JP2011146270A - Flat cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat cable capable of improving transmission characteristics of a high frequency signal. <P>SOLUTION: In the flat cable 10 having a first insulator 30, a conductor 20 laminated on the first insulator 30, a second insulator 40 laminated on the conductor 20 with at least one end of the conductor 20 in a state exposed, and shields 50, 60 laminated on the conductor 20 through the first insulator 30 or both the first and the second insulators 30, 40 and electrically shielding the conductor 20, a thickness H<SB>2</SB>of the first insulator 30 at a terminal section 12 where the conductor 20 is exposed and a thickness H<SB>1</SB>of the first insulator 30 at a body section 11 where the second insulator 40 is laminated are different from each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flat cable used for transmission of a high-frequency signal.

  As a flexible flat cable connected to a high-frequency circuit and transmitting a high-frequency signal, a cable in which a conductor is sandwiched between metal layers via an insulator from both sides is known (see, for example, Patent Document 1).

  In this flexible flat cable, the impedance of the flexible flat cable is matched with the impedance of the high-frequency circuit by adjusting the dielectric constant of the insulating layer.

JP 2003-31033 A

  However, in the above-described flexible flat cable, only impedance matching with a high-frequency circuit is studied, and impedance matching in the flexible flat cable is not studied. For this reason, this flexible flat cable may have inferior high-frequency signal transmission characteristics.

  The problem to be solved by the present invention is to improve the transmission characteristics of a high-frequency signal in a flat cable.

  The flat cable according to the present invention is laminated on the conductor with the first insulator, the conductor laminated on the first insulator, and at least one end of the conductor exposed. The second insulator and the first insulator, or both the first insulator and the second insulator, and stacked on the conductor to electrically connect the conductor. A flat cable having a shield that shields the first insulator in the end portion where the conductor is exposed, and the first body in the body portion in which the second insulator is laminated. It is characterized in that the thickness of the insulator is different.

  In the above invention, the thickness of the first insulator in the terminal portion may be relatively thinner than the thickness of the first insulator in the main body portion.

  In the above invention, the first insulator may have one or more insulating layers, and the number of the insulating layers in the terminal portion may be different from the number of the insulating layers in the main body portion.

  In the above invention, the impedance of the terminal portion may be substantially the same as the impedance of the main body portion.

  According to the present invention, since the thickness of the first insulator in the terminal portion is different from the thickness of the first insulator in the main body portion, the impedance in the flat cable is matched and the high-frequency signal in the flat cable is matched. The transmission characteristics are improved.

FIG. 1 is a perspective view of a flat cable according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 3 is an enlarged cross-sectional view of a portion III in FIG. FIG. 4 is a schematic cross-sectional view of a flat cable for explaining the operation of the first embodiment of the present invention. FIG. 5 is a cross-sectional view showing a modification of the flat cable in the first embodiment of the present invention. FIG. 6 is a cross-sectional view of a flat cable according to the second embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view of a portion VII in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< first embodiment >>
FIG. 1 is a perspective view of a flat cable according to the present embodiment, FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1, and FIG. 3 is an enlarged cross-sectional view of a portion III in FIG.

  A flexible flat cable (FFC: Flexible Flat Cable) 10 in the present embodiment is a cable that transmits a high-frequency signal as an image interface or internal wiring of a liquid crystal television or a plasma television, for example.

  Further, as shown in FIGS. 2 and 3, the flat cable 10 includes a conductor 20, a first insulator 30, a second insulator 40, a first shield 50, and a second shield. 60. In the flat cable 10, the conductor 20 is covered from both sides by the first and second insulators 30 and 40 and the first and second shields 50 and 60 in the main body 11 located at the center. On the other hand, in the terminal part 12 located at the end of the main body part 11, the conductor 20 is exposed from the second insulator 40 and the second shield 60.

  As shown in FIG. 1, the conductor 20 is composed of, for example, a flat annealed copper wire along the longitudinal direction of the flat cable 10. In the present embodiment, the six conductors 20 are arranged at a predetermined pitch in the short direction of the flat cable 10. The number of conductors 20 is not particularly limited.

