Open type resonator, and method for measuring conductivity using same

Abstract

Provided is an open type resonator that enables measuring a conductivity of a metal foil with higher accuracy. The open type resonator comprises: a concave reflection mirror that has a concave reflection surface made of metal; a signal input unit that is attached to a first excitation hole formed in the concave reflection mirror and inputs an input signal; a signal output unit that is attached to a second excitation hole formed in the concave reflection mirror and outputs an output signal; and a sample holding sheet which has a plane substantially perpendicular to a central axis of the reflection surface and disposed in a manner facing the reflection surface and on which a metal foil to be subject to resonance property measurement is to be sticked to the plane.

Description

Open resonator and method for measuring conductivity using the same

[0001] The present invention relates to an open resonator suitable for measuring the conductivity of metal foils.

[0002] Millimeter-wave frequencies are used in applications such as automotive radar, wireless communications, and high-speed digital devices. Improved position resolution in radar, increased communication speeds in wireless communications, and faster processing speeds in digital devices are essential challenges, and millimeter-wave frequencies are expected to continue to increase. Currently, the 75-80 GHz, 40 GHz, and 28 GHz bands are used in cutting-edge devices, respectively. Future frequencies are expected to exceed 100 GHz. Furthermore, discussions are underway regarding the use of frequencies up to 330 GHz for the sixth-generation (6G) communications network, which will replace the fifth-generation (5G) communications network. Accordingly, measurements of the material properties used in these devices using higher frequencies are becoming increasingly necessary. Among these material properties, energy loss due to the skin effect of millimeter waves at higher frequencies becomes a major issue, making measurement of material conductivity an essential task.

[0003] Patent Document 1 discloses a Fabry-Perot resonator for measuring the surface resistance in the millimeter wave band of a thin film material formed on a wafer by a sputtering process or a vapor deposition process. In the Fabry-Perot resonator of Patent Document 1, the thin film material deposited on the wafer is placed facing a spherical mirror, and the surface resistance of the thin film material is measured using a millimeter wave signal (see paragraphs 0001 to 0028 and FIG. 2 of Patent Document 1). In this case, the conductivity of the surface of the thin film material facing the spherical mirror is measured due to the skin effect. In other words, for thin film materials deposited on a wafer, the substantial conductivity of the surface of the thin film material deposited on the wafer, taking into account the influence of the skin effect, is important, but the Fabry-Perot resonator of Patent Document 1 cannot measure the conductivity of that surface.

[0004] Also, Non-Patent Document 1 discloses a Fabry-Perot resonator for measuring bulk conductivity.

[0005] In a Fabry-Perot resonator, an input signal with a frequency of, for example, approximately 100 GHz is input between a concave reflecting mirror and a planar metal sample, which are arranged opposite each other, to perform resonance measurement and obtain a resonance waveform. A network analyzer is often used for resonance measurement. The network analyzer is connected to the Fabry-Perot resonator to obtain a graph (resonance waveform) with frequency on the horizontal axis and transmitted signal strength (transmission coefficient) on the vertical axis, and the resonance characteristics are measured. Here, "resonance characteristics" refers to the center frequency of the resonance (resonance frequency) and the Q value (in this specification, the ratio (f / BW) of the center frequency (f) and the 3 dB bandwidth (BW)). The conductivity of a metal sample to be measured is typically calculated or simulated based on the resonance characteristics of a metal with known conductivity (e.g., copper or silver) and the resonance characteristics of the metal sample.

[0006] To perform stable conductivity measurements using a Fabry-Perot resonator, the distance between the metal sample being measured and the concave reflecting surface must be stabilized with an accuracy of the order of 10 nm. Because metal samples are typically film or foil-like (e.g., approximately 5 μm to 500 μm thick), it is difficult for the metal sample itself to stably fix its position. Due to this difficulty, previous conductivity measurements using a Fabry-Perot resonator have focused on plate-like objects with stable shapes, and no Fabry-Perot resonator has been available that can measure the conductivity of metal foils. Here, film or foil-like metal samples are not limited to those made of metal alone, but also include those with a dielectric bonded to the metal. In this case, the effective conductivity, taking into account the skin effect at the surface where the dielectric is bonded to the metal, is particularly important.

