Abstract:
A Raman spectroscopy system features free space optics, wherein an excitation laser beam is directed to a sample, and Raman scattered photons are collected from a desired point of the excitation beam&#39;s impact on the sample, through the air, without the use of fiber optics. The excitation laser is directed to a sample, such as fluid flowing in a pipe, through a sight glass in the pipe. A front lens assembly, having a fixed focal point at a predetermined z-axis distance in front of the front-most lens, collects Raman scattered photons, which pass through an optical system to a detector. The Collection Point (CP), or the point along the excitation beam (and within the sample) at which Raman scattered photons are collected—which coincides with the focal point of the front lens assembly—is controlled by physically translating the front lens assembly along the optical axis.

Description:
[0001]    This application also claims priority to U.S. Provisional Patent Application Ser. No. 61/720,317, titled, “Adaptive Front Lens for Raman Spectroscopy Free Space Optics,” filed Oct. 30, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to optics, and in particular to an adaptive front lens for a Raman spectroscopy system featuring free space optics. 
       BACKGROUND 
       [0003]    Raman spectroscopy is an analytic instrumentation methodology useful in ascertaining and verifying the molecular structures of materials. Raman spectroscopy relies on inelastic scattering, or Raman scattering, of monochromatic light, resulting in an energy shift in a portion of the photons scattered by a sample. From the shifted energy of the Raman scattered photons, vibrational modes characteristic to a specific molecular structure can be ascertained. This is the basis of using Roman spectroscopy to ascertain the molecular makeup of a sample. In addition, by analytically assessing the relative intensity of Raman scattered photons, the purity of a sample can be determined. 
         [0004]    Typically, a sample is illuminated with a laser beam. Light from the illuminated spot is collected by lenses and analyzed. Wavelengths close to the laser line due to elastic Rayleigh scattering are blocked or filtered out, while chosen bands of the collected light are directed onto a detector. 
         [0005]    The Raman effect occurs when light impinges upon a molecule and interacts with the electron cloud and the bonds of that molecule. For the spontaneous Raman effect, which is a form of light scattering, a photon excites the molecule from its ground state to a virtual energy state. The energy state is referred to as virtual since it is temporary, and not a discrete (real) energy state. When the molecule relaxes, it emits a photon and it returns to a different rotational or vibrational state. The difference in energy between the original state and this new state leads to a shift in the emitted photon&#39;s frequency away from the excitation wavelength. 
         [0006]    If the final vibrational state of the molecule is more energetic than the initial state, then the emitted photon will be shifted to a lower frequency in order for the total energy of the system to remain balanced. This shift in frequency is known as a Stokes shift. If the final vibrational state is less energetic than the initial state, then the emitted photon will be shifted to a higher frequency, which is known as an Anti-Stokes shift. Raman scattering is an example of inelastic scattering because of the energy transfer between the photons and the molecules during their interaction. 
         [0007]    The pattern of shifted frequencies is determined by the rotational and vibrational states of the sample, which are characteristic of the molecules. The chemical makeup of a sample may thus be determined by quantitative analysis of the Raman scattering. 
         [0008]    Conventional Raman spectroscopy relies on a complex, sensitive, carefully calibrated optical system comprising a laser providing a source beam; an array of photodetectors for detecting Stokes and anti-Stokes shifted photons; optics, including lenses, mirrors, and optical filters; and data processing systems. Conventional Raman spectroscopy systems are maintained in a controlled environment, such as a laboratory. 
         [0009]    In some applications, real-time (or near-real time) analysis of materials is required. For example, it may be advantageous to monitor the composition and purity of a liquid or gas flowing in a pipe, such as precursor gases in semiconductor manufacturing operations, various chemicals utilized in petroleum refineries, and the like. To monitor such material flows in situ, conventional, lab-based Raman spectroscopy systems deliver an incident laser beam into a pipe via an optical fiber running from the lab to the factory floor, and inserted through the pipe wall to a desired depth. Scattered photons are collected by a second optical fiber, and returned to the spectroscopy system. 
