Flexible resonant trap circuit

Abstract

A flexible resonant notch filter circuit is provided, comprising: a transmission line arranged to include a helical winding having a first helical winding segment and a second helical winding segment; and a capacitor coupled between the first helical winding segment and the second helical winding segment.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 685,920 entitled “FLEXIBLE RESONANT TRAP CIRCUIT”, filed November 15, 2019, which is a continuation of U.S. Provisional Patent Application No. 62 / 796,019 entitled “DNA Baluns”, filed January 23, 2019. Background Technology

[0003] Resonant notch circuit

[0004] A resonant notch filter is a functional resonant circuit that provides high impedance at one or more specific frequencies. In its most basic sense, a resonant notch filter filters current from a very narrow frequency band. For example, the inductance and capacitance of the notch filter can be determined through lumped components, circuit board design, or wiring. The inductance and capacitance of the notch filter together determine the resonant frequency being filtered by the notch filter. For example, a resonant notch filter can be coupled to a single conductor to be used as a radio frequency (RF) filter for a DC line. A resonant notch filter can also be coupled to other transmission lines with two or more conductors (e.g., coaxial cable, triaxial cable, planar transmission line, etc.).

[0005] A typical resonant notch filter circuit includes a capacitor coupled in parallel with an inductor. The impedance of a typical resonant notch filter circuit becomes very high at its resonant frequency. Multiple resonances can be obtained by adding more inductors and capacitors to the circuit. Resonant notch filter circuits are used in a wide range of RF applications. For example, in some applications, a resonant notch filter is used to prevent signals at the resonant frequency of the notch filter from reaching the load. For example, in radio tuner applications, a resonant notch filter may have a variable capacitor that can be used to tune a radio receiver to select one from multiple broadcast stations. For example, in antenna applications, a resonant notch filter circuit can be used to isolate one part of an antenna from another. For example, in MRI applications, a resonant notch filter circuit can be used in magnetic resonance imaging (MRI) systems to prevent RF excitation signals used to deposit energy into an object / structure from coupling to various transmission lines and cables in the system. Transmission lines in MRI are used to carry signals from a receiving antenna / coil to the MRI system. These signals are released from the object / structure and used to create an image. Other cables in the MRI system carry digital and analog control signals or power from various peripheral devices to the system.

[0006] Resonant notch circuit in MRI system

[0007] Magnetic resonance imaging (MRI) utilizes the nuclear spin of atomic nuclei of interest. Typically, the nuclear spin of hydrogen in a water molecule is used to image the human body. During MRI, the nuclei are polarized using a strong, uniform static magnetic field called B0. The magnetically polarized nuclear spins generate magnetic moments in the body. In a steady state, the magnetic moments are aligned parallel to the direction of the static magnetic field B0 and do not produce useful information. To acquire an image, the magnetic moments are disturbed by an excitation signal. During excitation, an RF transmission coil generates an excitation magnetic field called B1, which is perpendicularly aligned to the static magnetic field B0 and oscillates at a frequency closely matching the natural precession of the nuclear spins. This precession frequency—the Larmor frequency of protons in the B0 field—allows the excitation signal B1 to deposit energy into the nuclear spin system, causing a net rotation of the magnetic moments away from alignment with the static magnetic field B0. The effectiveness of the B1 field is determined by both the precession frequency and the amplitude and duration of the pulse. In MRI, the Larmor frequency, or precession frequency, refers to the rate of precession of the magnetic moments of protons around an external magnetic field. The precession frequency is defined by the strength of the magnetic field B0 and the atomic nuclei of interest. The amplitude and duration of the RF pulse determine how far the magnetization will tilt or flip, often referred to as the flip angle. During receive mode, the RF receive coil, tuned to the Larmor frequency, detects the precession magnetization as it returns to a steady state. The precession magnetization induces a current in the receive coil via electromagnetic induction. This induced current is the MR signal and represents the mixture of magnetizations from all tissues within the field of view (FOV) of the receive coil. Typically, the transmit RF coil can be used as the receive RF coil, or alternatively, the receive RF coil can be a separate, receive-only RF coil.

[0008] The amplitude of energy transmitted by the RF coil is much greater than the amplitude of energy of the induced current in the RF receiver coil. Without intervention, a receiver coil positioned close to the patient's body can be strongly coupled to the B1 field during excitation, posing a risk of damage to the receiver coil and potential harm to the patient from the generated strong local field. The transmission line used to send excitation pulses to the transmitter coil or to transmit MR signals from the receiver coil can exhibit antenna-like behavior within the system. Generally, any wire or cable—such as those used to carry electrical or digital / analog signals—will exhibit similar behavior. Similar to the resonant receiver coil, this can lead to coupling between the transmission line and the B1 field. Any coupling between the transmission line or the receiver coil and the B1 field can cause non-uniformity in the transmit flip angle. Non-uniform flip angles will degrade the information content within the induced MR signal and can serve as an indication of potential safety issues. To prevent undesirable antenna-like behavior that could degrade information content, a resonant notch filter is typically coupled to the receiver coil and the transmission line used to carry the induced MR signal.

[0009] In MRI, it is desirable for excitation and reception to be spatially homogeneous across the imaging volume for better image homogeneity. During excitation in a typical MRI system, excitation field homogeneity is usually achieved by transmitting through a whole-body volumetric RF coil. This whole-body transmitting coil is typically the largest RF coil in the system and is used to create a uniform B1 field. However, if a large coil is also used for reception, a lower signal-to-noise ratio (SNR) is produced, primarily due to its greater distance from the imaged tissue. Therefore, smaller, dedicated receiving coils, which can be easily positioned closer to the patient's body, are typically used for reception to improve the SNR from the smaller volume of interest. In practice, carefully designed specialized RF receiving coils are mechanically configured to fit as close as possible to the volume of interest and contribute to both patient handling and comfort.

[0010] There is a demand in the industry for flexible, well-shaped, and comfortable RF receiving coils. To ensure the safety of these coils, a compact frequency notch circuit is correspondingly required to prevent coupling between the B1 field and the inductive elements of the transmission line or receiving coil. This frequency notch circuit is mechanically configured to facilitate patient handling and comfort. More specifically, frequency notch circuits need to be mechanically flexible enough to adapt to the space adjacent to the patient's anatomy, allowing them to be positioned near a compact receiving coil located close to the patient's anatomy. For example, in MRI imaging performed close to the patient, flexible and comfortable frequency notch circuits are most useful if they can be bent and twisted without affecting their frequency notch behavior; therefore, these circuits need to be unaffected by arbitrary changes in bending or positioning. Summary of the Invention

[0011] In one aspect, a resonant notch filter circuit is provided, comprising: a conductor wire arranged to include a helical winding portion, the helical winding portion including a first helical winding segment and a second helical winding segment twisted together. A capacitor is arranged to provide capacitance between the first helical winding segment and the second helical winding segment.

[0012] On the other hand, resonant notch filters are used in magnetic resonance imaging systems. Wires used to deliver analog or digital control signals and analog image information are positioned within a magnetic field used to excite the nuclei of atoms in the object of interest. Resonant notch filters, electrically coupled to these wires, prevent them from coupling with the transmitting magnetic field.

[0013] In another aspect, a receiving circuit for a magnetic resonance imaging system is provided. The receiving circuit includes a receiving coil, a transmission line coupled to the receiving coil, and a resonant notch filter circuit. The resonant notch filter circuit includes: a portion of the transmission line arranged to include a helical winding portion; and includes a capacitor arranged to provide capacitance across the portion of the helical winding portion.

[0014] On the other hand, a receiver array pad for a magnetic resonance imaging system is provided. The receiver circuit includes: a plurality of receiver coils arranged such that each receiver coil covers at least a portion of another receiver coil; and a plurality of transmission lines, each transmission line coupled to a different receiver coil. Each respective transmission line is arranged to provide a respective resonant notch filter circuit. Each respective resonant notch filter circuit includes: a respective portion of the respective transmission line arranged to include a respective helical winding portion; and a respective capacitor arranged to provide capacitance across a portion of the respective helical winding portion.

[0015] On the other hand, a method for generating a resonant notch filter circuit is provided. The method includes twisting a portion of a transmission line to form a helical winding portion comprising a first helical winding segment and a second helical winding segment helically twisted together, and including a folded portion at the junction of the first and second helical winding segments. The method also includes a coupling capacitor between the first and second helical winding segments. Attached Figure Description

[0016] The patent or application documents contain at least one drawing made in color. Upon request and payment of the necessary fees, the Patent Office will provide a copy of the patent or application disclosure with the color drawing.

[0017] When read in conjunction with the accompanying drawings, various aspects of this disclosure are best understood in the following detailed description. It is emphasized that, in accordance with standard industry practice, the various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or decreased for clarity of discussion. Furthermore, reference numerals may be repeated in various examples within this disclosure. This repetition is for simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations discussed.

[0018] Figure 1A This is an illustrative diagram showing the RF transmitting coil and RF receiving coil positioned relative to the patient within an MRI system.

[0019] Figure 1B This is a partially transparent top view of an example array of pads including a receiving coil array coupled to a transmission line containing a resonant notch filter.

[0020] Figure 2 This is an illustrative schematic diagram showing an example transmitting circuit and an example receiving circuit.

[0021] Figure 3 This is an illustrative diagram showing a perspective view of an example resonant notch filter circuit coupled to a transmission line.

[0022] Figure 4AIt is a capacitor element coupled to the resonant circuit. Figure 3 Illustrative side cross-sectional views of the first and second segments of an example coaxial transmission line.

[0023] Figure 4B It is a capacitor element coupled to the resonant circuit. Figure 3 Example of a coaxial transmission line: a partial end cross-sectional view.

[0024] Figure 5A yes Figure 3 An illustrative side view of the helical winding portion of an example resonant notch filter.

[0025] Figure 5B It is shown by Figure 3 An illustration of a simulated magnetic field generated by the current flow on the outer surface of the spiral winding section of an example resonant notch filter.

