Abstract:
An apparatus and a method that achieve physical separation of sound sources by pointing directly a beam of coherent electromagnetic waves (i.e. laser). Analyzing the physical properties of a beam reflected from the vibrations generating sound source enable the reconstruction of the sound signal generated by the sound source, eliminating the noise component added to the original sound signal. In addition, the use of multiple electromagnetic waves beams or a beam that rapidly skips from one sound source to another allows the physical separation of these sound sources. Aiming each beam to a different sound source ensures the independence of the sound signals sources and therefore provides full sources separation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. US60/841,574 filed Sep. 1, 2006, the content of which is incorporated by reference herein. 

   FIELD OF THE INVENTION 
   The present invention relates to coherent electromagnetic waves and more specifically, to remote sensing of sound sources using coherent electromagnetic waves. 
   BACKGROUND OF THE INVENTION 
   Vibrometry is the technical field of measuring vibrations of an object. In remote vibrometry, the vibrations are measured from a distance (aka no-contact vibrometry). One of the common ways to achieve vibrations remote-sensing is by using coherent electromagnetic waves (usually laser) and exploiting their physical properties. 
   Specifically, the vibrating object acts as a transducer by modifying the properties of the electromagnetic waves that hit it, according to the vibrations, prior to reflecting back the electromagnetic waves. As any sound source generates vibrations, coherent electromagnetic waves may be used to detect and sense sound. And indeed, many attempts have been made in the art of remote sound sensing and detection using coherent electromagnetic waves. 
   The majority of the coherent electromagnetic-waves-based sound vibrometers available today are configured so that the coherent electromagnetic waves are not directed at the vibrating sound source. Rather, the electromagnetic waves in these sound vibrometers are directed at objects that reflect the sound waves, usually flat surfaces such as windows and walls in the proximity of the sound generating object. 
   For example, U.S. Pat. No. 6,317,237 which is incorporated by reference herein in its entirety discloses a system wherein a laser beam is directed at a window pane of a building and the reflecting laser beam is received and analyzed to extract the sound waves (specifically human voices) generated within the building. 
   U.S. Pat. No. 5,175,713 which is incorporated by reference herein in its entirety, discloses a method for under-water sound sensing using laser beams directed at reflectors and analyzing the reflected beams in order to detect and sense under-water sound propagation. 
   Presently available remote sensing sound vibrometers use a variety of techniques to extract the information from the reflected beam. The traditional solution comprises an interferometer that conducts interference between the reflected beam and a reference beam. Another common technique is based upon the Doppler Effect. According to this technique, since the wavelength of the reflected beam is changed in accordance with the vibrations of the vibrating object that reflects the electromagnetic waves therefore the change in wavelength correlates to certain vibrations which in turn represent a specific sound signal. Yet another technique involves the analysis of the speckle pattern. A speckle pattern is causes whenever a reflected beam of coherent light creates a spot containing a plurality of interferences. This result in a spot comprising varying intensity dotted pattern reflected from a vibrating surface. One of the ways to analyze a speckle pattern involves the use of a charge couple device (CCD) array or any other array of photosensitive cells serving as receiver units for the reflected speckle pattern, wherein digital signal processing methods help extract the sound signal. 
     FIG. 1  shows the general structure of a typical remote sound-sensing system according to the prior art.  FIG. 1  shows a laser Doppler vibrometer  100  (LDV) which is one of the common embodiments for Doppler vibrometry. The LDV  100  transmits an outgoing laser beam  120  directed at a flat surface  140 . The flat surface may be a window, a wall or a dedicated reflector that have been placed deliberately to act as sound reflector. A sound source  110  generates sound waves that hit the flat surface  140  which result in vibrations. The outgoing laser beam  120 , upon hitting the flat surface  140  is reflected back to the LDV  100  wherein the properties of the reflected laser beam  130  has been modified due to the vibrations of the flat surface  140 . Inside the LDV  100  the reflected beam is analyzed and compared with a reference beam (not shown) to reconstruct the sound that has been generated by the sound source. 
   The main drawback of currently available remote sound sensing systems is their poor ability of sound sources separation. This drawback is reflected in two manners: noise separation and blind sources separation. By relying on a beam reflected from a vibrating surface rather than directly the sound generating object, the systems according to the prior art are actually sensing the sound source&#39;s ambient, which may include noise that inherently reduces the quality of the sound sensing. In addition, by sensing a reflection from a surface, rather than the sound sources directly, the sound signal extracted actually represents the superposition of all the sound sources presented in the same close proximity. Noise filtering, as well as blind sources separation (the separation of the different unrelated sound sources) has to be performed using time-consuming and not always cost-effective digital signal processing (DSP) techniques. 
