Abstract:
An RFID biosensor detection system for detecting particular substances has an interrogator circuit to transmit a radio frequency signal, an input transducer mounted on a piezoelectric material to receive an input radio frequency signal and propagate a corresponding acoustic wave within the piezoelectric material. At least two chemically orthogonal or semi-orthogonal biolayers are mounted on the piezoelectric material to receive substances to be tested and cause corresponding changes in the acoustic wave. An output transducer is mounted on the piezoelectric material to receive the acoustic wave and transmit a corresponding output radio frequency signal. A receiver circuit receives the corresponding output radio frequency signal and provides separate channel data indicative of the substances received.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/088,809 filed Mar. 25, 2005, the contents of which are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This application relates to the differentiation and identification of analogous chemical and biological substances with RFID biosensors. 
     BACKGROUND OF THE INVENTION 
     Parent U.S. application Ser. No. 11/088,809 describes and claims a biosensor detection system for detecting a particular substance, said system having at least two biosensor devices, each biosensor device including a piezoelectric material, an input transducer mounted on the piezoelectric material to receive an input radio frequency signal and generate a corresponding acoustic wave within the piezoelectric material, an output transducer mounted on the piezoelectric material to receive the acoustic wave and transmit a corresponding output radio frequency signal, a biolayer mounted on the piezoelectric material to receive a substance to be tested and cause a corresponding change in the acoustic wave, and an oscillator circuit connected to the input transducer and to the output transducer, said oscillator circuit including an amplifier and providing an output signal indicative of a change in the acoustic wave, the biosensor devices having two different biolayers which are chemically orthogonal or semi-orthogonal to each other, whereby the output signals can be utilized to detect receipt of a particular substance by the biolayers of the biosensor devices. 
     SUMMARY OF THE INVENTION 
     The present invention provides acoustic wave (AW) radio frequency identification device (RFID) biosensors configured with chemically orthogonal or semi-orthogonal biolayers and a processing system which are capable of detecting differentiating and identifying analogous chemical and biological substances. 
     According to one aspect of the invention, an RFID biosensor detection system for detecting particular substances has an interrogator circuit to transmit a radio frequency signal, a piezoelectric material, an input transducer mounted on the piezoelectric material to receive an input radio frequency signal and propagate a corresponding acoustic wave within the piezoelectric material, at least two chemically orthogonal or semi-orthogonal biolayers mounted on the piezoelectric material to receive substances to be tested and cause corresponding changes in the acoustic wave an output transducer mounted on the piezoelectric material to receive the acoustic wave and transmit a corresponding output radio frequency signal, and a receiver circuit to receive the corresponding output radio frequency signal and provide separate channel data indicative of the substances received. 
     Classification of similar molecules in accordance with the present invention is based on the concept of the RFID biosensor having both the ability to detect using multiple chemically orthogonal or semi-orthogonal biolayers and to return back to a processing system an interrogation signal which has been suitably modified to contain multi-dimensional information. The processing system can then separate out the return signal and process the information to provide a multi-dimensional state-space map. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which: 
         FIG. 1  is a diagrammatic view of a multi-dimensional RFID biosensor and processing system in accordance with one embodiment of the invention, 
         FIG. 2  shows a dual track RFID biosensor configuration, 
         FIG. 3(   a ) shows the dual track RFID biosensor signals, 
         FIG. 3(   b ) shows a dual track RFID biosensor receiver, 
         FIG. 4  shows an RFID biosensor with multiple reflector arrays, 
         FIG. 5(   a ) shows RFID biosensor and multiple reflector array signals, 
         FIG. 5(   b ) shows an RFID biosensor and multiple reflector array receiver, 
         FIG. 6  shows basic elements and structure of a wireless five-bit bi-phase Barker coded RFID biosensor with multiple biolayers, 
         FIG. 7(   a ) is a graph showing a five-bit Barker code correlation as a function of biolayer X, 
         FIG. 7(   b ) is a graph showing a five-bit Barker code correlation as a function of biolayer Y, and 
         FIG. 8  shows an RFID biosensor correlation receiver. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, a multi-dimensional RFID biosensor and processing system  100  is shown in  FIG. 1 . A quantity of substances  110  is presented to an AW RFID  120  which has a suitable AW RFID antennal  123  attached to an AW RFID inter-digital transducer (IDT)  121 . The purpose of the AW RFID antenna  123  is to interface electromagnetic waves propagating in free space with the AW RFID IDT  121 . The purpose of the AW RFID IDT  121  is to convert a received electrical signal  130  to acoustic waves and, similarly, convert acoustic waves to an electrical signal  130 . Within the structure of the AW RFID  120 , there are several chemically orthogonal or chemically semi-orthogonal receptor areas to detect certain substances  110  specific to each of the receptor regions. The first receptor region is configured at an (X) channel detector  125 , the second receptor region is configured as (Y) channel detector  127  and continuing up to and including the (n th ) receptor region which is configured as the (n) channel detector  129 . Each channel detector  125 ,  127  and continuing up to and including the (n) channel detector  129  is structured such that each channel detector is chemically orthogonal or chemically semi-orthogonal to each of the other channel detectors. 
     The sequence of detection for the multi-dimensional RFID biosensor and processing system  100  begins when a processing system  140  initiates, via an interrogator and receiver system  150 , a signal  130  of suitable strength via an antenna  135  to stimulate the AW RFID  120 . The electrical signal  130  is conveyed via the AW RFID antenna  123  to the AW RFID IDT  121  and converted to appropriate acoustic waves. The acoustic waves interact with the (X) channel detector  125 , the (Y) channel detector  127  and continuing up to and including the (n) channel detector  129 . The acoustic waves are modified only if the (X) channel detector  125  has detected any analogous (X) substances or, similarly, if the (Y) channel detector  127  has detected any analogous (Y) substances, and, similarly, if a channel detector continuing up to and including the (n) channel detector  129  has detected any analogous substances. The acoustic waves will be modified in accordance with the following equation (1) which was published in W. D. Hunt et al., “Time-dependent signatures of acoustic wave biosensors,” IEEE Proceedings, Vol. 91, no. 6, pp. 890-901, June 2003; 
                     Δ   ⁢           ⁢   f     =     -         2   ⁢     f   u   2     ⁢     h   f             ρ   q     ⁢     μ   q           ⁡     [       Δ   ⁢           ⁢   ρ     -       Δ   ⁢           ⁢   μ       V   s   2         ]                 (   1   )               
where V s  is the acoustic velocity, ρ is the density of the film, h f  is the thickness of the film, μ q  and ρ q  are the shear stiffness and density of the quartz crystal respectively, μ is the stiffness of the film, and Δ is the difference between perturbed and unperturbed (denoted by subscript u) quantities. The stiffness of the film, μ, is affected by the conformational change of the recognition molecules.
 