[0026] Figure 5C It is shown Figure 3 An illustrative diagram illustrating an example simulation of the external surface current path within the helical winding section of an example resonant notch filter.

[0027] Figures 6A to 6C This is an explanatory diagram showing the flip angle in the example homogeneous water-filled region to illustrate the effect of the receiving coil, transmission line wiring, and resonant notch filter circuit on the B1 excitation.

[0028] Figure 7A This is an explanatory diagram showing a cross-sectional end view of the base of the first and second segments, including the unassembled arrangement of the flexible capacitor sheet and the helical winding.

[0029] Figure 7B It is shown Figure 7A The diagram illustrates a flexible capacitor sheet, wherein a first conductor plate is rolled up to contact the base of a first segment and a second conductor plate is rolled up to contact the base of a second segment.

[0030] Figure 8A This is an illustrative diagram showing an example resonant notch filter extending in a roughly linear arrangement.

[0031] Figure 8B It is shown Figure 8A The illustration shows the corresponding example frequency attenuation response of the resonant notch filter.

[0032] Figure 9A It is shown Figure 8A An illustration of an example resonant notch filter, wherein the helical winding bends at an angle of approximately 180 degrees at approximately the midpoint of the length of its helical winding portion.

[0033] Figure 9B It is shown Figure 9A The illustration shows the corresponding example frequency attenuation response of the folded resonant notch filter.

[0034] Figure 10A This is an illustrative diagram showing two example resonant notch filters, each of which is arranged side-by-side with... Figure 8A It is the same as the resonant notch filter.

[0035] Figure 10B It shows that it is aimed at Figure 10A An illustrative diagram illustrating the frequency attenuation of a side-by-side notch filter.

[0036] Figure 11A This is an illustrative side view showing an example resonant notch filter, which includes a transmission line that is folded and braided to produce three helical winding segments.

[0037] Figure 11B It is shown Figure 11A A simplified layout diagram of a resonant notch filter, representing the folding and weaving of three spiral winding segments.

[0038] Figure 11C yes Figure 11A An example electrical schematic of a resonant notch filter is shown.

[0039] Figure 11D It shows that it is aimed at Figure 11A An illustrative diagram of the example frequency attenuation response of an example resonant notch filter.

[0040] Figure 12A This is an illustrative perspective view of an example printed circuit board resonant notch filter circuit.

[0041] Figure 12B This is an illustrative side cross-sectional view of an example printed circuit board resonant notch circuit, showing multiple stacked flat conductor layers embedded in a substrate such as a dielectric material.

[0042] Figure 12C This is an illustrative diagram showing individual cross-sectional views of the stacked conductor layers of an example printed circuit board resonant notch filter circuit.

[0043] Figure 13 It is shown in Figures 12A to 12C Illustrative diagrams of example signal currents flowing upwards, downwards, and through within an example printed circuit board resonant notch filter circuit. Detailed Implementation

[0044] Figure 1AThis is an illustrative diagram showing RF transmit coils 110 and RF receive coils 112 arranged relative to a patient in receiver array pads 113 within an MRI system 100. The patient 102 is shown lying on a platform 104 within an MRI chamber 106. A main magnet 108 is arranged to generate a static magnetic field B0. During excitation mode, one or more transmit coils 110 transmit excitation magnetic field pulses that generate an excitation magnetic field B1 perpendicular to the static magnetic field B0 at a frequency of interest. Multiple receive coils 112 are positioned close to the patient's body. Following RF excitation, changes in magnetic flux resulting from the precession of net nucleation within the subject induce MR currents within the receive coils 112, which can be post-processed to extract frequency, phase, and amplitude information used to construct MR images. As explained below, safety considerations typically require a minimum spacing, typically about 5 mm, between the patient's anatomy and the receive coils 112 and associated electronics.

[0045] Figure 1B This is a partially transparent top view of an example receiver coil array pad 113 including a receiver coil array 112 coupled to a resonant notch filter 124. The coil arrays 112-1, 112-2 can be housed within a flexible housing 126, indicated by dashed lines. This flexible housing 126 can be formed of a soft, cushioning material such as fabric or foam to provide comfort when placed on a patient and to space the coils and associated circuitry from the patient. For example, the receiver coil 112 can be formed of a flexible conductive material such as flexible wire or conductive foil. A first transmission line 128-1 and a second transmission line 128-2 extend between the receiver coil array pad 113 and the MRI system 100. An example first set of three first receiver coils 112-1 are electrically coupled to the first transmission line 128-1, wherein one of the three first coils 112-1 is located between two other first coils 112-1 and wherein each of the three first coils 112-1 partially overlaps with an adjacent portion of one of the other two first coils 112-1, for example, 20% to 25%. Similarly, in the example second group, three second receiving coils 112-2 are electrically coupled to the second transmission line 128-2, wherein one of the three second coils 112-2 is located between the other two of the second coils 112-2, and each of the three second coils 112-2 overlaps with an adjacent portion of the other two first coils 112-2, for example, 20% to 25%. The example first group of receiving coils and the example second group of receiving coils are positioned side-by-side, wherein each coil in each group overlaps with at least one coil in the other group, but in practice they can also be spaced apart, overlapped, or offset.

[0046] Multiple array pads 113 can be placed at different locations on the patient's anatomy to capture the magnetic flux generated during precession. This captured flux is transmitted back to the MRI system 100 via transmission lines 128-1, 128-2 for reconstruction, thereby creating an image. Flexible transmission lines 128-1, 128-2, respectively coupled to the corresponding receiving coils 112-1, 112-2, will transmit the MR current induced in the coils 112-1, 112-2 back to the MRI system during precession. Figure 1B The figure depicts multiple transmission lines 128-1, 128-2 tightly bundled together to save space. In the example array pad 113, transmission lines 128-1, 128-2 are bundled into groups of three, with one transmission line coupled to each circular coil element. Individual or bundled transmission lines 128-1, 128-2 may exhibit antenna-like behavior. Corresponding resonant notch filters 124 are coupled at the output of each coil 112-1, 112-2 and are coupled along the individual transmission lines 128-1, 128-2 at intervals not exceeding a quarter wavelength, with the B1 signal excitation frequency. The resonant frequency of each notch filter 124 is matched to the excitation frequency. Preamplifier circuitry 130 is shown as a transmission line coupled to the resonant notch filter pair 124, but can be located at any point along the transmission line.

[0047] Therefore, it will be understood that the receiving coil array pads 113 can be compliant and shaped to fit the patient's anatomy. The receiving coils 112-1 and 112-2 are formed of a flexible material. The transmission lines 128-1 and 128-2 are flexible, and the resonant notch filter circuit 124 is formed by the arrangement of segments of the transmission lines 128-1 and 128-2. Therefore, the flexibility and thickness of the resonant notch filter circuit 124 are proportionate to the flexibility and thickness of the transmission lines 128-1 and 128-2. Finally, the receiving coils 112-1 and 112-2, the transmission lines 128-1 and 128-2, and the resonant notch filter circuit 124 are housed within a flexible housing 126 formed of soft foam material.

[0048] Figure 2This is an illustrative schematic diagram showing an example MRI system transmitting circuit 202 and an example MRI system receiving circuit 204. The example transmitting circuit 202 includes a transmitting coil 206, an RF power amplifier 207, a pulse generation circuit 208, a digital-to-analog converter (DAC) circuit 210, and a computer system 215. An excitation signal transmission line 214 couples the amplifier 207 and the pulse generation circuit 208 to the transmitting coil 206. The example receiving circuit 204 includes a receiving coil 212, an RF power amplifier circuit 218, an analog-to-digital converter (ADC) circuit 220, and a computer system 215. A receiving signal transmission line 228 couples the receiving coil 212 to the amplifier circuit 218. The receiving circuit 204 also includes a first example resonant notch filter 224a and a second example resonant notch filter 224b coupled to the receiving transmission line 228, sometimes referred to as baluns. As shown within the dashed lines of resonant notch filter 224a, each of the first resonant notch filter 224a and the second resonant notch filter 224b includes a parallel combination of a capacitor 225 and an inductor 226 coupled between portions of the receive transmission line 228. It will be understood that the resonant notch filter 224b includes a similar arrangement of capacitors and inductors (not shown). The first resonant notch filter 224a is positioned to couple to a portion of the receive transmission line 228 adjacent to the receive coil 212. Example: The first resonant notch filter 224a is typically placed mechanically as close as possible to the receive coil. Example: The first resonant notch filter 224a is used to prevent the inductor (not shown) of the receive coil 212 from appearing as part of the receive transmission line 228 in the scanner. Example: The second resonant notch filter 224b is shown positioned along the receive transmission line between the amplifier 218 and the ADC 220. In practice, for example, multiple additional resonant notch filters (not shown) may be placed on the connection between the receiving coil 212 and the amplifier 218, and on the connection between the amplifier 218 and the ADC 220. Typically, these resonant notch filters are positioned such that the length of the receiving transmission line 228 between the notch filters is less than a quarter wavelength (relative to the scanner's resonant frequency). This prevents standing wave behavior on the transmission line. Therefore, the location of the notch filters is typically determined by the total length of the cable / transmission line 228.

[0049] What will be understood is... Figure 2 The receiving circuit 204 represents a single receiving coil 212, a single transmission line 228 with corresponding resonant notch filters 224a and 224b, and electronic components (e.g., amplifiers and ADCs). However, as in Figures 1A to 1BAs shown in the illustrative accompanying drawings, the MRI system 100 typically includes multiple receiver circuits 204 arranged in an array, each receiver circuit 204 including a separate coil and transmission line, as well as a corresponding resonant notch filter and electronics. The coils are tightly packed together in an overlapping configuration to ensure adequate coverage of precession energy and to minimize coupling between the receiver coils. Furthermore, the coil arrangement is subject to safety standards. Therefore, it will be understood that the size and flexibility of the resonant notch filter located in the same location as the coils are factors in arranging the coils for effective operation.

