Method and apparatus for signal path equalization in a scanning acoustic microscope

• US 9,625,572 B2
• Filed: 04/30/2012
• Issued: 04/18/2017
• Est. Priority Date: 11/18/2011
• Status: Active Grant

• Current Assignee: Sonix, Inc. (Fortive Corp.)
• Original Assignee: Sonix, Inc. (Fortive Corp.)
• Inventors: Gopalan, Sriram, McKeon, James C. P.
• Primary Examiner(s): Raymond, Edward
• Application Number:
  US13/459,667
• Publication Number:
  US 20130128690A1
• Time in Patent Office: 1,814 Days
• Field of Search: 702103
• 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 configured to couple to two or more ultrasonic transducers;

a first signal path configured to couple first and second ultrasonic transducers of the two or more ultrasonic transducers to the signal processor, the first signal path comprising a first signal path equalizer configured to adjust a strength of a waveform from the first signal path and at least one of a shape and a phase of the waveform, and

a coefficient memory coupled to the first signal path equalizer, the coefficient memory configured to store a first set of equalization coefficients associated with the first ultrasonic transducer and a second set of equalization coefficients associated with the second ultrasonic transducer;

where, when the first signal path couples the first ultrasonic transducer to the processor, the first signal path equalizer is configured by the first set of equalization coefficients, such that the first signal path equalizer compensates, at least partially, for differences between the response characteristic of the first ultrasonic transducer and a reference transducer response, and where the first set of equalization coefficients are selected such that a waveform from the first ultrasonic transducer more closely matches a waveform from a reference transducer in both strength and shape or in both strength and phase, and

where, when the first signal path couples the second ultrasonic transducer to the processor, the first signal path equalizer is configured by the second set of equalization coefficients, such that the first signal path equalizer compensates, at least partially, for differences between the response characteristic of the second ultrasonic transducer and the reference transducer response, and where the second set of equalization coefficients are selected such that a waveform from the second ultrasonic transducer more closely matches a waveform from the reference transducer in both strength and shape or in both strength and phase.

2. A scanning acoustic microscope in accordance with claim 1, wherein the first signal couples to the first ultrasonic transducer during a first time period, and couples to the second ultrasonic transducer during a second time period.

3. A scanning acoustic microscope in accordance with claim 1 further comprising:

a second signal path,

wherein during a first time period the first signal path couples to the first ultrasonic transducer and second signal path couples to the second ultrasonic transducer.

4. A scanning acoustic microscope in accordance with claim 1, wherein the reference transducer response is determined dependent upon the response characteristics of a plurality of ultrasonic transducers.

5. A scanning acoustic microscope in accordance with claim 1, wherein the reference transducer response 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 3, wherein the second signal path comprises a second signal path equalizer and wherein the second signal path equalizer is configured by the second set of equalizer coefficients, such that the second signal path equalizer compensates, at least partially, for differences between the response characteristic of the second ultrasonic transducer and the reference transducer response.

7. A scanning acoustic microscope in accordance with claim 1, wherein at least the first set of equalization coefficients comprises a frequency domain transfer function.

8. A scanning acoustic microscope in accordance with claim 1, wherein at least the first set of equalization coefficients comprises a set of coefficients for a time domain filter, wherein the first signal path equalizer is held constant during operation of the scanning acoustic microscope.

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

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

11. A scanning acoustic microscope in accordance with claim 1, wherein the first signal path comprises a receiver, an amplifier and an analog-to-digital converter and wherein the signal processor comprises a digital signal processor.

12. A scanning acoustic microscope in accordance with claim 11, wherein the first signal path further comprises a pulse generator.

13. A scanning acoustic microscope in accordance with claim 11, wherein the first signal path equalizer is in the first signal path before the analog-to-digital converter.

14. A scanning acoustic microscope in accordance with claim 11, wherein the first signal path equalizer is in the first signal path after the analog-to-digital converter.

15. A scanning acoustic microscope in accordance with claim 1, wherein the first signal path comprises a time gate operable to receive signals from the signal path equalizer.

16. A scanning acoustic microscope in accordance with claim 1, wherein the first signal path comprises a time gate operable to pass signals to the first signal path equalizer.

