Measuring device, measuring method, and program

Abstract

An optical system (2): emits an electromagnetic wave (W) that enters from an electromagnetic wave source (1) toward a sample (S) held by a stage (3) that can be driven along the propagation direction of the electromagnetic wave (W); receives a reflected wave (Ws) from the sample (S); and emits a composite wave in which the reflected wave (Ws) and stray light (Wr) interfere with one another. A detector (4) detects the intensity of the composite wave and outputs a detection signal (DET) indicating the detection result. A control unit (6) controls the electromagnetic wave source (1) to switch the frequency of the electromagnetic wave (W) between a plurality of frequencies, and controls the stage (3) such that the stage (3) moves to a plurality of positions for the respective plurality of frequencies. A signal processing unit (5) measures the spectrum of the composite wave in response to the detection signal (DET), and acquires the spectrum of the reflected wave (Ws) by removing the spectrum of the stray light (Wr), acquired in advance, from the spectrum of the composite wave.

Description

Measurement device, measurement method, and program

[0001] The present disclosure relates to a measurement device, a measurement method, and a program.

[0002] The technique of irradiating an object with electromagnetic waves and measuring the reflected or transmitted electromagnetic waves is a useful means of understanding the shape, composition, and corrosion state of buried objects inside a structure, which cannot be determined from information obtained from the surface of the object. This technique is used in a wide range of fields, such as assessing the lifespan of buildings and inspecting the quality of industrial products.

[0003] For example, Non-Patent Document 1 proposes a method of measuring the internal structure of a structure by irradiating electromagnetic waves in the megahertz to gigahertz range onto a structure made of concrete, and detecting the electromagnetic waves reflected from the incident surface and the back surface opposite the incident surface, as well as the waves reflected from an iron ball embedded in the concrete.

[0004] Furthermore, in order to achieve both straightness and high resolution, the use of millimeter waves to terahertz waves has been attracting attention in recent years, and applications are beginning to emerge in fields closely related to our daily lives where safety is essential, such as distance measurement technology in autonomous driving and airport security inspections.

[0005] For example, Non-Patent Document 2 introduces a method of inspecting the presence or absence of voids in a cable by irradiating the cable with terahertz waves and detecting the electromagnetic waves that have passed through the cable.

[0006] JH Bungey, SG Millard, “Radar inspection of structures,” Proceedings of the Institution of Civil Engineers, Structures and Buildings, Volume 99, Issue 2, May 1993, pp. 173-186; Peter H. Siegel, “Terahertz Technology,” IEEE Transactions on Microwave Theory and Technology, Vol. 50, No. 3, March 2002, pp. 910-928; Yukio Kono, “High-Sensitivity Terahertz Wave Detector - Application to Near-Field Imaging,” Journal of Optics, Optical Society of Japan, Vol. 38, No. 2, pp. 81-88, 2009.

[0007] Common electromagnetic wave technology often uses single-wavelength measurements, which can identify materials or measure distances using radar technology by selecting a frequency that matches the transmission characteristics of the target medium, but it is difficult to determine whether the identified difference is due to a difference in the material or a change in its properties.

[0008] Meanwhile, technology for estimating the state of an object is being actively researched in the field of light, and in the visible light and near-infrared regions, technology has been developed to estimate the surface state of an object by measuring its spectrum.

[0009] Therefore, it is conceivable to estimate the internal structure of an object by irradiating it with electromagnetic waves in the millimeter to terahertz range and measuring the spectrum. However, it is known that electromagnetic waves in the millimeter to terahertz range have relatively long wavelengths and, depending on the principles of electromagnetic wave generation, have a long coherence length, which can result in a large effect of interference.

[0010] In the optical system used for the above-mentioned single-wavelength measurement, the effects of interference are suppressed by configuring the optical system to match the wavelength. In contrast, when performing spectrum measurement using electromagnetic waves of multiple wavelengths in the millimeter wave to terahertz wave bands, the optical system must be adjusted to reduce the effects of interference each time the electromagnetic wave wavelength is switched. This makes it difficult to irradiate an object with electromagnetic waves in the millimeter wave to terahertz wave bands and perform spectrum measurement within a feasible time and effort.

[0011] The present disclosure has been made in consideration of the above circumstances, and aims to efficiently measure the spectrum of reflected waves generated by irradiating an object with electromagnetic waves while suppressing the effects of interference.