         [0010]    Such remote Raman spectroscopy systems exhibit numerous deficiencies. The optical fibers cause a loss in the optical intensity of both the incident laser and the Raman scattered photons. This intensity loss may be nonlinear, and otherwise difficult to compensate. Additionally, the fiber itself has a Raman signature, which may interfere with analysis of the sample. Furthermore, precise positioning of the optical fibers with in the material pipe may be difficult to control, and cannot easily be dynamically adjusted, nor can positioning of the probe be easily replicated after routine maintenance, such as removal for cleaning. This makes consistent measurements difficult. 
         [0011]    The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section. 
       SUMMARY 
       [0012]    The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure and is not intended to identify key/critical elements of embodiments of the invention or to delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
         [0013]    According to one or more embodiments described and claimed herein, a Raman spectroscopy system features free space optics, wherein an excitation laser beam is directed to a sample, and Raman scattered photons are collected from a desired point of the excitation beam&#39;s impact on the sample, through the air, without the use of fiber optics. The excitation laser is directed to a sample, such as fluid flowing in a pipe, through a sight glass in the pipe. A front lens assembly, having a fixed focal point at a predetermined z-axis distance in front of the front-most lens, collects Raman scattered photons, which pass through an optical system to a detector. The excitation laser passes through the center of the front lens assembly with minimal distortion due to its compact size. This beam causes Raman scattering of all transparent or translucent material through which it passes, all along the length of the beam. The Collection Point (CP), or the point along the excitation beam (and within the sample) at which Raman scattered photons are collected—which coincides with the focal point of the front lens assembly—is controlled by physically translating the front lens assembly along the optical axis. 
         [0014]    One embodiment relates to a Raman spectroscopy system using free space optics to analyze a sample. The system includes an excitation laser source operative to selectively generate an excitation laser beam, the source positioned to deliver the beam along an optical axis and onto a sample. The system also includes a front lens assembly having a fixed focal distance defining a Collection Point (CP), the front lens assembly positioned on the optical axis and selectively moveable along the optical axis, the front lens assembly operative to collect Raman scattered photons from the sample primarily at the CP. The system further includes a detector positioned and operative to detect Raman scattered photons collected from the sample at the CP by the front lens assembly, and a data processor operative to analyze the spectra of Raman scattered photons detected by the detector. Substantially all Raman scattered photons collected from the sample are generated at the CP, and the CP may be positioned along the optical axis by moving the front lens assembly along the optical axis. 
         [0015]    Another embodiment relates to a method of performing Raman spectroscopy on a sample. An excitation laser beam is directed onto the sample, the excitation laser beam defining an optical axis. A front lens assembly having a fixed focal distance defining a Collection Point (CP) is positioned on the optical axis, the front lens assembly operative to collect Raman scattered photons from the sample primarily at the CP. The front lens assembly is moved along the optical axis to move the CP along the optical axis upon or within the sample. Raman scattered photons collected from the sample at the CP by the front lens assembly are detected, and the spectra of Raman scattered photons detected by the detector are analyzed. 
         [0016]    Yet another embodiment relates to a non-transient computer readable media storing program instructions operative to control a portable Raman spectroscopy system. The Raman spectroscopy system includes an excitation laser source operative to selectively generate an excitation laser beam along an optical axis and onto a sample; a front lens assembly having a fixed focal distance defining a Collection Point (CP), the front lens assembly positioned on the optical axis and selectively moveable along the optical axis, the front lens assembly operative to collect Raman scattered photons from the sample primarily at the CP; and a detector positioned and operative to detect Raman scattered photons collected from the sample at the CP by the front lens assembly. The program instructions are operative to cause a controller to control mechanical means to move the front lens assembly, and hence the CP, along the optical axis to a first position; and to analyze the spectra of Raman scattered photons collected primarily at the CP at the first position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
