Nonlinear and smart metamaterials for changing resonant frequency

Abstract

A passive MRI enhancement embodiment includes a plurality of resonators and increases the signal-to-noise ratio of a radio frequency signal transmitted by a specimen and captured by an MRI machine. The device increases the magnetic field component of the radio frequency energy during signal transmission from the MRI machine to the specimen and / or signal reception from the specimen to the MRI machine. Use of the device improves images generated by the MRI machine and / or reduces the time required for the MRI machine to capture images. An isolator embodiment has a nonlinear resonator and a second resonator that are controllably configured into an isolation configuration and a transmission configuration in an alternating manner. The nonlinear resonator is coupled to a communication port and is substantially communicatively isolated from the second resonator when the nonlinear resonator is in the isolation configuration and communicatively coupled to the second resonator when the nonlinear resonator is in the transmission configuration.

Description

[0001] Related applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 62 / 912,369, filed on October 8, 2019, entitled “Nonlinear and SmartMetamaterials Useful to Change Resonance Frequencies,” with inventors Xin Zhang, Stephan Anderson, Xiaoguang Zhao, and Guangwu Duan; and is also related to U.S. Non-Provisional Patent Application No. 16 / 443,126, filed on June 17, 2019, entitled “Apparatus for Improvement Magnetic Resonance Imaging,” [Practitioner File 32730-12503]; U.S. Non-Provisional Patent Application No. 16 / 443,126, filed on June 7, 2018, entitled “Apparatus for Improvement Magnetic Resonance Imaging,” with inventors Xin Zhang, Stephan Anderson, Guangwu Duan, and Xiaoguang Zhao. This application is a continuation-of U.S. non-provisional patent application No. 16 / 002,458 to Duan and Xiaoguang Zhao (now U.S. Patent No. 10,324,152 [Practitioner File 32730-12501]); U.S. Patent No. 10,324,152 claims priority to U.S. Provisional Patent Application No. 62 / 516,376 [Practitioner File 32730-11901], filed on June 7, 2017, and entitled “Apparatus for Improved Magnetic Resonance Imaging,” with inventors Xin Zhang, Stephan Anderson, Guangwu Duan, and Xiaoguang Zhao, the disclosure of each of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to resonant circuits, and in particular to circuits with controllable resonant frequency. Background Art

[0004] Magnetic resonance imaging (MRI) is a medical imaging technique that can capture images of a specimen's internal structure without the use of X-rays. An MRI machine applies a strong magnetic field and electromagnetic stimulation to the specimen, causing the specimen's atoms to emit electromagnetic signals in response. The MRI machine captures these electromagnetic signals and constructs an image based on them.

[0005] A known limitation of MRI machines is the signal-to-noise ratio (SNR) of the captured signal. Noise is generated by a variety of sources (including the circuitry of the MRI machine itself) and can corrupt and obscure the signal emitted by the specimen. The SNR can be improved by enhancing the signal (for example, by increasing the strength of the static magnetic field) or by reducing the noise (for example, by improving the signal processing circuitry of the MRI machine), or by a combination of both. These methods are less than ideal, but the amount of power that can be safely applied to certain specimens (such as living animals) is limited, and noise cannot be completely eliminated. Summary of the Invention

[0006] An exemplary embodiment discloses a signal amplification accessory for use within the bore of an MRI machine. The MRI machine has a transmitting coil configured to transmit an excitation signal having a transmit frequency to a specimen in the bore in a transmit mode, and a receiving coil configured to receive a response signal having a response frequency from the specimen in a receive mode.

[0007] In a first embodiment, an accessory includes a resonator array comprising a plurality of metamaterial resonators, each of the plurality of metamaterial resonators having a resonant frequency, the metamaterial resonators being configured to inductively couple to one another in response to an applied electromagnetic signal. An exemplary embodiment of the array includes at least two metamaterial resonators, but may also include more than two metamaterial resonators, for example, an N×M array of such resonators, where N and M are integers (e.g., 2, 3, 4, 5, 6, 7, 8).

[0008] The accessory also includes a nonlinear controlled resonator having (a) a resonator coil; and (b) a controllable impedance coupled to the resonator coil. The controlled resonator has a first resonant frequency when the controllable impedance is in a first impedance state, and has a second resonant frequency when the controllable impedance is in a second impedance state.

[0009] The resonator coil and the controllable impedance are selected such that the control resonator is configured to: (i) generate, together with the resonator array, a first array resonant frequency offset from the transmit frequency when the MRI machine is in the transmit mode; and (ii) generate, together with the resonator array, a second array resonant frequency equal to the response frequency to amplify the response signal when the MRI machine is in the receive mode.

[0010] The exemplary embodiment further includes a spacer layer disposed between the resonator array and the nonlinear resonator, the spacer layer defining a gap (d) between the resonator array and the nonlinear resonator.

[0011] In some embodiments, the resonator coil has a first end and a second end, and a controllable impedance is electrically coupled between the first end and the second end. For example, in some embodiments, the controllable impedance is a variable capacitance diode configured to assume the first impedance state in response to the variable capacitance diode receiving the excitation signal from the MRI machine when the MRI machine is in the transmit mode. As another example, in some embodiments, the resonator coil includes a split ring resonator, and the controllable impedance is or includes a variable capacitance configured to assume the first capacitance in response to receiving an RF excitation signal from the MRI machine in the transmit mode, and to assume the second capacitance when the MRI machine is in the receive mode. In some such embodiments, the variable capacitance diode is configured to assume the second impedance state in the absence of the excitation signal from the MRI machine when the MRI machine is in the receive mode.

[0012] In exemplary embodiments, the resonator array defines a resonator plane, and the control resonator is disposed substantially parallel to the resonator plane at a non-zero distance (d) from the resonator plane. For example, in some embodiments, the control resonator is disposed substantially parallel to the resonator plane at a distance (d) of 2 centimeters from the resonator plane. In other embodiments, the control resonator is disposed substantially parallel to the resonator plane at a distance (d) of 0 centimeters from the resonator plane. In these embodiments, the control resonator surrounds the resonator array.

[0013] Some embodiments further include a spacer device disposed in the spacer layer between the resonator array and the control resonator, the spacer device comprising a non-metallic, non-magnetic solid material, the spacer device maintaining the control resonator at a defined distance from the array. The spacer device disposed in the spacer layer between the resonator array and the control resonator. In a preferred embodiment, the spacer device is a non-metallic, non-magnetic solid material. The spacer device maintains the control resonator at a defined distance from the array.

[0014] Another embodiment discloses a method of amplifying a response signal from a specimen in a bore of an MRI machine.

[0015] The method includes providing a controllable array assembly, such as the one described above, in a bore of an MRI machine having an operating frequency. In some embodiments, the controllable array assembly includes (a) a resonator array comprising a plurality of metamaterial resonators configured to inductively couple to one another at the operating frequency of the MRI machine, and (b) a nonlinear controlled resonator having a controllable impedance.

[0016] The method includes configuring a steerable array assembly in a pass-through mode when the MRI machine is in a transmit mode, and configuring the steerable array assembly in a boost mode when the MRI machine is in a receive mode.

[0017] In some embodiments, configuring the controllable array assembly into the pass-through mode includes automatically configuring the nonlinear controlled resonator into a first resonant mode, wherein the nonlinear controlled resonator in the first resonator mode couples with the resonator array to generate an assembly resonant frequency in the controllable array assembly that is offset from the operating frequency of the MRI machine. In some such embodiments, automatically configuring the nonlinear controlled resonator into the first resonant mode includes providing a radio frequency excitation signal transmitted from the MRI machine to the controllable impedance.

[0018] In some embodiments, configuring the controllable array assembly into the amplification mode includes automatically configuring the nonlinear controlled resonator into a second resonant mode, wherein the nonlinear controlled resonator in the second resonator mode couples with the resonator array to produce an assembly resonant frequency in the controllable array assembly at the operating frequency of the MRI machine. In some such embodiments, automatically configuring the nonlinear controlled resonator into the second resonant mode includes blocking an excitation signal transmitted from the MRI machine from the controllable impedance.

[0019] However, other embodiments provide isolator circuits.

[0020] In one embodiment, such a circuit includes a first resonator having a characteristic resonant frequency; and a nonlinear resonator controllably configured into a first resonant state and a second resonant state, wherein in the first resonant state the nonlinear resonator has a first resonant frequency equal to the characteristic resonant frequency, and in the second resonant state the nonlinear resonator has a second resonant frequency different from the first resonant frequency.

[0021] In some such embodiments, the first resonator is configured to couple to a first port and the nonlinear resonator is configured to couple to a second port, and wherein: in the first resonant state, the nonlinear resonator is configured to inductively couple to the first resonator so as to communicatively couple a signal from the first resonator to the second port, and in the second resonant state, the nonlinear resonator is configured to isolate the second port from the first resonator.

[0022] To this end, in some embodiments, the nonlinear resonator includes a metamaterial resonator having a first end and a second end, and a coupler electrically disposed between the first end and the second end, wherein the coupler is controllably configured into a plurality of impedance states, the plurality of impedance states including: a first impedance state, the first impedance state configuring the nonlinear resonator into the first resonant state, and a second impedance state, the second impedance state configuring the nonlinear resonator into the second resonant state.

[0023] In some such embodiments, the metamaterial resonator comprises a split ring resonator.

[0024] In some embodiments, the coupler includes a variable capacitor configured to:

[0025] (a) having the second impedance state in response to a radio frequency signal incident on the coupler from the second port, such that the nonlinear resonator is in the second resonant state and the second port is isolated from the first resonator, and (b) having the first impedance state in the absence of such a radio frequency signal at a carrier frequency from the second port, such that the nonlinear resonator is in the first resonant state and is configured to communicatively couple the first resonator to the second port.

[0026] In other embodiments, the coupler includes a variable capacitor configured to:

[0027] (a) having the first impedance state in response to a radio frequency signal incident on the coupler from the second port, such that the nonlinear resonator is in the first resonant state and is configured to communicatively couple the second port to the first resonator, and (b) having the second impedance state in the absence of such a radio frequency signal at a carrier frequency from the second port, such that the nonlinear resonator is in the second resonant state and the second port is isolated from the first resonator.

[0028] In other embodiments, the coupler includes a switch, which may be a transistor or a MEMS switch, for example.

[0029] With respect to linear resonators, in some embodiments, the first resonator is a linear resonator, for example, a helical resonator.

[0030] Another embodiment provides a method comprising: providing a nonlinear resonator and a second resonator, wherein: the nonlinear resonator is controllably configured into an isolation configuration and a receiving configuration, the isolation configuration having an isolation mode resonant frequency, the receiving configuration having a receiving mode resonant frequency different from the isolation mode resonant frequency, and wherein the second resonator has a second resonant frequency equal to the receiving mode resonant frequency; and in a first mode, configuring the nonlinear resonator into the isolation configuration such that the nonlinear resonator is substantially communicatively isolated from the second resonator.

[0031] Some such methods further include, in a second mode, configuring the nonlinear resonator into the receiving configuration such that the nonlinear resonator is configured for resonant communication with the second resonator.

[0032] Furthermore, in some embodiments, the method further comprises, after configuring the nonlinear resonator into the receiving configuration, providing a signal to the second resonator; and receiving the signal at the nonlinear resonator.

[0033] In some embodiments, the method further comprises, after receiving the signal at the nonlinear resonator, configuring the nonlinear resonator into the isolation configuration to isolate the nonlinear resonator from the signal on the second resonator and to isolate the second resonator from another signal on the nonlinear resonator. In some such embodiments, the resonant coupling between the second resonator and the nonlinear isolator in the isolation configuration is at least 9 dB less than the resonant coupling between the second resonator and the nonlinear isolator in the receiving configuration.

[0034] Another embodiment provides a circuit comprising: a first resonant device for resonating in response to an applied electromagnetic signal, the first resonant device having a characteristic resonant frequency; and a nonlinear resonant device for selectively resonantly communicating with the first resonant device, the nonlinear resonant device being configurable into a first resonant state and a second resonant state, the first resonant state having a first resonant frequency equal to the characteristic resonant frequency, the second resonant state having a second resonant frequency different from the first resonant frequency.

