Patent Publication Number: US-2022211288-A1

Title: Detection of an analyte using different combinations of detector elements that can transmit or receive

Description:
FIELD 
     This disclosure relates generally to apparatus, systems and methods of detecting an analyte via spectroscopic techniques using an analyte sensor that includes at least two detector elements that can transmit and receive electromagnetic waves and that can be used as either a transmit detector element or as a receive detector element. 
     BACKGROUND 
     There is interest in being able to detect and/or measure an analyte within a target. One example is measuring glucose in biological tissue. In the example of measuring glucose in a patient, current analyte measurement methods are invasive in that they perform the measurement on a bodily fluid such as blood for fingerstick or laboratory-based tests, or on fluid that is drawn from the patient often using an invasive transcutaneous device. There are non-invasive methods that claim to be able to perform glucose measurements in biological tissues. However, many of the non-invasive methods generally suffer from: lack of specificity to the analyte of interest, such as glucose; interference from temperature fluctuations; interference from skin compounds (i.e. sweat) and pigments; and complexity of placement, i.e. the sensing device resides on multiple locations on the patient&#39;s body. 
     SUMMARY 
     This disclosure relates generally to apparatus, systems and methods of detecting an analyte via spectroscopic techniques using non-optical frequencies such as in the radio or microwave frequency bands of the electromagnetic spectrum or optical frequencies in the visible range of the electromagnetic spectrum. In an embodiment, the techniques described herein can be used for non-invasive detection of an analyte. In another embodiment, the techniques described herein can be used for in vitro detection of an analyte. An analyte sensor described herein includes a detector array having at least two detector elements that can transmit or receive electromagnetic waves. In one embodiment, the detector array can have at least three of the detector elements which can be antennas or light emitting elements such as light emitting diodes. Any one or more of the detector elements in the detector array can be selectively controlled to function as a transmit detector element that functions to transmit a generated transmit signal in a radio or microwave frequency range or a visible light range of the electromagnetic spectrum into a target containing an analyte of interest. In addition, any one or more of the detector elements in the detector array can be selectively controlled to function as a receive detector element that functions to detect a response resulting from transmission of the transmit signal by the transmit detector element into the target. A scan routine can be implemented that includes a plurality of scans, where each scan uses a different combination of the detector elements to transmit a signal and detect a response. In the following description, a detector element, whether it is an antenna or a light emitting diode, that is controlled to function as a transmit detector element may simply be referred to as a transmit element, while a detector element, whether it is an antenna or a light emitting diode, that is controlled to function as a receive detector element may simply be referred to as a receive element. 
     When the detector elements in the detector array are antennas, the antennas, whether functioning as a transit antenna or as a receive antenna, are decoupled from one another which helps to improve the detection capability of the non-invasive analyte sensor. The decoupling between the antennas can be achieved using any one or more techniques that causes as much of the signal as possible that is transmitted by the transmit antenna to enter the target and that minimizes or even eliminates the amount of electromagnetic energy that is directly received by the receive antenna from the transmit antenna without traveling into the target. The decoupling can be achieved by one or more intentionally fabricated configurations and/or arrangements between the antennas that is sufficient to decouple the antennas from one another. In one non-limiting embodiment, the decoupling can be achieved by the antennas having intentionally different geometries from one another. Intentionally different geometries refers to different geometric configurations of the antennas that are intentional, and is distinct from differences in geometry of antennas that may occur by accident or unintentionally, for example due to manufacturing errors or tolerances. 
     Another technique to achieve decoupling of the antennas is to use an appropriate spacing between each antenna, depending upon factors such as output power, size of the antennas, frequency, and the presence of any shielding, so as to force a proportion of the electromagnetic lines of force of the transmit signal into the target so they reach the analyte, thereby minimizing or eliminating as much as possible direct receipt of electromagnetic energy by the receive antenna directly from the transmit antenna without traveling into the target. This technique helps to ensure that the response detected by the receive antenna is measuring the analyte and is not just the transmitted signal flowing directly from the transmit antenna to the receive antenna. In one embodiment, the sensor can use a first pair of transmit and receive antennas that have a first spacing therebetween, and a second pair of transmit and receive antennas that have a second spacing therebetween that differs from the first spacing. 
     The techniques described herein can be used to detect the presence of the analyte of interest, as well an amount of the analyte or a concentration of the analyte within the target. The techniques described herein can be used to detect a single analyte or more than one analyte. The target can be any target, for example human or non-human, animal or non-animal, biological or non-biological, that contains the analyte(s) that one may wish to detect. For example, the target can include, but is not limited to, human tissue, animal tissue, plant tissue, an inanimate object, soil, a fluid, genetic material, or a microbe. The analyte(s) can be any analyte, for example human or non-human, animal or non-animal, biological or non-biological, that one may wish to detect. For example, the analyte(s) can include, but is not limited to, one or more of blood glucose, blood alcohol, white blood cells, or luteinizing hormone. 
     In one embodiment, a non-invasive analyte sensor system described herein can include a detector array having at least two detector elements that can emit electromagnetic waves. A transmit circuit is selectively electrically connectable to any one or more of the at least two detector elements, with the transmit circuit being configured to generate at least one transmit signal to be transmitted into a target containing at least one analyte of interest by the one or more of the at least two detector elements the transmit circuit is electrically connected to. In addition, a receive circuit is selectively electrically connectable to any one or more of the at least two detector elements, and the receive circuit is configured to receive a response detected by the one or more of the at least two detector elements the receive circuit is electrically connected to resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In another embodiment, a non-invasive analyte sensor system can include an antenna array having at least two antennas. A transmit circuit is selectively electrically connectable to any one or more of the at least two antennas, where the transmit circuit is configured to generate at least one transmit signal to be transmitted into a target containing at least one analyte of interest by the one or more of the at least two antennas the transmit circuit is electrically connected to, and the at least one transmit signal is in a radio or microwave frequency range of the electromagnetic spectrum. In addition, a receive circuit is selectively electrically connectable to any one or more of the at least two antennas, where the receive circuit is configured to receive a response detected by the one or more of the at least two antennas the receive circuit is electrically connected to resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In one embodiment, the antenna array can be a decoupled antenna array and the at least two antennas can be decoupled from one another. The decoupling can be achieved by an intentional difference in geometry between the antennas. In another embodiment, decoupling can be achieved by arranging the antennas with an appropriate spacing therebetween that is sufficient to decouple the antennas. 
     In another embodiment described herein, a non-invasive analyte sensor system can include a sensor housing and a detector array attached to the sensor housing. The detector array has at least three decoupled elements each of which can act as an antenna, and the at least three decoupled elements have geometries that differ from one another. A transmit circuit is disposed in the sensor housing and is selectively electrically connectable to any one or more of the at least three elements, where the transmit circuit is configured to generate at least one transmit signal to be transmitted into a target containing at least one analyte of interest by the one or more of the at least three elements the transmit circuit is electrically connected to, and the at least one transmit signal is in a radio or microwave frequency range of the electromagnetic spectrum. In addition, a receive circuit is disposed in the sensor housing and is selectively electrically connectable to any one or more of the at least three elements, where the receive circuit is configured to receive a response detected by the one or more of the at least three elements the receive circuit is electrically connected to resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In still another embodiment described herein, a non-invasive analyte sensor system can include a sensor housing and an antenna array attached to the sensor housing. The antenna array has at least six decoupled antennas, where the at least six decoupled antennas have geometries that differ from one another, and the antenna array does not exceed 30.0 mm by 30.0 mm. A transmit circuit is disposed in the sensor housing and is selectively electrically connectable to any one or more of the at least six antennas. The transmit circuit is configured to generate at least one transmit signal to be transmitted into a target containing at least one analyte of interest by the one or more of the at least six antennas the transmit circuit is electrically connected to. The at least one transmit signal can have a plurality of different frequencies, and each one of the different frequencies is in a range of about 10 kHz to about 100 GHz. In addition, a receive circuit is disposed in the sensor housing and is selectively electrically connectable to any one or more of the at least six antennas. The receive circuit is configured to receive a response detected by the one or more of the at least six antennas the receive circuit is electrically connected to resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. One or more controllers disposed in the sensor housing controls electrical connection of the transmit circuit to the any one or more of the at least six antennas and also controls electrical connection of the receive circuit to the any one or more of the at least six antennas. In addition, a rechargeable battery is disposed in the sensor housing, with the rechargeable battery providing electrical power to power operation of the sensor system. 
     In another embodiment described herein, a method of non-invasive detection of an analyte includes, in a detector array having at least two detector elements, selectively connecting a transmit circuit to any one or more of the at least two detector elements of the detector array. At least one transmit signal is generated using the transmit circuit, with the at least one transmit signal being in a radio or microwave frequency or a visible light range of the electromagnetic spectrum. The at least one transmit signal is then transmitted into a target containing at least one analyte of interest using the one or more of the at least two detector elements connected to the transmit circuit. In addition, a receive circuit is selectively connected to a different one or more of the at least two detector elements of the detector array. The receive circuit and the different one or more of the at least two detector elements of the detector array are used to detect a response resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In another embodiment described herein, a method of non-invasive detection of an analyte includes, in a detector array having at least three decoupled elements each of which can act as an antenna and where the at least three decoupled elements have geometries that differ from one another, selectively connecting a transmit circuit to one element of the at least three elements of the antenna array. At least one transmit signal is generated using the transmit circuit, with the at least transmit signal having at least two different frequencies each of which falls within a range of between about 10 kHz to about 100 GHz. The at least one transmit signal is transmitted into a target containing at least one analyte of interest using the one element of the at least three elements connected to the transmit circuit. In addition, a receive circuit is selectively connected to one different element of the at least three elements of the detector array. The receive circuit and the one different element of the at least three elements of the detector array are used to detect a response resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In another embodiment described herein, a method of non-invasive detection of an analyte includes implementing a scan routine using a detector array that is electrically connected to a transmit circuit and electrically connected to a receive circuit, the detector array having at least three detector element. The scan routine includes, in a first scan, using a first combination of two or more of the at least three detector elements to transmit a first transmit signal that is in a radio or microwave frequency or visible range of the electromagnetic spectrum into a target containing at least one analyte of interest and to detect a response resulting from transmission of the first transmit signal into the target containing the at least one analyte of interest. In a second scan, a second combination of two or more of the at least three detector elements, different from the first combination, is used to transmit a second transmit signal that is in a radio or microwave frequency or visible range of the electromagnetic spectrum into the target containing the at least one analyte of interest and to detect a response resulting from transmission of the second transmit signal into the target containing the at least one analyte of interest. 
     In still another embodiment described herein, a method of non-invasive detection of an analyte includes implementing a scan routine using an antenna array that is electrically connected to a transmit circuit and electrically connected to a receive circuit, with the antenna array having at least three antennas that have geometries that differ from one another and the at least three antennas are decoupled from one another. The scan routine includes conducting a plurality of scans, with each scan using a different combination of two or more of the at least three antennas to transmit signals that are in a radio or microwave frequency range of the electromagnetic spectrum into a target containing at least one analyte of interest and to detect responses resulting from transmission of the signals into the target containing the at least one analyte of interest. 
    