   It would be therefore advantageous to have an apparatus and a method that allows the physical separation of sources while monitoring the sound generated therefrom, as well as noise separation, without the use of complex DSP techniques, while retaining the high quality of remote sound sensing. 
   SUMMARY OF THE INVENTION 
   The present invention discloses an apparatus and a method that achieve physical separation of sound sources by pointing directly a beam of coherent electromagnetic waves (i.e. laser). Analyzing the physical properties of a beam reflected from the vibrations generating sound source enable the reconstruction of the sound signal generated by the sound source, eliminating the noise component added to the original sound signal. In addition, the use of multiple electromagnetic waves beams or a beam that rapidly skips from one sound source to another allows the physical separation of these sound sources. Aiming each beam to a different sound source ensures the independence of the sound signals sources and therefore provides full sources separation. 
   In some embodiments, the apparatus for sound source separation according to the present invention is a directional coherent electromagnetic wave based vibrometer. The vibrometer comprises a coherent electromagnetic wave beam transmitter connected to a control unit, which is connected in turn to a processing unit, which is connected in turn to a coherent electromagnetic wave beam receiver via said control unit. Upon operation, the transmitter transmits at least one coherent electromagnetic wave beam directly at least one vibrating sound source. the receiver then receives at least one coherent electromagnetic wave beam reflected directly from at least one vibrating sound source said the processing unit controls said transmitter&#39;s operation via said control unit that uses the information extracted from the reflected beam from said vibrating sound source to reconstruct the sound of said sound source whereby the sound of said sound source is being separated from other sound sources and ambient noise. 
   In some embodiments, a method for separating sound sources using remote sensing sound vibrometry is disclosed. The method comprises the following steps: transmitting at least one coherent electromagnetic wave beam directly at least one vibrating sound source; receiving at least one coherent electromagnetic wave beam reflected directly from at least one vibrating sound source and then analyzing information gathered from the coherent electromagnetic wave beam reflected directly from the vibrating sound source whereby the sound generated by said sound source is separated from other sound sources and ambient noise. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The subject matter regarded as the invention will become more clearly understood in light of the ensuing description of embodiments herein, given by way of example and for purposes of illustrative discussion of the present invention only, with reference to the accompanying drawings (Figures, or simply “FIGS.”), wherein: 
       FIG. 1  is a schematic diagram showing a laser Doppler vibrometer according to the prior art; 
       FIG. 2  is a schematic diagram showing the vibrometer according to the present invention; 
       FIG. 3  is a schematic diagram showing the general structure of the vibrometer according to the present invention; 
       FIG. 4  is a schematic diagram showing an embodiment according to the present invention; 
       FIG. 5  is a schematic diagram showing an embodiment according to the present invention; and 
       FIG. 6  is a flowchart showing the method according to the present invention; 
   

   The drawings together with the description make apparent to those skilled in the art how the invention may be embodied in practice. 
   Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  shows a schematic diagram of the operational environment according to the present invention. A remote sound sensing apparatus  200  generates an outgoing coherent electromagnetic waves beam  220  that is pointed directly on a vibrations generating sound source  210 . Upon hitting the vibrations generating sound source  210 , the outgoing coherent electromagnetic waves beam  220  is reflected and returns, with modified physical properties, as a reflected coherent electromagnetic waves beam  230 , to the remote sound sensing apparatus  200 . When directing the beam at the sound producing source the vast majority of the detected vibrations are related to the sound source. Since the vast majority of the sound producing vibrations related to a sound source are detected, a high degree of separation between the sound source and the ambient is thus achieved. This is due to the fact that the beam is pointed directly at the vibrations producing sound source. 
   According to some embodiments of the invention, the vibrations generating sound sources  210  may be human beings, wherein the vibrating object may be the skin around the face, lips and throat, but they may be any surface that is attached to the sounding board and/or source that created and/or amplifies the sound According to some embodiments of the invention, the information gathered from the reflected coherent electromagnetic waves beam  230  is extracted in more than one way. Existing techniques may be use. One technique is based on the Doppler Effect; another technique is performing a single interference; a third one is analyzing the speckle pattern—a spot containing multiple interferences. 
     FIG. 3  shows a schematic block diagram of the structure of the remote sound sensing apparatus  200  according to some embodiments of the invention. The remote sound sensing apparatus  200  comprises a coherent electromagnetic wave beam transmitter  310  connected to a control unit  330 , which is connected in turn to a processing unit, which is connected in turn to a coherent electromagnetic wave beam receiver  320  via said control unit  330 . Upon operation, the transmitter  310  transmits at least one coherent electromagnetic wave beam directly on at least one vibrating sound source  210 , the receiver  320  then receives at least one coherent electromagnetic wave beam reflected directly from at least one vibrating sound source  210  said the processing unit  340  controls said transmitter&#39;s operation via said control unit  330  that uses the information extracted from the reflected beam from said vibrating sound source  210  to reconstruct the sound of said sound source whereby the sound of said sound source is being separated from other sound sources and ambient noise. 
