PLANAR MICROSTRIP ANTENNA TO GENERATE HOMOGENEOUS MICROWAVE MAGNETIC FIELD FOR NV CENTER DIAMOND MAGNETOMETER

Abstract

A planar microstrip antenna to generate homogeneous microwave magnetic field for NV center diamond magnetometer is provided. The planar microstrip antenna 102 includes non-uniform transmission line 116 including shrunk section 118 that is positioned between two 50 Ohm characteristic impedance sections 122, and shrunk multiple wire trace 118A in shrunk section 118 including copper wires 120. Microwave power is received at transmission line 116 through first SMA connector 112A using control unit 104. The control unit 104 generates microwave magnetic fields from each copper wire by passing current through copper wires; and generates homogeneous microwave magnetic field by establishing planar homogeneous region at distance above trace 118A, where microwave magnetic fields from copper wires are combined. The microwave magnetic field is configured to manipulate NV centers in diamond plate. The microstrip antenna 102 includes a characteristic impedance tuning fixture 114 that tunes characteristic impedance of shrunk section 118. FIG. 1

Specification

Description:BACKGROUND
Technical Field
[0001] The embodiments herein generally relate to quantum devices and more particularly, to a planar microstrip antenna to generate homogeneous microwave magnetic field for nitrogen-vacancy (NV) center diamond magnetometer.
Description of the Related Art
[0001] In nitrogen-vacancy (NV) center diamond magnetometers, microwave antennas are utilized to generate microwave magnetic fields that manipulate the NV centers within the diamond plate. The NV center diamond plate is placed above the microwave antenna, and efficient microwave field generation is crucial for accurate manipulation. However, conventional antennas face limitations, such as low efficiency, weak microwave magnetic field (B1) strength, and reduced homogeneity of the field. The small area of the homogeneous field further restricts its application in NV center manipulation.
[0002] Conventional microstrip antennas, often connected via SMA connectors at both ends, generate weak fields and suffer from poor field homogeneity, limiting their utility in NV center diamond magnetometers. Furthermore, the mismatch in characteristic impedance between sections of the antenna caused by the different dielectric constants of the diamond and air results in reflections that compromise the antenna's efficiency. These limitations also cause antenna performance to vary with frequency, reducing the system's dynamic range and overall measurement capability.
[0003] Therefore, there arises a need to address the aforementioned technical drawbacks in existing systems in developing microstrip antennas to generate strong and uniform magnetic field without any mismatch in characteristic impedance.
SUMMARY
[0004] In view of a foregoing, an embodiment herein provides a system for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate. The system includes a planar microstrip antenna that includes a circuit board ground; a circuit board dielectric layer that is placed above the circuit board ground; and a non-uniform transmission line trace that is positioned above the circuit board dielectric layer. The circuit board ground, the circuit board dielectric layer and the non-uniform transmission line trace form a non-uniform transmission line. The non-uniform transmission line includes a shrunk section that is positioned between two 50 Ohm characteristic impedance sections of the non-uniform transmission line, and a shrunk multiple wire trace in the shrunk section. The shrunk multiple wire trace is narrower than the two 50 Ohm characteristic impedance section traces. The shrunk multiple wire trace includes two or more parallel copper wires with optimized width. The two or more parallel copper wires are separated by optimized distances with the shrunk section being symmetrical along the length axis of the shrunk multiple wire trace. The planar microstrip antenna further includes a first subminiature version A (SMA) connector that is mounted at one end of the non-uniform transmission line for receiving microwave power.
[0005] The system further includes a control unit that is communicatively connected with the planar microstrip antenna. When in operation, the control unit is configured to: (i) enable the non-uniform transmission line to receive microwave power from an input source through the first SMA connector; (ii) generate microwave magnetic fields from each copper wire in the shrunk multiple wire trace by passing the current through the two or more parallel copper wires; and(iii) generate a homogeneous microwave magnetic field by establishing a planar homogeneous region (A) at a specific distance (H) above the shrunk multiple wire trace, where the microwave magnetic fields from the two or more copper wires are combined. The homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate, when the diamond plate is placed above the shrunk multiple wire trace.
[0006] In some embodiments, the planar microstrip antenna includes a characteristic impedance tuning fixture that is placed under the shrunk multiple wire trace and is configured to tune a characteristic impedance of the shrunk section. The characteristic impedance tuning fixture includes (a) a tuning hole that is located at the center of the circuit board ground and partially penetrated into the circuit board dielectric layer; and (b) a tuning screw that is located in the tuning hole with threads inside the circuit board ground and the circuit board dielectric layer. The characteristic impedance tuning fixture tunes the characteristic impedance of the shrunk section when adjusting the distance between the shrunk multiple wire trace and the circuit board ground by turning the tuning screw.
[0007] In some embodiments, the characteristic impedance tuning fixture includes a locking nut and a washer to lock the tuning screw once tuning is complete.
[0008] In some embodiments, the other end of the non-uniform transmission line is connected to at least one of (i) a 50 Ohm terminator through a second SMA connector, (ii) a 50 Ohm resistor, or (iii) two 100 Ohm resistors in parallel.
[0009] In some embodiments, the circuit board dielectric layer includes a solder resist layer to which the diamond plate with NV centers is attached at the middle of the shrunk multiple wire trace. The length of the shrunk multiple wire trace is longer than the diamond plate.
[0010] In some embodiments, a width of the two or more copper wires in the shrunk multiple wire trace is of 0.7 mm, a distance between the two or more copper wires is of 1 mm. A width of the two 50 Ohm characteristic impedance section traces is of 3 mm.