  2 and 3, the conductor 20 has a first main surface 21 on the lower side in the drawing and a second main surface 22 on the upper side in the drawing. A first insulator 30 (described later) is laminated on the first main surface 21 from the main body portion 11 to the terminal portion 12, whereas only the main body portion 11 is formed on the second main surface 22. In addition, a second insulator 40 (described later) is laminated. That is, in the terminal portion 12 of the flat cable 10, both end portions 20a and 20b of the conductor 20 are exposed from the second insulator 40, and the flat cable 10 can be electrically connected to other electronic devices. .

  As shown in FIGS. 2 and 3, the first insulator 30 is laminated on the first main surface 21 of the conductor 20. The first insulator 30 includes a first adhesive layer 31, a first insulating layer 32, a second adhesive layer 33, a second insulating layer 34, and a third adhesive layer 35. Have.

The first adhesive layer 31 bonds the conductor 20 and the first insulating layer 32 (described later), and on the first main surface 21 of the conductor 20, the entire flat cable 10 (the main body portion 11 and the main cable 11). It is laminated over the terminal part 12). The first adhesive layer 31 is made of a thermoplastic adhesive made of, for example, polyester. In the present embodiment, the thickness of the first adhesive layer 31 and h _1.

The first insulating layer 32 protects the conductor 20 and is laminated over the entire flat cable 10 via the first adhesive layer 31 on the first main surface 21 of the conductor 20. Yes. The first insulating layer 32 is a film made of a flexible and insulating material such as polyethylene terephthalate (PET). In the present embodiment, the thickness of the first insulating layer 32 and h _2.

The second adhesive layer 33 bonds the first insulating layer 32 and the second insulating layer 34 (described later). The second adhesive layer 33 is stacked only on the first insulating layer 32 in the main body portion 11, but is not stacked on the first insulating layer 32 in the terminal portion 12. Similar to the first adhesive layer 31, the second adhesive layer 33 is made of an adhesive made of polyester, for example. In the present embodiment, the thickness of the second adhesive layer 33 and h _3.

As shown in FIGS. 2 and 3, the second insulating layer 34 is laminated on the first insulating layer 32 in the main body portion 11 via the second adhesive layer 33. Note that the second insulating layer 34 is not stacked on the first insulating layer 32 in the terminal portion 12. Similar to the first insulating layer 32, the second insulating layer 34 is a film made of a flexible and insulating material such as polyethylene terephthalate. In the present embodiment, the thickness of the second insulating layer 34 and h _4.

As shown in FIGS. 2 and 3, the third adhesive layer 35 adheres the second insulating layer 34 and the first shield 50 (described later) in the main body 11, and the first insulation in the terminal portion 12. The layer 32 and the first shield 50 are bonded. The third adhesive layer 35 is laminated from the second insulating layer 34 in the main body portion 11 to the first insulating layer 32 in the terminal portion 12. The third adhesive layer 35 is made of a thermoplastic adhesive made of polyester, for example. In the present embodiment, the thickness of the third adhesive layer 35 and h _5.

As described above, the first insulator 30 has the two insulating layers 32 and 34 and the three adhesive layers 31, 33, and 35 in the main body portion 11. The terminal portion 12 has a single insulating layer 32 and two adhesive layers 31 and 35. Therefore, in the first insulator 30, the second thickness in the terminal portion 12 with respect to the first thickness H ₁ in the main body portion 11 (H ₁ = h ₁ + h ₂ + h ₃ + h ₄ + h ₅ ). H ₂ (H ₂ = h ₁ + h ₂ + h ₅ ) is relatively thin (H ₂ <H ₁ ).

  As shown in FIGS. 2 and 3, the second insulator 40 is stacked on the second main surface 22 of the conductor 20 with both end portions 20 a and 20 b of the conductor 20 being exposed. That is, the second insulator 40 is laminated only on the main body 11 of the flat cable 10. Although not particularly illustrated, the second insulator 40 may be laminated on the second main surface 22 of the conductor 20 with only one end 20a, 20b of the conductor 20 exposed. .

The second insulator 40 includes a fourth adhesive layer 41, a third insulating layer 42, and a fifth adhesive layer 43.

