High-precision magnetic field vector distribution measurement system

Abstract

The utility model relates to the technical field of magnetic field vector distribution measurement, in particular to a high-precision magnetic field vector distribution measurement system. A controller mounted in a main body frame is connected with a coordinate space measurement system, a displacement control system and a computer for remote control through communication interfaces on the main body frame; the coordinate space measuring system is mounted on the main body frame and consists of a plurality of grating sensors; the displacement control system used for realizing spatial point selection is composed of a plurality of stepping motors, sliding blocks correspondingly connected with the stepping motors, and a cone-shaped body detachably installed on a coil assembly. Wherein the X-axis connecting slide block, the Y-axis connecting slide block and the Z-axis connecting slide block are connected with the main body frame in a sliding manner; and the X-axis grating sensor, the Y-axis grating sensor and the Z-axis grating sensor are matched with the three-axis magnetic field measuring probe in position. According to the utility model, the effectiveness of the magnetic field vector rotation theorem is supported, and the direction of the magnetic field vector is given during measurement.

Description

Technical Field

[0001] The utility model relates to the technical field of magnetic field vector distribution measurement, in particular to a high-precision magnetic field vector distribution measurement system. Background Art

[0002] As one of the basic physical quantities in nature, the study and exploration of magnetic field is of great significance. According to the magnetic field strength, it is generally divided into three categories: weak magnetic field, strong magnetic field and ultra-strong magnetic field. The measurement and detection of weak magnetic field is a measurement research direction that everyone is paying close attention to at present, and it is also a symbol of the development level of magnetic research in applied physics.

[0003] In the experimental teaching of university physics and magnetism, the magnetic field intensity measurement on the symmetry axis of the Helmholtz coil magnetic field is generally used. Students' experimental cognition of magnetic field vectors is insufficient. In particular, the in-depth understanding of magnetic field as a substance existing in the form of field is not in-depth, and the experimental teaching effect is not good. The existing Hall sensors and chip-level fluxgate sensors only have the function of measuring single-axis magnetic field components. Although the orthogonal arrangement of three magnetic field sensors can complete the measurement of magnetic field vectors in three-dimensional space, the sensitive axes of the three magnetic field sensors are limited by their principles, structures, packaging, pins and other factors. They can only measure the magnetic field vector near the spatial point, and the measurement error is very large. In the experiment, the millimeter scale is often used to establish the spatial coordinates. Therefore, in addition to the low measurement accuracy of the experimental results, the spatial resolution of the magnetic field vector is also insufficient.

[0004] Based on this, how to improve the drawbacks of the above-mentioned three-axis magnetic field component measurement has become a technical problem that technical personnel in this field need to solve urgently. Utility Model Content

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects existing in the above-mentioned prior art, thereby providing a high-precision magnetic field vector distribution measurement system.

[0006] A high-precision magnetic field vector distribution measurement system, comprising: a main frame, a coordinate space measurement system, a displacement control system, a three-axis magnetic field measurement probe, a power supply system, a controller, a coil assembly and a computer;

[0007] A controller installed in the main frame is connected to the coordinate space measurement system, the displacement control system and the computer for remote control through a communication interface on the main frame;

[0008] A coordinate space measurement system for realizing coordinate space measurement is installed on the main frame and is composed of an X-axis grating sensor, a Y-axis grating sensor, and a Z-axis grating sensor;

[0009] The displacement control system for realizing spatial point selection is composed of an X-axis stepping motor, an X-axis connecting slider, a Y-axis stepping motor, a Y-axis connecting slider, a Z-axis stepping motor, a Z-axis connecting slider and a cone body detachably mounted on the coil assembly; wherein the X-axis connecting slider, the Y-axis connecting slider and the Z-axis connecting slider are slidably connected to the main frame;

[0010] The X-axis grating sensor slidably connected to the top of the main frame is connected to the X-axis stepper motor signal through the X-axis connecting slider; the bottom end of the X-axis connecting slider is fixedly connected to the three-axis magnetic field measurement probe;