[0007] WO 00 / 08477

[0008] J. Cuper, B. Salski, T. Karpisz, A. Pacewicz, P. Kopyt, Conductivity measurement in mm-wave band with a Fabry-Perot open resonator, IEEE / MTT-S International Microwave Symposium, 996-998, 2020

[0009] An object of the present disclosure is to provide an open-type resonator that can measure the conductivity of a metal foil with higher accuracy.

[0010] An open-type resonator according to a first aspect of the present disclosure comprises a concave reflecting mirror having a concave reflecting surface made of metal, a signal input section attached to a first excitation hole formed in the concave reflecting mirror and inputting an input signal, a signal output section attached to a second excitation hole formed in the concave reflecting mirror and outputting an output signal, and a sample holding sheet having a flat surface that is substantially perpendicular to the central axis of the reflecting surface and arranged opposite the reflecting surface, and on which a metal foil whose resonance characteristics are to be measured is attached.

[0011] An open-type resonator according to a second aspect of the present disclosure includes a first concave reflecting mirror having a first concave reflecting surface made of metal, a second concave reflecting mirror having a second concave reflecting surface made of metal, a signal input unit attached to a first excitation hole formed in the first concave reflecting mirror and inputting an input signal, a signal output unit attached to a second excitation hole formed in the first concave reflecting mirror or the second concave reflecting mirror and outputting an output signal, and a sample holding sheet having a flat surface on which a metal foil whose resonance characteristics are to be measured is attached. The input signal is reflected toward the second concave reflecting mirror by the metal foil attached to the sample holding sheet, thereby generating resonance between the first concave reflecting mirror and the second concave reflecting mirror via the metal foil.

[0012] The method for measuring conductivity of the present disclosure is a method for measuring the conductivity of a metal foil using an open-type resonator according to the first or second aspect, and includes the steps of measuring a first resonance characteristic by reflecting the input signal by a metal having a known conductivity and detecting the output signal, attaching the metal foil to the sample holding sheet, measuring a second resonance characteristic by reflecting the input signal by the metal foil attached to the sample holding sheet and detecting the output signal, and calculating the conductivity of the metal foil using the known conductivity, the Q value obtained from the first resonance characteristic, and the Q value obtained from the second resonance characteristic.

[0013] According to the open-type resonator of the present disclosure, when measuring conductivity using a Fabry-Perot resonator, the position of the metal foil as the measurement object is stabilized, which stabilizes the measured resonance characteristics, thereby enabling the conductivity of the metal foil to be measured with high accuracy.

[0014] Schematic cross-sectional view showing the configuration of a Fabry-Perot resonator according to embodiment 1. Diagram showing attachment of a metal foil to a sample holding plate of a Fabry-Perot resonator according to embodiment 1. Diagrams showing (a1) a single metal foil before being attached to a glass film, (a2) a state in which a single metal foil is attached to a sample holding plate without using a glass film, (b1) a state in which the metal foil is attached to a glass film, and (b2) a state in which the metal foil attached to a glass film is attached to a sample holding plate. Diagrams showing resonance waveforms measured when a glass film is used (with glass film: solid line) and when a glass film is not used (without glass film: dashed line). Diagram showing movement of the resonance waveform when a glass film is not used (without glass film). Diagram comparing calculated electrical conductivity when a glass film is used (with glass film: solid line) and when a glass film is not used (without glass film: dashed line). Schematic cross-sectional view showing the configuration of a Fabry-Perot resonator according to embodiment 2.

