Inductor-capacitor resonant circuits and improved methods of using same

A tag which uses radio frequency waves transmitted from a scanning device in order to identify an item to which the tag is attached or with which the tag is associated. The tag includes a first insulating layer having a top surface and a bottom surface, and resonant circuits formed on the first insulating layer. Each of the resonant circuits are formed on one of the top surface and the bottom surface of the first insulating layer and have a resonant frequency associated therewith. Each of the resonant circuits include capacitance and inductance elements. The capacitance and inductance elements include an inwardly spiralled coil connected to an outwardly spiralled coil. The tag is associated with a binary number established by a pattern of ones and zeros depending on each circuits' resonance or nonresonance, respectively.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to electronic item identification
 systems and more particularly, to a radio frequency (RF) identification
 tag and method for identifying an item to or with which the tag is
 attached or associated, respectively, wherein each tag includes a
 plurality of circuits having a capacitance.
 2. Background of the Related Art
 Conventionally, transportation of goods is conducted by utilizing railways,
 trucks, ships, airplanes and so on. In recent years, however,
 transportation of light-weight parcels by small trucks or the like, called
 Takuhaibin, have become very popular because of its low cost. In this type
 of transportation, a forwarding agent collects and delivers parcels to
 destinations in a short period of time. This transportation is known by
 its simple procedure and fast delivery of parcels.
 In such transportation, parcels are attached with a label on which a
 sender, a destination and so on are filled in. A delivery man looks at the
 labels on the parcels and thereby checks the destinations and conducts
 sorting out of the parcels. Recently, checking of destinations and sorting
 out of the parcels have also been conducted in the following manners: in
 one method, destinations are coded, and sorting out of the parcels are
 conducted using the coded destinations. In another method, a delivery man
 carries with him or her a bar code system, and parcels carry on them a
 label on which bar codes representing a sender, destination and so on are
 printed.
 However, in this transportation method, parcels are often delivered to a
 wrong destination or lost before they reach the destinations. Such
 accidents cost a forwarding agent substantial sums of money for
 investigation and compensation.
 These accidents may be decreased by reinforcing visual checking of parcels.
 However, reinforcement of visual checking of parcels increases cost and
 prolongs the time for delivery. In any way, it requires manpower and
 limits reliability. Currently, electronic item identification systems are
 in widespread use today to identify a variety of items. A first type of
 electronic item identification system commonly used in industry is one in
 which bar code labels are used to identify items. These types of
 electronic item identification systems are typically used by supermarkets,
 distributors, shipping services and clothing retailers to scan the bar
 code labels for quick retrieval of an item's price or other information.
 The way conventional bar code identification systems work is as follows.
 Bar codes labels are made up of a series of lines of varying widths or
 thicknesses to establish a code which can be read by a scanner. A bar code
 label is usually read by a laser scanner. The data from the scanner is
 electronically fed to a receiver which determines the identification code
 or number associated with the bar code label. The identification code or
 number is then sent to a central processing unit or computer where each
 code or number is matched to data stored on a master list such as item
 price or other information. The central processing unit or computer then
 electronically sends the stored data associated with the identification
 code or number to the cash register or other tabulator to arrive at a
 final total or tabulated result.
 Another system of electronic item identification uses radio frequency (RF)
 identification tags to identify items. Radio frequency (RF) identification
 tags can be used to identify a variety of items to which the tags are
 attached or otherwise associated. In particular, radio frequency (RF)
 identification tags are currently used to identify passengers, luggage,
 library books, inventory items and other articles. Radio frequency (RF)
 identification tags will allow electronic identification of people or
 objects, moving or stationary, at distances of several feet.
 Prior art devices short out capacitors during interrogation and thus the
 circuit can never be restored to its original frequency to be read over
 again. It is therefore desirable to develop an electronic item
 identification system in which the radio frequency (RF) identification tag
 can be read any number of times while still generating the same binary
 number as was read the first time and in this manner the tag can be
 reused.
 It is also desirable to develop an electronic item identification system in
 which a radio frequency (RF) identification tag has numerous circuits made
 up of capacitor/inductor coil pairs at evenly spaced intervals on the
 surface of the tag so that the presence or absence of a circuit or the
 circuit's functionability could be programmed at the point of use with
 inexpensive equipment.
 SUMMARY OF THE INVENTION
 It is a feature and advantage of the present invention in providing an
 electronic item identification system in which the radio frequency (RF)
 identification tag can be read any number of times while still generating
 the same binary number as was read the first time and in this manner the
 tag can be reused.
