Surface acoustic wave component which can be interrogated by radio and has an optimum code size

• US 6,455,979 B2
• Filed: 06/25/2001
• Issued: 09/24/2002
• Est. Priority Date: 12/23/1998
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Sczesny, Oliver, Schmidt, Frank, Vossiek, Martin, Reindl, Leonhard
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US09/891,187
• Publication Number:
  US 20020005677A1
• Time in Patent Office: 456 Days
• Field of Search: 310/313.C, 310/313.D, 310/313.R, 340/572.1, 342/51
• US Class Current: 310/313.00D
• CPC Class Codes: H03H 9/6406 Filters characterised by a particular frequency characteristic
• CPC Class Codes: H04B 1/70712 with demodulation by means of convolvers, e.g. of the SAW type SAW convolvers in general G06G7/195

Abstract

A coding scheme is specified which, compared to the prior art and with the system having a structure resolution of the same magnitude, allows an enlarged code size for the same number of code elements, and/or by which fewer code elements are required per code for a predetermined code size. The code elements are disposed with basic values in a matrix defined in a novel manner, with the matrix having a finer subdivision of the basic values than the subdivision corresponding to the structure resolution. Further development with mean-value formations are possible.

Claims

1. A coded surface acoustic wave component for an ID tag radio interrogation system, the coded surface acoustic wave component comprising:

a substrate wafer having a surface with a piezoelectric material characteristic;

at least one electroacoustic transducer having an interdigital structure disposed on said surface of said substrate wafer, said electroacoustic transducer producing a surface acoustic wave in said surface with a main wave propagation direction governed by said interdigital structure; and

a reflector structure having reflectors functioning as code elements and spaced apart from one another in said main wave propagation direction on said surface of said substrate wafer;

said substrate wafer having a position matrix for positioning said reflectors at correct distances apart, said position matrix having basic values at equal distances from one another aligned in said main wave propagation direction, in said position matrix a size of a matrix spacing is dimensioned on a basis of a movement distance which the surface acoustic wave travels within a time period predetermined by a time-dimensioned measurement inaccuracy of a system, and of the basic values of said position matrix only the basic values occupied by said reflectors as positions distributed corresponding to a respective code are those for which distances between adjacent reflectors are always at least of equal magnitude to a structure resolution resulting from a frequency bandwidth of the system.

2. The component according to claim 1, wherein an equal number of said code elements are in each case assigned to individual codes with a predetermined code size.

3. The component according to claim 2, wherein said substrate wafer has a minimum physical length in a direction of said position matrix resulting from said interdigital structure of said electroacoustic transducer and the predetermined code size with regard to said position matrix.

4. The component according to claim 1, including at least one sensor structure disposed on said surface of said substrate wafer.

5. The component according to claim 1, wherein said code elements can be additionally weighted for enlarging a code size.

6. The component according to claim 1, including reference elements disposed on said substrate wafer.

7. A coded surface acoustic wave component for an ID tag radio interrogation system, comprising:

a substrate wafer having a surface with a piezoelectric material characteristic;

electroacoustic transducers having interdigital structures disposed on said surface of said substrate wafer, said elecrtoacoustic transducers producing surface acoustic waves in said surface with main wave propagation directions governed by said interdigital structures; and

resonator structures functioning as code elements each having a resonant frequency, said resonator structures each with respect to a respective one of said electroacoustic transducers, being disposed in a respective main wave propagation direction thereof, said resonator structures formed according to a frequency matrix having frequencies at equal intervals from one another as basic values of said frequency matrix for determining individual resonant frequencies of said resonator structures, a size of a frequency interval between said basic values within said frequency matrix dimensioned on a basis of a measurement inaccuracy with which a frequency can be measured in a system, and in said frequency matrix said resonant frequency for each of said resonator structures selected such that, within said frequency matrix, only resonant frequencies which are used for said resonator structures are those that a respective frequency separation between two of said resonator structures provided for adjacent resonant frequencies is at least of equal magnitude to a structure resolution of a frequency measurement resulting from a resonance duration of an individual resonator in the system.

8. The component according to claim 7, wherein an equal number of said code elements are in each case assigned to individual codes within a predetermined code size.

9. The component according to claim 7, including at least one sensor structure disposed on said substrate wafer.

10. The component according to claim 7, wherein said code elements can be additionally weighted for enlarging a code size.

11. The component according to claim 7, including reference elements disposed on said substrate wafer.

12. A method for carrying out a determination of a respective code of a coded surface acoustic wave component, which comprises the steps of:

detecting response signals of individual code elements of the respective code a number of times successively;

forming an average value from the response signals for each code element resulting in a plurality of average values; and

determining a measure representing a measurement inaccuracy from the response signals of the individual code elements of the respective code.

13. The method according to claim 12, which comprises deriving the measure representing the measurement inaccuracy as a mean deviation between measured values of the response signals of each code element and its mean value (=statistical standard deviation).

14. The method according to claim 12, which comprises detecting the response signals of the individual code elements a large number of times in such a manner that a determined mean measurement inaccuracy of all the averaged values is reduced to a measure such that the measure is less than a predetermined measure of the measurement inaccuracy on a basis of which a matrix size of the coded surface acoustic wave component is formed.

15. The method according to claim 13, which comprises detecting the response signals of the individual code elements a large number of times in such a manner that a determined mean measurement inaccuracy of a representative mean value is reduced to a measure such that the measure is less than a predetermined measure of the measurement inaccuracy on a basis of which a matrix size of the coded surface acoustic wave component is formed.

16. The method according to claim 12, which comprises:

carrying out the determination of the respective code of the coded surface acoustic wave component having reference elements;

interrogating the reference elements a number of times successively and at least one of averaged scaling values and offset values are determined from the response signals obtained a number of times; and

correcting the response signals of the code elements using the averaged scaling values and the offset values.

17. The method according to claim 14, which comprises detecting the response signals of the individual code elements a large number of times in such a manner that a determined mean measurement inaccuracy of a representative mean value is reduced to a measure such that the measure is less than a predetermined measure of the measurement inaccuracy on a basis of which a matrix size of the coded surface acoustic wave component is formed.