[0015] (Embodiment 1) Fig. 1 is a cross-sectional schematic diagram of a Fabry-Perot resonator according to embodiment 1. As shown in Fig. 1, the Fabry-Perot resonator 100 according to embodiment 1 has a fixing base 10, a concave reflecting mirror 11, a sample holder 20, and a sample holding plate 31. The Fabry-Perot resonator 100 is an example of an open-type resonator. In the following explanation, an XYZ orthogonal coordinate system shown in Fig. 1 will be used, in which the X direction corresponds to the up-down direction, the Y direction corresponds to the front-back direction, and the Z direction corresponds to the left-right direction.

[0016] As shown in FIG. 1 , a concave reflecting mirror 11 having a concave reflecting surface 12 is disposed on the fixing base 10 such that the central axis C of the reflecting surface 12 is parallel to the Z axis and the reflecting surface 12 faces the sample holder 20 and the sample holding plate 31. As will be described in detail later, the sample holding plate 31 holds a metal foil 35 (hereinafter sometimes referred to as a "sample"), the conductivity of which is to be measured, attached to a glass film 34. The sample holder 20 holds the sample holding plate 31, which sandwiches the glass film 34 and the metal foil 35. In this case, the metal foil 35 is disposed substantially perpendicular to the central axis C and faces the reflecting surface 12, with a predetermined distance D between the center of the reflecting surface 12 and the surface of the metal foil 35 facing it (the reflection reference surface). In the first embodiment, the distance D is 60 mm.

[0017] The reflecting surface 12 is a sphere with a radius R of 96 mm, a concave depth of 5 mm, and a circle with a radius of approximately 30.6 mm when projected onto the XY plane. The reflecting surface 12 is made of metal. In the Fabry-Perot resonator 100, the entire concave reflecting mirror 11 is made of copper, but the reflecting surface 12 may also be made of copper. Alternatively, it may be made of silver instead of copper. Furthermore, these metals may be plated or coated with resin.

[0018] 1, an input waveguide 41 and an output waveguide 42 are arranged in the concave reflecting mirror 11 near the central axis C. An input excitation hole 15 and an output excitation hole 16 having minute diameters for forming a coupling state that obtains desired resonance characteristics are formed at the tip openings of the input waveguide 41 and the output waveguide 42 on the reflecting surface 12 side. The input waveguide 41 is a signal input section to which an input signal for measuring the resonance characteristics of a sample is input, and the output waveguide 42 is a signal output section from which a detection signal is output.

[0019] The sample holder 20 has a first sample holder housing 21A (an example of a first sample holder housing) and a second sample holder housing 21B (an example of a second sample holder housing) that are arranged opposite each other. As shown in FIG. 1 , the sample holder 20 is fixed to the fixing table 10 so that the first sample holder housing 21A faces the concave reflecting mirror 11.

[0020] The first holding housing 21A is provided with a recess 22 and a through-hole 24. The recess 22 has walls on the −X, ±Y, and −Z direction sides and is open on the +X and +Z direction sides. A sample holding plate 31 composed of two sample holding plates (a first sample holding plate 31A and a second sample holding plate 31B) is placed in the recess 22 with a metal foil 35 attached to a glass film 34 sandwiched between them. The through-hole 24 is a circular hole formed in the recess 22 and penetrating in the Z direction.

[0021] The second holding housing 21B has a protrusion 23. The protrusion 23 is provided at a position corresponding to the recess 22 of the first holding housing 21A, protrudes in the −Z direction, and sandwiches the sample holding plate 31 between the protrusion 23 and the recess 22. When sandwiching the sample holding plate 31 holding the glass film 34 to which the metal foil 35 is attached between the first holding housing 21A and the second holding housing 21B, a magnet and a magnetic body may be disposed in the first holding housing 21A and the second holding housing 21B, respectively, so that the second holding housing 21B is attracted to the first holding housing 21A by the magnetic force generated between the magnet and the magnetic body. Alternatively, a spring may be disposed between the first holding housing 21A and the second holding housing 21B, so that the second holding housing 21B is attracted to the first holding housing 21A by the attractive force generated by the spring.

