RE-SCAN OPTICAL SYSTEMS AND METHODS

Abstract

A re-scan optical system scans a light spot over a plane to form an image and includes an illumination system for directing, and optionally focusing, light providing an illumination light spot. A directing element scans the spot over and/or through the sample, de-scans sample light from the sample and scans the sample light. A detection system directs the de-scanned light along a path running from the directing element back to the directing element so that the directing element scans the sample light. A prism inverts and/or reverts the light, and/or the re-scan system comprises one or more elements to cause at least two foci of the light in said path, and/or the path is provided with a deflecting prism to deflect the light without inverting the light and/or to deflect the light without reverting the light.

Claims

1. A re-scan optical system for scanning a sample light spot over an imaging plane of an imaging system in order to form an image of a sample, comprising: an illumination optical system configured to direct illumination light at the sample therewith providing an illumination light spot at the sample, the illumination light spot causing sample light; a detection optical system configured to focus at least part of the sample light onto an imaging plane of an imaging system herewith causing a sample light spot on the imaging plane; a light directing element configured to scan the illumination light spot over and/or through the sample and de-scan the sample light from the sample and scan the sample light spot over said imaging plane of the imaging system, wherein the detection optical system is configured to direct the de-scanned sample light along a light path running from the light directing element back to the light directing element so that the light directing element scans the sample light spot over said imaging plane, wherein the light path is provided with a prism configured to invert and/or revert the sample light, and/or wherein the re-scan optical system comprises one or more optical elements that is or are configured to cause at least two foci of the sample light in said light path, and/or wherein the light path is provided with a sample light deflecting prism configured to deflect the sample light without reverting the sample light and/or configured to deflect the sample light without inverting the sample light.

2. The re-scan optical system according to claim 1, wherein the light path is provided with a prism configured to invert and/or revert the sample light.

3. The re-scan optical system according to claim 2, wherein the light path is provided with two, and only two, lenses and two, and only two, mirrors configured to reflect the sample light and said prism.

4. The re-scan optical system according to claim 2, wherein said prism is a Dove prism or a Pechan prism or a Schmidt-Pechan prism or an Abbe-Koenig prism or a Porro-Abbe prism or a double Porro prism.

5. The re-scan optical system according to claim 1, wherein the light path is provided with a sample light deflecting prism configured to deflect the sample light without reverting the sample light and/or configured to deflect the sample light without inverting the sample light.

6. The re-scan optical system according to according to claim 5, wherein the sample light deflecting prism is a pentaprism or Bauernfeind prism.

7. The re-scan optical system according to claim 1, wherein the light directing element is configured to scan the sample light spot in a scan direction over the imaging plane, wherein a reversion or, respectively, inversion of the sample light in said light path causes an orientation of the sample light spot in the imaging plane to flip around a line that is perpendicular to said scan direction and that lies in the imaging plane of the imaging system, wherein said light path is configured to cause an even number of reversions or, respectively, inversions of the sample light in said light path.

8. The re-scan optical system according to claim 1, wherein the illumination light spot is a line-shaped illumination light spot.

9. The re-scan optical system according to claim 1, further comprising a light splitter that is configured to separate the illumination light from the sample light.

10. The re-scan optical system according to claim 1, wherein said light path is provided with a pinhole and/or optical slit.

11. The re-scan optical system according to claim 1, wherein the imaging system is configured to integrate sample light incident at the imaging plane over time.

12. The re-scan optical system according to claim 1, wherein the re-scan optical system is configured to move the illumination light spot over and/or through the sample at a first velocity and move the sample light spot over the imaging plane at a second velocity, such that the second velocity is different from, preferably higher than, more preferably approximately twice as high as, a baseline velocity, wherein the baseline velocity is defined as the first velocity multiplied by an optical magnification of the re-scan optical system.

13. The re-scan optical system according to claim 1, comprising: an objective configured to gather the sample light from the sample and focus the sample light on a primary imaging plane of the re-scan microscope system, wherein the detection optical system is configured to image images in the primary imaging plane onto the imaging plane of the imaging system.