     The result is that the AW RFID  120  now has generated acoustic waves with detection information pertaining to the (X) channel detector  125 , the (Y) channel detector  127  and continuing up to and including the (n) channel detector  129 . The AW RFID IDT  121  now combines and converts these acoustic waves to electrical signals which are conveyed via the AW RFID antenna  123  as a signal  130  returning to the processing system  140  and into the interrogator and receiver  150  via a system antenna  135 . The interrogator and receiver  150  receive these modified signals and processes them within a channel separation step  160  where the combined detection information from each of the (X) channel detector  125 , the (Y) channel detector  127  and continuing up to and including the (n) channel detector  129  is separated out and stored within a (X) location, a (Y) location and continuing up to and including the (n th ) location. Finally, the data from these stored locations is mapped using state-space mapping  170 . The final result is that each detected analogous substance is projected onto a multi-dimensional state-space map. 
     The main advantages of detecting, differentiating and identifying analogous chemical and biological substances using RFID biosensor type devices in accordance with the present invention:
         (1) encompassing n-chemically orthogonal or semi-orthogonal biolayers within the RFID biosensor structure,   (2) the returned interrogation signal has the means and capacity to contain the detected information from the n-biolayers,   (3) the receiver within the interrogation system can then separate out the n-orthogonal or semi-orthogonal channels and process the information to complete an n-dimensional state-space map.       