[0012] a signal processing unit that measures the spectrum of the composite wave, the spectrum having an intensity dependent on the frequency of the electromagnetic wave and the position of the stage, in accordance with the detection signal; and a signal processing unit that measures the spectrum of the composite wave, the spectrum having an intensity dependent on the frequency of the electromagnetic wave and the position of the stage, in accordance with the detection signal; and a signal processing unit that measures the spectrum of the composite wave, the spectrum having an intensity dependent on the frequency of the electromagnetic wave and the position of the stage, in accordance with the detection signal;

[0013] A measurement method according to one aspect of the present disclosure includes emitting an electromagnetic wave, using an optical system to emit the electromagnetic wave toward a measurement object held by a stage that can be driven along the propagation direction of the electromagnetic wave, receiving a reflected wave of the electromagnetic wave from the measurement object, and emitting a composite wave resulting from interference between the reflected wave and stray light generated by the incidence of the electromagnetic wave from a path different from the propagation path of the electromagnetic wave, detecting the composite wave emitted from the optical system, outputting a detection signal indicating the detection result, switching the frequency of the electromagnetic wave among a plurality of frequencies, moving the stage to a plurality of positions for each of the plurality of frequencies, measuring the spectrum of the composite wave having an intensity that depends on the frequency of the electromagnetic wave and the position of the stage according to the detection signal, and removing the spectrum of the stray light that was measured in advance from the spectrum of the composite wave, thereby obtaining the spectrum of the reflected wave.

[0014] a stage for holding a measurement object to be irradiated with the electromagnetic waves and capable of being driven in a propagation direction of the electromagnetic waves; an optical system for emitting the electromagnetic waves emitted from the electromagnetic wave source to the measurement object, receiving a wave of the electromagnetic waves reflected by the measurement object and emitting a composite wave resulting from interference between the reflected wave and stray light generated by the incidence of the electromagnetic waves, from a path different from the propagation path of the electromagnetic waves; and a detector for detecting the intensity of the composite wave emitted from the optical system and outputting a detection signal indicating the detection result, the program causes a computer to control the electromagnetic wave source to switch the frequency of the electromagnetic waves among a plurality of frequencies; a stage-controlling process for controlling the stage to move to a plurality of positions for each of the plurality of frequencies; a process for measuring the spectrum of the composite wave, which has an intensity that depends on the frequency of the electromagnetic waves and the position of the stage in accordance with the detection signal; and a process for obtaining the spectrum of the reflected wave by removing the spectrum of the stray light that was previously obtained from the spectrum of the composite wave.

[0015] According to the present disclosure, it is possible to efficiently measure the spectrum of reflected waves generated by irradiating an object with electromagnetic waves while suppressing the influence of interference.

[0016] 1 is a diagram schematically illustrating the configuration of a measurement device according to a first embodiment. FIG. 2 is a diagram illustrating the configuration of the measurement device according to the first embodiment in more detail. FIG. 3 is a diagram illustrating the relationship between the distance from the measurement device according to the first embodiment to a sample and the amplitude component of a detection signal. FIG. 4 is a diagram illustrating an example of the spectrum of a measured composite wave. FIG. 5 is a diagram illustrating an example of acquiring a spectrum at a specific distance. FIG. 6 is a diagram illustrating an example of acquiring distance dependency of electromagnetic wave interference at a specific frequency. FIG. 7 is a diagram illustrating an example of measurement conditions expressed by planes Px and Pf. FIG. 8 is a flowchart of spectrum measurement by the measurement device according to the first embodiment. FIG. 9 is a flowchart of spectrum separation processing by the measurement device according to the first embodiment. FIG. 10 is a diagram illustrating the spectrum of a composite wave and the spectrum of a background measured on a sample made of a polyethylene plate by the method of Comparative Example 1. FIG. 11 is a diagram illustrating the spectrum of a composite wave and the spectrum of a background measured on a sample made of a polyethylene plate by the method of Comparative Example 2. FIG. 12 is a diagram illustrating the spectrum measured in Example 1. FIG. 13 is a diagram illustrating the spectrum measured in Example 2. FIG. 14 is a diagram illustrating the spectrum measured in Example 3. FIG. 15 is a diagram schematically illustrating the configuration of a measurement device according to a second embodiment. FIG. 16 is a flowchart of spectrum separation processing by the measurement device according to the second embodiment. FIG. 17 is a diagram illustrating positional deviation. FIG. 18 is a diagram illustrating the relationship between the distance to the sample and the response when a sample in which an embedded object is buried is measured according to the second embodiment. Fig. 21 is a diagram showing a spectrum measured in Example 4. Fig. 22 is a diagram showing a spectrum measured in Example 5. Fig. 23 is a diagram showing a comparison result between the spectrum of the buried object in Fig. 19 and the spectrum of the buried object in Fig. 20. Fig. 24 is a diagram showing a spectrum measured in Example 6. Fig. 25 is a diagram showing an example of a hardware configuration.

