Abstract:
A portable wireless through-the-earth bi-directional communication system for sending and receiving text data using ultra-low-frequency electric current and the earth as the conductive media. A surface controller which executes application software which controls the communication functions of the system. A surface receiver and surface transmitter are connected to sets of electrodes which provide the electric current, and are in communication with the surface controller. Text data are encoded into data packets, modulated onto ultra-low-frequency electric carrier waves, and transmitted through the earth by the surface electrodes to a subsurface transceiver. The subsurface transceiver demodulates, converts and displays incoming signals into text messages. The subsurface transceiver has a user interface to allow subsurface users to submit text data to the surface receiver. The transceiver converts the text data into analog data packets, modulates the packets onto ultra-low-frequency carrier waves, and transmits the signal to the surface receiver.

Description:
This is an original utility patent application claiming priority to U.S. Provisional Patent Application No. 61/387,875, filed Sep. 29, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to ultra-low-frequency communication systems. More particularly, the present invention relates to a portable wireless through-the-earth bi-directional communication system for providing wireless communication between people physically separated by the earth or other material that prevents the ability to communicate by traditional open-air communication systems. The present invention eliminates the need for current loop antennae, magnetic flux coupling, or leaky feeder cabling to communicate through the earth. The present system employs ultra-low-frequency electric fields to penetrate the earth thereby transmit longer distances, and establishes a wireless bi-directional communication system used for sending and receiving text messages or predefined data encoded beacons. 
     2. Description of the Related Art 
     There exists in the prior art through-the-earth communication systems which employ electromagnetic waves and loop antennas for transmitting and receiving audio and digital data between the surface and subsurface components. However, such systems are characterized as having limited through-the-earth range. Moreover, such systems require coupling of the magnetic field between the antennas. Proper alignment of the surface and subsurface loop antennas is required to achieve maximum transmission distance. To increase transmission distance in these systems, larger loop antennas may be employed, such as wrapping a wire around a coal pillar inside a coal mine. 
     However, these modifications are impractical and perhaps impossible in underground emergencies such as cave-ins or explosions. Increasing the transmission distance by increasing current flow through the loop is usually not available because energy transmission must be limited in most underground environments for safety purposes, as a spark ignition of explosive gases is possible. Thus, these systems result in providing much shorter transmission distances through the earth than is desirable to communicate with trapped personnel to aid in their rescue. 
     There also exists in the prior art wireless communication systems in mines using “leaky feeders” as radiating transmission lines. However, these systems require radiating transmission lines to be in place within the mines or underground areas, and to survive explosions and/or cave-ins in order to work, which is often not the case in many underground emergency situations. Thus, the leaky feeder systems are not reliable to be operational in underground emergency situations. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is different than the prior art. The present invention provides a wireless through-the-earth communication system without the need for current loop antennae or leaky feeder cabling to transmit through the earth. The present invention allows for bi-directional communication between individuals on the earth&#39;s surface and individuals underground, even where all electrical infrastructures are obliterated or non-functional, and limited space is available underground. 
     The communication system of the present invention uses ultra-low electric frequencies to communicate through the earth. The present invention comprises a surface controller in wireless or serial communication with a surface receiver and a surface transmitter. The surface controller comprises a typical computer having wireless and serial connectivity capabilities. In one embodiment, the surface controller comprises a notebook or laptop computer with a central processor, wireless and serial connectivity ports, a hard drive, and an appropriate operating system to execute software. The surface controller has loaded thereon and provides the run-time platform for surface controller application software. The surface controller application software provides the user interface for the surface user, and contains a demodulation module which demodulates incoming ultra-low-frequency phase-modulated electric carrier waves that carry the signal data. The surface controller application software also controls and manages all communications of the communication system. 
     The surface receiver and surface transmitter are connected to a plurality of surface electrodes. The surface electrodes are electrodes that are inserted into the ground to transmit ultra-low-frequency phase-modulated electric carrier waves, once data packets, telemetry data and/or binary data are located thereon. In the preferred embodiment, the surface receiver and the surface transmitter are connected to two sets of surface electrodes. However, more or less than two sets of surface electrodes may be connected to the surface receiver and surface transmitter. The additional surface electrodes may be constructed and configured to additional signal conditioning channels in the surface receiver, which can be monitored or used for noise subtraction, if desired. 