[0011] In some embodiments, a thickness of the non-uniform transmission line trace is of 0.1 mm.
[0012] In one aspect, a method for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate is provided. The method includes (i) providing a planar microstrip antenna, where the planar microstrip antenna includes a non-uniform transmission line that is connected to a first SMA connector at one end ; a shrunk section that is positioned between two 50 Ohm characteristic impedance sections of a non-uniform transmission line trace; and a shrunk multiple wire trace in the shrunk section, where the shrunk multiple wire trace includes two or more parallel copper wires with optimized width and the two or more parallel copper wires are separated by optimized distances; (ii) receiving, at the non-uniform transmission line, microwave power through the first SMA connector from an input source using a control unit; (iii) generating, using the control unit, microwave magnetic fields from each copper wire in the shrunk multiple wire trace by passing current through the two or more parallel copper wires; and (iv) generating, by the control unit, a homogeneous microwave magnetic field by establishing a planar homogeneous region (A) at a specific distance (H) above the shrunk multiple wire trace, where the microwave magnetic fields from the two or more copper wires are combined. The homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate, when the diamond plate is placed above the shrunk multiple wire trace.
[0013] In some embodiments, the method includes tuning, by the control unit, a characteristic impedance of the shrunk section using a characteristic impedance tuning fixture of the planar microstrip antenna that is placed under the shrunk multiple wire trace of the shrunk section.
[0014] In some embodiments, the characteristic impedance of the shrunk section is tuned by (a) measuring, by the control unit; reflection coefficients of the planar microstrip antenna that is placed with the diamond plate including NV centers at 0.87 GHz, 2.87 GHz, and 4.87 GHz using a vector network analyzer; (b) verifying, by the control unit, if the reflection coefficients at 0.87 GHz, 2.87 GHz, and 4.87 GHz are below -20 dB; and (iii) turning a tuning screw of the characteristic impedance tuning fixture clockwise or counterclockwise to adjust the distance between the shrunk multiple wire trace and a circuit board ground until the reflection coefficient becomes more negative or below-20 dB, if at least one reflection coefficient is not below -20 dB.
[0015] The planar microstrip antenna of the present disclosure generates a stronger and more homogeneous microwave magnetic field across the surface of the diamond plate with NV centers due to its non-uniform transmission line. The inclusion of a characteristic impedance tuning fixture minimizes impedance mismatching, enhancing the planar microstrip antenna's efficiency, field strength, and bandwidth. As a result, the planar microstrip antenna achieves an improved signal-to-noise ratio (SNR), facilitating precise manipulation of NV centers in larger diamond plates. Moreover, the design of the planar microstrip antenna allows for greater homogeneity of the microwave magnetic field over a larger area, making it effective for applications that require fine control of NV centers. As constructed from printed circuit board (PCB) laminate, the planar microstrip antenna simplifies the fabrication process, reducing production complexity and costs. These innovations enhance the performance of NV center diamond magnetometers and make the planar microstrip antenna suitable for a wide range of advanced magnetometry applications.
[0016] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
[0018] FIG. 1 is a block diagram that illustrates a system for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate according to some embodiments herein;
[0019] FIG. 2A is a schematic diagram that illustrates a front view of a planar microstrip antenna of FIG. 1 according to some embodiments herein;
[0020] FIG. 2B is an exploded diagram that illustrates a bottom view of a planar microstrip antenna of FIG. 1 according to some embodiments herein;
[0021] FIG. 3A is an exemplary view that illustrates a non-uniform transmission line trace with two copper wires according to some embodiments herein;
[0022] FIG. 3B is an exemplary view that illustrates a mechanism to generate a homogeneous microwave magnetic field (B1) from two parallel copper wires according to some embodiments herein;
[0023] FIG. 3C is an exemplary view that illustrates a non-uniform transmission line trace with three copper wires according to some embodiments herein;
[0024] FIG. 4 is an exemplary view that illustrates a planar microstrip antenna that is mounted with a diamond plate with nitrogen vacancy (NV) centers according to some embodiments herein;
[0025] FIG. 5A is an exemplary view that illustrates a mechanism of a characteristic impedance tuning fixture to tune a characteristic impedance of a shrunk section according to some embodiments herein;
[0026] FIG. 5B is a flow diagram that illustrates a tuning process of a planar microstrip antenna that is mounted with a diamond plate with nitrogen vacancy (NV) centers using a characteristic impedance tuning fixture according to some embodiments herein;
[0027] FIGS. 6A-6B are exemplary views that illustrate a planar microstrip antenna of FIG. 1 according to some embodiments herein;
[0028] FIG. 7 is a method for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate according to some embodiments herein;
[0029] FIG. 8A is a graphical representation that illustrates a distribution of a microwave magnetic field (B1) that is generated using a planar microstrip antenna along X axis on top side of a NV center diamond plate according to some embodiments herein;
[0030] FIG. 8B is a graphical representation that illustrates a distribution of a microwave magnetic field (B1) that is generated using a planar microstrip antenna along Z axis according to some embodiments herein; and
[0031] FIG. 8C is a graphical representation that illustrates S11 parameter of a planar microstrip antenna according to some embodiments herein.
DETAILED DESCRIPTION OF THE DRAWINGS
[0032] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0033] As mentioned, there remains a need for developing microstrip antennas to generate strong and uniform microwave magnetic field without any mismatch in characteristic impedance. Various embodiments disclosed herein provide a system and method for generating a homogeneous microwave magnetic field using a planar microstrip antenna. The homogeneous microwave magnetic field that is generated by the planar microstrip antenna system of the present disclosure manipulates nitrogen-vacancy (NV) centers in a diamond plate, thereby enabling precise control of quantum states for applications in quantum computing, magnetic field sensing, and quantum cryptography. Referring now to the drawings, and more particularly to FIGS. 1 through 8C, where similar reference characters denote corresponding features consistently throughout the figures, preferred embodiments are shown.