[0022] FIG. 2 is a diagram showing the attachment of a sample to the sample holding plate 31 of the Fabry-Perot resonator 100. The first sample holding plate 31A has a circular through-hole 32. A glass film 34 with a metal foil 35 attached thereto is disposed between the first sample holding plate 31A and the second sample holding plate 31B and attached to the sample holding plate 31. The sample holding plate 31 holding the glass film 34 and the metal foil 35 is inserted into the sample holder 20 with the metal foil 35 exposed from the through-hole 32 facing the concave reflecting mirror 11, as shown in FIG. 1. In the first embodiment, the sample holding plate 31 is an aluminum plate. However, other non-magnetic metal or resin plates may also be used as the sample holding plate 31.

[0023] The metal foil 35, the subject of conductivity measurement, is attached to the glass film 34 so that the surface to be measured is exposed. This is because the purpose is to measure the conductivity of the surface of the metal foil 35, taking into account energy loss due to the skin effect of millimeter waves. The metal foil 35 is attached to the glass film 34 because the thickness of the metal foil 35 is approximately 9 μm to 35 μm and the metal foil 35 cannot stand on its own. Because the metal foil 35 cannot stand on its own, when measuring the resonance characteristics using a Fabry-Perot resonator, the flatness of the resonance surface is not maintained, resulting in unstable measured resonance characteristics. The surface of the glass film 34 to which the metal foil 35 is attached is a mirror finish, with a surface roughness Rz of 2 μm or less. In the first embodiment, the thickness of the glass film 34 is 0.4 mm, but a thickness in the range of 0.05 mm to 2.0 mm can be used. The glass film 34 is an example of a sample holding sheet.

[0024] FIG. 3 shows (a1) a free-standing metal foil 35 before being attached to a glass film 34, (a2) a state in which the free-standing metal foil 35 is attached to a sample holding plate 31 without using a glass film 34, (b1) a state in which the metal foil 35 is attached to a glass film 34, and (b2) a state in which the metal foil 35 attached to the glass film 34 is attached to a sample holding plate 31. The metal foil 35 shown in FIG. 3 is a copper foil with a thickness of 20 μm. As shown in FIG. 3(a1), when the free-standing copper foil before being attached to the glass film 34 is lifted, it is found that wrinkles and curvature occur due to its own weight, resulting in a decrease in flatness. When the free-standing copper foil in this state is attached to a sample holding plate 31, as shown in FIG. 3(a2), it is found that wrinkles and curvature are reduced, but still exist. In contrast, as shown in (b1) of FIG. 3 , the copper foil attached to the glass film 34 maintains its original flatness without wrinkles or the like. This indicates that even if the copper foil has wrinkles or curves before being attached to the glass film 34, the wrinkles or the like are removed by attaching it to the glass film 34. The copper foil is attached to the sample holding plate 31 in this wrinkle-free state (see (b2) of FIG. 3 ) and used to measure resonance characteristics. In the first embodiment, the metal foil 35 is brought close to the surface of the glass film 34, whereby the metal foil 35 is adsorbed to the glass film 34 by intermolecular forces. Note that, for example, adhesive or double-sided tape may be used to attach the metal foil 35 to the glass film 34.

