Abstract:
This invention relates to a scanning ultrasound detection device using two-wave mixing in photorefractive crystal interferometry. An interferometer with two-wave mixing in photorefractive crystal, and cooperates with a confocal lenses module to perform a scan and inspection of the surface of a target. A rotating unit is used for directing a signal beam for detection to be incident upon different locations of the target. The confocal lens module is used to compensate any changes of reflection path caused by the signal beam having different incident angles. Hence, a reflected signal beam and a reference beam can strike on a photo detector.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an ultrasound detection device, and more particularly, to a scanning ultrasound device using two-wave mixing in photorefractive crystal interferometry for non-destructive and non-contact inspection.  
           [0003]    2. Description of Related Art  
           [0004]    The inspection for defects in material structures is always a critical issue for monitoring and controlling quality in the manufacturing industry. In the conventional destructive inspection for defects, the whole package of a tested sample (e.g. an IC for inspection) is destructively taken apart. For example, in the inspection for insufficient solder or short circuit problem in an integrated circuit (IC), the packaged IC has to be dissolved with a corrosive solution, and then, pins of the IC are inspected with a microscope. However, this inspection process is complex, and is disadvantageous to real-time monitor quality assurance on-line.  
           [0005]    Recently, the industry has developed a non-destructive inspection system for monitoring and controlling quality. The process for the non-destructive inspection primarily uses X-rays, an ultrasound probe head as well as an ultrasound optical excitation and detection, etc. Especially, the ultrasound optical excitation and detection has become the main stream for developing the non-destructive inspection because of advantages of remote excitation and detection as well as real-time inspection.  
           [0006]    A Two-Wave Mixing in PhotoRefractive Crystal interferometer (TWM in PRC) is considered as the core part of the contemporary ultrasound optical detection system. To apply TWM in PRC to the non-destructive inspection by ultrasound in practice, scanning technology has to be adopted. The conventional solution is to displace or re-locate the whole interferometer system to achieve a scanning function. However, additional mechanism is necessary for this conventional solution, and thus, it complicates the inspection system and increases cost in volume production.  
           [0007]    Therefore, it is desirable to provide an optical scanning ultrasound device by TWM in PRC to mitigate and/or obviate the aforementioned problems.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a scanning ultrasound device using TWM in PRC so as to perform a surface scan and detection of an ultrasound wave.  
           [0009]    It is another object of the present invention to provide a scanning ultrasound device using TWM in PRC so as to have compact structure, increase system reliability and reduce cost in volume production.  
           [0010]    To attain the above objects, a scanning ultrasound device using TWM in PRC according to the present invention comprises a light source, an ultrasound-wave-generating-module and a target. The ultrasound-wave-generating-module generates at least an ultrasound signal to cause the target to bring about ultrasound vibrations. The ultrasound-wave-generating-module includes an interferometer of TWM in PRC for receiving light coming from the light source to generate a signal beam for detecting the ultrasound vibrations of the target and a reference beam having an interference with the signal beam, and a rotating unit for directing the signal beam to be incident upon different locations of the target to result in a scanning motion. The target described herein can be any substrate, package, test object, etc.  
           [0011]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic view of a structure of the scanning ultrasound device according to the present invention;  
         [0013]    [0013]FIG. 2 is a schematic view of a phase grating of a photorefractive crystal according to the present invention; and  
         [0014]    [0014]FIG. 3 is a schematic view of a rotating mechanism according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    [0015]FIG. 1 shows the structure of a preferred embodiment according to the present invention, and provides a schematic view of the structure. The scanning ultrasound device comprises a light source  1 , an ultrasound-wave-generating-module  2 , a photorefractive crystal  41 , a first convex lens  42 , a second convex lens  52 , a third convex lens  53 , a rotating mechanism  51  and a photo detector  43 . The photorefractive crystal  41  is supported in the rotating mechanism  51 , having a rotation axis  511  where the focal point of the second convex lens  52  and the focal point of the third convex lens  53  are located. The photo detector  43  is mounted at the focal point of the first convex lens  42 . As shown in FIG. 1, the first convex lens  42  locates on a position opposed to the focal point of the second convex lens  52  and the focal point of the third convex lens  53 . In this embodiment, the light source  1  preferably is a continue wave (CW) laser. When the light source  1  strikes on the photorefractive crystal  41 , the light beam reflected by the surface of photorefractive crystal  41  is defined as a signal beam  11  while the light beam passing through the photorefractive crystal  41  is defined as a reference beam  12 . A thin optical film may be coated on the surface of the photorefractive crystal  41  to adjust the intensity ratio of the signal beam and the reference beam, if necessary.  
