Abstract:
Methods and apparatuses of the present invention perform imaging using a metamaterial lens structure. The apparatus according to one embodiment comprises: a field source capable of generating an electromagnetic field directed to an area in an object or target; a field detector arranged downstream from the field source, the field detector being capable of detecting a field signature associated with the area in the object or target; and a metamaterial lens structure arranged downstream from the field source, the metamaterial lens structure concentrating the electromagnetic field produced by the field source to the area in the object or target, or concentrating the field signature from the area in the object or target to the field detector.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application is a continuation-in-part under 35 U.S.C. §120 of U.S. application Ser. No. 12/801,799 filed on Jun. 25, 2010, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/213,624 filed on Jun. 25, 2009, the entire contents of these applications being hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an imaging technique and imaging apparatus, and more particularly to a method and apparatus for direct magnetic imaging. 
         [0004]    2. Description of the Related Art 
         [0005]    Magnetic resonance imaging (MRI) is a technique which uses magnetic fields and RF waves to obtain pictures of structures inside the body. With this technique, a strong magnetic field is used to align the protons in a subject. Radio frequency (RF) waves are then transmitted into the subject at the proton&#39;s Larmor frequency, causing a transient magnetic field. When the RF signal is turned off the protons relax, emitting an RF signal in the process. The RF waves which are re-transmitted by protons are received by MRI RF coils. In order to produce an MRI image, the RF signal needs to be encoded for each dimension; otherwise, spatial information cannot be obtained. The information is encoded by adding a gradient to the static magnetic field that surrounds the subject, by using gradient coils, for example. Fourier Transform is used to retrieve an image from the collected signal, by transforming the encoded image to spatial domain to create a 3D picture. 
         [0006]    In the conventional MRI process no real magnetic image is obtained. As explained above, MRI requires sophisticated software analysis involving RF signal encoding and Fourier Transform to re-construct an image. These difficulties are due to the MRI process specifications which are set in connection with the Larmor frequency of the proton. For a 1.5 Tesla MRI machine, for example, the proton&#39;s Larmor frequency (for hydrogen atoms) is approximately 64 MHz, which corresponds to a wavelength of ˜4.7 meters, which is in the RF range of the electromagnetic spectrum. This wavelength is quite long and cannot individually resolve small anatomical features, such as features of organs and tissues, cancer formations, etc., that need to be imaged. In order to obtain a reasonable resolution with MRI, the gradient coils are used to encode a signal from the subject in each dimension, and Fourier Transform is used to retrieve an image from the collected signal. Without encoding, spatial information is not obtainable through traditional MRI, and, even with encoding, the magnetic image can be reconstructed only by sophisticated software analysis which is time consuming and computationally intensive. 
         [0007]    Traditional clinical MRI systems are also quite large and heavy because of the cryogenic cooling and magnetic shielding requirements. State-of-the-art portable MRI versions suffer from a lack of sensitivity and poor image quality. Traditional portable MRI systems have reduced sensitivity due to the fact that they operate at lower magnetic fields than what would be found in a hospital setting (typically in the 0.2-0.5 T range). The MRI signal is usually proportional to the magnetic field applied to the subject, so that lower field MRI devices have poorer signal to noise ratio. Furthermore, the quality of the gradient field which probes the patient for spatial information is affected by every inhomogeneity in the permanent magnetic field. Therefore, these portable MRI machines are typically used for extremity imaging only (e.g. knee, elbow, etc), not for whole body imaging. 
         [0008]    Disclosed embodiments of this application address these and other issues by providing imagers and methods for direct imaging, including, but not limited to, direct magnetic imaging. A Direct Magnetic Imager of the present invention includes one or more metamaterial lenses which focus a magnetic field down into an object or target and may also collect the signal back to a receiver. The Direct Magnetic Imager facilitates imaging in MRI and NMR applications, improving signal to noise ratio, resolution and sensitivity while decreasing acquisition time, device size and shielding requirements as compared with traditional imaging systems. The metamaterial lens(es) may replace gradient coils used in traditional MRI units to encode the RF signal in each spatial dimension, allowing focusing of the RF fields for direct imaging applications. The metamaterial lens(es) may also be added to state-of-the art imagers to improve sensitivity and detector SNR, without altering the system configuration. The metamaterial lens(es) in the Direct Magnetic Imager may be focused in multiple dimensions and may be tuned to specific frequencies in connection with frequencies detected by the detector/receiver. The Direct Magnetic Imager can be used for imaging, detection and sensing in a variety of fields, including medical, military and security applications. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to imaging methods and apparatuses. According to a first aspect of the present invention, an imager comprises: a field source capable of generating an electromagnetic field directed to an area in an object or target; a field detector arranged downstream from the field source, the field detector being capable of detecting a field signature associated with the area in the object or target; and a metamaterial lens structure arranged downstream from the field source, the metamaterial lens structure concentrating the electromagnetic field produced by the field source to the area in the object or target, or concentrating the field signature from the area in the object or target to the field detector. 
         [0010]    According to a second aspect of the present invention, an imaging method, comprises: generating an electromagnetic field directed to an area in an object or target; detecting a field signature associated with the area in the object or target; and concentrating, using a metamaterial lens structure, the electromagnetic field to the area in the object or target, and/or concentrating the field signature from the area in the object or target before the detecting step. 
