Abstract
An antenna system comprises an antenna structure configured to operate in at least two cellular communication frequency bands. The antenna structure comprising a ground plane and an antenna element. The ground plane comprises a two-dimensional surface of conductive material arranged within a border that has the shape of an irregular, non-periodic contour-curve, wherein a value Q is given by a ratio of a length of the border contour of the ground plane and a diameter of the smallest circle encompassing the ground plane entirely, wherein the value Q is at least 3. The antenna element is arranged substantially perpendicular to the ground plane, and the ground plane has an opening where the antenna element is arranged. The diameter of the smallest circle encompassing the ground plane entirely is less than one-fifth of a longest free operating wavelength of the antenna element.
Claims
1. An antenna system comprising: an antenna structure configured to operate in at least two cellular communication frequency bands, the antenna structure comprising: a ground plane on a circuit board, wherein the ground plane comprises a two-dimensional surface of conductive material arranged within a border that has the shape of an irregular, non-periodic contour-curve, and wherein a value Q is given by a ratio of a length of the border contour of the ground plane and a diameter of the smallest circle encompassing the ground plane entirely, wherein the value Q is at least 3; and an antenna element arranged substantially perpendicular to the ground plane, the ground plane having at least one opening where the antenna element is arranged, wherein the diameter of the smallest circle encompassing the ground plane entirely is less than one-fifth of a longest free operating wavelength of the antenna element.
2. The antenna system of claim 1, wherein the antenna element is arranged perpendicular to the ground plane.
3. The antenna system of claim 1, wherein the value Q is at least 3.2.
4. The antenna system of claim 3, wherein the value Q is at least 3.5.
5. The antenna system device of claim 1, wherein the diameter of the smallest circle encompassing the ground plane entirely is less than one-seventh of the longest free operating wavelength of the antenna element.
6. The antenna system of claim 1, wherein a border contour of the antenna element is shaped as a contour-curve, and wherein a second value Q is given by a ratio of a length of the border contour of the antenna element and a diameter of the smallest circle encompassing the antenna element entirely, wherein the second value Q is at least 3.
7. The antenna system of claim 6, wherein the second value Q is at least 3.2.
8. An antenna system comprising: an antenna structure configured to operate in at least two cellular communication frequency bands, the antenna structure comprising: a ground plane on a substrate, the ground plane having an opening, wherein the ground plane comprises a two-dimensional surface of conductive material arranged within a border that is shaped as an irregular, non-periodic contour-curve, and wherein a value Q is given by a ratio of a length of a perimeter of the contour-curve and a diameter of the smallest circle encompassing the contour-curve entirely, wherein the value Q is at least 3; and an antenna element, at least a portion of the antenna element extending outside of the ground plane, wherein the diameter of the smallest circle encompassing the contour-curve entirely is smaller than one-fifth of a longest free operating wavelength of the antenna element.
9. The antenna system of claim 8, wherein the value Q is at least 3.2.
10. The antenna system of claim 8, wherein the value Q is at least 3.5.
11. The antenna system of claim 8, wherein the diameter of the smallest circle encompassing the contour-curve entirely is smaller than one-seventh of the longest free operating wavelength of the antenna element.
12. The antenna system of claim 8, wherein a border contour of the antenna element is shaped as a contour-curve, and wherein a second value Q is given by a ratio of a length of the border contour of the antenna element and a diameter of the smallest circle encompassing the antenna element entirely, wherein the second value Q is at least 3.
13. The device of claim 8, wherein the second value Q is at least 3.2.
14. The device of claim 8, wherein the antenna element is arranged substantially perpendicular to the ground plane layer.
15. The antenna system of claim 8, wherein the antenna element extends across at least a portion of the opening.
16. An antenna system comprising: an antenna structure configured to operate in at least two non-overlapping cellular communication frequency bands, the antenna structure comprising: a ground plane on a circuit board, the ground plane having an opening, wherein the ground plane comprises a two-dimensional surface of conductive material arranged within a perimeter that has the shape of an irregular, non-periodic contour-curve, and wherein a value Q is given by a ratio of a length of the perimeter of the ground plane and a diameter of the smallest circle encompassing the ground plane entirely, wherein the value Q is at least 3; and an antenna element arranged within the opening and substantially perpendicular to the ground plane, wherein the diameter of the smallest circle encompassing the ground plane entirely is less than one-fifth of a longest free operating wavelength of the antenna element.