 It is another feature and advantage of the present invention in providing
 an electronic item identification system in which a radio frequency (RF)
 identification tag has numerous circuits made up of capacitor/inductor
 coil pairs at evenly spaced intervals on the surface of the tag so that
 the presence or absence of a circuit or the circuit's functionability
 could be programmed at the point of use with inexpensive equipment.
 In accordance with one embodiment of the invention, a tag uses radio
 frequency waves transmitted from a scanning device in order to identify an
 item to which the tag is attached or with which the tag is associated. The
 tag includes a first insulating layer having a top surface and a bottom
 surface, and resonant circuits formed on the first insulating layer. Each
 of the resonant circuits are formed on one of the top surface and the
 bottom surface of the first insulating layer and have a resonant frequency
 associated therewith. Each of the resonant circuits include capacitance
 and inductance elements. The capacitance and inductance elements include
 an inwardly spiralled coil connected to an outwardly spiralled coil. The
 tag is associated with a binary number established by a pattern of ones
 and zeros depending on each circuits' resonance or nonresonance,
 respectively.
 There has thus been outlined, rather broadly, the more important features
 of the invention in order that the detailed description thereof that
 follows may be better understood, and in order that the present
 contribution to the art may be better appreciated. There are, of course,
 additional features of the invention that will be described hereinafter
 and which will form the subject matter of the claims appended hereto.
 In this respect, before explaining at least one embodiment of the invention
 in detail, it is to be understood that the invention is not limited in its
 application to the details of construction and to the arrangements of the
 components set forth in the following description or illustrated in the
 drawings. The invention is capable of other embodiments and of being
 practiced and carried out in various ways. Also, it is to be understood
 that the phraseology and terminology employed herein are for the purpose
 of description and should not be regarded as limiting.
 As such, those skilled in the art will appreciate that the conception, upon
 which this disclosure is based, may readily be utilized as a basis for the
 designing of other structures, methods and systems for carrying out the
 several purposes of the present invention. It is important, therefore,
 that the claims be regarded as including such equivalent constructions
 insofar as they do not depart from the spirit and scope of the present
 invention.
 Further, the purpose of the foregoing abstract is to enable the U.S. Patent
 and Trademark Office and the public generally, and especially the
 scientists, engineers and practitioners in the art who are not familiar
 with patent or legal terms or phraseology, to determine quickly from a
 cursory inspection the nature and essence of the technical disclosure of
 the application. The abstract is neither intended to define the invention
 of the application, which is measured by the claims, nor is it intended to
 be limiting as to the scope of the invention in any way.
 These together with other objects of the invention, along with the various
 features of novelty which characterize the invention, are pointed out with
 particularity in the claims annexed to and forming a part of this
 disclosure. For a better understanding of the invention, its operating
 advantages and the specific objects attained by its uses, reference should
 be had to the accompanying drawings and descriptive matter in which there
 is illustrated preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
 The present invention relates to improvements to the inductor capacitor
 (LC) resonant tag. There are currently a few different tags. There is a
 bar code tag, there are other radio frequency (RF) tags out there mainly
 of silicon chip type. There are currently no known multiple LC circuit
 tags. Multiple LC tags are used for identification purposes; generally
 three or more LC circuit are needed for identification purposes, although
 less may be possible.
 In addition, in conjunction with the LC circuit is bar code identification,
 as well as using the RF silicon chip. This means that multiple types of
 reading must be done in order to identify a particular baggage or article.
 We have therefore discovered that multiple types of reading is required
 including reading of LC circuits, bar code and RF circuits for
 identification purposes.
 Accordingly, one improved identification tag includes a tag which has a
 combination of LC devices for identifications, as well as a bar code for
 identification. FIG. 1 illustrates this combination. See U.S. Pat. No.
 5,444,223 for an example of an LC circuit, incorporated herein by
 reference in its entirety. FIG. 1A illustrates an overall system for
 reading at least one of the bar code and/or LC Circuits. If both readers
 are utilized, then error correction and/or verification are possible by
 comparing the results of both readings, when available.
 A second improvement includes taking these little coils on the LC circuit
 and attaching an antenna to it, like a radio for receiving and for
 transmitting back. This will improve the distance for receiving and
 resonating signals, efficiency, and accuracy.
