Abstract:
Various embodiments are described that relate to a detector. The detector can include a loop functioning at a high frequency that emits a magnetic field. The magnetic field can be retrieved and a comparison can be made between the emitted magnetic field and the retrieved magnetic field. If there is substantially little difference between the emitted and retrieved field, then a determination can be that no object is present. Conversely, if there is a substantial difference between the emitted and retrieved field, then the determination can be that an object is present and thus the object is detected. If the object is present, the returned magnetic field can be further analyzed to determine the type of object that is detected.

Description:
GOVERNMENT INTEREST 
       [0001]    The innovation described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment of any royalty thereon or therefore. 
     
    
     BACKGROUND 
       [0002]    A popular activity can be attempting to find an item. In one example, tourists can visit an old battlefield to try to discover remnants of the battle. These tourists can attempt to find old bullets, former clothing items such as belt buckles, rank insignia, and other physical items to take home as souvenirs. Items can at times be difficult to find as some items may be buried underground. 
       SUMMARY 
       [0003]    In one embodiment, a system comprises a loop and a detection component. The loop can be configured to emit a magnetic field along a longitudinal axis of the loop. The loop can operate at a frequency of about 100 kilohertz or greater. The detection component can be configured to detect a presence of an object through an analysis of the magnetic field. 
         [0004]    In one embodiment, a system comprises a singular loop, an identification component, a classification component, and an output component. The singular loop can operate at a frequency of about 1 megahertz or greater, where the singular loop is configured to emit a magnetic field along a longitudinal axis of the singular loop and where the singular loop functions concurrently as a transmission loop and as a reception loop. The identification component can be configured to identify a new location for a frequency notch associated with the frequency based on reception of the magnetic field, where the frequency notch moves from a base location to the new location and where a change of the location from the base location to the new location indicates a presence of an object. The classification component can be configured to determine a classification for the object based, at least in part, on the new location. The output component can be configured to cause an output associated with the classification. 
         [0005]    In one embodiment, a system comprises a loop, an identification component, and an output component. The loop operates at a frequency of about 100 kilohertz or greater to about 1 gigahertz or lower. The loop is configured to receive a magnetic field. The identification component is configured to identify a new location for a frequency notch associated with the frequency based on reception of the magnetic field, where the frequency location moves from a base location to the new location and where the change of the location indicates an anomaly associated with the magnetic field. The output component is configured to cause an output associated with the anomaly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Incorporated herein are drawings that constitute a part of the specification and illustrate embodiments of the detailed description. The detailed description will now be described further with reference to the accompanying drawings as follows: 
           [0007]      FIG. 1  illustrates one embodiment of a system comprises a loop and a detection component, 
           [0008]      FIG. 2  illustrates one embodiment of a system comprising a real portion recognition component and an imaginary portion recognition component; 
           [0009]      FIG. 3  illustrates one embodiment of the loop, tuning and matching circuits, and the detection component; 
           [0010]      FIG. 4  illustrates one embodiment of a system comprising the loop, the tuning and matching circuits, a selection component, and the detection component; 
           [0011]      FIG. 5  illustrates one embodiment of a system comprising the loop, the detection component, and a classification component; 
           [0012]      FIG. 6  illustrates one embodiment of a system comprising a transmission loop, a reception loop, and the detection component; 
           [0013]      FIG. 7  illustrates one embodiment of a system comprising the loop, an identification component, the classification component, and an output component; 
           [0014]      FIG. 8  illustrates one embodiment of a system comprising the loop and an application area; 
           [0015]      FIG. 9  illustrates one embodiment of a Smith chart with example responses based on an object; 
           [0016]      FIG. 10  illustrates one embodiment of a graph that shows the frequency notch; 
           [0017]      FIG. 11  illustrates one embodiment of a system comprising a processor and a non-transitory computer-readable medium; and 
           [0018]      FIG. 12  illustrates one embodiment of a method comprising five actions. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    A metal and/or anomaly detector can be employed to identify a presence of an object. The detector can include a high-Q tuned loop antenna to use for metal/anomaly detection. The detector can measure a return loss and/or a voltage standing wave ratio and through this measurement the detector can detect a frequency notch. Phase and/or amplitude response can be monitored to provide object detection. This phase and/or amplitude monitoring technique can be used to ground balance the detector. As a metal object is moved along the longitudinal axis of the loop antenna a substantial shift in the frequency notch (e.g., phase and/or amplitude of the notch) occurs that the detector detects. For metal targets, the frequency shift can be positive and for ferrite and other targets the frequency shift can be negative. This frequency shift can be created by the proximity of the target causing a change in the impedance of the loop antenna. Long-range detection can occur with relatively low power requirements. In one example, the loop antenna is a singular loop with one winding can be used to transmit and receive. However, multiple loops and/or multiple windings can also be employed. The loop can function at a high to very high frequency (HF to VHF). 