         [0011]    According to a third aspect of the present invention, a metamaterial lens comprises multiple unit cells, each unit cell including at least one ring with lumped capacitors and/or inductors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further aspects and advantages of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a general block diagram of a Direct Magnetic Imager according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a general block diagram of a Direct Magnetic Imager according to a second embodiment of the present invention; 
           [0015]      FIG. 3  is a general block diagram of a Direct Magnetic Imager according to a third embodiment of the present invention; 
           [0016]      FIG. 4  is a general block diagram of a Direct Magnetic Imager according to a fourth embodiment of the present invention; 
           [0017]      FIG. 5  is a block diagram illustrating a Direct Magnetic Imager according to an embodiment of the present invention illustrated in  FIG. 3 ; 
           [0018]      FIG. 6  is a block diagram of a Direct Magnetic Imager according to an embodiment of the present invention illustrated in  FIG. 4 ; 
           [0019]      FIG. 7  is a block diagram of a Direct Magnetic Imager according to an embodiment of the present invention illustrated in  FIG. 3 ; 
           [0020]      FIG. 8  is a block diagram illustrating a Direct Magnetic Imager which includes an imaging system which has been modified to include metamaterial lens structures according to an embodiment of the present invention; 
           [0021]      FIG. 9  is a block diagram of a Direct Magnetic Imager including tunable metamaterial lens structure(s) according to an embodiment of the present invention illustrated in  FIG. 3 ; 
           [0022]      FIG. 10  is a block diagram of a Direct Magnetic Imager including tunable metamaterial lens structure(s) according to an embodiment of the present invention illustrated in  FIG. 4 ; 
           [0023]      FIG. 11  illustrates a method for direct magnetic imaging using metamaterial lens structure(s) according to embodiments of the present invention illustrated in  FIGS. 1-4 ; 
           [0024]      FIG. 12  illustrates an exemplary sensor which operates at room temperature and is used as a detector component in a Direct Magnetic Imager according to embodiments of the present invention illustrated in  FIGS. 1-4 ; 
           [0025]      FIG. 13  illustrates an exemplary MEMS device including multiple cantilever devices used for detection in a tunable Direct Magnetic Imager according to an embodiment of the present invention; 
           [0026]      FIG. 14A  illustrates imaging performance with an exemplary metamaterial lens according to an embodiment of the present invention, and  FIG. 14B  illustrates comparative imaging performance without a metamaterials lens; 
           [0027]      FIGS. 14C and 14D  illustrate wave propagation and enhancement in an exemplary metamaterial lens used in a Direct Magnetic Imager according to an embodiment of the present invention; 
           [0028]      FIGS. 15A ,  15 B,  15 C and  15 D illustrate exemplary metamaterial lenses included in a Direct Magnetic Imager according to an embodiment of the present invention; 
           [0029]      FIG. 15E  illustrates details and performance of exemplary metamaterial lenses used in a Direct Magnetic Imager according to an embodiment of the present invention; 
           [0030]      FIGS. 16A and 16B  illustrate exemplary measured transmission of a coil without and with the fabricated metamaterial lens shown in  FIG. 15A  for use in a Direct Magnetic Imager according to an embodiment of the present invention; and 
           [0031]      FIGS. 17A and 17B  illustrate the change in normalized magnetic field intensity with a change in distance from an object to be imaged with a metamaterials lens used in a Direct Magnetic Imager according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Aspects of the invention are more specifically set forth in the accompanying description with reference to the appended figures.  FIG. 1  is a general block diagram of a Direct Magnetic Imager  101  according to an embodiment of the present invention. The Imager  101  illustrated in  FIG. 1  includes the following components: a source  21 ; focusing systems  91 A and  91 B; a detector  41 ; and a processor  51 . Although the various components of  FIG. 1  are illustrated as discrete elements, such an illustration is for ease of explanation and it should be recognized that certain operations of the various components may be performed by the same physical device, e.g., by one or more apparatuses or (micro)processors. Operation of the Imager  101  in  FIG. 1  will become apparent from the following discussion. 
         [0033]    Source  21  generates an electromagnetic field or radiation which is applied to an object or target  31 . Source  21  may include one or more of a permanent magnet, a permanent magnet coil, a variable field magnet, an antenna, an RF transmitter or coils, or some other devices which produce an electromagnetic, magnetic, or electric field, radiation or wave pattern through an electrical, magnetic, mechanical or other type(s) of mechanism(s). In some applications, source  21  generates a low magnetic field which may be on the order of mT to μT. In other applications, source  21  generates a medium or a high magnetic field of the order of Tesla. 
         [0034]    Object  31  may be a person, an anatomical part, an inanimate item to be analyzed such as a vehicle, cargo, an environmental structure, etc. Target  31  may be an item that needs to be screened for presence or absence of certain substances or structures, such as, for example, a suspected explosive, a piece of luggage, a container with suspected substances, a suspected weapon or a case that might contain a weapon, a chemical or pharmaceutical composition or container thereof, etc. 
         [0035]    Focusing system  91 A concentrates the electromagnetic, magnetic or electric field/signal/waves generated by source  21  to object/target  31 . Focusing system  91 B receives a signal, radiation or field/field signature from object/target  31  and concentrates the signal, radiation or field/field signature to detector  41 . 
         [0036]    Focusing systems  91 A and  91 B include one or more metamaterial lens(es) or lens array(s) to concentrate the input and the output fields and decrease the need for shielding, subject proximity, and field strength, while maintaining imaging resolution. A metamaterial lens enables a focusing effect, allowing focusing down radiation below the typical diffraction limited spot and opening new applications for direct imaging of magnetic fields and long wavelength fields including RF fields. The term “metamaterial lens structure” is used herein to designate one or more metamaterial lenses and/or metamaterial lens array(s). 
         [0037]    A metamaterial lens is an engineered device which has a refractive index (n) equal to minus one, or a magnetic permeability (mu) or electric permittivity (epsilon) equal to minus one. A metamaterial lens is made of unit cells which provide specific advantageous lensing properties. For a magnetic metamaterial lens, in the quasi-magnetostatic limit, only mu could be equal to minus one in order for the metamaterial lens to act as a magnetic focusing device and achieve super resolution. Such magnetic metamaterial lens can focus into discrete areas of the object or target  31  and provide super resolution through direct magnetic imaging. For an electric metamaterial lens, in the quasi-electrostatic limit, only epsilon could be equal to minus one in order for the metamaterial lens to act as an electric focusing device and achieve super resolution. In the general case where n equals to minus one, the metamaterial lens acts as both a magnetic and electric field focusing device and achieves super resolution. 
         [0038]    Metamaterial lens structures  91 A and  91 B in  FIG. 1  may implement various applications or techniques that require imaging or magnetic and RF fields. Such applications or techniques include direct magnetic imaging for MRI and Nuclear Magnetic Resonance (NMR) spectroscopy applications, direct imaging of magnetic and long wavelength fields including RF fields, SQUID-based (super quantum interference detector) low field systems and other magnetic applications. The Imager of the present invention illustrated in  FIG. 1  is applicable to low-magnetic fields imaging (in the kHz range), in which SQUID detectors or uncooled magnetometer detectors are used as detector elements. The Imager of the present invention may also be applied to the electric component of the EM field. For example, the Imager may be an application in the optical and/or IR range in which a metamaterial lens with epsilon=−1 or n=−1 is used with the electric component of the EM field. 