  As shown in FIGS. 2 and 3, the fourth adhesive layer 41 bonds the conductor 20 and the third insulating layer 42 (described later) in the main body 11 of the flat cable 10. The fourth adhesive layer 41 is made of a thermoplastic adhesive made of polyester, for example.

  The third insulating layer 42 protects the conductor 20 from the second main surface 22 side. The third insulating layer 42 is a film made of a flexible and insulating material such as polyethylene terephthalate.

  As shown in FIGS. 2 and 3, the fifth adhesive layer 43 bonds the third insulating layer 42 and the second shield 60 (described later). The fifth adhesive layer 43 is made of a thermoplastic adhesive made of polyester, for example.

Here, the thickness H ₀ of the second insulator 40 is the sum of the thickness of the fourth adhesive layer 41, the thickness of the third insulating layer 42, and the thickness of the fifth adhesive layer 43. And substantially the same as the first thickness H ₁ of the first insulator 30 (H ₀ ≈H ₁ ).

  As shown in FIGS. 2 and 3, the first shield 50 electrically shields the conductor 20 and is laminated on the conductor 20 via the first insulator 30. In addition, the 1st shield 50 is the whole 1st insulator 30 so that the whole conductor 20 (all the main-body part 11 and the terminal part 12) may be electrically shielded from the 1st main surface 21 side. It is laminated over (the main body part 11 and the terminal part 12). The first shield 50 has a tape shape, and includes a first shield conductive layer 51 and a first shield insulating layer 52.

  As shown in FIGS. 2 and 3, the first shield conductive layer 51 is laminated on the third adhesive layer 35 of the first insulator 30. The first shield conductive layer 51 is made of a conductive material such as aluminum foil, copper foil, or tin plating.

  The first shield insulating layer 52 is stacked on the first shield conductive layer 51. The first shield insulating layer 52 is made of a flexible and insulating material such as polyethylene terephthalate.

  As described above, in the flat cable 10 according to the present embodiment, the first shield 50 is laminated over the entire flat cable 10 including the terminal portion 12, and therefore, electromagnetic interference (EMI : electromagnetic interference) can be suppressed.

  As shown in FIGS. 2 and 3, the second shield 60 electrically shields the conductor 20 in the main body 11, and is laminated on the conductor 20 via the second insulator 40. . The second shield 60 has a tape shape and has a second shield conductive layer 61 and a second shield insulating layer 62.

  As shown in FIGS. 2 and 3, the second shield conductive layer 61 is laminated on the fifth adhesive layer 43 of the second insulator 40. The second shield conductive layer 61 is made of a conductive material such as aluminum foil, copper foil, or tin plating.

  The second shield insulating layer 62 is laminated on the second shield conductive layer 61. The second shield insulating layer 62 is made of a flexible and insulating material such as polyethylene terephthalate.

  Next, the effect | action of the flat cable 10 in this embodiment is demonstrated.

  FIG. 4 is a schematic sectional view of a flat cable for explaining the operation of the present embodiment, and FIG. 5 is a sectional view showing a modification of the flat cable in the present embodiment.

In the main body 11 of the flat cable 10, as shown in FIG. 4, the conductor 20 extends from the first and second main surfaces 21, 22 via the first and second insulators 30, 40. The transmission line structure is a strip line. On the other hand, in the terminal portion 12 of the flat cable 10, as shown in the figure, the conductor 20 is exposed from the second insulator 40 and the second shield 60, and the structure of the transmission line becomes a microstrip line. ing. Here, the impedance Z ₁ of the strip line (main body 11) can be calculated by the following equation (1), the impedance Z ₂ of the microstrip line (terminal 12) is obtained by the following equation (2) be able to.

なお、上記（１）式及び（２）式において、Ｈ_１は本体部１１における第１の絶縁体３０の第１の厚さであり、Ｈ_２は端末部１２における第１の絶縁体３０の第２の厚さであり、Ｔは導電体２０（例えば平角軟銅線）の厚さであり、Ｗは導電体２０（例えば平角軟銅線）の幅であり、Ｅｒは第１及び第２の絶縁体３０,４０の比誘電率である。

In the above formulas (1) and (2), H ₁ is the first thickness of the first insulator 30 in the main body portion 11, and H ₂ is the first thickness of the first insulator 30 in the terminal portion 12. The second thickness, T is the thickness of the conductor 20 (for example, flat soft copper wire), W is the width of the conductor 20 (for example, flat soft copper wire), and Er is the first and second insulations. It is the relative dielectric constant of the bodies 30 and 40.