    
     
       DRAWINGS 
       References are made to the accompanying drawings that form a part of this disclosure, and which illustrate embodiments in which the apparatus, systems and methods described in this specification can be practiced. 
         FIG. 1  is a schematic depiction of a non-invasive analyte sensor system with a non-invasive analyte sensor relative to a target according to an embodiment. 
         FIGS. 2A-C  illustrate different example orientations of antenna arrays that can be used in the sensor system described herein. 
         FIGS. 3A-3I  illustrate different examples of transmit and receive antennas with different geometries. 
         FIGS. 4A, 4B, 4C and 4D  illustrate additional examples of different shapes that the ends of the transmit and receive antennas can have. 
         FIG. 5  is a schematic depiction of a sensor device according to an embodiment. 
         FIG. 6  is a flowchart of a method for detecting an analyte according to an embodiment. 
         FIG. 7  is a flowchart of analysis of a response according to an embodiment. 
         FIG. 8  is a schematic depiction of another embodiment of a non-invasive analyte sensor system with an antenna array having two antennas and configured so that either antenna can be used as a transmit antenna or as a receive antenna. 
         FIG. 9  is a schematic depiction of another embodiment of a non-invasive analyte sensor system with an antenna array having three antennas and configured so that either antenna can be used as a transmit antenna or as a receive antenna. 
         FIG. 10  is a schematic depiction of another embodiment of a non-invasive analyte sensor system with an antenna array having six antennas and configured so that either antenna can be used as a transmit antenna or as a receive antenna. 
         FIG. 11  depicts an example of results from a scan routine. 
         FIG. 12  depicts a system that includes the analyte sensor and an external device in communication with the analyte sensor, with the system including a notification device. 
         FIGS. 13-19  are top views of additional examples of antenna arrays and antenna configurations that can be used in the embodiments described herein. 
         FIG. 20  is a schematic depiction of a portion of another embodiment of a non-invasive analyte sensor system with a non-invasive analyte sensor that uses electromagnetic energy in the form of light to perform non-invasive analyte sensing described herein. 
         FIG. 21A  is a side view of the non-invasive analyte sensor of  FIG. 20  using one example combination of light emitter and light detector. 
         FIG. 21B  is another side view of the non-invasive analyte sensor of  FIG. 20  using a second example combination of light emitter and light detector. 
     
    
    