         [0039]    In an exemplary embodiment of the present invention illustrated in  FIG. 7 , metamaterial lens structures replace the gradient coils that are used in traditional imagers, such as MRI units, to encode the RF signal in each spatial dimension. The metamaterial lens structures thus allow directing and focusing down the RF fields into discrete areas in a subject, to enable direct magnetic imaging which is analogous to optical imaging. In another exemplary embodiment described in  FIG. 8 , metamaterial lens structures are added to a state-of-the-art imaging system to collect and focus the signal into the RF receiver coils and/or into a magnetometer detector and improve sensitivity and detector SNR. 
         [0040]    The metamaterial lens structures offer many imaging advantages including improved resolution, increased sensitivity, decreased acquisition time, and enhanced signal to noise ratio. The large Q-value and narrow bandwidth of metamaterial lens structures increase detector SNR, reduce shielding requirements, stand-off distance limitations and field strength requirements, while significantly improving imaging resolution. Details of exemplary metamaterial lens structures are presented in  FIGS. 14A-14D ,  15 A- 15 E,  16 A- 16 B and  17 A- 17 B which are described in more detail in below. 
         [0041]    Metamaterial lenses decrease the need for shielding due to their ability to concentrate the field into the object/target, and then subsequently into the detector. This boosts the signal part of SNR (&gt;5×, in exemplary embodiments) to overcome the noise component, since the signals from the object/target area of interest are concentrated more strongly from the area of interest, which also reduces the need for shielding from stray magnetic fields. The original field strength may then be decreased, depending on application output requirements. By contrast, in traditional imaging systems such as state-of-the-art MRI systems, the signal is boosted by increasing the magnetic field strength, and significant shielding is needed to remove external magnetic background and noise from detector and bring the SNR to an acceptable value. 
         [0042]    The metamaterial lens structures better concentrate the input and output signal, and therefore the stand-off distance from the area of interest within an object/target (i.e., how far away from the Imager device the object/target can be placed, whereby the Imager still performs imaging) and the distance between the device and the object/target can be increased without decreasing the ability of the Imager to image the object/target area of interest. The object/target may also be in direct contact with the Imager, depending on the application. Thus, the Imager provides significant flexibility for positioning the object/target relative to the imaging device. 
         [0043]    Detector  41  obtains data from focusing system  91 B, performs analysis of received data, and outputs the results to processor  51 . Detector  41  may include electrical, magnetic and mechanic components and combination devices such as MEMS devices, magnetometers, magnetorestrictive devices, SQUID detectors, antennas, RF coils, atomic magnetometers, MEMS magnetometers, magnetorestrictive MEMS devices, etc. Other electrical, magnetic and mechanic sensors may also be included in detector  41 . 
         [0044]    Processor  51  processes the data from detector  41  and outputs a representation, such as, for example, a graphical representation of the imaged object or target area, or other type of reconstruction data. Processor  51  may include one or more microprocessors, purpose built hardware such as, for example, FPGA, ASIC, etc., software systems and applications, software packages, etc. Software packages that may be part of processor  51  may be recorded on a computer readable medium such as a memory device, RAM, CD/DVD/USB drives, etc., and/or may be part of a physical device such as one or more (micro)processors. 
         [0045]    A user, e.g., a medical professional, military or security personnel, etc., may control parameters associated with the source  21 , focusing systems  91 A and  91 B, detector  41  and processor  51  and may view the output of processor  51  via a display  65  or other device that produces representations of the output of processor  51 , such as a printing unit  46  or an image output unit  55 . The user may input commands to the Imager  101  via a user input unit  75 . In the embodiment illustrated in  FIG. 1 , the user input unit  75  includes a keyboard  76  and a mouse  78 , but other conventional input devices could also be used. Elements of the Imager  101  may also be controlled automatically. 
         [0046]    Printing unit  46  receives the output of processor  51  and generates a hard copy of the processed image data. In addition to or as an alternative to generating a hard copy of the output of the processor  51 , the processed image data may be returned as an image file, e.g., via a portable recording medium or via a network (not shown). The output of processor  51  may also be sent to image output unit  55  that performs further operations on image data for various purposes. The image output unit  55  may be a module that performs further processing of the image data, a database that collects and compares images, etc. 
         [0047]    Focusing system  91 A may be bypassed, so that the signal/radiation/field from source  21  reaches the object/target  31  directly from source  21 . Alternatively, a first signal/radiation/field from source  21  may directly reach object/target  31 , while a second signal/radiation/field from source  21  may be focused by meta-structure  91 A to concentrate the second signal/radiation/field onto object/target  31 . 
         [0048]    Similarly, focusing system  91 B may be bypassed, so that the signal/radiation/field from object/target  31  reaches the detector  41  directly from object/target  31 . Alternatively, a first signal/radiation/field from object/target  31  may directly reach detector  41 , while a second signal/radiation/field from object/target  31  may pass through meta-structure  91 B before reaching detector  41 . 
         [0049]      FIG. 2  is a general block diagram of a Direct Magnetic Imager  102  according to a second embodiment of the present invention. The system  102  illustrated in  FIG. 2  includes the following components: a source  21 ; a focusing system  91 C; a detector  41 ; and a processor  51 . Focusing system  91 C is in the path of the electromagnetic field created by source  21  and performs a focusing function on the field/radiation/signal onto the object/target  31 . Focusing system  91 C also receives a signal, radiation, or field signature from object/target  31  and focuses it onto detector  41 . 
         [0050]    Detector  41  performs analysis of the received data, and outputs the results to processor  51 , which outputs a representation, such as, for example, a graphical representation of the imaged object or target area, or other type of reconstruction data. 
         [0051]    In one embodiment, a first signal/radiation/field from source  21  directly reaches object/target  31 , while a second signal/radiation/field from source  21  is focused through focusing system  91 C before reaching object/target  31 . Also, a first signal/radiation/field signature from object/target  31  may directly reach detector  41 , while a second signal/radiation/field signature from object/target  31  may be focused by focusing system  91 C onto detector  41 . 