[0035] In some embodiments, when the nonlinear resonant device is in the second resonant state, the nonlinear resonant device is substantially communicatively isolated from the first resonant device. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The patent or application file must contain at least one drawing executed in color. Copies of this patent or patent application publication and color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0037] The foregoing features of the embodiments will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0038] Figure 1A 、 Figure 1B 、 Figure 1C and Figure 1D Schematically illustrates an embodiment of an MRI machine;

[0039] Figure 2A is an MRI image captured without the use of a resonator array;

[0040] Figure 2B is an MRI image captured using an embodiment of a resonator array;

[0041] Figure 2C is an MRI image captured using another embodiment of the resonator array;

[0042] Figure 3A and Figure 3B Schematically illustrates an embodiment of a resonator array;

[0043] Figure 3C Schematically illustrating an embodiment of a cellular resonator array;

[0044] Figure 4A is a graph illustrating the quality factor of a resonant structure;

[0045] Figure 4B The relationship between the periodicity of a resonator array and its frequency response relative to the operating frequency of an MRI machine is graphically illustrated;

[0046] Figure 5A 、 Figure 5B and Figure 5C Schematically illustrates an embodiment of a helical resonator;

[0047] Figure 5D and Figure 5E Schematically illustrates operating features of embodiments of a helical resonator array;

[0048] Figure 5F Schematically illustrates a helical resonator unit with additional impedance;

[0049] Figure 5G and Figure 5HAn embodiment of a unit cell with water in a dish is schematically illustrated to demonstrate the relationship between the resonant frequency of the unit cell and the dielectric constant of the unit cell's internal volume;

[0050] Figure 5I Schematically illustrates the relationship between the resonant frequency of a unit cell and the dielectric constant of the volume inside the unit cell;

[0051] Figure 6A 、 Figure 6B 、 Figure 6C 、 Figure 6D and Figure 6E Schematically illustrates embodiments and some features of a broadside-coupled split-ring resonator;

[0052] Figure 7A and Figure 7B Schematically illustrating an embodiment of a flexible resonator array;

[0053] Figure 8A 、 Figure 8B 、 Figure 8C 、 Figure 8D 、 Figure 8E 、 Figure 8F and Figure 8G Schematically illustrates an embodiment of a tunable unit cell;

[0054] Figure 9 is a flow chart of a method for imaging a specimen;

[0055] Figure 10A Schematically illustrates an embodiment of a nonlinear resonator;

[0056] Figure 10B Schematically illustrates an embodiment of a nonlinear resonator;

[0057] Figure 11A Schematically illustrating an embodiment of a controllable array assembly;

[0058] Figure 11B Schematically illustrating another embodiment of a controllable array assembly;

[0059] Figure 11C is a graph showing the frequency spectrum of a controllable array assembly for different gaps between the array and the nonlinear resonator;

[0060] Figure 11D is a graph showing the spectrum of a controllable array component for high excitation and for low excitation;

[0061] Figure 11E is a graph showing the magnetic field (B) enhancement rate at points at different positions relative to the top surface of the array (LMM);

[0062] Figure 12A 、 Figure 12B 、 Figure 12C 、 Figure 12D 、 Figure 12E and Figure 12F Another embodiment of a controllable array assembly is schematically illustrated;

[0063] Figure 13 is a flow chart illustrating an embodiment of operating a controllable array assembly;

[0064] Figure 14A Schematically illustrating an embodiment of an isolator system;

[0065] Figure 14B Schematically illustrating an implementation of an isolator system on an integrated circuit;

[0066] Figure 15 is a flow chart illustrating an embodiment of operating an isolator. DETAILED DESCRIPTION

[0067] A device having multiple resonators increases the signal-to-noise ratio of radio frequency ("RF") signals emitted by a specimen and captured by an MRI machine, and does so without increasing the power transmitted by the MRI machine. In some embodiments, the device increases the magnetic field component of the RF energy during both the transmission of the RF energy from the MRI machine to the specimen and the transmission of the RF signal from the specimen to the MRI machine, while in other embodiments, the device increases the magnetic field component of the RF energy only during the transmission of the RF signal from the specimen to the MRI machine and does not increase the magnetic field component of the RF energy during the transmission of the RF signal from the MRI machine to the specimen. Furthermore, the device enhances specimen safety by substantially avoiding unnecessary electric field generation or increase. Use of the device improves images generated by the MRI machine and / or reduces the time required for the MRI machine to capture images.

[0068] definition

[0069] The term "transmit mode" with respect to an MRI machine refers to the mode in which the MRI machine provides an excitation signal to a specimen in the bore of the MRI machine.

[0070] The term "receive mode" with respect to an MRI machine refers to a mode in which the MRI machine receives a response signal from a specimen in the bore of the MRI machine.

[0071] The term "excitation signal" in relation to an MRI machine refers to a signal provided by the MRI machine to a specimen in the bore of the MRI machine in order to elicit a response signal from the specimen.

[0072] The term "response signal" (or "specimen response signal") in relation to an MRI machine refers to a signal generated by a specimen in the bore of the MRI machine in response to an excitation signal.

[0073] Figure 1A A cross-section of an MRI machine 100 is schematically illustrated, showing several well-known features of such machines. A specimen 99 to be scanned by the MRI machine is placed on a table 101. Typically, the specimen 99 must remain as still as possible for the duration of the scan, which can be 30 minutes or longer.

[0074] The MRI machine includes a "main" magnet 110 that generates a magnetic field around and through the specimen 99 (which may be referred to as a "main" magnetic field). In an exemplary embodiment, the main magnetic field is a static and uniform magnetic field. In some MRI machines 100, the main magnet 100 is a permanent magnet. In other MRI machines 100, the main magnet includes main magnetic field coils 110 that generate a magnetic field around and through the specimen 99. Some MRI machines 100 also include one or more shim coils 111 for correcting for deviations in the uniformity of the main magnetic field generated by the main magnetic field coils 110. Some MRI machines 100 also include one or more gradient coils 115 that create a variable magnetic field in addition to the magnetic field generated by the main magnetic field coils 110, which is used to locate the area to be scanned.

[0075] The MRI machine 100 has one or more systems (generally referred to as "RF coils" or "radio frequency coils") for transmitting radio frequency excitation signals to the specimen 99 and receiving MR signals (e.g., specimen response signals) generated by the specimen 99 in response to the excitation signals. Some RF coils may be referred to as "cage" coils. Historically, MRI machines have included coils, each with both transmit and receive capabilities. However, some MRI machines include a system (e.g., a collection of one or more coils) for transmitting radio frequency signals to the specimen 99, and a separate system (e.g., a collection of one or more coils) for receiving MR signals generated by the specimen 99. The exemplary embodiments described below include a body coil 120 that performs both transmission of radio frequency signals to the specimen 99 and reception of MR signals generated by the specimen 99. Some embodiments include a transmit coil for transmitting excitation signals to the specimen 99, and a receive coil, separate from the transmit coil, for receiving response signals from the specimen 99. Some examples of RF coils as components of MRI machines can be found in U.S. Patent Application Publication No. US2019 / 0041476 A1 to Otake et al. and U.S. Patent Application Publication No. US2009 / 0096456 to Biber et al.

[0076] In transmit mode, the body coil 120 transmits radio frequency signals, thereby subjecting the specimen 99 to electromagnetic (e.g., radio frequency) stimulation. Therefore, while the body coil 120 is referred to as a transmitter due to its own capabilities, the body coil 120 may be referred to as a "transmitting" coil, a "transmitter" coil, or a "driving" coil.

[0077] In response, the atoms of the specimen emit electromagnetic pulses (or "MR" signals) that are detectable by body coil 120 (in receive mode) and / or specimen coil 130. Specimen coils 130 (which may sometimes be referred to as "surface" coils) may be preferred in some circumstances because they can be positioned closer to specimen 99 and can produce signals with a greater signal-to-noise ratio ("SNR") than signals produced by the more distant body coil 120.

[0078] Computer 150 communicates data with MRI machine 100 (e.g., via communication link 151) and receives and processes signals received by body coil 120 and / or sample coil 130 to generate images of the internal structure of the sample. Body coil 120 and sample coil 130 are wired to MRI machine 100. Body coil 120 communicates power and control with MRI machine 100 to receive power and control signals required to generate electromagnetic stimulation. Both body coil 120 and sample coil 130 communicate data with MRI machine 100 to provide signals detected by them from sample 99 to MRI machine 100. To this end, some embodiments of the MRI machine include controller 140, which is configured to provide control signals to the MRI machine and / or an array described below in conjunction with control signal 821, and / or receive signals from body coil 120 and sample coil 130.

[0079] The quality of the image and the time required for the MRI machine 100 to acquire a sufficient number of emitted signals to produce an image depends in part on the signal-to-noise ratio ("SNR") of the received signal. As is known in the art, the signal-to-noise ratio is the ratio of the signal emitted by the specimen 99 in response to the stimulation of the specimen 99 by the MRI machine 100. The signal-to-noise ratio is a measure of the signal power (e.g., the power in the signal emitted by the specimen 99, which may be referred to as "signal power" or "P"). S ”) and the noise power in the signal received by the MRI machine (which may be called “noise power” or “P N ”). The signal-to-noise ratio is usually written as SNR = P S / P N The signal-to-noise ratio can be expressed in decibels (dB) according to the following formula: SNR (dB) = 10log 10 P S / P N , but not necessarily expressed in decibels.

[0080] Increasing the SNR may improve the output of the MRI and / or reduce the time required to acquire the signal from the sample 99.

[0081] Figure 1A and Figure 1B Each schematically illustrates an embodiment of a resonator array 300 for improving the operation and results of an MRI machine. In use, the resonator array 300 is disposed between the specimen 99 and the main magnetic field 110, the body coil 120, the shim coils 111, and the gradient coils 115. In the exemplary embodiment, in use, the resonator array 300 is disposed radially outside the specimen 99 and radially inside the main magnetic field 110, the body coil 120, the shim coils 111, and the gradient coils 115.

[0082] exist Figure 1A In the embodiment, the sample coil 130 is placed between the sample 99 and the resonator array 300, and Figure 1B In the example, resonator array 300 is positioned between specimen 99 (in this example, a limb or appendage 799 of specimen 99) and specimen coil 130. In some embodiments, resonator array 300 can be positioned in the bore 102 of an MRI machine without specimen coil 130, for example, when MRI machine 100 uses body coil 120 to receive electromagnetic pulses emitted by specimen 99. As used herein, the term "bore" 102 of MRI machine 100 refers to the location where specimen 99 is positioned when being imaged by MRI machine 100. For example, in a closed MRI machine 100, bore 102 is the interior of the machine's annular cross-section; in an open MRI machine 100, bore 102 is the space between the machine's top and bottom magnetic regions; and in an open upright MRI machine 100, bore 102 is the space between the machine's left and right magnetic regions. In exemplary embodiments, bore 102 of MRI machine 100 is defined by a component of MRI machine 100. For example, in the exemplary embodiment, components of the MRI machine 100 [e.g., the magnet 110 (including but not limited to the main magnetic field coil 110), the shim coils 111, the gradient coils 115, the body coil 120, although the sample coil 130 (if present) may be disposed within the bore 102].

[0083] Although 1A and Figure 1B The sample 99 is shown between the sample coil 130 and the resonator array 300 and the workbench. However, this is not a limitation on the use of the resonator array 300. The resonator array 300 (whether or not it has the sample coil 130) can be placed between the sample 99 and the workbench 101. Figure 1C and Figure 1D As shown schematically in .

[0084] In contrast to the body coil 120, the resonator array 300 is passive in that it does not require or receive a power signal, and in some embodiments does not require or receive a control signal to perform its function. As can be understood from the figures and the text, exemplary embodiments of the resonator array 300 are capable of passive operation, for example, to increase the signal-to-noise ratio of the signal emitted by the specimen. In exemplary embodiments, the resonator array 300 (including its unit cells 301) is separate from the MRI machine 100 and is not part of the MRI machine 100. In other words, in exemplary embodiments, the resonator array 300 is a component in addition to the components of the MRI machine 100 (e.g., in addition to the magnet 110 (including but not limited to the main magnetic field coil 110), the shim coils 111, the gradient coils 115, the body coil 120, and (if present) the specimen coil 130).

[0085] Furthermore, in the exemplary embodiment, the resonator array 300 (including its unit cells 301) is physically separated from the MRI machine 100 (e.g., the body coil 120 or the sample coil 130, the main magnetic field coil 110, the shim coils 111, and the gradient coils 115) and is not wired to the MRI machine 100 (e.g., the body coil 120 or the sample coil 130, the main magnetic field coil 110, the shim coils 111, and the gradient coils 115). Furthermore, in contrast to both the body coil 120 and the sample coil 130, the resonator array 300 does not perform data communication with the MRI machine 100.