     Various RFID biosensor structures in accordance with the invention can be fashioned to incorporate multiple chemically orthogonal or semi-orthogonal biolayers and produce signals which have the means and capacity to contain detected data from the multiple chemically orthogonal or semi-orthogonal biolayers, as will now be described. Receiver structures will also be described to illustrate how data from each channel can be separated out to distinguish X, Y and up to n data sets to formulate a multi-dimensional state-space map. 
     Dual Track RFID Biosensor 
     A schematic view of a dual track RFID biosensor configuration  200  is shown in  FIG. 2 . This concept is an extension of the DUAL TRACK SURFACE ACOUSTIC WAVE RIFD/SENSOR described in U.S. Pat. No. 7,005,964 (Edmonson et al.) issued Feb. 28, 2006. An interrogation signal interacts with an antenna  210  which is electrically connected to an input/output IDT  220 . A piezoelectric material  205  enables electrical signals within the input/out IDT  220  to be converted to acoustic waves. The antenna  210  is also electrically connected to track X IDT  230  and to track Y IDT  235  where similar interactions also convert electrical signals to acoustic waves. A chemically orthogonal or semi-orthogonal biolayer X  240  is suitably positioned within track X IDT  230  such that, if substances which are analogous to biolayer X  240  reach receptor sites within the biolayer X  240 , a perturbation of the acoustic waves as specific to those which interact with track X IDT  230  and the input/output IDT  220  will cause a modification of the returned interrogation signal, when the acoustic waves transform the perturbations into electrical signals via the input/output IDT  220  and track X IDT  230 . Similarly, a chemically orthogonal or semi-orthogonal biolayer Y  245  is suitably positioned within the track Y IDT  235  such that, if substances which are analogous to biolayer Y  245  reach receptor sites within the biolayer Y  245 , a perturbation of the acoustic waves specific to those which interact with track Y IDT  235  and the input/output IDT  220  will cause a modification of the returned interrogation signal, when the acoustic waves transform the perturbations into electrical signals via the input/output IDT  220  and the track Y IDT  235 . 
     The dual track RFID biosensor configuration  200  is shown with a split finger design, with both the width and spacing of the fingers being one-eighth of an acoustic wavelength. The dual track RFID biosensor configuration  200  can equally function with a typical quarter-wavelength design where both the width and spacing of the fingers are one-quarter of an acoustic wavelength. The key to this dual track configuration is the phase of offset of 90° or one-quarter of an acoustic wavelength between the track X IDT  230  and the track Y IDT  235 . This offset will produce a returned interrogation signal similar to the dual track RFID biosensor signal  300  shown in  FIG. 3(   a ). Signal X  304  is a result of the acoustic waves propagating by way of the area within the track X IDT  230 , and signal Y  308  is the result of the acoustic waves propagating by way of the area within the track Y IDT  235 . Signal X  304  is 90° phase displaced with respect to signal Y  308 . 
     The dual track RFID biosensor receiver  310  shown in  FIG. 3(   b ) demodulates and separates out the independent data from biolayer X  240  and biolayer Y  245 . The dual track RFID biosensor signals  315 , which are electrically phase displaced by 90°, are split along two paths so that two equally divided signals by the inputs for both mixer X  320  and mixer Y  325 . A voltage controlled oscillator (VCO)  330  signal is applied to down-convert within the mixer X  320  a signal which acts as the input to the channel X processor  340 . The channel X processor  340  suitably converts the signals such that X data  350  is a function of the substances which are analogous to biolayer X  240 . Similarly, for the Y data, the VCO  330  signal is electrically offset in phase by 90° by a phase shifter  335  as it is applied to down-convert within the mixer Y  325  a signal which acts as the input to the channel Y processor  345 . The channel Y processor  345  suitably converts the signals such that Y data  355  is a function of the substances which are analogous to biolayer Y  245 . 
     RFID Biosensor with Multiple Reflector Arrays 
       FIG. 4  shows another configuration utilizing AW RFID biosensors in accordance with the invention. An RFID biosensor  400  with multiple reflector arrays is used to embed the multiple biolayer information with any time-displaced signal. This concent is an extension of the concept disclosed in U.S. Pat. No. 7,053,524 (Edmonson et al.) issued May 30, 2006. An antenna  405  is electrically connected to an input/output IDT  410 , and an interrogation signal entering the antenna  405  is converted via the input/output IDT  410  to acoustic waves propagating outwards from both sides of the input/output IDT  410 . The acoustic waves intercept a reference reflector array  420 , a reflector array X  430  and a reflector array Y  440 . Other arrays can also be included, up to the n th  reflector array. The action of the reflector arrays  420 ,  430  and  440  is such that an incident acoustic wave will partially transmit through, but more importantly, partially reflect back towards the input/output IDT  410 . The reference reflector array  420  has no biolayer placed within its proximity and will reflect back an acoustic wave of similar characteristics to that of the incident propagating acoustic wave. 
     Reflector array X  430  has in its proximity a chemically orthogonal or semi-orthogonal biolayer X  435  where, if substances which are analogous to biolayer X  435  reach the receptor sites within biolayer X  435 , a perturbation of the acoustic waves specific to those which interact with reflector array X  430  will cause a modification of the characteristics of the reflected acoustic wave being propagated back to the input/output IDT  410 . Similarly, reflector array Y  440  has in its proximity a chemically orthogonal or semi-orthogonal biolayer Y  445  where, if substances which are analogous to biolayer Y  445  reach the receptor sites within biolayer Y  445 , a perturbation of the acoustic waves specific to those which interact with reflector Y  440  will cause a modification of the characteristics of the reflected acoustic wave being propagated back to the input/output IDT  410 . These collections of reflected acoustic waves from reflector arrays  420 ,  430  and  440  converge at separate times at the input/output IDT  410  and are converted to equivalent electrical signals which propagate back to the processing system  140  via the antenna  405 . 