14. A method for scanning a sample light spot over an imaging plane of an imaging system in order to form an image of a sample using a re-scan optical system comprising an illumination optical system configured to direct illumination light at the sample therewith providing an illumination light spot at the sample, the illumination light spot causing sample light, a detection optical system configured to focus at least part of the sample light onto an imaging plane of an imaging system herewith causing a sample light spot on the imaging plane, and a light directing element, wherein the detection optical system is configured to direct de-scanned sample light along a light path running from the light directing element back to the light directing element, the method comprising: causing the light directing element to scan the illumination light spot over and/or through the sample and de-scan the sample light from the sample and scan the sample light spot over said imaging plane of the imaging system; and/or directing the sample light through said light path.

15. The re-scan optical system according to claim 1 wherein the detection optical system is configured to image images in the primary imaging plane onto the imaging plane of the imaging system with an optical magnification of approximately 0.5.

16. The re-scan optical system according to claim 1 wherein the illumination optical system is configured to focus illumination light at the sample.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Aspects of the invention will be explained in greater detail by reference to exemplary embodiments shown in the drawings, in which:

[0076] FIG. 1 shows a re-scan optical system comprising a prism according to an embodiment

[0077] FIG. 2 shows a re-scan optical system comprising one or more elements that cause at least two foci in the static sample light path;

[0078] FIGS. 2A-2C illustrate further re-scan optical systems according to respective further embodiments wherein the light path is provided with a prism configured to invert and/or revert the sample light;

[0079] FIGS. 2D-2F illustrate further re-scan optical systems according to respective further embodiments wherein the light path is provided with a prism configured to deflect the sample light without reverting the sample light and/or configured to deflect the sample light without inverting the sample light;

[0080] FIG. 3 illustrates the scanning of the illumination light spot and re-scanning of the sample light spot according to an embodiment;

[0081] FIG. 4 illustrates the scanning of the illumination light spot and re-scanning of the sample light spot with a higher sweep factor according to an embodiment;

[0082] FIG. 5 illustrates the scanning of a line-shaped illumination light spot and the re-scanning of the sample light spot according to an embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

[0083] In the figures identical reference numerals indicate identical or similar elements.

[0084] FIG. 1 illustrates a re-scan optical system 2, e.g. a re-scan microscope system 2, for forming an image of a sample 22 according to an embodiment. This optical system 2 comprises a light source 4 that is configured to generate illumination light 6. However, it should be appreciated that the re-scan optical system does not per se comprise the light source. The re-scan optical system for example comprises means for receiving illumination light, such as an input connection for an optical fiber that provides the illumination light. The light source 4 may be a laser, such as a solid state laser or diode laser. The light source 4 may comprise a collimator (not shown) that is configured to make a parallel beam with a relatively large diameter, wherein preferably the cross section of the beam has a uniform intensity distribution. The collimator may comprise one or more negative lenses and one or more positive lenses to generate an expanded, collimated beam. Such collimator is shown in FIG. 6A (see reference numeral 70). In an example, the diameter of the light beam generated by the light source 4 is 10 mm. The sample light 6 is typically light that excites photons in the sample 22 and may therefore also be referred to as excitation light. However, the sample light may also be caused by other effects, such as reflection, Raman effect, Billouin radiation, et cetera. The illumination light 6 reflects from mirror 8 and hits cylindrical lens 10, which focuses the illumination light onto light direction element 14 herewith causing a horizontal line at mirror 14. Herein, horizontal may be understood to be parallel to the indicated x-z plane. The optical path distance between the cylindrical lens 10 and the aperture of the light source 4 is preferably as close to the focal length of the cylindrical lens 10 as possible

[0085] Before the illumination light 6 is incident on light directing element 14, it reflects from dichroic mirror 12. Preferably, dichroic mirror 12 is positioned at a 45 degrees angle with respect to the propagation direction of the incoming illumination light 6, so that the propagation direction of the illumination light 6, upon reflection, changes 90 degrees.