           [0018]      FIG. 1  is an optical schematic view of a Raman spectroscopy system having an adaptive front lens. 
           [0019]      FIGS. 2A and 2B  are graphs of Raman spectra. 
           [0020]      FIG. 3  is a flow diagram of a method of positioning a lens in a Raman spectroscopy system. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
         [0022]      FIG. 1  depicts a sectional, optical schematic view of some essential elements of a Raman spectroscopy system  10  utilizing free space optics, according to one embodiment of the present invention. A spectrometer  22  having a moveable front lens assembly  18  is adapted to perform Raman spectroscopy of a transparent or translucent sample  50 , for example a fluid  50  as it travels in a pipe  52  defined by pipe walls  54 . A sight glass  56  is affixed to an aperture in the pipe wall  54 , to allow remote Raman spectroscopy through the sight glass  56 , without touching the fluid  50 . Although embodiments of the present invention are described herein with respect to this environment, the present invention is not limited to performing Raman spectroscopy on fluids, or to the particular mechanical arrangement depicted in  FIG. 1 . 
         [0023]    The major optical components of the spectrometer  22  will now be described. A laser source  12  generates an excitation laser beam  14 . The excitation beam  14  is reflected by a dichroic mirror  16 , and thence defines an optical axis. The direction of the optical axis is referred to herein as the z-direction. The excitation beam  14  passes through a front lens assembly  18 . The front lens assembly  18 , as well as other optical components, is positioned along the optical axis defined by the excitation laser beam  14 . The front lens assembly  18  is attached to the spectrometer  22  by mechanical means, such as a stepper motor driven linear actuator (not shown), that allows the front lens assembly  18  to be selectively moved along the optical axis (i.e., in the z-direction) with respect to the spectrometer  22 . That is, the distance denoted z in  FIG. 1  between the spectrometer aperture  20  and the front of the front lens assembly  18  is selectively variable. 
         [0024]    The collimated excitation laser beam  14  has a small diameter compared to the lens  18 . It passes through the center of the lens  18  where the excitation beam  14  is normal to the lens surfaces and experiences little refraction, thus remaining substantially collimated. Additionally, the excitation beam  14  has a very small “dot” of cross-section area, and the lens  18  does little to focus or otherwise optically alter the excitation beam  14 . 
         [0025]    The front lens assembly  18  has a fixed focus, at a point z 0  in front of the front lens element  18   a,  in the z-direction, referred to herein as the Collection Point (CP). As one non-limiting example, the front lens assembly  18  may comprise a two-element inverse Galilean Telescope lens system, comprising anti-reflection coated quartz elements. In one embodiment, the front element  18   a  is plano-convex and of 2.5 cm diameter, and rear element  18   b  is plano concave of 1 cm diameter. The lens elements  18   a,    18   b  are selected and disposed so that light collected by the front lens element  18   a  is directed onto the rear lens element  18   b,  which then directs the collected light as a non-converging (infinite focal length) beam through the dichroic mirror  16  and into an aperture  20  in the spectrometer  22 . The CP may, for example, lie 100 mm in front of the lens element  18   a.  An optical path behind the front lens assembly  18  (to the left as depicted in  FIG. 1 ) is focused to infinity, allowing the front lens assembly  18  to move along the optical axis, in the z-direction, without substantially affecting the optical path of the spectroscopy system  10 . In other embodiments, the front lens assembly  18  may comprise more, or fewer, lenses and other optical elements, than the embodiment depicted in  FIG. 1 . 
         [0026]    Focusing lenses  24   a  and  24   b  focus the light collected by the front lens assembly  18  to a point, where it passes through a spectrometer aperture slit  26 , and back into an optical beam. The spectrometer aperture slit  26  isolates the interior of the spectrometer  22  (in particular, the detector  32 ) from extraneous photons. In one embodiment, a laser rejection dichroic filter  28  substantially blocks photons at the wavelength of the excitation laser beam  14 . This removes most non-Raman scattered photons (e.g., Rayleigh scattered photons), which have the same wavelength as the excitation laser beam  14 , from the optical signal, thus enhancing the signal to noise ratio (SNR) of the Raman spectroscopy signal. 
