Abstract:
An ultrasonic microscope for acquiring data from internal regions of a sample body is provided. The ultrasonic microscope includes an ultrasonic transmitter for providing a point source of ultrasonic waves for input-coupling into a sample body at a point in proportion to the dimensions of the sample body. Ultrasonically-induced excursions of a receiving tip can be detected with atomic resolution by using an ultrasonic detector that measures with high sensitivity resolution. The ultrasonic transmitter and the ultrasonic detector may be positioned relative to one another such that the ultrasonic detector can adopt several receiving positions for each transmitting position of the ultrasonic transmitter. A measurement data signal from the ultrasonic detector is stored and processed in a central processor. An image generator within the central processor uses a tomographic algorithm to reconstruct an image of at least one area inside the sample body from the measurement data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns an ultrasonic microscope including an ultrasonic transmitter by means of which ultrasonic waves can be input-coupled in a sample body, an ultrasonic detector disposed on the opposite side of the sample body from the ultrasonic transmitter and by means of which the ultrasonic waves coupled into the sample body can be detected and which can be positioned relative to the sample body, and a central processor by means of which, as the ultrasonic detector assumes a series of positions relative to the sample body, measurement data assigned to the amplitudes of the input-coupled ultrasonic waves and the amplitudes of the ultrasonic waves detected by the ultrasonic detector can be stored and processed. 
     2. Description of the Related Art 
     U.S. Pat. No. 5,675,075 teaches an ultrasonic microscope, including an ultrasonic transmitter by means of which an entire sample body can be irradiated with ultrasonic waves. The prior device also includes an ultrasonic detector which measures with local resolution and which is realized in the form of an atomic force microscope, and by means of which ultrasound-induced deformations occurring on a detecting surface of the sample body can be detected via excursions of a receiving tip of the force microscope. Elasticity properties of the sample body can thus be measured with very high local resolution. The known device has the disadvantage, however, that only measurement values averaged over the region of passage of the ultrasonic waves can be acquired. 
     SUMMARY OF THE INVENTION 
     The present invention provides an ultrasonic microscope by which data can be acquired even over spatially limited areas in the interior of the sample body. 
     This task is accomplished by means of an ultrasonic microscope in which ultrasonic waves can be coupled into the sample body by the ultrasonic transmitter in a dotwise or point-sized manner compared to the dimensions of the sample body, in that the ultrasonic transmitter and the ultrasonic detector can be positioned mutually independently on the sample body, and in that a reconstructing unit or image generator is provided by means of which at least one image of internal regions of the sample body can be generated from the ultrasonic amplitudes transmitted by the ultrasonic transmitter at a plurality of transmitting positions and detected by the ultrasonic detector at a plurality of receiving positions with respect to each transmitting positions 
     The fact that ultrasonic waves can be coupled into the sample body by the ultrasonic transmitter in a point-sized manner and the ultrasonic transmitter and the ultrasonic detector can be positioned independently in relation to each other, the ultrasonic detector being able to detect ultrasonic amplitudes at a plurality of receiving positions for each transmitting position of the ultrasonic transmitter, makes it possible to obtain measurement data by means of which internal regions of the sample body can be imaged sharply by the reconstructing unit, for example on the basis of known tomographic image-generating techniques. 
     In a preferred embodiment, the ultrasonic detector comprises a force microscope whose resolution is preferably in the atomic range, down to a few tens of nanometers; in a further embodiment, the ultrasonic detector is provided with a tunnel microscope whose resolution is preferably in the atomic range down to a few tens of nanometers. 
     When a force microscope is used, it is advantageous to provide an optically or capacitively functioning detection unit to detect the excursions of a receiving tip of the force microscope. 
     In various embodiments, the ultrasonic transmitter is a focusing ultrasonic lens coupled to an ultrasonic transducer, a force microscope coupled to an ultrasonic transducer, or an optical unit comprising an exciting light source, a modulator, and a focusing optic and serving to generate ultrasonic waves on the basis of the thermoelastic effect. 
     To produce a three-dimensional image of the sample body, it is provided to position the ultrasonic transmitter over the coupling-side surface of the sample body at a plurality of transmitting positions in a grid corresponding to the local resolving power of the ultrasonic transmitter, and, for each transmitting position of the ultrasonic transmitter, to position the ultrasonic detector, also in a grid corresponding to its local resolving power, at a plurality of receiving positions on a detecting surface opposite the coupling-side surface, over a detection-side surface of the sample body in a region where the ultrasound-induced deformation of the detecting surface can be detected. In this manner, data can be acquired from which a complete three-dimensional image of the sample body or images of any desired slices can be reconstructed. 