17. The antenna system of claim 16, wherein the value Q is at least 3.2.
18. The antenna system of claim 17, wherein the value Q is at least 3.5.
19. The antenna system of claim 16, wherein a border contour of the antenna element is shaped as a contour-curve, and wherein a second value Q is given by a ratio of a length of the border contour of the antenna element and a diameter of the smallest circle encompassing the antenna element entirely, wherein the second value Q is at least 3.
20. The device of claim 19, wherein the second value Q is at least 3.2.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0117] Embodiments of the invention are shown in the enclosed drawings. Herein shows:
[0118] FIGS. 1A to 1M: schematic views of possible ground plane shapes;
[0119] FIGS. 2A to 2C: 3-dimensional views of possible ground planes;
[0120] FIGS. 3A to 3F: possible formations of end portions;
[0121] FIGS. 4A to 4J: schematic views in order to explain definitions of open loops;
[0122] FIGS. 5A to 5G: schematic views of possible arrangements between the antenna element and the ground plane;
[0123] FIG. 6: a schematic view of antenna structure with a square open-loop ground plane including the antenna component;
[0124] FIG. 7: a schematic view of a light switch with an antenna structure, in particular a view of a wireless light switch, with the example square open-loop ground plane and the antenna component as of FIG. 6;
[0125] FIGS. 8A and 8B: a schematic view of the return loss and the antenna efficiency of an example antenna structure of the present invention, in particular the return loss and efficiency for the a ZigBee-900 monopole antenna with a square open-loop ground plane;
[0126] FIG. 9: another schematic view of an antenna structure;
[0127] FIGS. 10A and 10B: other schematic 3-dimensional views of antenna structures in particular views of a wireless wrist watch with an example antenna and a circular open-loop ground plane;
[0128] FIGS. 11A to 11U: examples of how to calculate the box counting dimension, and examples 1501 through 1514 of space filling curves for ground plane design (FIGS. 11C to 11P);
[0129] FIG. 12: an example of a curve featuring a grid-dimension larger than 1, referred to herein as a grid-dimension curve;
[0130] FIG. 13: the curve of FIG. 12 in the 32 cell grid, wherein the curve crosses all 32 cells and therefore NI=32;
[0131] FIG. 14: the curve of FIG. 12 in a 128 cell grid, wherein the curve crosses all 128 cells and therefore N2=128;
[0132] FIG. 15: the curve of FIG. 12 in a 512 cell grid, wherein the curve crosses at least one point of 509 cells; and
[0133] FIGS. 16A to 16I show examples of how to determine the ratio Q for contour-curves;
DETAILED DESCRIPTION
[0134] In FIGS. 1A to IM, some possible shapes of ground planes 1 are shown. Those ground planes are shaped as open loops, wherein an opening is indicated by reference number 2. The portion that would be required to close the opening 2 is preferably smaller than the portion of the open loop.
[0135] The opening 2 is located between end portions 3 and 4.
[0136] In FIG. 1A, the ground plane 1 is based on a square loop wherein, on one side of the square, the opening 2 is provided. The ground plane may also be stretched in one or the other directions such that the ground plane 1 is rectangular and not square. Furthermore, the corners may be rounded or shaped differently.
[0137] In FIG. 1B, the opening 2 is formed by taking away a side portion of a square or rectangular loop. The open loop is therefore formed by the three remaining sides of a square or of a rectangle.
[0138] In FIG. 1C, a case is shown where only a part of a side of a square or a rectangle is taken away such that a comparatively small opening 2 is formed. This allows for a longer electrically relevant length in comparison to FIG. 1B.
[0139] In FIG. 1D, the opening 2 is provided at the corner of the rectangular or square ground plane 1. Here a portion of the two sides namely, the upper and the left side has been taken away in order to form the opening and the two end portions 3 and 4.
[0140] In FIG. 1E, a ground plane 1 is shown which has a shape of a portion of a circle. The opening 2 is provided between the two end portions 3 and 4. In this example the circle is closed more than half, such that an open loop is given.
[0141] An almost closed circle with a very small opening 2 is shown in FIG. IF.
[0142] Instead of circles, also ellipses may be used as ground planes.