         [0020]    The detector can use a simple high-Q tuned loop antenna design with a canonical architecture. The loop antenna can be connected with a matching network with a particular arrangement that resonates with the loop antenna and produces an appropriate response of a reflection coefficient notch. The matching network is driven by a 50 Ohm source and 50 Ohm coaxial cable. The matching network can transform the loop impedance to 50 Ohm so that there is a notch with respect to frequency of the reflection coefficient looking into the matching network. The matching network can be designed so that the frequency of the notch shifts in a predictable manner when an object is placed in an aperture of the loop antenna. The impedance looking into the loop antenna can be defined as R+jX, where the resistance R is relatively independent of the presence of the target. The reactance X, however, can be relatively dependent on the target. With a metal target, X can become more capacitive and with a dielectric target X can become more inductive. A ferrite target can become more inductive and loss can also increase significantly. The detector can be calibrated without a target and function with the matching network. After calibration, a change in the reflection coefficient for a metal target can increase the frequency of the reflection coefficient notch. Similarly, a change in the reflection coefficient for the non-metal target can decrease the frequency of the reflection coefficient notch and loss can increase significantly. Thus, employing aspects disclosed herein can combine a small reactance shift along with a significant frequency shift. 
         [0021]    The following includes definitions of selected terms employed herein. The definitions include various examples. The examples are not intended to be limiting. 
         [0022]    “One embodiment”, “an embodiment”, “one example”, “an example”, and so on, indicate that the embodiment(s) or example(s) can include a particular feature, structure, characteristic, property, or element, but that not every embodiment or example necessarily includes that particular feature, structure, characteristic, property or element. Furthermore, repeated use of the phrase “in one embodiment” may or may not refer to the same embodiment. 
         [0023]    “Computer-readable medium”, as used herein, refers to a medium that stores signals, instructions and/or data. Examples of a computer-readable medium include, but are not limited to, non-volatile media and volatile media. Non-volatile media may include, for example, optical disks, magnetic disks, and so on. Volatile media may include, for example, semiconductor memories, dynamic memory, and so on. Common forms of a computer-readable medium may include, but are not limited to, a floppy disk, a flexible disk, a hard disk, a magnetic tape, other magnetic medium, other optical medium, a Random Access Memory (RAM), a Read-Only Memory (ROM), a memory chip or card, a memory stick, and other media from which a computer, a processor or other electronic device can read. In one embodiment, the computer-readable medium is a non-transitory computer-readable medium. 
         [0024]    “Component”, as used herein, includes but is not limited to hardware, firmware, software stored on a computer-readable medium or in execution on a machine, and/or combinations of each to perform a function(s) or an action(s), and/or to cause a function or action from another component, method, and/or system. Component may include a software controlled microprocessor, a discrete component, an analog circuit, a digital circuit, a programmed logic device, a memory device containing instructions, and so on. Where multiple components are described, it may be possible to incorporate the multiple components into one physical component or conversely, where a single component is described, it may be possible to distribute that single component between multiple components. 
         [0025]    “Software”, as used herein, includes but is not limited to, one or more executable instructions stored on a computer-readable medium that cause a computer, processor, or other electronic device to perform functions, actions and/or behave in a desired manner. The instructions may be embodied in various forms including routines, algorithms, modules, methods, threads, and/or programs including separate applications or code from dynamically linked libraries. 
         [0026]      FIG. 1  illustrates one embodiment of a system  100  comprises a loop  110  and a detection component  120 . The loop  110  can operate at a frequency of about 100 kilohertz or greater. A tuner component can be employed to tune a quality level (Q) of the loop to a desired bandwidth range. In addition, the loop  110  can be configured to emit a magnetic field along a longitudinal axis of the loop. The detection component  120  can be configured to detect a presence of an object through an analysis of the magnetic field. 