[0011] The Y-axis grating sensor fixed on the side of the main frame is connected to the Y-axis stepping motor signal through the Y-axis connecting slider; the Y-axis connecting slider sliding on the Y-axis grating sensor is fixedly connected to one end of the X-axis grating sensor;

[0012] The Z-axis grating sensor fixed on the side of the main frame is connected to the Z-axis stepper motor signal through the Z-axis connecting slider; the Z-axis connecting slider sliding in the vertical direction of the main frame is fixedly connected to the coil assembly;

[0013] The X-axis grating sensor, the Y-axis grating sensor and the Z-axis grating sensor are arranged orthogonally in pairs and are compatible with the three-axis magnetic field measurement probe.

[0014] Preferably, the main frame for providing support adopts a gantry frame structure.

[0015] Preferably, the gantry frame structure is a quadrangular column structure, which is composed of a top square frame, four vertical legs and a square base fixedly connected;

[0016] The top square frame is composed of a first horizontal leg, a first slide bar, a second horizontal leg and a second slide bar which are sequentially connected in a closed loop;

[0017] One end of the Z-axis grating sensor is fixed to the first horizontal leg, and the other end is fixed to the square base;

[0018] The Y-axis connecting slider is slidably connected to the first sliding rod, and two ends of the Y-axis grating sensor are fixed on two vertical legs connected to two ends of the first sliding rod;

[0019] One end of the X-axis grating sensor is connected to the first slide bar through the Y-axis connecting slider, and the other end is slidably connected to the second slide bar.

[0020] Preferably, a geomagnetic field shielding layer is provided on the surface of the square base.

[0021] Preferably, the coil assembly comprises: a magnetic field coil lifting bracket, a coil, a spiral screw rod and a limiting support component;

[0022] The coil is fixed to the top surface of the coil bracket of the magnetic field coil lifting bracket;

[0023] One end of the position-limiting support component that passes through the magnetic field coil lifting bracket is fixedly connected to the first horizontal leg, and the other end is fixedly connected to the square base;

[0024] The spiral screw fixed on the square base is threadedly connected to the magnetic field coil lifting bracket, and the magnetic field coil lifting bracket is fixedly connected to the Z-axis connecting slider, so that the Z-axis connecting slider and the magnetic field coil lifting bracket move synchronously.

[0025] Preferably, it also includes an image sensor;

[0026] The image sensor connected to the controller for communication is detachably mounted at the axis center of the top surface of the coil.

[0027] Preferably, the three-axis magnetic field measurement probe is a three-axis magnetic field measurement probe carrying a semiconductor laser component.

[0028] Preferably, the moving area range of the three-axis magnetic field measurement probe is 230mm*230mm.

[0029] Preferably, an armored spiral tube is provided on the outer surface of the signal line used for signal connection.

[0030] The technical solution of the utility model has the following advantages:

[0031] The utility model supports the validity of the magnetic field vector curl theorem, provides a more accurate and new teaching experimental equipment for physical experiment teaching, and gives the direction of the magnetic field vector in the measurement, which is different from the traditional magnetic field measurement. In addition, the utility model realizes the free selection of three-dimensional space test points through multiple stepper motors and spiral screws; and realizes accurate space vector field measurement by adopting a 24-bit ADC analog-to-digital conversion module and multiple high-precision grating sensors, with a spatial resolution of μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a schematic diagram of the overall structure of the main frame of the utility model;

[0034] Figure 2 This is a schematic diagram of the system circuit principle of the utility model;

[0035] Figure 3This is a schematic diagram of the installation structure of the communication interface, radiator and coil assembly of the utility model;

[0036] Figure 4 Schematic diagram of the coil structure of this embodiment.

