Frequency domain processing of scanning acoustic imaging signals

An acoustic micro imaging method useful in the inspection of a target, comprising:

• scanning the target with a focused pulsed acoustic beam;
• sensing the pulsed beam after it has been modified by interaction with the target and producing a time-domain signal indicative of the modifications;
• processing said time-domain signal to produce a frequency domain representation of frequency selective modifications to the pulsed acoustic beam produced by said interaction with said target;
• and
• producing an image-wise display of said frequency domain representation of the modifications, said image-wise display further comprising a plurality of pixels where each pixel is amplitude modulated by a phase component of the sensed pulsed beam from a respective portion of the target.

An acoustic micro imaging method useful in the inspection of a target, comprising:

• scanning the target with a focused pulsed acoustic beam;
• sensing the pulsed beam after it has been modified by interaction with respective portions of the target and producing a time-domain signal indicative of the modifications;
• gating the signal segment to isolate a pixel-representative segment thereof;
• converting the gate-isolated signal segment to a frequency domain representation of frequency selective modifications to the pulsed acoustic beam produced by said interaction with said target, in the frequency domain of the signal;
• identifying a selected frequency component of the signal;
• and
• producing an image-wise signal representing many pixels in an image wherein the information in the pixel-representative signal segment associated with each of said many pixels is amplitude modulated by a phase value of the said selected frequency component modified by the respective portion of the target.

A method of processing a time-domain signal derived from a scanning acoustic microscope, comprising:

• gating the signal to isolate a pixel-representative segment thereof;
• converting the signal into a frequency domain representation of the signal that shows frequency selective modifications to the signal caused by interaction of an acoustic signal with respective portions of a target;
• in the frequency domain of the signal, identifying a selected frequency component of the signal;
• and
• producing an image-wise signal representing many pixels in an image wherein the information associated with each of said many pixels is amplitude modulated by a phase value of the said selected frequency component of the pixel-representative signal segment from a respective portion of the target.

A method useful in the inspection of a target, comprising:

• scanning the target with a pulsed acoustic beam;
• sensing the pulsed beam after it has been modified by interaction with the target and producing a first time-domain signal indicative of the modifications;
• processing said time-domain signal to produce a frequency domain representation of frequency selective, phase modifications to the pulsed acoustic beam produced by said interaction with respective portions of said target;
• modifying said frequency domain signal using a predetermined filter function;
• and
• converting said modified frequency domain signal to a second time-domain signal, where said second time-domain signal further comprises a plurality of frequency components from the respective portions of the target that have been modified by the predetermined filter function.

A method of processing a first image-wise time-domain signal derived from an acoustic microscope, comprising:

• gating the signal to isolate a pixel-representative segment thereof;
• converting the signal into a frequency domain representation of the signal that shows frequency selective modifications to a phase of the signal caused by interaction of an acoustic signal with respective portions of a target;
• in the frequency domain of the signal, identifying a selected frequency component of the signal;
• modifying the frequency domain representation of the phase of the signal using a predetermined filter function;
• and
• inverse Fourier transforming the signal to produce a second image-wise time-domain signal representing many pixels in an image from respective portions of the target wherein the information in the pixel-representative signal segment associated with at least a number of said many pixels is amplitude modulated by respective phase versus frequency components within the pixel-representative segment and where said amplitude modulation has been altered due to said modification of said signal by the predetermined filter function while in the frequency domain.

Apparatus for inspecting a target and producing a frequency domain representation of a gated time domain signal, comprising:

• a scanning acoustic microscope having an acoustic pulser that produces a focused, pulsed acoustic beam;
• a signal processor including an acoustic pulse sensor, amplifier and pixel gate coupled to said pulser that produces a time-domain representation of the acoustic beam after it has been modified by interacting with respective portions of the target;
• and
• a frequency domain converter responsive to the output of said signal processor that produces a frequency domain representation of frequency selective modifications to a phase of the acoustic beam produced by said interacting with the target, said frequency domain representation further comprising a plurality of pixels where each pixel is amplitude modulated by a phase component of the sensed pulsed beam from a respective portion of the target.

Apparatus useful in the inspection of a target, comprising:

• means for scanning the target with a pulsed acoustic beam;
• means for sensing the pulsed beam after it has been modified by interaction with the target and producing a time-domain signal indicative of the modifications;
• means for gating the signal to isolate a pixel-representative segment thereof;
• means for converting the signal into a frequency domain representation of the signal that shows frequency selective modifications to a phase of the signal caused by interaction of an acoustic signal with respective portions of a target;
• means for identifying in the frequency domain a selected frequency component of the signal;
• and
• means for producing an image-wise signal representing many pixels in an image wherein the information in the pixel-representative signal segment associated with each of said many pixels is amplitude modulated by the phase of said selected frequency component from a respective portion of the target.

Apparatus useful in the inspection of a target, comprising:

• means for scanning the target with a pulsed acoustic beam;
• means for sensing the pulsed beam after it has been modified by interaction with the target and producing a first time-domain signal indicative of the modifications;
• means for processing said time-domain signal to produce a frequency domain representation of frequency selective modifications to a phase of the pulsed acoustic beam produced by said interaction with said target where said frequency domain representation is amplitude modulated by a phase of a frequency component of the sensed pulsed beam from a respective portion of the target.;
• means for modifying said frequency domain signal using a predetermined filter function;
• and
• means for converting said modified frequency domain signal to a second time-domain signal.