[0034] FIG. 1 is a block diagram that illustrates a system 100 for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate according to some embodiments herein. The system 100 includes a planar microstrip antenna 102, and a control unit 104. The planar microstrip antenna 102 includes a circuit board ground 106, a circuit board dielectric layer 108, a non-uniform transmission line trace 110, a first subminiature version A(SMA) connector 112A, a second SMA connector 112B, and a characteristic impedance tuning fixture 114. The circuit board ground 106, the circuit board dielectric layer 108, and the non-uniform transmission line trace 110 form a non-uniform transmission line 116.
[0035] The planar microstrip antenna 102 includes the circuit board ground 106 that may be made of copper and fabricated from a copper plate. The circuit board dielectric layer 108 is placed above the circuit board ground 106 and is made of flame retardant 4 (FR4). FR4 may be made from a woven glass fabric (or fiberglass) that is impregnated with epoxy resin. A thickness of the circuit board dielectric layer 108 is of 1.62 mm. The circuit board dielectric layer 108 has a coating of solder resist (i.e. a solder resist layer). A thickness of the solder resist layer may be of 0.15 mm.
[0036] The non-uniform transmission line 116 has a shrunk section 118 and two 50 Ohm characteristic impedance sections 122.The shrunk section 118 is positioned between the two 50 Ohm characteristic impedance sections 122. The non-uniform transmission line trace 110 in the non-uniform transmission line 116 is made of copper and is positioned above the circuit board dielectric layer 108. The shrunk section 118 includes a shrunk multiple wire trace 118A. The two 50 Ohm transmission line sections 122 include 50 Ohm characteristic impedance section traces 122A-B. The non-uniform transmission line trace 110 includes three sections including a shrunk multiple wire trace 118A and two 50 Ohm characteristic impedance section traces 122A-B. The shrunk multiple wire trace 118A is positioned between the two 50 Ohm characteristic impedance section traces 122A-B. In some embodiments, the shrunk multiple wire trace118A is narrower than the two 50 Ohm characteristic impedance section traces 122A-B. A width of the two 50 Ohm characteristic impedance section traces 122A-B is of 3 mm.
[0037] The shrunk multiple wire trace 118A has two or more parallel copper wires 120. The two or more parallel copper wires 120 may have optimized width and may be separated by optimized distances. In some embodiments, a width of copper wires 120 in the shrunk multiple wire trace 118A is of 0.7 mm. In some embodiments, a distance between the copper wires 120 in the shrunk multiple wire trace 118A is of 1 mm. The shrunk multiple wire trace 118A may be symmetrical along its length axis. The non-uniform transmission line trace 110 may be fabricated by etching. A thickness of the non-uniform transmission line trace 110 may be of 0.1 mm.
[0038] The SMA connectors 112A-B may be used to connect the planar microstrip antenna 102 to the circuit. The first SMA connector 112A is mounted at one end of the non-uniform transmission line116. In some embodiments, the first SMA connector 112A is connected to an input source of microwave and receives microwave power. Another end of the non-uniform transmission line116 may be mounted with the second SMA connector 112B. The second SMA connector 112B is configured to connect with a 50 Ohm terminator. In some embodiments, the planar microstrip antenna 102 includes a single SMA connector to connect with the input source. In some embodiments, the another end of the non-uniform transmission line116 is connected to (i) a 50 Ohm resistor, or (ii) two 100 Ohm resistors in parallel.
[0039] The characteristic impedance tuning fixture 114 is placed under the shrunk multiple wire trace 118A and is configured to tune a characteristic impedance of the shrunk section 118. The characteristic impedance tuning fixture 114 is configured to tune the characteristic impedance of the shrunk section 118 by adjusting the distance between the shrunk multiple wire trace 118A and the circuit board ground 106.
[0040] The diamond plate with NV centers is attached above the shrunk section 118. The diamond plate with NV centers may be attached with the solder resist layer at the middle of the shrunk multiple wire trace 118A. The length of the shrunk multiple wire trace 118A is longer than the diamond plate with NV centers.
[0041] The control unit 104 is communicatively connected with the planar microstrip antenna 102 and controls the planar microstrip antenna 102 to generate a homogeneous microwave magnetic field. When in operation, the control unit 104 is configured to enable the non-uniform transmission line 116 to receive microwave power from the input source through the first SMA connector 112A. The control unit 104 further passes the current through the two or more parallel copper wires 120 in the shrunk multiple wire trace 118A, thereby generating microwave magnetic fields from each copper wire 120.
[0042] The control unit 104 is further configured to establish a planar homogeneous region (A) at a specific distance (H) above the shrunk multiple wire trace 118A, where the magnetic fields from the two or more copper wires 120 are combined, thereby generating a homogeneous microwave magnetic field. The homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate.
[0043] FIG. 2A is a schematic diagram that illustrates a front view of a planar microstrip antenna 102 of FIG. 1 according to some embodiments herein. The planar microstrip antenna 102 includes a circuit board ground 106, a circuit board dielectric layer 108, a non-uniform transmission line trace 110, a first subminiature version A (SMA) connector 112A, a second SMA connector 112B which is connected to a 50 Ohm terminator 200, and a characteristic impedance tuning fixture 114. The arrangement and functions of the components of the planar microstrip antenna 102 are described earlier in FIG. 1.
[0044] FIG. 2B is an exploded diagram that illustrates a bottom view of a planar microstrip antenna 102 of FIG. 1 according to some embodiments herein. The planar microstrip antenna 102 includes a circuit board ground 106, a circuit board dielectric layer 108, a non-uniform transmission line trace (not shown), a first subminiature version A (SMA) connector 112A, and a second SMA connector 112B which is connected to a 50 Ohm terminator 200. The arrangement and functions of the components of the planar microstrip antenna 102 are described earlier in FIG. 1.