[0037] Description of reference numerals:

[0038] 11-top square frame, 112-first slide bar, 113-second horizontal leg, 114-second slide bar, 12-vertical leg, 13-square base, 111-first horizontal leg, 21-X-axis grating sensor, 22-Y-axis grating sensor, 23-Z-axis grating sensor, 311-X-axis connecting slider, 321-Y-axis connecting slider, 331-Z-axis connecting slider, 4-three-axis magnetic field measurement probe, 51-magnetic field coil lifting bracket, 511-coil bracket, 52-coil, 53-screw rod, 54-limiting support component, 6-U-shaped transmission rod, 7-radiator, 8-communication interface. DETAILED DESCRIPTION

[0039] The technical solution of the utility model will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0040] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0041] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] Example 1

[0044] A high-precision magnetic field vector distribution measurement system, comprising: a main frame, a coordinate space measurement system, a displacement control system, a three-axis magnetic field measurement probe 4, a power supply system, a controller, a coil assembly and a computer;

[0045] The controller installed in the main frame is connected to the coordinate space measurement system, the displacement control system and the computer for remote control through the communication interface 8 on the main frame;

[0046] like Figure 1 , 3 The coordinate space measurement system for realizing coordinate space measurement is installed on the main frame, and is composed of an X-axis grating sensor 21, a Y-axis grating sensor 22, and a Z-axis grating sensor 23;

[0047] The displacement control system for realizing spatial point selection is composed of an X-axis stepping motor, an X-axis connecting slider 311, a Y-axis stepping motor, a Y-axis connecting slider 321, a Z-axis stepping motor, a Z-axis connecting slider 331 and a cone body detachably mounted on the coil assembly; wherein the X-axis connecting slider 311, the Y-axis connecting slider 321 and the Z-axis connecting slider 331 are slidably connected to the main frame;

[0048] The X-axis grating sensor 21 slidably connected to the top of the main frame is connected to the X-axis stepping motor signal through the X-axis connecting slider 311; the bottom end of the X-axis connecting slider 311 is fixedly connected to the three-axis magnetic field measurement probe 4;

[0049] The Y-axis grating sensor 22 fixed on the side of the main frame is connected to the Y-axis stepping motor signal through the Y-axis connecting slider 321; the Y-axis connecting slider 321 sliding on the Y-axis grating sensor 22 is fixedly connected to one end of the X-axis grating sensor 21;

[0050] The Z-axis grating sensor 23 fixed on the side of the main frame is connected to the Z-axis stepping motor signal through the Z-axis connecting slider 331; the Z-axis connecting slider 331 sliding in the vertical direction of the main frame is fixedly connected to the coil assembly;

[0051] The X-axis grating sensor 21 , the Y-axis grating sensor 22 and the Z-axis grating sensor 23 are arranged orthogonally in pairs and are adapted to the three-axis magnetic field measurement probe 4 .

[0052] Specifically, in this embodiment, the main frame used to provide support is a gantry frame structure.

[0053] Furthermore, in this embodiment, the gantry frame structure is a quadrangular column structure, which is composed of a top square frame 11, four vertical legs 12 and a square base 13 fixedly connected;

[0054] The top square frame 11 is composed of a first horizontal leg 111, a first slide bar 112, a second horizontal leg 113 and a second slide bar 114 which are sequentially connected in a closed loop;

[0055] One end of the Z-axis grating sensor 23 is fixed to the first horizontal leg 111, and the other end is fixed to the square base 13;

[0056] The Y-axis connecting slider 321 is slidably connected to the first slide bar 112, and both ends of the Y-axis grating sensor 22 are fixed on two vertical legs 12 connected to both ends of the first slide bar 112;

[0057] One end of the X-axis grating sensor 21 is connected to the first slide bar 112 via the Y-axis connecting slider 321 , and the other end is slidably connected to the second slide bar 114 .

