Patterned transducer apparatus for correcting spurious signals in said devices

• US 5,023,605 A
• Filed: 01/19/1990
• Issued: 06/11/1991
• Est. Priority Date: 11/25/1988
• Status: Expired due to Fees

• Current Assignee: GTE Products Corporation (Ams-Osram AG)
• Original Assignee: GTE Laboratories Incorporated (Lumen Technologies, Inc.)
• Inventors: McColl, James R.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Weissman, Peter
• Application Number:
  US07/467,112
• Time in Patent Office: 508 Days
• Field of Search: 340/825.31, 340/825.34, 310/313 R, 310/313 B, 310/313 C, 310/313 D, 333/194, 333/196, 307/10.2, 307/10.3, 307/10.5, 307/10.6
• US Class Current: 340/5.61
• CPC Class Codes: B60R 25/04 operating on the propulsion system, e.g. engine or drive motor
• CPC Class Codes: B60R 25/20 Means to switch the anti-theft system on or off
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G07C 2009/00769 with data transmission performed by wireless means
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

The invention features a theft resistant security system for motor vehicles. The system has receptacle with a coupling coil. A SAW (surface acoustical wave) device associated with the receptacle for relative movement thereto is also provided. The SAW device has a code and its own coupling coil for interaction with the receptacle coupling coil. A testing mechanism is connected to the receptacle for determining whether the code of the SAW device is valid for operation of the motor vehicle. Problems of crosstalk and wave reflection may produce spurious code pulses in systems of this type. The invention provides techniques for eliminating or reducing these unwanted pulses.

Claims

1. A security device for a motor vehicle that provides a coded surface acoustical wave which is converted to an electrical signal for comparison with a preset code, said security device comprising:

a substrate having means defining an acoustical wave path; and

a pattern of transducers disposed upon said substrate for providing said coded surface acoustical wave, including a plurality of spaced-apart tap transducers disposed along said acoustical wave path and operatively connected to a main transducer, at least one of said tap transducers is disposed upon said substrate to produce a signal pulse of opposite phase but approximately equal amplitude with respect to a crosstalk signal pulse in order to cancel same, and said pattern of transducers being further characterized by being operative to propagate acoustical waves in a relative direction towards and away from said main transducer to provide a bidirectional wave propagation with respect to said substrate.

2. The security device of claim 1, wherein all of said tap transducers have electrode widths that are narrower than the electrode width of said main transducer.

3. The security device of claim 1, wherein said tap transducers are serially disposed along said substrate, and further wherein each tap transducer defines a given bit position in said code.

4. The security device of claim 3, wherein a first of a series and closest tap transducer with respect to said main transducer is disposed no closer than at a third bit position therefrom, defined by at least three bit lengths.

5. The security device of claim 4, wherein said first of a series and closest tap transducer with respect to said main transducer is placed at a bit length distance from said main transducer that includes an additional fractional part of a bit length more than three bit lengths in order to reduce crosstalk.

6. The security device of claim 1, wherein said operating frequency is approximately less than 50 MHz.

7. The security device of claim 1, wherein said operating frequency is approximately less than 100 MHz.

8. The security device of claim 1, wherein at least one tap transducer has an electrode gap pattern of opposite direction to all of the other tap transducers on said substrate, in order to reduce crosstalk.

9. The security device of claim 1, further including a transmission coil operatively connected across said transducers.

10. The security device of claim 9, wherein an additional resistance is associated with said coil to increase load conductance in order to reduce double wave transit interference.

11. The security device of claim 1, wherein at least one tap transducer does not acoustically interact with the other tap transducers in order to reduce double wave transit interference.

12. The security device of claim 11, wherein the non-interacting tap transducer comprises an acoustic absorber for acoustically isolating aid transducer.

13. A security device for a motor vehicle that provides a coded surface acoustical wave which is converted to an electrical signal for comparison with a preset code, said security device comprising:

a substrate having means defining an acoustical wave path; and

a pattern of transducers disposed upon said substrate for providing said coded surface acoustical wave, including a plurality of spaced-apart, bidirectionally wave propagating, tap transducers serially arranged along said acoustical path and operatively connected to a main transducer, each tap transducer defining a given bit position in said code, and wherein at least one tap transducer is disposed to produce a signal pulse of opposite phase but approximately equal amplitude with respect to a crosstalk signal pulse in order to cancel said crosstalk signal pulse.

14. The security device of claim 13, further including a transmission coil operatively connected across said transducers.

15. The security device of claim 14, wherein an additional resistance is associated with said coil to increase load conductance in order to reduce double wave transit interference.

16. The security device of claim 13, wherein at least one tap transducer does not acoustically interact with the other tap transducers in order to reduce double wave transit interference.

17. The security device of claim 16, wherein the non-interacting tap transducer comprises an acoustic absorber for acoustically isolating said transducer.