[0025] (Measurement of Conductivity) The process (steps) for measuring conductivity using the Fabry-Perot resonator 100 are as follows: 1) Connect the Fabry-Perot resonator 100, network analyzer, and controller with cables. 2) Insert the sample holder 31, which sandwiches a reference metal with known conductivity, into the sample holder 20, and measure the resonance characteristics (first resonance characteristics). Calculate the Q value Q0 from the bandwidth of the resonance waveform and the resonance frequency f0. 3) Attach the metal foil 35 to the glass film 34. 4) Insert the sample holder 31, which sandwiches the glass film 34 to which the metal foil 35 is attached, into the sample holder 20. 5) Measure the resonance characteristics (second resonance characteristics) of the metal foil 35, and calculate the Q value Qs from the bandwidth of the resonance waveform and the resonance frequency fs. 6) Calculate the conductivity of the metal foil 35 from the conductivity σ0, Q value Q0, resonance frequency f0, Q value Qs, and resonance frequency fs of the known metal. The resonance characteristics may be measured multiple times in steps 2) and 5) and averaged. When measuring the conductivity of multiple types of metal foils 35, steps 3) to 6) are repeated.

[0026] (Effects, etc.) In the Fabry-Perot resonator 100, by attaching the metal foil 35 to the glass film 34, the position of the metal foil 35, which is the sample, relative to the reflecting surface 12 of the concave reflecting mirror 11 is stabilized, and there are two main reasons why the resonance characteristics can be measured stably. The first reason is that there is a large difference between the frequency of the desired resonance and the frequency of the unwanted resonance, and the second reason is that the resonance waveform measured over time is stable with almost no movement.

[0027] 4 is a diagram for explaining the first factor, and shows the state of the resonance waveform measured in the measurement of the resonance characteristics in step 5) above, when a metal foil 35 is attached to a glass film 34 and sandwiched between sample holding plates 31 (with glass film: solid line) and when the metal foil 35 alone is sandwiched between sample holding plates 31 without using a glass film 34 (without glass film: dashed line). A copper foil with a thickness of 20 μm was used as the metal foil 35.

[0028] As shown in Figure 4, when the glass film 34 is not used (without glass film), an unwanted resonance appears near the desired resonance (frequency of approximately 58 GHz). The frequency of the unwanted resonance closest to the desired resonance frequency is approximately 58.030 GHz, and the difference from the desired resonance frequency is 0.030 GHz. In contrast, when the glass film 34 is used (with glass film), the frequency of the unwanted resonance closest to the desired resonance (frequency of approximately 58 GHz) is approximately 58.085 GHz, and the difference from the desired resonance frequency is 0.085 GHz.

[0029] When an unwanted resonance appears near a desired resonance, not only is it difficult to distinguish which of the observed resonance waveforms is the desired resonance, but the nearby unwanted resonance also affects the shape (bandwidth (BW)) of the desired resonance waveform, making it difficult to measure an accurate Q value. When the glass film 34 of embodiment 1 is used, the unwanted resonance that appears is relatively far from the desired resonance, making it relatively easy to distinguish the desired resonance waveform, and its influence on the shape of the desired resonance waveform is negligible. The position of the metal foil 35, which is the reflection surface of the resonance, needs to be stabilized with an accuracy of the order of 10 nm. However, when the glass film 34 is not used, the position of the reflection surface of the metal foil 35 is not stable, which is thought to result in unstable resonance characteristics.

[0030] FIG. 5 is a diagram illustrating the second factor and shows the shift of the resonant waveform when the glass film 34 is not used (no glass film). When the glass film 34 is not used, the resonant frequency may not be stable, and the resonant waveform may shift over time. The example shown in FIG. 5 shows how the measured resonant waveform gradually shifts toward lower frequencies over time, resulting in a decrease of approximately 0.1 GHz after 5 seconds. Since the frequency sweep (from left to right) is performed to measure the resonance characteristics, if the resonant waveform shifts toward lower frequencies (left), the bandwidth (BW) of the resonant waveform is measured to be smaller than the actual bandwidth, and the Q value, which is proportional to the inverse of the bandwidth, is measured to be larger. Conversely, if the resonant waveform shifts toward higher frequencies (right) over time, the bandwidth (BW) of the resonant waveform is measured to be larger than the actual bandwidth, and the Q value is measured to be smaller. Thus, if the position of the metal foil 35 sample moves during measurement, the Q value cannot be measured accurately. In contrast, when the metal foil 35 is attached to the glass film 34 and the measurement is performed, the position of the metal foil 35 is more stable during the measurement than when the glass film 34 is not used, and an accurate Q value can be measured.