[0058] In addition, in the present embodiment, a geomagnetic field shielding layer is provided on the surface of the square base 13, specifically, an EMC electromagnetic wave shielding sleeve cloth aluminum foil is pasted to the surface of the square base 13; and in the present embodiment, the axial part of the X-axis stepper motor, the axial part of the Y-axis stepper motor, the axial part of the Z-axis stepper motor, the magnetic field signal amplifier in the circuit of the three-axis magnetic field measurement probe 4, the ADC analog-to-digital conversion module, and the coordinate space measurement system are also partially isolated by pasting an EMC electromagnetic wave shielding sleeve cloth aluminum foil.

[0059] In this embodiment, the coil assembly includes: a magnetic field coil lifting bracket 51, a coil 52, a screw rod 53 and a position limiting support component 54; specifically:

[0060] The coil 52 is fixed to the top surface of the coil bracket 511 of the magnetic field coil lifting bracket 51;

[0061] One end of the position-limiting support component 54 that passes through the magnetic field coil lifting bracket 51 is fixedly connected to the first horizontal leg 111, and the other end is fixedly connected to the square base 13;

[0062] The spiral screw 53 fixed on the square base 13 is threadedly connected to the magnetic field coil lifting bracket 51, and the magnetic field coil lifting bracket 51 is fixedly connected to the Z-axis connecting slider 331, so that the Z-axis connecting slider 331 and the magnetic field coil lifting bracket 51 move synchronously. The coil bracket 511 adopts a square outer frame and a circular inner frame structure, and the inner frame and the outer frame are fixedly connected by four connecting rods;

[0063] The magnetic field coil lifting bracket 51 is fixedly connected to the Z-axis connecting slider 331, specifically: the magnetic field coil lifting bracket 51 is fixedly connected to the Z-axis connecting slider 331 through a U-shaped transmission rod 6, and the double-headed end is fixedly connected to one side of the square outer frame of the coil bracket 511, and the single-headed end is fixedly connected to the Z-axis connecting slider 331.

[0064] like Figure 4 Schematic diagram of the structure of the coil 52 in this embodiment. In this embodiment, the coil 52 has 740 turns and a wire diameter of 0.4 mm.

[0065] In addition, in this embodiment, an image sensor is also included;

[0066] The image sensor connected to the controller for communication is detachably mounted at the axis center of the top surface of the coil 52 .

[0067] The three-axis magnetic field measurement probe 4 is a three-axis magnetic field measurement probe 4 carrying a semiconductor laser component.

[0068] The moving area of ​​the three-axis magnetic field measurement probe 4 is 230 mm*230 mm.

[0069] An armored spiral tube is provided on the outer surface of the signal line used for signal connection.

[0070] In addition, in this embodiment, a heat sink 7 connected to the controller inside the base is also provided on the side wall of the square base 13.

[0071] The circuit principle adapted to the system of this embodiment is as follows Figure 2 The X-axis magnetic flux sensor, Y-axis magnetic flux sensor and Z-axis magnetic flux sensor in the three-axis magnetic field measuring probe 4 for measuring the X, Y and Z direction components of the magnetic field vector are connected to the controller through an ADC analog-to-digital conversion module.

[0072] Related technical parameters: 1. Grating ruler sensor: 0-300mm; resolution 5m.

[0073] 2. Stepper motor control accuracy: 1 / 64 division;

[0074] 3. Temperature range: -40℃+40℃, relative humidity ≤95%RH;

[0075] 4. Environment: Ensure that the measurement is performed in an environment without interference magnetic fields.

[0076] 5. Overall dimensions: 460mm long × 460mm wide × 650mm high;

[0077] 6. Magnetic field strength measurement range: 0.5μT-1100;

[0078] 7. System magnetic field measurement accuracy: 1.5%; system measurement standard deviation: 1.79nT;

[0079] 8. The direction cosine of the system magnetic field vector is greater than -1 and less than +1;

[0080] 9. System magnetic field vector measurement space: 230mm×230mm×300mm.