[0086] The inventors have found that using Figures 1A to 1D The resonator array 300 schematically shown in FIG, with or without the sample coil 130, can improve the signal-to-noise ratio of radio frequency signals transmitted from the MRI machine 100 to the sample 99, improve the SNR of signals transmitted by the sample 99 and received by the MRI machine 100, improve the quality of MRI output images, and / or reduce the time required to scan the sample 99, each of which represents an improvement over existing MRI technology. Due to its unusual properties, the resonator array 300 and / or its resonators 301 can be considered a metamaterial. However, this does not require that the resonator array 300 and / or its unit cells 301 have a negative refractive index, a negative dielectric constant, and / or a negative permeability. In various embodiments, the resonator array 300 and / or its unit cells 301 can have a positive refractive index, a positive dielectric constant, and / or a positive permeability.

[0087] For example, Figure 2A The results of an MRI scan using conventional MRI techniques without the resonator array 300 are shown. To generate these results, the inventors scanned the MRI machine at nine locations ( Figure 2AThe inventors measured signal strength at three locations (numbered 1-9) on the MRI machine and measured noise at three locations (numbered 10-11). They then averaged the noise measurements and calculated the SNR as each signal measurement divided by the average of the noise measurements. The results are shown below and show that the SNR ranged from 33.2 to 39.0. These results can be referred to as "baseline" SNRs.

[0088] Signal strength (average)

[0089] 1 2 3 4 157.2 173.2 178.5 178.1 5 6 7 8 9 158.5 166.3 172.3 151.3 184.8

[0090] Noise level (standard deviation)

[0091] 10 11 12 Find the average 4.4 4.6 5.2 4.7

[0092] SNR

[0093] 1 2 3 4 33.2 36.6 37.7 37.6 5 6 7 8 9 33.5 35.1 36.4 32.0 39.0

[0094] and Figure 2A The opposite results are shown in Figure 2B and Figure 2C , respectively, show the results of MRI scans performed at the same nine locations using the same 1.5T MRI machine, where the unit cell 301 of the resonator array 300 is a helical resonator 500 (eg, Figures 5A to 5C ). In order to produce these results, the inventors combined the above Figure 2A The described approach measures signal and noise, but achieves a significantly improved SNR.

[0095] exist Figure 2B In the implementation of , the SNR is significantly higher than the baseline SNR. The results are shown below and show that the SNR is between 68.4 and 277.3. Figure 2B The SNR of position 1 in Figure 2A Comparing the results of position 1 in the figure, the results show a significant increase in SNR, i.e., from a baseline SNR of 33.2 to an improved SNR of 277.3.

[0096] Signal strength (average)

[0097] 1 2 3 4 1174 640.4 546.6 481.1 5 6 7 8 9 193.1 404.5 428.6 267.6 289.7

[0098] Noise level (standard deviation)

[0099] 10 11 12 Find the average 4.1 4.7 3.9 4.2

[0100] SNR

[0101] 1 2 3 4 277.3 151.3 129.1 113.6 5 6 7 8 9 45.6 95.5 101.2 63.2 68.4

[0102] exist Figure 2CIn an embodiment, an array 300 is presented in which a unit cell 301 is used to generate Figure 2B The arrays have different periodicities (i.e., different spacings between each other). This embodiment also produces SNRs at the same nine locations that are significantly higher than the baseline SNR. The results are shown below and show that the SNRs range from 46.2 to 401.5. Figure 2C The SNR of position 1 in Figure 2A Comparing the results of position 1 in the figure, the results show a significant increase in SNR, i.e., from a baseline SNR of 33.2 to an improved SNR of 401.5.

[0103] Signal strength (average)

[0104] 1 2 3 4 1258.0 605.9 498.2 381.7 5 6 7 8 9 95.9 363.6 343.1 156.6 144.9

[0105] Noise level (standard deviation)

[0106] 10 11 12 Find the average 2.7 3.5 3.2 3.1

[0107] SNR

[0108] 1 2 3 4 401.5 193.4 159.0 121.8 5 6 7 8 9 30.6 116.0 109.5 50.0 46.2

[0109] In general, the resonator array 300 increases the SNR of the signals emitted by the specimen. For a given MRI machine, embodiments of the resonator array 300 increase the SNR of these signals to at least 45.6, 50, 60, 95, 100, 120, 150, and / or at least 193.4, or any point between 45 and 401, relative to the SNR of the signals received by the MRI machine without the resonator array.

[0110] Resonator array

[0111] Figure 3A and Figure 3B An exemplary embodiment of a resonator array 300 is schematically illustrated. The array 300 in this embodiment includes 16 unit cells 301 in a 4x4 array, but other embodiments may use more or fewer unit cells 301 and may be arranged in different arrangements, such as square, honeycomb, or [ Figure 3C ] or rectangle.

[0112] Each unit cell 301 may also be referred to as a "resonator" because it is configured to resonate in response to an applied electromagnetic signal, such as a signal applied to the specimen 99 by the MRI machine 100 and / or a signal received by the unit cell 301 from the specimen 99 in the MRI machine 100. For example, each unit cell may have an inductance (L) and a capacitance (C) and thus may resonate like an LC resonator known in the art of electrical engineering. Each unit cell 301 has a resonant frequency and a Q (as combined with the Figure 4A described).

[0113] Figure 4A The quality factor of a resonant device is graphically illustrated. A resonant unit cell can be characterized in part by its quality factor, which may be referred to as its "Q factor," or simply its "Q." The Q factor of a unit cell is a measure of its resonant characteristics.

[0114] For example, unit cell 301 may receive electromagnetic signals emitted by atoms of sample 99 in MRI machine 100 or from the MRI machine itself, and this electromagnetic energy may include energy of one or more frequencies. The energy will resonate in unit cell 301 in a manner known from LC circuits in the field of electrical engineering.

[0115] Ideally, the energy at the resonant frequency f of the unit cell o (401), although the unit cell 301 can also resonate at a lower frequency to a certain extent, such as Figure 4A The maximum energy can be found at frequency f o (401), which can be called the center frequency (indicated by the amplitude A1). At other frequencies, the energy is less than the energy at the center frequency 401, as also Figure 4A At a certain frequency 402 above the center frequency 401 (which may be referred to as the upper 3dB frequency) and another frequency 403 below the center frequency (which may be referred to as the lower 3dB frequency), the energy in the resonant signal will be half of the energy at the center frequency 401. Figure 4A The spectrum 400 in FIG. 4 shows that some of the energy resonating in the unit cell 301 is above the noise floor, as shown by point 405 .

[0116] Then, the Q of the unit cell 301 is defined as the center frequency (f o ) divided by the ratio of the difference between the upper 3dB frequency and the lower 3dB frequency (Δf or δf). Figure 4A , Q is the center frequency 401 divided by the frequency difference 410 between the upper 3dB frequency 402 and the lower 3dB frequency 403. Therefore, Q is a dimensionless parameter.

[0117] In operation, unit cell 301 can receive electromagnetic energy packets (e.g., RF energy) from one or more atoms in sample 99, with the electromagnetic energy having a frequency equal to or close to the operating frequency of the MRI machine. For example, in a preferred embodiment, the electromagnetic energy having a frequency within + / - 5% (inclusive) of the MRI machine's operating frequency is defined as equal to or close to the MRI machine's operating frequency. Over time (e.g., during operation of the MRI machine), each unit cell 301 will receive many electromagnetic energy packets and store the sum of these energy packets. The higher the Q of unit cell 301, the more efficiently the unit cell 301 stores the energy it receives.

[0118] Furthermore, as the unit cell 301 resonates, it amplifies the magnetic field component of the received electromagnetic energy and increases the signal-to-noise ratio of the received electromagnetic energy. Thus, each unit cell 301 individually has the ability to resonate, regardless of other unit cells (if any) that may be nearby, and has some ability to amplify the magnetic field component of the received electromagnetic energy.

[0119] However, the inventors have discovered several limitations in the use of individual unit cells 301. First, a single unit cell 301 has a limited ability to amplify the magnetic field component of received electromagnetic energy. Second, a unit cell 301 may have a resonant frequency that does not match that of the MRI machine 100, in which case its ability to amplify the magnetic field component of received electromagnetic energy is less efficient than it would otherwise be. Third, it is not possible to change the resonant frequency and / or Q of an individual unit cell 301, at least without disassembling and reconstructing the unit cell 301.

[0120] However, the inventors have also discovered that the array 300 of unit cells 301 has characteristics that are different from a simple aggregation of the characteristics of its constituent unit cells 301. In other words, the resonator array 300 exhibits a synergistic effect.

[0121] For example, the array of unit cells 300 provides uniform amplification of the magnetic field component of the received electromagnetic energy (see, for example, Figure 5D and the text describing the figure).

[0122] Furthermore, the resonant frequency of the array 300 can be different from the resonant frequencies of its constituent unit cells 301. Instead, the unit cells 301 are coupled to each other to produce the resonant frequency of the array 300. To this end, in a preferred embodiment, the unit cells 301 are magnetically coupled to each other and are not wired to each other.

[0123] Furthermore, the resonant frequency of the array 300 can be tuned by adjusting the spacing of the unit cells 301 within the array 300 .

[0124] Furthermore, the array 300 is modular in that unit cells 301 can be added to the array 300 at the same periodicity (i.e., X pitch 310 and / or Y pitch 311) of the unit cells 301 already present in the array 300 without significantly changing the resonant characteristics of the array 300. Adding unit cells 301 to the array 300 at the same periodicity as the unit cells 301 already present in the array 300 does not change the resonant characteristics of the array as would changing the periodicity of the unit cells 301 of the array 300. Adding unit cells in this manner may be desirable, for example, to increase the size of the array 300 to image a larger specimen 99 or a larger portion of a specimen 99.

[0125] Similarly, a unit cell 301 already present in the array 300 having a given periodicity may be removed from the array 300 without significantly changing the resonant characteristics of the array 300. Removing a unit cell 301 from the array 300 having a given periodicity does not change the resonant characteristics of the array as much as changing the periodicity of the unit cells 301 of the array 300. Removing unit cells may be desirable, for example, to reduce the size of the array to fit within the bore 102 of the MRI machine 100, or to image a smaller specimen 99 or a smaller portion of a specimen 99.

[0126] The resonator array 300 is configured to have a resonant frequency that is equal to or close to the operating frequency of the MRI machine 100 (i.e., the resonant frequency of the array is within + / - 5% (inclusive) of the operating frequency of the MRI machine 100). For example, the operating frequency (or "operating frequency") of a 1.5 Tesla (i.e., 1.5 T) MRI machine is approximately 64 MHz (which is a radio frequency for the purposes of this disclosure), while the operating frequency of a 3 Tesla (i.e., 3 T) MRI machine is approximately 128 MHz (which is also a radio frequency for the purposes of this disclosure).

[0127] The resonant frequency of the resonator array 300 is determined in part by the periodicity (spacing) of the unit cells 301 of the array 300 and also by the resonant frequency of a single unit cell 301. Figure 3A and Figure 3BIn the exemplary resonator array 300 of FIG. 1 , the resonators are evenly spaced: each unit cell 301 is separated by a certain dimension along the X-axis (X pitch 310 of 37.33 mm) and a certain dimension along the Y-axis (Y pitch 311 of 37.33 mm). In this configuration, the resonant frequency 463 of the resonator array 300 is centered around the operating frequency 452 of the MRI machine 100. Typically, the difference between the operating frequency 452 of the MRI machine and the resonant frequency of the resonator array 300 can be specified by the designer or operator of the MRI machine. In a preferred embodiment, the resonant frequency of the resonator array 300 is within + / - 5% (inclusive) of the operating frequency 452 of the MRI machine.

[0128] At greater periodicity (ie, larger X-pitch 310 and Y-pitch 311), the resonant frequency of resonator array 300 decreases, and at lower periodicity (ie, smaller X-pitch 310 and Y-pitch 311), the resonant frequency of resonator array 300 increases. Figure 4B The relationship between the periodicity of the resonator array 300 and its frequency response relative to the operating frequency 452 of the MRI machine is graphically illustrated. Curve 462 schematically illustrates the resonance of the array 300 tuned to the operating frequency 452 of the MRI machine 100, with the resonant frequency at point 463. In contrast, curve 460 schematically illustrates the resonance of the array 300 tuned to a frequency 450 slightly below the operating frequency 452 of the MRI machine 100, with the resonant frequency at point 461, and curve 464 schematically illustrates the resonance of the array 300 tuned to a frequency 454 slightly above the operating frequency 452 of the MRI machine, with the resonant frequency at point 465.

[0129] Thus, the resonant frequency of the resonator array 300 can be adjusted and established based on the needs or desires of a given MRI machine or application. For example, the inventors have recognized that the presence of soft tissue near the array 300 may change the dielectric constant of the area surrounding the array 300. If such a change in dielectric constant interferes with or degrades the operation of the MRI machine 100 or the resonator, the resonant frequency of the resonator array 300 can be adjusted by changing the spacing of the unit cells 301 of the resonator array 300.