 One type of antenna is just a wire antenna; the antenna alone with no
 physical contact to the individual LC circuits (see FIG. 2). Another type
 of antenna is where there is an electrical connection to each of the
 inductor coils. This will generally provide a varied frequency that will
 be resonated from each of the LC circuits in a predetermined manner. For
 example, it might throw the frequency off by say half. So there might be
 an offset with the tradeoff of improved distance for receiving and
 resonating the signal. See FIG. 3 for one example of connecting the
 antenna to the different LC circuits. Of course, other type of connections
 to the LC circuit are contemplated within the present invention.
 Another improvement relates to the use of magnetic material that has
 natural inductive properties for the LC circuit. Magnetic material is
 conductive and its also magnetic, with magnetic properties. When the
 material is not magnetized, the LC circuit will resonate at a certain
 frequency, and when the magnetic material becomes magnetized the inductive
 property changes and the frequency shifts as a result. So this improvement
 to the LC circuit involves making the inductor coil of magnetic material
 which can be magnetized to change its resonant frequencies, thereby
 providing an entire set of different frequencies that are resonated by the
 tag when the tag is magnetized.
 This tag works with for example a reader that is looking at frequencies,
 for example, 1 MHz, 2 MHz, 3 MHz and so on. If all the LC circuits are
 magnetized, the 1 MHz frequency will be sifted to, for example, 1 1/2
 which will not be read. FIG. 4 illustrates this principle conceptually. In
 this case, the reader could go through the exercise of looking for a
 magnetized frequency to assure that there are two positive reads versus a
 positive and negative. So that would be an advantage of the magnetized not
 magnetized scenario. It is better to look for two positive readings than a
 negative reading because the negative reading is more difficult to read.
 This magnetized/unmagnetized embodiment leads to a potential third state,
 as well. That is, a positive magnetized, a positive non-magnetized, and a
 zero for the destroyed LC circuit. Thus, even more data can be obtained
 using less LC circuits. In a three state system the circuit is not simply
 resident or nonresident but instead has high quality residence, low
 quality residence, or is nonresidence.
 There are several methods of reading the LC circuits. We have discovered
 that a sweep scan, for example one megahertz to forty, forty to fifty, and
 sweep all the way up through every frequency that is expected to be
 resonated by the LC circuits. Another type of reader is a step reader
 which would step, 1 mg, 2 mg, and the like all the way up. The reader
 shoots or transmits a signal at the tag and the determines whether the
 signal has been resonated back.
 A third type of reading method is pulsing the signal and looking for a ring
 back signal that is resonated back. Accordingly, if the signal is
 transmitted as one megahertz, we have determined that the LC circuit
 stores enough energy to start oscillating. Once the reader has stopped
 transmitting the signal, the LC circuit is going to oscillate until the
 energy is used which is called the ring back. The first byte of the data
 will always be the same frequency represented by one LC circuit, the
 second byte will be a second frequency represented by another LC circuit,
 and so on.
 Thus, the reading in general is as follows: first, a one megahertz signal
 is transmitted, at the whole tag. When a one megahertz LC Circuit is
 activated on the tag, a signal is resonated back to the reader. Only one
 of these LC circuits will answer when its tuned to one megahertz. The
 other LC circuits will stay dormant since its not the correct signal. So,
 if the one megahertz signal comes back, its a one in the place of that
 location of the binary number. Two megahertz signal, and so on, until all
 forty of the LC circuit are transmitted. If a signal is resonated back
 that location is a one, and if it does not come back, its a zero.
 Another improvement in the tag is to selectively physically burn out, punch
 out or destroy the LC circuits to prevent selective LC circuits from
 resonating a signal back, therefore,` providing a zero value for that
 destroyed LC circuit.
 Another improved tag is if there is cross coupling between the LC circuits.
 For example, if the inductor coils of two LC circuits are connected
 together, there should be three resonant signals resulting in this
 combination. The first resonant signal is generated by the natural
 resonant frequency of the first LC circuit. The second resonant signal is
 generated by the natural resonant frequency of the second LC circuit. The
 third resonant signal is generated by the natural resonant frequency of
 the combination of the first and second LC circuits. FIG. 5 illustrates
 this combination of connecting pairs of LC circuits. Of course, more than
 two LC circuits can be connected to further generate additional
 frequencies. FIG. 6 illustrates the circuit diagram of FIG. 5
 corresponding to this connection.