[0081] In actual measurement: axial reference and cone are also included;

[0082] First, the semiconductor laser in the three-axis magnetic field measurement probe 4 is adjusted to be located at the center of the spatial position through the displacement control system, with the reverse direction of the semiconductor laser beam emission as the Z-axis direction;

[0083] Secondly, a cone coaxial with the coil 52 is installed in the coil 52, specifically, the tip of the cone passes through the center of the coil 52, and the outer edge of the plane end of the cone is clamped with the coil 52; the interior of the cone is hollow;

[0084] The laser beam passes through the image sensor, the coil 52 and the cone in sequence;

[0085] Finally, the position of the coil 52 is adjusted by the displacement control system so that the spot image at the tip of the cone is symmetrical under the mapping of the axial reference object, and the center position of the coil 52 is adjusted. It should be noted that in this embodiment, the image sensor collects the spot image and transmits it to the computer. Based on the analysis result of the computer, the position of the coil 52 is adjusted to make the result more accurate.

[0086] Verification results:

[0087] A closed loop integration measurement of the magnetic field vector was performed:

[0088] Determine the closed curve path using the standard parametric equations for a space ellipse.

[0089] ;

[0090] in are the coordinates of the center of the space ellipse, , are the lengths of the major and minor axes of the ellipse, and represents the basis vectors of the ellipse, and No co-linearity, , A vector representing the parametric equation of an ellipse in space, where t represents the parameter.

[0091] To simplify the calculation, the length of the major axis and the length of the minor semiaxis Ride in and , we get the vector and vector , and specify the input and satisfy ,get and is the major axis vector of the ellipse.

[0092] At this time, the parameters of the ellipse are expressed as:

[0093] ;

[0094] Input Parameters , the system will automatically measure the size and direction of the vector field on the space ellipse, and then calculate the circulation in, is the unit line element on the circular path, and its direction is the tangent direction of point i; there are n points in total on the circular path.

[0095] The closed loop selected in the experiment is selected according to the stepper motor control principle to control the operation of the X-axis stepper motor, the Y-axis stepper motor and the Z-axis stepper motor. The closed loop of the space elliptic equation is used in the experiment.

[0096] The experimental results are shown in Table 1.

[0097] Table 1 Circulation integral of magnetic field vector

[0098]

[0099] Furthermore, by creating a rotation angle of The rotation matrix , realize the principal axis vector and Rotate around the Z axis. for:

[0100] ;

[0101] Use the principal axis vectors Multiply , and get the result .

[0102] ;

[0103] Similarly, use the same method to rotate get , after substituting the parameters into the equation, we get the parametric equation of the ellipse after rotation around the Z axis:

[0104]

[0105] Bring in and , and obtain the loop integration result:

[0106] Table 2 Integral results after the integral path rotates around the Z axis by an angle θ

[0107]

[0108] The conclusions of the three experiments consistently show that the minimum value of the closed curve loop measured is 133.6 nanotesla nT, and the data collected after rotation show a high degree of consistency. Taking into account the measurement error, the experimental results support the validity of the magnetic field vector curl theorem.

[0109] It turns out that: ;

[0110] In the experiment, , m represents the number of paths, The magnetic field vector can be specifically determined according to the sampling rate.

[0111] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention of the utility model.