   According to some embodiments of the invention, each and every module of the invention may be implemented in any hardware or software form. For example, it may be implemented as an application specific integrated circuit (ASIC), as a digital signal processor (DSP), a field programmable gates array (FPGA), a software-based microprocessor or any combination thereof. Moreover, the receiver may be implemented with any array of electromagnetic sensitive cells, such as photo resistive transistors and/or diodes, built in charge coupled device (CCD) and complementary metal oxide silicon (CMOS) technologies and the like. 
   According to some embodiments, the Doppler Effect is used to extract the vibrations generated by the sound generating object and reconstruct the sound signals. 
   According to some embodiments of the invention, sound sources separation is achieved by spatial scanning of a plurality of sound sources, whereby at each time, only one beam is assigned at time to one sound source. Specifically, the apparatus according to the present invention generates a plurality of beams or alternatively, one beam that discretely scans the space according to a predefined pattern. At any specific time, a specific beam hits a specific sound source in a mutual exclusive manner and so the information gathered from this beam relates separately to the specific sound source. Thus, physical sources separation is achieved. 
     FIG. 4  shows an embodiment according to the invention. According to the embodiment, the vibrometer comprises a self-mixing diode  410  operated by a driver  430  and a collimating lens  420  that focuses the light and directs it on a vibrating sound source  470 . The out-coming beam also passes through a modulator  450  that transfers part of the out coming beam to the photo diode  460 . Additionally, the beam reflected from the sound source  470  hits a photo diode  460  that in turn transfers the signal to the processing unit  440  the reflecting beam enters the photo diode and cause instabilities that are analyzed in order to reconstruct the sound signal of the sound source. 
     FIG. 5  shows the remote sound sensing apparatus  200  surrounded by a plurality of vibrating sound sources  510 A- 510 D. The remote sound sensing apparatus  200  assigns a specific outgoing coherent electromagnetic waves beam  511 ,  521 ,  531  and  541 , to each of the vibrating sound sources  210 A- 210 D respectively. The reflected beams  512 ,  522 ,  532  may be related to each of the specific sound sources  210 A- 210 D in a mutual exclusive manner and therefore source separation is achieved. Multi beam configuration may be is achieved either by one beam that scans the space according to a discrete predefined pattern or by using several beams simultaneously. The scanning scheme is set by the processing unit  340  and controlled by the control unit  330  according to the sound sources spatial position. 
   According to some embodiments, in the case of several sound sources, the vibrometer may utilize several scanning scheme that may define the size of the spatial angular step which determines the size of a ‘cell’ in which a sound source may be detected independently. The scanning scheme may be also determined by the scanning frequency and the amount of time the beam stays directed at each discrete step. 
     FIG. 6  shows a flowchart describing the steps of the method disclosed according to the present invention. In block  610  at least one coherent electromagnetic wave beam is transmitted directly on at least one vibrating sound source; Then, in block  620  at least one coherent electromagnetic wave beam reflected directly from at least one vibrating sound source is received and finally, in block  630  the information gathered from the coherent electromagnetic wave beam reflected directly from the vibrating sound source is analyzed whereby the sound generated by said sound source is separated from other sound sources and ambient noise. 
   According to other embodiments of the invention, various DSP techniques may be used to further enhance the quality of the sound signal reconstructed from the information extracted from the reflecting beam. Specifically, these DSP techniques may be used to improve the separation of the sound source that has been greatly improved by the present invention. 
   In the above description, an embodiment is an example or implementation of the inventions. The various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments. 
   Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. 
   Reference in the specification to “some embodiments”, “an embodiment”, “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions. 
   It is understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only. 
   The principles and uses of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples. 
   It is to be understood that the details set forth herein do not construe a limitation to an application of the invention. 
   Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description below. 
   It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers. 
   If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element. 
   It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element. 
   It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. 
   Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. 
   Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks. 
   The term “method” may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs. 
   The descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only. 
   Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. 
   The present invention can be implemented in the testing or practice with methods and materials equivalent or similar to those described herein. 
   Any publications, including patents, patent applications and articles, referenced or mentioned in this specification are herein incorporated in their entirety into the specification, to the same extent as if each individual publication was specifically and individually indicated to be incorporated herein. In addition, citation or identification of any reference in the description of some embodiments of the invention shall not be construed as an admission that such reference is available as prior art to the present invention. 
   While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the embodiments. Those skilled in the art will envision other possible variations, modifications, and applications that are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents. Therefore, it is to be understood that alternatives, modifications, and variations of the present invention are to be construed as being within the scope and spirit of the appended claims.