         [0052]    Focusing system  91 C includes one or more metamaterial lens(es) or lens array(s) to focus magnetic fields. Metamaterial lens structure  91 C may implement various imaging applications such as direct magnetic imaging for MRI and Nuclear Magnetic Resonance (NMR) spectroscopy applications, direct imaging of magnetic and long wavelength fields including RF fields, SQUID-based (super quantum interference detector) low field systems and other magnetic applications. The present invention illustrated in  FIG. 2  is also applicable to low-magnetic fields (in the kHz range), in which SQUID or uncooled magnetometer detectors may be used for detector  41 . The Imager illustrated in  FIG. 2  can also be applied to the electric component of the EM field, to focus the electric component using one or more metamaterial lens(es) or array(s) which form the focusing system  91 C. 
         [0053]      FIG. 3  is a general block diagram of a Direct Magnetic Imager  103  according to a third embodiment of the present invention. The Direct Magnetic Imager  103  illustrated in  FIG. 3  includes: a source  21 ; focusing systems  91 D and  91 E; a detector  41 ; a processor  51 ; and a control unit  99 .  FIG. 4  is a general block diagram of a Direct Magnetic Imager  104  according to another embodiment of the present invention. The Direct Magnetic Imager  104  illustrated in  FIG. 4  includes: a source  21 ; a focusing system  91 F; a detector  41 ; a processor  51 ; and a control unit  99 . 
         [0054]    In accordance with these third and fourth embodiments of the present invention, the source  21 , focusing systems  91 D,  91 E and  91 F, detector  41  and processor  51  may function in like manner to the corresponding elements of the first and second embodiment. In accordance with the third and fourth embodiments illustrated in  FIGS. 3 and 4 , control unit  99  controls one or more of the following units: focusing systems  91 D,  91 E and  91 F, source  21  and detector  41 . Control unit  99  may, for example, control and adjust focusing parameters and tuning parameters in focusing systems  91 D,  91 E and  91 F, source  21  and detector  41 . For example, control unit  99  may adjust focusing parameters and frequency tuning parameters for the metamaterial lens(es) or metamaterial lens array(s) in the focusing systems  91 D,  91 E and  91 F, depending on parameters of source  21  and/or detector  41 . 
         [0055]    Control unit  99  may include one or more microprocessors, purpose built hardware such as, for example, FPGA, ASIC, etc., software systems and applications, software packages, etc. Software packages that may be part of control unit  99  may be recorded on a computer readable medium such as a memory device, RAM, CD/DVD/USB drives, etc., and/or may be part of a physical device such as one or more (micro)processors. Control unit  99  may be a standalone unit, or may be incorporated into one or more focusing systems, source and detector, or may include multiple units each incorporated in a focusing system, source and detector. For example, control unit  99  may be composed of a plurality of control units, each included in source  21 , focusing systems  91 D,  91 E,  91 F, and detector  41 , respectively, so that source  21  communicates with focusing systems  91 D or  91 F, detector  41  communicates with focusing systems  91 E and  91 F, and focusing systems  91 D and  91 E communicate with each other, to reciprocally adjust parameters and settings. 
         [0056]      FIG. 5  is a block diagram illustrating a Direct Magnetic Imager  103 A according to an embodiment of the present invention illustrated in  FIG. 3 . The Direct Magnetic Imager  103 A illustrated in  FIG. 5  includes a magnetic/RF source  21 A, metamaterial lens(es) or lens arrays  91 G and  91 H, magnetic/RF detector  41 A, processor  51 A, and switching control unit  99 A. Source  21 A may include magnets, antennas, RF coils, as well as other components. Detector elements included in magnetic/RF detector  41 A may be SQUID detectors, atomic magnetometers, cooled and uncooled magnetometers, MEMs magnetometers, antennas, RF coils/receivers, etc. The object or target  31  may be a person, an anatomical part, explosives, cargo, weapons, vehicles, etc. 
         [0057]    The metamaterial lens structure  91 G focuses down radiation and/or magnetic fields from magnetic/RF source  21 A into object/ target  31 . Metamaterial lens structure  91 H focuses and collects the signal emitted by object/target  31  to magnetic/RF detector  41 A. Changes in focusing depth of metamaterial lens structure  91 G are achieved via mechanical or electrical switching of the meta-lens array  91 G, by switching control unit  99 A. The focusing volume of metamaterial lens structures  91 G and  91 H determines resolution of Imager  103 A and may provide a one-to-one correspondence between the pixelated source plane and the image plane. 
         [0058]      FIG. 6  is a block diagram of a Direct Magnetic Imager  104 A according to an embodiment of the present invention illustrated in  FIG. 4 . The Direct Magnetic Imager  104 A illustrated in  FIG. 6  includes a magnetic/RF source and detector  123 , metamaterial lens(es) or metamaterial lens array(s)  91 J, processor  51 B and switching control unit  99 B. Sources in unit  123  may include magnets, antennas, and RF coils. Detector elements included in unit  123  may include SQUID detectors, atomic magnetometers, cooled and uncooled magnetometers, MEMs magnetometers, antennas, and RF coils/receiver. The object/target  31  may be a person, an anatomical part, explosives, cargo, weapons, vehicles, etc. 
         [0059]    Magnetic/RF source and detector  123  may be one unit that performs the functions of source and detector at the same time. Magnetic/RF source and detector  123  may also include multiple units, each dedicated to be either a source or a detector. For example, a transmitter (source) and a receiver (detector) in unit  123  may be located in the same plane, or at positions that are adjacent to each other. 
         [0060]    Metamaterial lens structure  91 J focuses down radiation and/or magnetic fields from the magnetic/RF source  123  into object/target  31  and focuses back and collects the signal emitted by object/target  31  to the detector  123 . Changes in the focusing depth for metamaterial lens structure  91 J are achieved via mechanical or electrical switching of the meta-lens array by switching control unit  99 B. Resolution of the imager  104 A is determined by the focusing volume of metamaterial lens structure  91 J. 
         [0061]    In an exemplary embodiment, a permanent magnet may be used in the source  21 A/ 123  in  FIGS. 5 and 6 , to first align the protons in the object/target  31 . This magnetic field can be permanent or it can be terminated at any time during the imaging procedure. An AC magnetic field, which may be at the Larmor&#39;s frequency/frequencies of element(s) in object/target  31 , is then applied to achieve proton precession. The metamaterial lens structures  91 G and  91 J focus the field down into object/target  31 , while metamaterial lens structure  91 H collects the signal to receiver  41 A, or the same metamaterial lens structure  91 J collects the signal back to receiver  123 . These systems perform direct imaging like an optical imaging system, and 3D spatial information is obtained by re-focusing the metamaterial lens(es) into different dimensions. For example, the metamaterial lens(es) may be re-focused along the z-axis. Re-focusing may be performed in other directions as well, separately or simultaneously. The output signal is used to create an actual magnetic image into detector  41 A/ 123 . 