[0050] During excitation mode, DAC 210 converts the digital signal provided by computer system 215 into an analog signal provided to pulse generator 208. Pulse generator 208 generates short excitation pulse signals at the Larmor frequency of the MRI system, which are then amplified by RFPA 207 and then transmitted via transmit coil 206 to the patient tissue to cause a change in the net rotation of the magnetic moment of the atomic nuclei 230 within the tissue. During excitation mode, first resonant notch filter 224a and second resonant notch filter 224b coupled to receive circuit 204 absorb the common-mode current induced in transmission line 228 by the excitation pulse. During receive mode, a current is induced in the receive coil at the Larmor frequency due to the precession magnetization 232 of the atomic nuclei 230 within the target tissue as they relax back to steady state. This induced signal is transmitted as a differential signal down transmission line 228 to amplifier circuit 218, which amplifies the induced excitation signal. The second section of transmission line 228 then transmits the amplified signal to ADC 220, where it is converted into digital form for processing at computer system 215. All received signals are transmitted as differential signals. Here they are depicted as being transmitted along transmission line 228. A first resonant notch filter 224a and a second resonant notch filter 224b are coupled to not interfere with differential signal transmission during receive mode and to block only common-mode current.

[0051] Figure 3This is an illustrative diagram showing a perspective view of an example resonant notch filter circuit 300. The example resonant notch filter 300 includes a portion of a receiving transmission line 302 that is twisted to form a helical winding portion 304 for use as an inductor, and includes a capacitor 306 coupled between segments of the helical winding portion 304. The example resonant notch filter—also referred to as a resonant loop circuit or a balun—provides maximum resistance at a selected frequency known as its resonant frequency. In the example resonant notch filter 300, each of the capacitor and inductor can be adjusted to select the resonant frequency. The example resonant circuit has a resonant frequency selected to provide maximum resistance at the Larmor frequency of an MRI system. The receiving transmission line 302 is mechanically flexible, and the helical winding portion comprising a continuous portion of the receiving transmission line 302 is also flexible. The portion of the transmission line constituting the helical winding portion 304 of the resonant notch filter determines the flexibility of the resonant notch filter. Each leg of the helical section 304 retains the flexibility of its original unwound form; however, the radius of curvature of the entire helical winding section 304 is limited by the total radius of the helical winding. Figure 4A It is capacitor 306 coupled to resonant notch filter 300. Figure 3 An illustrative side cross-sectional view of the first and second segments of the example transmission line 302. Figure 4B It is capacitor 306 coupled to resonant notch filter 300. Figure 3 A partial end cross-sectional view of an example transmission line 302. The example transmission line 302 includes a first conductor 310 and a second conductor 312. Figures 4A to 4B Example transmission lines include coaxial transmission lines comprising a first conductor 310 positioned as an inner conductor of transmission line 302 and a second conductor 312 positioned as an outer conductor of transmission line 302. Example transmission line 302 includes a dielectric material 314 inserted between the first conductor 310 and the second conductor 312 to electrically isolate the first (inner) conductor 310 and the second (outer) conductor 312. Due to the skin effect, the inner surface 316 and outer surface 318 of the outer (second) conductor 312 act as electrically separated surfaces, although they are continuous portions of the outer conductor 312. Example capacitor 306 couples between corresponding outer surface portions 318 of the second conductor line 312 at the bases 307a, 307b of opposite helical winding segments 308a, 308b of the helical winding. As explained below, a resonant notch filter prevents current from flowing freely on the outer surface of the second conductor line at a selected frequency, such as a Larmor frequency.

[0052] Refer again Figure 3The example resonant notch filter 300 includes a transmission line 302 that is folded and twisted to form a continuous helical winding portion 304. A capacitor 306 is electrically coupled between portions of the transmission line at corresponding first bases 307a and second bases 307b of the helical winding 304 opposite to the folded portion 320. The helical winding portion 304 includes a first helical winding segment 308a extending between the first base 307a of the helical winding 304 and the folded portion 320 at the apex of the helical winding 304. The helical winding 304 includes a second helical winding segment 308b extending between the second base 307b of the helical winding and the folded portion 320 at the apex of the helical winding 304. When the helical winding 304 is arranged to extend in a linear layout, a longitudinal axis 322 extends through the folded portion 320 and between the centers of the first helical winding segment 308a and the second helical winding segment 308b, and between the first base 307a and the second base 307b.

[0053] The first helical winding segment 308a and the second helical winding segment 308b together have a radius of curvature that is at least partially determined by the radius of curvature of the transmission line 302. In the example resonant notch filter 300, the minimum radius of curvature of the helical winding portion 304 is twice the diameter of the transmission line 302, or, when the helix is ​​tightly wound, the minimum radius of curvature of the helical winding portion 304 is the diameter of the helical winding portion as a whole. By placing a spacer between the two legs of the helix, the helix can be wound less tightly, thereby effectively increasing the radius of the helix. By reducing the thickness of the outer insulation layer of the transmission line, the helix can be wound more tightly. The minimum radius of curvature for this resonant notch filter is limited by the diameter of the helix as a whole. The maximum diameter of the helix is ​​generally dependent on the application and is a function of the self-shielding characteristics of the notch filter required by the application. The self-shielding characteristics depend on how tightly the resonant notch filter is wound (twist per length) and how close the two legs of the twist are to each other (helix radius). The specific application determines the required level of self-shielding.

[0054] The first transmission line segment 308a and the second transmission line segment 308b, as components of a continuous transmission line section, are joined at a junction defined by the fold portion 320. A portion of the outer insulation layer of the transmission line 302 is stripped to allow for fine tuning of the inductance. In the example resonant notch filter 300, an example capacitor 306—which may be an integrated circuit capacitor or a ceramic chip capacitor, for example—electrically couples the first base 307a of the first helical winding segment 308a and the second base 307b of the second helical winding segment 308b. A portion of the outer insulation layer of the transmission line 302 is also stripped to expose opposing portions 313a, 313b of the outer surfaces 318, allowing the capacitor 306 to be electrically coupled (e.g., soldered) between them. In an alternative example resonant notch filter, multiple individual capacitors (not shown) may be coupled in a longitudinally distributed manner between the first helical winding segment 308a and the second helical winding segment 308b. In another alternative embodiment, a single distributed capacitive element may be coupled along the length of the helical twist 304. As explained above, the first helical winding segment 308a and the second helical winding segment 308b each include a portion of the continuous transmission line 302.

[0055] An external current, sometimes referred to as common-mode current, flows in opposite directions within the first helical winding segment 308a and the second helical winding segment 308b of the helical twist 304. For example, a common-mode current can be induced in a resonant notch filter during excitation mode when a high-energy excitation pulse is transmitted by the transmitting coil. The current flows in a first direction within the first helical winding segment 308a between the first base 307a and the folded portion 320. The current flows in a second direction opposite to the first direction within the second helical winding segment between the second base 307b and the folded portion 320. In this way, the current flows in either direction along a continuous path on the outer surface 318 of the portion of the transmission line 312 that is twisted to form the helical twisted portion 304, for example, along a path from the base 307a through the first helical winding segment 308a to the folded portion 320, and then along the second helical winding segment 308b back to the base 307b.

[0056] The resonant frequency of the resonant circuit is determined by factors including the total length of the transmission line included in the helical twist portion 304, the approximate cross-sectional area of ​​the helical twist portion 304, the number of turns in the helical twist portion 304, and the value and location of the capacitor 306. Furthermore, a resonant circuit with more than one resonant frequency can be generated by providing different capacitors across different regions of the helical winding portion 304. Additionally, the inductance can depend on the dielectric properties associated with the transmission line 302. During transmission mode, the inductance of the helical winding portion 304, combined with the capacitance of the capacitor 306, forms a resonant circuit on the outer conductor surfaces 318 of the first and second helical winding segments 308a and 308b to create a high-impedance circuit. This high impedance prevents current from flowing freely within the helical winding portion 304 along the outer surfaces of the first and second helical winding segments 308a and 308b. During the receive mode, due to the skin effect of the current in the second conductor 312 of the cable, the differential current flowing in opposite directions along the first (inner) conductor 310 of the transmission line and along the inner surface 316 of the second conductor 312 flows undisturbed through the center of the resonant notch filter. In the example resonant notch filter 300, the inner surface 316 of the first conductor 310 and the second conductor 312 serves as a differential line to conduct differential signals. The outer surface 318 of the second conductor 312 does not host differential current but will serve as a conductive surface to carry common-mode current.

[0057] While example transmission line 302 is implemented using coaxial cable, alternative example resonant notch filters may include, for example, triaxial or biaxial cables. Example resonant notch filters may include planar transmission lines, including but not limited to, striplines, microstrip lines, coplanar waveguides, coplanar stripes, slot lines, substrate-integrated waveguides, fin lines, image lines, or any multilayer variant of such lines. Example resonant notch filters may include balanced lines, including but not limited to twisted pairs, shielded pairs, star-struck four-wire cables, two-leads, Lecher lines, or parallel or parallel wire transmission lines. For example, example resonant notch filters may include metallic or dielectric waveguides. For example, each of the above example transmission lines may be implemented as one or more layers on a flexible printed circuit board, a standard printed circuit board, or created using solution processing (e.g., printed electronics).

[0058] Figure 5A yes Figure 3 An illustrative side view of the helical winding portion 304 of an example resonant notch filter 300. Figure 5B It is shown by Figure 3 An illustration of a simulated magnetic field generated by the current flow on the outer surface of the helical winding portion 304 within an example resonant notch filter 300. Figure 5C It is shown Figure 3An illustrative diagram illustrating an example simulation of the current path on the outer surface within the helical winding portion 304 of an example resonant notch filter 300.