[0130] Helical unit cell

[0131] Figure 5A 、 Figure 5B and Figure 5C An exemplary embodiment 500 of a unit cell 301 in the form of a helical resonator 500 is schematically illustrated in FIG. The resonator 500 comprises a helical conductor 510 surrounding a low dielectric core 520.

[0132] The spiral conductor 510 may be copper, which is wound around a core 520 such that each successive turn ( 513 ) (or “loop”) around the core is separated from the previous turn by a gap 515 .

[0133] The unit cell 301 has both inductance (L) and capacitance (C). The inductance originates from the coil conductor 510, and the capacitance originates from the gaps 515 between consecutive turns 513 of the conductor 510. Therefore, the resonant frequency of the unit cell 301 is determined at least in part by the number of turns 513 of the conductor 510 and the size of the gaps 515 between the turns 513. Therefore, the designer can establish the inductance and capacitance, and thus the resonant characteristics of the unit cell 301, by specifying the characteristics of the coil conductor 510 (e.g., the number of turns 513 and / or the gaps 515) and / or the dielectric constant (k) and / or loss angle of the core 520 to suit the desired application. In addition, the resonant frequency of the array 300 of unit cells 301 can be tuned by specifying or adjusting the resonant characteristics of the unit cell 301, for example, by increasing or decreasing the number of turns 513 of the conductor 510 and / or increasing or decreasing the gaps 515 between the turns 513 of the conductor 510.

[0134] In some embodiments, conductor 510 does not overlap itself, but in other embodiments, conductor 510 may overlap itself as long as there is no direct electrical contact between different areas of conductor 510. For example, if conductor 510 includes an electrically insulating coating 512, conductor 510 may overlap itself.

[0135] Figure 5C The core 520 is schematically illustrated without the conductor 510. In some embodiments, the outer surface 523 of the core 520 includes a helical groove 530 for accommodating the conductor 510 and defining its helical shape.

[0136] The ends 511 of the conductor 510 are not connected to each other, to another conductor, or to another resonator's conductor 510. Therefore, the conductor 510 may be referred to as a split-ring resonator, a split-ring coil, or a split-ring spiral resonator.

[0137] In a preferred embodiment, the core 520 has a low dielectric constant (k) and a low loss factor. For example, the core 520 can be made of a material such as polyvinyl chloride ("PVC"), which has a dielectric constant of 3 (k=3). As used herein, a dielectric constant (relative dielectric constant) less than 15 is considered a "low dielectric constant" (or "low relative dielectric constant"), while a dielectric constant (relative dielectric constant) greater than or equal to 15 is considered a "high dielectric constant" (or "high relative dielectric constant").

[0138] However, in some embodiments, the dielectric constant of the core 520 can be greater than 3, which reduces the size of the unit cell 301 while maintaining the same resonant characteristics, possibly by adjusting other properties of the unit cell 301. Figure 5G 、 Figure 5H and Figure 5I As shown schematically, the inventors conducted experiments using water, which has a dielectric constant of about 80 at 20 degrees Celsius. The unit cell 500 was placed in a dish 560 surrounded by a connection loop 561 connected to a network analyzer. When the dish 560 was filled with only air, the resonant frequency of the unit cell 500 was 63 MHz, as shown in FIG. Figure 5I However, when the dish contains water in such a way that the water fills about ten percent (10%) of the core 520 (the surface 566 of the water is at 10%), the resonant frequency of the unit cell 500 is 55 MHz, as shown by point 567 in FIG. Figure 5I When the dish contains water in such a way that the water fills about twenty percent (20%) of the core 520 (the surface 566 of the water is at 20%), the resonant frequency of the unit cell 500 is 39 MHz, as shown by point 568 in FIG. Figure 5I , as shown by point 569 in FIG. Thus, it can be appreciated that by including a material having a higher dielectric constant than air within a given unit cell 500, the resonant frequency of the unit coil 500 is reduced. Conversely, to produce a unit cell 500 having a given resonant frequency, the unit cell 500 can be made smaller (e.g., having a smaller number of turns 513), with the interior 503 of the unit cell 500 having a relatively higher relative dielectric constant (e.g., between 86 and 173) relative to a unit cell 500 having air within its core 520. For example, some embodiments include a core having a dielectric constant between 86 and 173. In some embodiments, the relative dielectric constant can even be greater than 173. Some such embodiments include a core 520 made of titanium dioxide.

[0139] Some embodiments omit the core 520 and include a conductor 510 fixed in a helical shape (see, for example, Figure 5B ). In these embodiments, in air, the volume within the helical coil 510 has an air dielectric constant close to 1 (k=1).

[0140] The characteristics of the helical resonators 500 may be determined by the type of MRI machine in which they will be used. Figure 5AIn the embodiment of FIG5 , core 520 is a hollow cylinder having an outer diameter 522, an inner diameter 521, and a height 525. However, this shape and those dimensions are not limiting for all embodiments, and other solid or hollow shapes may be used, including shapes having square or triangular cross-sections (to name a few examples). Features of exemplary embodiments of spiral resonator 500 for a 1.5T MRI machine and a 3T MRI machine are given below.

[0141]

[0142] Operation of the resonator array

[0143] In operation, the resonator array 300 is placed on or near the specimen 99 in the MRI machine 100, as shown in FIG. Figure 1A 、 Figure 1B 、 Figure 1C and Figure 1D As shown in the schematic diagram.

[0144] The resonator array 300 resonates at or near the operating frequency 452 of the MRI machine 100, thereby increasing the magnetic field strength of the RF signal emitted by the specimen 99. Thus, the RF SNR is increased.

[0145] Resonator array 300 increases the magnetic field component of radio frequency energy during transmission from MRI machine 100 to specimen 99 and during reception of radio frequency energy from specimen 99 to the MRI machine.

[0146] For example, in an embodiment of the resonator array 300 where the unit cells 301 are helical resonators 500, Figure 5D The magnetic field strength at different heights above the top 302 of the unit cell 301 (eg, on the Z-axis) is graphically illustrated. Figure 5E The magnetic field enhancement rate at the center point of the array 300 as a function of distance from the middle 303 of the unit cell 301 is graphically illustrated, and shows that the enhancement is greatest near the middle 303 of the unit cell 301 and decreases with distance from the middle 303 of the unit cell 301. It should be noted that Figure 5D It can be seen that the magnetic field enhancement is substantially uniform across the resonator array 300. In the helical resonator 500, the magnetic field enhancement occurs due to the overlap between the self-resonant frequency of the helical resonator 500 and the excitation frequency of the magnetic field.

[0147] Advantageously, resonator array 300 also substantially avoids the generation of electric fields, or minimizes the increase in the electric field component of these RF signals. For example, the electric field created at one end 501 of resonator 500 almost completely cancels the electric field at the other end 502. Furthermore, in various embodiments, the increase in the electric field component of these RF signals is less than the increase in the magnetic field component of these RF signals. This is beneficial for specimen safety, as electric fields can cause burns to the specimen. Specifically, helical resonators 500 are configured so that they are decoupled from the electric field of the RF signal, thereby mitigating the amplification of the electric field component of the RF signal by helical resonators 500 and array 300.

[0148] Figure 5F An alternative embodiment of a helical resonator 500 is schematically illustrated, including an additional fixed reactance 550 electrically coupled between the ends 511 of the conductor 510 of the unit cell. The additional reactance 550 is in addition to the inductance and / or capacitance of the conductor 510. The additional reactance 550 can be a capacitor (C) or an inductor (L). In practice, the additional reactance 550 interacts with the capacitance or inductance of other structures of the helical resonator 500. For example, because the resonant frequency of the helical resonator 500 is determined by Including an inductor (L) in the additional reactance 550 produces a spiral conductor 500 having the same resonant characteristics as described above, but with a smaller number of turns 513 and / or a smaller diameter 521 of the spiral. Similarly, including a capacitor (C) in the additional reactance 550 produces a spiral conductor 500 having the same resonant characteristics as described above, but requiring less capacitance from the spiral conductor 510.

[0149] BC-SRR unit cell

[0150] Figure 6A An embodiment of a unit cell 301 in the form of a broadside coupled split ring resonator 600 ("BC-SRR") is schematically illustrated. The BC-SRR resonator 600 includes two "C" shaped split ring resonators 610, 620, each defining a gap 611 and 621, respectively. The split ring resonators 610, 620 are arranged in a manner similar to the embodiment of the present invention. Figure 6A are arranged parallel to each other in the XY plane and do not intersect or physically touch each other. Figure 6A As shown, split ring resonators 610, 620 are positioned so that their gaps 611 and 621 are diametrically opposed to each other (i.e., 180 degrees from each other). The BC-SRR unit cell resonates well even if gaps 611 and 621 are not 180 degrees from each other, but this is the preferred arrangement because the inventors have found that this arrangement produces the lowest electric field. For reference, the top split ring resonator 610 defines the top surface 601 of the BC-SRR 600 and the bottom surface 602 of the BC-SRR 600.

[0151] In BC-SRR unit cell 600, magnetic field enhancement occurs due to the overlap between the self-resonant frequency of unit cell 600 and the excitation frequency of the magnetic field. BC-SRR unit cells are configured so that the excited electric dipoles exhibit cancellation, thereby mitigating the amplification of the electric field component of the RF signal by unit cell 301 and array 300.

[0152] Figures 6B to 6D The operating characteristics of the BC-SRR 600 are schematically illustrated when configured to resonate at 64 MHz.

[0153] Figure 6B The cross section of the magnetic field (Bz) distribution of a single unit cell BC-SRR 600 in the XZ plane is schematically illustrated, and Figure 6C The magnetic field distribution in the XY plane 10 mm away from the top surface 601 of the BC-SRR 600 is schematically illustrated. Figure 6D The figure schematically illustrates the magnetic field enhancement factor at a point 10 mm away from the top surface 601 of the BC-SRR 600. In this embodiment, the electric field created at one end of the BC-SRR 600 (i.e., the end closest to the top surface 601) almost completely cancels the electric field at the other end (i.e., the end closest to the bottom surface 602).

[0154] Figure 6E Schematically illustrated is an array 300 of BC-SRR unit cells 600. In this embodiment, the BC-SRRs are photolithographically fabricated on a high dielectric constant substrate 650.

[0155] Implementations of the resonator array 300 can be rigid or flexible. For example, Figure 6E The array 300 of BC-SRR resonators can be rigid, while Figure 7A and Figure 7B The array 300 is flexible. Figure 7A The BC-SRR array 300 has a flexible substrate 700 and is Figure 7A As shown, for example, the flexible substrate 700 can even be wrapped around a limb 799 of the specimen 99. Similarly, the array 300 of helical resonators 500 has a flexible substrate 700 and can be contoured to be part of the body of the specimen 99, or even formed into a cone.

[0156] In some applications, it may be desirable to increase the magnetic field component of the RF energy only during RF signal transmission from the specimen to the MRI machine, and not during RF energy transmission from the MRI machine 100 to the specimen 99. To this end, some embodiments include a tunable array 300 and a tunable unit cell 301.

[0157] Figures 8A to 8G Schematically illustrated is an embodiment of a tunable unit cell 301. An array 300 having tunable unit cells 301 can be tuned by tuning its constituent unit cells 301.

[0158] Figure 8A Schematically illustrated is a tunable unit cell 301. The tunable unit cell 301 may include, for example, the helical coil 500 as described above or the BC-SRR 600 as described above and a coupler 801.

[0159] Coupler 801 has at least two electrical states (or "impedance" states), including a first state in which the conductivity of coupler 801 is lower than its conductivity in a second state. Alternatively, the electrical impedance of coupler 801 in the first state is higher than its electrical impedance in the second state. The resonant characteristics of unit cell 301 vary depending on the state of coupler 801.

[0160] exist Figure 8A In a preferred embodiment, coupler 801 electrically couples between two ends 511 of a helical coil (e.g., 500), but can be coupled to one or more unit cells in a number of ways, as described below. In its first state, the impedance of coupler 801 is sufficiently high that the unit cell 301 operates as described above. However, in its second state, the impedance of the coupler is lower, thereby creating an electrical connection via the conductive path between two ends 511 of coil 500. This electrical connection alters the properties of helical coil 500, causing it to no longer resonate or shifting its resonant frequency to a frequency away from the MRI machine's operating frequency 452. Generally, when coupler 801 is in the second state, the difference between the MRI machine's operating frequency 452 and the resonant frequency of the helical coil can be specified by the MRI machine's designer or operator. For example, in a preferred embodiment, when coupler 801 is in the second state, the resonant frequency of helical coil 500 is altered such that (if it were fully resonant) its resonant frequency differs by at least + / - 15% from the MRI machine's operating frequency 452 and / or differs by at least + / - 15% from the resonant frequency when coupler 801 is in the first state. Thus, changing the state of coupler 801 changes the resonant characteristics of unit cell 301. Typically, a unit cell 300 (in this example, helical coil 500) is said to be "effectively non-resonant" when its resonant frequency differs by at least + / - 15% from the operating frequency 452 of the MRI machine and / or differs by at least + / - 15% from the resonant frequency when coupler 801 is in the first state.

