Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Sound source localization provides important information on positions of voices of speakers while people are increasingly interested in Human-robot interaction worldwide. The present invention relates to multi-cantilever MEMS (Micro-Electro-Mechanical System) sensor functioning as a mechanical sensor having a plurality of cantilevers, replacing a conventional DSP (Digital Signal Processor) based sound source localization algorithm and reducing production cost when the MEMS sensor applied to mass-produced robots, a manufacturing method thereof, a sound source localization apparatus using the multi-cantilever MEMS sensor and a sound source localization method using the sound source localization apparatus. 
     2. Background of the Related Art 
     A method using time delay of arrival (TDOA) between microphones, a method using a head related transfer function database of a platform, a beam forming method using a plurality of microphone arrays and so on are used for sound source localization. 
     A conventional sound source localization method measures the sound pressure of a sound according to a plurality of microphones in real time when the sound source is radiated to a three-dimensional space and performs post-processing on the measured sound pressure to localize the sound source position. When the sound source position is localized using the aforementioned method, a DSP chip is required to apply the post-processing to cases other than a PC environment. When the DSP chip is used, lots of computations are required for sound source localization to thereby result in an increase in system costs. 
     Furthermore, a procedure of performing the post-processing using a DSP chip while collecting information on the sound pressure measured in real time needs considerable buffering. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made in view of the above-mentioned problems occurring in the prior art, and it is a primary object of the present invention to provide a multi-cantilever MEMS sensor capable of localizing a sound source position, which does not uses a DSP chip so as to reduce the manufacturing cost and improve a data processing speed, a manufacturing method thereof, a sound source localization apparatus using the multi-cantilever MEMS sensor and a sound source localization method using the sound source localization apparatus. 
     To accomplish the above object of the present invention, in one aspect, the present invention provides a multi-cantilever MEMS sensor comprising: a plurality of cantilevers  100  each of which includes a piezoresistor  20  and a sensing part  30  for sensing a predetermined signal generated according to the piezoresistor  20 ; and a terminal T for detecting the signal generated according to the piezoresistor  20 , wherein one end of each cantilever is a free end and the other end thereof is a fixed end of each cantilever, the piezoresistor  20  and the sensing part  30  are formed at the fixed end, and the free ends of the plurality of cantilevers  100  have different lengths. 
     The piezoresistor  20  may comprise boron. 
     An electrode pattern of the sensing part  30  or the terminal T may be formed through lithography. 
     To accomplish the above object of the present invention, in another aspect, the present invention also provide a method of manufacturing a multi-cantilever MEMS sensor, comprising: a cleaning step of cleaning a substrate  99  consisting of a first silicon layer  14 , an insulating layer  12  and a second silicon layer  10 ; a first oxide layer forming step of forming a first oxide layer  16  on the substrate  99 ; a sensing part groove forming step of etching the first oxide layer  16  to form a sensing part groove  18 ; a growing step of growing a piezoresistor  20  in the sensing part groove  18 ; a second oxide layer forming step of forming a second oxide layer  22  on the substrate  99 ; a first bulk etching step of bulk-etching the bottom of the substrate  99  to form a support  10   a ; an oxide layer removal step of removing predetermined portions of the first and second oxide layers  16  and  22  other than portions  16   a  and  22   a  of the first and second oxide layers, which correspond to the sensing part groove  18 , and the insulating layer  12 ; an electrode pattern forming step of forming a terminal T and a sensing part  300  on the substrate  99 ; and a free end forming step of etching the side of the first silicon layer  14 , opposite to the sensing part  30 , to form a free end. 
     The method of manufacturing a multi-cantilever MEMS sensor may further comprise a cutting step of cutting the substrate including a plurality of cantilevers  100  and a second bulk etching step of bulk-etching the bottom of the substrate between the first bulk etching step and the oxide layer removal step. 
     The cleaning step is performed according to the order represented in the following Table 1. 
     The first oxide layer  16  may be SiO 2 . 
     The sensing part groove forming step may etch the first oxide layer using fluorine oxide. 
     The second oxide layer  22  may be formed by oxidizing silicon through low temperature oxidation. 
     The first bulk etching step may perform a directional etching process using TMAH solution. 
     The directional etching process may determine the size of a mask used during the etching according to the following Equation 1 and perform the etching using the mask. 
     The oxide layer removal step may dip a portion of the substrate other than the portions  16   a  and  22   a  of the first and second oxide layers corresponding to the sensing part groove  18  in a BHF solution to remove the predetermined portion of the first and second oxide layers  16  and  22  and the insulating layer  12 . 
     The free end forming step may use reactive ion etching. 
     To accomplish the above object of the present invention, in still another aspect, the present invention also provides a sound source localization apparatus using a multi-cantilever MEMS sensor, comprising: at least two multi-cantilever MEMS sensors  210  comprising a plurality of cantilevers  100  each of which includes a piezoresistor  20  and a sensing part  30  for sensing a predetermined signal generated according to the piezoresistor  20 ; and a terminal T for detecting the signal generated according to the piezoresistor  20 , wherein one end of each cantilever is a free end and the other end thereof is a fixed end of each cantilever, the piezoresistor  20  and the sensing part  30  are formed at the fixed end, and the free ends of the plurality of cantilevers  100  have different lengths; an electric circuit  220  for detecting signals generated from corresponding cantilevers of the multi-cantilever MEMS sensors  210  and counting a TDOA from a sound source  1  to the at least two multi-cantilever MEMS sensors; and a position estimator  230  for localizing the position of sound source  1  from the TDOA. 