[0143] In FIGS. 1G and 1H, the case is shown where parts of the ground plane 1 overlap in a region 5. Here, the opening 2 is provided between the two overlapping parts which are given by the end portions 3 and 4.
[0144] While in FIGS. 1G and 1H, the overlapping portion 5 is comparatively small, much larger overlapping portions may be given such that at least 10, 15, 20, 30, 40, 50, 60, 70, 80 or 90 percent of the ground plane or the whole plane is overlapping with another part of the ground plane.
[0145] FIG. 11 shows an example where the ground plane is formed in a 3-dimensional way and where there is a crossing section 7 where parts of the ground plane overlap, although this overlap is not at the end portions 3, 4. The two parts of the ground plane that cross at the crossing 7 are not in direct electrical contact.
[0146] FIG. 1J shows another example of a ground plane in 3-dimensions where there is an overlap between the end portions 3 and 4 in the area 5 by the end portion 3 being above the end portion 4.
[0147] In FIG. 1K, an example of a ground plane 1 is shown which is less regular than the previous examples. Here the ground plane is composed of curved and straight segments which also intersect at angles different from 90°. This is an example only showing that the ground plane may have an irregular shape which is composed of different straight segments and/or different curved segments. Different curved segments may be identified by having a curvature in a different direction (left or right curvature). Furthermore, it is shown that it is not necessary that the ground plane has a constant width along its length since the width may vary at different portions of the ground plane.
[0148] FIG. 1L is an example of a ground plane which shows that the ground plane may have more than two end portions 3, 4. As can be seen in FIG. 1L, on the right hand side there is a third end portion. This additional end portion may or may not end at a second opening. Also four, five or more end portions may be provided.
[0149] As is, furthermore, shown in FIG. 1M, along the loop of the open loop, there may be more than one opening 2. In FIG. 1M, an example is shown of a ground plane 1 which has two openings 2 and 2′. It is, however, preferred, that the open loop has no further opening at least in the portion which connects the two end portions 3, 4 of the opening 2.
[0150] The examples shown in FIGS. 1A-1M are non-limiting examples.
[0151] In FIG. 2A, an example of a realization of a ground plane 1 on a circuit board 6 is shown. The ground plane 1 may be, e.g., a copper layer which is printed on the circuit board 6 or etched from a copper layer provided on the circuit board 6.
[0152] The ground plane extends along the edge of the circuit board 6. The ground plane 1, however, may also be provided in such a way that part of the edge of the circuit board 6 is not provided with a portion of the ground plane 1. Instead of copper, other good conductors such as gold, brass, aluminum or the like may be used.
[0153] In FIG. 2B, the circuit board is provided with an opening 24. This opening is in particular useful for other components of the wireless device. E.g., a mechanical connector for the light switch may be located therein or other mechanical or electrical components. More than one opening 24 may be provided. As can be seen in FIG. 2B, the ground plane can be fitted on the area around the opening 24. This leads to a good use of little available space.
[0154] FIG. 2C shows an example of a ground plane 1 which extends in a 3-dimensional fashion. The open loop character of the ground plane can be seen in a cross section which is parallel to the front surface of the ground plane. This cross section has a shape similar to that of FIG. 1A.
[0155] Instead of extending the third dimension in a direction perpendicular to a characteristic cross section, the 3-dimensional geometry of the ground plane may be achieved also by an extension away from the cross section in other angles than 90° such as any angle between 10° and 170°.
[0156] Further, it is not necessary that the extension in the direction away from the characteristic cross section is the same at all portions of the ground plane. Some portions may extend further away from the cross section than others.
[0157] In FIGS. 3A to 3F, possible end formations of the end portions 3, 4 or other end portions of the ground plane 1 are shown. The examples shown in FIGS. 3A to 3F, however, are non-limiting examples.
[0158] In FIG. 3A, the end portion ends perpendicular to the trace while in FIG. 3B the end portions 3, 4 is cut at a tilted direction. In FIG. 3C, the end portion is rounded and in FIG. 3D, the end portion is provided with two peaks. Further, in FIGS. 3E and 3F, it is shown that the width of the ground plane may vary towards the end thereof.
[0159] One end portion 3 may have another shape than another end portion 4 or any of further end portions of the ground plane 1.