     Such RFID biosensors with multiple reflector array signals  500  are shown in  FIG. 5(   a ) where the axes are magnitude  503  and time  506 . A reference signal  512  is the first signal to be returned back to the interrogation system, because normal positioning of the reference reflector array  420  dictates that it be located geometrically closest to the input/output IDT  410 . Signal X  515  is separate in time and will be distinct in characteristics from both the reference signal  512  and signal Y  518  if substances which are analogous to biolayer X  435  reach the receptor sites within biolayer X  435 . Similarly, signal Y  518  is separate in time and will be distinct in characteristics from both the reference signal  512  and signal X  515  if substances which are analogous to biolayer Y  445  reach the receptor sites within biolayer Y  445 . The time separation between the electrical signals  512 ,  515  and  518  is a function of the spatial layout of the reference reflector array  420 , reflector array X  430  and reflector array Y  440 . A person skilled in the art will take care in positioning the input/output IDT  410 , the reference reflector  420 , reflector array X  430  and reflector array Y  440  and any other reflector arrays so as not to cause interference within the RFID biosensor with multiple reflector array signals  500  ( FIG. 5(   a )). A person skilled in the art will also take advantage of the multiple reflections which occur in time after signal Y  518  due to the multiplicity of reflections which occur in the acoustic wave path between reflector array X  430  and reflector array Y  440 . 
     An RFID biosensor multiple reflector array receiver  520  is shown in  FIG. 5(   b ). RFID biosensor multiple reflector array signals  525  are the input to a mixer  530  along with a VCO  535  signal to produce a down-converted signal for channel processing  540 . The channel processing  540  uses the reference signal  512  to null out any irregularities due to temperature and other physical changes and separate out data signals such that data X  550  is a function of the substances which are analogous to biolayer X  435  and such that data Y  555  is a function of the substances which are analogous to biolayer Y  445 . 
     The RFID biosensor with multiple reflector arrays  400 , the RFID biosensor with multiple reflector array signals  500  and the RFID biosensor with multiple reflector array receiver  520  can be extended to an n-dimensional system capable of producing n-dimensional state-space mapping for analogous substances, as will now be readily apparent to a person skilled in the art. 
     RFID Biosensors With Correlation Based Detection Schemes 
     A useful feature which is inherent in AW RFID biosensors is the ability to encode the interdigital transducers such that the encoding process of the AW RFID device expands the data over a specific frequency range and that, within the receiver, a reference compressor then correlates the data to produce a correlation function which is time based and convenient for extraction of certain information. Any deviation of the signals within the AW RFID biosensor expander will then alter the peak and sidelobes of the final correlation function when using a reference compressor which remains constant. These encoding methods have previously been described in U.S. Pat. No. 7,053,524 (Edmonson et al.) issued May 30, 2006, with a more detailed description of the correlation functions being found in P. J. Edmonson, “SAW pulse compression using combined Barker codes, Masters Thesis in Electrical Engineering, McMaster University, Hamilton, Ontario, 124 pages, March 1989. 
     A 5-bit bi-phase Barker coded RFID biosensor with multiple chemically orthogonal or semi-orthogonal biolayers  600  is shown in  FIG. 6 . Initially, an antenna  610  accepts an interrogation signal from a processing system  140  ( FIG. 1 ) located some distance away. This signal is converted to an acoustic wave via an input/output interdigital transducer IDT  620  and progresses towards the coded IDT section constituting Bit # 1   631 , Bit # 2   632 , Bit # 3   633 , Bit # 4   634  and Bit # 5   635 . Similarly, the signal from the antenna  610  is also electrically connected to the coded IDT section constituting Bit # 1   631 , Bit # 2   632 , Bit # 3   633 , Bit # 4   634  and Bit # 5   635  to generate another acoustic wave which progresses towards the input/output IDT  620 . These acoustic waves interact with the multiple IDTs  620 ,  631 ,  632 ,  633 ,  634  and  635  to convert the acoustic waves back to a coded electrical system which is transmitted back out from the antenna  610  to the processing system  140 . 
     The geometric positioning of the fingers, which dictates the polarity of the IDTs is important for bi-phase coded structures. In this embodiment, each bit is made up of two finger pairs, with each finger pair being made up of oppositely positioned fingers. The finger pairs are continuous for Bit #  1   631 , Bit # 2   632  and Bit # 3   633  but are interchanged during the transition from Bit # 3   633  to Bit # 4   634  and during the transition from Bit # 4   634  to Bit # 5   635 . This sequence of finger geometry now represents the 5-bit bi-phase Barker code of 1, 1, 1, −1, 1 where there is a 180° phase transition between the third and fourth and fourth and fifth bits. Also, in this embodiment, chemically orthogonal or semi-orthogonal biolayer X  650  is positioned within the finger structure of Bit # 2   632 , and chemically orthogonal or semi-orthogonal biolayer Y  655  is positioned within the finger structure of Bit # 4   634 . 
     The correlation function can be derived by using signal processing techniques on the coded electrical signal which is transmitted back out from the antenna  610  to the processing system  140 . This signal processing technique comprises a series of time inversion multiplications, shifting and summing between the returned coded signal (expander) and a reference code (compressor). The following Table 1 illustrates this correlation process for a 5-bit bi-phase Barker code of sequence (1, 1, 1, −1, 1). 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Row # 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 −1 
                 1 
                 1 
                 1 
                   