Here, for example, when the flat cable 10 is connected to a high-frequency circuit with an impedance of 50Ω, an example of the thickness h ₁ of the first adhesive layer 31 is 20 μm, and an example of the thickness h ₂ of the first insulating layer 32 is 142 μm, 25 μm as an example of the thickness h ₃ of the second adhesive layer 33, 130 μm as an example of the thickness h ₄ of the second insulating layer 34, and 3 μm as an example of the thickness h ₅ of the third adhesive layer 35 Can be mentioned. In this case, the first thickness H ₁ (H ₁ = h ₁ + h ₂ + h ₃ + h ₄ + h ₅ ) of the first insulator 30 is 320 μm, and the second thickness of the first insulator 30 is The height H ₂ (H ₂ = h ₁ + h ₂ + h ₅ ) is 165 μm.

An example of the thickness of the fourth adhesive layer 41 is 20 μm, an example of the thickness of the third insulating layer 42 is 297 μm, and an example of the thickness of the fifth adhesive layer 43 is 3 μm. In this case, the thickness H ₀ of the second insulator 40 is 320 μm, which is the same as the first thickness H ₁ of the first insulator 30 (H ₀ = H ₁ ).

Further, 35 μm is an example of the thickness T of the conductor 20, 300 μm is an example of the width W of the conductor 20, and 3.4 is an example of the relative dielectric constant Er of the first and second insulators 30 and 40. Can do. In this case, the impedance Z ₁ of the main body portion 11 is 50.1Ω from the above equation (1), and the impedance Z ₂ of the terminal portion 12 is 50.7Ω from the above equation (2). Thus, in the flat cable 10 in the above example, the impedances of the high frequency circuit and the flat cable 10 are matched, and the impedances Z ₁ and Z ₂ in the flat cable 10 are substantially the same (Z ₁ ≈ Z ₂ ), which is excellent in transmission characteristics for high-frequency signals.

Here if, the second thickness _{H 2} of the first insulator 30 in the terminal unit 12, and 320 .mu.m (e.g., laminating a second adhesive layer 33 in the terminal portion 12 and the second insulating layer 34 If the first thickness H ₁ of the first insulator 30 in the main body portion 11 is the same, the impedance Z ₂ ′ of the terminal portion 12 is about 77Ω, and the impedance (50Ω) of the high-frequency circuit and the main body This is greatly different from the impedance Z ₁ (50.1Ω) of the portion 11.

On the other hand, in the flat cable 10 according to the present embodiment, as shown in FIG. 3, the second thickness H ₂ of the first insulator 30 in the terminal portion 12 is equal to the first insulator 30 in the main body portion 11. since the first thinner relatively than the thickness _{H 1} of the impedance _{Z 2} of the terminal portion 12, body portion 11 and the thickness _{H 1} of the first insulator 30 in the terminal section 12, _{H 2} Can be made smaller than the impedance Z ₂ ′ of the terminal portion 12 when they are the same, and the impedances Z ₁ and Z ₂ in the flat cable 10 can be matched. Thereby, the transmission characteristic with respect to the high frequency signal of the flat cable 10 can be improved.

Further, in the flat cable 10 according to the present embodiment, one insulating layer 32 is laminated on the first insulator 30 in the terminal portion 12, and two insulating layers are formed on the first insulator 30 in the main body portion 11. 32 and 34 are laminated. In addition, adhesive layers 31, 33, and 35 are stacked on the first insulator 30 in order to stack these insulating layers 32 and 34. That is, the first insulator 30 in the terminal portion 12 is composed of three layers, whereas the first insulator 30 in the main body portion 11 is composed of five layers.
As a result, the second thickness H ₂ becomes thinner than the first thickness H ₁ , and the impedances Z ₁ and Z ₂ are matched.

