Patent Publication Number: US-7215429-B2

Title: Vertical displacement device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a Divisional Patent Application of patent application Ser. No. 10/835,344, filed Apr. 29, 2004 now U.S. Pat. No. 6,940,630, which claims the benefit of U.S. Provisional Application No. 60/467,225, filed May 1, 2003. 

   FIELD OF THE INVENTION 
   This invention is directed generally to vertical displacement devices, and more particularly to microelectromechanical vertical displacement devices and use of these devices in biomedical applications. 
   BACKGROUND 
   Microelectromechanical system (MEMS) devices are devices that operate on a very small scale, typically in a range of tens of microns to a few millimeters. MEMS devices mostly are fabricated using integrated circuits (IC) technology. Production of MEMs devices, likewise, enables one to realize relatively low manufacturing costs because of the batch fabrication techniques and the small size of the devices. In some applications MEMS devices are imperceptible to the unaided human eye. MEMS devices include many different devices used for a variety of purposes. One device in particular is a movable micromirror having the capability of rotating about a pivot point or an axis. One end of the micromirror is coupled to an anchor, which may be a substrate, using a bimorph actuator that may be activated by sending an electrical current to a heating element in the actuator. The current causes the temperature of the actuator in the micromirror to increase, which in turn causes the actuator to bend. While the micromirror may be rotated about a pivot point, the micromirror may not be translated to another position. Instead, the micromirror is fixedly attached to the anchor. 
   Numerous actuation devices have been used with MEMS devices to achieve vertical displacement. For instance, displacements of between about 7.5 μm and about 50 μm have been achieved through the use of electrostatic vertical comb drives. In addition, electrostatic and electromagnetic actuators have generated displacements of about 6 μm and about 20 μm. However, the displacements of most displacement devices have been limited to these ranges. Thus, a need exists for larger amounts of vertical displacement within MEMS devices. 
   Many applications exist in which a micromirror having the ability to be moved relative to a Z-axis could be used rather than simply pivoting about an anchor. For instance, axial scanning of an optical coherence tomography (OCT) imaging system requires translational mirrors capable of moving out-of-plane along a z-axis. OCT is an imaging technology that can be used to obtain cross-sectional imaging of biological tissues for noninvasive or minimally invasive medical diagnosis. OCT is based on low coherence interferometery and fiber optic technology, and has very high spatial resolution (&lt;10 μm). OCT has been successfully used to detect various cancers. 
   Another application that could benefit from a micromirror or microlens movable along a Z-axis is optical coherence microscopy (OCM). OCM has been used to obtain cross-sectional information of biological or biomedical tissues, which is the same as OCT, and is based on low coherence interferometry. However, OCM differs from OCT in that OCM produces higher lateral resolution because it uses a sharply focused laser beam, which in some applications may be about 1 μm. In contrast, OCT requires 1–3 mm focus depth, which limits the laser spot size to about 10 μm. Currently, axial scanning of a reference mirror is accomplished using Plumbum (lead) Zirconate Titanate (PZT) actuators and relies on motorized stages to perform z-scanning and x-y scanning. As a result, the current OCM devices are bulky and slow. Thus, a need exists for a more compact and more time efficient device for enabling z-scanning and x-y scanning. 
   SUMMARY OF THE INVENTION 
   This invention relates to a vertical displacement device capable of raising one or more vertically displaceable platforms relative to a base. In particular, the vertical displacement device may be capable of raising a vertically displaceable platform so that the vertically displaceable platform remains generally parallel to a base. In at least one embodiment, the vertical displacement device may be a MEMS device. The vertically displaceable platform may be, but is not limited to, a microlens, a micromirror, or other device. 
   The vertical displacement device may be formed from one or more frames rotatably coupled to an anchor. In at least one embodiment, a first member of the frame is coupled to an anchor with one or more piston-motion thermal actuators. The thermal actuator may be configured so that when a current is applied to the actuator, the actuator bends. Thus, when a current is applied to the thermal actuator coupling the frame to the anchor, the thermal actuator causes the frame to rotate about the anchor. A vertically displaceable platform may be coupled to a second member of the frame that is generally opposite to the first member using one or more thermal actuators. The vertically displaceable platform may be configured to fit into a cavity formed by the frame. 