[0031] 6 is a graph comparing the conductivity actually calculated in step 6) above between a case where the metal foil 35 was attached to the glass film 34 (with glass film: solid line) and a case where the glass film 34 was not used (without glass film: dashed line). When the glass film 34 was not used (without glass film), the resonance characteristics were measured with only the metal foil 35 sandwiched between the sample holding plate 31. Copper foil with a thickness of 20 μm was used as the metal foil 35.

[0032] As shown in FIG. 6, when the glass film 34 was used (with glass film), the conductivity calculated in the frequency range of 18 GHz to 110 GHz was approximately 5.6 to 6.2 (×10 ７In contrast, when the glass film 34 is not used (without glass film), the conductivity calculated in the frequency range of 18 GHz to 110 GHz is approximately 1.4 to 6.0 (×10 ７ It can be seen that the saturation voltage (V) fluctuates greatly.

[0033] When the glass film 34 is not used, the position of the reflective surface of the metal foil 35, which needs to be stabilized with an accuracy of the order of 10 nm, is not stable, which results in unstable resonance characteristics, an inaccurate measurement of the Q value, and an inaccurate calculation of the conductivity.

[0034] (Embodiment 2) In the first embodiment, the Fabry-Perot resonator 100 using one concave reflecting mirror 11 has been described. In the second embodiment, a Fabry-Perot resonator 200 using two concave reflecting mirrors will be described. FIG. 7 is a schematic diagram showing a cross section of the Fabry-Perot resonator 200 according to the second embodiment. As shown in FIG. 7, the Fabry-Perot resonator 200 has two concave reflecting mirrors 211 and 213 (a first concave reflecting mirror and a second concave reflecting mirror). The concave reflecting mirror 211 has a concave reflecting surface 212 (a first reflecting surface), and the concave reflecting mirror 213 has a concave reflecting surface 214 (a second reflecting surface). The reflecting surface 212 is a spherical surface having a central axis C1 and a radius R1 of 96 mm, and the reflecting surface 214 is a spherical surface having a central axis C2 and a radius R2 of 96 mm. The central axis C1 is parallel to the Z axis, and the central axis C2 is parallel to the Y axis, and the two concave reflecting mirrors 211, 213 are disposed at a position where the central axis C1 of the reflecting surface 212 and the central axis C2 of the reflecting surface 214 intersect at a right angle. The distances D1, D2 between the centers of the reflecting surfaces 212, 214 and the surface of the metal foil 35 (reflection reference surface) are both 60 mm.

[0035] Concave reflecting mirror 211 has excitation hole 215 penetrating concave reflecting mirror 211 in the direction of central axis C1, and input waveguide 241 (signal input section) is arranged in excitation hole 215, while concave reflecting mirror 213 has excitation hole 216 penetrating concave reflecting mirror 213 in the direction of central axis C2, and output waveguide 242 (signal output section) is arranged in excitation hole 216. In the second embodiment, from the viewpoint of ease of manufacture, excitation holes 215, 216 are formed on central axes C1, C2, respectively, but they do not necessarily have to be formed on central axes C1, C2, and may be formed in concave reflecting mirrors 211, 213. In addition, in embodiment 2, from the viewpoint of ease of manufacturing, excitation holes 215 and 216 are formed in concave reflectors 211 and 213, respectively. However, it is also possible to form two excitation holes 215 and 216 in one of concave reflectors 211 and 213, and to place input waveguide 241 and output waveguide 242 in one of concave reflectors 211 and 213.