     Like reference numbers represent like parts throughout. 
     DETAILED DESCRIPTION 
     The following is a detailed description of apparatus, systems and methods of non-invasively detecting an analyte via spectroscopic techniques using non-optical frequencies such as in the radio or microwave frequency bands of the electromagnetic spectrum or optical frequencies in the visible range of the electromagnetic spectrum. A non-invasive analyte sensor includes at least one detector element that functions as a transmit detector element (which may also be referred to as a transmit element) and that functions to transmit a generated transmit signal that is in a radio or microwave frequency or visible range of the electromagnetic spectrum into a target containing an analyte of interest, and at least one detector element that functions as a receive detector element (which may also be referred to as a receive element) and that functions to detect a response resulting from transmission of the transmit signal by the transmit detector element into the target. When the detector elements are antennas, transmit antenna and the receive antenna are decoupled from one another which improves the detection performance of the sensor. 
     The following description together with  FIGS. 1-19  will initially describe the detector elements as being antennas and the detector array that includes the antenna as an antenna array. Later in the following description, together with  FIGS. 20-21A -B, the detector elements will be described as being light emitting devices such as light emitting diodes (LEDs) and the detector array that includes the LED as an LED array. 
     The transmit antenna and the receive antenna can be located near the target and operated as further described herein to assist in detecting at least one analyte in the target. The transmit antenna transmits a signal, which has at least two frequencies in the radio or microwave frequency range, toward and into the target. The signal with the at least two frequencies can be formed by separate signal portions, each having a discrete frequency, that are transmitted separately at separate times at each frequency. In another embodiment, the signal with the at least two frequencies may be part of a complex signal that includes a plurality of frequencies including the at least two frequencies. The complex signal can be generated by blending or multiplexing multiple signals together followed by transmitting the complex signal whereby the plurality of frequencies are transmitted at the same time. One possible technique for generating the complex signal includes, but is not limited to, using an inverse Fourier transformation technique. The receive antenna detects a response resulting from transmission of the signal by the transmit antenna into the target containing the at least one analyte of interest. 
     The transmit antenna and the receive antenna are decoupled (which may also be referred to as detuned or the like) from one another. Decoupling refers to intentionally fabricating the configuration and/or arrangement of the transmit antenna and the receive antenna to minimize direct communication between the transmit antenna and the receive antenna, preferably absent shielding. Shielding between the transmit antenna and the receive antenna can be utilized. However, the transmit antenna and the receive antenna are decoupled even without the presence of shielding. 
     The signal(s) detected by the receive antenna can be analyzed to detect the analyte based on the intensity of the received signal(s) and reductions in intensity at one or more frequencies where the analyte absorbs the transmitted signal. An example of detecting an analyte using a non-invasive spectroscopy sensor operating in the radio or microwave frequency range of the electromagnetic spectrum is described in WO 2019/217461, the entire contents of which are incorporated herein by reference. The signal(s) detected by the receive antenna can be complex signals including a plurality of signal components, each signal component being at a different frequency. In an embodiment, the detected complex signals can be decomposed into the signal components at each of the different frequencies, for example through a Fourier transformation. In an embodiment, the complex signal detected by the receive antenna can be analyzed as a whole (i.e. without demultiplexing the complex signal) to detect the analyte as long as the detected signal provides enough information to make the analyte detection. In addition, the signal(s) detected by the receive antenna can be separate signal portions, each having a discrete frequency. 
     In one embodiment, the sensor described herein can be used to detect the presence of at least one analyte in a target. In another embodiment, the sensor described herein can detect an amount or a concentration of the at least one analyte in the target. The target can be any target containing at least one analyte of interest that one may wish to detect. The target can be human or non-human, animal or non-animal, biological or non-biological. For example, the target can include, but is not limited to, human tissue, animal tissue, plant tissue, an inanimate object, soil, a fluid, genetic material, or a microbe. Non-limiting examples of targets include, but are not limited to, a fluid, for example blood, interstitial fluid, cerebral spinal fluid, lymph fluid or urine, human tissue, animal tissue, plant tissue, an inanimate object, soil, genetic material, or a microbe. 
     The analyte(s) can be any analyte that one may wish to detect. The analyte can be human or non-human, animal or non-animal, biological or non-biological. For example, the analyte(s) can include, but is not limited to, one or more of blood glucose, blood alcohol, white blood cells, or luteinizing hormone. The analyte(s) can include, but is not limited to, a chemical, a combination of chemicals, a virus, a bacteria, or the like. The analyte can be a chemical included in another medium, with non-limiting examples of such media including a fluid containing the at least one analyte, for example blood, interstitial fluid, cerebral spinal fluid, lymph fluid or urine, human tissue, animal tissue, plant tissue, an inanimate object, soil, genetic material, or a microbe. The analyte(s) may also be a non-human, non-biological particle such as a mineral or a contaminant. 
     The analyte(s) can include, for example, naturally occurring substances, artificial substances, metabolites, and/or reaction products. As non-limiting examples, the at least one analyte can include, but is not limited to, insulin, acarboxyprothrombin; acylcarnitine; adenine phosphoribosyl transferase; adenosine deaminase; albumin; alpha-fetoprotein; amino acid profiles (arginine (Krebs cycle), histidine/urocanic acid, homocysteine, phenylalanine/tyrosine, tryptophan); andrenostenedione; antipyrine; arabinitol enantiomers; arginase; benzoylecgonine (cocaine); biotinidase; biopterin; c-reactive protein; carnitine; pro-BNP; BNP; troponin; carnosinase; CD4; ceruloplasmin; chenodeoxycholic acid; chloroquine; cholesterol; cholinesterase; conjugated 1-β hydroxy-cholic acid; cortisol; creatine kinase; creatine kinase MM isoenzyme; cyclosporin A; d-penicillamine; de-ethylchloroquine; dehydroepiandrosterone sulfate; DNA (acetylator polymorphism, alcohol dehydrogenase, alpha 1-antitrypsin, cystic fibrosis, Duchenne/Becker muscular dystrophy, analyte-6-phosphate dehydrogenase, hemoglobin A, hemoglobin S, hemoglobin C, hemoglobin D, hemoglobin E, hemoglobin F, D-Punjab, beta-thalassemia, hepatitis B virus, HCMV, HIV-1, HTLV-1, Leber hereditary optic neuropathy, MCAD, RNA, PKU,  Plasmodium vivax , sexual differentiation, 21-deoxycortisol); desbutylhalofantrine; dihydropteridine reductase; diptheria/tetanus antitoxin; erythrocyte arginase; erythrocyte protoporphyrin; esterase D; fatty acids/acylglycines; free β-human chorionic gonadotropin; free erythrocyte porphyrin; free thyroxine (FT4); free tri-iodothyronine (FT3); fumarylacetoacetase; galactose/gal-1-phosphate; galactose-1-phosphate uridyltransferase; gentamicin; analyte-6-phosphate dehydrogenase; glutathione; glutathione perioxidase; glycocholic acid; glycosylated hemoglobin; halofantrine; hemoglobin variants; hexosaminidase A; human erythrocyte carbonic anhydrase I; 17-alpha-hydroxyprogesterone; hypoxanthine phosphoribosyl transferase; immunoreactive trypsin; lactate; lead; lipoproteins ((a), B/A-1, β); lysozyme; mefloquine; netilmicin; phenobarbitone; phenytoin; phytanic/pristanic acid; progesterone; prolactin; prolidase; purine nucleoside phosphorylase; quinine; reverse tri-iodothyronine (rT3); selenium; serum pancreatic lipase; sissomicin; somatomedin C; specific antibodies (adenovirus, anti-nuclear antibody, anti-zeta antibody, arbovirus, Aujeszky&#39;s disease virus, dengue virus,  Dracincilus medinensis, Echinococcus granulosus, Enamoeba histolytica , enterovirus,  Giardia duodenalisa, Helicobacter pylori , hepatitis B virus, herpes virus, HIV-1, IgE (atopic disease), influenza virus,  Leishmania donovani , leptospira, measles/mumps/rubella,  Mycobacterium leprae, Mycoplasma pneumoniae , Myoglobin,  Onchocerca volvulus , parainfluenza virus,  Plasmodium falciparum , polio virus,  Pseudomonas aeruginosa , respiratory syncytial virus, rickettsia (scrub typhus),  Schistosoma mansoni, Toxoplasma gondii, Trepenoma pallidum, Trypanosona cruzi /rangeli, vesicular  stomatis  virus,  Wuchereria bancrofti , yellow fever virus); specific antigens (hepatitis B virus, HIV-1); succinylacetone; sulfadoxine; theophylline; thyrotropin (TSH); thyroxine (T4); thyroxine-binding globulin; trace elements; transferrin; UDP-galactose-4-epimerase; urea; uroporphyrinogen I synthase; vitamin A; white blood cells; and zinc protoporphyrin. 
     The analyte(s) can also include one or more chemicals introduced into the target. The analyte(s) can include a marker such as a contrast agent, a radioisotope, or other chemical agent. The analyte(s) can include a fluorocarbon-based synthetic blood. The analyte(s) can include a drug or pharmaceutical composition, with non-limiting examples including ethanol; cannabis (marijuana, tetrahydrocannabinol, hashish); inhalants (nitrous oxide, amyl nitrite, butyl nitrite, chlorohydrocarbons, hydrocarbons); cocaine (crack cocaine); stimulants (amphetamines, methamphetamines, Ritalin, Cylert, Preludin, Didrex, PreState, Voranil, Sandrex, Plegine); depressants (barbiturates, methaqualone, tranquilizers such as Valium, Librium, Miltown, Serax, Equanil, Tranxene); hallucinogens (phencyclidine, lysergic acid, mescaline, peyote, psilocybin); narcotics (heroin, codeine, morphine, opium, meperidine, Percocet, Percodan, Tussionex, Fentanyl, Darvon, Talwin, Lomotil); designer drugs (analogs of fentanyl, meperidine, amphetamines, methamphetamines, and phencyclidine, for example, Ecstasy); anabolic steroids; and nicotine. The analyte(s) can include other drugs or pharmaceutical compositions. The analyte(s) can include neurochemicals or other chemicals generated within the body, such as, for example, ascorbic acid, uric acid, dopamine, noradrenaline, 3-methoxytyramine (3MT), 3,4-Dihydroxyphenylacetic acid (DOPAC), Homovanillic acid (HVA), 5-Hydroxytryptamine (5HT), and 5-Hydroxyindoleacetic acid (FHIAA). 
     Referring now to  FIG. 1 , an embodiment of a non-invasive analyte sensor system with a non-invasive analyte sensor  5  is illustrated. The sensor  5  is depicted relative to a target  7  that contains an analyte of interest  9 . In this example, the sensor  5  is depicted as including an antenna array that includes a transmit antenna/element  11  (hereinafter “transmit antenna  11 ”) and a receive antenna/element  13  (hereinafter “receive antenna  13 ”). The sensor  5  further includes a transmit circuit  15 , a receive circuit  17 , and a controller  19 . As discussed further below, the sensor  5  can also include a power supply, such as a battery (not shown in  FIG. 1 ). In some embodiments, power can be provided from mains power, for example by plugging the sensor  5  into a wall socket via a cord connected to the sensor  5 . 
     The transmit antenna  11  is positioned, arranged and configured to transmit a signal  21  that is the radio frequency (RF) or microwave range of the electromagnetic spectrum into the target  7 . The transmit antenna  11  can be an electrode or any other suitable transmitter of electromagnetic signals in the radio frequency (RF) or microwave range. The transmit antenna  11  can have any arrangement and orientation relative to the target  7  that is sufficient to allow the analyte sensing to take place. In one non-limiting embodiment, the transmit antenna  11  can be arranged to face in a direction that is substantially toward the target  7 . 
     The signal  21  transmitted by the transmit antenna  11  is generated by the transmit circuit  15  which is electrically connectable to the transmit antenna  11 . The transmit circuit  15  can have any configuration that is suitable to generate a transmit signal to be transmitted by the transmit antenna  11 . Transmit circuits for generating transmit signals in the RF or microwave frequency range are well known in the art. In one embodiment, the transmit circuit  15  can include, for example, a connection to a power source, a frequency generator, and optionally filters, amplifiers or any other suitable elements for a circuit generating an RF or microwave frequency electromagnetic signal. In an embodiment, the signal generated by the transmit circuit  15  can have at least two discrete frequencies (i.e. a plurality of discrete frequencies), each of which is in the range from about 10 kHz to about 100 GHz. In another embodiment, each of the at least two discrete frequencies can be in a range from about 300 MHz to about 6000 MHz. In an embodiment, the transmit circuit  15  can be configured to sweep through a range of frequencies that are within the range of about 10 kHz to about 100 GHz, or in another embodiment a range of about 300 MHz to about 6000 MHz. In an embodiment, the transmit circuit  15  can be configured to produce a complex transmit signal, the complex signal including a plurality of signal components, each of the signal components having a different frequency. The complex signal can be generated by blending or multiplexing multiple signals together followed by transmitting the complex signal whereby the plurality of frequencies are transmitted at the same time. 
     The receive antenna  13  is positioned, arranged, and configured to detect one or more electromagnetic response signals  23  that result from the transmission of the transmit signal  21  by the transmit antenna  11  into the target  7  and impinging on the analyte  9 . The receive antenna  13  can be an electrode or any other suitable receiver of electromagnetic signals in the radio frequency (RF) or microwave range. In an embodiment, the receive antenna  13  is configured to detect electromagnetic signals having at least two frequencies, each of which is in the range from about 10 kHz to about 100 GHz, or in another embodiment a range from about 300 MHz to about 6000 MHz. The receive antenna  13  can have any arrangement and orientation relative to the target  7  that is sufficient to allow detection of the response signal(s)  23  to allow the analyte sensing to take place. In one non-limiting embodiment, the receive antenna  13  can be arranged to face in a direction that is substantially toward the target  7 . 