   In another embodiment, which is capable of performing 2-D scanning, a second frame may be coupled to the second side of the frame using one or more thermal actuators and may be sized to fit in the cavity of the frame. A third frame may be coupled to any side of the second frame using a thermal actuator. A vertically displaceable platform may be coupled to the third frame on a side of the third frame that is generally opposite to a side of the frame to which the second frame is coupled. This embodiment enables 2-D scanning to be performed using the vertical displacement device. 
   The vertical displacement device may raise a vertically displaceable platform by sending a current to the thermal actuators. The current causes the temperature of thermal actuators to increase and bend. The bending action causes the frame to rotate about the anchor in a first direction and causes the vertically displaceable platform to rotate about the second member of the frame in a second direction that is generally opposite to the first direction when viewed from the same perspective. The vertical displacement device may operate in modes where the tilt of the vertical displacement device relative to the frame is equal to the tilt of the frame relative to a base, which equates to the vertically displaceable platform being moved along the z-axis and the frame to be placed generally orthogonal to the Z-axis. The vertical displacement device may also operate in modes where the tilt of the vertical displacement device and the tilt of the frame are not equal, which results in the vertically displaceable platform being tilted relative to the Z-axis and not positioned in a plane orthogonal to the Z-axis. 
   The large vertical displacement (˜1 mm) may be achieved because the platform is located at the tip of a rotating arm. Thus, even small changes in an angle may result in a large tip displacement. The rotational motion may be converted to translational vertical motion by using a counter-tilt frame. The counter-tilt frame also enables the vertically displaceable platform to be raised from a surface without tilting the platform. The large vertical displacement achievable by the platform is large relative to microelectromechanical systems. 
   The vertical displacement device may be used in numerous embodiments such as, but not limited to, wave-front shaping in adaptive optics, biomedical imaging, interferometry systems, laser beam scanning, and spatial light modulators. For example, the vertical displacement device may be used as a part of a MEMS based OCT system. In at least one embodiment, the MEMS based OCT system may be used for early lung cancer detection. In another embodiment, the vertical displacement device may be used as a part of a MEMS based OCM system. These and other embodiments are described in more detail below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention. 
       FIG. 1  is a top view of an exemplary vertical displacement device according to one or more aspects of this invention. 
       FIG. 2  is a cross-sectional view of the vertical displacement device shown in  FIG. 1 . 
       FIG. 3A  is a cross-sectional view of an exemplary vertical displacement device according to one or more aspects of this invention and is a basic structure of a 1D mirror. 
       FIG. 3B  is a top view of the vertical displacement device shown in  FIG. 3A . 
       FIG. 4A  is a perspective view of a vertical displacement device according to aspects of this invention. 
       FIG. 4B  is a top view of an alternative thermal actuator usable with this invention. 
       FIG. 4C  is a top view of an alternative thermal actuator usable with this invention. 
       FIG. 5A–D  illustrate a four step process of forming a vertical displacement device of the instant invention. 
       FIG. 6  is a side view of a vertical displacement device in an unactuated condition. 
       FIG. 7  is a top view of a vertical displacement device having one or more extension arms. 
       FIG. 8  is a side view of the vertical displacement device shown in  FIG. 7 . 
       FIG. 9  is a top view of a vertical displacement device including an attached microlens. 
       FIG. 10  is a side view of the vertical displacement device shown in  FIG. 9 . 
       FIG. 11  is a top view of a vertical displacement device including an integrated microlens. 
       FIG. 12  is a side view of the vertical displacement device shown in  FIG. 11 . 
       FIG. 13  is a top view of a vertical displacement device including a polymer droplet functioning as a microlens. 
       FIG. 14  is a side view of the vertical displacement device shown in  FIG. 13 . 
       FIG. 15  is a top view of an alternative embodiment of a vertical displacement device with another vertical actuator cascaded orthogonally to extend the vertical displacement range and perform two-dimensional (2D) scanning. 
       FIG. 16  is a schematic diagram of an OCT system including a vertical displacement device for axial scanning and a vertical displacement device for transverse scanning. 
       FIG. 17  is a schematic diagram displaying a vertical displacement device enabled miniature OCT system installed in a working channel of a bronchoscope. 