[0045] The planar microstrip antenna 102 further includes a tuning hole 202, a tuning screw 204, a locking nut 206 and a washer 208 which are altogether represented as a characteristic impedance tuning fixture 114. The tuning hole 202 is located at the center of the circuit board ground 106 and partially penetrated into the circuit board dielectric layer 108.The tuning hole 202 is positioned directly beneath the shrunk multiple wire trace 118A. The tuning screw 204 is located in the tuning hole 202 with threads 204A inside the circuit board ground 106 and the circuit board dielectric layer 108.The tuning screw 204 may work as a part of the circuit board ground 106. The tuning screw 204, with a top end sized to match the shrunk multiple wire trace 118A as closely as possible, is inserted without extending under the 50 Ohm characteristic impedance section traces 122A-B. Essentially, the diameter of the tuning screw's top end is equal to the length of the shrunk multiple wire trace 118A. In some embodiments, the characteristic impedance tuning fixture 114 tunes the characteristic impedance of the shrunk section 118 when adjusting the distance (Dtune) between the shrunk multiple wire trace 118A and the circuit board ground 106 by turning the tuning screw 204. The locking nut 206 is used to hold the position of the tuning screw 204. Once the tuning is finished the tuning screw 204 is locked by the washer 208 and the locking nut 206. The washer 208 may avoid the locking nut 206 scratching the circuit board ground 106.
[0046] The planar microstrip antenna 102 further includes two dents 210A-B at two ends of the circuit board ground 106 for mounting of SMA connectors 112A-B. The planar microstrip antenna 102 further includes mounting holes 212 to mount the planar microstrip antenna 102 into a NV center diamond magnetometer.
[0047] FIG. 3A is an exemplary view that illustrates a non-uniform transmission line trace 110 with two copper wires 120 according to some embodiments herein. The non-uniform transmission line 116 includes two 50 Ohm characteristic impedance sections 122, and a shrunk section 118. The shrunk section 118 includes a shrunk multiple wire trace 118A where two parallel copper wires (left and right) are present. The shrunk multiple wire trace 118A is positioned between the two 50 Ohm characteristic impedance section traces 122A-B. In some embodiments, the shrunk multiple wire trace 118A is narrower than the two 50 Ohm characteristic impedance section traces 122A-B.
[0048] The two parallel copper wires may have optimized width and may be separated by optimized distance. If width of the left and right copper wires is W1 and the separation between these two copper wires is W2, the geometrical constraints are depicted as follows:
[0049] 𝑾𝟑 > 2 × 𝑾𝟏 + 𝑾𝟐, where W3 is width of the two 50 Ohm characteristic impedance section traces 122A-B.
[0050] In some embodiments, a width of the two 50 Ohm characteristic impedance section traces 122A-B is of 3 mm, a width of copper wires in the shrunk multiple wire trace 118A is of 0.7 mm, and a distance between the copper wires in the shrunk multiple wire trace 118A is of 1 mm. The arrangement and functions of the components of the non-uniform transmission line trace 110 are described earlier in FIG. 1.
[0051] FIG. 3B is an exemplary view that illustrates a mechanism to generate a homogeneous microwave magnetic field (B1) from two parallel copper wires 120 according to some embodiments herein. A control unit 104 is configured to pass the current (I) through a non-uniform transmission line trace 110. The current I in 50 Ohm characteristic impedance section traces122A-B is split into left current I1 and right current I2 and flowing through the left copper wire 120L and the right copper wire 120R in a shrunk multiple wire trace 118A respectively, where I = I1+ I2.
[0052] In FIG. 3B, Fluxleft and Fluxright represent the magnetic flux lines produced by currents I1 and I2 flowing through the left copper wire 120L and right copper wire 120R, respectively. At point A, located at a height H above the shrunk multiple wire trace 118A, Fluxleft and Fluxright intersect. According to I =I1 +I2., the total microwave magnetic field B1total at point A is the vector sum of the microwave magnetic fields B1left and B1right generated by the left copper wire 120L and right copper wire 120R, respectively. Similarly, the microwave magnetic fields at other points are also the vector sums of the corresponding microwave magnetic fields created by the left copper wire 120L and right copper wire 120R at those locations.
[0053]
[0054] By selecting a width of the copper wires (W1) and a distance between these two copper wires (W2), a planar homogeneous region 300 can be established at a distance H above the top surface of the shrunk multiple wire trace 118A, where a strong homogeneous magnetic field B1 is present.
[0055] FIG. 3C is an exemplary view that illustrates a non-uniform transmission line trace 110 with three copper wires 120 according to some embodiments herein. A non-uniform transmission line 116 includes two 50 Ohm characteristic impedance sections 122, and a shrunk section 118. The shrunk section 118 includes a shrunk multiple wire trace 118A where three parallel copper wires (left, middle and right) are present.
[0056] The three parallel copper wires may have optimized width and may be separated by optimized distances. If width of the left, middle and right copper wires is W1, W2 andW1 respectively and the separation between these two copper wires is W3, the geometrical constraints are depicted as follows:
[0057] 𝑾𝟒> 2 × 𝑾𝟏 + 𝑾𝟐+ 𝟐 × 𝑾𝟑where W4 is width of the two 50 Ohm characteristic impedance section traces 122A-B.
[0058] The current I in 50 Ohm characteristic impedance section traces 122A-B is split into left current I1, middle current I2 and right current I3 flowing through the left copper wire, the middle copper wire and the right copper wire in the shrunk multiple wire trace 118A respectively, where 𝑰 = 𝑰𝟏+ 𝑰𝟐+ 𝑰𝟑. According to this, at a point a certain distance above the top surface of the shrunk multiple wire trace 118A, the total microwave magnetic field B1total is the vector sum of the microwave magnetic fields B1left, B1middle, and B1right generated by the left copper wire, middle copper wire and right copper wire respectively.
[0001] 𝑩𝟏𝒕𝒐𝒕𝒂𝒍= 𝑩𝟏𝒍𝒆𝒇𝒕+ 𝑩𝟏𝒎𝒊𝒅𝒅𝒍𝒆+ 𝑩𝟏𝒓𝒊𝒈𝒉𝒕
[0002] By choosing W1, W2 and W3 delicately there can be planar regions over a certain distance above the top surface of the shrunk multiple wire trace where there is a strong and homogeneous B1 field.