         [0027]    In one embodiment, the loop receives a returned magnetic field that is a returned version of the magnetic field that is emitted by the loop  110 . The detection component  120  can be configured to detect the presence of the object through identification of a phase change between the emitted magnetic field and the returned magnetic field. In one example, absent an object being present the returned magnetic field is substantially unchanged from the emitted magnetic field. This is because nothing is present to change the returned magnetic field. Conversely, if an object is present (e.g., metal or dielectric), then that object influences the magnetic field and the returned magnetic field is substantially changed from the emitted magnetic field. The detection component  120  can make a comparison of the two magnetic fields and determination that the object is present. 
         [0028]    In one embodiment, the detection component  120  can be configured to detect the presence of the object through a recognition of an impedance plot change between the emitted magnetic field and the returned magnetic field. In one embodiment, the detection component  120  performs identification of the impedance plot change through use of a reflection coefficient chart (e.g., a Smith chart). 
         [0029]      FIG. 2  illustrates one embodiment of a system  200  comprising a real portion recognition component  210  and an imaginary portion recognition component  220 . The real portion recognition component  210  can be configured to recognize a real part of the impedance plot change by way of a first tone that is emitted by the loop  110  of  FIG. 1 . Along with the first tone the loop can  110  of  FIG. 1  can emit a second tone that is different from the first tone. The imaginary portion recognition component  220  can be configured to recognize an imaginary part of the impedance plot change by way of the second tone. The recognition of the impedance plot change by the detection component  220  of  FIG. 1  can occur through use of the real part and the imaginary part. In one example, with the imaginary part and the real part recognized, the detection component  220  of  FIG. 1  can look-up a value for a combination of the real part with the imaginary part and this combination an indicate presence of the object and/or provide specific information on the object (e.g., the combination an indicate if the object is a metal or dielectric). In one embodiment, the real portion recognition component  210  and/or the imaginary portion recognition component  220  are part of the detection component  120  of  FIG. 1 . 
         [0030]      FIG. 3  illustrates one embodiment of the loop  110 , tuning and matching circuits  310 , and the detection component  120 . The tuning and matching circuits  310  (e.g., a set of tuning and matching circuits that comprise one or more tuning and matching circuit) can be a set of capacitors that are configured to match an impedance of the loop  110  with impedance of a power supply that supplies power to the loop. The impedance for the system  300  can be represented by (when the tuning and matching circuits  310  comprise three capacitors C 1 , C 2 , &amp; C 3 ): 
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         [0000]    where impedance for the loop  110  can be: 
         [0000]      ( U ) Z   loop   =jωL+R   (2)
 
         [0000]    with R being the real part recognized by the real portion recognition component  210  of  FIG. 2  and L being the imaginary part recognized by the imaginary portion recognition component  220  of  FIG. 2 . The impedance can be determined as looking into the loop  110 . 
         [0031]      FIG. 4  illustrates one embodiment of a system  400  comprising the loop  110 , the tuning and matching circuits  310 , a selection component  410 , and the detection component  120 . The selection component  410  can be configured to select a value set for the tuning and matching circuits  310 . The tuning and matching circuits  310 , when implemented with the value set, can cause the impedance to match the impedance of the power supply discussed in  FIG. 3 . The loop  110  and the power supply can be evaluated and based on a result of this evaluation the selection component  410  can select the value set such that impedances match. 
         [0032]      FIG. 5  illustrates one embodiment of a system  500  comprising the loop  110 , the detection component  120 , and a classification component  510 . The detection component  120  can be configured to detect the presence of the object through detection of a frequency notch shift of a frequency notch associated with the frequency of the loop  110 . The classification component  510  can be configured to make a classification for the object based, at least in part, on a location of the frequency notch shift. The frequency notch can be a graphical illustration of the frequency and the shift can be an illustration of the frequency change. The frequency notch shift can be produced from the object changing an impedance of the loop  110 . 
         [0033]    In one embodiment, the classification can be as a metal when the frequency notch shift is at a first value. Similarly, the classification can be as a non-metal (e.g., dielectric) when the frequency notch shift is at a second value different from the first value. In one example, the classification component  510  can have access to a look-up table. Entries in the look-up table can show correspondence between values and classifications. For example, a first range of values can be given for a metal classification and a second range of values can be given for a non-metal classification. A value can be identified by the classification component  510  and the classification component  510  can find the value in the first range or the second range. Based on a result of this finding the classification component  510  can determine if a metal or non-metal object is present. 