[0059] Figure 5A A longitudinally extending axis of symmetry 510 is shown within the helical winding portion 304, which is equidistant from the first winding segment 308a and the second helical winding segment 308b. Figure 5B The first strongest magnetic field region 502, indicated in red, and the second weakest magnetic field region 504, indicated in blue, are shown. The first strongest magnetic field region 502 is located where the surfaces of the opposing helical winding segments 308a and 308b face each other, and the second weakest magnetic field region 504 is located where the surfaces of the opposing helical winding segments 308a and 308b are away from each other. Figure 5C The arrows indicate the direction of current flow. The size and color of the arrows indicate the magnitude of the current flow. Larger arrows indicate larger current flows, and smaller arrows indicate smaller current flows. The direction of the arrows indicates the direction of current flow. Red arrows indicate the maximum current magnitude, and blue arrows indicate the minimum current magnitude. The current flows in opposite directions along the opposite helical winding segments 308a and 308b. Figure 5C The diagram shows a larger current flowing along the surface portions of the opposing helical winding segments 308a and 308b that face each other, where the magnetic field is strongest; and a smaller current flowing along the surface portions of the opposing helical winding segments 308a and 308b that are opposite each other, where the magnetic field is weakest.

[0060] More specifically, the electromagnetic simulation of the operation of the example resonant notch filter circuit shows that the outer surface current—such as the surface current induced by the excitation pulse—follows the shortest induction path. Figure 5C As shown, in the case of example helical winding 304, the shortest path between the respective first base 307a and second base 307b of helical winding 304 and the folded portion 320 is the path along the inner surface portion of the first and second transmission segments of the helical winding. Figure 5C As shown, currents such as common-mode currents flow in opposite directions along the inner surfaces of the first helical winding segment 308a and the second helical winding segment 308b. Figure 5BAs shown, the magnetic field generated by the common-mode current flow is thus confined to the central portion of the helical winding 304 between the facing portions of the opposing helical winding segments 308a, 308b. Therefore, the resultant magnetic field from each leg 308a, 308b of the helical winding is self-shielded, rather than radiated. This inherent self-shielding of the helical winding 304 makes the example resonant circuit 300 less sensitive to external magnetic fields and load variations, and prevents radiation and field sensitivity problems. For example, an optional conductive cap formed of braid, foil, or tube can be placed over the entire resonant notch filter assembly to provide, for example, additional electromagnetic shielding.

[0061] The example resonant notch filter 300 can be tuned by selecting a capacitor 306 of appropriate size for electrically coupling the bases of the first helical winding segment 308a and the second helical winding segment 308b. The technique of incorporating the capacitor 306 into the helical winding 304 generally does not affect the performance of the resonant notch filter circuit 300, provided that a mechanically strong and flexible electrical connection is achieved (e.g., welding, crimping, joining, etc.). The resonant frequency of the resonant notch filter follows... In the form of a circuit, where L is the inductance of the resonant notch filter, dominated by the helical twisted inductance, and the distributed capacitance C of the circuit includes a lumped capacitor 306. For fine frequency tuning, the position where the capacitor 306 is coupled to the first and second helical winding segments can be selected before joining to adjust the inductor length, because changing the position of the capacitor changes the length of the helix and thus the inductance. Furthermore, for fine tuning, a selectable amount of conductive material 324, such as solder, can be added to the folded region 320 at the apex of the helical winding to adjust the inductance by changing the current flow path, effectively adjusting, for example, the inductor length. By way of illustration, for example, consider the folded region 320 as a small loop, and the addition of solder will fill some areas of this loop, effectively making the loop smaller, and therefore the inductance smaller. Furthermore, for frequency tuning, the diameter of the spiral winding can be adjusted to modify the total inductance, for example, by placing a spacer between the first and second spiral winding segments, by increasing or decreasing the radius or number of turns per length of the winding by changing the twist on the spiral winding portion 304, or by changing the thickness of the outer coating on the transmission line. Increasing the spacing increases the radius of the spiral and thus increases the cross-sectional area of ​​the spiral. Increasing the radius should increase the inductance, although it does reduce some of the distributed capacitance along the spiral, thus its linearity is slightly worse. The capacitance of the lumped capacitance element 306 or the distributed capacitance element can also be adjusted for frequency tuning.

[0062] For use in MRI, the example resonant notch filter 300 can be tuned to resonate at the scanner's Larmor frequency. As an example, a resonant circuit with a helical inductor has been tuned to operate at 127 MHz on a 3T MRI system. Depending on the cable length, the measured reduction in common-mode current is between -10 dB and -30 dB, with a typical reduction of -15 dB for a resonant circuit with a helical winding length of approximately 3.5 cm. Therefore, the example resonant notch filter can have a resonant frequency suitable for operation at 3 Tesla, which is approximately 127 MHz. The example resonant notch filter can have a resonant frequency suitable for operation at 1.5 Tesla, which is approximately 64 MHz. The example resonant notch filter can have a resonant frequency suitable for operation at 7 Tesla, which is approximately 300 MHz. Currently available scanners (non-clinical) range from 0.35T to 10.5T (14 MHz to 450 MHz). The blocking at these frequencies differs for these scanners, and the total length, radius, and number of turns in the helix will need to be varied accordingly to produce a reasonable blocking effect.

[0063] In the example resonant notch filter circuit 300 tuned to operate at 127MHz, the frequency blocking was measured to be between 10dB and 30dB. Industry standards for cable notch filters are also frequency-specific, typically: blocking at 3T > 15dB / blocking at 1.5T > 20dB. The amount of blocking also affects B1 disturbance and coil heating. Sufficient blocking should result in minimal change in B1. Figures 6A to 6C And it passes the temperature tests of each of the IEC 60601-1 and IEC 60601-2-33 guidelines.

[0064] Figures 6A to 6C This is an explanatory diagram showing the flip angle within an example structure consisting of two homogeneous water-filled regions, illustrating the effect of the receiving coil, transmission line wiring, and resonant notch filter on the B1 excitation. Figure 6A The baseline flip angle is shown in a slice of a region where no receiver coil is present, and can be considered the "gold standard" for performance. Figures 6B to 6C The following are examples of the results without a resonant notch filter coupled to the receiving coil array ( Figure 6B In the case of ) and when there is a resonant notch filter coupled to the receiving coil array ( Figure 6C The flip angle of the same slice directly below the receiving coil is shown in the figure when there is no resonant notch filter on the coil. Figure 6B ) relative to baseline ( Figure 6A The figure () has a large flip angle deviation, while the figure from the receiving coil with a resonant notch filter is () Figure 6C More like a baseline map Figure 6ATherefore, the absence of a resonant notch filter at the receiving coil and / or along the receiving transmission line to absorb excitation energy increases the likelihood of a non-uniform B1 flip angle, which degrades MRI results. Significant deviations in B1 are also considered a safety concern for MRI, as local variations in B1 often occur simultaneously with local variations in SAR. This figure illustrates that a resonant notch filter can provide a high-impedance block to absorb excitation energy and prevent interference from the receiving coil and transmission line with B1 excitation.

[0065] Figures 7A to 7B This is an illustrative diagram showing an alternative example of a flexible capacitor 700, including a first flexible conductive plate 702a and a second flexible conductive plate 702b separated by a flexible dielectric 704. Figure 7A This is an explanatory diagram showing cross-sectional end views of the unassembled arrangement of the flexible capacitor layer 700 and the corresponding first base 307a and second base 307b of the first and second segments of the helical winding. Figure 7B It is shown Figure 7A An explanatory diagram of the flexible capacitor layer 700 is shown, wherein a first conductor 702a is rolled up to contact a first base 307b and wherein a second conductor 702b is rolled up to contact a second base 307a. More specifically, Figure 7B This is an illustrative diagram showing a flexible capacitor arranged such that a first conductor 702a is in electrical contact with the outer surface 318 of a second conductor 312 at a first base 307a, and a second conductor 702b is in electrical contact with the outer portion 318 of the second conductor 312 at a second base 307b. The flexible capacitor 700 is bonded to bases 307a and 307b to establish an electrically stable connection (e.g., solder). In this example flexible capacitor, copper-clad laminates coated with a flexible dielectric material on each side are used as the capacitor elements. The flexible capacitor is then, for example, soldered to a spirally wound transmission line at bonding points 307a and 307b, ensuring that the two plates of the flexible capacitors 702a and 702b are bonded to opposite sides of the spiral. The flexible capacitor can then be wound around the spiral, ensuring no electrical contact between 702a and 702b.

[0066] For example, an example flexible capacitor may include a first conductive plate and a second conductive plate formed in a flexible printed circuit board (PCB) material. Alternatively, for example, an example flexible capacitor may include a first conductive plate and a second conductive plate formed by copper cladding on either side of a flexible dielectric sheet. The value of the example flexible capacitor may be tuned based on one or more factors—such as the material properties of the dielectric, the thickness of the dielectric, and the area of ​​the conductive sheet. The capacitance may also vary based on the number of internal conductive layers between the outer conductive surface 702a and the outer conductive surface 702b within the dielectric 704. Therefore, the flexible capacitor can add another way to tune the resonant frequency of the example resonant notch filter. For example, since the area of ​​the conductor plate determines the capacitance, the resonant notch filter can be tuned by changing the total area of ​​the flexible capacitor (e.g., cutting the capacitor sheet to reduce the area size and thus reduce the capacitance). Additionally, changing the thickness of the dielectric of the flexible capacitor can change the capacitance. Furthermore, as Figure 7B As shown, a flexible capacitor element 700 can be wound around a portion of the transmission line to reduce the profile of the resonant notch filter without diminishing its flexibility. Furthermore, longer, coiled windings of the capacitor allow for the use of longer capacitors without shorting the sides together (702a, 702b) or significantly increasing the size / profile of the resonant notch filter. Arrow 713 indicates how the winding can optionally continue.

