Single phase unidirectional surface acoustic wave transducer and improved reflectors

• US 20050099090A1
• Filed: 10/08/2004
• Published: 05/12/2005
• Est. Priority Date: 10/08/2003
• Status: Active Grant

• Current Assignee: RF Saw Components Incorporated
• Original Assignee: RF Saw Components Incorporated
• Inventors: Hartmann, Clinton S., Plesski, Viktor P.
• Granted Patent: US 7,173,360 B2
• Time in Patent Office: Days
• US Class Current: 310/313.00D
• CPC Class Codes: H03H 9/02685 Grating lines having particular arrangements
• CPC Class Codes: H03H 9/02771 Reflector banks
• CPC Class Codes: H03H 9/14505 Unidirectional SAW transducers

Abstract

A unidirectional transducer for a surface acoustic wave (SAW) device. In one embodiment the device includes (1) a defined area on a piezoelectric substrate within which is located an open circuit reflector perpendicular to the SAW direction of propagation; and a pair of low reflectivity transducer electrodes located within the defined area and connected to opposing bus bars, the electrodes perpendicular to the direction of the SAW propagation and positioned with the excitation center of the pair of electrodes located about seven-eighths of a Rayleigh wavelength at a center frequency of the SAW from the reflector.

Claims

23. A SAW device, comprising:

a piezoelectric substrate having a SAW transducer located thereon; and

a reflector on said substrate for reflecting a response to an interrogation pulse generated by said SAW transducer, said reflector arranged on said substrate to substantially match the diffraction field of said interrogation pulse.

1. A surface acoustic wave (SAW) device, comprising:

a defined area on a piezoelectric substrate within which is located an open circuit reflector perpendicular to the SAW direction of propagation; and

a pair of low reflectivity transducer electrodes located within said defined area and connected to opposing bus bars, said electrodes perpendicular to the direction of said SAW propagation and positioned with the excitation center of said pair of electrodes located about seven-eighths of a Rayleigh wavelength at a center frequency of said SAW from said reflector.

2. The device as recited in claim 1 wherein said defined area is a distance about equal to twice said Rayleigh wavelength at a center frequency of said SAW, plus said Rayleigh wavelength of a center frequency of said SAW multiplied by a positive integer minus one.

3. The device as recited in claim 1 wherein said electrodes are separated by a distance of about one-half of said Rayleigh wavelength at a center frequency of said SAW.

4. The device as recited in claim 1 wherein said electrodes each have a width of about one-fourth of said Rayleigh wavelength at a center frequency of said SAW.

5. The device as recited in claim 1 wherein said open circuit reflector is aluminum.

6. The device as recited in claim 1 wherein said electrodes are aluminum.

7. The device as recited in claim 6 wherein said electrodes have a low total reflectivity.

8. The device as recited in claim 6 wherein said electrodes have a thickness about equal to one-tenth of said Rayleigh wavelength at a center frequency of said SAW.

9. The device as recited in claim 1 further comprising utilizing a piezoelectric substrate such that the mechanical reflectivity has an opposite sign as compared to the electrical part of the reflectivity of said pair of electrodes and said reflector.

10. The device as recited in claim 1 wherein said piezoelectric substrate is 128°

LiNbO3.

11. The device as recited in claim 1 wherein the width of said electrodes is less than one-quarter wavelength.

12. The device as recited in claim 1 wherein the width of said reflector is between 0.3 wavelength and 0.5 wavelength.

13. The device as recited in claim 1 further comprising at least two open circuit reflectors having a width of about one-fourth wavelength and separated by a distance of about one-half wavelength.

14. The device as recited in claim 1 wherein said excitation center of said pair of electrodes located about seven-eighths of a Rayleigh wavelength at a center frequency of said SAW from said reflector is varied by an amount equal to plus or minus ten percent of said seven-eighths of a Rayleigh wavelength.

15. The device as recited in claim 1 further comprising at plurality of pairs of electrodes, each of said pairs of electrode offset at a distance equal to a number of wavelengths and connected to the same bus bars in the same sequence of polarity.

16. The device as recited in claim 1 further comprising a plurality of equivalent reflectors, with each reflector offset at a distance equal to a number of wavelengths from each other such that said reflectors do not overlap said electrodes.

17. The device as recited in claim 1 further comprising a periodic set of said defined areas.

18. The device as recited in claim 17 wherein said periodic set of said defined areas are situated quasi-periodically with the period equal to the length of said defined area or greater than the said length by an integer number of wavelengths, said wavelength slowly changing (chirped) along the length of said piezoelectric substrate.

20. The device as recited in claim 1 wherein said device is used as a unidirectional SAW transducer for application with low loss.

21. The device as recited in claim 1 further comprising a plurality of said defined areas are placed in parallel acoustic sub channels, separated by a distance comparable to the wavelength in the direction perpendicular to the propagation direction of the wave, and electrically connected in parallel.

22. The device as recited in claim 1 wherein said defined space is located on a SAW identification tag.

24. The device as recited in claim 23 wherein said reflector is located in the far field of said interrogation pulse.

25. The device as recited in claim 23 wherein said reflector is located in the near field of said interrogation pulse.

26. The device as recited in claim 23 further comprising a plurality of reflectors arranged on said substrate.

27. The device as recited in claim 26 wherein at least one of said plurality of reflectors is located in the near field and at least one of said plurality of reflectors is located in the far field of said interrogation pulse.

28. The device as recited in claim 23 wherein said reflector is curved to substantially match a contour of constant phase in the diffraction field of said interrogation pulse.

29. The device as recited in claim 23 wherein said reflector is curved to substantially match a contour of constant amplitude in the diffraction field of said interrogation pulse.

30. The device as recited in claim 23 wherein said reflector is curved to substantially match the contour of constant phase and the contour of constant amplitude in the diffraction field of said interrogation pulse.

32. The device as recited in claim 23 wherein said reflector is segmented to form a substantial curvature shape to substantially match either the contour of constant phase or the contour of constant amplitude in the diffraction field of said interrogation pulse.

33. The device as recited in claim 23 wherein said reflector is an open circuit metallic strip.

34. The device as recited in claim 23 wherein said reflector is an short circuit metallic strip

35. The device as recited in claim 23 wherein said reflector is non-metallic.

36. The device as recited in claim 23 wherein said reflector is segmented.

37. The device as recited in claim 36 wherein the space between each of said segments is about equal to one-quarter of a wavelength.

38. The device as recited in claim 23 wherein said reflector encompasses the main lobe and first sidelobes of said interrogation pulse.

39. The device as recited in claim 28 wherein said reflector encompasses the main lobe and first sidelobes of said interrogation pulse and eight segments are used for said main lobe and four segments are used for each of said sidelobes.

32-1. The device as recited in claim 30 wherein said reflector focuses a reflected pulse at said transducer that substantially matches the amplitude and phase distribution of said interrogation pulse generated by said transducer.

40. A SAW device, comprising:

a piezoelectric substrate having a SAW transducer located thereon; and

a reflector on said substrate for reflecting a response to an interrogation pulse generated by said SAW transducer, said reflector arranged on said substrate in a substantially curvature configuration to substantially match the amplitude and phase of the diffraction field of said interrogation pulse.