In the present embodiment, when the impedances Z ₁ and Z ₂ in the flat cable 10 are matched in this way, the number of insulating layers may be different between the main body 11 and the terminal 12, and the impedances Z ₁ and Z ₂ Easy to align.

  In the flat cable 10 according to the present embodiment, one insulating layer 32 is laminated on the first insulator 30 in the terminal portion 12, and two insulating layers 32, 34 is laminated, but is not particularly limited, and the insulating layer of the first insulator 30 in the terminal portion 12 and the insulating layer in the main body portion 11 of the first insulator 30 may each have two or more layers. Good. For example, two insulating layers may be stacked on the first insulator 30 in the terminal portion 12, and three or four or more insulating layers may be stacked on the first insulator 30 in the main body portion 11.

Further, in the flat cable 10 according to the present embodiment, in the first insulator 30, the number of insulating layers of the terminal portion 12 is relatively smaller than the number of insulating layers of the main body portion 11, but is particularly limited. However, the number of insulating layers of the terminal portion 12 is relatively larger than the number of insulating layers of the main body portion 11, and the second thickness H ₂ of the terminal portion 12 is set to the first thickness of the main body portion 11. and it may be relatively thicker than H _1.

  Further, in the present embodiment, the first and second shields 50 and 60 are laminated on both the first and second insulators 30 and 40, but there is no particular limitation, and as shown in FIG. The first shield 50 may be stacked only on the first insulator 30.

As described above, even if the second shield 60 is not laminated, the impedance Z can be reduced between the main body 11 and the terminal 12 because the second insulator 40 is laminated on the main body 11. _1, there is a case where Z ₂ is inconsistent. In such a case, the first insulator 30, by relatively thin than the second thickness H ₂ first thickness H _1, the impedance Z ₁ of the flat cable within 10, Z ₂ Therefore, transmission characteristics for high frequency signals can be improved.

<< Second Embodiment >>
Next, a second embodiment will be described.

  FIG. 6 is a cross-sectional view of the flat cable in the present embodiment, and FIG.

  The flat cable 10a in the present embodiment is different from the first embodiment in the configuration of the first insulator 70, but the other configurations are the same as those in the first embodiment. Only the differences from the first embodiment will be described below, and portions having the same configuration as in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The first insulator 70 in the present embodiment has a sixth adhesive layer 71, a fourth insulating layer 72, and a seventh adhesive layer 73.

The sixth adhesive layer 71 adheres the conductor 20 and the fourth insulating layer 72 (described later), and the entire flat cable 10a (the main body 11 and the terminal) on the first main surface 21 of the conductor 20. Part 12). The sixth adhesive layer 71 is made of a thermoplastic adhesive made of polyester, for example. In the present embodiment, the thickness of the adhesive layer 71 of the sixth and h _6.

  The fourth insulating layer 72 is laminated on the sixth adhesive layer 71. The fourth insulating layer 72 is made of a flexible and insulating material such as polyethylene terephthalate.

The fourth insulating layer 72 has a thickness _{h 8} in the terminal section 12 is thinner relatively than the thickness _{h 7} of the main body _{11 (h 8 <h 7)} . For example, such a fourth insulating layer 72 is configured so that the number of times of application of the terminal portion 12 is relatively smaller than the number of times of application of the main body portion 11 when the material to be the fourth insulating layer 72 is applied (laminated). Can be formed.

The seventh adhesive layer 73 bonds the fourth insulating layer 72 and the first shield 50, and is laminated over the entirety of the fourth insulator 72 (the main body portion 11 and the terminal portion 12). Yes. The seventh adhesive layer 73 is made of a thermoplastic adhesive made of polyester, for example. In the present embodiment, the thickness of the adhesive layer 73 of the seventh and h _9.

As described above, in the flat cable 10 a according to the present embodiment, the fourth thickness H ₄ (H ₄ = h ₆ + h ₈ + h ₉ ) of the first insulator 70 in the terminal portion 12 is the same as that in the main body portion 11. The first insulator 70 is relatively thinner than the third thickness H ₃ (H ₃ = h ₆ + h ₇ + h ₉ ) (H ₄ <H ₃ ).