[0059] By selecting a width of the copper wires (W1, W2) and a distance between these two copper wires (W3), planar homogeneous regions can be established over a certain distance above the top surface of the shrunk multiple wire trace where there is a strong and homogeneous B1 field.
[0003] FIG. 4 is an exemplary view that illustrates a planar microstrip antenna 102 that is mounted with a diamond plate 400 with nitrogen vacancy (NV) centers according to some embodiments herein. The diamond plate 400 with NV centers is attached to the planar microstrip antenna 102. As shown in FIG. 4, the diamond plate 400 with NV centers is positioned at the center of the top surface of a solder resist layer of the planar microstrip antenna 102. The square shaped-diamond plate 400 with NV centers measures 2.2 mm in width and 0.5 mm in thickness, with most NV centers located near the top surface of the diamond plate 400. The shrunk multiple wire trace 118A extends longer than the diamond plate 400 with NV centers to ensure that the homogeneous microwave magnetic field is not affected by the traces from neighboring sections. The coordinate system depicted in FIG. 4 has the XY plane on the top surface of the diamond plate 400 with NV centers, with the X axis aligned along the width of the trace and the Y axis along its length. The Z axis is perpendicular to the top surface of the trace. The NV centers in the diamond plate 400 are manipulated by the homogeneous microwave magnetic field that is generated by the shrunk multiple wire trace 118A.
[0004] FIG. 5A is an exemplary view that illustrates a mechanism of a characteristic impedance tuning fixture 114 to tune a characteristic impedance of a shrunk section 118 according to some embodiments herein. The width of a shrunk multiple wire trace 118A is narrower than that of 50 Ohm characteristic impedance section traces 122A-B of the planar microstrip antenna 102. Additionally, a NV center diamond plate is mounted on top of the shrunk multiple wire trace 118A, causing the characteristic impedance of the shrunk section 118 to deviate from 50 Ohms without impedance compensation technology. To minimize impedance mismatch, a characteristic impedance tuning fixture is utilized.
[0005] The characteristic impedance (Z0) of the shrunk section 118 of a non-uniform transmission line 116 may be described by a formula:
[0006]
[0007] where L and C are the inductance and capacitance per unit length, respectively. The capacitance between the shrunk multiple wire trace 118A of the shrunk section 118 of the non-uniform transmission line 116 and a circuit board ground 106 is given by the following equation:
[0008] , where epsilon ϵ is the dielectric constant of a circuit board dielectric layer 108, A is the area of the shrunk multiple wire trace 118A, and Dtune is the distance between the shrunk multiple wire trace 118A and the circuit board ground 106.
[0009] A greater distance between the shrunk multiple wire trace 118A of the shrunk section 118 of the non-uniform transmission line 116 and the circuit board ground 106 reduces capacitance per unit length, increasing the characteristic impedance of the shrunk section 118 of the non-uniform transmission line 116. Conversely, a smaller distance increases capacitance, lowering the characteristic impedance. Therefore, as shown in FIG. 5A, the characteristic impedance (Z0) of the shrunk section 118 can be adjusted by varying the distance between the shrunk multiple wire trace 118A and the circuit board ground 106. This adjustment or tuning is achieved through the characteristic impedance tuning fixture 114.
[0010] FIG. 5B is a flow diagram that illustrates a tuning process of a planar microstrip antenna 102 that is mounted with a diamond plate 400 with nitrogen vacancy (NV) centers using a characteristic impedance tuning fixture 114 according to some embodiments herein. At step 502, reflection coefficients (S11 parameters) of the planar microstrip antenna 102 that is placed with the diamond plate 400 comprising NV centers is measured by a control unit 104 at 0.87 GHz, 2.87 GHz, and 4.87 GHz using a vector network analyzer.
[0011] At step 504, it is verified that if the reflection coefficients at 0.87 GHz, 2.87 GHz, and 4.87 GHz are below -20 dB by the control unit 104. At step 506, if the reflection coefficients at 0.87 GHz, 2.87 GHz, and 4.87 GHz are below -20 dB, no further tuning is needed. At step 508, a tuning screw 204 of the characteristic impedance tuning fixture 114 is turned clockwise to adjust the distance between a shrunk multiple wire trace 118A and a circuit board ground 106, if at least one reflection coefficient is not below -20 dB. While turning the tuning screw 204, all the reflection coefficients either decrease or increase. At step 510A, the tuning screw 204 is turned clockwise until the reflection coefficients become more negative or below-20 dB, if the reflection coefficients decrease. At step 510B, the tuning screw 204 is turned counterclockwise until the reflection coefficients become more negative or below-20 dB, if the reflection coefficients increase.
[0012] Thus, the planar microstrip antenna 102 is adjusted to the highest efficiency before being used in a NV center diamond magnetometer.
[0013] FIGS. 6A-6B are exemplary views that illustrate a planar microstrip antenna 102 of FIG. 1 according to some embodiments herein. FIG. 6A shows the planar microstrip antenna 102 with one SMA connector at one end and a 50 Ohm chip resistor 602 at other end. That is, in some embodiments, two SMA connectors and a 50 Ohm terminator(shown in FIGS. 2A-2B) are replaced with one SMA connector and a 50 Ohm chip resistor 602.
[0014] FIG. 6B shows the planar microstrip antenna 102 with one SMA connector at one end and two 100 Ohm chip resistors 604 in parallel at other end. That is, in some embodiments, one SMA connector and a 50 Ohm chip resistor (shown in FIG. 6A) are replaced with one SMA connector and two 100 Ohm chip resistors 604. To reduce the parasitic inductance of the 50 Ohm chip resistor, two 100 Ohm chip resistors 604 may be connected in parallel to form a 50 Ohm resistor with approximately half of the parasitic inductance of the original 50 Ohm chip resistor.
[0015] FIG. 7 is a method for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate according to some embodiments herein. At step 702, a planar microstrip antenna 102 is provided. The planar microstrip antenna 102 includes a non-uniform transmission line 116 that is connected to a first SMA connector 112A at one end; a shrunk section 118 that is positioned between two 50 Ohm characteristic impedance sections 122; and a shrunk multiple wire trace 118A in the shrunk section 118. The shrunk multiple wire trace 118A includes two or more parallel copper wires 120 with optimized width. The two or more parallel copper wires are separated by optimized distances.