         [0027]    A transmission grating  30  then directs the collected, Raman scattered photons to a detector  32 . In one embodiment, the transmission grating  30  is a holographic transmission grating comprising a transparent window with periodic optical index variations, which diffract different wavelengths of light from a common input path into different angular output paths. In one embodiment, the holographic transmission grating  30  comprises a layer of transmissive material, such as dichromated gelatin, sealed between two protective glass or quartz plates. The phase of incident light is modulated, as it passes through the optically thick gelatin film, by the periodic stripes of harder and softer gelatin. In another embodiment, the transmission grating  30  comprises a “ruled” reflective grating, in which the depth of a surface relief pattern modulates the phase of the incident light. In all embodiments, the spacing of the periodic structure of the transmission grating  30  determines the spectral dispersion, or angular separation of wavelength components, in the diffracted light. In one embodiment, the detector  32  comprises a charge-coupled device (CCD) array. The detector  32  converts incident photonic energy to electrical signals, which are processed by readout electronics  34 . 
         [0028]    The spectroscopy data from the readout electronics  34  are analyzed by a signal processor  36 , such as an appropriately programmed Digital Signal Processor (DSP) or other microprocessor, also operatively connected to memory  38 . Data representing the processed Raman spectra may be stored, output to a display, transmitted across a wired or wireless network, or the like, as known in the art. In addition to analyzing Raman spectra data, the signal processor  36 —or another processor (not shown in FIG.  1 )—may additionally control the overall operation of the system  10 , including initialization, calibration, testing, automated data acquisition procedures, user interface operations, remote communications, and the like. The memory  38  may comprise any non-transient machine-readable media known in the art or that may be developed, including but not limited to magnetic media (e.g., floppy disc, hard disc drive, etc.), optical media (e.g., CD-ROM, DVD-ROM, etc.), solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, Flash memory, etc.), or the like. The memory  38  is operative to store program instructions  40  operative to implement the functionality described herein, as well as general purpose control functions for analytical instrumentation, as well known in the art. 
         [0029]    The excitation laser beam  14  excites molecules of the sample  50  all along its length (as well as those of the intervening air, the lens elements  18   a ,  18   b,  and the sight glass  56 ). These molecules relax to a different vibration or spin state and generate Raman scattered photons all along the length of the beam  14 . However, under normal spectroscopy conditions, substantially the only Raman scattered photons collected, and hence analyzed, by the optics of the system  10  are those generated at the CP. At the CP, Raman scattering may be modeled as a point source optical phenomenon, with isotropic emission. In practice, of course, the CP is not actually a point, but rather a very short range of distance in the z-direction. However, the CP may be conceptualized as a point, and is referred to as such herein, with those of skill in the art appreciating that the size of the CP is limited by achievable optical resolution. 
         [0030]    “Normal spectroscopy conditions,” as contemplated by the embodiment of the present invention depicted in  FIG. 1 , are performing Raman spectroscopy on a transparent or translucent sample  50 , such as a fluid. Under these conditions, as stated above, substantially all of the Raman photons collected and analyzed originate at the CP. Under some conditions, such as where the sample  50  or the optical path is highly scattering or lossy—e.g., where the sample  50  is cloudy, a dark liquid, or an opaque state such as a powder—the CP would be hidden by the interposed lossy material. In this case, the Raman emissions would be weak, and would be dominated by poorly-focused surface emission from the sample  50 , which is not at the CP. To perform spectroscopy in such cases, the CP would be placed at the outer surface of the sample  50  (e.g., using adaptive optics), and it would not be possible to collect Raman scattered photons from deep within the sample  50 . For the purposes of explanation herein, a transparent or translucent sample  50  is assumed, in which substantially all of the Raman scattered photons captured for analysis originate at the CP. When the sample  50  has low optical translucence or is opaque, the CP is assumed to be focused at the surface, and substantially all of the Raman scattered photons captured for analysis will also originate at the CP in this case. 
         [0031]    Representative Raman spectra are depicted in  FIGS. 2A and 2B , discussed in greater detail below. Raman shifts are typically described as wavenumbers, which have units of inverse length [cm −1 ]. A wavenumber relates to frequency shift by 
         [0000]    
       