                   
                   
                   
               
               
                 2 
                   
                 1 
                 −1 
                 1 
                 1 
                 1 
               
               
                 3 
                   
                   
                 1 
                 −1 
                 1 
                 1 
                 1 
               
               
                 4 
                   
                   
                   
                 −1 
                 1 
                 −1 
                 −1 
                 −1 
               
               
                 5 
                   
                   
                   
                   
                 1 
                 −1 
                 1 
                 1 
                 1 
               
               
                 6 
               
               
                 7 
                 1 
                 0 
                 1 
                 0 
                 5 
                 0 
                 1 
                 0 
                 1 
               
               
                   
               
             
          
         
       
     
     In row # 1 , the time reversed code is placed within each bit being multiplied by the first bit of the Barker sequence, which in this example is a “1”. Similarly, in row # 2 , the time reversed code is shifted by one bit period and multiplied by the second bit of the Barker sequence, which in this example is a “1”. For row # 3 , the time reversed code is again shifted by one bit period and multiplied by the third bit of the Barker sequence, which in this example is a “1”. For row # 4 , the time reversed code is again shifted by one bit period and multiplied by the fourth bit of the Barker sequence, which in this example is a “−1” and for row # 5 , the time reversed code is again shifted by one bit period and multiplied by the fifth bit of the Barker sequence, which in this example is a “1”. Row # 7  is the sum of the bits positioned in the columns directly above each value. The resulting correlation function is then, 1, 0, 1, 0, 5, 0, 1, 0, 1. 
     Perturbations within the area of the biolayers will change the correlation function. The changes are both distinguishable and distinct to each separately placed biolayer. Such perturbations are caused due to substances which are analogous to biolayer X  650  interacting with the receptor sites within biolayer X  650  to produce a perturbation of the acoustic waves specific to those which interact with bit # 2   632 . Similarly, perturbations which are caused due to substances that are analogous to biolayer Y  655  interacting with the receptor sites within biolayer Y  655  produce a perturbation of the acoustic waves specific to those which interact with bit # 4   634 . 
     The following Table 2 illustrates a correlation process for a 5-bit bi-phase Barker code of sequence (1, 0.75, 1, −1, 1) when the second bit is first perturbed, for this embodiment from a value of “1” to a value of “0.75”. This perturbation would be the result of a change within the biolayer X  650  which is positioned in proximity to Bit # 2   632 . 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Row # 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 −1 
                 1 
                 0.75 
                 1 
                   
                   
                   
                   
               
               
                 2 
                   
                 1 
                 −1 
                 1 
                 0.75 
                 1 
               
               
                 3 
                   
                   
                 1 
                 −1 
                 1 
                 0.75 
                 1 
               
               
                 4 
                   
                   
                   
                 −1 
                 1 
                 −1 
                 −0.75 
                 −1 
               
               
                 5 
                   
                   
                   