[0086] The light directing element 14 reflects the illumination light 6 towards a scan lens that is configured to focus the sample light on a primary image plane 16, also referred to as interface plane 16, of a microscope 17 that comprises a tube lens 18 and objective 20. The re-scan optical system does not per se comprise a microscope. It may for example be configured to make an optical connection with the microscope. In the depicted embodiment, the scan lens 15 creates a vertical line at primary image plane 16. Herein, vertical may be understood to be parallel to the indicated y axis. The distance between the scan lens 15 and light directing element 14 is approximately equal to the focal distance of scan lens 15. In an example, the effective focal distance of scan lens 15 is approximately 75 mm. The scan lens 15 for example has a diameter of 2 inch.

[0087] Each microscope may have a different focal length for the tube lens 18. The distance between the primary image plane 16 and the tube lens is preferably equal to the focal distance of the tube lens.

[0088] In re-scan microscope systems as described herein, similarly for any microscope system, the objective 20 is preferably the NA-limiting component of the total optical system. NA stands for Numerical Aperture.

[0089] The objective 20 is configured to focus the illumination light onto sample 22 herewith causing an illumination light spot 24 on or in the sample 22. The illumination light spot 24 causes sample light 28 from the sample 22. This sample light 28 may be illumination light that is reflected from the sample. However, typically, the illumination light 6 causes photoluminescence, such as fluorescence and/or phosphorescence, in the sample and, typically, the sample light 28 is photo luminescent light, such as fluorescent light and/or phosphorescent light.

[0090] The objective 20 is configured to capture the sample light 28 coming from the sample. On the way back, from the objective 20 up to the dichroic filter 12, the sample light 28 travels along the same path as the illumination light 6 did on its way to the sample. In other words, from objective 20 to dichroic filter 12, the sample light path is substantially identical to the illumination light path.

[0091] In this embodiment, the sample light 28 passes through filter 12. At the same time, the filter reflects any illumination light that has reflected from sample 22. As such, the filter 12 may be understood to separate the illumination light 6 from the sample light 28.

[0092] After having passed through filter 12, the sample light is incident on lens 30. Preferably the distance between lens 30 and the light directing element 14 is approximately equal to the focal length of lens 30. In an example, the focal length of lens 30 is 80 mm.

[0093] The lens 30 focuses the sample light 28, via mirror 32, at the optical slit 34. In an example, the optical slit has a width of approximately 50 micrometers and a length of 2-3 cm. After the sample light 28 has passed optical slit 34, it reflects from mirror 36 and meets lens 38. The optical distance between the optical slit 34 and lens 38 is preferably equal to the focal length of lens 38. Lens 38 may be identical to lens 30.

[0094] After lens 38, the sample light is incident on prism 40 that inverts and/or reverts the sample light. This prism may be a Dove prism as shown in FIG. 1. Alternatively, it can be any other type of prism, such as a Pechan prism, Schmidt-Pechan prism, Abbe-Koenig prism, Porro-Abbe prism, double Porro prism. These other types of prisms can be positioned between lens 38 and rescanning mirror 14, just as the Dove prism 40. The prism 40 is configured to revert and/or invert the sample light, and thus also revert and/or invert the sample light spot 63 in the imaging plane 44, in such manner that the sample light spot is moved in the correct direction.

[0095] After prism 40, the sample light is incident on light directing element 14 again. The optical distance between lens 38 and light directing element 14 is preferably close, e.g. equal, to the focal length of lens 38. In this embodiment, the sample light 28 hits the light directing element 14 at a different angle than the angle at which the illumination light 6 hits the light directing element. When the sample light 28 hits the light directing element 14, the light directing element 14 functions as a re-scanner that scans the sample light 28 over the imaging plane 44 of imaging system 46.

[0096] Thus, the static sample light path in the embodiment of FIG. 1 is provided with [0097] two, and only two, lenses and [0098] two, and only two, mirrors for reflecting the sample light and [0099] said prism.

[0100] The imaging system for example comprises a camera, such as a CCD camera. The imaging plane preferably comprises a plurality of pixels that are arranged in a predefined manner, e.g. in a 2D lattice.

[0101] Before the sample light 28 reaches imaging plane 44, it is incident on a re-scan lens 42 that is configured to focus the sample light onto the imaging plane 44. Preferably, the distance between the light directing element 14 and lens 42 is equal to the focal length of lens 42. In an embodiment lens 42 is identical to lens 15. Lens 42 may have a focal length of 75 mm.