         
           
             
               Δ 
                
               
                   
               
                
               w 
             
             = 
             
               ( 
               
                 
                   1 
                   
                     λ 
                     0 
                   
                 
                 - 
                 
                   1 
                   
                     λ 
                     1 
                   
                 
               
               ) 
             
           
         
       
     
         [0000]    where 
         [0032]    w is the wavenumber; 
         [0033]    λ 0  is the wavelength of the excitation laser beam  14 ; and 
         [0034]    λ 1  is the wavelength of the Raman scattered photon. 
         [0035]    According to embodiments of the present invention, the position of the CP may be varied in the z-direction by moving the front lens assembly  18  forwards (towards the sample  50 ) or backwards (towards the spectrometer  22 ). The optical system behind the front lens assembly  18  is focused to infinity; accordingly, the distance denominated as z in  FIG. 1  may be varied over a wide range, such as 5 cm in one embodiment, without adversely impacting optical integrity. The focal distance of the CP, denoted z 0  in  FIG. 1 , is fixed. In this manner, the depth within a transparent or translucent sample  50  at which Raman spectroscopy is performed may be selectively varied. 
         [0036]    As one representative example of an advantage of a selectively locatable CP,  FIG. 1  depicts a free space optics Raman spectroscopy system  10  analyzing a fluid sample  50  moving through a pipe  52 . A transparent sight window  56  is disposed in one wall  54  of the pipe  52 . By moving the front lens assembly  18  in the z-direction, the depth of the CP within the sample  50  may be controlled. This may be advantageous for several reasons. 
         [0037]    In one embodiment, as depicted in  FIG. 1 , the sight glass  56  inserted into the pipe wall  54  may leave a space, or void, behind it, which may alter the flow characteristics of the sample fluid  50 . For example, an eddy current may form, tending to trap sample fluid  50  immediately behind the sight glass  24 . To ensure that Raman spectra is obtained from “fresh” sample material  50 , the CP may be positioned well beyond the inner surface of the sight glass  56 , in the main flow of sample fluid  50 . 
         [0038]    Similarly, a flowing sample fluid  50  may comprise a viscous fluid. Viscous fluids may flow in a less turbulent, more laminar or essentially laminar mode than lower viscosity fluids, meaning they tend to “hug” the pipe walls  56 , forming an essentially stationary boundary layer. Fluid exchange at the walls of such a pipe, and similarly in any sight glass mount, etc. may be much slower than the center of the flow, and may depend on diffusion, which can be slow. The fluid in such regions thus may not reflect changes in composition of the flowing material promptly. By moving the front lens assembly  18  in the z-direction, the CP may be positioned to obtain Raman spectra from the desired region of the fluid  50 . 
         [0039]    In one embodiment, Raman spectroscopy may be used to position the CP within the sample fluid  50 . The spectroscopy system  10  is positioned, and the position of the front lens assembly  18  adjusted, such that the CP falls outside the sample fluid  50  of interest—for example, outside of the sight glass  56 . Data is obtained from the detector  32  and analyzed. The front lens assembly  18  is then moved forward a predetermined distance, and another spectroscopy reading is obtained. The process continues until the optimal CP position is determined. For example, the Raman spectra characteristic of a sample fluid  50  may increase in intensity as the CP moves into through a “dead zone” and into an active region of the sample fluid  50 , and consequently decrease in intensity as the CP moves out of the active region. In one embodiment, an optimal CP position is selected based on a quality metric associated with Raman spectral analysis at each of a plurality of CP positions. For example, the optimal CP position may be the CP position that generates the largest signal to noise ratio for particular spectral peaks. As another example, the CP position that generates reasonably large spectral peaks characteristic of the largest number of different sample fluids  50  may be considered optimal. In one embodiment, a plurality of candidate CP positions are determined based on quality metrics associated with the Raman spectra obtained, and a user selects one or more of the candidate CP points at which to perform further Raman spectroscopy. In general, for any given application, the CP may be positioned within the sample fluid  50  to obtain optimal Raman spectroscopy results based on the spectra obtained and the corresponding z values denoting the position of the front lens assembly  18 . 