       FIG. 18  is a schematic diagram of an OCM system including a vertical displacement device for axial scanning and another vertical displacement device with a microlens for focal point tuning and transverse image scanning. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIGS. 1–18 , this invention is directed to a vertical displacement device  10 , which may be referred to as a large vertical displacement device (LVD), capable of raising one or more vertically displaceable platforms  12  along a Z-axis relative to a base  14 . In particular, vertical displacement device  10  may be capable of raising vertically displaceable platform  12  along a Z-axis so that vertically displaceable platform  12  remains generally parallel to base  14 . Generally, the vertical displacement device  10  lies in a single plane while in an unactuated position. The vertical displacement device  10  may be moved along the Z-axis by actuating at least two thermal actuators using an electrical current. In at least one embodiment, vertical displacement device  10  is a microelectromechanical (MEMS) device that is capable of functioning on a small scale. Vertically displaceable platform  12  may be, but is not limited to, a microlens, a micromirror, a micro-grating, or other device. 
   Vertical displacement device  10 , as shown in  FIGS. 1 and 2 , may be formed from one or more frames  16 . In at least one embodiment, frame  16  may be formed in a generally rectangular shape forming a cavity  18 , which may be referred to as a trench, for containing vertically displaceable platform  12 . However, frame  16  is not limited to having this shape. Rather, frame  16  may have any shape enabling vertically displaceable platform  12  to move relative to base  14 . In the embodiment shown in  FIG. 1 , cavity  18  has a generally square shape. Frame  16  may be formed from a first member  20  and an opposing second member  22 . In at least one embodiment, frame  16  may be substantially square and may be formed from first member  20  and opposing member  22  coupled together by a third member  24  and a fourth member  26 . 
   Frame  16  may be configured to rotate about an anchor  28 . Anchor  28  may or may not be an integral part of base  14 . Frame  16  may be coupled to anchor  28  using one or more thermal actuators  30 . In at least one embodiment, thermal actuator  30  may be, but is not limited to, a bimorph actuator. Thermal actuator  30  may be a thin-film structure and may undergo significant bending when heated, as shown in  FIGS. 3A–5D . 
   Thermal actuator  30  may be formed from two or more materials having different thermal expansion coefficients. A first material  32  may form a top surface  34  of thermal actuator  30 , and a second material  36  may form a bottom surface  38 . In at least one embodiment, first material  32  may be a metal, such as, but not limited to, aluminum, and second material  36  may be a dielectric, such as, but not limited to, silicon dioxide, an oxide, or other material. In at least one embodiment, the second material  36  may be formed into a mesh, as shown in  FIG. 4A , having generally longitudinal and latitudinal members,  35  and  37  respectively, and the first material  32  may be coupled generally to the longitudinal members  35  of the second material  36 . In other embodiments, the first material  32  may be coupled generally to the latitudinal members  37 , as shown in  FIG. 4B . In yet another embodiment, the second material  36  may include only longitudinal members  35 , and the first material  32  may be coupled to the longitudinal members  35  of the second material  36 , as shown in  FIG. 4C . 
   As shown in  FIG. 2 , both thermal actuators  30  and  31  curl. Thus, the frame  16  coupled to thermal actuator  30  forms an initial tilt angle θ with respect to base  14 , and the platform  12  coupled to thermal actuator  31  forms the same initial tilt angle θ with respect to frame  16 . As a result, vertically displaceable platform  12  is parallel to base  14 . 
   As the thermal actuator  30 ,  31  is heated, a first end of the thermal actuator  30  or  31  bends up or down. If the second material  36  expands at a greater rate than the first material  32 , then the thermal actuator  30  or  31  bends about the first material  32 , or upwards. If the first material  36  expands at a greater rate than the second material  36 , then the thermal actuator  30  or  31  bends about the second material  36 , or downwards. In one embodiment, the first material  32  expands at a greater rate than the second material  36 . In other words, the thermal expansion coefficient of the first material  32  is greater than that of the second material  36 ). When heated simultaneously, thermal actuators  30  and  31  both bend downwards and thus, platform  12  stays parallel to base  14 . Therefore, large vertical displacement (LVD) is achieved by converting the large tip displacement of a rotating frame  16  into vertical displacement of the platform  12 . The vertical displacement may be determined by multiplying the length L of frame  16  by 2 sin θ. For example, where L equals 2 mm, and the initial tilt angle θ equals 30°, the vertical displacement is about 1 mm. The initial tilt angle θ is due to the residual stress and thermal expansion coefficient difference of the first material  32  and second material  36 . 