         [0034]    In one embodiment, absent the presence of the object the frequency notch can be at a base value. The classification component  510  can make the classification of a metal when the base value of the frequency notch increases. In addition, the classification component  510  can make the classification of a non-metal when the base value of the frequency notch decreases. 
         [0035]    In one embodiment, the selection component  410  of  FIG. 4  can select values for the tuning and matching circuits  310  of  FIG. 4  such that the base value of the frequency notch is at a desired value. In one example, a desired base value of the notch can be at about 24.052 MHz (Megahertz). The capacitors can be set such that C 1  is equal to about 7.752349 pF while C 2  and C 3  can be set to about 33.4 pF. At its base value when no object is present the impedance of the loop can be equal to about 50 Ohms. The frequency notch can increase to about 24.135 MHz and as such the impedance can change to about 60.2+j82.9 Ohms. This change in the notch and/or the impedance can be indicative of an object being present. Similarly, the frequency notch can decrease to about 23.885 MHz and as such the impedance can change to about 30.5−j127.5 Ohms. This change in the notch and/or the impedance can be indicative of an object being present. The detection component  120  can identify one of these changes to identify presence of the object. 
         [0036]      FIG. 6  illustrates one embodiment of a system  600  comprising a transmission loop  610 , a reception loop  620 , and the detection component  120 . The loop  110  of  FIG. 1  can function as the transmission loop  610 . The reception loop  620  can be configured to receive the magnetic field from the transmission loop  610 . The detection component  120  can be operatively coupled to the reception loop  620  and/or the transmission loop  610 . The detection component  120  can detect the presence of the object through use of the magnetic field that is received by the reception loop  620  from the transmission loop  610 . 
         [0037]    In one embodiment, the presence is detected when the object passes between the transmission loop  610  and the reception loop  620 . In this, the magnetic field can transfer from the transmission loop  610  to the reception loop  620 . When the magnetic field sent by the transmission loop  610  is disturbed by the object, the magnetic field received by the reception loop  620  can be different from the magnetic field sent by the transmission loop  610 . The detection component  120  can compare the sent and received magnetic fields and based on the comparison determine that the object is between the loops  610  and  620 . The system  600  can function such that the object is detected when the object is not between the loops  610  and  620 . 
         [0038]      FIG. 7  illustrates one embodiment of a system  700  comprising the loop  110 , an identification component  710 , the classification component  510 , and an output component  720 . The loop  110  can be a singular loop (one loop), multiple loops (two or more loops), a loop set (one or more loops) with wire winding, etc. The loop  110  can function concurrently as the transmission loop  610  of  FIG. 6  (e.g., to emit the magnetic field) and as the reception loop  620  of  FIG. 6  (e.g., to receive the magnetic field), function as the transmission loop  610  of  FIG. 6 , or function as the reception loop  620  of  FIG. 6 . In one embodiment, the system  700  can comprise the tuning and matching circuits  310  of  FIG. 3  that are configured to match an impedance of the loop  110  with a power supply (e.g., a power supply that operates at about 1 MHz or greater with a source impedance of about 25 Ohms or less) that supplies power to the loop  110 . The loop  110  can operate at a frequency of about 100 kHz or greater (e.g., 1 MHz or greater, at least about 100 kHz and not more than about 1 gigahertz) and be configured to emit a magnetic field along a longitudinal axis of the loop  110 . 
         [0039]    The identification component  710  can be configured to identify a new location for a frequency notch associated with the frequency based on reception of the magnetic field. The frequency notch moves from a base location to the new location resulting in a location change for the frequency notch. Absent the presence of the object the frequency notch can be at the base location. The frequency notch can shift from the base location to the new location due to the object changing an impedance of the loop  110 . The location change for the frequency notch can be from the base location to the new location. The location change can indicate an anomaly associated with the magnetic field, such as indicating the presence of the object. 
         [0040]    The classification component  510  can be configured to determine that the anomaly is the presence of the object and/or be configured to determine a classification for the object based, at least in part, on the new location. The classification can be of a metal when the new location increases from the base location. Additionally, the classification can be of a non-metal when the new location decreases from the base location. Based on a specific value of the new location the classification component  510  can determine a metal or non-metal type. 