[0160] FIGS. 4A to 4J are provided in order to explain some of the concepts in order to define the open loop geometry.
[0161] FIG. 4A shows a ground plane 1 which is an open loop since a circle 8 exists which contacts the ground plane 1 at three distinct points.
[0162] In FIG. 4B, a ground plane 1 with the shape of an open loop is shown since there exists an ellipse 9 which contacts the ground plane at three distinct points.
[0163] The ground plane is on the outside of the circle or ellipse. Instead of three, also it may be possible that there is contact between the circle or the ellipse at four or more points. The said three, four or more points, however, always should be distinct, which means that they are not provided directly next to each other or connected by a continuous line of contact between the circle or the ellipse and the open loop shape.
[0164] In FIG. 4C, a ground plane 1 is shown which extends at the end portion 3 in a direction 10. Following the trace or path of ground plane 1, the lower portion of the ground plane 1 then extends in the direction 11 anti-parallel to the direction 10. The same applies to FIG. 4D.
[0165] In FIG. 4E, an example of a ground plane 1 with an open loop shape is shown. The ground plane 1 has an envelope 12 which is formed by straight lines enclosing the ground shape 1. The straight lines forming the envelope do not have an angle between each other of more than 180 degrees on the inside of the envelope 12. The envelope 12 defines an enclosed area 13 (hatched area) which is enclosed by the envelope 12 but outside of the ground plane 1. The largest diameter of this enclosed area 13 is indicated with the line 14. This line 14 is longer than the shortest possible connection 15, which would be needed in order to close the loop.
[0166] Further, in FIG. 4F a ground plane 1 with an open loop geometry is shown since the largest diameter 16 of the enclosed area is larger than the separation of the two end portions 3 and 4 which is indicated by line 15. Further line 15 is shorter than the length of for example 80% of the largest extension of the ground plane 1.
[0167] In FIG. 4F, e.g., on the right hand side the envelope would consist of infinite small straight lines or in other words the envelope is rounded according to the shape where outer portions thereof would be touched by a point of an envelope line only. The same rules for an envelope in two dimensions may be used to define envelops to three-dimensional objects using planes instead of straight lines.
[0168] In FIG. 4G, an open loop ground plane 1 is shown since there exists a point 21 which has a viewing angle onto the ground plane 1 of larger than 270 degrees. The viewing angle is indicated by reference number 20 and is the angle between the lines 18 and 19 which are the limiting ends of the ground plane 1 on the side of lines 18 and 19 where the ground plane 1 is provided. A similar case is shown in FIG. 4H.
[0169] In case of a shape such as shown in FIGS. 1G and 1H, the viewing angle 20 will be said to be more than 360 degrees. This expresses that there exists a point from which there appears an overlap.
[0170] FIG. 4I shows a case of an open loop ground plane 1 where there exists a portion “a” of the borderline of the ground plane 1, where in a direction (see line “c”) perpendicular to that portion or that point “a,” there is another portion “b” of the ground plane 1. The same is shown in FIG. 4J which also defines a ground plane with an open loop shape.
[0171] In FIG. 5A, the relation between an antenna element 22 and the ground plane 1 is shown. The antenna element is provided in proximity to the end portion 3 of the ground plane 1. As can be seen in FIG. 5A, the extension 23 and 25 plus 26 of the antenna element is smaller than that of the ground plane 1. In particular the width 23 is smaller than the width 24. The width 23, however, may also be equal to the width 24 or be larger than the width 24.
[0172] Furthermore, it can be seen that the antenna element 22 is in partial overlap with the ground plane end portion 3. The antenna element 22 is overlapping at a portion 25 of the antenna element 22 with the ground plane 3 while the portion 26 does not overlap with the ground plane 3.
[0173] The arrangement shown in FIG. 5A may, e.g., be suitable for a monopole antenna element 22 arranged substantially parallel to the ground plane. The size of the portions 25 and 26 may vary. While in FIG. 5A a case is shown where the overlapping portion 25 is smaller than the non-overlapping portion 26, the opposite may be the case or both portions may have equal size. It is also possible that there is no overlap portion 25 or no non-overlap portion 26. The latter means that the antenna element is provided entirely above the ground plane 1. In this case the antenna element 22 may be a patch or micro-strip antenna, or a monopole antenna arranged substantially orthogonal to the ground plane.