   Thermal actuator  30  may also include a third material  40  encapsulated in second material  36 . Third material  40  may be, but is not limited to, polysilicon. Third material  40  may act as a heating element in thermal actuator  30 . In at least one embodiment, third material  40  may have a resistance of about 2.4 kΩ and may carry a maximum current of about 18 mA before thermal damage occurs. 
   Vertically displaceable platform  12  may be coupled to frame  16  so that vertical displacement device  12  can rotate relative to frame  16 . In at least one embodiment, vertically displaceable platform  12  may be coupled to second member  22  of frame  16  with a thermal actuator  31 . In this embodiment, vertically displaceable platform  12  is coupled to second member  22  so that vertically displaceable platform  12  is positioned in cavity  18  while vertical displacement device  10  is in an unactuated position, as shown in  FIG. 6 . 
   In one embodiment, as shown in  FIGS. 7 and 8 , vertical displacement device  10  may include one or more extension arms  42  for supporting vertically displaceable platform  12 . Extension arm  42  may be coupled to frame  16  using one or more thermal actuators  31 . In the embodiment shown in  FIGS. 7 and 8 , extension arm  42  may be sized and configured to fit in cavity  18 ; however, extension arm  42  may extend outside cavity  18  for at least some applications. In addition,  FIGS. 7 and 8  depict use of two extension arms  42 ; however, vertical displacement device  10  is not limited to this number of extension arms  42  but may have one or more extension arms  42 . Extension arms  42  enable the displacement of vertically displaceable platform  12  to be increased without having to increase the dimensions of vertically displaceable platform  12 . The extension arm  42  enables the vertically displaceable platform  12  to be moved a substantial distance relative to the size of the device  10  and conventional systems. 
   As previously mentioned, vertically displaceable platform  12  may include a micromirror  44 , as shown in  FIG. 1 . Micromirror  44  and all other LVD devices discussed may be fabricated using a deep reactive-ion-etch (DRIE) complementary metal oxide semiconductor (CMOS)-MEMS process, as shown in  FIGS. 5A–5D , which is described in detail at “Post—CMOS Processing for High-Aspect-Ratio Integrated Silicon Microstructures” by H. Xie, L. Erdmann, X. Zhu, K. Gabriel, and G. Fedder in the  Journal of Microelectromechanical Systems,  11 (2002) 93–101. The process flow, as shown in  FIGS. 5A–5D , starts with CMOS chips from a foundry CMOS process and includes a poly-Si layer  100  forming a SCS membrane, a metal-1 layer  102 , a metal-2 layer  104 , and a metal-3 layer  106 . The CMOS starting chips or wafers can be made from standard thin-film deposition and lithography processes. 
   The backside silicon DRIE step, as shown in  FIG. 5A , leaves a 10 μm to 100 μm-thick structural single-crystal silicon (SCS) membrane. The SCS membrane keeps the platform  12  flat. This step controls the thickness of the microstructure and forms a cavity that allows the microstructure to move freely. The depth of the cavity may be determined by the thickness of the CMOS chips. Next, an anisotropic dielectric etch is performed from the front side, as shown in  FIG. 5B , followed by DRIE of silicon, as shown in  FIG. 5C . There exists an oxide layer  108  that may be about 5 μm thick and a silicon substrate  110  that may be about 40 μm thick, as shown in  FIGS. 5B and 5C . At the end of this step, a thick SCS layer remains underneath the CMOS layer, resulting in a flat released microstructure. Finally, a brief isotropic silicon etch is performed, as shown in  FIG. 5D . Any beam produced with a half-width less than the silicon undercut may not have a SCS layer underneath the beam. This type of beam may be used to form electrically isolated SCS islands, purposefully curled-up structures or z-compliant springs. 