 In accordance with FIG. 5, three distinct frequencies are resonatable from
 the circuit. However, the following combinations are possible. For
 example,
 (1) frequency of LC #1 only (L #2 destroyed)
 (2) frequency of LC #2 only (LC #1 destroyed)
 (3) frequency of LC #1 and LC #2 only (no connection between LC #1 and LC
 #2)
 (4) frequency of LC #1 and LC #2 and combined frequencies (connection
 exists between LC #1 and LC #2) (5) no frequencies
 Of course, all frequencies are unique in the combination of pairs of LC
 circuits, as well with other LC circuits to prevent confusion and ensure
 accurate identification. This then permits multiple states as well as to
 decrease the number of LC circuits to make the tag smaller. So now that
 there are potentially five states out of the combination of two LC
 circuits. The number of coils is reduced and the tag gets smaller.
 As an alternative connection between LC resonant circuits, the capacitors
 of each of the LC circuits can be connected as well as inductors. See FIG.
 7 for this design, as well as FIG. 8 for an illustration of the conceptual
 circuit diagram. Note that the LC circuits are electrically connected in
 parallel. Of course, other modifications are also contemplated, such as
 only connecting the capacitors to form the combined resonant circuit, as
 well as other types of connections. the important discovery is that if LC
 circuits are electrically connected, then there will be a potential third
 frequency that can be resonated back.
 The double spiral configuration of the coil provides an inherent LC
 resonant circuit as well. See FIG. 9 for an illustration of this double
 spiral configuration. Note that the inward or outward spiral references
 are merely illustrative of the spiral LC circuit concepts, and are not to
 be interpreted to limit the particular flow of the current therein. The
 spiral configuration of conductors are place on (or perhaps even disposed
 in) a dielectric substrate, similar to the configuration of the LC
 resonant tags previously described.
 The spiral configuration is designed to minimize the manufacturing process.
 When it comes down to producing or manufacturing the LC circuit and tag
 associated therewith, the more steps the more costs. Therefore, we have
 determined that there is a natural state that exists between conductive
 material. For example, when there is a conductive material, a gap, and a
 conductive material there creates capacitance.
 In the spiral configuration illustrated in FIG. 9, the L (inductance)
 negates itself because of the lines of flux. However, between the two
 conductors that are spiralling in and out, the number of lines and gaps is
 increased which creates its own capacitance that can be resonated like an
 ordinary LC circuit once a signal is transmitted to it.
 Thus, the spiral configuration allows us to delete or remove the capacitor
 by just spiralling in and coming out. From a manufacturing stand point it
 is superior and easier to manufacture. The L is not generally increased,
 but the L is generally nullified the zero with some minor noise likely
 being present. That is, from the manufacturing standpoint, the end of the
 inductor does not need to be connected to a capacitor. Therefore, there is
 no need for a separate capacitor at the center of the tag.
 The next improved LC circuit design is the coiled capacitor design. We
 observed the standard LC resonant circuit did not have enough area to pick
 up the magnetic flux. On this basis, we decided to utilize an antenna as
 described above. However, we also discovered that there are significant
 advantages of putting one LC resonant circuit inside the other as
 illustrated in FIG. 10. As a result, there will be more combinations
 because LC circuit #1 resonates at, for example, frequency 1, LC circuit
 #2 resonates at, for example, frequency 2, and so forth. The combination
 of LC #1 and LC #2 will provide another frequency. Thus, the number of
 combinations of LC circuits in the tag are huge (approximately the
 factorial of the number of LC circuits in the tag that are inserted into
 one another).
 Therefore, instead of having the LC circuits in rows and columns, the LC
 circuits are inside the other, inside the other, and so on. This
 combination of LC circuits can then be used for identification purposes.
 Each of the LC circuits are then selectively activated to arrive at a
 unique binary number than can be identified or associated with a
 particular article, in a similar manner the selective activation is
 conducted in U.S. Pat. No. 5,444,223, incorporated herein by reference.
 See, for example, FIG. 11 illustrating one configuration of a selectively
 activated LC circuit, where the binary number that identifies the tag as a
 result of this selective activation is: 1010, starting from the first LC
 circuit as the most significant bit, plus one or more additional
 frequencies that are a result of the coupling between LC circuit described
 in detail above, for example, in connection with electrically connecting
 LC circuits together. However, as is readily apparent in FIG. 11, there is
 no physical connection required between the LC circuits, but there is an
 inductive connection or coupling between the LC circuits. In addition,
 there is no specific magnetic coupling required, as discussed above in
 connection with magnetized and non-magnetized LC circuits.