     The surface transmitter of the present invention is in communication and interfaces with a subsurface transceiver via the surface electrodes, using ultra-low-frequency phase modulated electric carrier waves. In one embodiment, the subsurface transceiver is connected to infrastructure metal within the mine via at least two conductive clamps, which serve as subsurface electrodes. In another embodiment, the subsurface transceiver is attached via conductive connectors to a plurality of steel pipes that are driven into the earth within the mine, which serve as the subsurface electrodes. The subsurface transceiver is in communication and interfaces with the surface receiver via the subsurface electrodes, using ultra low-frequency phase-modulated electric carrier waves. 
     The surface controller application software controls the communication system of the present invention. The surface controller application software comprises a module containing predefined beacons of data which are contained and organized on a user-interface menu for selection by the user. The predefined beacons are displayed as predetermined text messages on the user interface of the surface controller. 
     Once selected by the user, the predefined beacon is transformed from digital to analog data and is configured into command data packets by the surface controller application software, and then sent to the surface transmitter. The surface controller application software modulates the current driven through the earth by the surface electrodes. In one embodiment, QPSK modulation is used to modulate the electric current. However, other modulation could be used as well. 
     The surface transmitter converts the command data packets to phase-modulated electric carrier waves and transmits the carrier waves to the subsurface transceiver through the electric field current created by the surface electrodes. The output driver of the surface transmitter mates with on-board connectors to attach to the surface electrodes. The output driver drives the phase-modulated electric carrier waves to the surface electrodes, which transmit through the earth to the subsurface electrodes. 
     In one embodiment, the surface electrodes comprise a plurality of steel pipes that are manually embedded into the earth. However, any material suitable for establishing a low impedance ground connection conducive to producing/receiving ultra-low-frequency electric fields there through can be used. At least two sets of surface electrodes are spaced a predefined distance from each other to establish an electrical current, with the earth being the conductive media there between. The surface electrodes provide an ultra-low-frequency electric current through the earth, and are used to transmit the phase-modulated electric carrier waves to the subsurface transceiver, and receive the same therefrom. 
     In configuring the surface electrodes, the resistivity of the soil is measured using a four-pole method. Four ground stakes are inserted into the earth in a line. A known current is generated through the outer two stakes, and a drop in voltage potential is measured between the two inner ground stakes. The stakes are turned ninety degrees, and this process is repeated, and the resistivity measurements are averaged. Once the resistivity of the soil is known, the required size and orientation of the surface electrodes can be determined from predetermined data sets. The resistance between the surface electrodes should be minimized. In the preferred embodiment, at least two sets of surface electrodes are configured for providing an ultra-low-frequency electric current there between and transmitting and receiving signals on the surface. 
     The present invention uses differential voltage measuring to detect transmissions through the electric field. The voltage difference between the sets of surface electrodes produces the electric current. The current distribution is set up between the sets of surface electrodes. The surface receiver measures the voltage differential across the electric field. Measuring the voltage differential allows the receiver to detect an incoming signal from the subsurface transceiver. 
     The subsurface transceiver is preferably a battery-powered unit having a CPU, a controller, data acquisition module, conditioner for signal conditioning, and an output driver. The subsurface transceiver uses the CPU to perform the transmission and reception functions. In one embodiment, the CPU is an ARM 7-core, 32-bit processor with at least 4 MB of in circuit reprogrammable flash memory. However, other CPU&#39;s with other specifications could be used. The subsurface transceiver is, in the preferred embodiment, connected to at least two sets of subsurface electrodes. In one embodiment, the subsurface electrodes comprise a plurality of steel pipes embedded into the earth in a configuration similar to the surface electrodes. The subsurface electrodes produce an electric current for the transmission of phase modulated electric carrier waves in the same manner as the surface electrodes. In an alternative embodiment, electrodes may be made by clamping a set of clamps to existing metal infrastructure within the mine. In such an embodiment, the claims have attached thereto a set of modular electrical connections that connect into the subsurface transceiver. 