[0017] Specific embodiments will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity of explanation, the following description and drawings have been simplified as appropriate. The same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0018] A measurement device 100 according to embodiment 1 will be described. The measurement device 100 is configured as a device that measures the spectrum of a medium of a sample by irradiating the sample, which is an object to be measured, with electromagnetic waves while switching frequencies and receiving the reflected waves.

[0019] In a typical measurement device designed for single-wavelength measurements, as described above, it is necessary to eliminate changes in the interference state caused by the influence of the coherence length of the electromagnetic wave each time the frequency is switched, which requires adjustment of the measurement distance and the interference state within the optical system that guides the electromagnetic wave.

[0020] In contrast, the measurement device 100 can automatically and efficiently acquire the spectrum of the reflected wave from the sample even when the frequency of the electromagnetic wave is changed, without the need to adjust the measurement distance or the optical system.

[0021] 1 schematically shows the configuration of a measurement apparatus 100 according to the first embodiment. The measurement apparatus 100 includes an electromagnetic wave source 1, an optical system 2, a stage 3, a detector 4, a signal processing unit 5, and a control unit 6.

[0022] The electromagnetic wave source 1 is configured to emit electromagnetic waves of a predetermined frequency, for example, in the millimeter wave to terahertz wave range, to the optical system 2. The millimeter wave frequency is 30 GHz to 300 GHz (equivalent to approximately 1 mm to 10 mm in wavelength), and the terahertz wave frequency is, for example, 300 GHz to 3 THz (equivalent to approximately 100 μm to 1 mm in wavelength). The electromagnetic wave source 1 emits electromagnetic waves of a desired frequency within the millimeter wave band and terahertz wave band to the optical system 2. Hereinafter, the electromagnetic waves emitted by the electromagnetic wave source 1 will be referred to as electromagnetic waves W. Note that the frequency of the electromagnetic waves W is not limited thereto, and may be, for example, centimeter waves with frequencies of 3 GHz to 30 GHz (equivalent to approximately 1 cm to 10 cm in wavelength) or frequencies in the microwave range (frequency 300 MHz to 1 m, equivalent to approximately 1 mm to 1 m in wavelength) including the millimeter waves. The frequency of the electromagnetic waves W can be set appropriately depending on the object to be measured.

[0023] The optical system 2 emits an electromagnetic wave W incident from the electromagnetic wave source 1 to a sample S placed on a stage 3, and also emits a reflected wave W reflected by the sample S.ｓ 2 shows a more detailed configuration of the measurement apparatus 100 according to the first embodiment. The optical system 2 includes a lens 21, a beam splitter 22, lenses 23 and 24, and a housing 25.

[0024] The electromagnetic wave W emitted from the electromagnetic wave source 1 is collimated by a lens 21, and then a portion of the wave passes through a beam splitter 22. The electromagnetic wave W that has passed through the beam splitter is converged by a lens 23 and is incident on a sample S placed on a stage 3.

[0025] A part or all of the electromagnetic wave W incident on the sample S is reflected by the surface of the sample S, resulting in a reflected wave W ｓ The reflected wave W incident on the lens 23 ｓ is reflected by the beam splitter 22 and enters the lens 24. Then, the reflected wave W ｓ is converged by the lens 24 and enters the detector 4 .