[0174] FIGS. 5B and 5C show other possible arrangements of the antenna element 22. The antenna element 22 may be provided at a corner of the end portion 3, or at a side portion of the end portion 3. Also, in this configuration, the antenna element may be moved further away in the direction of the corner in the case of FIG. 5B, or in the direction to the side (in FIG. 5C upwards) such that no overlap is given.
[0175] Further, in FIG. 5D to 5G, the case is shown where the antenna element 22 is provided in the proximity to two end portions 3, 4. In FIG. 5D the antenna element 22 has an overlapping portion 27 with end portion 4 and an overlapping portion 29 with end portion 3. Further, a non-overlapping portion 28 is provided within the opening which is defined between the end portions 3 and 4.
[0176] Here also, the overlapping portions 27 and 29 do not necessarily have to be of equal size, but may be of different size. Furthermore, the overlapping portion 27 and/or 29 may be larger than the non-overlapping portion 28. Also, all three portions 27, 28 and 29 may have the same size.
[0177] As explained for FIG. 5A, the width of the antenna element 22 may be the same size as the width of the end portion 3 and/or 4 or be larger than the respective widths.
[0178] In FIG. 5E, the case is shown where the antenna element 22 is provided in overlap with two corners of the end portion 3 and 4. It may, however, also be possible that the two end portions 3 and 4 are not directly in front of each other such that the antenna element 22 overlaps only with one corner, e.g., of end portion 3 and with an end part of end portion 3, 4 as shown in FIG. 5D.
[0179] Also, the antenna element 22 as explained above may have no overlap with the end portions 3 and 4 (FIG. 5F). Still, however, the antenna element 22 is provided in close proximity to the end portion 3 and 4. The distance d between the end portion 3 and/or 4 and the antenna element 22 should preferably not be larger than, e.g., twice the size of the antenna element 22.
[0180] In FIG. 5G, a cross section of FIG. 5D is shown. On a circuit substrate 6, the ground plane end portions 3 and 4 are provided as a thin conducting layer. The antenna element is affixed to the circuit substrate by contact points 23a and 23b. The antenna is electrically directly connected to the ground plane end portion 3 through the contact point 23a. The solder point 23b may be used to hold the antenna element 22. This solder point may also be used to feed the antenna element 22. The antenna element 22 may be provided at a certain separation s between the antenna element 22 and the ground plane end portion 3 and/or 4. The separation is preferably small or even zero for flat antenna structures.
[0181] Although the antenna element 22 is provided above or below the end portion 3, 4 of the ground plane 1, the antenna element is said to be within the opening since in the view of FIG. 5D it is within the opening.
[0182] FIG. 6 illustrates an example of an open-loop or semi-loop ground plane. The ground plane 1 is a conductive material forming an open-loop structure. The ground plane 1 may, for example, be fabricated on or otherwise attached to a dielectric substrate material, such as a printed circuit board. For instance, in the example of FIG. 6, the opening 2 between two end portions 3, 4 of the broken loop 1 is located in the upper left-hand corner. More particularly, FIG. 6 illustrates a square open-loop ground plane 1 with an opening 2 formed between two end portions 3, 4 at the upper left-hand corner of the square. It should be understood, however, that the loop may be shaped other than square.
[0183] Also illustrated in FIG. 6 is an antenna component 22 located within the opening 2 formed between the two end portions 3, 4 of the open-loop ground plane 1 and overlapping one of the end portions 3 of the ground plane 1. FIG. 6 includes a close-up view to further illustrate the position of the antenna component 22 with respect to the open-loop ground plane 1. The position of the antenna overlapping an end portion of the ground plane 1 and within the opening 2 defined by the open-loop structure of the ground plane 1 may enhance the antenna performance (e.g., antenna bandwidth and efficiency). The improved antenna performance afforded by its position with respect to the open-loop ground plane may be particularly apparent in the case of a monopole antenna because of the feeding scheme of a typical monopole antenna.
[0184] The three corners of the substrate are not covered with a portion of the ground plane 1 such that it will be possible to provide fixing means such as drilling holes in those corners.
[0185] The opening 2 is provided in the left side of the square of the ground portion 1. As can be seen in FIG. 6, the width of the ground plane 1 varies. The width in the upper portion is smaller than the width in the left-hand portion.