     It is also advantageous to provide a sample-body displacing device by means of which the sample body can be displaced in relation to the ultrasonic transmitter to permit irradiation at additional transmitting positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantageous embodiments of the invention will become more apparent and the invention itself will be better understood by reference to the following description of exemplary embodiments provided with reference to the following drawings wherein: 
     FIG. 1 is a block circuit diagram of an exemplary embodiment of an ultrasonic microscope with an ultrasonic lens for point-sized input coupling of ultrasonic waves; 
     FIG. 2 is a block circuit diagram of a further exemplary embodiment of an ultrasonic microscope with a force atomic microscope for point-sized input coupling of ultrasonic waves; 
     FIG. 3 is a block circuit diagram of a further exemplary embodiment of an ultrasonic microscope with a force microscope modified with respect to the exemplary embodiment of FIG. 2; 
     FIG. 4 is a block circuit diagram of a further exemplary embodiment of an ultrasonic microscope with an optical arrangement for point-sized generation of ultrasonic waves; and 
     FIG. 5 is a block circuit diagram of an exemplary embodiment of a central processing unit of an ultrasonic microscope. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block circuit diagram of an exemplary embodiment of an ultrasonic microscope. The ultrasonic microscope according to FIG. 1 is provided with an ultrasonic transmitter  1 , comprising an ultrasonic transducer  3  connected to a high-frequency generator  2 . Said ultrasonic transducer  3  is coupled to an ultrasonic lens  4 , by means of which an ultrasonic beam  5  can be focused on a input-coupling surface  6  of a sample body  7 . The diameter of the focal spot of the ultrasonic lens  4  is typically in the range of a few micrometers to a few tens of micrometers and is therefore dot-sized or point-sized in comparison to the size of typical macroscopic sample bodies  7  so that the electronic beam appears to have been generated by a point source. Both the ultrasonic transducer  3  and the ultrasonic lens  4  are connected mechanically to a transmission displacing unit  8 , by means of which an emitted ultrasonic beam  5  can be positioned at a number of transmitting positions on the input-coupling surface  6 . 
     The ultrasonic microscope according to FIG. 1 is provided with a central processing unit or processor  9 , by means of which transmission displacing unit  8  can be driven via a transmission positioning line  10  to effect defined positioning of the ultrasonic beam  5 . Ultrasonic amplitude values corresponding to the amplitude of ultrasonic beam  5  can be stored as measurement data in central processing unit  9  via a transmission amplitude line  11 . 
     The ultrasonic microscope according to FIG. 1 further comprises a receiving force microscope  12  forming part of an ultrasonic detector  13  and preferably operating in the near field, i.e., in a substantially aperture-limited manner. Receiving force microscope  12  is provided with a receiving tip  14 , which, with a local resolution preferably in the range of typically no more than a few tens of nanometers, especially preferably with atomic resolution, can be positioned at a distance from a detecting surface  15  opposite the input-coupling surface  6  of the sample body  7  such that at said distance the magnitude of the wavelength of the input-coupled ultrasonic waves has no significant effect on the intensity distribution at the detecting surface  15 , preferably in the near field of the ultrasonic waves emanating from the point-sized input coupling region. Receiving tip  14  is fastened at one end to a receiving spring  16 , realized, for example, as a leaf spring, the other end of which is disposed on a receiving-spring mounting  17 . Receiving-spring mounting  17  is connected mechanically to a reception displacing unit  18  by means of which receiving tip  14  can be positioned at a plurality of receiving positions over detecting surface  15  for each transmitting position. 
     The ultrasonic detector  13  according to FIG. 1 is further provided with a scanning light source  19 , realized, for example, as a lager, whose emitted scanning beam  20  can be focused via a scanning focusing optic  21  on an at least partially reflective scanning face  22  of receiving tip  14  or receiving spring  16 . The portion of scanning beam  20  reflected by scanning face  22  can be guided to an optical detection unit  24  via a scanning deflection unit  23 . Optical detection unit  24  is provided with a beam splitter  25 , by means of which the portion of scanning beam  20  incident on optical detection unit  24  can be guided to a segment detector  26  and, via a deflector unit  27  and a focusing detection optic  28  and passing through a partial-shadow-forming element  29  disposed in the focal region of detection optic  28 , to a shadow detector  30 . 