         [0062]    The Direct Magnetic Imaging apparatuses of the present invention offer multiple advantages, as they facilitate direct magnetic imaging in MRI and NMR applications, including portable MRI and NMR systems. Alternate, non-portable configurations and applications may also be implemented. Non-portable applications include traditional clinical MRI machines (e.g. 3 T, 1.5 T) in which the metamaterial lens is used as an add-on/external component to the MRI machine to concentrate/focus the magnetic fields into areas of interest inside the body allowing to increase the signal to noise ratio. Prostate imaging is a good example of an application for a modified MRI machine including a metamaterial lens. Another example is the use of the metamaterial lens as a replacement of the gradient coils in the traditional non-portable MRI machines. 
         [0063]    In another exemplary embodiment illustrated in  FIG. 7 , the metamaterial lens structure replaces the gradient coils which are typically used in MRI units, for example, to encode the RF signal in each spatial dimension. The imaging system of  FIG. 7  thus allows focusing of the RF fields for direct imaging applications. The Imager in  FIG. 7  includes a source  21 B which may be magnets or RF coils which pre-polarize the atoms, a metamaterial lens structure  91 K which focuses a field from source  21 B into a subject  31 , and another metamaterial lens structure  91 L which focuses a signal/field from subject  31  into the detector/receiver  41 B which may be an RF coil or a magnetometer. In one embodiment, one of metamaterial lens structures  91 K and  91 L may be bypassed. Detector/receiver  41 B may detect a change in the magnetic field (for example, by looking for resonance) or spatially map magnetic fields received from subject  31 . The change in magnetic fields detected by detector/receiver  41 B is a function of the input field applied. In exemplary embodiments, the field change detected by detector/receiver  41 B may be of the order of μT, mT, or Tesla. The detector/receiver  41 B may include an RF receiver for MRI, SQUID detectors, and cooled and uncooled magnetometers to collect the signal, for additional applications. 
         [0064]    Co-pending U.S. application Ser. No. 12/801,799 filed on Jun. 25, 2010, the entire contents of which are being hereby incorporated by reference, describes a Bio-Magnetic Imager which includes metamaterial lens structures and can be used for detection of anatomical features. In an exemplary embodiment in U.S. application Ser. No. 12/801,799, one or more metamaterial lens structures concentrate an ultra low magnetic field to a person of interest, and then concentrate the magnetic signature from the person into to a detector. A contrast agent may be applied to the subject for detection of a signature of a certain type of anatomical change, or to a non-biological subject (for example, for magnetic imaging for border patrol or underwater vehicle sensing) for detection of a change in a material characteristic or for materials characterization. 
         [0065]    As mentioned before, traditional magnetic imaging approaches, whether in high field or low field, do not use a “direct” magnetic imaging approach to produce an image. Traditional MRI approaches are limited by the fact that RF wavelengths (in the meter range) cannot focus down to the resolution spot size that is required for diagnostic and spectroscopic purposes. The conventional approach for increasing resolution in an MRI system is to increase the magnetic field strength, with the drawback that the higher magnetic field systems are more costly, bulkier, and require additional infrastructure. For instance, a 3 Tesla MRI system costs ˜$3M, while a 1.5 Tesla MRI system costs ˜$1.5M; thus, the traditional MRI imaging approach has limited capability to increase sensitivity and decrease the acquisition time. For these reasons, traditional magnetic imaging approaches have limited applicability. 
         [0066]    The direct magnetic imaging approach described in the present invention enables new applications such as high resolution portable MRI systems and adjacent market applications such as airport security, underwater vehicle detection, etc., by integrating a metamaterial lens system in a traditional magnetic imager, as is shown in  FIG. 8 . In the Imager of  FIG. 8 , gradient coils are used with the metamaterial lens, which acts as a concentrator to enhance SNR. In  FIG. 7 , the gradient coils are replaced by the metamaterial lens, taking advantage of the super resolution offered by the lens to be able to image localized areas in the object/subject without the need for the gradient coils to provide the spatial encoding. 
         [0067]    Imager  103 C in  FIG. 8  includes an imaging system, which may be an MRI system, which has been modified from its traditional form, to include metamaterial lens structures. In order to obtain reasonable resolution for an MRI application, the meter long wavelengths are focused down to millimeter sizes (˜on the order of lambda/1000) by the metamaterial lens structure. 
         [0068]    A metamaterial lens structure may also used as an external component added to traditional NMR systems, traditional SQUID-based low field systems and other magnetic applications, to improve sensitivity and detector SNR, without altering the underlying system configuration. Each atomic nuclei (all materials) have a distinct signature that is largely unperturbed by surrounding environment. These distinct signatures could be detected through NMR if the signal-to-noise ratio (SNR) becomes good enough to interpret the signature. For traditional NMR spectroscopy, the signal to noise ratio is limited by the strength of the magnetic response of the multiple atoms composing the sample. Identification is performed by discriminating among the different Larmor&#39;s frequencies associated with the sample. Physical techniques (e.g. sample rotation) need to the employed in order to boost the SNR, making the traditional NMR technique only useful in laboratory settings. 
         [0069]    When a metamaterial lens system is integrated in an NMR imaging system and is tuned to the desired Larmor frequencies, a focused signal into the object/target and/or into the receiver is created. The meta-structures focus down radiation below the typical diffraction limited spot and enable detection of distinct signatures of nuclei or atoms through NMR, by boosting the signal portion without the need for boosting the magnetic field, to obtain a high SNR and interpret the signature. Detection provided by the metamaterial lens structure enables identification of biological changes and non-biological materials and chemicals even when the materials and chemicals are embedded inside other objects. 
         [0070]    The use of a metamaterial lens structure in a traditional MRI or NMR or other magnetic system improves sensitivity and signal to noise ratio without altering the basic system configuration. The Fourier Transform is still used to reconstruct the image in the MRI system. The detector/receiver in such a modified MRI/NMR system may include an RF receiver for MRI, and may also include SQUID detectors, and cooled and uncooled magnetometers to collect the signal, for additional applications. 