[0016] At step 704, microwave power is received at the non-uniform transmission line 116 through the first SMA connector 112A from an input source using a control unit 104. At step 706, microwave magnetic fields are generated from each copper wire 120 in the shrunk multiple wire trace 118A by passing current through the two or more parallel copper wires 120 by the control unit 104. At step 708, a homogeneous microwave magnetic field is generated by the control unit 104 by establishing a planar homogeneous region at a specific distance above the shrunk multiple wire trace 118A, where the magnetic fields from the two or more copper wires are combined. The generated homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate, when the diamond plate is placed above the shrunk multiple wire trace 118A.
[0017] FIG. 8A is a graphical representation that illustrates a distribution of a microwave magnetic field (B1) that is generated using a planar microstrip antenna 102 along X axis on top side of a NV center diamond plate according to some embodiments herein. The graphical representation shows the distribution of B1 field along X axis on the top side of the NV center diamond plate (that is, 0.5 mm above the top of the solder resist layer of the planar microstrip antenna 102) under 1 watt input microwave power at 2.87 GHz. │B1│ is the magnitude of B1 field. The generated microwave magnetic field strength at the center of the top side of the NV center diamond plate can exceed 2 Gauss, with an efficiency greater than 2 Gauss/Watt. The microwave magnetic field varies by less than 10% from -0.5 mm to 0.5 mm along the X axis, indicating high field homogeneity. The width of the homogeneous region is at least 1 mm.
[0018] FIG. 8B is a graphical representation that illustrates a distribution of a microwave magnetic field (B1) that is generated using a planar microstrip antenna 102 along Z axis according to some embodiments herein. The graphical representation shows the distribution of ∣B1∣ along the Z axis, with the origin located at the center of the top side of the solder resist of the planar microstrip antenna 102. The B1 field distribution within a NV center diamond plate is between 0 mm and 0.5 mm along the Z axis, while the distribution in the air above the NV center diamond plate is between 0.5 mm and 1 mm. By carefully optimizing the configuration and dimensions of the shrunk multiple wire trace 118A, the maximum ∣B1∣ can be achieved on the top surface of the NV center diamond plate, along with optimal efficiency.
[0019] FIG. 8C is a graphical representation that illustrates S11 parameter of a planar microstrip antenna 102 according to some embodiments herein. By delicately tuning a characteristic impedance of a shrunk section 118 of a non-uniform transmission line 116 of the planar microstrip antenna 102 through turning a tuning screw, the S11 parameter can be maintained below -20 dB between 0.87 GHz and 4.87 GHz. In this wide frequency range, the microwave power reflection of the antenna is less than 1%, and the efficiency varies by less than 1%. As a result, the planar microstrip antenna 102 operates uniformly between 0.87 GHz and 4.87 GHz, with a bandwidth of at least 4 GHz. This broad bandwidth allows an NV center diamond magnetometer using this planar microstrip antenna 102 to achieve a measurement dynamic range of approximately 700 Gauss based on the following equation.
[0020]
[0021] In view of the above, by utilizing shrunk multiple wire trace technology and characteristic impedance (Z0) tuning fixture technology, the planar microstrip antenna 102 of the present disclosure achieves high efficiency, generates a strong and homogeneous microwave magnetic field, offers broad bandwidth, and provides a high measurement dynamic range. Additionally, the performance of the planar microstrip antenna 102 is less dependent on the properties of the NV center diamond plate, making fabrication simpler and reducing production costs.
[0022] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications without departing from the generic concept, and, therefore, such adaptations and modifications should be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
, Claims:I/We Claim:
1. A system (100) for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate, wherein the system (100) comprising:
a planar microstrip antenna (102) that comprises
a circuit board ground (106);
a circuit board dielectric layer (108) that is placed above the circuit board ground (106); and
characterized in that,
a non-uniform transmission line trace (110) that is positioned above the circuit board dielectric layer (108), wherein the circuit board ground (106), the circuit board dielectric layer (108) and the non-uniform transmission line trace (110) form a non-uniform transmission line (116), wherein the non-uniform transmission line (116) comprises
a shrunk section (118) that is positioned between two 50 Ohm characteristic impedance sections (122) of the non-uniform transmission line (116); and
a shrunk multiple wire trace (118A) in the shrunk section (118), wherein the shrunk multiple wire trace (118A) is narrower than the two 50 Ohm characteristic impedance section traces (122A-B), wherein the shrunk multiple wire trace (118A) comprises two or more parallel copper wires (120) with optimized width, wherein the two or more parallel copper wires (120) are separated by optimized distances with the shrunk section (118) being symmetrical along the length axis of the shrunk multiple wire trace (118A); and
a first subminiature version A (SMA) connector (112A) that is mounted at one end of the non-uniform transmission line (116) for receiving microwave power; and
a control unit (104) that is communicatively connected with the planar microstrip antenna (102), wherein when in operation, the control unit (104) is configured to:
enable the non-uniform transmission line (116) to receive microwave power from an input source through the first SMA connector (112A);
generate microwave magnetic fields from each copper wire (120) in the shrunk multiple wire trace (118A) by passing the current through the two or more parallel copper wires (120); and
generate a homogeneous microwave magnetic field by establishing a planar homogeneous region (A) at a specific distance (H) above the shrunk multiple wire trace (118A), where the microwave magnetic fields from the two or more copper wires (120) are combined, wherein the homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate, when the diamond plate is placed above the shrunk multiple wire trace (118A).