   This post-CMOS micromachining may require only four dry etch steps and is compatible with foundry CMOS electronics. This process does not produce a substrate or thin-film layer directly above or below the micromirror  44  structure. Thus, there are no mechanical limits to the actuation range. Micromirror  44  may be a SCS backing layer that may be about 40 μm thick and provide good flatness across the surface of micromirror  44 . 
   In other embodiments, vertically displaceable platform  12  may include a microlens  46 , as shown in  FIGS. 9–12 . Microlens  46  may be fabricated from a membrane, such as, but not limited to, a SCS, which is generally transparent to infrared light. Thus, the SCS microlens may be widely used in fiber-optic communications in which infrared lasers, such as, but not limited to, 1.3 μm and 1.55 μm lasers, are the light sources. Microlens  46  may be an attached microlens, as shown in  FIGS. 9 and 10 , an integrated microlens, as shown in  FIGS. 11 and 12 , or other devices. 
   In yet another embodiment, vertically displaceable platform  12  may include a tunable microlens that may be fabricated by injecting one or more droplets of a polymer material, such as but not limited to, photoresist, onto the hollow platform, as shown in  FIGS. 13 and 14 . While vertically displaceable platform  12  has been described as including a micromirror, a microlens, and a tunable micro-grating, the vertically displaceable platform  12  is not limited to containing only these items. Rather, vertically displaceable platform  12  may include other appropriate items as well. 
   In an alternative embodiment, vertical displacement device  10 , as shown in  FIG. 15 , may include a first frame  50 , a second frame  52 , and a third frame  54 , and may be referred to as a 2-D scanning device. First frame  50  may be coupled to an anchor  56  using one or more thermal actuators  58 . Second frame  52  may be coupled to first frame  52  at a side opposite to thermal actuator  58  using one or more thermal actuators  60 . This configuration allows second frame  52  to be moved along the Z-axis relative to base  14 . Third frame  54  may be coupled to second frame  52  using one or more thermal actuators  62  capable of rotating third frame  54  about second frame  52 . Third frame  54  may be coupled to any side of second frame  52 . In one embodiment, as shown in  FIG. 15 , third frame  54  may be coupled to a side of second frame  52  that is generally orthogonal to a side to which thermal actuator  60  is coupled. A vertically displaceable platform  12  may be coupled to third frame  54  using one or more thermal actuators  64 . Vertically displaceable platform  12  may be coupled to third frame  54  on a side of third frame  54  opposite to a side to which second frame  52  is attached to third frame  54 . Thus, this embodiment has four thermal actuators,  58 ,  60 ,  62 , and  64 . Vertically displaceable platform  12  may be moved along the Z-axis substantially parallel to base  14 . Vertically displaceable platform  12  may also be positioned at other positions relative to base  14 . In at least one embodiment, third frame  54  may be sized to fit inside second frame  52 , and second frame  52  may be sized to fit inside first frame  50 . 
   Vertical displacement device  10  operates in at least five modes. In a first mode, thermal actuator  30  may be heated, which causes frame  16  to rotate in a first direction relative to base  14  while thermal actuator  31  remains unactuated. In a second mode, thermal actuator  31  may be heated, which causes vertically displaceable platform  12  to rotate in a second direction that is generally opposite to the first direction about second member  22  of frame  16  while thermal actuator  30  remains unactuated. 
   In a third mode, vertical displacement device  10  may move vertically displaceable platform  12  substantially along the Z-axis, as shown in  FIG. 2 . Vertical displacement device  10 , as shown in  FIG. 6 , lies generally in a single plane while vertical displacement device  10  is in an unactuated position. Vertically displaceable platform  12  may be moved along a Z-axis relative to base  14  by heating thermal actuators  30  and  31  using an electrical current. Heating thermal actuator  30  may cause second material  36  to expand greater than first material  32 . As a result, frame  16  may rotate about anchor  28 . As frame  16  is rotated about anchor  28 , thermal actuator  31  may be heated, which may cause vertically displaceable platform  12  to rotate about frame  16 . In one example, thermal actuator  30  may be rotated in a first direction, and thermal actuator  31  may be rotated in a second direction that is generally opposite to the first direction when viewed from the same perspective to move vertically displaceable platform  12  above base  14 . Thus, the tilt of frame  16  may be substantially equal to the tilt of vertically displaceable platform  12 . Movement of vertically displaceable platform  12  in this manner enables vertically displaceable platform  12  to remain substantially parallel to base  14  though displaced along the z-axis. 