[0036] 7 , the glass film 34 to which the metal foil 35 is attached is arranged so that the angle θ1 between the normal N to the plane of the glass film 34 and the central axis C1 is 45°, and the angle θ2 between the normal N to the plane of the glass film 34 and the central axis C2 is 45°. By arranging the glass film 34 to which the metal foil 35 is attached relative to the concave reflecting mirrors 211 and 213 in this manner, an input signal input from the input waveguide 241 is reflected by the surface of the metal foil 35 toward the concave reflecting mirror 213, and resonance occurs between the concave reflecting mirror 211 and the concave reflecting mirror 213 via the metal foil 35. Note that when the resonance characteristics of a reference metal are measured in step 2) of the conductivity measurement described in the first embodiment, the input signal is reflected by the surface of the reference metal, and resonance occurs between the concave reflecting mirror 211 and the concave reflecting mirror 213 via the reference metal. Although omitted in Figure 7, the glass film 34 to which the metal foil 35 is attached may be held by the sample holding plate 31 described in embodiment 1, or the sample holding plate 31 to hold the glass film 34 to which the metal foil 35 is attached may be arranged using a sample holder 20 fixed to the fixing table 10.

[0037] In embodiment 2, an example was described in which concave reflectors 211, 213 and glass film 34 with metal foil 35 attached are arranged so that angles θ1 and θ2 are 45°, but angles θ1 and θ2 do not have to be 45°, and may be, for example, 30° as long as angles θ1 and θ2 are the same.

[0038] Other Embodiments In the first embodiment, an example has been described in which the glass film 34 to which the metal foil 35 is attached is disposed between the first sample holding plate 31A and the second sample holding plate 31B, and the sample holding plate 31 holding the metal foil 35 and the glass film 34 is disposed in the sample holder 20. The glass film 34 to which the metal foil 35 is attached only needs to be disposed so that the metal foil 35 faces the reflecting surface 12 substantially perpendicular to the central axis, and does not necessarily have to be disposed in the sample holding plate 31 and the sample holder 20. Alternatively, the glass film 34 to which the metal foil 35 is attached may be disposed in the sample holder 20 without using the sample holding plate 31. Alternatively, the sample holding plate 31 holding the glass film 34 to which the metal foil 35 is attached may be disposed so that the metal foil 35 faces the reflecting surface 12 substantially perpendicular to the central axis without using the sample holder 20.

[0039] In the Fabry-Perot resonators 100 and 200 of the first and second embodiments, an example has been described in which a metal foil 35 is used as the sample to be measured. The sample is not limited to a single metal foil 35, and a dielectric may be bonded to the metal foil 35. Even when a dielectric is bonded to the metal foil 35, if the overall thickness is 500 μm or less, the position of the bonded surface between the metal foil 35, which serves as the reflection reference surface, and the dielectric is unstable. Therefore, the conductivity of the metal foil 35 can be accurately measured by attaching it to a glass film 34 and measuring the resonance characteristics. In this case, if the surface of the metal foil 35 to which the dielectric is bonded is defined as the first surface, the resonance characteristics are measured with the second surface of the metal foil 35 opposite the first surface attached to the glass film 34. That is, the input signal passes through the dielectric and is reflected by the metal foil 35, so the conductivity of the surface of the metal foil 35 bonded to the dielectric is measured. In calculating the conductivity of the metal foil 35 to which the dielectric is adhered, the conductivity of the metal foil 35 is calculated using the thickness, dielectric constant, and dielectric loss tangent of the dielectric adhered to the metal foil 35 in addition to the conductivity σ, Q value Q, resonant frequency f, Q value Q, and resonant frequency f of the known metal in the calculation of the conductivity in step 7).

[0040] In the Fabry-Perot resonators 100 and 200 of the first and second embodiments, a glass film 34 having a mirror surface is used as the sample holding sheet. Resin metal films, resin films, and porcelain sheets can be used as the sample holding sheet. Furthermore, the surface to which the metal foil 35 is attached does not necessarily have to be a mirror surface, as long as it is a flat surface to which the metal foil 35 can be stably attached.