[0161] Furthermore, in such an array 300 of unit cells 301, changing the state of the coupler 801 changes the operational characteristics of the array 300. For example, when the coupler 801 is in the first state, each unit cell 301 and the array 300 of such unit cells 301 are as described above in conjunction with Figures 3A to 3C 、 Figures 4A to 4B 、 Figures 5A to 5F and Figures 6A to 6E When coupler 801 is in the second state, the resonant characteristics of array 300 change, resulting in a reduced amplification of the magnetic field generated by array 300. In effect, each unit cell 301 and array 300 can be "turned on" by placing coupler 801 in the first state and "turned off" by placing coupler 801 in the second state. Various coupler 801, unit cell 301 configurations, and array 300 configurations are described below. In general, coupler 801 can be referred to as a nonlinear material or a nonlinear device.

[0162] Figure 8B Schematically illustrated is an array 300 of BC-SRRs 600. Each BC-SRR unit cell includes at least one coupler 801, and in some embodiments more than one coupler 801. Figure 8B Coupler 801 in FIG. 8 is referred to as semiconductor patch 810. For example, semiconductor patch 810 may be doped silicon that changes its impedance in response to RF energy from MRI machine 100 (but not in response to the typically much lower amount of RF energy from the signal of specimen 99). The semiconductor patch may be said to be nonlinear.

[0163] In an exemplary embodiment, the semiconductor material of the semiconductor patch 810 can be GaAs, InAs, or InSb, to name a few examples. The preferred embodiment uses GaAs as the semiconductor material. The carrier density of undoped intrinsic GaAs is 2.1*10 6 cm -3 .

[0164] The properties of semiconductors are tuned by doping. Doping is well known in the semiconductor field. In an exemplary embodiment, GaAs is doped to have a 3*10 7 cm -3 carrier density.

[0165] In an exemplary embodiment, the semiconductor patch 810 can be prepared from a 2-inch or 4-inch wafer (0.5 mm thick) of a doped semiconductor (e.g., GaAs doped as described above). The wafer is cut into 3 mm x 5 mm patches and the patches are cut with micron-sized gaps (e.g., 2 x 10 mm) in a manner known in semiconductor technology. -6 m) Patterning two electrodes onto the patch.

[0166] like Figure 8A As schematically shown in FIG, semiconductor patch 810 is electrically coupled (e.g., soldered) to unit cell 301. By applying an alternating magnetic field (e.g., a radio frequency electromagnetic signal), a strong electric field of up to 400 kV / cm can be induced at the micron-sized gap to stimulate impact ionization at the gap.

[0167] In the exemplary embodiment, when the MRI machine 100 does not apply such an alternating magnetic field (eg, a radio frequency electromagnetic signal), the conductivity of the semiconductor patch 810 is approximately 1*10 -7 (ohm cm) -1 (In an exemplary embodiment, the carrier density is as high as 10 7 cm -3 ). In contrast, when the MRI machine 100 applies stimulation as described above, the conductivity of the doped GaAs of the semiconductor patch 810 increases to about 20 (ohm cm) -1 (In an exemplary embodiment, the carrier density is as high as 10 18 cm -3 ), resulting in a shift in the resonant frequency of the unit cell 301 described herein.

[0168] Taking doped silicon semiconductor patch 810 as an example, during RF energy transmission from the MRI machine 100, the electric field in the gap of the BC-SRR 600 or within the metal spiral 500 is very high, thus exciting the carrier density of doped silicon semiconductor patch 810 to a level much higher than in the absence of such RF energy. In this state, doped silicon semiconductor patch 810 can be considered a conductor. Therefore, during RF energy transmission from the MRI machine 100, the resonant frequency of unit cell 301 deviates from the frequency of the RF energy transmitted by the MRI machine 100.

[0169] In contrast, during the period when the unit cell 301 receives an RF signal from the sample 99 (which occurs when the MRI machine 100 is not transmitting RF energy), the electric field strength is much lower, and thus the doped silicon semiconductor patch 810 is not an effective conductor. Therefore, when the doped silicon semiconductor patch 810 acts as an isolator, the resonant frequency of each unit cell 301 remains consistent with the operating frequency 452 of the MRI machine 100.

[0170] The semiconductor patch 810 is disposed within the first gap 611 of the first SRR 610 in the BC-SRR 600 and changes its state in response to RF energy from the MRI machine 100. More specifically, in the absence of RF energy from the MRI machine 100, the semiconductor patch 810 is in the first state (high impedance), and thus the behavior of the BC-SRR 600 is as described above in conjunction with Figures 6A to 6EHowever, when the MRI machine transmits RF energy, the semiconductor patch 810 changes its impedance to a second state (low impedance), thereby electrically coupling the opposite ends 612, 612 of the first gap 611, thereby changing the physical and resonant characteristics of the BC-SRR 600, and thus changing the operating characteristics of the array 300, as described above.

[0171] In some embodiments, each of the SRRs 610 , 620 of the BC-SRR 600 includes a semiconductor patch 810 as described above to further alter the characteristics of each unit cell 301 and the array 300 .

[0172] Figure 8C Schematically illustrating an array 300 of spiral unit cells 500. In this embodiment, semiconductor patches 810 are coupled between respective ends 511 of adjacent unit cells 301, and if the spiral coil itself is surrounded, for example, by spiral turns 513, the semiconductor patches 810 are preferably arranged within the interior 802. In this configuration, in the absence of RF energy from the MRI machine 100, the semiconductor patches 810 are in a first state (high impedance), and thus the resonator 500 behaves as described above in conjunction with Figures 5A to 5F However, when the MRI machine transmits RF energy, the semiconductor patch 810 changes its impedance to a second state (low impedance), thereby coupling adjacent unit cells 301 together, thereby changing the operating characteristics of the array 300 as described above.

[0173] Figure 8D and Figure 8E Schematically illustrated are alternative embodiments of couplers 801, wherein coupler 801 is a switch 820, and alternative embodiments of arrays 300 having such couplers 801. Although the unit cells 301 in these embodiments are responsive to control signals 821 (and therefore can be said to be in control communication with the MRI machine 100 or its controller 140), each of the arrays 300 can still be considered passive in that it does not require external energy input to amplify the magnetic field and increase the SNR of the signal from the specimen 99.

[0174] exist Figure 8D In the embodiment of the present invention, at least one SRR 610 in each BC-SRR 600 has a switch 820 disposed in its gap 611. A control signal 821 from the MRI machine (e.g., from the controller 140) changes the switch 820 between a first state (high impedance) and a second state (low impedance), thereby electrically coupling opposite ends 612, 612 of the first gap 611. These two states change the resonant characteristics of the BC-SRR 600, thereby changing the operating characteristics of the array 300, as described above in conjunction with Figure 8BIn some embodiments, each of the SRRs 610 , 620 of the BC-SRR 600 includes a switch 820 as described above to further change the characteristics of each unit cell 301 and the characteristics of the array 300 .

[0175] Figure 8E Schematically illustrating an array 300 of spiral unit cells 500. In this embodiment, a switch 820 is coupled between each end 511 of adjacent unit cells 301. A control signal 821 from the MRI machine switches the switch 820 between a first state (high impedance) and a second state (low impedance). These two states change the resonant characteristics of the spiral unit cells 500, thereby changing the operating characteristics of the array 300, as described above in conjunction with Figure 8C As stated.

[0176] Figure 9 9 is a flow chart of an embodiment of a method for performing magnetic resonance imaging on a sample 99. Step 901 requires providing an MRI machine 100 having an aperture 102 and an operating frequency. For example, the MRI machine 100 can be a 1.5 Tesla MRI machine operating at a frequency of 64 MHz or a 3 Tesla MRI machine operating at a frequency of 128 MHz.

[0177] Step 902 includes placing a sample in the well 102, and step 903 includes placing the array 300 of unit cells 301 in the well with the sample. It should be noted that steps 902 and 903 may be performed in any order relative to each other.

[0178] In a preferred embodiment, array 300 is sized to be positioned within bore 102 of MRI machine 100 with specimen 99 in bore 102 while MRI machine 100 is imaging specimen 99. For example, array 300 of unit cells 301 may be any of the arrays 300 described above.

[0179] In a preferred embodiment, each unit cell 301 of the array 300 has a resonant frequency, and the array 300 has a resonant frequency that is equal to or close to the operating frequency of the MRI machine 100 .

[0180] At step 904, the method images the specimen 99 using an MRI machine in a manner known in the art.

[0181] In some embodiments, step 904 further comprises controlling coupler 801 to be in its first state (high impedance) when the MRI machine is not applying electromagnetic (e.g., radio frequency) stimulation to specimen 99, and to be in its second state (low impedance) when the MRI machine is applying such stimulation to specimen 99. For example, if coupler 801 is a switch 820, step 904 may comprise controlling switch 820 using control signal 821 from controller 140, as described above. As another example, if coupler 801 is a semiconductor patch 810, step 904 may comprise controlling semiconductor patch 810 to be in its first state (high impedance) by withholding electromagnetic stimulation from MRI machine 100, and to be in its second state (low impedance) by applying electromagnetic stimulation from MRI machine 100. In these embodiments, when the MRI is not applying electromagnetic stimulation to the specimen, the coupler 801 is in a high impedance state (so that the unit cell 301 is resonant), and when the MRI is applying such electromagnetic stimulation to the specimen, the coupler 801 is in a low impedance state (so that the unit cell 301 is effectively non-resonant).

[0182] Nonlinear steerable array

[0183] In some applications, it may be desirable to control the metamaterial array 300 so that the metamaterial array 300 amplifies the response signal from the specimen 99 in the MRI machine 100, rather than amplifying the excitation signal provided by the MRI machine 100 to the specimen 99. Furthermore, it may be desirable to automatically control the metamaterial array 300 for this purpose, without requiring the MRI machine or a separate controller to coordinate control of the metamaterial array with operation in the transmit and receive modes of the MRI machine.

[0184] To this end, the embodiments described below describe a controllable array assembly 1100 (which may be referred to as a nonlinear metamaterial, or "NLMM") that includes a linear metamaterial ("LMM") 300 (e.g., one or more metamaterial arrays described above in this application) and a nonlinear controlled resonator 1000 (e.g., a variable capacitance loaded split ring resonator ("VLSRR")).

[0185] The nonlinear metamaterial 1100 is configured to be deployed within the bore 102 of the MRI machine 100 and to operate to enhance the SNR of the MRI, thereby achieving a significant improvement in performance. It should be noted that the linear metamaterial 300 and / or the nonlinear metamaterial 1100 are not part of the MRI machine 1000 (e.g., they are not part of the body coil 102 or other coils of the MRI machine 100). Instead, the nonlinear metamaterial 1100 can be described as an accessory for use with the MRI machine 1000.

[0186] In an exemplary embodiment, the resonance of the controllable array assembly 1100 is suppressed in response to higher levels of RF excitation intensity (from the MRI machine 100) and is restored during subsequent periods of lower excitation intensity (from the MRI machine 100), thereby exhibiting intelligent or nonlinear behavior by passively sensing the intensity of the excitation signal from the MRI machine 100 and responding accordingly. The nonlinear response of the NLMM 1100 enables such embodiments to improve the signal-to-noise ratio during magnetic resonance imaging to an unprecedented degree. Such embodiments demonstrate intelligent and nonlinear metamaterials that can adaptively change their resonant response based on excitation intensity.

[0187] Some embodiments may be described as "adaptive" or having an "adaptive" response. During the RF transmit phase of the MRI machine 100, a strong excitation RF magnetic field induces a nonlinear response in the steerable array assembly 1100, effectively shutting down its magnetic field enhancement performance due to its resonant shift. During the RF receive phase of the MRI machine 100, the steerable array assembly 1100 becomes active, operating at the resonant frequency of the MRI machine 100 and enhancing the received RF response signal.

[0188] Figure 10A Schematically illustrates an embodiment of a nonlinear resonator 1000, which may be referred to as a controlled resonator. The nonlinear characteristics of the nonlinear resonator 1000 arise from its resonant characteristics, as it has at least two different resonant frequencies and can be controlled to assume a first of these resonant frequencies and then switch to a second of these resonant frequencies.