 Variable capacity is the next improvement. The idea of variable capacity is
 the process of manufacturing a variable capacitor. The coil is on the
 substrate. Then a dielectric layer is placed over the coil. A metal or
 other conductive plate is then placed top of the dielectric layer. The
 metal plate is then varied from LC circuit to LC circuit to provide a
 varied and different frequency that is resonated from each of the
 different LC circuits. The metal plate is varied during the process of
 initializing the tag by taking a laser and cutting off the excess portion
 of the metal plate in a predetermined fashion. The coil is then
 electrically connected to the metal plate using standard means, such as a
 conductive material. FIG. 12 illustrates this configuration where the
 dielectric layer is smaller that the coil. FIG. 13 illustrates the use of
 multiple LC resonant circuit in accordance with the embodiment illustrated
 in FIG. 13.
 By varying the metal or conductive plate, a different resonant frequency
 will result. The reason is that we have determined is that the determining
 factor of the capacitance of a capacitor is the area of the conductive
 plate with the dielectric layer and the coil that is underneath. So there
 are essentially two plates, the top conductive plate, and the conductive
 coil below. By changing the area of the top conductive plate, the overall
 capacitance is being changed. Therefore, in the manufacturing process of
 the tag or conductive plate where the conductive plate has been
 manufactured the same size, the next steps will be initializing the tag
 and LC circuits by varying the area of the metal plate.
 For example, it may be presumed that there is a mathematical relationship
 between the amount of area of the metal plate and the resulting
 capacitance/resonant frequency emanated therefrom. For example, by taking
 off the conductive plate an area of 0.2%, the overall change in frequency
 resonated therefrom will be, for example, 2 megahertz. Thus, the same
 inductive coil structure will be able to provide multiple resonant
 frequencies which can be customized on a tag by tag basis providing more
 frequencies for less LC circuits, resulting in a smaller tag area required
 for the LC circuits. yes, that will give us one coil with multiple
 frequency
 In another embodiment of this LC circuit design, the dielectric will
 actually cover the whole area of the coil, as illustrated in FIG. 4.
 Multiple LC circuits according to this design are then utilized as
 illustrated similarly in FIG. 13. It is important for this variable
 capacitor to, of course, have two plates. Thus, in both FIGS. 12 and 14,
 the area of the coil itself is being used as the second, bottom conductive
 plate to create the appropriate capacitance.
 The next improved LC resonant circuit for use in identification purposes is
 the dipole LC resonant circuit. The dipole is basically an antenna. We
 have determined that an antenna has the characteristics of LC resonant
 circuits. An antenna or a frequency is equal to, or a function of, a
 particular length for an antenna of conductive material. FIG. 15
 illustrates this combination of antennas according to one dipole design.
 Now any one of the conductors/antennas illustrated in FIG. 15 could
 provide, for example, a resonant frequency of a quarter wave which is
 detectable. That is, the length of the conductor is a function of a
 particular frequency. Therefore, sticks or lines of wire or conductive
 material in actuality can be read by resonating different frequencies. In
 addition, by having multiple antennas within a predetermined distance,
 inductive coupling or affects result thereby resonating additional
 frequencies as a result of the inductive coupling, similar to the effects
 described in connection with FIG. 10.
 Functionally, the operation of transmitting signals to the tags operate by
 transmitting a signal and receiving a frequency resonated back. So each
 antenna in FIG. 15 will have its own frequency that it resonates at, and
 by virtue of receiving a signal resonated back, it is deduced that a
 particular dipole corresponding to a specific binary location is there,
 which gives you a one basically.
 Now the frequency can also be changed by changing the characteristics of
 the dipole antenna. Therefore, instead of just having the dipole antenna
 as a straight line, it can be modified by making the antenna longer than
 the width of the tag. Thus, the frequency does not have to be a function
 of the width of the tag. FIG. 16 illustrates this configuration. In one
 design, the antenna is zig-zaged, in another embodiment the antenna is
 bent or overlapped, and in yet another embodiment, the antenna is both
 bent and zig-zaged.
 According to this embodiment, there is not generally going to be any
 inductive coupling between these antennas, however, inductive coupling is
 also contemplated between antennas as well. The reason why inductive
 coupling is unlikely is because the frequencies used for the dipole
 antenna in FIGS. 15 and 16 are likely going to be in the gigahertz range
 as opposed to the LC circuits described above that are in the 10 megahertz
 range. Because the higher the frequency is used, the shorter the length of
 the antenna is needed. And at the higher frequencies there is less of a
 chance of inductive coupling.