     The electric circuit may comprise: a signal amplifier  222  for amplifying the signals generated from the corresponding cantilevers of the multi-cantilever MEMS sensors to a predetermined level; a filter  224  for removing noise from the amplified signals; and a trigger  226  for processing the noise-free signals into square-wave signals. 
     To accomplish the above object of the present invention, in still yet another, the present invention also provides a sound source localization method using at least two multi-cantilever MEMS sensors  210  and  210 ′, comprising: a signal generating step S 100  in which corresponding cantilevers  100   n  and  100   n ′ among a plurality of cantilevers of the respective multi-cantilever MEMS sensors  210  and  210 ′ generate signals according to a sound pressure variation; a TDOA extracting step S 200  in which an electric circuit  220  processes the generated signals to counted digital sequence of a TDOA; and a localization step S 300  in which a position estimator  230  localizes a position of sound source  1  from the TDOA. 
     The sound source localization method may further comprise a compensation step S 250  of subtracting or adding a phase difference between the corresponding cantilevers  100   n  and  100   n ′, which are previously stored in a database, from or to the counted TDOA between the TDOA extracting step S 200  and the localization step S 300 . 
     The multi-cantilever MEMS sensor, the manufacturing method thereof and a sound source localization sensor according to the present invention have the following advantages. 
     The multi-cantilever MEMS sensor according to the present invention has a processing speed higher than a conventional method and reduces the manufacturing cost in mass production. Furthermore, additional post-processing is not required, and thus a data collecting process is omitted. Accordingly, sound source localization irrespective of buffering can be performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front view of a multi-cantilever MEMS sensor according to the present invention; 
         FIG. 2  is a perspective view of a cantilever; 
         FIGS. 3   a  through  3   j  are cross-sectional views illustrating a method of manufacturing a multi-cantilever MEMS sensor according to the present invention; 
         FIG. 4  is a block diagram of a sound source localization apparatus using a multi-cantilever MEMS sensor according to the present invention; 
         FIG. 5  is a flow chart of a method of using the multi-cantilever MEMS sensor according to the present invention; 
         FIG. 6  illustrates a signal processing flow of the sound source localization apparatus using a multi-cantilever MEMS sensor according to the present invention; 
         FIG. 7   a  is a graph illustrating magnitude response according to frequencies of corresponding cantilevers of two multi-cantilever MEMS sensors; 
         FIG. 7   b  is a graph illustrating phase response according to frequencies of corresponding cantilevers of two multi-cantilever MEMS sensors; and 
         FIG. 7   c  is a graph illustrating a phase difference according to frequencies of corresponding cantilevers of two multi-cantilever MEMS sensors. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the present invention will be explained with reference to attached drawings. 
     &lt;Configuration of a Multi-Cantilever MEMS Sensor&gt; 
       FIG. 1  is a plan view of a multi-cantilever MEMS sensor according to the present invention and  FIG. 2  is a perspective view of a cantilever  100 . The multi-cantilever MEMS sensor includes a plurality of cantilevers (referred to as a cantilever group hereinafter) including terminals T a1 , T a2 , T b1 , . . . , T h1  and T h2  for detecting electric signals. The cantilever group means a plurality of cantilevers  100  having different lengths. Although the multi-cantilever MEMS sensor includes eight cantilevers  100   a ,  100   b ,  100   c ,  100   d ,  100   e ,  100   f ,  100   g  and  100   h  in the present invention, the number of multi-cantilevers is not limited to eight. More cantilevers  100  having different free ends make the sound source localization more facilitated. 
     One end of the cantilever  100  is fixed to a substrate and the other end is a free end. The fixed end of the cantilever  100  has a sensing part groove  18  in which a piezoresistor  20  is grown and a sensing part  30  is formed thereon. The free end of the cantilever  100  vibrates according to a sound pressure variation. 
     Each cantilever  100  of the cantilever group has two terminals T a1  and T a2 , T b1  and T b2  . . . , T h1  and T h2  for detecting a predetermined signal generated according to the piezoresistor  20 , sensed by the sensing part  30 . 
     &lt;Method of Manufacturing a Multi-Cantilever MEMS Sensor&gt; 
     A method of manufacturing a multi-cantilever MEMS sensor according to the present invention is explained with reference to  FIGS. 3   a  through  3   j.    
     First of all, a substrate  99  is cleaned (S 10 ). The substrate used in the present invention includes an insulating layer  12  formed between first and second semiconductor layers  10  and  14 , as illustrated in  FIG. 3   a . Preferably, an SOI (Silicon On Insulator) wafer including silicon oxide SiO 2  formed between a first silicon layer  14  and a second silicon layer  10  as the insulating layer  12  is used. The thickness of the SOI wafer is selected in consideration of the thickness of the first silicon layer  14  which will become the cantilever  100 . 
     The substrate  99  is cleaned in order to improve performance and increase yield through removal of contaminants. It is preferable to clean the substrate  99  according to the order represented in Table 1. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Method (mixture 
                   