[0067] For example, flexible capacitor elements can exhibit improved mechanical stability, such as improved resistance to damage due to impact. The mechanical limitation of flexible capacitors (under impact) is the connection between the cable and the capacitor, while ceramic chip capacitors or integrated circuit capacitors can break more easily under impact. A resonant notch filter with a flexible capacitor can be tuned by cutting a capacitor sheet rolled into contact with the base of the first and second segments. Therefore, a resonant notch filter with a flexible capacitor can be relatively easy to tune.

[0068] Figure 8A This is an illustrative diagram showing an example resonant notch filter 800 having a helical winding (not visible) enclosed within a cover 802 and including a wound capacitor 804, wherein the helical winding (below the cover) extends in a generally linear arrangement. Figure 8B It is shown Figure 8A An illustrative diagram showing the frequency attenuation response of the resonant notch filter at 127 MHz, as measured as an example. A cover—which may be plastic, for example—prevents the spiral from unwinding.

[0069] Figure 9A It is shown Figure 8A An illustration of an example resonant notch filter 800, wherein the helical winding (not visible) within the cover 802 bends at an angle of approximately 180 degrees at approximately the midpoint of the length of its helical winding portion. Figure 9BThis is an illustrative diagram showing the frequency attenuation response of a folded notch filter at approximately 127 MHz, as measured as a corresponding example. Therefore, the bending of the helical winding portion of the resonant notch filter has a small effect on the frequency blocking characteristics. More specifically, the self-shielding provided by the helical winding portion 304 causes the resonant notch filters 300 and 800 to be substantially unaffected by bending along the central axis 510. Furthermore, the self-shielding also causes the resonant notch filters 300 and 800 to be substantially unaffected by twisting about the central axis 510. Moreover, the absence of a rigid solid core material within the notch filter 800 and the lack of a rigid Faraday cage surrounding the notch filter 800 allow for flexibility in the windings, enabling it to be folded without altering its frequency attenuation.

[0070] Figure 10A This is an illustrative diagram showing two example resonant notch filters 800A and 800B, where each resonant notch filter is arranged side by side with... Figure 8A It is the same as the 800 resonant notch filter. Figure 10B This is an illustrative diagram showing the frequency attenuation response of two side-by-side notch filters 800A and 800B at 127MHz, as measured as corresponding examples. It will be understood that the inherent self-shielding of the elastic notch filters 800A and 800B allows them to be arranged close to each other without altering the frequency attenuation of either one. The self-shielding of the spiral structure 304 makes the resonant notch filter insensitive to changes in external fields and loads.

[0071] Figure 11A This is an illustrative side view showing an example resonant notch filter 1100, which includes a transmission line that is folded and braided to produce three helical winding segments 1108a, 1108b, and 1108c. Figure 11B This is a simplified layout schematic diagram of a resonant notch filter 1100, showing the folding and weaving of three helical winding segments 1108a, 1108b, and 1108c. The resonant notch filter 1100 includes a first folded portion 1120a between the second segment 1108b and the third segment 1108c, and a second folded portion 1120b between the third segment 1108c and the first segment 1108a. For simplicity, the second segment 1108b is shown as a straight line. Figure 11C This is an example electrical schematic representation of a resonant notch filter 1100. A first capacitor 1106a is coupled between the second segments 1108b and 1120b, and at the junction between the first segment 1108a and the third segment 1108c. A second capacitor 1106b is coupled between the first segments 1108a and 1120a, and at the junction between the second segment 1108b and the third segment 1108c. Figure 11DThis is an illustrative diagram showing the corresponding example frequency attenuation response of the example resonant notch filter 1100 at 75MHz and 160MHz. It will be understood that more than three helical winding segments can be wound within the notch filter circuit, and corresponding capacitor circuitry can be provided to add additional attenuation response. However, adding more segments increases the stiffness of the notch filter and reduces its flexibility. Capacitors and inductors can also be selected in their respective sub-sections to tune each sub-section of the notch filter to a single frequency, thereby providing additional resistance points for common-mode current.

[0072] Figure 12A This is a perspective view of an example printed circuit board (PCB) (hereinafter referred to as 'PCB notch filter') resonant notch circuit 1200. Figure 12B This is an illustrative side cross-sectional view of an example PCB notch filter 1200, showing multiple stacked flat conductive layers embedded in a substrate such as a dielectric material—e.g., a polymer or ceramic material—arranged to form corresponding first helical segments 1208a and second helical segments 1208b of a helical winding 1204. The flexibility of the PCB notch filter is directly related to the flexibility of the substrate layers. If the example PCB notch filter is printed on a flexible film, such as a polyimide film, the PCB notch filter will inherently be flexible, while if the example PCB notch filter is printed on a non-flexible film such as XPC, the PCB notch filter will not be flexible. Figure 12C It is shown Figure 12B This illustration schematically shows six separate cross-sectional views of single stacked conductive layers arranged side-by-side. The example PCB notch filter 1200 includes conductive layers 1-6. Conductive layer 1 is located at the top of the PCB notch filter, and conductive layer 6 is located at the bottom of the PCB. Each of substrate layers 1 to 6 is printed on a separate layer of the PCB notch filter, and vias are used to electrically connect the different layers of the PCB together. References to top, bottom, and vertical directions are used for convenience only and are not intended to be limiting. Other example PCB notch filters (not shown) may include different numbers of layers. It will be understood that, for example, the PCB notch filter may include striplines, microstrip lines, or other microstrip lines constructed from flexible circuit boards.

[0073] Reference Figure 12A The top conductive layer 1 of the PCB notch filter 1200 includes a first signal pad 1222 and a second signal pad 1224, as well as a first ground pad 1226 and a second ground pad 1228. Capacitor 1230 is not shown. (See reference...) Figure 12B Similar to Figure 3 The first base 1207a of the first helical segment 1208a of the resonant notch filter 300 307a is positioned similarly to the first signal pad 1222 and the first ground pad 1226. Figure 3The resonant notch filter 300 extends between the folded portion 320 and the vertex portion 1220. Similar to... Figure 3 The second base 1207b of the second helical segment 1208b of the resonant notch filter 300 307b extends between the position of the second signal pad 1224 and the second ground pad 1228 and the vertex portion 1220. The first helical segment 1208a and the second helical segment 1208b form a continuous circuit extending through the vertex portion 1220, such that, for example, current can flow upward to one of the first helical segment 1208a and the second helical segment 1208b, and downward to the other. In operation, the first helical segment 1208a and the second helical segment 1208b are connected by... Figure 3 The resonant notch filter 300 has the same self-shielding mechanism to shield each other from external magnetic fields.

[0074] Reference Figures 12B to 12C The spiral winding segments 1208a and 1208b include three conductive traces that pass between layers on the PCB to create a spiral twist. Referring to the first spiral winding segment 1208a as an example, differential signals are transmitted to the notch filter at the signal pad input 1222 and the ground pad input 1226, respectively. The signal transmitted to 1222 is then guided to layer 2 through a via and travels along path 1208a, passing between layers 2 and 5, reaching the vertex portion 1220. The ground reference on the PCB transmitted through pad 1226 is connected to path 1208a directly on layer 1 and through a via to path 1208a on layer 3. The ground trace then travels along 1208a, passing back and forth between layers 1 and 3 and between layers 4 and 6, reaching the vertex 1220. Example conductor layers 1 and 3 are wider than example conductor layer 2 and... Figure 12B In the vertically stacked configuration, signal conductor layer 2 serves as the signal conductor trace located between ground conductor layer 1 and ground conductor layer 3, and ground conductor layer 1 and ground conductor layer 3 together serve as a ground plane surrounding the signal. Similarly, example conductor layer 4 and example conductor layer 6 serve as ground, and example conductor layer 5 serves as the signal conductor trace. Example conductor layer 4 and example conductor layer 6 are also wider than example conductor layer 5, and... Figure 12B In the stacked structure, the signal conductor layer 5 is located between the ground conductor layer 4 and the ground conductor layer 6.

[0075] Each conductive via formed in the substrate material is electrically coupled to its corresponding location in conductor layers 2 and 5. Each conductive via formed in the dielectric material is also electrically coupled to its corresponding location in external ground conductor layers 1 and 6. Each conductive via formed in the dielectric material can also be positioned to be electrically coupled to its corresponding location between equivalent ground layers 1 and 3 and 4 and 6 (not shown).

[0076] The current within the PCB notch filter takes the shortest path along the conductor layers within the PCB notch filter 1200, just as they... Figure 5C As shown in the resonant notch filter 300. Ground conductor layers 3 and 4 are the closest inward-facing ground layers to each other within the PCB notch filter, and therefore, the largest current flow is likely to occur within ground conductor layers 3 and 4. For example, this is similar to... Figure 3 The coaxial cable resonant notch filter 300 exhibits greater current flow at the inward-facing portions of the first helical winding section 308a and the second helical winding section 308b. Grounding conductor layers 1 and 6 are the outermost layers furthest apart from each other, and therefore, the least current flow is likely to occur within grounding conductor layers 1 and 6. For example, this is similar to... Figure 3 A small current flows at the outward-facing portions of the first helical winding section 308a and the second helical winding section 308b of the coaxial cable resonant notch filter 300.

[0077] Ground layer 1 is electrically coupled to the first ground pad 1226. A corresponding via connects the second ground pad 1228 to ground layer 6. A corresponding via connects the first signal pad 1222 to signal conductor layer 2. A corresponding via connects the second signal pad 1224 to signal conductor layer 5. The first terminal of capacitor 1230 is electrically coupled to ground conductor layer 1, and a via at pad 1230 connects the second terminal of capacitor to ground conductor layer 6.