[0102] The optical magnification of the re-scan microscope system may be understood to be determined by the optical magnification provided by the combination of objective 20 and tube lens 18, referred to as Mmicr in De Luca, and by the optical magnification M2 of the detection optical system. In the depicted embodiment, the optical magnification of the detection optical system is determined by scan lens 15, lenses 30 and 38 and re-scan lens 42. In the depicted embodiment, the optical magnification M2 of the detection optical system is given by M2=(f_30*f_42)/(f_115*f_38), wherein f_x denotes the focal length of lens x.

[0103] It should be appreciated that the velocity of an image of the sample light spot in primary image plane 16, v_16, is given by the multiplication of a first velocity, v_1, i.e. the actual velocity of the illumination light spot 24 over and/or through the sample 22, with the optical magnification of the combination of objective 30 and tube lens 28, i.e. v_16=v_1×Mmicr.

[0104] The baseline velocity, v_B, in the depicted embodiment is then given by v_B=v_1×Mmicr×M2.

[0105] In one embodiment, the second velocity, i.e. the velocity with which the sample light spot moves over the imaging plane 44, is approximately twice as high as the baseline velocity, v_2≈2×v_B. Note that the second velocity is equal to the velocity with which the image 60 of the illumination light spot in the imaging plane 44 moves over the imaging plane 44. This can for example be achieved by configuring the detection optical system such that it images an image in the primary image plane 16 onto the imaging plane 44 of the imaging system 46 with an optical magnification of approximately 0.5, M2≈0.5. In this manner, the second velocity is twice as high as the baseline velocity if v_16 and v_2 are equal.

[0106] As described in De Luca, the so called sweep factor M is preferably approximately equal to 2. In the depicted embodiment, the respective amplitudes of the scanning and re-scanning mirror are the same, of course, because the same mirror is used as scanning and re-scanning mirror. Therefore, in the depicted embodiment, the sweep factor M is given by M=(f_38)/(f_30).

[0107] In FIG. 1, the illumination optical system comprises, mirror 8, lens 10, dichroic mirror 12, scanning mirror 14, scan lens 15. The detection optical system in FIG. 1 comprises scan lens 15, scanning mirror 14, which in the context of detection may also be referred to as de-scanning mirror 14, dichroic mirror 12, lens 30, mirror 32, optical slit 34, mirror 36, lens 38, prism 40, scanning mirror 14, which in the context of detection may also be referred to as re-scanning mirror 14 and lens 42.

[0108] The duration of a single scan may be between 25 ms and 10 seconds.

[0109] In the embodiment of FIG. 1, the lenses 30 and 38 cause a focus of the sample light in the static sample light path, in particular at the optical slit 34. Hence, the two lenses 30 and 38 cause an inversion and a reversion of the sample light (and thus a reversion and inversion of the sample light spot at the imaging plane 44). Further, mirror 32 causes a reversion, mirror 36 causes a reversion and prism 40 causes another reversion of the sample light. Hence, in the static sample light path, the sample light is reversed four times and inverted once. In the depicted embodiment we may assume that a reversion flips the sample light spot's orientation in the imaging plane 44 around a vertical axis and that an inversion flips the sample light spot's orientation around a horizontal axis, while the sample light spot is only scanned in the horizontal direction. Therefore, the number of reversions of the sample light in the static sample light path should be even and the number of inversions may be any number. Since the sample light is reversed four times in the static sample light path, this is correct.

[0110] FIG. 2 shows a re-scan optical system according to another embodiment. In this embodiment, the static sample light path is provided with four and only four lenses and two and only two mirrors for reflecting the sample light. In this embodiment, the static sample light path from light directing element 14 back to light directing element 14 namely comprises four lenses 30, 38, 48, 49 and two mirrors 32 and 36. In this particular embodiment, the static sample light path does not comprise a prism.

[0111] It should be appreciated that the two additional lenses 48 and 49 introduce an additional inversion and an additional reversion in the static sample light path and thus also influence the orientation of the sample light spot in the imaging plane. Hence, these lenses cause that the scanning direction of the sample light spot at the imaging plane 44 is correct.