               
               
                   
                 ratio and 
               
               
                 Order 
                 temperature) 
                 Time 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Piranha (spm, 
                 H 2 SO 4 :H 2 O 2  = 2:1 
                 15 
                 minutes 
               
               
                 H 2 SO 4 clean) 
               
               
                 DI clean 
                   
                 3 
                 minutes 
               
               
                 DHF (Diluted HF) 
                 HF:H 2 O = 1:150, 25° C. 
                 10 
                 seconds 
               
               
                 DI clean 
                   
                 30 
                 seconds 
               
               
                 SCI (Standard 
                 NH 4 OH:H 2 O 2 :H 2 O = 1:1:5, 75° C. 
                 5 
                 minutes 
               
               
                 Clean-1, APM) 
               
               
                 DI clean 
                   
                 5 
                 minutes 
               
               
                 DHF (Diluted HF) 
                 HF:H 2 O = 1:150, 25° C. 
                 15 
                 seconds 
               
               
                 DI clean 
                   
                 30 
                 seconds 
               
               
                 SC2 (Standard 
                 HCl:H 2 O 2 :H 2 O = 1:1:6, 75° C. 
                 10 
                 minutes 
               
               
                 Clean-2, HPM) 
               
               
                 DI clean 
                   
                 20 
                 seconds 
               
               
                 DHF (Diluted HF) 
                 HF:H 2 O = 1:50, 25° C. 
                 10 
                 seconds 
               
               
                 DI clean 
                   
                 30 
                 seconds 
               
               
                   
               
             
          
         
       
     