     The data acquisition module of the subsurface transceiver detects an incoming message by measuring the voltage differential across the subsurface electrodes. The CPU of the subsurface transceiver demodulates the phase-modulated electric carrier waive, and acquires the data therein through the data acquisition module. The conditioner conditions the analog signal into digital format and displays the digital signal in the form of a text message on the user interface of the transceiver. 
     The transceiver is equipped with a user interface device such as a controller or keypad that allows the user to select the predefined beacon of data which corresponds to a text message from a predefined beacon menu. Alternatively, text messages can be input by the user using the keypad. Once the user sends the beacon or message, the CPU of the receiver converts the data from digital to analog, modulates the signal in the ultra-low-frequency electric carrier wave, and sends the same to the output driver of the transceiver. The output driver of the transceiver sends the signal through the subsurface electrodes via an electric field to the surface receiver, where the signal is demodulated, converted to digital format, and sent to display on the surface controller as a text message, all of which is performed by the surface controller application software. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view showing an installation of the present invention in the preferred embodiment; 
         FIG. 1B  is a side view showing an installation of the present invention in an alternative embodiment; 
         FIG. 2  is a block diagram showing the subcomponents of the surface receiver of the present invention; 
         FIG. 3  is a block diagram showing the subcomponents of the surface transmitter of the present invention; 
         FIG. 4  is a flowchart showing the phase sync detection performance of the surface controller application software of the present invention; 
         FIG. 5  is a block diagram showing the subcomponents of the subsurface transceiver of the present invention; 
         FIG. 6  is a perspective view of a subsurface electrode of the present invention; and 
         FIG. 7  is a perspective view of a subsurface electrode of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1A  a typical installation of the communication system  10  of the preferred embodiment is disclosed. The communication system  10  uses ultra-low-frequency electric waves to communicate through the earth with people beneath the earth&#39;s surface, such as in mines. The surface components of the communication system  10  of the preferred embodiment comprise a surface controller  12 , a surface receiver  20 , a surface transmitter  30  and more than one set of surface electrodes  70 . As shown and described herein, the surface receiver  20  and surface transmitter  30  are separate units. However, the surface receiver  20  and surface transmitter  30  could be combined within the same housing, forming a single unit which performs the functions of both the surface receiver  20  and surface transmitter  30 . 
     In the preferred embodiment, the surface controller  12  comprises a notebook or laptop computer with a central processor (not shown), wireless and serial connectivity ports (not shown), a hard drive (not shown), and an appropriate operating system (not shown) to execute software (not shown). The surface controller  12  has a keypad (not shown) or keyboard (not shown) and a monitor  14  which provide the surface user interface for the communication system  10 . The surface controller  12  has loaded thereon and provides the ran-time platform for surface controller application software (not shown). The surface controller application software provides the central control for the entire communication system  10 . 
     The surface controller  12  interfaces with the surface receiver  20  either wirelessly or through a USB port  21   c . Referring to  FIG. 2 , a block diagram of the subcomponents of the surface receiver  20  is disclosed. The surface receiver  20  comprises a processing unit  21 , which has receiver module  21   a , system control module  21   b  and a USB port  21   c . The USB port  21   c  provides the interface  22  between the surface receiver  20  and the surface controller  12 . The surface controller  12  interfaces with the surface receiver  20  and the surface controller application software is in communication with the digital control module  24  and data acquisition module  23  of the surface receiver  20 . As shown in  FIG. 2 , the surface receiver comprises multiple channels  27 ,  28  and  29 . Three channels  27 ,  28  and  29  are shown for exemplary purposes only. It should be understood that more or fewer channels may exist on receiver  20  within the scope of the present invention. Moreover, fewer than all of the channels  27 ,  28  and  29  may be utilized. Each channel  27 ,  28  and  29  is connected via a set of electrode connectors  26  to surface electrodes  70 . Each channel  27 ,  28  and  29  is in communication with a conditioner  25  that performs digital-to-analog signal conditioning upon receiving an incoming signal from surface electrodes  70 . 