 On the other hand, we have also realized that at the higher frequencies,
 there is a greater chance of a bouncing effect. The bouncing effect is
 caused by anything that gets into the signals way and the signal just
 bounces off of it. A scatter of noise may be present. Therefore, the
 dipole antenna configuration is designed to also include or compensate for
 this bouncing effect.
 Accordingly, we have determined that the multiple use of dipole antennas
 for identification purposes is possible.
 Another aspect of the invention involves different methods of reading the
 LC resonant tags. One way the tag is read is using inductive coupling,
 where the tag is placed between a transmitter and a receiver as
 illustrated in FIG. 17. A continuous sweep can be utilized to transmit the
 signal for resonating the combination of LC circuits, a pulse or step, as
 described before. In addition, the phase shift between the transmitted
 signal and the resonated signal can also be used.
 Instead of placing the tag between receive and transmit antennas, another
 method of reading the tags for inductive coupling is done with a single
 antenna. The one antenna which is both a transmit and receive antenna as
 illustrated in FIG. 18. Multiple ways of transmitting the signal can be
 utilized as described above in connection with using multiple antennas.
 The ringback can be used for detecting phaseshift using a sweep or pulse
 signal. The ringback is the signal which is resonated back.
 Another signal we have also determined can be used for detecting whether
 the LC circuit is resonating is the dip or fallout in the transmitted
 signal, illustrated in FIG. 19. What happens is that the inductor coil
 first absorbs the signal and charges the capacitor based on receipt of a
 signal at which it resonates at. This results in a dip initially of the
 signal that is detected by the reader, and is based on the load on the
 antenna dropping, as the capacitor charges. Because the signal that is
 received by the LC circuit is the signal at which it resonates at, the
 energy of the signal is going to be sucked up by the coil and fed to the
 capacitive structure of the LC circuit for charging.
 Once the capacitor is fully charged that there is no signal transmitted to
 the LC circuit at the resonant frequency, the LC circuit going to blast or
 resonate the energy back to the coil which is called the ringback signal.
 So, in general, we have determined that there is a dip of the energy on
 the antenna during capacitive charging, and then there is a blast of
 resonant energy back from that LC circuit. Thus, we have determined that
 either the ringback signal or the dip condition can be used to determined
 whether an LC circuit has resonated, thereby providing, for example, an
 indicator (such as a 1) for use in identification purposes.
 Further, we have also determined that the combination of dip and ringback
 can be used to determine whether an LC circuit has resonated on the tag.
 This combination of signals has the additional benefit of verification or
 confirmation that an LC circuit has resonated.
 FIG. 19 illustrates the dip in the signal where the center frequency is 44
 megahertz. The dip spans plus or minus 7 megahertz so its 38, 37
 megahertz. The reader sweeps through different frequencies for signals
 transmitted to the tag. The ringback would look pretty similar to the dip,
 except an upward spike would be encountered one cycle after the dip.
 Returning to the use of phase shift to determine whether a specific LC
 circuit is active, if a one MHz signal is transmitted to the tag, and a
 phase shift is detected in that signal, then it has therefore been
 determined that there is a coil out there at the one MHz position that is
 active. If there is no phase shift, then the LC circuit does not exist, or
 has been deactivated.
 Another aspect of the present invention involves the use of the Frequency
 Modulator Continuous Waves (FM CW) as reading resonance. This FM CW signal
 is used to gauge resonance. The different ways of transmitting the FM CW
 include, as discussed above, the sweep scan and step scan as discussed
 above, or the blasting of all the frequencies at one time and reading all
 the resonant signals simultaneously.
 Another aspect of the present invention further includes the detection of
 the resonant signal based on signal quality. For example, FIG. 20
 illustrates a resonant signal with high quality since the signal is quite
 sharp, similar to the signal illustrated in FIG. 19. On the other hand,
 FIG. 21 illustrates a resonant signal with low quality since the signal
 spans a wide area of frequencies. The high quality signal is, for example,
 considered as a 1 for a binary identification scheme, and the low quality
 signal is considered, for example as a 0. Of course, the low and high
 quality signal can be used in conjunction with other signals or lack
 thereof to create a three level or stage value for identification
 purposes.
 The many features and advantages of the invention are apparent from the
 detailed specification, and thus, it is intended by the appended claims to
 cover all such features and advantages of the invention which fall within
 the true spirit and scope of the invention. Further, since numerous
 modifications and variations will readily occur to those skilled in the
 art, it is not desired to limit the invention to the exact construction
 and operation illustrated and described, and accordingly, all suitable
 modifications and equivalents may be resorted to, falling within the scope
 of the invention.