     Then, a first oxide layer  16  is formed on the outer face of the cleaned substrate (S 20 ). As illustrated in  FIG. 3   b , the first oxide layer  16  protects the substrate from the following processes and is formed using SiO 2 , preferably. 
     Subsequently, the sensing part groove  18  is formed (S 30 ). The sensing part groove  18  is filed with the piezoresistor  20  for the purpose of measuring mechanical vibration of cantilevers. As illustrated  FIG. 3   c , a predetermined portion of the surface of the substrate is etched using HF to form the sensing part groove  18 . 
     The piezoresistor  20  is formed through doping (S 40 ). A well-known material can be used as a piezoresistive material of the piezoresistor  20 . Preferably, boron (B) is used as the piezoresistive material. As illustrated in  FIG. 3   d , boron ions are doped into the sensing part groove  18  to grow the piezoresistor  20  in the sensing part groove  18 . 
     Referring to  FIG. 3   e , a second oxide layer  22  is formed (S 50 ). The second oxide layer  22  protects the substrate in a first bulk etching step which will be explained later. The second oxide layer  22  is formed through PECVD or LTO (Low Temperature Oxidation). When the first bulk etching step uses TMAH solution, LTO is used because PECVD is vulnerable to a base. 
     Referring to  FIG. 3   f , the first bulk etching step using wet etching is performed (S 60 ). Preferably, the bottom of the substrate, that is, the second silicon layer  10  is dipped in TMAH solution to form a support  10   a . Then, a space S is formed at the bottom of the substrate according to the first bulk etching. The space S is a region for vibration of the free end of the cantilever  100 . When the second silicon layer  10  is dipped in the TMAH solution, the second silicon layer  10  is etched with etching directivity. The size of the to-be-etched portion of the second silicon layer  10  can be estimated because the directivity of the silicon layer is used. Accordingly, a predetermined mask can be fabricated and used. Silicon has directivity of approximately 54.74 degrees in (100) direction. Thus, Equation 1 can be used as follows:
 
 W   m   =W   o +2 cotan(54.74°) z   [Equation 1]
 