   The height at which vertically displaceable platform  12  may be raised above base  14  may be calculated as follows. A height H, as shown in  FIG. 2 , is equal to L multiplied by 2 sin θ, where L represents a length L of frame  16  and θ is the tilt angle of frame  16 . For example, if L equals 1.5 millimeters (mm) and θ is about 10 degrees, then vertically displaceable platform  12  is suspended about 260 μm above base  14 . In other words, if thermal actuators  30  and  31  both rotate 10 degrees, vertically displaceable platform  12  will travel vertically along the Z-axis 260 μm. In yet another example, if L equals 2 mm and θ equals 30 degrees, vertically displaceable platform  12  may be moved about 1.0 mm along the Z axis. The height through which vertically displaceable platform  12  may move relative to base  14  may vary depending on the length L of frame  16  and angle θ. 
   In a fourth mode, thermal actuators  31  need not move vertically displaceable platform  12  at an angle θ 1  relative to frame  16  that is equal to an angle θ between frame  16  and base  14 . Instead, angle θ 1  may have values other than the values for angle θ. In other words, the tilt of vertically displaceable platform  12  relative to frame  16  may be different than the tilt of frame  16  relative to base  14 . This allows vertically displaceable platform to be moved vertically along a Z-axis relative to base  14 , yet be positioned in planes not parallel to base  14 . 
   In a fifth mode, vertical displacement device  10 , as shown in  FIG. 15 , may be used to perform 2-D scanning. A current may be applied to thermal actuators  58  and  60  to move vertically displaceable platform  12  along the Z-axis in a position that is substantially parallel to base  14  and orthogonal to the Z-axis. Thermal actuators  62  and  64  may be actuated when vertically displaceable platform  12  is at various positions along the Z-axis to perform 2-D scanning at each position of the vertically displaceable platform  12  along the Z-axis. This enables 2-D laser scanning to be achieved. 
   In one embodiment, the thermal actuators  30 ,  31 ,  58 ,  60 ,  62 , or  64  in any of the embodiments shown in the figures may be formed from different materials enabling the thermal actuators to bend at different amounts while receiving the same amount of electrical current. Thus, the thermal actuators  30 ,  31 ,  58 ,  60 ,  62 , or  64  may be used in many different applications where different amounts of movement are necessary. 
   Vertical displacement device  10  may be used in a variety of situations. For example, vertical displacement device  10  may be used with optical coherence tomography (OCT), as shown in  FIG. 16 . Vertical displacement device  10  may be included as a part of a MEMS based OCT system  66 . MEMS based OCT system  66  may include one or more broadband sources  68  coupled to a beam splitter  70 . MEMS based OCT system  66  may include a 1-D vertically scanning micromirror  72  for axial reference scanning coupled to beam splitter  70 , and a 1-D or 2-D micromirror  74 , otherwise referred to as a bidirectional rotating micromirror for transverse sample scanning coupled to the beam splitter  70 . A photodetector  77  may used to detect interference light signals from reference MEMS micromirror  72  and sample scanning micromirror  74 . Another application of the MEMS based OCT system is shown in  FIG. 17 , where an MEMS-OCT imaging probe  66  can be incorporated in bronchoscope  76  to be used for early lung cancer detection. 
   In another example, as shown in  FIG. 18 , vertical displacement device  10  may be used in a MEMS based optical coherence microscopy (OCM) system  78 . MEMS based OCM system  78  may include one or more broadband sources  80  coupled to a beam splitter  82 . MEMS based OCM system  78  may include a reference scanning micromirror  74  coupled to beam splitter  82 , and a sample scanning microlens  86  coupled to beam splitter  82 . A photodetector  88  may be used to capture an optical signal. MEMS based OCM system  78  using reference MEMS micromirror  84  and scanning MEMS microlens  86  is significantly smaller than conventional systems and has increased imaging speed, as shown in  FIG. 18 . Reference MEMS micromirror  84  and scanning MEMS microlens  86  enable MEMS based OCM system  78  to be portable for field use and to form compact OCM probes for in vivo, minimally invasive 3-D imaging of internal organs. 
   The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.