2. The system (100) as claimed in claim 1, wherein the planar microstrip antenna (102) comprising a characteristic impedance tuning fixture (114) that is placed under the shrunk multiple wire trace (118A) and is configured to tune a characteristic impedance of the shrunk section (118), wherein the characteristic impedance tuning fixture (114) comprises
a tuning hole (202) that is located at the center of the circuit board ground (106) and partially penetrated into the circuit board dielectric layer (108); and
a tuning screw (204) that is located in the tuning hole (202) with threads (204A) inside the circuit board ground (106) and the circuit board dielectric layer (108), wherein the characteristic impedance tuning fixture (114) tunes the characteristic impedance of the shrunk section (118) when adjusting the distance between the shrunk multiple wire trace (118A) and the circuit board ground (106) by turning the tuning screw (204).


3. The system (100) as claimed in claim 2, wherein the characteristic impedance tuning fixture (114) comprises a locking nut (206) and a washer (208) to lock the tuning screw (204) once tuning is complete.


4. The system (100) as claimed in claim 1, wherein the other end of the non-uniform transmission line (116) is connected to at least one of (i) a 50 Ohm terminator (200) through a second SMA connector (112B), (ii) a 50 Ohm resistor (602), or (iii) two 100 Ohm resistors (604) in parallel.