[0078] Figure 13 This is an illustrative schematic diagram showing an example signal current flowing upwards, downwards, and through within a PCB notch filter 1200 between signal conductor layers 2 and 4. Example current 1340 flows into the PCB through pad 1222 on layer 1 and is transmitted to layer 2 via a via. The current then flows along signal conductor segment 1251 through layer 2 and through via 1351 to signal conductor segment 1252 in layer 5. Current 1340 then flows along signal conductor segment 1252 through layer 5 and through via 1352 to signal conductor segment 1253 in layer 2. Current 1340 then flows along signal conductor segment 1253 through layer 2 and through via 1353 to signal conductor segment 1254 in layer 5. Current 1340 then flows along signal conductor segment 1254 through layer 5 and through via 1354 to signal conductor segment 1255 in layer 2. Note that via 1354 typically corresponds to... Figure 3The folded region 320 at the apex of the helical winding 300. Current 1340 then flows along signal conductor segment 1255 through layer 2 and through via 1355 to signal conductor segment 1256 in layer 5. Current 1340 then flows along signal conductor segment 1256 through layer 5 and through via 1356 to signal conductor segment 1257 in layer 2. Current 1340 then flows along signal conductor segment 1257 through layer 2 and through via 1357 to signal conductor segment 1258 in layer 5. The signal is then passed back to pad 1224 on layer 1 through the via. Example conductor segments 1251, 1252, 1253, and 1254 are components of the first helical segment 1208a. Example conductor segments 1255, 1256, 1257, and 1258 are components of the second helical segment 1208b. Figure 13 In the color version, the current path 1340 portion within the first helical segment 1208a is marked in white, and the current path 1340 portion within the second helical segment 1208b is marked in blue. Therefore, the example arrangement of signal conductor segments 1251, 1253, 1255, and 1257 in substrate layer 2 and the arrangement of signal conductors 1252, 1254, 1256, and 1258 in substrate layer 5, along with the coupling of the segments through vias 1351 to 1357, such that current flows along a helical path within the substrate material of the PCB notch filter 1200, is similar to... Figure 3 The spiral current flows within the resonant notch filter 300. Those skilled in the art will understand that ground conductor layers 1, 3, 4 and 6 are similarly arranged to follow segments of a spiral ground conductor path within the substrate material of the PCB notch filter 1200, with conductor segments between them.

[0079] The example resonant notch filter circuits 300, 1100, and 1200 have a wide range of applications. Electric power lines carrying digital or analog electrical control signals can extend through magnetic fields. For example, the example resonant notch filter circuits can be used to prevent electric power lines from being used as antennas by attenuating signals at the frequency of the magnetic field in its presence. A resonant notch filter essentially cuts the electric power line into shorter segments that will not resonate in the presence of a magnetic field. For example, the example resonant notch filter circuits can be used in other radio frequency (RF) applications such as mobile phones, RF broadband, and laptops.

[0080] Various examples

[0081] Examples of resonant notch filters can include:

[0082] Example 1 includes a resonant notch filter circuit comprising: a conductor wire arranged to include a helical winding portion comprising a first helical winding segment and a second helical winding segment twisted together; and a capacitor arranged to provide capacitance between the first helical winding segment and the second helical winding segment.

[0083] Example 2 may include the subject matter of Example 1, wherein the flexibility of the helical winding portion is commensurate with the flexibility of the conductor wire.

[0084] Example 3 may include the subject matter of Example 1, wherein the resonant notch filter has a frequency-dependent resistance; wherein the helical winding portion includes an axis of symmetry that is equidistant from the first helical winding segment and the second helical winding segment and extends longitudinally within the helical winding portion; and wherein the helical winding portion is capable of bending along the axis of symmetry without substantially altering the frequency attenuation response.

[0085] Example 3 may include the subject of Example 3, wherein the helical winding portion is capable of bending up to 180 degrees along the axis of symmetry without substantially altering the frequency decay response.

[0086] Example 5 may include the subject matter of Example 1, wherein the resonant notch filter has a frequency decay response; wherein the helical winding portion includes an axis of symmetry that is equidistant from the first helical winding segment and the second helical winding segment and extends longitudinally within the helical winding portion; and wherein the helical winding portion is capable of deforming about the axis of symmetry without substantially altering the frequency decay response.

[0087] Example 6 may include the subject of Example 3, wherein the helical winding portion is capable of deforming up to 360 degrees about the axis of symmetry without substantially altering the frequency decay response.

[0088] Example 7 may include the subject of Example 1, wherein the thickness of the helical winding is proportional to the thickness of the conductor wire.

[0089] Example 8 may include the subject of Example 1, wherein the thickness of the helical winding is proportional to the number of winding segments in the helical winding section.

[0090] Example 9 may include the subject of Example 1, wherein the helical winding portion is arranged to include a folded portion that defines the junction of a first helical winding segment and a second helical winding segment.

[0091] Example 10 may include the subject of Example 1, and also includes:

[0092] Conductive material is deposited on a portion of the folded section to adjust the inductance of the helical winding portion.

[0093] Example 11 may include the subject of Example 1, wherein the conductor segment is arranged to include a folded portion having a 180-degree fold at the junction of the first helical winding segment and the second helical winding segment.

[0094] Example 12 may include the subject matter of Example 1, wherein the helical winding portion includes a folded portion at the junction of a first helical winding segment and a second helical winding segment; wherein the first helical winding segment includes a first base and extends between the first base and the folded portion; and wherein the second helical winding segment includes a second base and extends between the second base and the folded portion.

[0095] Example 13 may include the subject matter of Example 1, wherein the capacitor includes a self-capacitance between the first helical winding segment and the second helical winding segment.

[0096] Example 14 may include the subject matter of Example 1, wherein the capacitor includes at least one external capacitor electrically coupled between the first base and the second base.

[0097] Example 15 may include the subject matter of Example 1, wherein the first helical winding segment includes one or more corresponding first-facing-inner-surface portions; wherein the second helical winding segment includes one or more corresponding second-facing-inner-surface portions; and wherein the one or more first-facing-inner-surface portions face the one or more second-facing-inner-surface portions.

[0098] Example 16 may include the subject of Example 1, wherein the opposing surfaces of the first and second helical winding segments are arranged within the helical portion to self-shield the magnetic and electric fields caused by the current flow within the helical winding portion.

[0099] Example 17 may include the subject matter of Example 1, wherein the conductor wire includes a transmission line, and the helical winding portion includes a continuous portion of the transmission line.

[0100] Example 18 may include the subject matter of Example 1, wherein the conductor line includes a transmission line, the transmission line including a first conductor, a second conductor and a dielectric material between the first conductor and the second conductor; and wherein the capacitor includes at least one external capacitor coupled between a portion of the second conductor at a first helical winding segment and a portion of the second conductor at a second helical winding segment.

[0101] Example 19 may include the subject matter of Example 1, wherein the conductor wire includes a coaxial cable, the coaxial cable including an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor;

[0102] The capacitor includes at least one external capacitor coupled between a portion of the outer conductor at a first helical winding segment and a portion of the outer conductor at a second helical winding segment.

[0103] Example 20 may include the subject of Example 1, wherein the conductor line includes a transmission line, and the transmission line includes at least two conductors separated by a dielectric.

[0104] Example 21 may include the subject matter of Example 1, wherein the capacitor includes at least one external capacitor coupled between a first helical winding segment and a second helical winding segment; wherein the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric; and wherein at least a portion of the at least two conductors is coupled to the at least one capacitor, and at least another portion of the at least two conductors is not coupled to the at least one capacitor.

[0105] Example 22 may include the subject matter of Example 1, wherein the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric; wherein at least a portion of the at least two conductors serves as a differential signal line; and wherein at least another portion of the at least two conductors serves as a potential reference for the differential signal line.

[0106] Example 23 may include the subject matter of Example 1, wherein the capacitor includes at least one external capacitor coupled between a first helical winding segment and a second helical winding segment; wherein the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric; wherein the transmission line includes a differential line and a grounding shield; and wherein at least one capacitor is coupled between a portion of the grounding shield at the first helical winding segment and a portion of the grounding shield at the second helical winding segment.

[0107] Example 24 may include the subject of Example 1, wherein the at least one capacitor comprises a plurality of capacitive elements.

[0108] Example 25 may include the subject matter of Example 1, wherein the at least one capacitor includes distributed capacitance between a first helical winding segment and a second helical winding segment.

[0109] Example 26 may include the subject matter of Example 1, wherein the conductor wire includes a coaxial cable, the coaxial cable including an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor; and wherein the at least one capacitor includes distributed capacitance supplied by one of two or more shields of the coaxial cable.

[0110] Example 27 may include the subject matter of Example 1, wherein the capacitor includes at least one external capacitor coupled between a first helical winding segment and a second helical winding segment; wherein the at least one capacitor includes a dielectric layer comprising a first conductor layer and a second conductor layer on opposite sides thereof, the first conductor layer and the second conductor layer being arranged such that the first conductor layer mechanically contacts and / or electrically contacts the first helical winding segment and the second helical winding segment mechanically contacts and / or electrically contacts the second helical winding segment.

[0111] Example 28 may include the subject matter of Example 27, wherein the dielectric material includes a flexible dielectric material.

[0112] Example 29 may include the subject matter of Example 1, and further includes: a flexible cover that surrounds at least a portion of the helical winding portion and prevents the helical winding portion from unwinding.

[0113] Example 30 may include the subject of Example 1, wherein the conductor lines comprise multilayer printed circuits.

[0114] Example 31 may include the subject matter of Example 30, wherein the multilayer printed circuit includes a layered dielectric substrate and conductor traces coupled to a signal conductor and a ground conductor located at different layers within the layered dielectric substrate; wherein both the signal conductor trace and the ground conductor trace follow parallel helical paths within the substrate.

[0115] Example 32 may include the subject matter of Example 30, and further include: a rigid layered dielectric substrate or a flexible layered dielectric substrate; wherein the conductor line includes a first ground conductor and a second ground conductor located at different layers within the substrate and following a helical path within the substrate; and wherein the conductor line also includes a signal conductor located between the first ground conductor and the second ground conductor within the substrate and following a helical path within the substrate.

[0116] Example 33 may include the subject of Example 1, wherein the helical winding portion further includes a third helical winding segment; wherein the first helical winding segment, the second helical winding segment, and the third helical winding segment are twisted together, and further includes: capacitance between the second helical winding segment and the first helical winding segment or the third helical winding segment.