     The receive circuit  17  is electrically connectable to the receive antenna  13  and conveys the received response from the receive antenna  13  to the controller  19 . The receive circuit  17  can have any configuration that is suitable for interfacing with the receive antenna  13  to convert the electromagnetic energy detected by the receive antenna  13  into one or more signals reflective of the response signal(s)  23 . The construction of receive circuits are well known in the art. The receive circuit  17  can be configured to condition the signal(s) prior to providing the signal(s) to the controller  19 , for example through amplifying the signal(s), filtering the signal(s), or the like. Accordingly, the receive circuit  17  may include filters, amplifiers, or any other suitable components for conditioning the signal(s) provided to the controller  19 . In an embodiment, at least one of the receive circuit  17  or the controller  19  can be configured to decompose or demultiplex a complex signal, detected by the receive antenna  13 , including a plurality of signal components each at different frequencies into each of the constituent signal components. In an embodiment, decomposing the complex signal can include applying a Fourier transform to the detected complex signal. However, decomposing or demultiplexing a received complex signal is optional. Instead, in an embodiment, the complex signal detected by the receive antenna can be analyzed as a whole (i.e. without demultiplexing the complex signal) to detect the analyte as long as the detected signal provides enough information to make the analyte detection. 
     The controller  19  controls the operation of the sensor  5 . The controller  19 , for example, can direct the transmit circuit  15  to generate a transmit signal to be transmitted by the transmit antenna  11 . The controller  19  further receives signals from the receive circuit  17 . The controller  19  can optionally process the signals from the receive circuit  17  to detect the analyte(s)  9  in the target  7 . In one embodiment, the controller  19  may optionally be in communication with at least one external device  25  such as a user device and/or a remote server  27 , for example through one or more wireless connections such as Bluetooth, wireless data connections such a 4G, 5G, LTE or the like, or Wi-Fi. If provided, the external device  25  and/or remote server  27  may process (or further process) the signals that the controller  19  receives from the receive circuit  17 , for example to detect the analyte(s)  9 . If provided, the external device  25  may be used to provide communication between the sensor  5  and the remote server  27 , for example using a wired data connection or via a wireless data connection or Wi-Fi of the external device  25  to provide the connection to the remote server  27 . 
     With continued reference to  FIG. 1 , the sensor  5  may include a sensor housing  29  (shown in dashed lines) that defines an interior space  31 . Components of the sensor  5  may be attached to and/or disposed within the housing  29 . For example, the transmit antenna  11  and the receive antenna  13  are attached to the housing  29 . In some embodiments, the antennas  11 ,  13  may be entirely or partially within the interior space  31  of the housing  29 . In some embodiments, the antennas  11 ,  13  may be attached to the housing  29  but at least partially or fully located outside the interior space  31 . In some embodiments, the transmit circuit  15 , the receive circuit  17  and the controller  19  are attached to the housing  29  and disposed entirely within the sensor housing  29 . 
     The receive antenna  13  is decoupled or detuned with respect to the transmit antenna  11  such that electromagnetic coupling between the transmit antenna  11  and the receive antenna  13  is reduced. The decoupling of the transmit antenna  11  and the receive antenna  13  increases the portion of the signal(s) detected by the receive antenna  13  that is the response signal(s)  23  from the target  7 , and minimizes direct receipt of the transmitted signal  21  by the receive antenna  13 . The decoupling of the transmit antenna  11  and the receive antenna  13  results in transmission from the transmit antenna  11  to the receive antenna  13  having a reduced forward gain (SM) and an increased reflection at output (S 22 ) compared to antenna systems having coupled transmit and receive antennas. 
     In an embodiment, coupling between the transmit antenna  11  and the receive antenna  13  is 95% or less. In another embodiment, coupling between the transmit antenna  11  and the receive antenna  13  is 90% or less. In another embodiment, coupling between the transmit antenna  11  and the receive antenna  13  is 85% or less. In another embodiment, coupling between the transmit antenna  11  and the receive antenna  13  is 75% or less. 
     Any technique for reducing coupling between the transmit antenna  11  and the receive antenna  13  can be used. For example, the decoupling between the transmit antenna  11  and the receive antenna  13  can be achieved by one or more intentionally fabricated configurations and/or arrangements between the transmit antenna  11  and the receive antenna  13  that is sufficient to decouple the transmit antenna  11  and the receive antenna  13  from one another. 
     For example, in one embodiment described further below, the decoupling of the transmit antenna  11  and the receive antenna  13  can be achieved by intentionally configuring the transmit antenna  11  and the receive antenna  13  to have different geometries from one another. Intentionally different geometries refers to different geometric configurations of the transmit and receive antennas  11 ,  13  that are intentional. Intentional differences in geometry are distinct from differences in geometry of transmit and receive antennas that may occur by accident or unintentionally, for example due to manufacturing errors or tolerances. 
     Another technique to achieve decoupling of the transmit antenna  11  and the receive antenna  13  is to provide appropriate spacing between each antenna  11 ,  13  that is sufficient to decouple the antennas  11 ,  13  and force a proportion of the electromagnetic lines of force of the transmitted signal  21  into the target  7  thereby minimizing or eliminating as much as possible direct receipt of electromagnetic energy by the receive antenna  13  directly from the transmit antenna  11  without traveling into the target  7 . The appropriate spacing between each antenna  11 ,  13  can be determined based upon factors that include, but are not limited to, the output power of the signal from the transmit antenna  11 , the size of the antennas  11 ,  13 , the frequency or frequencies of the transmitted signal, and the presence of any shielding between the antennas. This technique helps to ensure that the response detected by the receive antenna  13  is measuring the analyte  9  and is not just the transmitted signal  21  flowing directly from the transmit antenna  11  to the receive antenna  13 . In some embodiments, the appropriate spacing between the antennas  11 ,  13  can be used together with the intentional difference in geometries of the antennas  11 ,  13  to achieve decoupling. 
     In one embodiment, the transmit signal that is transmitted by the transmit antenna  11  can have at least two different frequencies, for example upwards of 7 to 12 different and discrete frequencies. In another embodiment, the transmit signal can be a series of discrete, separate signals with each separate signal having a single frequency or multiple different frequencies. 
     In one embodiment, the transmit signal (or each of the transmit signals) can be transmitted over a transmit time that is less than, equal to, or greater than about 300 ms. In another embodiment, the transmit time can be than, equal to, or greater than about 200 ms. In still another embodiment, the transmit time can be less than, equal to, or greater than about 30 ms. The transmit time could also have a magnitude that is measured in seconds, for example 1 second, 5 seconds, 10 seconds, or more. In an embodiment, the same transmit signal can be transmitted multiple times, and then the transmit time can be averaged. In another embodiment, the transmit signal (or each of the transmit signals) can be transmitted with a duty cycle that is less than or equal to about 50%. 
       FIGS. 2A-2C  illustrate examples of antenna arrays  33  that can be used in the sensor system  5  and how the antenna arrays  33  can be oriented. Many orientations of the antenna arrays  33  are possible, and any orientation can be used as long as the sensor  5  can perform its primary function of sensing the analyte  9 . 
     In  FIG. 2A , the antenna array  33  includes the transmit antenna  11  and the receive antenna  13  disposed on a substrate  35  which may be substantially planar. This example depicts the array  33  disposed substantially in an X-Y plane. In this example, dimensions of the antennas  11 ,  13  in the X and Y-axis directions can be considered lateral dimensions, while a dimension of the antennas  11 ,  13  in the Z-axis direction can be considered a thickness dimension. In this example, each of the antennas  11 ,  13  has at least one lateral dimension (measured in the X-axis direction and/or in the Y-axis direction) that is greater than the thickness dimension thereof (in the Z-axis direction). In other words, the transmit antenna  11  and the receive antenna  13  are each relatively flat or of relatively small thickness in the Z-axis direction compared to at least one other lateral dimension measured in the X-axis direction and/or in the Y-axis direction. 
     In use of the embodiment in  FIG. 2A , the sensor and the array  33  may be positioned relative to the target  7  such that the target  7  is below the array  33  in the Z-axis direction or above the array  33  in the Z-axis direction whereby one of the faces of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned to the left or right sides of the array  33  in the X-axis direction whereby one of the ends of each one of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned to the sides of the array  33  in the Y-axis direction whereby one of the sides of each one of the antennas  11 ,  13  face toward the target  7 . 
     The sensor  5  can also be provided with one or more additional antenna arrays in addition the antenna array  33 . For example,  FIG. 2A  also depicts an optional second antenna array  33   a  that includes the transmit antenna  11  and the receive antenna  13  disposed on a substrate  35   a  which may be substantially planar. Like the array  33 , the array  33   a  may also be disposed substantially in the X-Y plane, with the arrays  33 ,  33   a  spaced from one another in the X-axis direction. 
     In  FIG. 2B , the antenna array  33  is depicted as being disposed substantially in the Y-Z plane. In this example, dimensions of the antennas  11 ,  13  in the Y and Z-axis directions can be considered lateral dimensions, while a dimension of the antennas  11 ,  13  in the X-axis direction can be considered a thickness dimension. In this example, each of the antennas  11 ,  13  has at least one lateral dimension (measured in the Y-axis direction and/or in the Z-axis direction) that is greater than the thickness dimension thereof (in the X-axis direction). In other words, the transmit antenna  11  and the receive antenna  13  are each relatively flat or of relatively small thickness in the X-axis direction compared to at least one other lateral dimension measured in the Y-axis direction and/or in the Z-axis direction. 
     In use of the embodiment in  FIG. 2B , the sensor and the array  33  may be positioned relative to the target  7  such that the target  7  is below the array  33  in the Z-axis direction or above the array  33  in the Z-axis direction whereby one of the ends of each one of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned in front of or behind the array  33  in the X-axis direction whereby one of the faces of each one of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned to one of the sides of the array  33  in the Y-axis direction whereby one of the sides of each one of the antennas  11 ,  13  face toward the target  7 . 
     In  FIG. 2C , the antenna array  33  is depicted as being disposed substantially in the X-Z plane. In this example, dimensions of the antennas  11 ,  13  in the X and Z-axis directions can be considered lateral dimensions, while a dimension of the antennas  11 ,  13  in the Y-axis direction can be considered a thickness dimension. In this example, each of the antennas  11 ,  13  has at least one lateral dimension (measured in the X-axis direction and/or in the Z-axis direction) that is greater than the thickness dimension thereof (in the Y-axis direction). In other words, the transmit antenna  11  and the receive antenna  13  are each relatively flat or of relatively small thickness in the Y-axis direction compared to at least one other lateral dimension measured in the X-axis direction and/or in the Z-axis direction. 
     In use of the embodiment in  FIG. 2C , the sensor and the array  33  may be positioned relative to the target  7  such that the target  7  is below the array  33  in the Z-axis direction or above the array  33  in the Z-axis direction whereby one of the ends of each one of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned to the left or right sides of the array  33  in the X-axis direction whereby one of the sides of each one of the antennas  11 ,  13  face toward the target  7 . Alternatively, the target  7  can be positioned in front of or in back of the array  33  in the Y-axis direction whereby one of the faces of each one of the antennas  11 ,  13  face toward the target  7 . 
     The arrays  33 ,  33   a  in  FIGS. 2A-2C  need not be oriented entirely within a plane such as the X-Y plane, the Y-Z plane or the X-Z plane. Instead, the arrays  33 ,  33   a  can be disposed at angles to the X-Y plane, the Y-Z plane and the X-Z plane. 
     Decoupling Antennas Using Differences in Antenna Geometries 
     As mentioned above, one technique for decoupling the transmit antenna  11  from the receive antenna  13  is to intentionally configure the transmit antenna  11  and the receive antenna  13  to have intentionally different geometries. Intentionally different geometries refers to differences in geometric configurations of the transmit and receive antennas  11 ,  13  that are intentional, and is distinct from differences in geometry of the transmit and receive antennas  11 ,  13  that may occur by accident or unintentionally, for example due to manufacturing errors or tolerances when fabricating the antennas  11 ,  13 . 
