METHOD AND APPARATUS FOR SIGNAL PATH EQUALIZATION IN A SCANNING ACOUSTIC MICROSCOPE

• US 20130128690A1
• Filed: 04/30/2012
• Published: 05/23/2013
• Est. Priority Date: 11/18/2011
• Status: Active Grant

• Current Assignee: Sonix, Inc. (Fortive Corp.)
• Original Assignee: Sonix, Inc. (Fortive Corp.)
• Inventors: McKeon, James C.P., Gopalan, Sriram
• Granted Patent: US 9,625,572 B2
• Time in Patent Office: Days
• US Class Current: 367/7
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01N 29/0681 by acoustic microscopy, e.g. scanning acoustic microscopy
• CPC Class Codes: G01N 29/44 Processing the detected response signal , e.g. electronic circuits specially adapted therefor digital signal processing per se G06F17/00
• CPC Class Codes: G01Q 30/06 for error compensation
• CPC Class Codes: G01S 15/8938 using transducers mounted for mechanical movement in two dimensions
• CPC Class Codes: G01S 7/5205 Means for monitoring or calibrating

Abstract

A scanning acoustic microscope includes a signal processor and one or more signal paths. In operation, each signal path couples an ultrasonic transducer to the signal processor that processes signals received from the signal paths to produce an ultrasonic scan image. Each signal path has a response characteristic that includes a response characteristic of the ultrasonic transducer. In order to compensate for variations between the signal paths or variations between different transducers in the same signal path, at least one of the signal paths includes a signal path equalizer. The equalizer may be responsive to a set of equalization coefficients. The coefficients are selected such that the response characteristic of the signal path including the equalizer more closely matches a reference characteristic response. The equalizer may operate on a transmitted or received signal or be used to generate an ultrasonic pulse.

Claims

1. A scanning acoustic microscope comprising:

a signal processor; and

one or more signal paths, each signal path of the one or more signal paths being operable to couple an ultrasonic transducer to the signal processor, and each signal path of the one or more signal paths having a response characteristic that comprises a response characteristic of the ultrasonic transducer of the signal path;

where at least one first signal path of the one or more signal paths comprises a signal path equalizer, and

where the signal processor is operable to process signals received from the one or more signal paths and produce an ultrasonic scan image from the received signals.

2. A scanning acoustic microscope in accordance with claim 1, wherein the signal path equalizer is responsive to a set of equalization coefficients.

3. A scanning acoustic microscope in accordance with claim 2, wherein the set of equalization coefficients are selected such that the response characteristic of the at least one first signal path more closely matches a reference characteristic response.

4. A scanning acoustic microscope in accordance with claim 3, wherein the reference characteristic response is dependent upon the response characteristics of a plurality of ultrasonic transducers.

5. A scanning acoustic microscope in accordance with claim 3, wherein the reference response characteristic comprises an average of the response characteristics of a plurality of ultrasonic transducers from a plurality of scans.

6. A scanning acoustic microscope in accordance with claim 2, further comprising a memory operable to store the set of equalization coefficients associated with the at least one first signal path.

7. A scanning acoustic microscope in accordance with claim 2, wherein the set of equalization coefficients comprises a frequency domain transfer function.

8. A scanning acoustic microscope in accordance with claim 2, wherein the set of equalization coefficients comprises a set of coefficients for a time domain filter.

9. A scanning acoustic microscope in accordance with claim 2, wherein the set of equalization coefficients comprises gain values for each signal path.

10. A scanning acoustic microscope in accordance with claim 1, wherein the signal path equalizer comprises a programmed processor operable to execute a program of instructions.

11. A scanning acoustic microscope in accordance with claim 1, wherein the signal path equalizer comprises a hardware filter external to the signal processor.

12. A scanning acoustic microscope in accordance with claim 1, wherein a signal path of the one or more signal paths comprises a receiver, an amplifier and an analog-to-digital converter and wherein the signal processor comprises a digital signal processor.

13. A scanning acoustic microscope in accordance with claim 12, wherein the signal path of the one or more signal paths further comprises a pulse generator.

14. A scanning acoustic microscope in accordance with claim 12, wherein the signal path equalizer is in the signal path before the analog-to-digital converter.

15. A scanning acoustic microscope in accordance with claim 12, wherein the signal path equalizer is in the signal path after the analog-to-digital converter.

16. A scanning acoustic microscope in accordance with claim 1, wherein a signal path of the one or more signal paths comprises a time gate operable to receive signals from the signal path equalizer.

17. A scanning acoustic microscope in accordance with claim 1, wherein a signal path of the one or more signal paths comprises a time gate operable to pass signals to the signal path equalizer.

18. A scanning acoustic microscope in accordance with claim 1,

wherein the scanning acoustic microscope comprises a pulse-echo scanning acoustic microscope,

an ultrasonic transducer of the one or more ultrasonic transducers is operable to generate and receive ultrasound, and

the characteristic response of the signal path comprises both the generation and reception response characteristics of the ultrasonic transducer.