                   
                 1 
                 −1 
                 1 
                 0.75 
                 1 
               
               
                 6 
               
               
                 7 
                 1 
                 0 
                 1 
                 −0.25 
                 4.75 
                 −0.25 
                 1.25 
                 −0.25 
                 1 
               
               
                   
               
             
          
         
       
     
     One of the distinct features of this perturbed correlation function is that the changes occur near the middle and to the right hand side of the correlation function. 
     The following Table 3 illustrates a correlation process for a 5-bit bi-phase Barker code of sequence (1, 1, 1, −0.75, 1) when the fourth bit is perturbed, in this example from a value of “−1” to a value of “−0.75”. This perturbation would be the result of a change within the biolayer Y  655  which is positioned in proximity to Bit # 4   634 . 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Row # 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 7 
                 1 
                 −0.75 
                 1 
                 1 
                 1 
                   
                   
                   
                   
               
               
                 2 
                   
                 1 
                 −0.75 
                 1 
                 1 
                 1 
               
               
                 3 
                   
                   
                 1 
                 −0.75 
                 1 
                 1 
                 1 
               
               
                 4 
                   
                   
                   
                 −1 
                 0.75 
                 −1 
                 −1 
                 −1 
               
               
                 5 
                   
                   
                   
                   
                 1 
                 −0.75 
                 1 
                 0.75 
                 1 
               
               
                 6 
               
               
                 7 
                 1 
                 0.25 
                 1.25 
                 0.25 
                 4.75 
                 0.25 
                 1 
                 0 
                 1 
               
               
                   
               
             
          
         
       
     
     One of the distinct features of Table 3 is that the perturbed correlation function changes occur near the middle and to the left hand side of the correlation function, which is opposite to that of Table 2. 
     A comparison of a 5-bit Barker code correlation as a function of biolayer X  700  is shown in  FIG. 7(   a ). The graph outlining no perturbation on biolayer X  710  shows an unperturbed correlation function (solid line) as calculated from row  7  of Table 1, and a perturbed correlation function derived from a perturbation on biolayer X  720  (dashed line) as calculated from row  7  of Table 2. Similarly, a comparison of a 5-bit Barker code correlation as a function of biolayer Y  750  is shown in  FIG. 7(   b ). The graph outlining no perturbation on biolayer Y  760  shows an unperturbed correlation function (solid line) as calculated from row  7  of Table 1, and a perturbed correlation function derived from a perturbation on biolayer Y  770  (dashed line) as calculated from row  7  of Table 3. Another distinct feature of the four correlation functions  710 ,  720 ,  760  and  770  is that the extreme sidelobes never change in value, allowing for a built-in amplitude reference to compare other peak and sidelobe amplitude changes with. 
     An RFID biosensor correlation receiver  800  is shown in  FIG. 8 . A variety of RFID biosensor expanded signals  810  are inputted to a mixer  820  and, with the use of the VCO  825 , are down-converted for further correlation and processing  830 . The correlation and processing  830  separates out data signals depending upon the encoding used, such that data X  840  is a function of the substances which are analogous to biolayer X  650  and data Y  845  is a function of the substances which are analogous to biolayer Y  655 . 
     The above example describing a 5-bit bi-phase Barker coded RFID biosensor with multiple chemically orthogonal or semi-orthogonal biolayers  600 , the correlation as a function of biolayer X  700 , the correlation as a function of biolayer Y  750  and an RFID biosensor correlation receiver  800  can be extended by those skilled in the art to an n-dimensional chemically orthogonal or semi-orthogonal system capable of producing n-dimensional state-space mapping. 
     The previously described three methods of utilizing AW RFID biosensors to detect, differentiate and identify analogous chemical and biological substances are not limited to only the two-dimensional X and Y data for the construction of a state-space map, but can be expanded by those skilled in the art to n-dimensional configurations. One technique to include several chemically orthogonal and semi-orthogonal biolayers would be to combine the structures of the dual track RFID biosensor configuration  200  ( FIG. 2 ) with that of the RFID biosensor with multiple reflector arrays  400  ( FIG. 4 ). Expansion of the 5-bit bi-phase Barker coded RFID biosensor with multiple biolayers  600  may include but not be limited to the use of other Barker codes such as the 13 bit Barker code and combined Barker codes, pseudorandom (PN) codes, linear frequency modulation (FM) codes, non-linear FM codes and Frank codes. 
     Other embodiments and advantages of the invention will now be readily apparent to a person skilled in the art, the scope of the invention being defined in the appended claims.