     The different geometries of the antennas  11 ,  13  may manifest itself, and may be described, in a number of different ways. For example, in a plan view of each of the antennas  11 ,  13  (such as in  FIGS. 3A-I ), the shapes of the perimeter edges of the antennas  11 ,  13  may be different from one another. The different geometries may result in the antennas  11 ,  13  having different surface areas in plan view. The different geometries may result in the antennas  11 ,  13  having different aspect ratios in plan view (i.e. a ratio of their sizes in different dimensions; for example, as discussed in further detail below, the ratio of the length divided by the width of the antenna  11  may be different than the ratio of the length divided by the width for the antenna  13 ). In some embodiments, the different geometries may result in the antennas  11 ,  13  having any combination of different perimeter edge shapes in plan view, different surface areas in plan view, and/or different aspect ratios. In some embodiments, the antennas  11 ,  13  may have one or more holes formed therein (see  FIG. 2B ) within the perimeter edge boundary, or one or more notches formed in the perimeter edge (see  FIG. 2B ). 
     So as used herein, a difference in geometry or a difference in geometrical shape of the antennas  11 ,  13  refers to any intentional difference in the figure, length, width, size, shape, area closed by a boundary (i.e. the perimeter edge), etc. when the respective antenna  11 ,  13  is viewed in a plan view. 
     The antennas  11 ,  13  can have any configuration and can be formed from any suitable material that allows them to perform the functions of the antennas  11 ,  13  as described herein. In one embodiment, the antennas  11 ,  13  can be formed by strips of material. A strip of material can include a configuration where the strip has at least one lateral dimension thereof greater than a thickness dimension thereof when the antenna is viewed in a plan view (in other words, the strip is relatively flat or of relatively small thickness compared to at least one other lateral dimension, such as length or width when the antenna is viewed in a plan view as in  FIGS. 3A-I ). A strip of material can include a wire. The antennas  11 ,  13  can be formed from any suitable conductive material(s) including metals and conductive non-metallic materials. Examples of metals that can be used include, but are not limited to, copper or gold. Another example of a material that can be used is non-metallic materials that are doped with metallic material to make the non-metallic material conductive. 
     In  FIGS. 2A-2C , the antennas  11 ,  13  within each one of the arrays  33 ,  33   a  have different geometries from one another. In addition,  FIGS. 3A-I  illustrate plan views of additional examples of the antennas  11 ,  13  having different geometries from one another. The examples in  FIGS. 2A-2C and 3A -I are not exhaustive and many different configurations are possible. 
     With reference initially to  FIG. 3A , a plan view of an antenna array having two antennas with different geometries is illustrated. In this example (as well as for the examples in  FIGS. 2A-2C and 3B-3I ), for sake of convenience in describing the concepts herein, one antenna is labeled as the transmit antenna  11  and the other antenna is labeled as the receive antenna  13 . However, the antenna labeled as the transmit antenna  11  could be the receive antenna  13 , while the antenna labeled as the receive antenna  13  could be the transmit antenna  11 . Each of the antennas  11 ,  13  are disposed on the substrate  35  having a planar surface  37 . 
     The antennas  11 ,  13  can be formed as linear strips or traces on the surface  37 . In this example, the antenna  11  is generally U-shaped and has a first linear leg  40   a , a second linear leg  40   b  that extends perpendicular to the first leg  40   a , and a third linear leg  40   c  that extends parallel to the leg  40   a . Likewise, the antenna  13  is formed by a single leg that extends parallel to, and between, the legs  40   a ,  40   c.    
     In the example depicted in  FIG. 3A , each one of the antennas  11 ,  13  has at least one lateral dimension that is greater than a thickness dimension thereof (in  FIG. 3A , the thickness dimension would extend into/from the page when viewing  FIG. 3A ). For example, the leg  40   a  of the antenna  11  extends in one direction (i.e. a lateral dimension) an extent that is greater than a thickness dimension of the leg  40   a  extending into or out of the page; the leg  40   b  of the antenna  11  extends in a direction (i.e. a lateral dimension) an extent that is greater than a thickness dimension of the leg  40   b  extending into or out of the page; and the leg  40   c  of the antenna  11  extends in one direction (i.e. a lateral dimension) an extent that is greater than a thickness dimension of the leg  40   c  extending into or out of the page. Likewise, the antenna  13  extends in one direction (i.e. a lateral dimension) an extent that is greater than a thickness dimension of the antenna  13  extending into or out of the page. 
     The antennas  11 ,  13  also differ in geometry from one another in that the total linear length of the antenna  1 I (determined by adding the individual lengths L 1 , L 2 , L 3  of the legs  40   a - c  together) when viewed in plan view is greater than the length L 13  of the antenna  13  when viewed in plan view. 
       FIG. 3B  illustrates another plan view of an antenna array having two antennas with different geometries. In this example, the antennas  11 ,  13  are illustrated as substantially linear strips each with a lateral length L 11 , L 13 , a lateral width W 11 , W 13 , and a perimeter edge E 11 , E 13 . The perimeter edges E 11 , E 13  extend around the entire periphery of the antennas  11 ,  13  and bound an area in plan view. In this example, the lateral length L 11 , L 13  and/or the lateral width W 11 , W 13  is greater than a thickness dimension of the antennas  11 ,  13  extending into/from the page when viewing  FIG. 3B . In this example, the antennas  11 ,  13  differ in geometry from one another in that the shapes of the ends of the antennas  11 ,  13  differ from one another. For example, when viewing  FIG. 3B , the right end  42  of the antenna  11  has a different shape than the right end  44  of the antenna  13 . Similarly, the left end  46  of the antenna  11  may have a similar shape as the right end  42 , but differs from the left end  48  of the antenna  13  which may have a similar shape as the right end  44 . It is also possible that the lateral lengths L 11 , L 13  and/or the lateral widths W 11 , W 13  of the antennas  11 ,  13  could differ from one another. 
       FIG. 3C  illustrates another plan view of an antenna array having two antennas with different geometries that is somewhat similar to  FIG. 3B . In this example, the antennas  11 ,  13  are illustrated as substantially linear strips each with the lateral length L 11 , L 13 , the lateral width W 11 , W 13 , and the perimeter edge E 11 , E 13 . The perimeter edges E 11 , E 13  extend around the entire periphery of the antennas  11 ,  13  and bound an area in plan view. In this example, the lateral length L 11 , L 13  and/or the lateral width W 11 , W 13  is greater than a thickness dimension of the antennas  11 ,  13  extending into/from the page when viewing  FIG. 3C . In this example, the antennas  11 ,  13  differ in geometry from one another in that the shapes of the ends of the antennas  11 ,  13  differ from one another. For example, when viewing  FIG. 3C , the right end  42  of the antenna  11  has a different shape than the right end  44  of the antenna  13 . Similarly, the left end  46  of the antenna  11  may have a similar shape as the right end  42 , but differs from the left end  48  of the antenna  13  which may have a similar shape as the right end  44 . In addition, the lateral widths Wi, W n of the antennas  11 ,  13  differ from one another. It is also possible that the lateral lengths L 11 , L 13  of the antennas  11 ,  13  could differ from one another. 
       FIG. 3D  illustrates another plan view of an antenna array having two antennas with different geometries that is somewhat similar to  FIGS. 3B and 3C . In this example, the antennas  11 ,  13  are illustrated as substantially linear strips each with the lateral length L 11 , L 13 , the lateral width W 11 , W 13 , and the perimeter edge E 11 , E 13 . The perimeter edges E 11 , E 13  extend around the entire periphery of the antennas  11 ,  13  and bound an area in plan view. In this example, the lateral length L 11 , L 13  and/or the lateral width Wu, Wu is greater than a thickness dimension of the antennas  11 ,  13  extending into/from the page when viewing  FIG. 3D . In this example, the antennas  11 ,  13  differ in geometry from one another in that the shapes of the ends of the antennas  11 ,  13  differ from one another. For example, when viewing  FIG. 3D , the right end  42  of the antenna  11  has a different shape than the right end  44  of the antenna  13 . Similarly, the left end  46  of the antenna  11  may have a similar shape as the right end  42 , but differs from the left end  48  of the antenna  13  which may have a similar shape as the right end  44 . In addition, the lateral widths W 11 , W 13  of the antennas  11 ,  13  differ from one another. It is also possible that the lateral lengths L 11 , L 13  of the antennas  11 ,  13  could differ from one another. 
       FIG. 3E  illustrates another plan view of an antenna array having two antennas with different geometries on a substrate. In this example, the antenna  11  is illustrated as being a strip of material having a generally horseshoe shape, while the antenna  13  is illustrated as being a strip of material that is generally linear. The planar shapes (i.e. geometries) of the antennas  11 ,  13  differ from one another. In addition, the total length of the antenna  11  (measured from one end to the other) when viewed in plan view is greater than the length of the antenna  13  when viewed in plan. 
       FIG. 3F  illustrates another plan view of an antenna array having two antennas with different geometries on a substrate. In this example, the antenna  11  is illustrated as being a strip of material forming a right angle, and the antenna  13  is also illustrated as being a strip of material that forms a larger right angle. The planar shapes (i.e. geometries) of the antennas  11 ,  13  differ from one another since the total area in plan view of the antenna  13  is greater than the total area in plan view of the antenna  11 . In addition, the total length of the antenna  11  (measured from one end to the other) when viewed in plan view is less than the length of the antenna  13  when viewed in plan. 
       FIG. 3G  illustrates another plan view of an antenna array having two antennas with different geometries on a substrate. In this example, the antenna  11  is illustrated as being a strip of material forming a square, and the antenna  13  is illustrated as being a strip of material that forms a rectangle. The planar shapes (i.e. geometries) of the antennas  11 ,  13  differ from one another. In addition, at least one of the width/length of the antenna  11  when viewed in plan view is less than one of the width/length of the antenna  13  when viewed in plan. 
       FIG. 3H  illustrates another plan view of an antenna array having two antennas with different geometries on a substrate. In this example, the antenna  11  is illustrated as being a strip of material forming a circle when viewed in plan, and the antenna  13  is also illustrated as being a strip of material that forms a smaller circle when viewed in plan surrounded by the circle formed by the antenna  11 . The planar shapes (i.e. geometries) of the antennas  11 ,  13  differ from one another due to the different sizes of the circles. 
       FIG. 3I  illustrates another plan view of an antenna array having two antennas with different geometries on a substrate. In this example, the antenna  11  is illustrated as being a linear strip of material, and the antenna  13  is illustrated as being a strip of material that forms a semi-circle when viewed in plan. The planar shapes (i.e. geometries) of the antennas  11 ,  13  differ from one another due to the different shapes/geometries of the antennas  11 ,  13 . 
       4 A-D are plan views of additional examples of different shapes that the ends of the transmit and receive antennas  11 ,  13  can have to achieve differences in geometry. Either one of, or both of, the ends of the antennas  11 ,  13  can have the shapes in  FIGS. 4A-D , including in the embodiments in  FIGS. 3A-I .  FIG. 4A  depicts the end as being generally rectangular. FIG.  4 B depicts the end as having one rounded corner while the other corner remains a right angle.  FIG. 4C  depicts the entire end as being rounded or outwardly convex.  FIG. 4D  depicts the end as being inwardly concave. Many other shapes are possible. 
     Another technique to achieve decoupling of the antennas  11 ,  13  is to use an appropriate spacing between each antenna  11 ,  13  with the spacing being sufficient to force most or all of the signal(s) transmitted by the transmit antenna  11  into the target, thereby minimizing the direct receipt of electromagnetic energy by the receive antenna  13  directly from the transmit antenna  11 . The appropriate spacing can be used by itself to achieve decoupling of the antennas  11 ,  13 . In another embodiment, the appropriate spacing can be used together with differences in geometry of the antennas  11 ,  13  to achieve decoupling. 
     Referring to  FIG. 2A , there is a spacing D between the transmit antenna  11  and the receive antenna  13  at the location indicated. The spacing D between the antennas  11 ,  13  may be constant over the entire length (for example in the X-axis direction) of each antenna  11 ,  13 , or the spacing D between the antennas  11 ,  13  could vary. Any spacing D can be used as long as the spacing D is sufficient to result in most or all of the signal(s) transmitted by the transmit antenna  11  reaching the target and minimizing the direct receipt of electromagnetic energy by the receive antenna  13  directly from the transmit antenna  11 , thereby decoupling the antennas  11 ,  13  from one another. 
     Referring to  FIG. 5 , an example configuration of the sensor device  5  is illustrated. In  FIG. 5 , elements that are identical or similar to elements in  FIG. 1  are referenced using the same reference numerals. In  FIG. 5 , the antennas  11 ,  13  are disposed on one surface of a substrate  50  which can be, for example, a printed circuit board. At least one battery  52 , such as a rechargeable battery, is provided above the substrate  50 , for providing power to the sensor device  5 . In addition, a digital printed circuit board  54  is provided on which the transmit circuit  15 , the receive circuit  17 , and the controller  19  and other electronics of the second device  5  can be disposed. The substrate  50  and the digital printed circuit board  54  are electrically connected via any suitable electrical connection, such as a flexible connector  56 . An RF shield  58  may optionally be positioned between the antennas  11 ,  13  and the battery  52 , or between the antennas  11 ,  13  and the digital printed circuit board  54 , to shield the circuitry and electrical components from RF interference. 