Claims

1. A high-precision magnetic field vector distribution measurement system, characterized in that: include: A main frame, a coordinate space measurement system, a displacement control system, a three-axis magnetic field measurement probe (4), a power supply system, a controller, a coil assembly, and a computer; A controller installed in the main frame is connected to the coordinate space measurement system, the displacement control system and the computer for remote control via a communication interface (8) on the main frame; A coordinate space measurement system for realizing coordinate space measurement is installed on the main frame and is composed of an X-axis grating sensor (21), a Y-axis grating sensor (22) and a Z-axis grating sensor (23); The displacement control system for realizing spatial point selection is composed of an X-axis stepping motor, an X-axis connecting slider (311), a Y-axis stepping motor, a Y-axis connecting slider (321), a Z-axis stepping motor, a Z-axis connecting slider (331), and a cone body detachably mounted on the coil assembly; wherein the X-axis connecting slider (311), the Y-axis connecting slider (321), and the Z-axis connecting slider (331) are slidably connected to the main frame; An X-axis grating sensor (21) slidably connected to the top of the main frame is connected to an X-axis stepping motor signal via an X-axis connecting slider (311); the bottom end of the X-axis connecting slider (311) is fixedly connected to a three-axis magnetic field measuring probe (4); The Y-axis grating sensor (22) fixed to the side of the main frame is connected to the Y-axis stepping motor signal through the Y-axis connecting slider (321); the Y-axis connecting slider (321) sliding on the Y-axis grating sensor (22) is fixedly connected to one end of the X-axis grating sensor (21); The Z-axis grating sensor (23) fixed to the side of the main frame is connected to the Z-axis stepping motor signal via the Z-axis connecting slider (331); the Z-axis connecting slider (331) sliding in the vertical direction of the main frame is fixedly connected to the coil assembly; The X-axis grating sensor (21), the Y-axis grating sensor (22), and the Z-axis grating sensor (23) are arranged orthogonally in pairs and are compatible with the three-axis magnetic field measurement probe (4).

2. A high-precision magnetic field vector distribution measurement system according to claim 1, characterized in that: The main frame used to provide support is a gantry frame structure.

3. A high-precision magnetic field vector distribution measurement system according to claim 2, characterized in that: The gantry frame structure is a quadrangular column structure, which is composed of a top square frame (11), four vertical legs (12) and a square base (13) that are fixedly connected; The top square frame (11) is composed of a first horizontal support leg (111), a first sliding rod (112), a second horizontal support leg (113), and a second sliding rod (114) which are sequentially connected in a closed loop; One end of the Z-axis grating sensor (23) is fixed to the first horizontal support leg (111), and the other end is fixed to the square base (13); The Y-axis connecting slider (321) is slidably connected to the first slide bar (112), and two ends of the Y-axis grating sensor (22) are fixed on two vertical legs (12) connected to two ends of the first slide bar (112); One end of the X-axis grating sensor (21) is connected to the first slide bar (112) via a Y-axis connecting slider (321), and the other end is slidably connected to the second slide bar (114).

4. A high-precision magnetic field vector distribution measurement system according to claim 3, characterized in that: A geomagnetic field shielding layer is provided on the surface of the square base (13).

5. A high-precision magnetic field vector distribution measurement system according to claim 3, characterized in that: The coil assembly comprises: a magnetic field coil lifting bracket (51), a coil (52), a spiral screw rod (53), and a position-limiting support component (54); The coil (52) is fixed to the top surface of the coil bracket (511) of the magnetic field coil lifting bracket (51); One end of a position-limiting support component (54) that passes through the magnetic field coil lifting bracket (51) is fixedly connected to the first horizontal support leg (111), and the other end is fixedly connected to the square base (13); A spiral screw rod (53) fixed on the square base (13) is threadedly connected to the magnetic field coil lifting bracket (51), and the magnetic field coil lifting bracket (51) is fixedly connected to the Z-axis connecting slider (331), so that the Z-axis connecting slider (331) and the magnetic field coil lifting bracket (51) move synchronously.

6. A high-precision magnetic field vector distribution measurement system according to claim 5, characterized in that: Also included is an image sensor; An image sensor connected to the controller for communication is detachably mounted at the axis center of the top surface of the coil (52).

7. A high-precision magnetic field vector distribution measurement system according to claim 6, characterized in that: The three-axis magnetic field measurement probe (4) is a three-axis magnetic field measurement probe (4) carrying a semiconductor laser component.

8. A high-precision magnetic field vector distribution measurement system according to claim 7, characterized in that: The moving area of ​​the three-axis magnetic field measurement probe (4) is 230 mm*230 mm.

9. A high-precision magnetic field vector distribution measurement system according to claim 7, characterized in that: An armored spiral tube is provided on the outer surface of the signal line used for signal connection.

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