     The surface receiver  20  comprises a digital control module  24  and data acquisition module  23  which are in communication processing unit  21  which is in communication with the surface controller application software via the surface controller/surface receiver interface  22 . The digital control module  24  accepts gain adjustment commands from the surface control application software via the processing unit  21 . The digital signal gain is preferably incrementally adjustable. The conditioner  25 , which is attached to the multiple channels  27 ,  28  and  29  performs band pass filtering to reject incoming frequencies outside of the ultra-low range utilized by the communication system  10 , and pass the ultra-low-frequency modulated waves. The data acquisition module  23 , digitizes the analog waveforms from the incoming signal from the subsurface transceiver  50  into binary words. The binary words are sent to the data acquisition module  23  of the surface receiver  20 , which streams the digitized binary data to the surface controller  12  via the interface  22 . The digitized binary data is then processed by the integration module (not shown) and demodulation module (not shown) of the surface control application software. 
     Referring to  FIG. 3 , a block diagram of the subcomponents of the surface transmitter  30  are disclosed. In the preferred embodiment, the surface transmitter  30  transmits predefined beacons of information from the surface controller  10  to the subsurface transceiver  50 . The surface transmitter  30  comprises an alternate current input  32  which supplies power  34  to an output driver  37  of the surface transmitter  30 . The surface transmitter  30  is in communication with the surface controller  12  via a surface controller/surface transmitter interface  33 . In the preferred embodiment, interface  33  is established via serial connection. However, USB, wireless or Bluetooth interface is possible as well. 
     The user (not shown) of the surface controller  12  can select a predefined text message from a predefined message menu on the surface controller application software, which corresponds to a beacon or beacons of information in the form of binary data. The selected predefined digital text message is converted by the surface controller application software to analog binary data. The binary data are transmitted as command packets from the surface controller  12  to the processing unit  31  of the surface transmitter  30 . 
     The processing unit  31  converts the command packets into phase-modulated carrier waves, and transmits those waves through a pulse width modulation module  35  to an output driver  37 . The PWM module  35  encodes the analog carrier waves and the output driver  37  transmits the carrier waves through electrode connectors  39  to surface electrodes  70 , as shown in  FIG. 1A . The carrier waves are transmitted across the ultra-low-frequency electric current created by the surface electrodes  70  to the subsurface transceiver  50 . Because the earth is a lossy conductor, transmitting using ultra-low-frequency minimizes loss between the surface transmitter  30  and subsurface transceiver  50 . 
     A command-based protocol (not shown) is implemented by the surface controller application software that allows all needed functions and error handling to be accessed by the surface controller  12 . The surface transmitter  30  has multiple user-selected power settings, and is capable of efficiently driving 0.25-500 Ohm loads. 
     Referring to  FIG. 5 , the subcomponents of the subsurface transceiver  50  are disclosed. The subsurface transceiver  50  is preferably battery powered by a battery supply  51 . The subsurface transceiver  50  comprises a display  53   a  and an input device  53   b , such as a keyboard (not shown) or keypad (not shown), a CPU  52 , a data acquisition module  54 , a PWM module  55 , an output driver  56 , a conditioner  57 , a safety barrier  58  and at least one set of subsurface electrode connectors  59 . In one embodiment, all of the subcomponents of the subsurface transceiver  50  are contained within a single housing (not shown) that is suitable to eliminate explosion hazards in gassy mine environments. 
     The CPU  52  of the subsurface transceiver  50  performs the transmit and receive functions of the subsurface transceiver  50 . As a phase modulated carrier wave is received by the subsurface electrodes  80 , the signal is sent through the safety barrier  58  to the conditioner  57 . The conditioner  57  performs band pass filtering to reject incoming frequencies outside of the ultra-low range utilized by the communication system. The data acquisition module  54  digitizes the analog waveforms from the incoming signal from the surface transmitter  30  into binary words, which are then streamed to the CPU  52 . The digitized binary data is then processed and demodulated by the CPU  52 , and sent as a text message or text data to display  53   a.    
     A subsurface user of the subsurface transceiver  50  may use the input device  53   b  to select a predefined beacon from a predefined beacon menu stored on the CPU  52 , or may use the input device  53   b  to create a text message to send to the surface receiver  20 . The CPU  52  controls the PWM  55  module to convert the digital binary words to analog form, which sends the phase modulated carrier wave with the analog signal thereon to the output driver  56 , which transmits the signal through the ultra-low-frequency electric current created by the subsurface electrodes  80  to the surface receiver  20 . 