     Segment detector  26 , which is constructed of two adjacent detecting surfaces, has a comparatively small bandwidth that is smaller than the frequency of the ultrasonic waves coupled into sample body  7 . The outputs of segment detector  26 , each of which is assigned to a detecting surface, are connected to a normalizing amplifier  31 , which normalizes the difference between the photoelectric voltages of the detecting surfaces of segment detector  26  to their cumulative value and amplifies said value. Segment detector  26  thus serves to detect low-frequency deflections of receiving tip  14  that are caused in particular by the topography of detecting surface  15  and are slower than ultrasound-induced high-frequency excursions of the receiving tip  14 . 
     Shadow detector  30 , which is provided with only one detecting surface, has a bandwidth that corresponds at least to the frequency of the ultrasonic waves  5  coupled into sample body  7 . Shadow detector  30  serves to detect the ultrasound-induced high-frequency excursions of receiving tip  14 , which condense into an alternating partial intensity of scanning beam  20  that is induced by partial-shadow-forming element  29  and is incident on shadow detector  30 . 
     Central processor  9  is able to store the output signals from normalizing amplifier  31  via a low-frequency-signal line  32  and the output signals from shadow detector  30  via a high-frequency-signal line  33 . Furthermore, reception displacing unit  18  can be driven by central processing unit  9  via a drive line  34 , in which case receiving-position signals assigned to the receiving position of receiving tip  14  can be transmitted via a receiving-position line  35  from reception displacing unit  18  to central processing unit  9 . 
     With the ultrasonic microscope according to FIG. 1, ultrasonic beam  5  and receiving tip  14  can preferably be positioned relative to each other when sample body  7  is at rest. In a preferred measurement technique, at each position of ultrasonic beam  5 , receiving tip  14  is positioned at least over the region of detecting surface  15  in which an ultrasound-induced high-frequency excursion of receiving tip  14  can be detected. The output signals from high-frequency generator  2  corresponding to the input-coupled ultrasonic amplitudes, on the one hand, and the intensity signals from shadow detector  30  and normalizing amplifier  31  corresponding to the amplitudes of the deflections and to the high-frequency excursions, on the other hand, can be stored as measurement data by central processing unit  9  as a function of each transmitting position of ultrasonic beam  5  and the receiving positions of receiving tip  14  that are assigned to said transmitting position. 
     FIG. 2 is a block circuit diagram of a further exemplary embodiment of an ultrasonic microscope, which, as a modification with respect to the exemplary ultrasonic microscope of FIG. 1, effects the coupling of ultrasonic waves into sample body  7  by the use of a force transmitting microscope  37  comprising a transmitting tip  36  and possessing a high local resolving power of, typically, a few tens of nanometers. Said transmitting tip  36  is mounted at one end on a transmission spring  38  realized as a leaf spring, whose other end is fastened to a transmission-spring mounting  39 . Transmission-spring mounting  39  is connected mechanically to a transmission displacing unit  40 , by means of which transmitting tip  36  can be positioned over the input-coupling surface  6  of sample body  7 . Mounted on transmitting tip  36  is an ultrasonic transducer  41 , preferably realized as a piezoelectric device, which is connected to the high-frequency generator  2  of the ultrasonic transmitter  1 . When ultrasonic transducer  41  is impacted on by a high frequency that can be generated by means of high-frequency generator  2 , ultrasonic waves that are point-sized in comparison to the dimensions of sample body  7  can be coupled into sample body  7  via transmitting tip  36 . 
     FIG. 3 shows a further exemplary embodiment of an ultrasonic microscope, in which, as a modification with respect to the exemplary embodiment of FIG. 2, an ultrasonic transducer  42  is coupled to the transmission-spring mounting  39 . When transmission-spring mounting  39  is impacted by ultrasonic waves generated by the high-frequency generator  2  connected to ultrasonic transducer  42  and by ultrasonic transducer  42 , transmission spring  38  is set in high-frequency vibration, so that transmitting tip  36  acts as a point source and induces ultrasonic waves dotwise or pointwise in sample body  7 . 
     FIG. 4 shows a further exemplary embodiment of an ultrasonic microscope; the components corresponding to the exemplar embodiments of FIGS. 1 to  3  are provided with the same reference numerals and are not described below in further detail. The ultrasonic transmitter  1  in the ultrasonic microscope of FIG. 4 is provided with an exciting light source  43 , preferably realized as a laser, which can be driven by a power supply unit  44  to emit an exciting light beam  45  which is substantially parallel in the exemplary embodiment of FIG.  4 . Disposed after the exciting light source  43  is an exciting light modulator  46 , by which the intensity of an exciting light beam  45  incident thereon can be high-frequency-modulated under the control of a modulator drive unit  47 . 