[0112] In particular, the four lenses 30, 38, 48 and 49 cause two foci of the sample light in the static sample light path. Hence, in the depicted embodiment, the four lenses together cause two reversions and two inversions and mirror 32 causes a reversion and mirror 36 causes a reversion. Hence, in this static path, the sample light 28 is reversed four times and inverted twice. In the depicted embodiment, we may assume that a reversion causes a flip of the sample light spot around a vertical line whereas the sample light spot is horizontally scanned. Thus, in light of the above, the number of reversions of the sample light in the static sample light path should be even, which it is, because there are four reversions of the sample light in the static sample light path.

[0113] In this embodiment, the sweep factor M as defined in De Luca is given by M=(f_38*f_49)/(f_30*f_48). This formula shows that the additional two lenses 48 and 49 provide flexibility in how to achieve a desired sweep factor of for example M=2. If for example, lenses 30 and 38 are identical, then a sweep factor of M=2 can be obtained by selecting the focal length of lens 49 twice as large as the focal length of lens 48.

[0114] In FIG. 2, the illumination optical system comprises mirror 8, lens 10, dichroic mirror 12, scanning mirror 14 and scan lens 15. The detection optical system in FIG. 2 comprises the scan lens 15, scanning mirror 14, which in the context of detection may also be referred to as de-scanning mirror 14, dichroic mirror 12, lens 30, mirror 32, optical slit 34, mirror 36, lens 38, lens 48, lens 49, scanning mirror 14, which in the context of detection may also be referred to as re-scanning mirror 14 and re-scan lens 42.

[0115] FIG. 2A illustrates an embodiment wherein the light path is provided with a prism that is configured to invert and/or revert the sample light. In this embodiment, a Schmidt-Pechan prism is used (only schematically shown). As a side note, in this embodiment, two prisms 29a and 29b are used to deflect the sample light. As explained above, the number of reversions in the static light path should be even in this embodiment. The number of inversions in the static light path are irrelevant, since sample light is only scanned in one direction, because the sample light spot is a line-shaped. The lens pair 30 and 38 may be understood to cause one reversion (because they cause a focus at the slit 34), prism 29a causes one reversion, prism 29b causes one reversion, and the Schimdt-Pechan prism causes one reversion as well. Thus the total number of reversions of sample light in the static light path is four, an even number and therefore correct.

[0116] FIG. 2B illustrates an embodiment wherein the light path is provided with a prism that is configured to invert and/or revert the sample light. In this embodiment, an Abbe-Koenig prism 39b is used (only shown schematically). In this embodiment, a convex mirror 29c and a regular mirror 36 are used to deflect the sample light. The number of reversions is four: the convex mirror together with the lens 38 causes two reversions, the mirror 36 causes one reversion, and the Abbe-Koenig prism 39b causes one reversion of the sample light. Of course, any other prims could be used in this embodiment that causes one reversion of the sample light.

[0117] FIG. 2C illustrates an embodiment wherein the light path is provided with a prism that is configured to invert and/or revert the sample light. In this embodiment, an Abbe-Koenig prism 39b is used (only shown schematically). In this embodiment, a convex mirror 29c and a convex mirror 29d are used to deflect the sample light. The number of reversions is four: the convex mirrors 29c and 29d cause three reversions of the sample light, and the Abbe-Koenig prism 39b causes one reversion of the sample light. Of course, any other prims could be used in this embodiment that causes one reversion of the sample light.

[0118] FIG. 2D illustrates an embodiment wherein the static light path is provided with a sample light deflecting prism 35 configured to deflect the sample light without reverting the sample light and/or configured to deflect the sample light without inverting the sample light. In this embodiment, the sample light deflecting prism 35 is a Bauernfeind prism. Such prism deflects the sample light without reverting or inverting the sample light. The total number of reversions of the sample light in the static light path is two: the lens pair 30 and 38 causes one reversion, the prism 35 does not cause a reversion and the mirror 36 causes one reversion.

[0119] FIG. 2E illustrates an embodiment wherein the static light path is provided with a sample light deflecting prism 37 configured to deflect the sample light without reverting the sample light and/or configured to deflect the sample light without inverting the sample light. In this embodiment, the sample light deflecting prism 37 is a pentaprism. Such prism deflects the sample light without reverting or inverting the sample light. The total number of reversions of the sample light in the static light path is two: the lens pair 30 and 38 causes one reversion, the prism 37 does not cause a reversion and the mirror 32 causes one reversion.