         [0016]    The signal beam  11  is reflected from the surface of the photorefractive crystal  41 , and then strikes on the surface of the test object  3  through the third convex lens  32 . Thereafter, the light beam is reflected back from the surface of the test object  3  to the photorefractive crystal  41 . The signal beam  11  reflected back to the photorefractive crystal  41  combines with the reference beam  12  to form interference fringe patterns in the photorefractive crystal  41 , and then the beam  11  passing through the photorefractive crystal  41  becomes a signal beam  111 . The signal beam  111  passing through the photorefractive crystal  41  is further incident on the photo detector  43  through the second convex lens  52  and the first convex lens  42 . Because of photorefractive effect, The interference fringe patterns inside the photorefractive crystal  41  generate a phase grating  411 . (FIG. 2) The wavefront and wave propagation direction of the diffracted reference beam  121  by means of the phase grating  411  is the same as that of the signal beam  111  passing through the photorefractive crystal  41 .  
         [0017]    When an ultrasound signal from the ultrasound-wave-generating-module  2  strikes on the test object  3  to cause the ultrasound vibrations of the surface of the test object  3 , the frequency of signal beam  11  reflected from the surface of the test object  3  is Doppler shifted by the ultrasonic vibrations. The signal beam  11  for detection passes through the photorefractive crystal  41 , and superimposes the diffracted reference beam  121  by means of the photorefractive crystal  41  to generate an interference so that the Doppler shift is demodulated by light intensity thereof. The interfered beam is incident on the photo detector  43  through the convex lenses  52 ,  42 . The photo detector  43  converts the interfered signal into an electrical signal, and then is output to an oscilloscope or a computer apparatus for displaying the inspection results of the test object  3 .  
         [0018]    In the scanning process, the photorefractive crystal  41  is rotated by means of a rotating mechanism  51  on which the photorefractive crystal  41  is supported to alter the reflection angle of the signal beam  11 . The signal beam having a changed reflection angle passes through the third convex lens  53  to be incident on the surface of the test object  3 . Because the third convex lens  53  is focused on the rotation axis  511  of the rotating mechanism  51 , the signal beam  11  passing though the third convex lens  53  will always be incident vertically on the surface of the test object  3 . Namely, the signal beam  11  strikes perpendicularly on the surface of the test object  3  through the third convex lens  53 . The signal beam  111  reflected back from the surface of the test object  3  is incident on the rotation axis  511  of the rotating mechanism  51 . Hence, the signal beam is driven to perform a linear scan of the surface of the test object when the rotating mechanism  51  is rotated in a single-axial direction. In addition, the signal beam  11  is able to perform a two-dimensional surface-wide scan of the test object  3  when the rotating mechanism  51  is rotated in a biaxial direction.  
         [0019]    [0019]FIG. 3 is a schematic view of a rotating mechanism. In this embodiment, the rotating mechanism  51  can be any single-axial mechanism or biaxial rotating mechanism. For example, the rotating mechanism  51  maybe a motorized kinetic mount driven by a piezoelectric actuator. The photorefractive crystal  41  is supported in the rotating mechanism  51 . A voltage (Vx, Vy) is input by a controller driving the piezoelectric actuator so that the photorefractive crystal  41  is rotated around the X-axis or the Y-axis. When the photorefractive crystal  41  is rotated around the X-axis, the signal beam  11  performs a linear scan in a Y-axis direction. When the photorefractive crystal  41  is rotated around the Y-axis, the signal beam  11  performs a linear scan in an X-axis direction. When the photorefractive crystal  41  is rotated around both the X- and the Y-axes, the signal beam performs a two dimensional surface-wide (X-Y) scan.  
         [0020]    The aforesaid signal beam  11  is reflected back from the surface of the test object  3  to the photorefractive crystal  41 , and passes through the photorefractive crystal  41  to form the signal beam  111 . Then, the signal beam  111  enters the second convex lens  52 . Because the focal point of the second convex lens  52  is also located at the rotation axis  511 , the signal beam  111  passing through the second convex lens  52  will become a parallel beam. The diffracted reference beam  121  by means of the phase grating  411  is parallel to and superimposed on the passed-through signal beam  111  to generate the interference. Subsequently, the beams are focused on the photo detector  43  through the first convex lens  42 . The photo detector  43  receives an interfering signal and converts the interfering signal into an electrical signal.  
         [0021]    It is understandable from the above description that the present invention adopts the light source, the ultrasound-wave-generating-module, the photorefractive crystal, the convex lens, the confocal convex lenses, the rotating mechanism and the photo detector to inspect the test object in a non-destructive and non-contact manner. Also, the present invention is able to execute a linear scan or a two-dimensional surface-wide scan to have compact structure, increase system reliability and reduce cost in volume production.  
         [0022]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.