         [0071]    An MRI system includes a magnet, gradient coils, and RF receivers. A signal is obtained by the RF receivers by applying an AC magnetic field (RF field) corresponding to the hydrogen&#39;s Larmor frequency. In the embodiment illustrated in  FIG. 8 , metamaterial lens structure  91 P collects and focuses the signal into detector/receiver  41 C, metamaterial lens structure  91 N focuses the signal from gradient coils  21 D into a subject  31 . Another metamaterial lens structure  91 M focuses the signal from source  21 C into subject  31 . In alternative embodiments, one or two metamaterial lens structures among  91 M,  91 N and  91 P may be omitted. In exemplary embodiments, source  21 C includes magnets and/or RF coils, and detector/receiver  41 C may be a MRI detector/receiver, and/or may include an RF coil or a magnetometer. 
         [0072]    In other exemplary configurations, a tunable/multi-frequency magnetometer (e.g., a MEMS based magnetometer) detector is used in conjunction with metamaterial lens structures which are tuned to one or more specific collecting frequencies of the sensor, to increase sensitivity, SNR and applicability, and to reduce the need for shielding and high magnetic fields. Such Imagers are illustrated in  FIGS. 9 and 10 , in which a tuning unit  99 D communicates with metamaterial lens structures  91 D,  91 E and  91 F and with tunable multi-frequency detector/receiver  41 D for tuning to the specific collecting frequency or frequencies of the detector/receiver. The tuning unit  99 D may be a standalone unit, or may include multiple units incorporated in the metamaterial lens structures and/or in the detector/receiver. In one embodiment, only one metamaterial lens structure in  FIG. 9  is tunable. 
         [0073]    In an exemplary embodiment, the components of the Direct Magnetic Imager system are tuned to specific frequencies to facilitate NMR type applications by tuning to the desired Larmor frequencies. In such systems, a tuning unit may communicate with one or more metamaterial lens structures, with the NMR source and/or with the detector, to tune to specific frequencies associated with desired Larmor frequencies of one or more elements in the object or target. The resonance of the Imager may also be selected based on the external magnetic field strength, frequency of an RF coil included in the detector and/or frequency of an RF gradient coil used to interrogate the sample/subject in order to obtain information. 
         [0074]    Magnetic resonance can be tuned to specific elements, in which case the frequency response will change based on applied field strength, by orders of magnitude. The Direct Magnetic Imager including metamaterial lens structures enables precise tunability in the input/output signal, allowing for imaging to be tuned to specific elements other than hydrogen. Tunability may be provided by tunable elements included in/on the lens, or by a stacking of metamaterial lenses where each lens is tuned to a specific frequency or frequency range and has a narrow operating bandwidth, and each metamaterial lens can be selected based on the desired frequency response, by tuning through the field range. Thus, the resonance of the Imager can be switched through an entire field range. The detector may also be designed to detect in multiple frequencies or frequency ranges. The range or magnitude of magnetic fields from the source, and the spatial or frequency-dependent characteristics of the detector can be selected in connection with the resonant frequencies to be detected by the Imager, to improve tunability of the device. The Imager of the present invention can be used to select resonance signals based on an external magnetic field strength as well as frequency of detector and/or frequency of a device used to interrogate the sample/subject in order to obtain information. Currently, no other imaging technique has the capability to enable precise tunability while allowing for imaging to be tuned to specific elements other than hydrogen. 
         [0075]      FIG. 11  illustrates a method for direct magnetic imaging using metamaterial lens structure(s) according to embodiments of the present invention illustrated in  FIGS. 1-4 . A first electromagnetic field is generated (S 301 ) and transmitted to an object or target (S 303 ). Additional electromagnetic fields may be generated (S 305 ) and sent to object/target (S 306 ) to superimpose with the original field and cause specific changes in the object/target. In an exemplary embodiment, the first field may be a static magnetic field, and the additional field may be a transient RF wave which is superimposed on the static field. The first field and/or the additional fields may be focused by metamaterial lens structure(s) into the object/target (S 307 ). A metamaterial lens structure may also collect and focus a field signal into an intermediary field generator (S 308 ), such as a generator of RF waves. A metamaterial lens structure may also collect and focus a signal emitted from the object/target and send the signal to a detector/receiver (S 309 ) which creates an actual image of an area in the object/target (S 311 ). The metamaterial lens structure may be tuned to specific collecting frequency/frequencies of the sensor (S 313 ). The signal from object/target may also be sent directly to the detector/receiver (S 310 ). 
         [0076]    The other metamaterial lens structures may also be tuned in frequency (S 315 ). Focusing parameters of the metamaterial lens structures may be changed based on imaging requirements (S 317 ). 
         [0077]      FIG. 12  illustrates a sensor  141  which operates at room temperature and may be used as a detector component in a detector  41  of a Direct Magnetic Imager according to embodiments of the present invention illustrated in  FIGS. 1-4 . The sensor in  FIG. 12  is a magnetorestrictive sensor which includes a magnetoelectric multilayer portion including layers  301 ,  302  and  303 . Layer  303  is a semiconductor material such as silicon. 
         [0078]    In an exemplary embodiment of the sensor  141 , layer  301  may be a FeGa layer and layer  302  may be a piezoelectric material such as, for example, PZT. In the exemplary embodiment, the length of the sensor between points A and B is ˜20 mm, the cantilever thickness is on the order of 10&#39;s of microns, the thickness of layer  301  is ˜1.5 micron and the thickness of layer  302  is ˜1.5 micron. 
         [0079]    In an exemplary embodiment, a MEMS device in the detector is a cantilevered, thin film coated magnetorestrictive device. Such detector component has a performance comparable to that of a SQUID device used currently in low field MRI, but does not require the cryogenic cooling required by SQUID devices, thus reducing the power and cooling required to run the imager. Such exemplary magnetorestrictive sensors have shown room temperature sensitivity down to 10 −7  to 10 −10  Tesla. 
         [0080]    In an exemplary embodiment, the detector component may be a low magnetic field detector in the range of sub-μT, which operates at room temperature and provides high sensitivity comparable to, or higher than, the sensitivity of a cooled SQUID device. In other exemplary embodiments, the detector component may be a high magnetic field detector in the range of Tesla, or a medium magnetic field detector. 