[0026] In this configuration, the detector 4 receives a reflected wave W from the sample S. ｓ In addition, stray light W due to internal reflection of the optical system 2 ｒ is incident on the beam splitter 22. A portion of the electromagnetic wave W incident on the beam splitter 22 is reflected by the beam splitter 22 in a direction different from that of the electromagnetic wave W that passed through the beam splitter 22. The electromagnetic wave W reflected by the beam splitter 22 is scattered by the housing 25 and the like, and becomes stray light inside the optical system 2. Note that the cause of stray light is not limited to this, and it can be caused by various factors such as reflection by components other than the beam splitter 22 and scattering caused by other components. Stray light Wr, which is a composite wave of stray light caused by these various factors, is converged by the lens 24 and enters the detector 4.

[0027] That is, a composite wave resulting from interference between the reflected wave Ws converged by the lens 24 and the stray light Wr is incident on the detector 4 .

[0028] The stage 3 is configured to be movable in both directions along the beam axis of the electromagnetic wave W. That is, the stage 3 can move along the beam axis of the electromagnetic wave W in a direction from a far position to a near position with respect to the emission port of the electromagnetic wave W of the optical system 2, and in a direction from a near position to a far position.

[0029] As described above, the detector 4 receives the reflected wave W ｓ and stray light W ｒ Therefore, the detector 4 detects the reflected wave W ｓ and stray light W ｒ The detector 4 detects a composite wave resulting from interference between the two and outputs a detection signal DET indicating the detection result to the signal processing unit 5. The detector 4 is configured as an electronic device detector using, for example, a Schottky barrier diode, and outputs a current signal indicating the light intensity of the incident composite wave as the detection signal DET. The electromagnetic wave detector is not limited to the above example, and various detectors can be used. When the electromagnetic wave is a terahertz wave, various detectors such as thermal and quantum detectors other than the above electronic device detector can be used, for example, as described in Non-Patent Document 3. Note that the detection signal DET output by the detector 4 is not limited to a current signal, and may be a voltage signal depending on the detection method.

[0030] The signal processing unit 5, the details of which will be described later, monitors the detection signal DET to obtain the spectrum of the amplitude of the reflected wave Ws. However, even if the composite wave is observed as it is, the reflected wave Ws indicating information about the sample S is not obtained. ｓ In addition, since the state of interference of the stray light generated in the optical system 2 changes depending on the frequency of the electromagnetic wave, the stray light W incident on the detector 4 ｒ varies depending on the frequency. ｓ To selectively observe the stray light W ｒ Therefore, the signal processing unit 5 removes the influence of the reflected wave W included in the composite wave according to the following principle and procedure. ｓ and stray light W ｒ and are spectrally separated.

[0031] The control unit 6 controls the operations of the electromagnetic wave source 1, the stage 3 and the signal processing unit 5 by outputting control signals CON1 to CON3 to the electromagnetic wave source 1, the stage 3 and the signal processing unit 5, respectively.

[0032] Next, the principle of spectrum separation in the signal processing unit 5 will be explained. Here, it is assumed that there is no reflecting object in the medium that constitutes the sample S. In this case, when the frequency of the electromagnetic wave is f, the composite wave W incident on the detector 4 is ｃ is expressed by the following formula: In addition, c ０ is the speed of light in a vacuum. ｒ (f) is the stray light W ｒ is the amplitude of ｓ (f) is the reflected wave W on the surface of the sample S. ｓ x is the distance from the measuring device 100 to the sample S, that is, the distance from the exit of the optical system 2 for the electromagnetic wave W to the surface of the sample S. The stray light W incident on the detector 4 ｒ is a composite wave of multiple stray lights generated inside the optical system 2, and θ is the stray light W ｒ The phase shift of C ｒｓ (f, x) is the composite wave W incident on the detector 4 ｃ is the amplitude of θ ｓ (f, x) is generated by interference and is the phase shift of the composite wave with respect to the electromagnetic wave W emitted from the electromagnetic wave source 1. For simplicity, in the following, C ｒ (f), C ｓ (f), C ｒｓ (f, x) and θ ｓ (f, x) are simply C ｒ , C ｓ , C ｒｓ and θ ｓ It can also be written as:

[0033] The detection signal DET output by the detector 4 can be considered to represent the amplitude component of equation [1]. Hereinafter, the voltage of the voltage signal representing the amplitude of the detection signal DET will also be referred to as a response voltage. When the detection signal DET is a current signal, the detection signal DET may be used as is as the response voltage. When the detection signal DET is a current signal, a voltage signal converted from the detection signal DET by the signal processing unit 5 may be used as the response voltage. The amplitude component I ｓ (f, x) is expressed by the following formula. For simplicity, I ｓ (f, x) simply as I ｓ It can also be written as: however, 3 shows the relationship between the distance x from the measurement device 100 to the sample S and the amplitude component I of the detection signal DET. ｓ In this way, the amplitude component I of the detection signal DET ｓ is the origin (0,0) and the point (C ｒ , 0) with radius C ｓ As shown in Figure 3, point P moves on the circle according to the change in Θ. In this case, the amplitude I when the distance x is a typical value is ｓ is expressed as follows:

[0034] Here, when measurements are performed while changing the distance x, as can be seen from equation [2] and FIG. 3, the amplitude component I ｓ is the maximum value maxI ｓ and the minimum value minI ｓ The stray light W ｒ The amplitude C ｒ and the reflected wave W ｓ The amplitude C ｓ When the cases are divided according to the magnitude relationship between the stray light W ｒ The amplitude C ｒ and reflected wave W ｓ The amplitude C ｓ is expressed as follows:

[0035] C ｒ >C ｓ In this case, the stray light W ｒ The amplitude C ｒ and reflected wave W ｓ The amplitude Cｓ is expressed as follows: C ｒ <C ｓ In this case, the amplitude C of the stray light Wr ｒ and reflected wave W ｓ The amplitude C ｓ is expressed as follows: C ｒ =C ｓ In the case of ｓ = 0, so the stray light W ｒ The amplitude C ｒ and reflected wave W ｓ The amplitude C ｓ is expressed as follows:

[0036] From the above, the stray light W ｒ The amplitude C ｒ and the reflected wave W ｓ The amplitude C ｓ If the magnitude relationship between ｒ The amplitude C ｒ and the reflected wave W ｓ The amplitude C ｓ It can be determined that:

[0037] In addition, stray light W ｒ The amplitude C ｒ and the reflected wave W ｓ The amplitude C ｓ The magnitude relationship between the reflected wave W and the reflected wave W can be determined in advance by various methods. For example, a preliminary measurement is performed using an electromagnetic wave absorber as the sample S, and the reflected wave W from the sample is ｓ can be suppressed to zero or a negligibly small level. ｒ The amplitude C ｒ Only the ion concentration can be measured.

[0038] As a result, the amplitude I of the composite wave when measured using the sample to be measured is ｓ The reflected wave W contained in ｓ The amplitude C ｓ is calculated by subtracting the stray light W ｒ The amplitude C ｒ can be separated using

[0039] Based on the above principle, the signal processing unit 5 calculates the amplitude I of the composite wave. ｓ , stray light W ｒ The amplitude C ｒ and the reflected wave W ｓ The amplitude C ｓ and the reflected wave W ｓ The amplitude C ｓ Only the following can be extracted.

[0040] Next, we will explain the spectrum measurement by the measurement apparatus 100. The measurement apparatus 100 measures the spectrum while changing the frequency f of the radio waves output by the electromagnetic wave source 1 and also changing the distance between the measurement apparatus 100 and the stage.

[0041] The frequency switching of the electromagnetic wave W in spectrum measurement will be described. The frequency of the electromagnetic wave W output from the electromagnetic wave source 1 is sequentially switched to one of a plurality of frequencies spaced apart by a predetermined interval in the band to be measured. For example, Nf frequencies are set within the frequency measurement range, and the lower limit frequency is set as f １ , the upper limit frequency is f Ｎｆ , the interval between two adjacent frequencies is Δf. Here, Nf is an arbitrary integer equal to or greater than 2. If j is an integer equal to or greater than 1 and equal to or less than Nf, the jth frequency f counting from the low frequency side is ｊ is f ｊ = f １ +(j-1)Δf.

[0042] Next, the movement of the stage 3 during spectrum measurement will be described. The stage 3 moves sequentially to one of a plurality of positions that are spaced apart by a predetermined distance within the driving range during measurement. For example, Nx positions are set within the driving range of the stage 3, and the position farthest from the measurement device 100 is designated as x. １ , the closest position is x Ｎｘ , the distance between two adjacent positions is Δx. Here, Nx is an arbitrary integer equal to or greater than 2. If k is an integer equal to or greater than 1 and equal to or less than Nx, the kth position x counting from the side farthest from the measuring device 100 is ｋ is x ｋ = x １ +(k-1)Δx.