     Here, W m  represents the size of a mask to be used during the etching, W o  represents the size of a to be-etched portion of the substrate, and z denotes the thickness of the to-be-etched substrate. 
     The first bulk etching is performed on the second silicon layer  10  corresponding to the bottom face of the substrate, as illustrated in  FIG. 3   f . When the substrate is dipped in the TMAH solution for approximately 10 hours, etching is automatically stopped by the insulating layer  12  corresponding to the middle layer of the substrate. 
     After the first bulk etching step (S 60 ), the substrate is cut into a desired size (S 62 ), and then a second bulk etching step (S 64 ) is carried. The second bulk etching step completely removes the remainder of the second silicon layer  10 , which is not eliminated by the first bulk etching step. The second bulk etching is automatically stopped by the insulating layer  12  (silicon oxide layer) of the substrate. The substrate cutting step and the second bulk etching step are performed for efficient mass production. 
     Referring to  FIG. 3   h , the substrate is dipped in a BHF solution for approximately 10 seconds to remove the first and second oxide layers  16  and  22  and the insulating layer  12  (silicon oxide layer) (S 70 ). Here, portions of the first and second oxide layers  16  and  22 , which correspond to the fixed end at which the sensing part groove  18  is formed, are left. When predetermined portions of the first and second oxide layers  16  and  22  and the insulating layer  12  are removed, only the first silicon layer  14  of the substrate is left. The multi-cantilever group is formed on the first silicon layer  14 . 
     Subsequently, an electrode pattern is formed (S 80 ). Since the present invention uses a piezoresistive method which induces a resistance variation according to a mechanical stress variation to detect a signal, the electrode pattern for detecting the signal, that is, the sensing part  30  or/and the terminal T is formed, as illustrated in  FIG. 3   j . The electrode pattern is formed using lithography. 
     Then, the side of the substrate, opposite to the fixed end at which the sensing part  30  is formed, is dry-etched to form the free end of the cantilever  100 , as illustrated in  FIG. 3   j  (S 90 ). Here, it is preferable to use RIE (Reactive Ion Etching) as a dry etching method. Since a plurality of cantilevers are formed, a plurality of free ends are formed. Here, the respective free ends of the plurality of cantilevers have different lengths. 
     &lt;Sound Source Localization Apparatus Using MEMS Sensors&gt; 
     Referring to  FIG. 4 , a sound source localization apparatus  200  includes at least two multi-cantilever MEMS sensors  210  and  210 ′, an electric circuit  220  and a position estimator  230 . 
     Each of the multi-cantilever MEMS sensors  210  and  210 ′ includes a plurality of cantilevers  100  that vibrate according to voiced sounds and functions as a mechanical filter. Free ends of the plurality of cantilevers  100  of the multi-cantilever MEMS sensor  210  have different lengths, and thus the cantilevers have different resonant frequency bands. Accordingly, the pitch frequency of a sound generated from a sound source  1 , that is, a voiced sound, is included in the resonant frequency band of one of the plurality of cantilevers  100 . In the present invention, the cantilever having the resonant frequency band including the pitch frequency of the voiced sound generated from the sound source  1  is referred to as “corresponding cantilever  100   n′.    
     Even when the voiced sound generated from the sound source  1  has a different pitch frequency, the sound source  1  can be localized by using the corresponding cantilever  100   n  having a resonant frequency band that considerably reacts to the pitch frequency of the voiced sound among the plurality of cantilevers  100   a ,  100   b , . . . ,  100   h  having different resonant frequency bands. 
     More specifically, a sound signal, particularly, a voiced sound consists of a pitch frequency (basic frequency) and a harmonic component corresponding to an integer multiple of the pitch frequency. This voiced signal provisionally vibrates the corresponding cantilever  100   n  and the corresponding cantilever  100   n  remarkably vibrates. The vibration of the corresponding cantilever  100   n  is output as a predetermined signal according to the piezoresistor  20 . 
     The operation of the sound source localization apparatus  200  is explained for the corresponding cantilever  100   n  of the multi-cantilever MEMS sensor  210  and the corresponding cantilever  100   n ′ of the multi-cantilever MEMS sensor  210 ′ for convenience of explanation. 
     The electric circuit  220  processes signals generated from corresponding cantilevers  100   n  and  100   n ′ having the same length among cantilevers included in the multi-cantilever MEMS sensors  210  and  210 ′ to count a TDOA (Time Delay of Arrival) between the multi-cantilever MEMS sensors  210  and  210 ′. 
     Preferably, the electric circuit  220  includes a trigger  226  for rectifying the signals into square-wave signals in order to easily extract the TDOA, a signal amplifier  222  for amplifying signals generated according to the piezoresistors  20  to a predetermined level and a filter  224  (for example, a low pass filter) for removing noise from the amplified signals, as illustrated in  FIG. 6 . 
     Furthermore, the electric circuit  220  compensates a phase difference between the multi-cantilever MEMS sensors  210  and  210 ′ in order to correct errors in length and thickness differences between the corresponding cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′ to improve the accuracy of sound source localization. Phase difference compensation will be described in detail later in a sound source location method using a multi-cantilever MEMS sensor. 
     The position estimator  230  localizes the position of sound source  1  based on the counted TDOA. 