         [0041]    The output component  720  can be configured to cause an output associated with the classification. In one example, a light can flash on portion of a metal detector handle and/or a sound can emit from a speaker when the anomaly is detected. In one example, text can be presented on a display that indicates the classification. The classification can be as a metal or non-metal (e.g., text reads ‘metal’) as well as be more specific (e.g., list a non-metal type). Other information can be provided as well by the output component, such as a depth of the object if the object is underground. 
         [0042]      FIG. 8  illustrates one embodiment of a system comprising the loop  110  and an application area  810 . The application area  810  can be a hardware box that retains various items, such as the tuning and matching circuits  310  of  FIG. 3  as three capacitors—C 1 , C 2 , and C 3 . These three capacitors can form an impedance matching network that appropriate translates a reactive shift presented by the loop  110 . Further, the application area  810  can retain various other hardware disclosed herein, such as the processor  1010  and/or the non-transitory computer-readable medium  1020  discussed below with regard to  FIG. 10 . In one example, the application area is able to locate a hot spot around the loop  110  where detection performance can greatly increase. The hot spot can be at different locations depending on the object. 
         [0043]      FIG. 9  illustrates one embodiment of a Smith chart  900  with example responses based on potential presence of the object. Four example responses for the Smith chart  900  are provided: no object (combination dashed and dotted line), a ferrite object (shorter dashed line), a metal (longer dashed line), and a polyethylene (dotted line). The Smith chart can have an increasing frequency, such as through a clockwise rotation (e.g., the arrows of the responses travel clockwise). The Smith chart  900  can be configured such that positive values converge to the right and negative values converge to the left. The detection component  120  of  FIG. 1  can employ the Smith chart  900  to determine if an object is present and/or what specific object is present. 
         [0044]    As an example use of the Smith chart  900  the loop  110  of  FIG. 1  can be tuned to, and thus operate at, a frequency of 24.052 MHz. With no object the Zin can be 50 Ohms while the zin can be 1. The Zin can be the actual value while the zin can be a scaled version to a base of 1. The ferrite object can have a Zin of 113+j 160 Ohms and a zin of 2.26+j3.2. Similarly, the polyethylene can have a Zin of 44−j2.6 Ohms and a zin of 0.88−j0.05. Conversely the metal can have a Zin of 40−j47 Ohms and a zin of 0.8−j0.94. Thus, the Zin and zin go in one direction for the metal as compared to no object and in another direction with the ferrite while the polyethylene can have little effect on the frequency response. The Smith chart  900  can be retained in a memory. 
         [0045]      FIG. 10  illustrates one embodiment of a graph  1000  that shows the frequency notch. The frequency notch (e.g., a reflection notch) can be where a maximum return loss for the loop  110  of  FIG. 1  occurs. In one embodiment, the frequency notch can move left if a non-metal object is detected and move to the right if a metal object is detected. 
         [0046]      FIG. 11  illustrates one embodiment of a system  1100  comprising a processor  1010  and a non-transitory computer-readable medium  1120 . In one embodiment the non-transitory computer-readable medium  1120  is communicatively coupled to the processor  1010  and stores a command set executable by the processor  1110  to facilitate operation of at least one component disclosed herein (e.g., the detection component  120  of  FIG. 1 ). In one embodiment, at least one component disclosed herein (e.g., the tuner component discussed with regard to  FIG. 1 ) can be implemented, at least in part, by way of non-software, such as implemented as hardware by way of the system  1100 . In one embodiment the non-transitory computer-readable medium  1120  is configured to store processor-executable instructions that when executed by the processor  1110  cause the processor  1110  to perform a method disclosed herein (e.g., the method  1200  discussed below). 
         [0047]      FIG. 12  illustrates one embodiment of a method  1200  comprising five actions  1210 - 1250 . At  1210  values can be set for the capacitors C 1 , C 2 , and C 3  as discussed above. This can be done in constructing a system and/or be changed mechanically or electronically though use of a variable capacitor. At  1220  the loop  110  of  FIG. 1  can be supplied a current (e.g., a current of about 1 Amp or greater) which can cause emission of a magnetic field from the loop  110  of  FIG. 1 . Emission of this magnetic field can be in the longitudinal direction. At  1230  the loop  110  of  FIG. 1  can capture a return of the magnetic field. At  1240  the detection component  120  of  FIG. 1  can determine the presence of the object based on the return of the magnetic field, such as through comparison of the frequency notch from the emitted field against the returned field. The presence can be further specified at  1250 , such as a determination of a non-metal/metal or further specificity such as between a ferrite object and a polyethylene.