     In one aspect of the present invention, the surface control application software, in communication with the subsurface transceiver  50  through the surface transmitter  30 , contains a monitoring module (not shown) which queries the subsurface transceiver  50  using downlink query commands (not shown) to request data on predefined parameters of the subsurface transceiver  50 . Upon reception of the query command, the subsurface transceiver  50  returns the requested data via uplink transmission. Examples of parameters that are queried by the monitoring module are battery power/voltage, impedance between the subsurface transceiver  50  and the subsurface electrodes  80 , RMS voltage of the last received downlinked transmission and temperature of the subsurface transceiver  50 . 
     In another aspect of the present invention, the surface control application software provides a correction module (not shown) which executes an error correction algorithm (not shown). Before a byte of data is transmitted to the surface transmitter  30 , the correction module calculates a “checksum” of the data byte. The computation of the checksum is at least a three step process whereby the data byte is inverted to create a checksum byte, the checksum byte is bit reversed and then XOR&#39;ed with the original data byte to produce the final checksum. Thereafter, the correction module sends out redundancy data packets, which can contain up to eight copies of the same data (a data set being one byte plus its checksum) sent to the surface receiver  20 . However, more or fewer than eight copies of data could be sent. 
     The surface receiver  20  then performs bit averaging wherein bits for each data set are averaged to compile a “composite” byte where the bits in the composite byte are the average of all 8 of the received bytes. In this manner, a composite byte is created for Data and Checksum. These bytes are then added to the packet and used as a 9 th  pair for checksum comparison. Each data byte is compared to the checksum byte, including the composite byte. If a valid match is found after calculating the checksum from the data byte, that data/checksum pair is saved. Each data byte is checked against the remaining checksum bytes. 
     It is possible (and likely in high error conditions) that multiple valid checksums will be found with data bytes that are in error. For this reason, the correction module executes an algorithm counts how many of each valid data byte were found. The data byte value that has the highest count is then compared to a predefined threshold. If the number of occurrences of this data byte are over the threshold, and the data further meets the “confidence factor”, then a valid received message is generated. Once the data bytes are determined an additional step is taken to verify that the error corrected data is valid data. This confidence factor is a correlation of a theoretical packet based on the error corrected data and the actual received data. If the correlation of the received data to the theoretical data is higher than a defined minimum, the data is considered to be valid. 
     Referring to  FIG. 4 , the phase detection algorithm  40  of the surface controller application software is shown. The phase detection algorithm  40  detects and recovers the uplinked signal data, or incoming signal  41  and transforms the input signal into input vectors  42 , based on the QPSK modulation scheme. The input phase angles  43  of the vectors are then calculated to determine if the angles match  44 . A match indicates that a phase synchronization header has potentially been discovered in the received signal, and the data is then passed to the demodulation module that converts the data into meaningful symbols corresponding to beacons, text or other data. 
     Referring to  FIG. 6  and  FIG. 7 , two different embodiments of the subsurface electrodes are disclosed. Referring to  FIG. 6  and  FIG. 1B , in one embodiment, the subsurface electrode  60  provides a special connection device that allows for rapid connection to metallic infrastructure  66  within the mine. Most coal mines have a roof structure that is supported by metallic roof bolts  68 , roof straps (not shown) and the like. Grounding connections can be made using electrode  60  by tightening the threaded shank  62  such that the infrastructure metal is clamped tightly between the head  63  of the shank  62  and the arm  64  of the electrode  60 . The head  63  of the shank  62  may use various surface designs to aid in penetrating corrosion to ensure adequate electrical conductivity is achieved. Connectors  61  are attached to the electrode  60  and connect into the subsurface transceiver  50 . 
     Referring to  FIG. 7  and  FIG. 1A , in the preferred embodiment, the subsurface electrodes  80  comprise a plurality of steel pipes. The subsurface electrode  80  has a longitudinal slit  82  that extends the length of the subsurface electrode  80 . One end of the electrode  80  has a tapered end  84 , which aides in inserting the electrode  80  into the earth, and driving it therein. As the electrode  80  is inserted into the earth, slit  82  allows the electrode  80  to collapse, thereby creating a tight connection with the surrounding earth. Connectors  59  are connected via nut and bolt  86 , or any other appropriate attaching mechanism, to the electrode  80 . Connectors  59  then connect to the subsurface transceiver  80 . 