[0189] To this end, the nonlinear resonator 1000 includes a resonator coil 1010 having a first end 1011 and a second end 1012. The resonator coil 1010 has inductance and capacitance and an electrical resonant frequency.

[0190] In some embodiments, the resonator coil 1010 is a split ring resonator, wherein the first end 1011 and the second end 1012 form a gap 1013 in the split ring. In other embodiments, the resonator coil 1010 is a conductive loop or spiral coil, such as Figure 10B As shown schematically, a first end 1011 and a second end 1012 are ends of the coil 1010 and form a gap 1013 .

[0191] The nonlinear resonator 1000 further includes a control coupler 1020 electrically coupled between the first end 1011 and the second end 1012. The control coupler 1020 has a controllably variable impedance.

[0192] For example, in some embodiments, the coupler 1020 has a capacitance that can be controllably changed between a first impedance state (eg, a first capacitance) and a second impedance state (eg, a second capacitance). For example, such a controllable coupler 1020 can be a variable capacitor.

[0193] In other embodiments, the control coupler 1020 can be a transistor, such as a field effect transistor or a micro-electromechanical (“MEMS”) switch. In some embodiments, the connector 1020 is soldered to the ends 1011 , 1012 of the coil 1010 .

[0194] The resonant frequency of nonlinear resonator 1000 is determined by the resonant frequency of resonator coil 1010 and the impedance of coupler 1020. Because the impedance of coupler 1020 is controllably variable between a first impedance state and a second impedance state, the resonant frequency of nonlinear resonator 1000 is controllably configured to be in the first resonant state and the second resonant state. In other words, when coupler 1020 is in the first impedance state, nonlinear resonator 1000 is in the first resonant state, and when coupler 1020 is in the second impedance state, nonlinear resonator 1000 is in the second resonant state.

[0195] In the exemplary embodiment, the controllable array assembly 1100 is composed of a linear spiral resonator array 300 and a split ring resonator 1000 loaded with coupled variable capacitance, thereby having a bi-stable nonlinear response characteristic under high power RF excitation.

[0196] Figure 11A An embodiment of a controllable array component (or nonlinear metamaterial component) 1100 is schematically illustrated. Figure 11B Another embodiment of a steerable array assembly 1100 and its components is schematically shown. The exemplary embodiment remains silent during the transmit phase of MRI, thereby allowing uniform and optimal excitation of the specimen 99, and becomes active during the receive phase, resulting in an enhanced magnetic field and amplified signal-to-noise ratio of the response signal from the specimen 99.

[0197] In the exemplary embodiment, the controllable array assembly 1100 is configured to amplify specific signals in the bore 102 of the MRI machine 100 and can be referred to as a signal amplification system. It should be noted that the controllable array assembly 1100 is not part of the MRI machine 100, but rather an accessory that can be used with the MRI machine 100.

[0198] The controllable array assembly 1100 includes a metamaterial resonator array 300. For example, the metamaterial resonator array 300 can be any of the metamaterial resonator arrays 300 disclosed herein. The exemplary embodiment of the array 300 includes at least two metamaterial resonators, but can also include more than two metamaterial resonators, for example, an N×M array of such resonators, where N and M are integers (e.g., where N and / or M can be any of 2, 3, 4, 5, 6, 7, 8).

[0199] The controllable array assembly 1100 also includes a nonlinear resonator 1000 (which may be referred to as a "control resonator" 1000) positioned adjacent to the metamaterial resonator array 300. The nonlinear resonator 1000 and the array 300 define a gap 1111 therebetween. In some embodiments, for example, the gap 1111 may be 2 cm. However, in other embodiments, the gap 1111 may be greater or less than 2 cm. For example, in some embodiments, the nonlinear resonator 1000 may be positioned coplanar with the array 300 such that the gap 1111 is 0 cm (zero centimeters). Figure 11E Graph showing the magnetic field (B) enhancement rate at points at different positions relative to the top surface of the array (LMM).

[0200] An exemplary embodiment of the controllable array assembly 1100 includes a spacer layer 1110 disposed between the nonlinear resonator 1000 and the array 300. In some embodiments, the spacer layer 1110 comprises a non-metallic and non-magnetic material, such as plastic or foam. In other embodiments, the spacer layer 1110 can be a vacuum or a gas (e.g., air).

[0201] Figure 11C is a graph showing the frequency spectrum of the controllable array assembly 1100 for different gaps 1111 between the array 300 and the nonlinear resonator 1000 .

[0202] Figure 11D 1 is a graph showing the frequency spectrum of the controllable array assembly 1100 for high excitation (i.e., during the transmit phase of the MRI machine 100 operation, during which the MRI machine 100 provides an excitation signal to the specimen 99 in the bore 102 of the MRI machine) and for low excitation (i.e., during the receive phase of the MRI machine 100 operation, during which the specimen 99 generates its response to the excitation signal). For high excitation (the transmit phase of the MRI operation), the resonance is off (line 1191), while for low excitation (the receive phase of the MRI operation), the resonance is on (line 1192), thereby enhancing the magnetic field of the response signal generated by the specimen 99.

[0203] Figure 12A 、 Figure 12B 、 Figure 12C 、 Figure 12D、 Figure 12E and Figure 12F Another embodiment of a controllable array assembly 1100 and its components is schematically illustrated.

[0204] The response of the array 300 can be expressed by the following formula (Equation 1), where a1 represents the mode amplitude of the resonator, 1 / τ e1 and 1 / τ 01 are the attenuation rates due to radiation loss and ohmic loss, respectively, and s + Indicates the excitation signal:

[0205]

[0206] For a linear metamaterial composed of a spiral array 300, such as Figure 12A As shown, the response of its collective mode can be simply modeled using Equation (1), and the oscillation intensity of the resonator array is maximum at the resonant frequency. + |) is independent of the excitation intensity, e.g. Figure 12B As illustrated by the results shown, the resonance of the metamaterial array 300 induces a magnetic field enhancement in the near field of the array 300. It is worth noting that coupled mode theory ("CMT") provides a lumped parameter description of the response but ignores design details, so this approach remains valid for linear metamaterial arrays 300 composed of any number of units (e.g., a single unit cell, 2×1 unit cells, or 4×4 unit cells, to name a few examples).

[0207] Unlike the response of the linear metamaterials described above (e.g., array 300), in the presence of existing nonlinear components 1000 within the resonator 1100, for example, the variable capacitance in a split ring resonator (SRR, such as Figure 12C As shown in FIG1 , the response of the resonator 1100 depends on the excitation intensity. In the case of the split ring resonator 1000 loaded with a variable capacitance (VLSRR), its resonant frequency varies with the oscillation intensity in the resonator 1000. When the oscillation intensity in the split ring resonator 1000 is relatively low, the variable capacitance 1020 maintains its original capacitance. However, when the oscillation intensity in the split ring resonator 1000 is higher (i.e., relatively high), the rectification effect in the variable capacitance 1020 acts as a driving voltage for the variable capacitance 1020 and increases its capacitance, which in turn reduces the resonant frequency in the split ring resonator 1000. The excitation power-dependent response in the split ring resonator 1000 is modeled by the following formula (Equation 2):

[0208]

[0209] where a2 is the mode amplitude in the split-ring resonator 1000, ω o2is the original resonant frequency in the split-ring resonator 1000, 1 / τ e2 and 1 / τ 02 are the attenuation rates due to radiation loss and ohmic loss, respectively, and λ0 is a nonlinear coefficient determined by the characteristics of the variable capacitor 1020 .

[0210] When the excitation intensity is low (e.g., |s + |=0.001), the split ring resonator 1000 operates in a linear manner with its peak amplitude (1211) at the specified resonant frequency (ω o2 ),like Figure 12D As shown in Figure 1, the resonant frequency of the VLSRR shifts to a lower frequency (1212) as the excitation intensity increases. When the excitation intensity is high enough, the split ring resonator 1000 exhibits a sudden change in the spectrum as the frequency increases. This is due to the bi-stable nonlinear behavior in the amplitude response of the split ring resonator 1000. As the frequency shifts, the peak oscillation amplitude in the resonator decreases.

[0211] When the controllable array 1100 is composed of the spiral resonator array 300 and the split ring resonator 1000 close to each other, a nonlinear metamaterial (NLMM) is formed, such as Figure 12E The coupling factor (k) is introduced into the system to describe the interaction between the resonator array 300 and the split ring resonator 1000, as shown in Equation 3:

[0212]

[0213] In this system 1100, two parameters Δω and k are variables, while all other parameters can be determined by material properties and structural design. Figure 12E The coupling factor of the exemplary embodiment is k=0.2, which represents a moderate degree of coupling between the helical resonator array 300 and the split ring resonator 1000, and Δω=0.3 represents an arbitrary resonant frequency difference. Figure 12F The calculated oscillation mode amplitudes under different excitation intensities are shown. Due to the coupling effect between the spiral resonator array 300 and the split ring resonator 1000, two resonance peaks (1231; 1232) appear in the spectrum under low excitation conditions. In the first mode, the resonances of the spiral resonator array 300 and the split ring resonator 1000 are in phase, while in the second mode they are out of phase. Qualitatively speaking, when the excitation is low, the strong oscillation amplitude (peak 1231) in the first mode produces a strong magnetic field enhancement near the controllable array 1100. As the excitation power increases, both resonant modes shift to lower frequencies, and when the excitation exceeds the critical excitation intensity, a bistable response occurs. The peak oscillation amplitude decreases significantly (peak 1232), which results in a reduction in the magnetic field enhancement.

[0214] Figure 13 is a flow chart illustrating the operation of an embodiment of the controllable array assembly 1100 .

[0215] At step 1310, the method includes providing a controllable array assembly 1100. The exemplary embodiment of the controllable array assembly 1100 includes a resonator array 300 configured to amplify signals at an operating frequency of the MRI machine 100, but for coupling to the resonator array 300 of the control resonator 1000 in a first mode, as described below.

[0216] At step 1320, the method includes placing the steerable array assembly 1100 in the bore 102 of the MRI machine 100 (if it is not already in that position). In a preferred embodiment, the steerable array assembly 1100 is placed in the bore 102 of the MRI machine 100 along with the specimen 99 to be imaged by the MRI machine 100.

[0217] Step 1330 includes configuring steerable array assembly 1100 into a first mode (or “pass-through” mode) in which steerable array assembly 1100 does not substantially amplify the excitation signal provided to specimen 99 by MRI machine 100 .

[0218] To this end, step 1330 includes configuring the control coupler 1020 to a first impedance state (Z1) so as to configure the control resonator 1000 to a first resonant state. The control resonator 1000 is coupled to the resonator array 300 (e.g., to each resonator in the resonator array 300) to establish a through-resonant frequency (F1) of the controllable array assembly 1100. In this through-resonant mode, the resonant frequency (F1) of the controllable array assembly 1100 is offset from the operating frequency (ω) of the MRI machine 100 (either greater than or less than the operating frequency of the MRI machine 100), thereby resulting in less amplification of the stimulation signal provided by the body coil 120 of the MRI machine 100 to the specimen 99. In the through-resonant mode, the resonator array 300 amplifies the stimulation signal provided by the body coil 120 of the MRI machine 100 to the specimen 99 to a lesser extent than in the amplified mode, as described below.

[0219] Step 1335 includes controlling the MRI machine 100 to enter a transmit mode and providing an excitation signal from the MRI machine 100 to the specimen 99 .

[0220] Step 1340 includes controlling the MRI machine 100 to enter a receiving mode and using the MRI machine 100 to capture the response signal generated by the sample 99. In a preferred embodiment, step 1345 is performed only after the MRI machine 100 is transitioned to the receiving mode.

[0221] Step 1345 includes configuring steerable array assembly 1100 into a second mode (or "amplification" mode) in which steerable array assembly 1100 substantially amplifies signals generated by the specimen and provided by the specimen to MRI machine 100. In a preferred embodiment, step 1345 of configuring steerable array assembly 1100 into the amplification mode is not performed when MRI machine 100 is in the transmit mode.

[0222] To this end, step 1345 includes configuring the control coupler 1020 to a second impedance state (Z2) so as to configure the control resonator 1000 to a second resonant state. In this state, the control resonator 1000 is coupled to the resonator array 300 (e.g., to each resonator in the resonator array 300) to establish an amplified resonant frequency of the controllable array assembly 1100. In this amplified mode, the resonant frequency (F2) of the controllable array assembly 1100 is substantially equal to the frequency of the response signal generated by the specimen 99 and received by the body coil 120 (and / or the patient coil 130), and thus the resonator array 300 amplifies the signal generated by the specimen 99 in the manner described above for the array 300. In the amplified mode, the resonator array 300 amplifies the stimulation signal provided by the body coil 120 of the MRI machine 100 to the specimen 99 to a greater extent than in the pass-through mode described above.