     As depicted in  FIG. 5 , all of the elements of the sensor device  5 , including the antennas  11 ,  13 , the transmit circuit  15 , the receive circuit  17 , the controller  19 , the battery  52  and the like are contained entirely within the interior space  31  of the housing  29 . In an alternative embodiment, a portion of or the entirety of each antenna  11 ,  13  can project below a bottom wall  60  of the housing  29 . In another embodiment, the bottom of each antenna  11 ,  13  can be level with the bottom wall  60 , or they can be slightly recessed from the bottom wall  60 . 
     The housing  29  of the sensor device  5  can have any configuration and size that one finds suitable for employing in a non-invasive sensor device. In one embodiment, the housing  29  can have a maximum length dimension L H  no greater than 50 mm, a maximum width dimension W H  no greater than 50 mm, and a maximum thickness dimension T H  no greater than 25 mm, for a total interior volume of no greater than about 62.5 cm 3 . 
     In addition, with continued reference to  FIG. 5  together with  FIGS. 3A-3I , there is preferably a maximum spacing D max  and a minimum spacing D min  between the transmit antenna  11  and the receive antenna  13 . The maximum spacing D max  may be dictated by the maximum size of the housing  29 . In one embodiment, the maximum spacing D max  can be about 50 mm. In one embodiment, the minimum spacing D min  can be from about 1.0 mm to about 5.0 mm. 
     With reference now to  FIG. 6  together with  FIG. 1 , one embodiment of a method  70  for detecting at least one analyte in a target is depicted. The method in  FIG. 6  can be practiced using any of the embodiments of the sensor device  5  described herein. In order to detect the analyte, the sensor device  5  is placed in relatively close proximity to the target. Relatively close proximity means that the sensor device  5  can be close to but not in direct physical contact with the target, or alternatively the sensor device  5  can be placed in direct, intimate physical contact with the target. The spacing between the sensor device  5  and the target  7  can be dependent upon a number of factors, such as the power of the transmitted signal. Assuming the sensor device  5  is properly positioned relative to the target  7 , at box  72  the transmit signal is generated, for example by the transmit circuit  15 . The transmit signal is then provided to the transmit antenna  11  which, at box  74 , transmits the transmit signal toward and into the target. At box  76 , a response resulting from the transmit signal contacting the analyte(s) is then detected by the receive antenna  13 . The receive circuit  17  obtains the detected response from the receive antenna  13  and provides the detected response to the controller  19 . At box  78 , the detected response can then be analyzed to detect at least one analyte. The analysis can be performed by the controller  19  and/or by the external device  25  and/or by the remote server  27 . 
     Referring to  FIG. 7 , the analysis at box  78  in the method  70  can take a number of forms. In one embodiment, at box  80 , the analysis can simply detect the presence of the analyte, i.e. is the analyte present in the target. Alternatively, at box  82 , the analysis can determine the amount of the analyte that is present. 
     The interaction between the transmitted signal and the analyte may, in some cases, increase the intensity of the signal(s) that is detected by the receive antenna, and may, in other cases, decrease the intensity of the signal(s) that is detected by the receive antenna. For example, in one non-limiting embodiment, when analyzing the detected response, compounds in the target, including the analyte of interest that is being detected, can absorb some of the transmit signal, with the absorption varying based on the frequency of the transmit signal. The response signal detected by the receive antenna may include drops in intensity at frequencies where compounds in the target, such as the analyte, absorb the transmit signal. The frequencies of absorption are particular to different analytes. The response signal(s) detected by the receive antenna can be analyzed at frequencies that are associated with the analyte of interest to detect the analyte based on drops in the signal intensity corresponding to absorption by the analyte based on whether such drops in signal intensity are observed at frequencies that correspond to the absorption by the analyte of interest. A similar technique can be employed with respect to increases in the intensity of the signal(s) caused by the analyte. 
     Detection of the presence of the analyte can be achieved, for example, by identifying a change in the signal intensity detected by the receive antenna at a known frequency associated with the analyte. The change may be a decrease in the signal intensity or an increase in the signal intensity depending upon how the transmit signal interacts with the analyte. The known frequency associated with the analyte can be established, for example, through testing of solutions known to contain the analyte. Determination of the amount of the analyte can be achieved, for example, by identifying a magnitude of the change in the signal at the known frequency, for example using a function where the input variable is the magnitude of the change in signal and the output variable is an amount of the analyte. The determination of the amount of the analyte can further be used to determine a concentration, for example based on a known mass or volume of the target. In an embodiment, presence of the analyte and determination of the amount of analyte may both be determined, for example by first identifying the change in the detected signal to detect the presence of the analyte, and then processing the detected signal(s) to identify the magnitude of the change to determine the amount. 
       FIGS. 8-10  are schematic depictions of additional embodiments of a non-invasive analyte sensor system  100 . The systems  100  depicted in  FIGS. 8-10  includes at least two or more antennas, at least three or more antennas, or at least six or more antennas. However, a different number of antennas can be used. In each of the embodiments, the system  100  is configured so that one or more of the antennas of the antenna array can be used as either a transmit antenna or as a receive antenna. In  FIGS. 8-10 , like elements are referenced using the same reference numerals. In one embodiment, a scan routine can be implemented using the system  100  where the scan routine includes a plurality of scans, where each scan uses a different combination of the antennas to transmit a signal and detect a response. As with the previously described embodiments in  FIGS. 1-7 , the antenna array can be a decoupled antenna array and the antennas of the antenna array can be decoupled from one another. However, in some embodiments, the antennas of the system  100  may not be decoupled from one another. In one embodiment, the antennas used in the arrays in  FIGS. 8-10  can have different geometries from each other. 
     In the embodiment in  FIG. 8 , the antenna array of the system  100  has two antennas  102   a ,  102   b  each of which can be disposed on a substrate  106  or disposed on separate substrates. The antennas  102   a ,  102   b  can have a construction similar to the construction described above with respect to  FIGS. 1-7 . The antennas  102   a ,  102   b  have different geometries from each other, and the antennas  102   a ,  102   b  are decoupled from each other. Switches  108   a ,  108   b  are electrically connected to each one of the antennas  102   a ,  102   b , and one or more transmit and receive switch controllers  110  can be electrically connected each of the switches  108   a ,  108   b . The switches  108   a ,  108   b  can have any mechanical and/or electrical construction suitable for performing the functions of the switches  108   a ,  108   b , such as directing either one or more transmit signals to the respective antenna  102   a ,  102   b  or receiving a response detected by the other one of the antennas  102   a ,  102   b .  FIG. 8  illustrates the switches  108   a ,  108   b  as single pole, double throw switches, but other switch constructions can be used. 
     The switch controller(s)  110  can have any mechanical and/or electrical construction suitable for performing the functions of the switch controller  110 , including controlling electrical connection of the transmit circuit  112  to any one of the antennas  102   a ,  102   b  to direct a generated transmit signal to the desired antenna  102 , a,  102   b  to act as a transmit antenna and controlling electrical connection of the receive circuit  114  to one of the antennas  102   a ,  102   b  to act as a receive antenna. The switch controller(s)  110  can be considered to have a transmit side that is suitable for controlling the transmit function, for example by suitably controlling the positions of the either one of the switches  108   a ,  108   b  to connect to the appropriate antenna  102   a ,  102   b  and directing the transmit signal generated by a transmit circuit  112  to the appropriate antenna  102   a ,  102   b . The switch controller(s)  110  can also be considered to have a receive side that is suitable for controlling the receive function, for example by suitably controlling the positions of the either one of the switches  108   a ,  108   b  to connect to the appropriate antenna  102   a ,  102   b  for receiving the response and directing the response to a receive circuit  114 . The switch controller(s)  110  can have one or more controllers integrated therewith or suitably connected thereto for managing and controlling the control functions of the switch controller(s)  110 . 
     Control of the switch controller(s)  110  may alternatively be achieved using one or more other controllers of the system  100 , for example a controller associated with the transmit circuit  112 , a controller associated with the receive circuit  114 , a main controller  116  of the system  100 , or one or more other controllers. 
     The transmit circuit  112  and the receive circuit  114  are each electrically connected to the switch controller  110 . The transmit circuit  112  is similar in function to the transmit circuit  15  described above in that the transmit circuit  112  is configured to generate at least one transmit signal in the radio or microwave frequency range of the electromagnetic spectrum, for example about 10 kHz to about 100 GHz, to be transmitted into the target containing the at least one analyte of interest by whichever one of the antennas  102   a ,  102   b  is acting as the transmit circuit as determined by the switch controller  110 . In addition, the receive circuit  114  is similar in function to the receive circuit  17  described above in that the receive circuit  114  is configured to receive a response detected by whichever one of the antennas  102   a ,  102   b  is acting as the receive antenna, where the response results from transmission of the at least one transmit signal into the target. The main controller  116  is connected to the transmit circuit  112  to control generation of the transmit signal(s) by the transmit circuit  112 . The controller  116  (or a separate controller) is also connected to the receive circuit  114  and is similar in function to the controller  19  described above, for example to store the response(s) detected by the receive antenna in suitable storage/memory and/or to analyze the response(s). 
     In  FIG. 8 , one or more of the elements  108   a ,  108   b ,  110 ,  112 ,  114  and  116  can be combined together functionally and/or mechanically rather than being separate elements. In addition, the transmit and receive switch controller  110  can be physically separated into a transmit switch controller that is separate from a receive switch controller as described below with respect to  FIGS. 9 and 10 . In addition, communications between one or more of the elements  108   a ,  108   b ,  110 ,  112 ,  114  and  116  can be achieved via wired connections and/or via wireless connections. Further, the operational positions of the switches  108   a ,  108   b  and the switch controller(s)  110  can be controlled using any suitable means, for example software and/or hardware, to ensure that at any moment in time, the switch controller(s)  110  is not connected to the same switch  108   a ,  108   b  at the same time. Moreover, when implementing a scan routine as described below, suitable techniques, such as the use of time stamps, can be used to differentiate between and/or identify the results of each scan, as well as indicate the frequency(ies) at which each scan was conducted. 
     The construction in  FIG. 8  is such that a scan routine can be implemented where the scan routine includes a plurality of scans. In one scan of the scan routine, the antenna  102   a  can be used as the transmit antenna while the antenna  102   b  is used as the receive antenna. In another scan, the antenna  102   b  can be used as the transmit antenna while the antenna  102   a  is used as the receive antenna. The results of the two scans can then be analyzed to determine the analyte, for example as described above, and optionally determine the amount of the analyte that is present. 
       FIG. 9  illustrates another embodiment of the system  100  that functions similarly to the system  100  in  FIG. 8 . In the embodiment in  FIG. 9 , the antenna array of the system  100  has three antennas  102   a ,  102   b ,  102   c  each of which is disposed on the substrate  106 . The system further includes three of the switches  108   a ,  108   b ,  108   c , a receive switch controller  110   a , and a transmit switch controller  110   b  separate from the receive switch controller  110   a.    
     In the embodiment in  FIG. 9 , the number of scans of the scan routine is greater than in  FIG. 8 . The following table (Table 1) lists a portion of a scan routine showing some of the scans using different antenna combinations that can be implemented. The scan routine can include a larger or smaller number of scans, and other scans using different antenna combinations can be implemented. The results of the scans can then be analyzed to determine the analyte, for example as described above, and optionally determine the amount of the analyte that is present. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Scan # 
                 Tx antenna 
                 Rx antenna 
               