[0186] The antenna element 22 is provided in partial overlap with the top portion of ground plane 1.
[0187] This can be seen in the enlarged view which shows in a 3-dimensional way that in the arrangement the antenna element 22 is provided on top of the ground plane 1.
[0188] In case of FIGS. 5A to 5F, the antenna element 22 may be provided a little bit above (see FIG. 5G) or below the end portion 3 and/or 4. The separation in the direction perpendicular to the plane of the drawings in FIG. 5A to FIG. 5F between the antenna element 22 and the end portion 3 and/or 4 shall usually not be larger than, e.g., twice the thickness of the antenna element 22 or twice the largest dimension of the antenna element 22 (e.g. in the drawing plane) or of the ground plane or a fraction of one of those.
[0189] As can be seen in FIG. 6, in the enlarged view the separation between the antenna element 22 and the ground plane 1 is less than the thickness of the antenna element 22.
[0190] FIG. 7 shows an example of the light switch which is provided with an antenna structure as shown in FIG. 6. The light switch is a square wireless light switch having a square open-loop ground plane. This is a wall mounted RF transmitter with dimmer and on/off switch for home automation.
[0191] FIGS. 8A and 8B show two graphs illustrating an example performance of an antenna component positioned between the end portions of an open-loop ground plane, as shown in FIG. 6. For the purposes of this example, the antenna component is a monopole antenna tuned to resonate at the 900 MHz ZigBee band (902-928 MHz). The upper graph illustrates the return loss of the example antenna structure, and the lower graph illustrates the antenna efficiency.
[0192] It should be understood, however, that an open-loop ground plane with an antenna component, as described herein, may also be used for other cellular standards and communication systems, such as Bluetooth, UltraWideBand (UWB), WiFi (IEEE802.11a,b,g), WiMAX (IEEE802.16), PMG, digital radio and television devices (DAB, DBTV), satellite systems such as GPS, Galileo, SDARS, GSM900, GSM1800, PCS1900, Korean PCS (KPCS), CDMA, WCDMA, UMTS, 3G, GSM850, and/or other applications.
[0193] Another configuration of the antenna element 22 is shown in FIG. 9. Here, the antenna element 22 overlaps with end portions 3 and 4 which form the opening 2.
[0194] With this arrangement, it is easily possible, e.g., to couple the antenna by ohmic contact or electromagnetic coupling at one end of the ground plane, while the antenna is also excited at the other end of the ground plane. The antenna may therefore be operated or working as a loop antenna.
[0195] Another example of the antenna structure is shown in FIGS. 10A and 10B. These figures show a wrist watch having a ring shape open-loop ground plane located in the band portion of the wrist watch. The antenna element 22 is provided in small overlap with the end portion 4. The antenna element 22 is essentially flat, and is provided essentially parallel to the end of the end portion 4. While the end portion 4 is shown flat it may also be curved in the same or a different way as the remainder of that ground plane. In FIG. 10B, the case is shown where the ground plane 1 is closed more than 360 degrees such that there is an overlap between the end portions 3 and 4. However, there is no direct electrical contact between the end portions 3 and 4 such that the ground plane still is an open loop. The overlap has a width which is less than the width of the end portion 4.
[0196] The antenna element 22 is provided in close proximity to the overlap.
[0197] As is shown in FIG. 10B, the end portion 3 may have a smaller width than the remainder or other portions of the ground plane 1. Thereby, it is possible, e.g., to provide the opening for the antenna element 22. The antenna element 22, in this case, is not covered in a major portion (at least 50%) at the top or at the bottom thereof by the ground plane 1 such that the antenna element may properly radiate electromagnetic waves.
[0198] The arrangement as shown in FIGS. 10A and 10B is, in particular, suitable to a monopole antenna element 22.
[0199] Further, the arrangement shown in FIGS. 10A and 10B is, in particular, suitable for any device which may be provided at the wrist or at the ankle of a user. The hand or a feet may be passed through the ground plane 1.
[0200] The ground plane 1 may, e.g., be integrated into the band portion of a wrist watch or any other wrist sensor.
[0201] The ground plane 1 here may be integrated into textile or other flexible material. It is therefore advantageous that the ground plane 1 is flexible.
[0202] While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.