[0120] FIG. 2F is the same embodiment as FIG. 2E with the only difference that the lens pair creates a focus of the sample light at mirror 32 and that slit is present on the mirror.

[0121] FIG. 4 schematically illustrates what happens if the sweep factor M, referred to in De Luca, is equal to 2, M=2. As in FIG. 3, the left hand side of the figure shows what happens on the sample 22. The illumination light spot 24 scans over the sample and illuminates first particle 56 and then particle 58. Further, columns D, E and F illustrate what may happen at the imaging plane 44 depending on the direction of movement of the sample light spot (and thus the direction of movement of the illumination light spot image 60), over the imaging plane 44 and depending on the orientation of the sample light spot (and thus on the orientation of the image 60 of the illumination light spot).

[0122] Columns D and F illustrate respective examples where the direction of movement of the illumination light spot image is correct. Column E illustrates an example wherein the direction of movement of the illumination light spot image 60 is incorrect. The obtained image 64E of column E is highly distorted. However results 64D and 64F, which are mirror images of each other, each clearly show two high intensity regions that respectively correspond to particles 56 and 58. This illustrates that a sweep factor higher than 1, preferably a sweep factor of approximately 2 (see De Luca) yields better images in terms of sharpness. Images 64D and 64F obtained with M=2 are better than images 64A and 64C obtained with M=1. Whereas in images 64A and 64C no two separate high intensity regions can be distinguished, which would correspond with the two particles 56 and 58, in images 64D and 64F two high intensity regions can be distinguished.

[0123] FIG. 5 illustrates an embodiment wherein the illumination light spot 24 is a line-shaped illumination light spot. Such an illumination light spot is for example formed by the embodiments shown in FIGS. 1 and 2. An advantage of a line-shaped illumination light spot is that it enables to quickly scan a sample.

[0124] Such line-shaped illumination light spot 24 also has a spatial intensity distribution. Reference numeral 52 indicates the light intensity in the illumination light 24 along line 54.

[0125] Similarly as in FIGS. 3 and 4, the right hand side of FIG. 5 indicates in three columns G, H and I what may happen at the imaging plane 44 of imaging system 46. In particular, the position of sample light 28 is shown at different time instances t1-7. Also indicated is the image 62, in the imaging plane 44, of the high intensity region of the line-shaped illumination light spot 24. Image 62 indicates where in the imaging plane 44 the (high intensity region of) illumination light that has been reflected from sample 22 would be positioned, were it not that reflected illumination light is blocked by a filter, e.g. by dichroic mirror 12. Further shown is the (line-shaped) sample light spot 63. The dashed-dotted lines indicate the boundaries of the sample light spot 63. For clarity, the sample light spot 63 is only shown in column H, in truncated form. It should be appreciated that 63 is a center region of both the illumination light spot image (not indicated in FIG. 5) and the sample light spot 63.

[0126] FIG. 6A illustrates the optical train of the re-scan optical system of FIG. 1 The top part of FIG. 6A shows the optical train of the illumination light and the bottom part of FIG. 6A the optical train of the sample light. Herein, 6a and 6b depict the illumination light as viewed from two orthogonal directions respectively. These views differ because cylindrical lens 10 causes a line focus in 14, and not a point focus, which ultimately results in a line-shaped illumination light spot at the sample

[0127] In this embodiment, plane 14, i.e. the light directing element, is a conjugate plane of the back focal plane 72 of the microscope 17. Further, planes 19, 16, 34 (the aperture slit), are conjugate planes of the focal plane of the microscope 17, i.e. the plane at which the illumination light is focused.

[0128] FIG. 6B illustrates the optical train for off-axis sample light originating from the sample. The optical axis is indicated by 76.

[0129] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0130] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of embodiments of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present invention. The embodiments were chosen and described in order to best explain the principles and some practical applications of the present invention, and to enable others of ordinary skill in the art to understand the present invention for various embodiments with various modifications as are suited to the particular use contemplated.