         [0081]    Exemplary magnetorestrictive sensors that may be used as a sensor in the Direct Magnetic Imager of the present invention are described in US Patent Application Publication US 2007/0252593 A1 (U.S. Pat. No. 7,345,475) by Takeuchi et al, the entire contents of this patent being hereby incorporated by reference. 
         [0082]    The sensor illustrated in  FIG. 12  is a magnetorestrictive sensor that operates at room temperature and can replace cryo-cooled SQUID based MRI systems, to reduce power usage and packaging size and volume for the Imager. Unoptimized sensors have already shown ability to detect sub-μT magnetic fields. Optimization of the sensor performance has also been achieved, further improving the sensitivity to enhance the imaging capabilities the Imager of the present invention for enhanced imaging performance in any field location, coupled with the ability to image areas of arbitrarily small size. In exemplary embodiments, the Imager of the present invention can image areas in cm, mm or sub-mm ranges. In an exemplary embodiment, imaging to a focal spot of ˜1 cm was demonstrated. The magnetic fields may vary from high fields (such as 3 T) to ultra-low fields (e.g., micro-T). 
         [0083]      FIG. 13  illustrates a MEMS device  142  including multiple cantilever devices for use in a tunable Direct Magnetic Imager according to an embodiment of the present invention. The MEMS device  142  can be used as a detector component in a detector  41 , in connection with metamaterial lens structures which are tuned to one or more specific collecting frequency or frequencies of the sensor. These frequencies depend on the length of the cantilevers in sensor  142 . 
         [0084]      FIG. 14A  illustrates imaging performance when a metamaterial lens is used according to an embodiment of the present invention, and  FIG. 14B  illustrates comparative imaging performance without a metamaterial lens. As can be seen in FIGS.  14 A and  14 B, two sources which cannot be resolved without a metamaterial (MM) lens, are easily resolved when the imaging is performed using the MM lens. 
         [0085]    Inclusion of a metamaterial lens has already been shown to give a 10× signal improvement in simulations, and a 4× signal improvement has been experimentally shown. The magnetically hyperspectral metamaterial device/solution which includes lens tunability to certain frequencies or to other imaging parameters may surpass the performance of one metamaterial lens. The magnetically hyperspectral device is a tunable metamaterial lens or a stacking of metamaterial lenses designed for specific frequencies and which can be turned on and off in order to probe at different frequencies. 
         [0086]      FIGS. 14C and 14D  illustrate wave propagation in an exemplary metamaterial lens used in a Direct Magnetic Imager according to an embodiment of the present invention. The exemplary metamaterial lens in  FIGS. 14C and 14D  is described in publication “Negative Refraction Makes a Perfect Lens”, by Pendry, Physical Review Letters, Vol. 85 (18), October 2000, pp. 3966-3969, the entire contents of this publication being hereby incorporated by reference. The wave propagation patterns in  FIGS. 14C and 14D  are for a Negative Index Metamaterial (NIM) with n or μ=−1 (ε=μ=−1) metamaterial lens. As can be seen in  FIGS. 14A-14D , metamaterials enable enhanced imaging performance/resolution while decreasing the need for shielding, subject proximity and field strength. 
         [0087]      FIGS. 15A ,  15 B,  15 C and  15 D illustrate exemplary metamaterial lenses for use in a Direct Magnetic Imager according to an embodiment of the present invention. The metamaterial lenses illustrated in  FIGS. 15A-15D  include a 3 T metamaterial lens ( FIG. 15A ) which has been experimentally fabricated. In an exemplary embodiment, the 3 T metamaterial lens may be used in an MRI imager. 
         [0088]    The metamaterial lens illustrated in  FIG. 15A  includes multiple unit cells shown in  FIG. 15B . Each unit cell illustrated in  FIG. 15B  includes rings with capacitors.  FIG. 15C , which illustrates the same unit cell as  FIG. 15B , shows the location of the capacitors in the unit cell.  FIG. 15D  illustrates a partially fabricated metamaterial lens based on the lens shown in  FIG. 15A . In exemplary embodiments, the lens is an isotropic lens in which said unit cells are arranged in an array, and each unit cell may include at least one ring with lumped capacitors and/or inductors. 
         [0089]      FIG. 15E  illustrates details and performance of metamaterial lenses included in a Direct Magnetic Imager according to an embodiment of the present invention. The lens in the first row of the table is disclosed in publication “Experimental Demonstration of a μ=−1 Metamaterials Lens for Magnetic Resonance Imaging”, by Freire et al., Applied Physics Letters, 93, 231108, (2008), the entire contents of this publication being hereby incorporated by reference. 
         [0090]    Design  1  is for a metamaterial lens which includes rings with capacitors. The lens of Design  2  includes a ring with capacitors (“caps”) and meander line inductors. In a meander line antenna, the wire is continuously folded to reduce the resonant length. Increasing the total wire length in an antenna of fixed axial length lowers its resonant frequency. The lens of Design  3  lens includes split rings with lumped capacitors and inductors. An SRR (split ring resonator) element is an electromagnetic analog of an LC circuit, in which the ring acts as an inductor and the gap as a capacitor. As a gap is brought into the ring to build a split ring configuration, the ring geometry becomes an open boundary instead of a closed one. The lenses of the other designs shown in the other rows of the table are 3 T designs with or without magnetic materials (Designs  5  and  4 ), 0.2 T designs without magnetic materials (Design  6 ), with magnetic materials in inductors (Design  7 ), and with magnetic materials in inductors and capacitors (Design  8 ), and a 2 kHz lens design (Design  9 ). In an exemplary lens embodiment, one split ring is a split ring resonator element including a metal strip and a gap, wherein the split ring acts as the unit cell and the gap is filled with a capacitor or inductor. The last column in the table illustrates figures of merit (FOM) for lens performance. 
         [0091]    The lenses of the various designs have different resonant structure forms, and differ from the lens of Freire et al. in their arrangement of elements (capacitors and/or inductors) on the individual unit cells. The arrangement of elements in the unit cells determines the design for a lens and the form of its resonant structure. 
         [0092]      FIGS. 16A and 16B  illustrate exemplary measured transmission of a coil without ( FIG. 16A ) and with ( FIG. 16B ) the fabricated metamaterial lens shown in  FIG. 15A , which can be used in the Direct Magnetic Imager of the present invention. As can be seen in  FIG. 16B , the addition of the metamaterial lens achieves a 100× signal improvement.  FIGS. 16A and 16B  were obtained by measurements performed at ˜132 MHz frequency where highest Q-value (˜100 enhancement) is observed with a focusing spot of ˜1.2 cm. 