Here, also in the present embodiment, as in the first embodiment, the main body portion 11 of the flat cable 10a is a strip line, and the terminal portion 12 of the flat cable 10a is a micro strip line. The impedance Z ₃ of the main body 11 (strip line) can be obtained by the following equation (3), and the impedance Z ₄ of the terminal portion 12 (microstrip line) can be obtained by the following equation (4). Can do.

なお、上記（３）式及び（４）式において、Ｈ_３は本体部１１における第１の絶縁体７０の第３の厚さであり、Ｈ_４は端末部１２における第１の絶縁体７０の第４の厚さである。

In the above formulas (3) and (4), H ₃ is the third thickness of the first insulator 70 in the main body portion 11, and H ₄ is the first thickness of the first insulator 70 in the terminal portion 12. The fourth thickness.

Here, for example, when the flat cable 10a is connected to a high-frequency circuit having an impedance of 50Ω, the thickness h ₆ of the sixth adhesive layer 71 is 20 μm as an example, and the thickness of the fourth insulating layer 72 in the main body 11 is the same. An example of h ₇ is 297 μm, an example of the thickness h ₈ of the fourth insulating layer 72 in the terminal portion 12 is 142 μm, and an example of the thickness h ₉ of the seventh adhesive layer 73 is 3 μm. In such a case, the third thickness H ₃ of the first insulator 70 in the main body portion 11 is 320 μm, and the fourth thickness H ₄ of the first insulator 70 in the terminal portion 12 is 165 μm. Become.

Further, according to the above equations (3) and (4), the impedance Z ₃ of the main body 11 is 50.1Ω, and the impedance Z ₄ of the terminal 12 is 50.7Ω. Thus, in the flat cable 10 in the above example, the impedances of the high frequency circuit and the entire flat cable 10a are matched, and the impedances Z ₃ and Z ₄ are substantially the same (Z ₃ ≈Z ₄ ). Excellent transmission characteristics for high frequency signals.

Thus, also in this embodiment, fourth thickness H ₄ of the second insulator 70 in the terminal section 12, second insulator 70 third relative than the thickness H ₃ of the main body 11 As a result, the impedances Z ₃ and Z ₄ can be matched, and the transmission characteristic of the flat cable 10a with respect to the high-frequency signal is improved.

In the present embodiment, the thicknesses h ₇ and h _{8 of} the fourth insulating layer 72 are different between the main body portion 11 and the terminal portion 12, but the thickness of the sixth adhesive layer 71 is different from that of the main body portion 11. The unit 11 and the terminal unit 12 may be different. For example, the thickness of the sixth adhesive layer 71 in the terminal portion 12 may be relatively thinner than the thickness of the sixth adhesive layer 71 in the main body portion 11. In this way, the fourth thickness H ₄ of the first insulator 70 in the terminal portion 12 is made relatively thinner than the third thickness H ₃ of the first insulator 70 in the main body portion 11. May be.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10,10a ... Flat cable 11 ... Main-body part 12 ... Terminal part 20 ... Conductor 30,40,70 ... Insulator 32,34,42,72 ... Insulating layer 31,33,35,41,43,71,73 ... Adhesive layer 50, 60 ... Shield 51, 61 ... Shield conductive layer 52, 62 ... Shield insulation layer

Claims (4)

A first insulator;
A conductor laminated on the first insulator;
A second insulator stacked on the conductor with at least one end of the conductor exposed; and
A shield that is stacked on the conductor via the first insulator or both the first insulator and the second insulator and electrically shields the conductor; A flat cable,
The thickness of the first insulator in the terminal portion where the conductor is exposed is different from the thickness of the first insulator in the main body portion where the second insulator is laminated. And flat cable. The flat cable according to claim 1,
The flat cable characterized in that a thickness of the first insulator in the terminal portion is relatively thinner than a thickness of the first insulator in the main body portion. The flat cable according to claim 1 or 2,
The first insulator has one or more insulating layers;
The number of the said insulating layers in the said terminal part differs from the number of the said insulating layers in the said main-body part, The flat cable characterized by the above-mentioned. The flat cable according to any one of claims 1 to 3,
The flat cable according to claim 1, wherein the impedance of the terminal portion is substantially the same as the impedance of the main body portion.

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