     The ultrasonic transmitter  1  according to FIG. 4 is further provided with an exciting-light deflecting optic  48  and a diffraction-limited exciting-light focusing optic  49 , by means of which the intensity-modulated exciting light  45  can be focused on the coupling surface  6  of sample body  7 , it being possible on the principle of the thermoelastic effect to generate ultrasonic waves as a point source in a very small region compared to the dimensions of the sample body  7 . 
     Exciting-light deflecting optic  48  and exciting-light focusing optic  49  are connected mechanically to a transmission displacing unit  50 , by means of which the focal region of the exciting light beam  45  can be guided over coupling surface  6  of sample body  7 . Transmission displacing unit  50  is connected to central processing unit  9  for purposes of control. 
     FIG. 5 is a block circuit diagram of an exemplary embodiment of the central processing unit or processor  9  according to the ultrasonic microscope described in exemplary fashion with reference to FIGS. 1 to  4 . Central processing unit  9  is provided with a clock  51  to which is connected a transmitting-position adjusting element  52 . By means of transmitting-position adjusting element  52 , ultrasonic beam  5 , transmitting tip  36 , and the focal region of exciting light beam  45  can respectively be positioned in a set manner in a plurality of transmitting positions with respect to coupling surface  6  when the respective transmission displacing unit  8 ,  40 ,  50  is acted upon by suitable control signals via transmitting-position line  10 . Further, clock  51  is connected to reception displacing unit  18  via control line  34 , so that at each transmitting position of ultrasonic beam  5 , transmitting tip  36  or focused exciting light beam  45 , respectively, receiving tip  14  is positioned at a plurality of receiving positions for detecting the ultrasound-induced high-frequency excursions and the topographically induced low-frequency deflections at detecting surface  15  opposite coupling surface  6 . 
     Transmitting-position signals delivered by transmitting-position adjusting unit  52  and assigned to the position of ultrasonic beam  5 , transmitting tip  36 , and the focal region of focused exciting light beam  45 , as well as detection-position signals delivered by the reception displacing unit  18  and assigned to the receiving position of receiving tip  14 , can be sent to a data memory  53  for storage together with the amplitudes of the amplitude signals assigned to the input-coupled ultrasonic waves and present on transmission-amplitude line  11 , as well as the intensity signals present on low-frequency line  32  and high-frequency line  33 . A reference location signal from a reference location generator  54  can also be stored in data memory  53  and serves as a reference signal for making the conversion into absolute spatial coordinates. 
     After the termination of a measurement cycle, including the relative positioning of receiving tip  14  with respect to the ultrasonic lens  4  generating the ultrasonic waves, the transmitting tip  36 , and the exciting-light focusing optic  49  focusing the exciting light beam  45 , a reconstructing unit or image generator  55  disposed after data memory  53  can be used to combine the measurement data on the basis of image-generating tomographic algorithms to form a locally resolved intensity image of at least one internal layer of sample body  7 . 
     The tomographic algorithm can be made in each case to take advantage of the fact that the attenuation of the ultrasonic waves coupled into sample body  7  at input-coupling surface  6  can be detected substantially at each relative position by receiving tip  14  operating in the near field, and given the displacement of the ultrasonic beam  5 , the transmitting tip  36 , and the focal region of the exciting light beam  45  and the repeated positioning of transmitting tip  14  at each of these transmitting positions, by appropriate combination of the location data and intensity data stored in data memory  53  at least one predetermined layer can be reconstructed with a sharpness that corresponds to a total resolving power determined by the size of the point-sized coupling region and the local resolving power of ultrasonic detector  13 . If a large number of layers is reconstructed with a precision that does not exceed the total resolving power, it is even possible to reconstruct a three-dimensional image of the internal structure of the sample body  7 . 
     In the exemplary embodiments depicted in FIGS. 6 -9, the ultrasonic detector is comprised of tunnel microscope unit  57 . Tunnel microscope unit  57  is comprise of tunnel microscope  59  and suspension unit  58 . 
     In the exemplary embodiments depicted in FIG. 5, the data processed by means of reconstructing unit or image generator  55  can be output in an output unit or display  56  as tomograms or three-dimensional representations. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.