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

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

the first and second ultrasonic transducers are operable to generate and receive ultrasound, and

the response characteristic of the first ultrasonic transducer comprises both the generation and reception response characteristics of the first ultrasonic transducer, and

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

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

wherein the first ultrasonic transducer comprises an ultrasonic transmitter and the second ultrasonic transducer comprises an ultrasonic receiver,

wherein the first signal path comprises a transmission path that couples the first ultrasonic transducer to the signal processor and a reception path that couples the second ultrasonic transducer 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, and

wherein the first signal path equalizer is configured by a third set of equalization coefficients, such that the first signal path equalizer compensates, at least partially, for differences between the response characteristic of the first and second ultrasonic transducer and the reference transducer response.

19. A scanning acoustic microscope in accordance with claim 1, further comprising one or more second signal paths, each second signal path comprising a second signal path equalizer responsive to a set of equalization coefficients, stored in the coefficient memory, that are dependent upon the response characteristic of an ultrasonic transducer coupled to the signal processor via the second signal path.

31. A scanning acoustic microscope in accordance with claim 1, wherein the first ultrasonic transducer is configured to generate ultrasound in response to an excitation waveform transmitted along the first signal.

33. A scanning acoustic microscope in accordance with claim 1, wherein the first ultrasonic transducer is configured to receive ultrasound and, in response, produces a response signal that is transmitted along the first signal path.

34. A scanning acoustic microscope in accordance with claim 1, wherein the first ultrasonic transducer is configured to both generate and receive ultrasound, wherein the first signal path includes a transmission path and a reception path and wherein the first signal equalizer is in the transmission path or the reception path.

35. A scanning acoustic microscope in accordance with claim 1, wherein configuration of the first signal path equalizer is held constant during operation of the scanning acoustic microscope.

20. A method for performing an ultrasonic scan of an object using

two or more ultrasonic transducers, the method comprising:

at each of a plurality of scan points, in response to an ultrasound pulse incident upon the object;

receiving a first response waveform from a first ultrasonic transducer of the two or more ultrasonic transducers, the first response waveform related to the incident ultrasound pulse by a first transducer response characteristic;

receiving a second response waveform from a second ultrasonic transducer of the two or more ultrasonic transducers, the second response waveform related to the incident ultrasound pulse by a second transducer response characteristic;

transmitting the first response waveform along a first signal path that couples the first ultrasonic transducer to a signal processor;

transmitting the second response waveform along a second signal path that couples the second ultrasonic transducer to the signal processor; and

processing, in the signal processor, the first and second response waveforms from each of the plurality of scan points to produce the ultrasonic image,

where transmitting the first response waveform along the first signal path comprises compensating the strength and at least one of the shape and phase of the first response waveform in a first signal path equalizer, to compensate, at least partially, for differences between the transducer response characteristic of the first ultrasonic transducer and a reference transducer response, such that the first response waveform more closely matches a waveform from a reference transducer, and

where transmitting the second response waveform along the second signal path comprises equalizing the second response waveform in a second signal path equalizer, to compensate, at least partially, for differences between the transducer response characteristic of the second ultrasonic transducer and the reference transducer response, such that the second response waveform more closely matches a waveform from the reference transducer.

21. A method in accordance with claim 20, wherein equalizing the first response signal comprises:

determining frequency domain 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.

22. A method in accordance with claim 21, wherein equalizing the first response signal comprises passing the first response signal through a time domain filter, wherein the characteristic of the time domain filter is held constant during the ultrasonic scan.

23. A method in accordance with claim 22, wherein the time domain filter comprises a sampled data filter.

24. A method in accordance with claim 20, further comprising:

holding the first and second ultrasonic transducers spaced apart from one another; and

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

25. A method in accordance with claim 20, further comprising:

measuring responses from one or more ultrasonic transducers; and

combining the responses to produce a reference transducer response,

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

26. A method in accordance with claim 20, 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 transducer response,

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

27. A method in accordance with claim 20, further comprising:

at each of a plurality of scan points;

generating the ultrasound pulse incident upon the object from the first and second ultrasonic transducers.