         [0040]    In one embodiment, the CP may be located in a predetermined position with a high degree of accuracy by using a marker material on the sight glass  56 . A small dot of material having a known, distinct Raman spectral signature, such as Polystyrene or Calcite, may be applied to the front of the sight glass  56  where the excitation laser beam  14  passes through it. This material is referred to herein as a marker material. As described above, Raman spectra are obtained and analyzed as the front lens assembly  18  is moved, changing the position of the CP. The Raman spectra characteristic of a marker material will be obtained when the CP is coincident with the outer surface of the sight glass  56 . The corresponding position of the front lens assembly  18  is noted as a reference position. The CP may then be precisely positioned, for example, just inside the sight glass  56 , by moving the front lens assembly  18  a known distance from the reference position. 
         [0041]      FIG. 2A  depicts a representative spectrum when the CP is incident on the marker material. The Raman peaks  60  and  62  are characteristic of the sample fluid  50 , and have a low intensity since the CP is not located within the fluid  50 . The peak  64  is characteristic of the marker material, and has a high intensity when the CP is coincident with the marker material (i.e., on the front surface of the sight glass  56 ).  FIG. 2B  depicts the spectrum when the CP is moved past the sight window  56  some predetermined distance, into the sample fluid  50 . The peaks  60  and  62  characteristic of the sample fluid  50  have a high intensity. The peak  64  characteristic of the marker material still appears, as the excitation laser beam  14  passes through the marker material and some Raman scattered photons are emitted in the direction of the spectroscopy system  10 . However, the intensity of the peak  64  is low, since the CP is not coincident with the marker material. Of course, the spectra of  FIGS. 2A and 2B  are only for explanation, and do not necessarily represent any actual Raman spectroscopy results. 
         [0042]    The capability to precisely locate the CP at known distances may be useful for analyzing highly dispersive sample fluid  50 , which necessitates positioning the CP a minimal depth into the fluid  50 . As another example, some fluid  50  may leave deposits, such as through crystallization, on the inner walls  54  of the pipe  52 , including the inner surface of the sight glass  56 . By locating the CP at the outer surface of the sight glass  56  using the marker material Raman spectral response, then moving the front lens assembly  18  forward a distance corresponding to the known thickness of the sight glass  56 , the CP may be positioned at the point of sample fluid  50  surface deposits, with a high degree of precision. In another embodiment, the crystallization of sample fluid  50  at the inner surface of the sight glass  56  may be detected by noting a different Raman spectral response due to phase and density differences from the sample  50 . 
         [0043]    Embodiments of the present invention present numerous advantages over the prior art. By providing a portable Raman spectrometer  22 , and utilizing free space optics, Raman spectroscopy of a sample  50  may be performed remotely, without touching the sample  50  material or exposing it to air. In this manner, Raman spectroscopy may safely be performed on hazardous or sensitive materials  50 , such as materials that are highly toxic, pharmacologically potent, infectious, reactive, explosive, radioactive, materials which must be kept sterile or exceptionally clean, and the like, without physical contact with the analyzer, as is required using fiber optic probes and cables. By moving the front lens assembly  18  with respect to the spectrometer  22 , the depth of the CP within a sample  50  may be varied, to perform Raman spectroscopy of specific components of the sample  50  (e.g., selected flow zones, surface or boundary phenomena, or the like). It is not possible to selectively collect Raman returns from different z-axis positions using fiber optic cables. By utilizing Raman spectral analysis in a CP-positioning feedback loop, the spectroscopy results may be used to precisely position the CP at an optimal point. By using marker materials, the CP may be precisely positioned at predetermined positions. Neither of these techniques of positioning the CP is possible using fiber optic cables. 
         [0044]    The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.