     &lt;Sound Source Localization Method Using Multi-Cantilever MEMS Sensors&gt; 
     A sound source localization method using multi-cantilever MEMS sensors uses at least two multi-cantilever MEMS sensors  210  and  210 ′. Referring to  FIG. 5 , the sound source localization method includes a signal generating step S 100  in which corresponding cantilevers  100   n  and  100   n ′ among a plurality of cantilevers  100  of the multi-cantilever MEMS sensors  210  and  210 ′ generate signals according to a sound pressure variation, a TDOA extracting step S 200  in which the electric circuit  220  processes the signals to extract a TDOA, and a localization step S 300  of localizing the position of sound source  1  from the TDOA. 
     In the signal generating step S 100 , when the pitch frequency of a voice corresponds to the resonant frequency bands of the cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′, a sound pressure variation of the voice vibrates the cantilevers  100   n  and  100   n ′. Vibrations of the cantilevers  100   n  and  100   n ′ are transferred to predetermined signals according to the piezoresistors  20  of the multi-cantilever MEMS sensors  210  and  210 ′ and detected as predetermined signals according to the sensing parts  30  and  30 ′ and the terminals T and T′ of the multi-cantilever MEMS sensors  210  and  210 ′. 
     Then, the TDOA extracting step S 200  is described.  FIG. 6  illustrates a signal processing flow of the electric circuit  220  and signals processed by the electric circuit  220 . Signals generated from the corresponding cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′ are processed into square-wave signals by the trigger  226 , preferably, Schmitt trigger, in order to easily extract a TDOA. Prior to being processed into the square-wave signals, the signals can be amplified by the amplifier  222  or filtered by the filter  224  to remove noise. An XOR operation is performed on the square-wave signals according to an XOR operation unit  228 . Finally, counting is performed to estimate TDOA by using the suitable oscillator as illustrated in  FIG. 6 . 
     In an embodiment of the present invention, if the corresponding cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′ have the same length and thickness and have little error in the manufacturing process thereof (if a manufacturing error is ignorably small), the corresponding cantilevers  100   n  and  100   n ′ have the same natural frequency. In this case, when the corresponding cantilevers  100   n  and  100   n ′ generate vibrations, a phase difference between signals generated according to the vibrations is negligible. Then, a TDOA can be counted from the signals obtained from the corresponding cantilevers  100   n  and  100   n ′ having the same length and the position of sound source  1  can be localized from the counted TDOA. That is, though phase difference compensation is not required when a phase difference is negligibly small as described above, it is preferable to add a TDOA compensation step S 250  in order to improve measurement accuracy if an error in the lengths or/and thicknesses of the corresponding cantilevers  100   n  and  100   n  is not ignorable. 
     That is, the TDOA compensation step S 250  compensates a phase difference caused by an error in the lengths or/and thicknesses of the corresponding cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′. The TDOA is compensated in such a manner that a phase difference between the corresponding cantilevers  100   n  and  100   n ′ of the multi-cantilever MEMS sensors  210  and  210 ′ is previously stored in a database and the phase difference is subtracted from or added to the counted TDOA which has been subjected to the TDOA extracting step S 200 . This is described in more detail with reference to  FIGS. 7   a ,  7   b  and  7   c.    
       FIG. 7   a  illustrates magnitude response of the corresponding cantilevers  100   n  and  100   n ′ of the two multi-cantilever MEMS sensors. In  FIG. 7   a , x-axis represents a frequency (kHz) and y-axis represents a predetermined physical magnitude (pressure, voltage and the like). It can be known from  FIG. 7   a  that the corresponding cantilevers  100   n  and  100   n ′ have different resonant frequency bands as illustrated in a region Z due to an error in the thicknesses or lengths of the corresponding cantilevers  100   n  and  100   n′.    
       FIG. 7   b  is a graph illustrating the phase response of the corresponding cantilevers  100   n  and  100   n ′ with respect to frequency and  FIG. 7   c  is a graph illustrating a phase difference between the corresponding cantilevers  100   n  and  100   n ′ with respect to frequency. In  FIGS. 7   b  and  7   c , x-axis represents a frequency and y-axis represents a phase. As illustrated in  FIG. 7   c , a phase difference between the corresponding cantilevers  100   n  and  100   n ′ is not a constant, and thus a compensation value must be determined by taking mean value of phase difference of desired frequency band (mean value of boxed area). Accordingly, it is preferable that the phase difference is previously stored in the electric circuit  220  or the position estimator  230  as a database. 
     Finally, the sound source localization step S 300  localizes the position of sound source  1  based on the counted TDOA (S 300 ). Sound source localization from the TDOA is well known in the art so that detailed explanation thereof is omitted. 
     Modified Embodiment 
     In another embodiment, the multi-cantilever MEMS sensor according to the present invention functions as a mechanical sensor and it can be applied to any industrial field using a conventional sound source localization algorithm operating based on a DSP. In particular, the multi-cantilever MEMS sensor according to the present invention can be used for a human-robot interaction which people are increasingly interested worldwide. 
     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Technology Category: 5