               
                   
               
             
            
               
                 1 
                 102a 
                 102b 
               
               
                 2 
                 102a 
                 102c 
               
               
                 3 
                 102b 
                 102a 
               
               
                 4 
                 102b 
                 102c 
               
               
                 5 
                 102c 
                 102a 
               
               
                 6 
                 102c 
                 102b 
               
               
                 7 
                 102a + 102b 
                 102c 
               
               
                 8 
                 102a 
                 102b + 102c 
               
               
                 9 
                 102b + 102c 
                 102a 
               
               
                 Etc. 
                 Etc. 
                 Etc. 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 1, a single scan can use one antenna as a transmit antenna and one antenna as a receive antenna, or use two antennas as transmit antennas and one antenna as a receive antenna, or use one antenna as a transmit antenna and two antennas as receive antennas. In some embodiments, it is also possible that in a single scan, an antenna could be used as both a transmit antenna and as a receive antenna. 
       FIG. 10  illustrates still another embodiment of the system  100  that functions similarly to the systems  100  in  FIGS. 8 and 9 . In the embodiment in  FIG. 10 , the antenna array of the system  100  has six antennas  102   a - f  each of which is disposed on the substrate  106 , and six of the switches  108   a - f . In one embodiment, the antenna array formed by the six antennas  102   a - f  can have dimensions E 10 ×F 10  which does not exceed 30.0 mm by 30.0 mm. Due to the larger number of antennas in  FIG. 10  compared with  FIGS. 8 and 9 , the system  100  in  FIG. 10  permits implementation of scan routines using a larger number of scans using a larger number of antenna combinations. Table 2 below lists a portion of a scan routine showing some of the scans using different antenna combinations that can be implemented. The scan routine can include a larger or smaller number of scans, and other scans using different antenna combinations can be implemented. The results of the scans can then be analyzed to determine the analyte, for example as described above, and optionally determine the amount of the analyte that is present. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Scan # 
                 Tx antenna 
                 Rx antenna 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 102a 
                 102b 
               