28. A method in accordance with claim 20, further comprising:

at each of a plurality of scan points;

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

29. A method for performing an ultrasonic scan of an object using scanning acoustic microscope, the method comprising:

coupling a first ultrasonic transducer of two of more ultrasonic transducers to a signal processor of the scanning acoustic microscope along a first signal path;

retrieving a first set of equalization coefficients, associated with the first ultrasonic transducer, from a coefficient memory that contains sets of equalization coefficients associated with each of the two or more ultrasonic transducers;

compensating the strength and shape of an excitation waveform, dependent upon the first set of equalization coefficients, to produce an equalized excitation waveform, where the first set of equalization coefficients are selected such that an ultrasound waveform generated from the first ultrasonic transducer more closely matches an ultrasound waveform from a reference transducer in both strength and shape;

at each of a plurality of scan points;

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

receiving ultrasound, produced in response to the ultrasound pulses 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.

30. A scanning acoustic microscope comprising:

a signal processor;

a signal path configured to couple any selected 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 selected ultrasonic transducer;

a coefficient memory configured to store a set of one or more equalization coefficients for each of the plurality of ultrasonic transducers; and

a signal path equalizer, in the signal path and coupled to the coefficient memory, the signal path equalizer configured by a set of one or more equalization coefficients of the selected ultrasonic transducer retrieved from the coefficient memory and the signal path equalizer configured to adjust the strength of a waveform from the selected ultrasonic transducer and at least one of the shape and phase of the waveform;

where the signal processor is operable to process signals received from the signal path to produce an ultrasonic scan image, and

where the set of one or more equalization coefficients of the selected ultrasonic transducer are determined, dependent upon a transducer response characteristic of the selected ultrasonic transducer, such that the response characteristic of the signal path, including the selected ultrasonic transducer, more closely matches a reference transducer response characteristic in strength and shape, in strength and phase, or in strength, shape and phase.

32. A scanning acoustic microscope in accordance with claim 30, where the coefficient memory comprises a remote memory, the scanning acoustic microscope further comprising:

a network interface operable to link the scanning acoustic microscope, via a network, to the remote memory.

36. A scanning acoustic microscope comprising:

a signal processor configured to couple to two or more ultrasonic transducers having non-identical response characteristics;

a first equalizer in a first signal path that couples a first ultrasonic transducer of the two or more ultrasonic transducers to the signal processor, the first equalizer configured by a first set of equalization coefficients associated with the first ultrasonic transducer to adjust a strength of a waveform from the first ultrasonic transducer and at least one of a shape and a phase of the waveform; and

a second equalizer in a second signal path that couples a second ultrasonic transducer of the two or more ultrasonic transducers to the signal processor, the second equalizer configured by a second set of equalization coefficients associated with the second ultrasonic transducer to adjust a strength of a waveform from the second ultrasonic transducer and at least one of a shape and a phase of the waveform; and

wherein the first equalization coefficients are selected, such that the waveform from the first ultrasonic transducer more closely matches a waveform from a reference transducer in strength and shape, in strength and phase, or in strength, shape and phase and

wherein the second equalization coefficients are selected, such that the waveform from the second ultrasonic transducer more closely matches a waveform from the reference transducer in strength and shape, in strength and phase, or in strength, shape and phase.

37. A scanning acoustic microscope comprising:

a signal processor configured to couple to an ultrasonic transducer selected from a set of two or more ultrasonic transducers having non-identical response characteristics;

a coefficient memory configured to store sets of equalization coefficients associated with the two or more ultrasonic transducers; and

a waveform equalizer in a signal path that couples the selected ultrasonic transducer of the set of ultrasonic transducers to the signal processor, the waveform equalizer configured by a set of equalization coefficients retrieved from the coefficient memory and associated with the selected ultrasonic transducer;

wherein the waveform equalizer adjusts a strength of a waveform from the selected ultrasonic transducer and at least one of a shape and a phase of the waveform;

wherein the set of equalization coefficients associated with the selected ultrasonic transducer are determined such that the waveform from the selected ultrasonic transducer more closely matches a waveform from a reference transducer in strength and shape, in strength and phase, or in strength, shape and phase, so that the waveform equalizer compensates, at least partially, for differences between the response characteristic of the selected ultrasonic transducer and a reference transducer response.