[0043] Then, by measuring the amplitude Is of the composite wave expressed by equation [2] for each of Nf × Nx measurement conditions consisting of Nf frequencies and Nx positions, the spectrum of the composite wave can be measured as a function of frequency f and position x.

[0044] Needless to say, the control unit 6 controls the operations of the electromagnetic wave source 1, stage 3, and signal processing unit 5 using the control signals CON1 to CON3, thereby making it possible to perform measurements under Nf×Nx different measurement conditions.

[0045] FIG. 4 shows an example of the spectrum of a measured composite wave. Here, the horizontal axis represents frequency f, and the vertical axis represents distance x. The vertical axis represents the response voltage V corresponding to amplitude Is. Unless otherwise specified, graphs showing the distance dependence of spectrum and interference display voltage V instead of amplitude Is. Using the above-described measurement method, the spectrum of the composite wave can be measured as a curved surface in three-dimensional space consisting of Nf × Nx observed values ​​of amplitude Is (or voltage V) of the composite wave. From the measurement results, it is possible to obtain the spectrum of the composite wave at a specific distance, or the distance dependence of electromagnetic wave interference at a specific frequency.

[0046] An example of obtaining a spectrum at a specific distance is shown in Figure 5. As shown in Figure 5, the spectrum at a specific distance can be obtained by slicing the spectrum of the composite wave measured on a plane Px parallel to the fV plane corresponding to the specific distance (250 mm in Figure 5).

[0047] An example of obtaining the distance dependency of electromagnetic wave interference at a specific frequency is shown in Figure 6. As shown in Figure 6, by slicing the spectrum of the composite wave measured on a plane Pf parallel to the x-V plane corresponding to a specific frequency (15 GHz in Figure 6), the state of electromagnetic wave interference at the specific frequency can be obtained.

[0048] Furthermore, the point where the plane Px and the plane Pf intersect represents one measurement condition. Figure 7 shows an example of measurement conditions represented by the plane Px and the plane Pf. As shown in Figure 7, the intersection of the plane Px (250 mm) and the plane Pf (15 GHz) corresponds to a single measurement value of the amplitude Is.

[0049] 8 shows a flowchart of spectrum measurement by the measurement apparatus 100 according to the first embodiment. The measurement apparatus 100 executes the following steps ST1 to ST3 to measure the spectrum of a composite wave including a reflected wave from the sample S, and separates the spectrum of the reflected wave. Note that the storage unit 51 of the signal processing unit 5 has equations [5] to [7] stored in advance.

[0050] Step ST1: There is no sample to be measured on the stage 3, or a dummy sample such as a radio wave absorber that does not reflect radio waves is placed on the stage 3, so that the spectrum in the measurement band is measured in a state where no reflected waves are returned to the measurement device 100. This allows the stray light W generated by the measurement device 100, which does not contain any reflected wave components, to be measured. ｒ The spectrum measured here is used as the stray light W ｒ The spectrum is kept as a reference spectrum.

[0051] Stray light W ｒ As described above, the measurement of the reference spectrum of is assumed to be in a state where there is no reflected wave, and therefore is considered to be independent of the position of the stage 3. In other words, by switching the frequency of the electromagnetic wave W in Nf ways without moving the stage 3, the stray light W ｒ It should be noted that, for example, when unwanted reflected waves from the stage 3 and its surrounding members and devices are incident on the measuring device 100, these unwanted reflected waves may be reflected as stray light W ｒ In this case, as described above, the stage 3 is moved to Nx positions for each of the Nf frequencies of the electromagnetic wave W, and the stray light W ｒ By observing the maximum value of ｒ A reference spectrum of may be measured.

[0052] Step ST2: Next, the sample S to be measured is placed on the stage 3, and the spectrum in the measurement band is measured. ｓ and stray light W ｒ The spectrum of the composite wave produced by the interference between the two is measured.

[0053] Step ST3: The signal processing unit 5 calculates the stray light W measured in advance in step ST1. ｒ Using the reference spectrum, the reflected wave W is calculated from the spectrum of the composite wave measured in step ST2. ｓ 9 is a flowchart showing the spectrum separation process performed by the measurement apparatus 100 according to the first embodiment.

[0054] Step S1: Set 1 as the initial value of the counter value j that specifies the frequency (j=1).