[0223] The following table summarizes the aforementioned modes for an MRI machine 100 having an operating frequency "ω".

[0224]

[0225] Step 1350 includes processing signals received from the specimen by the MRI machine 100 in response to excitation signals provided by the MRI machine 100 to the specimen.

[0226] The foregoing describes a signal amplification accessory 1100 for use within the bore 102 of an MRI machine 100 having a transmit coil 120 configured to transmit an excitation signal having a transmit frequency to a specimen 99 in the bore 102 in a transmit mode, and a receive coil (120 and / or 130) configured to receive a response signal having a response frequency from the specimen 99 in a receive mode. The accessory 1100 includes a resonator array 300 having a plurality of metamaterial resonators, each of the plurality of metamaterial resonators having a resonant frequency, the metamaterial resonators configured to inductively couple to one another in response to an applied electromagnetic signal.

[0227] Accessory 1100 also includes a nonlinear controlled resonator 1000 having (i) a resonator coil 1010 and (ii) a controllable impedance 1020 coupled to the resonator coil. Controlled resonator 1000 has a first resonant frequency when controllable impedance 1020 is in a first impedance state and a second resonant frequency when controllable impedance 1020 is in a second impedance state.

[0228] The exemplary embodiment of the accessory 1100 also has a spacer layer 1110 disposed between the resonator array 300 and the control resonator 1000, the spacer layer 1100 defining a gap (d) 1111 between the resonator array 300 and the nonlinear control resonator 1000. The resonator coils 1000 and the controllable impedance 1020 are selected such that the control resonator 1000 is configured to (i) generate, with the resonator array 300, a first array resonant frequency that is offset from the transmit frequency of the MRI machine 100 when the MRI machine 100 is in a transmit mode, and (ii) generate, with the resonator array 300, a second array resonant frequency that is equal to the response frequency when the MRI machine 100 is in a receive mode, so as to amplify the response signal.

[0229] Isolator

[0230] Figure 14A An embodiment of a controllable isolator assembly 1400 is schematically illustrated. Figure 14B An implementation of a controllable isolator component 1400 on an integrated circuit 1401 is schematically illustrated.

[0231] The controllable isolator assembly 1400 operates based on the nonlinear effects in strongly coupled resonators, which provide a sharp contrast between forward-propagating RF signals and reverse-propagating RF signals. The exemplary embodiment includes two resonators 1000, 1430 between two ports 1421, 1411, one of which (1000) is loaded with a variable capacitor (e.g., 1020) that can achieve a nonlinear response. The variable capacitor 1020 can be designed to automatically open and close based on the power received by the resonator 1000. For example, for a signal from port 1421 to port 1411, the resonator can be "closed", thereby disabling transmission, while for a signal from port 1411 to port 1421, the resonator 1000 can be "opened".

[0232] In the exemplary embodiment, when an RF signal is incident from port 1421, the electric field across variable capacitor 1020 in nonlinear resonator 1000 is high, which shifts the resonant frequency of nonlinear resonator 1000 and reduces the resonance amplitude in nonlinear resonator 1000. This results in weak transmission of the signal from port 1421 to port 1411. However, when an RF signal is incident from port 1411, a strong resonance is induced in linear resonator 1430, but the resonance in nonlinear resonator 1000 is relatively smaller, which does not change the resonant frequency of nonlinear resonator 1000. In this case, the transmission from port 1411 to port 1421 is strong.

[0233] Thus, the controllable isolator assembly 1400 allows a first signal to be transmitted from the first resonator 1430 to the nonlinear resonator 1000 across the gap 1440 , but suppresses or inhibits a second signal from being transmitted in the opposite direction, i.e., from the nonlinear resonator 1000 to the first resonator 1430 across the gap 1440 .

[0234] To this end, the first resonator 1430 has a characteristic resonant frequency (Fc). In some embodiments, the first resonator 1430 is a linear resonator, such as a metamaterial resonator, to name just one example.

[0235] The nonlinear resonator 1000 is controllably configured to have a first resonant state and a second resonant state. In the first resonant state, the nonlinear resonator 1000 has a first resonant frequency (F1), which is equal to the characteristic resonant frequency (Fc=F1) of the first resonator 1430. In the second resonant state, the nonlinear resonator 1000 has a second resonant frequency (F2) different from the first resonant frequency. For example, the nonlinear resonator 1000 has the first resonant frequency (F1) when its control coupler 1020 is in the first impedance state (Z1), and has the second resonant frequency (F2) when its control coupler 1020 is in the second impedance state (Z2).

[0236] When a signal having a frequency equal to the characteristic resonant frequency (Fc) (e.g., the center frequency of the carrier frequency) is provided to the first resonator 1430, the first resonator 1430 resonates and inductively induces a copy of the signal on the nonlinear resonator 1000. In an exemplary embodiment, the signal on the first resonator 1430 is insufficient to induce a change in the impedance state in the control coupler 1020 across the isolator gap 1440.

[0237] In contrast, when such a signal is provided to the nonlinear resonator 1000, the power in the signal impacts the control coupler 1020 and changes the impedance of the control coupler 1020 to a second impedance state (Z2), thereby configuring the nonlinear resonator 1000 to a mode in which the nonlinear resonator has a second resonant frequency (F2). Because the second resonant frequency (F2) is different from the characteristic frequency (Fc) of the first resonator 1430 (or at least further away from the characteristic frequency (Fc) than the first resonant frequency (F1)), the inductive coupling of the signal from the first resonator 1430 to the nonlinear resonator is suppressed relative to the inductive coupling from the nonlinear resonator 1000 to the first resonator 1430 as described above.

[0238] It should be noted that although Figure 14A and Figure 14B The nonlinear resonator 1000 and the linear resonator 1430 in FIG. 1 are shown as a single device, but embodiments are not limited to such a single device. For example, in an exemplary embodiment, the nonlinear resonator 1000 may be a set of one or more nonlinear resonators, and / or the linear resonator 1430 may be a set of one or more linear resonators.

[0239] Figure 15 is a flow chart describing a method of operation of the isolator 1400. The method includes providing the nonlinear resonator 1000 and the second resonator 1430 at step 1510, as described above. Figure 14A and / or Figure 14B Schematically shown in FIG. The second resonator 1430 has a characteristic resonant frequency. The nonlinear resonator has an isolation resonant frequency different from the characteristic resonant frequency and a transmit resonant frequency equal to the characteristic resonant frequency. Step 1510 may include coupling the nonlinear resonator 1000 to a first port 1421 (such as a port 1421 coupled to a signal source, a network, or a transceiver 1420).

[0240] Step 1520 includes configuring the nonlinear resonator 1000 into an isolation configuration (such that the isolator 1400 is in an "isolation mode"), in which the nonlinear resonator 1000 has an isolation resonant frequency. In the isolation configuration (and mode), the resonant coupling between the nonlinear resonator 1000 and the second resonator 1430 is weak (at least weaker than the coupling in the transmission mode described below), such that a signal provided to the nonlinear resonator 1000 at step 1530 (e.g., via the first port 1421) is weakly coupled, if at all, to the second resonator 1430.

[0241] At step 1540, the method configures the nonlinear resonator 1000 into a transmit configuration (such that the isolator 1400 is in a "transmit mode"). In the transmit configuration (and mode), the nonlinear resonator 1000 has a transmit resonant frequency and can be described as being in a "receive configuration." In this configuration (and mode), the resonant coupling between the nonlinear resonator 1000 and the second resonator 1430 is strong (at least stronger than in the isolation mode described above), such that the signal provided to the nonlinear resonator 1000 at step 1550 (e.g., via the second port 1411) is well coupled to the nonlinear resonator 1000.

[0242] For example, in one embodiment, the inventors evaluated the transmission of a 300 MHz signal provided at -5 dBm. When the signal was provided to port 1421, the signal transmission from port 1421 to port 1411 was weak because the nonlinear resonator 1000 was in the isolation configuration. In contrast, when the signal was provided to port 1411 and the nonlinear resonator 1000 was in the transmit configuration (or receive configuration), the signal transmission from port 1411 to port 1421 was stronger. The inventors found that the difference (contrast) between the two transmissions was 15 dB. In other words, the transmission from port 1411 to port 1421 was 15 dB greater than the transmission from port 1421 to port 1411. In other embodiments, the isolator 1400 can be configured (e.g., by specification and selection of component dimensions; gap 1440) to produce a difference in transmission of at least 3 dB, 6 dB, 9 dB, or 12 dB, to name a few examples. According to the aforementioned exemplary embodiments, the nonlinear resonator 1000 and the linear resonator 1430 are considered to be substantially isolated from each other if the difference in emission between isolation mode and emission mode is at least 3 dB, 6 dB, 9 dB, 12 dB, or 15 dB. A person of ordinary skill in the art having access to this specification can specify the ratio defining the substantial isolation based on, for example, the requirements of the isolator 1400 to be implemented.

[0243] Then, at step 1560 , some embodiments of the method configure the nonlinear isolator 1400 back to the isolation configuration (and mode).

[0244] As described above, some embodiments include a circuit having a first resonator and a nonlinear resonator, the first resonator having a characteristic resonant frequency; the nonlinear resonator being controllably configured to have a first resonant state and a second resonant state, wherein the nonlinear resonator has a first resonant frequency equal to the characteristic resonant frequency and has a second resonant frequency different from the first resonant frequency. In an exemplary embodiment, the first resonator is configured to be coupled to a first port, and the nonlinear resonator is configured to be coupled to a second port, and wherein in the first resonant state, the nonlinear resonator is configured to be inductively coupled to the first resonator so as to communicatively couple a signal from the first resonator to the second port, and in the second resonant state, the nonlinear resonator is configured to isolate the second port from the first resonator.

[0245] The following is a list of reference numbers used in this article.

[0246] 99: sample;

[0247] 100: MRI machine in cross section;

[0248] 101: workbench;

[0249] 102: The hole of the MRI machine;

[0250] 110: main magnetic field coil;

[0251] 111: shim coil;

[0252] 115: gradient coil;

[0253] 120: body coil;

[0254] 130: sample coil;

[0255] 140: MRI machine controller;

[0256] 150: Computer;

[0257] 151: Computer communication link;

[0258] 300: resonator array;

[0259] 301: unit cell;

[0260] 302: top of unit cell;

[0261] 303: middle of unit cell;

[0262] 310: X pitch;

[0263] 311: Y pitch;

[0264] 400: Response of the resonator;

[0265] 401: center frequency;

[0266] 402: upper 3dB point;

[0267] 403: lower 3dB point;

[0268] 405: noise level;

[0269] 410: frequency increment;

[0270] 450: A frequency lower than the operating frequency of the MRI machine;

[0271] 452: Operating frequency of the MRI machine;

[0272] 454: A frequency higher than the operating frequency of the MRI machine;

[0273] 460: The resonant response of the array when tuned to a frequency below the operating frequency of the MRI machine;

[0274] 461: The resonant frequency of the array is tuned to a frequency lower than the operating frequency of the MRI machine;

[0275] 462: The resonant response of the array tuned to the operating frequency of the MRI machine;

[0276] 463: The resonant frequency of the array is tuned to the operating frequency of the MRI machine;

[0277] 464: The resonant response of the array when tuned to a frequency higher than the operating frequency of the MRI machine;

[0278] 465: a resonant frequency of the array tuned to a frequency higher than the operating frequency of the MRI machine;

[0279] 500: Helical resonator;

[0280] 501: top of the resonator;

[0281] 502: bottom end of the resonator;

[0282] 503: The interior of the resonator;

[0283] 510: conductor;

[0284] 511: end of the conductor;

[0285] 512: Electrically insulating covering layer;

[0286] 513: turn;

[0287] 515: conductor gap;

[0288] 520: core;

[0289] 521: core outer diameter;

[0290] 522: Core inner diameter;

[0291] 523: outer surface of the core;

[0292] 525: core height;

[0293] 530: slot;

[0294] 550: additional reactance;

[0295] 560: Disk-shaped dish;

[0296] 561: coupling loop;

[0297] 565: Water;

[0298] 566: Water surface;

[0299] 567: dry resonant frequency;

[0300] 568: resonant frequency of 10% water;

[0301] 569: resonant frequency of 20% water;

[0302] 600: BC-SRR resonator;

[0303] 601: top surface of BC-SRR;

[0304] 602: bottom surface of BC-SRR;

[0305] 610: first split ring resonator;

[0306] 611: first gap;

[0307] 612 to 613: opposite ends of the first gap;

[0308] 620: second split ring resonator;

[0309] 621: Second gap;

[0310] 650: high dielectric constant substrate;

[0311] 700: flexible substrate;

[0312] 799: Specimen's limbs;

[0313] 801: coupler;

[0314] 802: The interior of the spiral coil;

[0315] 810: semiconductor chip;

[0316] 820: switch;

[0317] 1000: nonlinear resonator;

[0318] 1010: Nonlinear resonator circuit;

[0319] 1011, 1012: ends of the nonlinear resonator loop;

[0320] 1013: gap;

[0321] 1020: Nonlinear resonator controlled coupler;

[0322] 1100: Controllable array component;

[0323] 1110: spacer;

[0324] 1111: spacer gap;

[0325] 1400: Isolator system;

[0326] 1401: Integrated Circuits;

[0327] 1410: first transceiver or network;

[0328] 1411: first port;

[0329] 1420: second transceiver or network;

[0330] 1421: Second port;

[0331] 1430: Linear metamaterial resonator;

[0332] 1440: Transmission gap.