5. The system (100) as claimed in claim 1, wherein the circuit board dielectric layer (108) comprises a solder resist layer to which the diamond plate with NV centers is attached at the middle of the shrunk multiple wire trace (118A), wherein the length of the shrunk multiple wire trace (118A) is longer than the diamond plate.


6.The system (100) as claimed in claim 1, wherein a width of the two or more copper wires (120) in the shrunk multiple wire trace (118A) is of 0.7 mm, a distance between the two or more copper wires (120) is of 1 mm, wherein a width of the two 50 Ohm characteristic impedance section traces (122A-B) is of 3 mm.


7. The system (100) as claimed in claim 1, wherein a thickness of the non-uniform transmission line trace (110) is of 0.1 mm.


8. A method for generating a homogeneous microwave magnetic field to manipulate nitrogen-vacancy (NV) centers in a diamond plate, wherein the method comprising,
characterized in that,
providing a planar microstrip antenna (102), wherein the planar microstrip antenna (102) comprises a non-uniform transmission line (116) that is connected to a first SMA connector (112A) at one end ; a shrunk section (118) that is positioned between two 50 Ohm characteristic impedance sections (122) of a non-uniform transmission line trace (110); and a shrunk multiple wire trace (118A) in the shrunk section (118), wherein the shrunk multiple wire trace (118A) comprises two or more parallel copper wires (120) with optimized width, wherein the two or more parallel copper wires (120) are separated by optimized distances;
receiving, at the non-uniform transmission line (116), microwave power through the first SMA connector (112A) from an input source using a control unit (104);
generating, using the control unit (104), microwave magnetic fields from each copper wire (120) in the shrunk multiple wire trace (118A) by passing current through the two or more parallel copper wires (120); and
generating, by the control unit (104), a homogeneous microwave magnetic field by establishing a planar homogeneous region (A) at a specific distance (H) above the shrunk multiple wire trace (118A), where the microwave magnetic fields from the two or more copper wires (120) are combined, wherein the homogeneous microwave magnetic field is configured to manipulate the nitrogen-vacancy (NV) centers in the diamond plate, when the diamond plate is placed above the shrunk multiple wire trace (118A).


9. The method as claimed in claim 8, wherein the method comprising tuning, by the control unit (104), a characteristic impedance of the shrunk section (118) using a characteristic impedance tuning fixture (114) of the planar microstrip antenna (102) that is placed under the shrunk multiple wire trace (118A) of the shrunk section (118).


10. The method as claimed in claim 9, wherein the characteristic impedance of the shrunk section (118) is tuned by
measuring, by the control unit (104); reflection coefficients of the planar microstrip antenna (102) that is placed with the diamond plate comprising NV centers at 0.87 GHz, 2.87 GHz, and 4.87 GHz using a vector network analyzer;
verifying, by the control unit (104), if the reflection coefficients at 0.87 GHz, 2.87 GHz, and 4.87 GHz are below -20 dB; and
turning a tuning screw (204) of the characteristic impedance tuning fixture (114) clockwise or counterclockwise to adjust the distance between the shrunk multiple wire trace (118A) and a circuit board ground (106) until the reflection coefficient becomes more negative or below-20 dB, if at least one reflection coefficient is not below -20 dB.


Dated this November 19, 2024

Arjun Karthik Bala
(IN/PA 1021)
Agent for Applicant

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