[0117] Examples of receiving circuits may include:

[0118] Example 34 includes a receiving circuit for a magnetic resonance imaging system, comprising: a receiving coil; a transmission line coupled to the receiving coil; and a first resonant notch filter circuit, the first resonant notch filter circuit including: a first portion of the transmission line arranged to include a first helical winding portion; and a first capacitor arranged to provide capacitance across a portion of the first helical winding portion.

[0119] Example 35 may include the subject of Example 34, wherein the first capacitor includes a self-capacitance across a portion of the first helical winding.

[0120] Example 36 may include the subject of Example 34, wherein the first capacitor includes at least one external capacitor coupled across a portion of the first helical winding.

[0121] Example 37 may include the subject matter of Example 34, and further include: two or more resonant notch circuits, each including: a corresponding second portion of a transmission line arranged to include a second helical winding portion; and a corresponding second capacitor arranged to provide capacitance across a portion of the second helical winding portion.

[0122] Example 38 may include the subject of Example 37, wherein the first resonant notch filter and the corresponding second resonant notch filter have matched frequency attenuation; wherein the first resonant notch filter circuit and the corresponding second resonant notch filter circuit are spaced apart from each other by no more than a quarter wavelength of the resonant frequency.

[0123] Example 39 may include the subject of Example 37, wherein a first resonant notch filter and a corresponding second resonant notch filter attenuate different frequencies.

[0124] Example 40 may include the subject of Example 35, wherein a first resonant notch circuit and a corresponding second resonant notch circuit are positioned side by side.

[0125] Example 41 may include the subject of Example 35, wherein at least one of the first resonant notch circuit and the corresponding second resonant notch circuit is folded at least 180 degrees.

[0126] Example 42 may include the subject of Example 34, wherein the receiving coil is formed of a flexible material.

[0127] Examples of receiver circuit array pads may include:

[0128] Example 43 includes a receiver circuit array pad for a magnetic resonance imaging system, comprising: a plurality of receiver coils arranged such that each receiver coil covers at least a portion of another receiver coil; a plurality of transmission lines, each transmission line coupled to a different receiver coil; and wherein each respective transmission line is arranged to provide a respective first resonant notch circuit, the first resonant notch circuit including: a respective first portion of the respective transmission line arranged to include a respective first helical winding portion; and a respective first capacitor arranged to provide capacitance across a portion of the respective first helical winding portion.

[0129] Example 44 may include the subject of Example 43, wherein the corresponding first capacitor includes self-capacitance across the corresponding first helical winding portion.

[0130] Example 45 may include the subject of Example 43, wherein the corresponding first capacitor includes at least one corresponding external capacitor coupled across the corresponding first helical winding portion.

[0131] Example 46 may include the subject of Example 43, wherein each corresponding transmission line is arranged to provide a corresponding second resonant notch circuit, the corresponding second resonant notch circuit comprising: a corresponding second portion of the transmission line arranged to include a corresponding second helical winding portion; and a corresponding second capacitor arranged to provide capacitance across a portion of the corresponding second helical winding portion.

[0132] Example 47 may include the subject of Example 46, wherein a first resonant notch filter and a second resonant notch filter formed by a corresponding transmission line attenuate different frequencies; wherein the first resonant notch filter circuit and the second resonant notch filter circuit formed by the corresponding transmission line are spaced apart from each other by no more than one-quarter wavelength of the resonant frequency.

[0133] Example 48 may include the subject of Example 43, wherein the receiving coil is formed of a flexible material.

[0134] Example 49 may include the subject of Example 44, and also includes:

[0135] A housing surrounding multiple receiving coils, the housing being formed of a flexible material.

[0136] Examples of manufacturing methods may include:

[0137] Example 50 includes a method for generating a resonant notch circuit, comprising: twisting a portion of a transmission line to form a helical winding portion, the helical winding portion including a first helical winding segment and a second helical winding segment twisted together helically, and including a folded portion at the junction of the first helical winding segment and the second helical winding segment; and coupling at least one capacitor between the first helical winding segment and the second helical winding segment.

[0138] Example 51 may include the subject matter of Example 50, wherein the coupling includes coupling capacitors between corresponding grounded shield portions of the transmission line at respective first and second helical winding segments.

[0139] Example 52 may include the subject of Example 50, wherein the coupled capacitive element is made of a flexible dielectric sheet covered on both sides with a flexible conductive coating; wherein the flexible capacitive element is wound in a spiral twist around the transmission line in a rolled manner, thereby reducing the outline of the circuit without short-circuiting the capacitor.

[0140] Example 53 may include the subject of Example 52, wherein the second-order inductance and capacitance of the coiled adjustment element are tightened or loosened.

[0141] Example 54 may include the subject of Example 50, and also includes: adjusting the inductance of the helical winding.

[0142] Example 55 may include the subject of Example 54, wherein adjusting the inductance of the spiral winding includes adjusting the amount of conductor at the folded portion.

[0143] Example 56 may include the subject of Example 54, wherein adjusting the inductance of the helical winding includes adjusting the radius of the helical winding portion.

[0144] Example 57 may include the subject of Example 54, wherein adjusting the inductance of the helical winding includes adjusting the amount of conductive shielding around the helical winding.

[0145] Example 58 may include the subject of Example 54, wherein adjusting the inductance of the helical winding includes adjusting the position of the capacitor coupled to the helical winding.

[0146] Example 59 may include the subject of Example 50, and also includes: placing a flexible cover around the helical winding.

[0147] Example 60 may include the subject of Example 50, wherein a transmission line passes through a helical winding to form an additional leg of the helix.

[0148] Example 61 may include the subject of Example 60, wherein the transmission line forming the additional leg of the helix is ​​electrically continuous with the transmission line forming one of the first two legs of the helical winding.

[0149] Example 62 may include the subject of Example 60, wherein a transmission line is added to a helical winding comprising more than two parts.

[0150] Example 61 may include the subject of Example 60, wherein a capacitor is coupled between a grounded shield of an additional leg of the helix and one or more of the original helical windings.

[0151] The above description is presented to enable any person skilled in the art to create and use resonant notch filters. Various modifications to the examples will be apparent to those skilled in the art, and the general principles defined herein can be applied to other examples and applications without departing from the spirit and scope of the invention. In the foregoing description, numerous details have been set forth for illustrative purposes. However, those skilled in the art will recognize that the examples in this disclosure can be practiced without using these specific details. In other instances, well-known processes are shown in block diagram form to avoid obscuring the description of the invention with unnecessary detail. The same reference numerals are used in some places to denote different views of the same or similar items in different figures. Therefore, the foregoing description and figures of the embodiments and examples are merely illustrative of the principles of the invention. It will be understood that those skilled in the art can make various modifications to the embodiments without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A resonant trap circuit, comprising: a conductor wire arranged to include a spiral winding portion, the spiral winding portion including a first spiral winding segment and a second spiral winding segment spirally twisted together; and a capacitor arranged to provide capacitance between the first spiral winding segment and the second spiral winding segment, wherein the spiral winding portion includes a symmetry axis extending longitudinally within the spiral winding portion equidistant from the first spiral winding segment and the second spiral winding segment.

2. The resonant trap circuit of claim 1, wherein a flexibility of the spiral winding portion commensurate with a flexibility of the conductor wire.

3. The resonant trap circuit of claim 1, wherein the resonant trap circuit having a frequency dependent resistance; and wherein the spiral winding portion is bendable along the symmetry axis without materially altering the frequency attenuation response.

4. The resonant trap circuit of claim 3, wherein, the spiral winding portion is bendable along the symmetry axis up to one hundred eighty degrees without materially altering the frequency attenuation response.

5. The resonant trap circuit of claim 1, wherein the resonant trap circuit having a frequency attenuation response; and wherein the spiral winding portion is deformable about the symmetry axis without materially altering the frequency attenuation response.

6. The resonant trap circuit of claim 3, wherein, the spiral winding portion is deformable about the symmetry axis up to three hundred sixty degrees without materially altering the frequency attenuation response.

7. The resonant trap circuit of claim 1, wherein a thickness of the spiral winding portion is commensurate with a thickness of the conductor wire.

8. The resonant trap circuit of claim 1, wherein a thickness of the spiral winding portion is commensurate with a number of winding segments in the spiral winding portion.

9. The resonant trap circuit of claim 1, wherein, the spiral winding portion is arranged to include a fold portion, the fold portion demarcating a juncture of the first spiral winding segment and the second spiral winding segment.

10. The resonant trap circuit of claim 9, further comprising: a conductor material deposited on a portion of the fold portion to adjust an inductance of the spiral winding portion.

11. The resonant trap circuit of claim 1, wherein, the conductor wire is arranged to include a fold portion having a one hundred eighty degree fold at a juncture of the first spiral winding segment and the second spiral winding segment.

12. The resonant trap circuit of claim 1, wherein the spiral winding portion includes a fold portion at a juncture of the first spiral winding segment and the second spiral winding segment; wherein the first spiral winding segment includes a first base portion and extends between the first base portion and the fold portion; and wherein the second spiral winding segment includes a second base portion and extends between the second base portion and the fold portion.

13. The resonant trap circuit of claim 1, wherein the capacitor includes a self-capacitance between the first spiral winding segment and the second spiral winding segment.

14. The resonant trap circuit of claim 12, wherein The capacitor includes at least one external capacitor electrically coupled between the first base and the second base.

15. The resonant trap circuit of claim 1, wherein the first spiral winding segment includes one or more respective first inward-facing surface portions; wherein the second spiral winding segment includes one or more respective second inward-facing surface portions; and wherein the one or more first inward-facing surface portions face the one or more second inward-facing surface portions.

16. The resonant trap circuit of claim 1, wherein oppositely facing surfaces of the first spiral winding segment and the second spiral winding segment are arranged within the spiral winding portion to self-shield magnetic and electric fields caused by current flow within the spiral winding portion.