               
                 2 
                 102b 
                 102c 
               
               
                 3 
                 102b 
                 102d 
               
               
                 4 
                 102c 
                 102f 
               
               
                 5 
                 102e 
                 102a 
               
               
                 6 
                 102f 
                 102b 
               
               
                 7 
                 102a + 102b 
                 102c 
               
               
                 8 
                 102a + 102b 
                 102c + 102d 
               
               
                 9 
                 102a + 102c 
                 102f 
               
               
                 10 
                 102a + 102c 
                 102b + 102d 
               
               
                 11 
                 102b 
                 102a + 102f 
               
               
                 Etc. 
                 Etc. 
                 Etc. 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 2, a single scan can use one antenna as a transmit antenna and one antenna as a receive antenna, use two or more antennas as transmit antennas and one antenna as a receive antenna, use one antenna as a transmit antenna and two or more antennas as receive antennas, use two or more antennas as transmit antennas and two or more antennas as receive antennas, etc. In some embodiments, it is also possible that in a single scan, an antenna could be used as both a transmit antenna and as a receive antenna. 
     The systems  100  of  FIGS. 8-10  can be used for non-invasive detection of an analyte. For example, in the systems  100 , in the antenna array having the at least two antennas, the transmit circuit  112  can be selectively connected to any one or more of the at least two antennas of the antenna array, for example using the switch controller  110 ,  110   a . At least one transmit signal is generated using the transmit circuit  112 , where the at least one transmit signal has at least two different frequencies each of which is in a radio or microwave frequency range of the electromagnetic spectrum. The at least one transmit signal is transmitted into a target containing at least one analyte of interest using the one or more of the at least two antennas connected to the transmit circuit  112 . In addition, the receive circuit  114  is selectively connected to a different one or more of the at least two antennas of the antenna array. The receive circuit and the different one or more of the at least two antennas of the antenna array are then used to detect a response resulting from transmission of the at least one transmit signal into the target containing the at least one analyte of interest. 
     In operation of either one of the systems  100  of  FIGS. 8-10 , a scan routine can implemented using the antenna array. In a first scan, a first combination of two or more of the antennas is used to transmit a first transmit signal that is in a radio or microwave frequency range of the electromagnetic spectrum into a target containing at least one analyte of interest and used to detect a response resulting from transmission of the first transmit signal into the target containing the at least one analyte of interest. In a second scan, a second combination of two or more of the antennas, different from the first combination, is used to transmit a second transmit signal that is in a radio or microwave frequency range of the electromagnetic spectrum into the target containing the at least one analyte of interest and used to detect a response resulting from transmission of the second transmit signal into the target containing the at least one analyte of interest. Depending upon the number of antennas in the array, the scan routine can include additional scans using additional combinations of two or more of the antennas to transmit the transmit signal and to detect a response. 
     The scan routine can be implemented at a number of discrete frequencies over a range of frequencies as described in WO 2019/217461, the entire contents of which are incorporated herein by reference. In the scan routine, for each scan at each frequency, a transmit signal can be transmitted by whichever antenna(s) is functioning as the transmit antenna and a response is detected a plurality of times, for example 20 times, at the antenna(s) that is functioning as the receive antenna. The detected responses can then be averaged to obtain the Sn value. 
     The analyte can be detected as described above. In one embodiment, a min/max subtraction method can be used at selected frequencies across the various scans of the scan routine. In another embodiment, a difference between power received by the antenna(s) acting as the receive antenna(s) at selected frequencies can be used. For example,  FIG. 11  illustrates an example where an antenna (A 3 ) is used as the transmit antenna Tx and antennas (A 1  and A 2 ) are used as receive antennas Rx. A baseline response spectra over a frequency range of interest is illustrated, and a response spectra detected by the antennas (A 1 , A 2 ) is also depicted. A change in spectra between the baseline response spectra and the detected response spectra is different between the receive antennas (A 1 , A 2 ). At particular frequencies F 1 , F 2 , F 3 , etc., a signal (represented by the vertical bar indicating the difference between the two dB values of the detected response spectra) correlating to analyte concentration can be calculated. 
     As indicated above, the data obtained by the sensor  5  needs to be analyzed. The analysis can occur on the sensor  5  or on one or more devices or systems separate from the sensor  5 . Unless otherwise indicated by the Applicant, the term devices or systems is intended to be construed broadly as encompassing any type of devices or systems that can analyze the data obtained by the sensor  5 . Examples of devices or system that can be used to analyze the data include, but are not limited to, hardware-based computing devices or systems; cloud-based computing devices or systems; machine learning devices or systems including active learning devices or systems; artificial intelligence-based devices or systems; neural network-based devices or systems; combinations thereof; and any other types of devices and systems that are suitable for analyzing the data. 
     One or more output signals resulting from or based on the analysis are then generated. In some embodiments, the output signal(s) is generated by the device(s) or system(s) that analyze the data. The output signal(s) is directed to one or more other devices or systems that implement an action based on the output signal(s). In one embodiment, the output signal(s) is directed to one or more notification devices (discussed further below) which generates at least one human perceptible notification for example to provide a perceptible signal or alert to the patient and/or a caregiver of the patient. In this embodiment, the output signal(s) may be referred to as a notification signal(s). In another embodiment, the output signal(s) may be directed to one or more other machine(s) or system(s), for example a medical device such as an insulin pump, that modifies the operation of the other machine(s) or system(s). In one embodiment, the output signal(s) or separate output signals can be directed to both one or more notification devices and one or more other machine(s) or system(s). In one embodiment, the output signal(s) can be stored in a suitable data storage separately from, or in addition to, being sent to one or more notification devices and/or to one or more other devices or systems. 
       FIG. 12  illustrates one non-limiting example of an output signal generation. In this example, an output signal is sent to a notification device  130  included in the system  100  to generate at least one human perceptible notification resulting from the analysis. The notification device  130  can be connected, directly or indirectly, to the system  100 . For example, in one embodiment, the notification device  130  can be incorporated on the sensor  5  to provide the at least one human perceptible notification directly to the person using or wearing the device  5 . In another embodiment, the notification device  130  can be incorporated into a device  132  that is physically separate from the device  5  including, but not limited to, a mobile phone (a.k.a. cell phone, smartphone); a tablet computer; a laptop computer; a personal computer; a wearable device such as a watch or a head-mounted device or clothing; a video game console; furniture such as a chair; a vehicle such as a car, automobile or truck; lightbulbs; smart home appliances such as a smart refrigerator; and a use specific device similar to these devices that is specifically designed to function with the sensor  5 . The at least one human perceptible notification generated by the notification device  130  can be one or more of an audible sound notification, a visual notification, a haptic notification, or an olfactory notification. Operation of the notification device  130  can be triggered by a notification or output signal that is generated resulting from the analysis. The notification signal can be generated by the device  5 , for example by the main controller thereof, or by a separate device or system as described above that performs the analysis after receiving the data from the device  5 . 
     In each of the embodiments in  FIGS. 8-10 , the systems  100  can be used like in the embodiments in  FIGS. 1 and 5 , where the system includes the sensor housing  29 , the antenna array is attached to the sensor housing, the transmit circuit  112  is disposed in the sensor housing, the receive circuit  114  is disposed in the sensor housing, and the battery  52  disposed in the sensor housing provides electrical power to the components including the switch controller  110 ,  110   a ,  110   b , the transmit circuit  112 , the receive circuit  114 , and the controller  116 . 
       FIGS. 13-19  are top views of additional examples of antenna arrays and antenna configurations and shapes that can be used in any of the embodiments described herein including the system  100  in  FIG. 10 . In each of the embodiments in  FIGS. 13-19 , the antennas of each array have different geometries from one another and the antennas are decoupled from one another. 
     The embodiments in  FIGS. 13-16  each depicts a decoupled antenna array with six antennas  120   a - f . However, each antenna array can use a smaller or larger number of antennas. In testing conducted to date, the Applicant has determined that the antenna array depicted in  FIG. 10  and the antenna depicted in  FIG. 13  achieve the best results when compared to the antenna arrays in  FIGS. 14-16 . 
       FIG. 17  depicts another embodiment of a decoupled antenna array with six primary or larger antennas  120   a - f , as well as a number of smaller point antennas  122  disposed to each side of the larger antennas  120   a - f . The use of the point antennas  122  increase the number of antennas that can be located in the array, thereby increasing the number of scans and antenna combinations that can be utilized in a scan routine using the antenna array in  FIG. 17 . 
       FIG. 18  depicts another embodiment of a decoupled antenna array with three antennas  124   a - c . One or more of the antennas  124   a - c  is formed with holes  126  therein which helps to change the geometry of the antennas  124   a - c.    
       FIG. 19  depicts another embodiment of a decoupled antenna array with five antennas  128   a - e  and antenna ports  130   a - e  for connecting to each antenna  128   a - e.    
       FIGS. 20, 21A and 21B  schematically depict another example of a non-invasive analyte sensor  150  that forms a portion of another embodiment of a non-invasive analyte sensor system. The non-invasive analyte sensor  150  uses electromagnetic energy in the form of light waves at selected electromagnetic frequencies to perform non-invasive analyte sensing described herein. The sensor  150  includes a housing  152  and a sensor array that includes a plurality of detector elements  154  each of which can emit electromagnetic energy in the form of light as well as act as a light detector (or photodetector). The illustrated example depicts the array as having a total of twelve of the detector elements  154  arranged into a 3×4 or 4×3 array. However, a larger or smaller number of the detector elements  154  can be provided in the array. In addition, the array can have other arrangements including being disposed in a circular array. The emitted light penetrates the target and reflects from an analyte, with at least one detector element detecting the reflected light. 
     Referring to  FIGS. 21A and 21B , some or all the detector elements  154  may be flush with a surface  156  of the housing  152  so that light emitted by each detector element  154  may be transmitted from the sensor  150  and each detector element  154  may detect returning light. In another embodiment, some or all of the detector elements  154  may be recessed within the housing  152  but the light from each detector element  154  is suitably channeled to the outside and returning light suitably channeled to the detector elements  154 . In still another embodiment, some or all of the detector elements  154  may project (partially or completely) from the housing  152 . 
     The detector elements  154  are controlled in a manner whereby any one or more of the detector elements  154  can emit light and any one or more of the detector elements  154  can act as a light detector. In one embodiment, the detector elements  154  may be light emitting diodes (LEDs) and the array that includes the LEDs can be referred to as an LED array. LEDs that can be selectively controlled to emit light (i.e. a photoemitter) or detect light (i.e. a photodetector) are known. See Stojanovic et al., An optical sensing approach based on light emitting diodes, Journal of Physics: Conference Series 76 (2007); Rossiter et al., A novel tactile sensor using a matrix of LEDs operating in both photoemitter and photodetector modes, Proc of 4th IEEE International Conference on Sensors (IEEE Sensors 2005). See also U.S. Pat. No. 4,202,000 the entire contents of which are incorporated herein by reference. 
     The LEDs that are used preferably permit at least two different wavelengths of light to be emitted (in other words, one LED emits light having a first wavelength and a second LED emits light having a second wavelength different than the first wavelength). In another embodiment, at least three or more different wavelengths of light can be emitted by the various LEDs. In one embodiment, each one of the LEDs can emit a different wavelength of light. In one embodiment, two or more of the LEDs can emit the same wavelength of light. The LED&#39;s can emit wavelengths that are in the human visible spectrum (i.e. about 380 nm to about 760 nm) including, but not limited to, wavelengths that are visibly perceived as blue light, red light, green light, white light, orange light, yellow light, and other colors, as well as emit wavelengths that are not in the human visible spectrum including, but not limited to, infrared wavelengths and ultraviolet wavelengths. Combinations of wavelengths in the visible and non-visible spectrums may also be used. The light waves emitted by the sensor  150  function in a manner similar to the RF waves emitted by the sensors in  FIGS. 1-19  since both are electromagnetic waves. For example, referring to  FIG. 21A , the light waves  158  penetrate into a target and reflect from an analyte in the target to form the returning light waves  160  which are detected. 
     The detector elements  154  can be controlled using a control system similar to the control system depicted in  FIGS. 8-10  including the switches, switch controllers, transmit circuit, receive circuit, and controller described in  FIGS. 8-10 . For example,  FIG. 21A  depicts an example where the detector element  154   a  on the left is controlled to function as a photoemitter emitting light waves  158  and the detector element  154   b  on the right is controlled to function as a photodetector that detects returning light waves  160  resulting from the transmission of the light waves  158 .  FIG. 21B  depicts an example where the detector element  154   b  on the right is controlled to function as a photoemitter emitting light waves  162  and the detector element  154   c  in the center is controlled to function as a photodetector that detects returning light waves  164  resulting from the transmission of the light waves  162 . 
     A scan routine can be implemented with the sensor  150  at a number of discrete electromagnetic frequencies over a range of electromagnetic frequencies based on the different wavelengths of the LEDs. A response spectra is detected by each of the detector element(s)  154  functioning as the photodetector with the response spectra being correlated to a particular analyte and analyte concentration. 
     In another embodiment, a non-invasive sensor can include both two or more antennas as described herein as well as two or more of the LEDs described herein. The antennas and the LEDs can be used together to detect an analyte. In another embodiment, the antennas can be used to perform a primary detection while the LEDs can confirm the primary detection by the antennas. In another embodiment, the LEDs can be used to perform a primary detection while the antennas can be used to confirm the primary detection by the LEDs. 
     The terminology used in this specification is intended to describe particular embodiments and is not intended to be limiting. The terms “a,” “an,” and “the” include the plural forms as well, unless clearly indicated otherwise. The terms “comprises” and/or “comprising,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components. 
     The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.