuit; and

a magnetic field generating means for generating, in an interrogation zone, a spatially heterogeneous magnetic bias field by which the permeability of said element of magnetic material is affected.

5. Device according to claim 4, wherein said element of magnetic material is mechanically anchored to prevent mechanical oscillation.

6. Device according to claim 4, wherein said label is provided with a combination of mechanically anchored and mechanically free elements of magnetic material.

7. Device according to claim 4, wherein said electric resonant circuit comprises a plurality of elements of magnetic material having different magnetic characteristics.

8. Device according to claim 4, wherein said label comprises a combination of resonant circuits collectively forming an item code of the object.

9. Device according to claim 4, wherein said means for generating a magnetic field is formed to generate an adjustably modulated signal for generating a modulated bias field.

10. Device according to claim 4, wherein said element of magnetic material is made of an amorphous material.

11. Device according to claim 10 wherein said inductive element and said magnetic element are combined into a web like structure.

12. Method for determining in three dimensions the position and orientation of objects marked with at least one label including at least one electric resonant circuit having an inductive element and capacitive element, the method comprising the steps of:

exciting said resonant circuit to oscillation at a resonant frequency within the radio frequency spectrum; and

detecting the resonant frequency of the resonant circuit by the electromagnetic energy transmitted from said resonant circuit, the detecting step including the steps of

inductively coupling an element made of magnetic material of a varying permeability to said inductive element such that the resonant frequency of said resonant circuit is controlled by the permeability of the element made of magnetic material,

exposing the element made of magnetic material to an external magnetic bias field which is known in all points with a desired resolution with regard to strength and/or direction, through which bias field the permeability of said element made of magnetic material is affected, and

determining the position and orientation of the objects using the resonant frequency detected and controlled by said magnetic bias field.

13. Method of remote sensing of objects, comprising the steps of:

providing an object with an element made of a material, the characteristics thereof being influenced by a surrounding magnetic field;

exposing said element to a magnetic field strength H;

detecting the influence of the field strength on the characteristics by receiving a signal of magnetic or electromagnetic radiation from said element;

varying the magnetic field strength H according to a predetermined function;

comparing said received signal to said predetermined function; and

using any parts of the received signal having a predetermined correlation with the predetermined function for the remote sensing of the object.

14. Method according to claim 13, wherein the predetermined function is a function varying in time with a certain frequency, said received signal is fed to a Phase Locked Loop (PLL) comprising a voltage controlled oscillator and a phase detector, the output thereof controlling the frequency of the oscillator, the output signal of said phase detector being related to the frequency of the varying function when said loop has been locked to the received signal, and wherein the output level of the phase detector is compared to a predetermined level corresponding to a certain frequency of the varying function, a correlation between the output level and the predetermined level indicating that the received signal originates from a remotely detected element.

15. Method according to claim 14, wherein said magnetic field strength H is controlled to vary in time and a time varying part of the received signal is separated and used for the remote sensing.

16. Method for coding remotely detected labels, comprising the steps of:

providing at least two elements for each label, the characteristics thereof being changed by an external magnetic field, said label being exposed to a biasing magnetic field covering a detecting volume that is larger than the label for detecting the characteristics of said elements changed by said magnetic field;

orienting elements of each label in predetermined mutual relationships for providing an identity to the label determined by said relationships when said elements are exposed to a sequence of different field distributions, the local field distribution of the biasing field over said label being continuously determined;

wherein the mutual relationship between the elements is determined depending on the orientation of each element in the local field distribution by comparing actual properties of the elements influenced by said magnetic field, and expected properties of elements arranged in predetermined relationships to each other in the local field distribution.

17. Method according to claim 16, wherein said elements are elongated, and said elements are oriented in fixed mutual angle relationships with regard to the longitudinal direction of said elements.

18. Method according to claim 16, wherein said elements are elongated, and said elements are oriented with fixed mutual distances in a direction transverse to the longitudinal direction of said elements.

19. Method according to claim 16, wherein the orientation of the elements is determined in relation to a reference element.

20. Method according to claim 19, wherein the local field distribution is determined by providing at least two reference elements on the label, said reference elements being located with a known mutual orientation.