[0055] Step S2: Refer to the spectrum of the composite wave and find the jth frequency f ｊ Position x at １ ~x Ｎｘ From the Nx measured values ​​at ｓ and the minimum value minI ｓ and asks for.

[0056] Step S3: Obtained maximum value maxI ｓ and the minimum value minI ｓ By substituting into the following equation, the jth frequency f ｉ The reflected wave W ｓ The amplitude C ｓ and stray light W ｒ The amplitude C ｒ The first amplitude C １ and the second amplitude C ２ Calculate. Here, it is to be understood that the first amplitude C １ is the second amplitude C ２ is greater than (C １ >C ２ In the following steps, the calculated first amplitude C １ is the second amplitude C ２ By determining the magnitude relationship between the reflected wave W ｓ The amplitude C ｓ It is possible to determine whether it is appropriate to use it for separation.

[0057] Step S4: First amplitude C １ is the second amplitude C ２ Is it equal to (C １ =C ２ ) is determined.

[0058] Step S5: First amplitude C １ is the second amplitude C ２ (Step S4: YES), the amplitude I of the measured composite wave is calculated using Equation [7]. ｓ Reflected light W contained in ｓ The amplitude C ｓ Then, the process proceeds to step S9.

[0059] Step S6: First amplitude C １ is the second amplitude C ２ If it is different from (step S4: NO), the first amplitude C １ and the second amplitude C ２ Which of the following is the stray light W? ｒ The j-th frequency f ｉ Reference amplitude C at ｒ＿ＲＥＦ Determine whether it is close to

[0060] Step S7: First amplitude C １ is the second amplitude C ２ Stray light W ｒ Reference amplitude C ｒ＿ＲＥＦ (step S6: YES), the reflected light W ｓ The amplitude C ｓ That is, the first amplitude C １ is the stray light W ｒ The amplitude C ｒ , the second amplitude C ２ is the reflected light W ｓ The amplitude C ｓ Then, the process proceeds to step S9.

[0061] Step S8: Second amplitude C ２ is the first amplitude C １ than the reference amplitude C ｒ＿ＲＥＦ (step S6: NO), the reflected light W ｓ The amplitude C ｓ That is, the second amplitude C ２ is the stray light W ｒ The amplitude C ｒ , the first amplitude C １ is the reflected light W ｓ The amplitude C ｓThen, the process proceeds to step S9.

[0062] Step S9: Determine whether the counter value j is the maximum value Nf (j=Nf).

[0063] Step S10: If the counter value j is not the maximum value Nf (step S9: NO), the counter value j is incremented by 1, and the process returns to step S2.

[0064] Step S11: If the counter value j is the maximum value Nf (step S9: YES), the calculated frequency f １ ~f Ｎｆ Nf amplitudes C ｓ Based on this, the reflected light W ｓ Construct a spectrum of.

[0065] By the above procedure, the measurement apparatus 100 can separate the spectrum of the reflected wave from the spectrum of the composite wave.

[0066] Next, an example of measuring the spectrum of a reflected wave using the measurement device 100 will be described. Here, measurements were performed using samples of three different materials in a frequency range of 7.5 to 24 GHz and a distance measurement range of 35 mm, 235 to 270 mm away from the measurement device 100. When acquiring the interference state by varying the distance at a certain frequency, the period of the change in intensity of the response voltage is half the wavelength of the electromagnetic wave. Therefore, the period is approximately 20 mm at a frequency of 7.5 Hz and approximately 6.25 mm at a frequency of 24 Hz. Therefore, a measurement range of at least approximately 20 mm is required in the frequency range of 7.5 to 24 GHz. Furthermore, since the period is approximately 6.25 mm at a frequency of 24 Hz, the distance between two adjacent sampling points must be 3.125 mm or less. In the following examples, the distance step size was set to 0.5 mm in order to measure the phase shift described below.

[0067] Furthermore, to examine the effects of this method, spectra obtained by two different measurement methods were used as comparative examples. Comparative Example 1 is a spectrum measured by adjusting the distance to the sample so that the response was maximized at each frequency. Comparative Example 2 is a spectrum measured by fixing the distance from the measurement device to the sample at the focal position of the optical system. In Comparative Examples 1 and 2, a background was acquired in advance, and the spectrum of the composite wave was obtained by taking the difference between the measurement data and the background.