[0041] In the Fabry-Perot resonator according to the first embodiment, a waveguide is used for the signal input section and the signal output section. Depending on the measurement frequency, a coaxial cable having a loop antenna at its tip can be used instead of the waveguide.

[0042] The open resonator of the present invention is suitable for measuring the conductivity of metal foil with higher accuracy.

[0043] REFERENCE SIGNS LIST 10 Fixing base 11, 211, 213 Concave reflecting mirror 12, 212, 214 Reflecting surface 15, 215 Excitation hole 16, 216 Excitation hole 20 Sample holder 21A, 21B Holding housing 22 Concave portion 23 Convex portion 24 Through hole 31, 31A, 31B Sample holding plate 32 Through hole 34 Glass film 35 Metal foil 41, 241 Input waveguide 42, 242 Output waveguide 100, 200 Fabry-Perot resonator C, C1, C2 Central axis D, D1, D2 Spacing R, R1, R2 Radius of reflecting surface N Normal

Claims

1. An open resonator comprising: a concave reflecting mirror having a concave reflecting surface made of metal; a signal input section attached to a first excitation hole formed in said concave reflecting mirror and inputting an input signal; a signal output section attached to a second excitation hole formed in said concave reflecting mirror and outputting an output signal; and a sample holding sheet having a flat surface that is substantially perpendicular to the central axis of said reflecting surface and disposed opposite said reflecting surface, said sample holding sheet having a metal foil whose resonance characteristics are to be measured attached to said flat surface.

2. An open resonator comprising: a first concave reflecting mirror having a first concave reflecting surface made of metal; a second concave reflecting mirror having a second concave reflecting surface made of metal; a signal input section attached to a first excitation hole formed in the first concave reflecting mirror and inputting an input signal; a signal output section attached to a second excitation hole formed in the first concave reflecting mirror or the second concave reflecting mirror and outputting an output signal; and a sample holding sheet having a flat surface to which a metal foil whose resonance characteristics are measured is attached, wherein the input signal is reflected in the direction of the second concave reflecting mirror by the metal foil attached to the sample holding sheet, causing resonance between the first concave reflecting mirror and the second concave reflecting mirror via the metal foil.

3. An open resonator as described in claim 1 or 2, further comprising a first sample holding housing and a second sample holding housing having a through hole, and the sample holding sheet to which the metal foil is attached is positioned between the first sample holding housing and the second sample holding housing with the metal foil exposed from the through hole.

4. An open resonator as described in claim 1 or 2, further comprising a first sample holding plate and a second sample holding plate having through holes, wherein the sample holding sheet to which the metal foil is attached is positioned between the first sample holding plate and the second sample holding plate with the metal foil exposed from the through holes.

5. The open resonator according to claim 1 or 2, wherein the sample holding sheet is made of glass.

6. The open resonator according to claim 1 or 2, wherein the sample holding sheet is made of metal.

7. An open resonator according to claim 1 or 2, wherein a dielectric is adhered to a first surface of said metal foil, and a second surface of said metal foil opposite to said first surface is attached to said sample holding sheet.

8. A method for measuring the conductivity of a metal foil using the open resonator described in claim 1 or 2, comprising the steps of: measuring a first resonance characteristic by reflecting the input signal by a metal having a known conductivity and detecting the output signal; attaching the metal foil to the sample holding sheet; measuring a second resonance characteristic by reflecting the input signal by the metal foil attached to the sample holding sheet and detecting the output signal; and calculating the conductivity of the metal foil using the known conductivity, the Q value obtained from the first resonance characteristic, and the Q value obtained from the second resonance characteristic.

9. The method for measuring electrical conductivity according to claim 8, wherein a dielectric is adhered to a first surface of the metal foil, and a second surface of the metal foil opposite to the first surface is attached to the sample holding sheet.

Images