19. A scanning acoustic microscope in accordance with claim 1, wherein a signal path of the one or more signal paths is operable to couple an ultrasonic transmitter and an ultrasonic receiver to the signal processor and wherein the characteristic response of the signal path comprises the response characteristic of the ultrasonic transmitter and the response characteristic of the ultrasonic receiver.

20. A scanning acoustic microscope in accordance with claim 1, wherein the one or more signal paths comprise a plurality of signal paths, each signal path of the plurality of signal paths comprising a signal path equalizer responsive to a set of equalization coefficients that are dependent upon the response characteristic of the signal path.

21. A method for performing an ultrasonic scan of an object using one or more ultrasonic transducers, the method comprising:

at each of a plurality of scan points;

receiving ultrasound at one or more ultrasonic transducers, the ultrasound produced in response to one or more ultrasound pulses incident upon the object;

transmitting a plurality of response signals from the one or more ultrasound pulses along one or more signal paths, each signal path comprising an ultrasonic transducer of the one or more ultrasonic transducers; and

processing the plurality of response signals from the plurality of scan points to produce the ultrasonic image,

where transmitting a first response signal of the plurality of response signals along a first signal path of the one or more signal paths comprises equalizing the first response signal to compensate, at least partially, for differences between the response characteristic of the first signal path and a reference response characteristic.

22. A method in accordance with claim 21, wherein equalizing the first response signal comprises:

determining spectral components of the first response signal;

scaling the spectral components by transfer function values to obtain scaled spectral components; and

generating an equalized first response signal from the scaled spectral components.

23. A method in accordance with claim 22, wherein equalizing the first response signal comprises passing the first response signal through a time domain filter.

24. A method in accordance with claim 23, wherein the time domain filter comprises a sampled data filter.

25. A method in accordance with claim 21, wherein the one or more ultrasonic transducers comprise a plurality of ultrasonic transducers, the method further comprising:

holding the plurality of ultrasonic transducers spaced apart from one another; and

moving the plurality of ultrasonic transducers together in a scan path between the plurality of scan points such that the spacing between ultrasonic transducers is maintained.

26. A method in accordance with claim 21, further comprising:

measuring responses from one or more ultrasonic transducers; and

combining the responses to produce a reference response,

wherein equalizing the first signal produces an equalized response that substantially matches the reference response.

27. A method in accordance with claim 21, further comprising:

measuring one or more responses along the first signal path; and

determining a relationship between the one or more responses and the reference response,

wherein equalizing the first response signal, to substantially compensate for differences between the response of the first signal path and a reference response, is dependent upon the relationship between the one or more responses and the reference response.

28. A method in accordance with claim 21, further comprising:

at each of a plurality of scan points;

generating the one or more ultrasound pulses incident upon the object from the one or more ultrasonic transducers.

29. A method in accordance with claim 21, further comprising:

at each of a plurality of scan points;

generating the one or more ultrasound pulses incident upon the object from one or more further ultrasonic transducers.

30. A method for performing an ultrasonic scan of an object using a plurality of ultrasonic transducers, the method comprising:

for one or more signal paths of a plurality of signal paths that each comprise one or more ultrasonic transducers;

equalizing an excitation waveform to compensate, at least partially, for differences between the response characteristic of the signal path and a reference response characteristic, to produce an equalized excitation waveform for the associated signal path; and

at each of a plurality of scan points;

transmitting each equalized excitation waveform along the associated signal path of the plurality of signal paths to produce ultrasound pulses incident upon the object;

receiving ultrasound, produced in response to the ultrasound pulses, at a plurality of ultrasonic transducer to produce a plurality of response signals; and

processing the plurality of response signals from the plurality of scan points to produce the ultrasonic image.

31. A scanning acoustic microscope comprising:

a signal processor;

a signal path operable to couple an ultrasonic transducer of a plurality of ultrasonic transducers to the signal processor, the signal path having a response characteristic that comprises a response characteristic of the ultrasonic transducer; and

a signal path equalizer, in the signal path, responsive to a set of equalization coefficients that are selected, dependent upon the ultrasonic transducer in the signal path, such that the response characteristic of the signal path more closely matches a reference characteristic response,

the signal processor being operable to process signals received from the signal path to produce an ultrasonic scan image.

32. A scanning acoustic microscope in accordance with claim 31, further comprising a memory operable to store a plurality of sets of equalizer coefficients, each set of equalizer coefficients of the plurality of sets of equalizer coefficients corresponding to an ultrasonic transducer of the plurality of ultrasonic transducers.

33. A scanning acoustic microscope in accordance with claim 31, further comprising:

a network interface operable to link, via a network, to a remote memory, wherein the remote memory is operable to store a plurality of sets of equalizer coefficients, each set of equalizer coefficients of the plurality of sets of equalizer coefficients corresponding to an ultrasonic transducer of the plurality of ultrasonic transducers.