[0333] Various embodiments may be characterized by potential claims listed in the paragraphs following this paragraph (and preceding the actual claims provided at the front of this application). These potential claims form part of the written description of this application. Therefore, the subject matter of the following potential claims may be presented as actual claims in subsequent proceedings related to this application or any application based on the priority claimed by this application. The inclusion of such potential claims should not be interpreted as meaning that the actual claims do not cover the subject matter of the potential claims. Therefore, a decision not to present these potential claims in subsequent proceedings should not be interpreted as donating the subject matter to the public.

[0334] Without limitation, potential subject matter that may be claimed (prefaced with the letter "P" to avoid confusion with the actual claims presented herein) includes:

[0335] P1. A circuit comprising: a first resonant device and a nonlinear resonant device, wherein the first resonant device is used to resonate in response to an applied electromagnetic signal, and the first resonant device has a characteristic resonant frequency; the nonlinear resonant device is used to selectively perform resonant communication with the first resonant device, and the nonlinear resonant device can be configured into a first resonant state and a second resonant state, the first resonant state has a first resonant frequency equal to the characteristic resonant frequency, and the second resonant state has a second resonant frequency different from the first resonant frequency.

[0336] P2. The circuit of P1, wherein when the nonlinear resonant device is in the second resonant state, the nonlinear resonant device is substantially communicatively isolated from the first resonant device.

[0337] P3. A signal amplification accessory for use within a bore of an MRI machine having a body coil configured to transmit an excitation signal having a transmit frequency to a sample in the bore in a transmit mode and to receive a response signal having a response frequency from the sample in a receive mode, the accessory comprising: a resonator array comprising a plurality of metamaterial resonators, each of the plurality of metamaterial resonators having a resonant frequency, the metamaterial resonators configured to inductively couple to each other in response to an applied electromagnetic signal; and a nonlinear control device configured to (i) generate, with the resonator array, a first array resonant frequency offset from the transmit frequency when the MRI machine is in the transmit mode; and (ii) generate, with the resonator array, a second array resonant frequency equal to the response frequency when the MRI machine is in the receive mode, so as to amplify the response signal.

[0338] P4. The signal amplification accessory of P3, wherein the plurality of metamaterial resonators comprises a plurality of helical coil resonators.

[0339] P5. The signal amplification accessory of P3, wherein the plurality of metamaterial resonators comprises a plurality of split ring resonators.

[0340] P6. The signal amplification accessory of P3, wherein the plurality of metamaterial resonators comprises a plurality of broadside-coupled split-ring resonators.

[0341] P7. A signal amplification accessory according to P3, wherein the nonlinear control device includes a split ring resonator defining a gap and a variable capacitor electrically coupled within the gap.

[0342] The embodiments of the invention described above are intended to be exemplary only; many variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the invention as defined in any appended claims.

Claims

1. A circuit, comprising: a first resonator having a characteristic resonant frequency; as well as a nonlinear resonator controllably configured to enter a first resonant state and a second resonant state, wherein in the first resonant state, the nonlinear resonator has a first resonant frequency equal to the characteristic resonant frequency, and in the second resonant state, the nonlinear resonator has a second resonant frequency different from the first resonant frequency, wherein the first resonator is configured to be coupled to a first port, and the nonlinear resonator is configured to be coupled to a second port, and the circuit is configured to receive a radio frequency signal from the first port or the second port, The resonant coupling of the radio frequency signal between the first resonator and the nonlinear resonator in the second resonant state is at least 9 dB smaller than the resonant coupling between the first resonator and the nonlinear resonator in the first resonant state.

2. The circuit according to claim 1, wherein: In the first resonant state, the nonlinear resonator is configured to inductively couple to the first resonator to communicatively couple a signal from the first resonator to the second port, and In the second resonant state, the nonlinear resonator is configured to isolate the second port from the first resonator.

3. The circuit of claim 2, wherein: The nonlinear resonator includes a metamaterial resonator having a first end and a second end, and a coupler electrically disposed between the first end and the second end, wherein the coupler is controllably configurable into a plurality of impedance states, the plurality of impedance states comprising: a first impedance state, the first impedance state configuring the nonlinear resonator into the first resonant state, and A second impedance state configures the nonlinear resonator into the second resonant state.

4. The circuit according to claim 3, wherein The metamaterial resonator includes a split ring resonator.

5. The circuit according to claim 3, wherein The coupler includes a variable capacitor configured to: (a) having the second impedance state in response to a radio frequency signal incident on the coupler from the second port, so that the nonlinear resonator is in the second resonant state and the second port is isolated from the first resonator, and (b) having the first impedance state in the absence of such a radio frequency signal at a carrier frequency from the second port, such that the nonlinear resonator is in the first resonant state and being configured to communicatively couple the first resonator to the second port.

6. The circuit according to claim 3, wherein The coupler includes a variable capacitor configured to: (a) having the first impedance state in response to a radio frequency signal incident on the coupler from the second port, such that the nonlinear resonator is in the first resonant state and is configured to communicatively couple the second port to the first resonator, and (b) having the second impedance state in the absence of such a radio frequency signal at a carrier frequency from the second port, such that the nonlinear resonator is in the second resonant state and the second port is isolated from the first resonator.

7. The circuit according to claim 3, wherein The coupler includes a switch.

8. The circuit according to claim 7, wherein The switch includes a transistor.

9. The circuit according to claim 2, wherein The first resonator is a linear resonator.

10. The circuit according to claim 9, wherein The linear resonator is a helical resonator.

11. A method for controlling an isolation circuit, the method comprising: A nonlinear resonator and a second resonator are provided, wherein: The nonlinear resonator is controllably configurable into an isolation configuration having an isolation mode resonant frequency and a reception configuration having a reception mode resonant frequency different from the isolation mode resonant frequency, and wherein, the second resonator having a second resonant frequency equal to the receive mode resonant frequency; configuring the nonlinear resonator in the isolation configuration such that the nonlinear resonator is substantially communicatively isolated from the second resonator in a first mode to isolate the nonlinear resonator from a signal on the second resonator and to isolate the second resonator from another signal on the nonlinear resonator; and in a second mode, configuring the nonlinear resonator into the receiving configuration such that the nonlinear resonator is configured for resonant communication with the second resonator, wherein the resonant coupling between the second resonator and the nonlinear resonator in the isolation configuration is at least 9 dB smaller than the resonant coupling between the second resonator and the nonlinear resonator in the receiving configuration.

12. The method according to claim 11, further comprising: providing a signal to the second resonator after configuring the nonlinear resonator into the receiving configuration; as well as The signal is received at the nonlinear resonator.

13. The method according to claim 11, further comprising: Upon receiving a signal at the nonlinear resonator, the nonlinear resonator is configured into the isolation configuration to isolate the nonlinear resonator from another signal on the second resonator and to isolate the second resonator from another signal on the nonlinear resonator.

14. A signal amplification accessory for use within a bore of an MRI machine having a transmitting coil and a receiving coil, wherein the transmitting coil is configured to transmit an excitation signal having a transmit frequency to a specimen in the bore in a transmit mode, and the receiving coil is configured to receive a response signal having a response frequency from the specimen in a receive mode, the accessory comprising: a resonator array comprising a plurality of metamaterial resonators, each of the plurality of metamaterial resonators having a resonant frequency, the metamaterial resonators configured to inductively couple to one another in response to an applied electromagnetic signal; A nonlinear controlled resonator, comprising: a resonator coil; and a controllable impedance coupled to the resonator coil, The nonlinear controlled resonator has a first resonant frequency when the controllable impedance is in a first impedance state, and has a second resonant frequency when the controllable impedance is in a second impedance state; a spacer layer disposed between the resonator array and the nonlinear control resonator, the spacer layer defining a gap between the resonator array and the nonlinear control resonator; and The resonator coil and the controllable impedance are selected such that the nonlinear controlled resonator is configured to: (i) generate, together with the resonator array, a first array resonant frequency shifted from the transmit frequency when the MRI machine is in the transmit mode; and (ii) generate, together with the resonator array, a second array resonant frequency equal to the response frequency to amplify the response signal when the MRI machine is in the receive mode.

15. The signal amplification accessory according to claim 14, wherein: The resonator coil includes a first end and a second end, and the controllable impedance is electrically coupled between the first end and the second end.

16. The signal amplification accessory according to claim 14, wherein: The resonator coil includes a split ring resonator, and the controllable impedance includes a variable capacitance configured to exhibit a first capacitance in response to receiving a radio frequency excitation signal from the MRI machine in a transmit mode and to exhibit a second capacitance when the MRI machine is in a receive mode.

17. The signal amplification accessory according to claim 14, wherein: The controllable impedance is a variable capacitance diode configured to assume the first impedance state in response to the variable capacitance diode receiving the excitation signal from the MRI machine when the MRI machine is in the transmit mode.

18. The signal amplification accessory according to claim 17, wherein: The variable capacitance diode is configured to assume the second impedance state in the absence of the excitation signal from the MRI machine when the MRI machine is in the receive mode.

19. The signal amplification accessory according to claim 14, wherein: The resonator array defines a resonator plane, and wherein the nonlinear control resonator is disposed substantially parallel to the resonator plane at a non-zero distance from the resonator plane.

20. The signal amplification accessory according to claim 14, wherein: The resonator array defines a resonator plane, and wherein the nonlinear control resonator is arranged substantially parallel to the resonator plane at a distance of 2 centimeters from the resonator plane.

21. The signal amplification accessory according to claim 14, wherein: The resonator array defines a resonator plane, and wherein the nonlinear control resonator is arranged substantially parallel to the resonator plane at a distance of 0 centimeters from the resonator plane.

22. The signal amplification accessory of claim 14 , further comprising a spacer device disposed in the spacer layer between the resonator array and the nonlinear control resonator, the spacer device comprising a non-metallic and non-magnetic solid material, the spacer device maintaining the nonlinear control resonator at a defined distance from the array.

23. The signal amplification accessory according to claim 14, wherein: The resonator array includes at least two metamaterial resonators.

24. A method of amplifying a response signal from a sample in a bore of an MRI machine, the method comprising: Providing a steerable array assembly in the bore of the MRI machine having an operating frequency, the steerable array assembly comprising: a resonator array comprising a plurality of metamaterial resonators configured to inductively couple to each other at the operating frequency of the MRI machine; and a nonlinear controlled resonator having controllable impedance; configuring the steerable array assembly in a pass-through mode when the MRI machine is in a transmit mode; and The steerable array assembly is configured in a magnification mode while the MRI machine is in a receive mode.

25. The method according to claim 24, wherein Configuring the steerable array assembly to the pass-through mode includes automatically configuring the nonlinear controlled resonator to a first resonant mode, wherein the nonlinear controlled resonator in the first resonant mode couples with the resonator array to produce an assembly resonant frequency in the steerable array assembly that is offset from the operating frequency of the MRI machine.

26. The method according to claim 25, wherein Automatically configuring the nonlinear controlled resonator to a first resonant mode includes providing a radio frequency excitation signal transmitted from the MRI machine to the controllable impedance.

27. The method according to claim 24, wherein Configuring the steerable array assembly to the amplification mode includes automatically configuring the nonlinear controlled resonator to a second resonant mode, wherein the nonlinear controlled resonator in the second resonant mode couples with the resonator array to produce an assembly resonant frequency in the steerable array assembly at the operating frequency of the MRI machine.

28. The method according to claim 27, wherein Automatically configuring the nonlinear controlled resonator to the second resonant mode includes blocking an excitation signal transmitted from the MRI machine from the controllable impedance.

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