     Referring to  FIG. 1A , it is contemplated by the present invention that the subsurface electrodes  80  are inserted within the earth in certain predetermined areas of a mine, typically in pre-designated emergency chambers or areas. Subsurface transceivers  50  are likewise stored in close proximity to the subsurface electrodes in the predetermined areas of the mine. In operation of the present communication system  10 , the subsurface users set up the subsurface transmitter  50  by connecting subsurface electrode connectors  59  to the subsurface electrodes  80 . 
     On the surface, the user of the surface components first connects the surface electrodes  70  to the surface receiver  20  and surface transmitter  30 , and establishes connection of the surface controller with surface receiver  20  through interface  22 , and surface transmitter  30  through interface  33 . The surface electrodes  70  are then configured to measure the resistivity of the earth and determine proper alignment of the surface electrodes  70  using the four-pole method described herein above. After proper alignment of the surface electrodes, the ultra-low-frequency electric current C is established between the surface electrodes  70 . 
     In operation, a surface user may select from the predefined beacon menu on the surface controller&#39;s monitor  14  a predefined beacon of text data to send to the subsurface transceiver  50 . Alternatively, the surface user may use a keyboard (not shown) or keypad (not shown) to create a customized text message to send to the transceiver. The predefined beacon of text data corresponds to a beacon or beacons of information in the foul of binary data. The selected predefined digital text message is converted by the surface controller application software to analog binary beacon data. The binary data are transmitted as command packets from the surface controller  12  to the processing unit  31  of the surface transmitter  30 . 
     The processing unit  31  provides a set of commands to the pulse width modulation (PWM) module  35 , which converts the command packets into phase-modulated carrier waves, and transmits those waves through the PWM module  35  to an output driver  37 . The PWM module  35  encodes the analog carrier waves and the output driver  37  receives a set of commands from the processing unit  31 , and transmits the carrier waves through electrode connectors  39  to surface electrodes  70 . The carrier waves are transmitted across the ultra-low-frequency electric current C created by the surface electrodes  70  to the subsurface transceiver  50 . Because the earth is a lossy conductor, transmitting through ultra-low-frequency minimizes loss between the surface transmitter  30  and subsurface transceiver  50 . 
     As the phase modulated carrier wave is received by the subsurface electrodes  80 , the signal is sent through the safety barrier  58  to the conditioner  57  of the subsurface transceiver  50 . The conditioner  57  performs band pass filtering to reject incoming frequencies outside of the ultra-low range utilized by the communication system. The data acquisition module  54  digitizes the analog waveforms from the incoming signal which are then streamed to the CPU  52  The digitized binary data is then processed and demodulated by the CPU  52 , and sent as a text message or text data to display  53   a.    
     A subsurface user of the subsurface transceiver  50  may use the input device  53   b  to select a predefined beacon from a predefined beacon menu stored on the CPU  52 , or may use the input device  53   b  to create a text message to send to the surface receiver  20 . The CPU  52  controls the PWM module  55  to convert the digital binary words to analog form, which sends the phase modulated carrier wave with the analog signal thereon to the output driver  56 , which transmits the signal through the ultra-low-frequency electric current created by the subsurface electrodes  80  to the surface receiver  20 . 
     As the incoming signal from the subsurface transceiver  50  is received by the surface electrodes  70 , the analog signal is transmitted to the conditioner  25  of the surface receiver  20  via electrode connectors  26 . The conditioner  25  is in communication with the processing unit  21 , which provides a set of instructions for the condition  25  to condition the incoming signal. The conditioner  25  performs band pass filtering to reject incoming frequencies outside of the ultra-low range utilized by the communication system. The digital control module  24  is in communication with the processing unit  21  and receives a set of commands there from to perform the gain adjustment commands from the amplification module of the surface controller application software. The binary words are then sent to data acquisition module  23  of the surface receiver  20 , which streams the digitized binary data to the surface controller  12  via the interface  22 . The digitized binary data is then processed by the integration module (not shown) and demodulation module (not shown) of the surface control application software, and displayed on the monitor  14  of the surface controller as text data. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon the reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications that fall within the scope of the invention.