         [0093]      FIGS. 17A and 17B  illustrate the change in normalized magnetic field intensity with a change in distance from an object to be imaged with a metamaterial lens used in an exemplary Direct Magnetic Imager according to an embodiment of the present invention. The physical setup for the measurements is shown in  FIG. 17A  for various image planes. The dimension “d” is the thickness of the metamaterial lens. The lens thickness can be engineered depending on the application, and the lens may include multiple layers. 
         [0094]    The Direct Magnetic Imager of the present invention may be arranged in an array such as a hemisphere array or a portable sensor array such as a vest, to obtain detailed spatial information from multiple locations of a subject/object which are within relevant sensing distance from the sensors in sensor array of the Imager. Other form factors that may be used for the arrangement and shape of the Imager include a helmet for traumatic brain injury (TBI) assessment, line arrays for airport security, etc. 
         [0095]    The Direct Magnetic Imaging device of the present invention has multiple advantages over state-of-the art imagers. The Imager provides tunability of the input magnetic field with reduced need for power, and is a broader band device. The Imager also exhibits selectivity of the detector to specific frequencies across a broad band without loss of sensitivity. The metamaterials lens acts as a resonant device having a relatively narrow bandwidth, which can therefore act as a filter as well as a concentrator. Metamaterials lenses in the Imager can be tuned, and can be used in a broad magnetic field range, from low magnetic fields such as, for example, μT fields or mT fields, to medium and large magnetic fields (e.g., 0.1T range and Tesla range magnetic fields or larger fields). 
         [0096]    Due to the lensing effect (both in input field and detected field), enhanced signal gathering from a target may decrease the need for extensive shielding and allow for larger distances to target, for stand off detection. Therefore, an object or target imaged with the Imager of the present invention does not have to be in direct contact with the detector, as it could be located at various distances from detector. In exemplary embodiments, the distances from an object/target to the detector may be on the order of centimeter, meter or larger than 1 meter, and the Imager may be used to process signals transmitted or reflected by the object/target. For example, the Imager may be used in airport security or underwater object detection. An Imager used in airport security may be shaped as an enclosing system, to include, for example, a “tunnel” for luggage to pass through for inspection. An Imager used for underwater detection may be a single sided system which interrogates an underwater object, such as an underwater rock formation, an underwater device/vehicle, etc. The underwater object can be interrogated by the Imager without being surrounded by the Imager or located in its proximity. The underwater object may be interrogated by an electric, magnetic, or electric and magnetic wave/field sent by the source of the Imager, so that a reflected signal is generated from the underwater object and received by the Imager&#39;s detector/receiver. The detector/receiver may be located in the vicinity of the source. One or more metamaterial lenses concentrate the signal/field sent to the underwater object by the source and/or concentrate the reflected field/signal from the underwater object before the signal is received by the detector/receiver. This Imager configuration may also be used on land for imaging objects located at a distance, or for imaging objects in other media besides water. 
         [0097]    The Imager has the ability to specifically tune by frequency or other imaging parameter, to differentiate between multiple material types, anatomical tissue types, substances, etc. at various location inside or on a surface of an object/target. For example, the Imager may be tuned by turning on or off different layers of the metamaterial lens. 
         [0098]    For example, in a metamaterial lens which includes multiple unit cells of one type (i.e., cells with magnetic permeability mu=−1, or cells with electric permittivity epsilon=−1, or cells with refractive index n=−1), the focusing depth of the lens may be changed by turning on or off various cell layers via mechanical or electrical switching of the meta-lens array. 
         [0099]    In a metamaterial lens which includes layers of different types, such as one layer with magnetic permeability mu=−1 and another layer with refractive index n=−1, the magnetic permeability mu=−1 layer or the refractive index n=−1 layer may be turned on or off to change the type of field enhancement of the lens (i.e., magnetic focusing versus magnetic and electric field focusing). In a metamaterial lens which includes layer(s) with magnetic permeability mu=−1, and/or layer(s) with electric permittivity epsilon=−1, and/or layer(s) with refractive index n=−1, different types of layers may be selectively turned on or off to provide magnetic and/or electric and/or magnetic and electric field focusing. Layers with magnetic permeability mu=−1 and/or layer(s) with electric permittivity epsilon=−1 and/or layer(s) with refractive index n=−1 included in one metamaterial lens may also be used simultaneously, to provide multiple types of field enhancement for the lens, at the same time. 
         [0100]    Simulations and preliminary testing of individual components of the Direct Magnetic Imager have been performed. These include simulations, fabrication, and measurement of the metamaterial lens and characterization of a single magnetometer sensor. 
         [0101]    The Direct Magnetic Imager of the present invention has the ability to perform imaging portably and on the field, and can therefore be used in any location, for clinical and emergency response and diagnostics, in the field military and surveillance applications, mobile security analysis, etc. The imager of the present invention can be used in various locations, in various climates, and may be designed to be easily carried to any field location, for example by a person physically transporting the imager carrying it in a cart, to perform immediate imaging without compromising detection quality. The Direct Magnetic Imager may be integrated into a compact form factor, to perform imaging portably in any setting. The form factor with which the device may be integrated may be, for example, a helmet-like form factor, or a portable unit for security imaging. When the device is integrated in a helmet-like form factor, the source, metamaterial lenses and detector are included in the helmet, to detect localized damage in the head of a subject. 
         [0102]    Principles of the present invention are applicable to various types of anatomical detection, as well as non-anatomical detection and imaging. Applications for the Direct Magnetic Imager of the present invention include underwater magnetic sensing and vehicle detection, imaging for weapons, airport security, imaging for metal containers, magnetic imaging for border patrol, and advanced sensors. While some aspects of the Direct Magnetic Imager have been described in the context of MRI or NMR detection, the principles of the current invention apply equally to direct detection of other features through magnetic or electric imaging techniques that detect signatures/characteristics of substances/materials based on changes in an electromagnetic field. 
         [0103]    Furthermore, although detailed embodiments and implementations of the present invention have been described above, it should be apparent that various modifications are possible without departing from the spirit and scope of the present invention.