17. The resonant trap circuit of claim 1, wherein the conductor line includes a transmission line, and the spiral winding portion includes a continuous portion of the transmission line.

18. The resonant trap circuit of claim 1, wherein the conductor line includes a transmission line, the transmission line including a first conductor, a second conductor, and a dielectric material between the first conductor and the second conductor; and wherein the capacitor includes at least one external capacitor coupled between a portion of the second conductor at the first spiral winding segment and a portion of the second conductor at the second spiral winding segment.

19. The resonant trap circuit of claim 1, wherein the conductor line includes a coaxial cable, the coaxial cable including an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor; wherein the capacitor includes at least one external capacitor coupled between a portion of the outer conductor at the first spiral winding segment and a portion of the outer conductor at the second spiral winding segment.

20. The resonant trap circuit of claim 1, wherein, the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric.

21. The resonant trap circuit of claim 1, wherein, the capacitor includes at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric; and wherein at least a portion of the at least two conductors is coupled to the at least one external capacitor, and at least another portion of the at least two conductors is not coupled to the at least one external capacitor.

22. The resonant trap circuit of claim 1, wherein, the conductor line includes a transmission line, the transmission line including at least two conductors separated by a dielectric; wherein at least a portion of the at least two conductors is used as a differential signal line; and wherein at least another portion of the at least two conductors is used as a potential reference for the differential signal line.

23. The resonant trap circuit of claim 1, wherein, the capacitor includes at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric; wherein the transmission line comprises a differential line and a ground shield; and wherein the at least one external capacitor is coupled between a portion of the ground shield at the first spiral winding segment and a portion of the ground shield at the second spiral winding segment.

24. The resonant trap circuit of claim 1, wherein the capacitor comprises a plurality of capacitive elements.

25. The resonant trap circuit of claim 1, wherein the capacitor comprises a distributed capacitance between the first spiral winding segment and the second spiral winding segment.

26. The resonant trap circuit of claim 1, wherein the conductor line comprises a coaxial cable comprising an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor; and wherein the capacitor comprises a distributed capacitance supplied by one of two or more shields of the coaxial cable.

27. The resonant trap circuit of claim 1, wherein, the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the at least one external capacitor comprises a dielectric layer comprising a first conductor layer and a second conductor layer on opposite sides thereof, the first conductor layer and the second conductor layer arranged such that the first conductor layer mechanically and / or electrically contacts the first spiral winding segment and the second conductor layer mechanically and / or electrically contacts the second spiral winding segment.

28. The resonant trap circuit of claim 27, wherein, the dielectric layer comprises a flexible dielectric material.

29. The resonant trap circuit of claim 1, further comprising: a flexible cover around at least a portion of the spiral winding portion and preventing unspooling of the spiral winding portion.

30. The resonant trap circuit of claim 1, wherein, the conductor line comprises a multi-layer printed circuit.

31. The resonant trap circuit of claim 30, wherein the multi-layer printed circuit comprises a layered dielectric substrate and conductor traces coupled to signal and ground conductors at different layers within the layered dielectric substrate; wherein both the signal conductor line and the ground conductor line follow parallel spiral paths within the substrate.

32. The resonant trap circuit of claim 30, further comprising: a rigid or flexible layered dielectric substrate; wherein the conductor line comprises a first ground conductor and a second ground conductor at different layers within the substrate and following spiral paths within the substrate; and wherein the conductor line further comprises a signal conductor between the first ground conductor and the second ground conductor within the substrate and following a spiral path within the substrate.

33. The resonant trap circuit of claim 1, wherein the spiral winding portion further comprises a third spiral winding segment; wherein the first spiral winding segment, the second spiral winding segment, and the third spiral winding segment are twisted together, and further comprising: a first end of the first spiral winding segment and a second end of the first spiral winding segment. a capacitance between the second helical winding segment and the first helical winding segment or the third helical winding segment.

34. A receive circuit for a magnetic resonance imaging system, comprising: a receive coil; a transmission line coupled to the receive coil; and a first resonant trap circuit comprising: a first portion of the transmission line arranged to comprise a first helical winding portion, the first helical winding portion comprising a first helical winding segment and a second helical winding segment helically twisted together; and a first capacitor arranged to provide a capacitance between the first helical winding segment and the second helical winding segment, wherein the first helical winding portion comprises a symmetry axis extending longitudinally within the first helical winding portion equidistant from the first helical winding segment and the second helical winding segment.

35. The receive circuit of claim 34, wherein the first capacitor comprises a self-capacitance across the first helical winding portion.

36. The receive circuit of claim 34, wherein, the first capacitor comprises at least one external capacitor coupled across the first helical winding portion.

37. The receive circuit of claim 34, further comprising: two or more second resonant trap circuits each comprising: a respective second portion of the transmission line arranged to comprise a second helical winding portion; and a respective second capacitor arranged to provide a capacitance across a portion of the second helical winding portion.

38. The receive circuit of claim 37, wherein, the first resonant trap circuit and the respective second resonant trap circuits have matched frequency attenuation; wherein the first resonant trap circuit and the respective second resonant trap circuits are spaced no more than a quarter wavelength of a resonant frequency apart from one another.

39. The receive circuit of claim 37, wherein, the first resonant trap circuit and the respective second resonant trap circuits attenuate different frequencies.

40. The receive circuit of claim 37, wherein the first resonant trap circuit and the respective second resonant trap circuits are positioned side-by-side.

41. The receive circuit of claim 37, wherein at least one of the first resonant trap circuit and the respective second resonant trap circuits is folded by at least one hundred and eighty degrees.

42. The receive circuit of claim 34, wherein the receive coil is formed from a flexible material.

43. A receive circuit array pad for a magnetic resonance imaging system, comprising: a plurality of receive coils arranged such that each receive coil covers at least a portion of another receive coil; a plurality of transmission lines, each transmission line coupled to a different receive coil; and wherein each respective transmission line is arranged to provide a respective first resonant trap circuit, the first resonant trap circuit comprising: a respective first portion of the respective transmission line arranged to comprise a respective first helical winding portion, the respective first helical winding portion comprising a respective first helical winding segment and a respective second helical winding segment helically twisted together; and a respective first capacitor arranged to provide a capacitance across a portion of the respective first helical winding portion, wherein the respective first spiral winding portion includes a symmetry axis extending longitudinally within the respective first spiral winding portion equidistant from the respective first spiral winding segment and the respective second spiral winding segment.

44. The receive circuit array pad of claim 43, wherein the respective first capacitor includes a self-capacitance across the respective first spiral winding portion.

45. The receive circuit array pad of claim 43, wherein the respective first capacitor includes a respective at least one external capacitor coupled across the respective first spiral winding portion.

46. The receive circuit array pad of claim 43, wherein, each respective transmission line is arranged to provide a respective second resonant notch circuit, the respective second resonant notch circuit including: a respective second portion of the transmission line arranged to include a respective second spiral winding portion; and a respective second capacitor arranged to provide a capacitance across a portion of the respective second spiral winding portion.

47. The receive circuit array pad of claim 46, wherein the respective first and second resonant notches formed by the respective transmission line each attenuate different frequencies; wherein the respective first and second resonant notch circuits formed by the respective transmission line are spaced no more than a quarter wavelength of a resonant frequency apart from one another.

48. The receive circuit array pad of claim 43, wherein the receive coil is formed from a flexible material.

49. The receive circuit array pad of claim 44, further comprising: a housing surrounding the plurality of receive coils, the housing formed from a flexible material.

50. A method for producing a resonant notch circuit, comprising: twisting a portion of a transmission line to form a spiral winding portion, the spiral winding portion including a first spiral winding segment and a second spiral winding segment twisted together helically and including a fold portion at a junction of the first spiral winding segment and the second spiral winding segment; and coupling at least one capacitor between the first spiral winding segment and the second spiral winding segment, wherein the spiral winding portion includes a symmetry axis extending longitudinally within the spiral winding portion equidistant from the first spiral winding segment and the second spiral winding segment.

51. The method of claim 50, wherein coupling includes coupling the at least one capacitor between respective grounded shield portions of the transmission line at the respective first spiral winding segment and the second spiral winding segment.

52. The method of claim 50, wherein the at least one capacitor is made from a flexible dielectric sheet covered on both sides with a flexible conductive coating; wherein the at least one capacitor is wrapped in a roll-like manner around the twisted portion of the transmission line such that a profile of the resonant notch circuit is reduced without shorting the at least one capacitor.

53. The method of claim 52, wherein tightening or loosening the roll-like manner in which the at least one capacitor is wrapped adjusts a second order inductance and capacitance of the at least one capacitor.

54. The method of claim 50, further comprising: adjusting an inductance of the spiral winding portion.

55. The method of claim 54, wherein Adjusting the inductance of the spiral winding portion includes adjusting the amount of conductor at the folded portion.

56. The method of claim 54, wherein, Adjusting the inductance of the spiral winding portion includes adjusting the radius of the spiral winding portion.

57. The method of claim 54, wherein Adjusting the inductance of the spiral winding portion includes adjusting the amount of conductive shielding surrounding the spiral winding portion.

58. The method of claim 54, wherein Adjusting the inductance of the spiral winding portion includes adjusting the position at which the at least one capacitor is coupled to the spiral winding portion.

59. The method of claim 50, further comprising: placing a flexible cover around the spiral winding portion.

60. The method of claim 50, wherein a length of transmission line passes through the spiral winding portion, forming an additional leg of the spiral winding portion.

61. The method of claim 60, wherein the length of transmission line forming the additional leg of the spiral winding portion is electrically continuous with the transmission line forming one of the first two legs of the spiral winding portion.

62. The method of claim 60, wherein an additional transmission line is added to a spiral winding containing more than two portions.

63. The method of claim 60, wherein an additional capacitor is coupled between the ground shield of the additional leg of the spiral winding portion and one or more of the original spiral winding.

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