[0068] Example 1 Spectral measurements were carried out using a polyethylene plate as a sample under the above-mentioned measurement conditions.

[0069] FIG. 10 shows the spectrum of the synthetic wave and the background spectrum measured on a sample made of a polyethylene plate using the method of Comparative Example 1. FIG. 11 shows the spectrum of the synthetic wave and the background spectrum measured on a sample made of a polyethylene plate using the method of Comparative Example 2. As can be seen from FIGS. 10 and 11 , these methods are significantly affected by electromagnetic wave interference, and the spectrum of the synthetic wave and the background spectrum are similar. Depending on the frequency, there are cases where the amplitude of the background is larger than the amplitude of the synthetic wave. Therefore, even if the difference between the spectrum of the synthetic wave and the spectrum of the background is taken, it is theoretically difficult to accurately obtain the spectrum of the reflected wave.

[0070] 12 shows a comparison of the spectrum measured by this method with the spectra obtained by Comparative Examples 1 and 2. In Comparative Example 1, the voltage value fluctuates greatly due to the influence of interference, and it is thought that the reliability of the measurement results is low. In Comparative Example 2, although an improvement over Comparative Example 1, the voltage value fluctuates greatly, and it is thought that the reliability of the measurement results is still low. In contrast, with this method, it is possible to suppress or eliminate the influence of interference, so that the fluctuations in the voltage value are small and it is clear that the reflected wave can be suitably extracted.

[0071] Example 2 Next, spectrum measurement was performed using an aluminum plate as a sample under the above-described measurement conditions. Note that the measurement conditions were the same as in Example 1 except for the sample. Figure 13 shows the spectrum measured in Example 2. As can be seen from Figure 13, the measurement device 100 was able to suppress or eliminate the influence of interference and preferably extract the reflected wave, just as in Example 1, even though the sample was different.

[0072] Example 3 Next, a spectrum was measured using a plate made of ZEONEX® 480, a cycloolefin polymer manufactured by Zeon Corporation, as a sample. The measurement conditions were the same as in Examples 1 and 2, except for the different sample. Figure 14 shows the spectrum measured in Example 3. As can be seen from Figure 14, the measurement device 100 was able to suppress or eliminate the influence of interference and preferably extract the reflected wave, similar to Examples 1 and 2, even though the sample was different.

[0073] As described above, according to this configuration, even if the materials of the samples to be measured are different, by performing spectral separation, it is possible to obtain the spectrum of the reflected wave from the sample without the need to adjust the measurement distance, etc.

[0074] In the first embodiment, the stray light W ｒ The amplitude C ｒ and reflected light W ｓ The amplitude C ｓ Since the magnitude relationship between the reflected light W and the reflected light W is unknown, the condition determination shown in steps S4 and S6 of FIG. ｓ The amplitude C ｓ In contrast, in the present embodiment, the equation used for separating the stray light W ｒ The amplitude C ｒ and reflected light W ｓ The amplitude C ｓ By fixing the magnitude relationship between the reflected light W ｓ The amplitude C ｓ A measuring device for separating the above will be described.

[0075] 15 is a schematic diagram showing the configuration of a measurement apparatus 200 according to the second embodiment. Compared to the measurement apparatus 100, the measurement apparatus 200 further includes a reflector 26 in the optical system 2. The other configuration of the measurement apparatus 200 is similar to that of the measurement apparatus 100, and therefore a description thereof will be omitted.

[0076] A part of the incident electromagnetic wave W is reflected by the beam splitter 22. Here, the electromagnetic wave reflected by the beam splitter 22 is referred to as the electromagnetic wave W ａ The reflector 26 reflects, for example, the electromagnetic wave W ａ is provided in the direction in which the electromagnetic wave W ａ The electromagnetic wave W reflected by the reflector 26 is ａ A part of the light passes through the beam splitter 22 and reaches the detector 4 as stray light W ｒ It is incident as

[0077] In this way, the reflector 26 is provided in the optical system 2 to prevent the stray light W incident on the detector 4 from ｒ By increasing the intensity of the stray light W ｒ The amplitude C ｒ , the reflected light W ｓ The amplitude C ｓ Always be larger than (C ｒ >C ｓ ) can be done.

[0078] Next, a procedure for measuring a spectrum in the measurement apparatus 200 will be described. In the spectrum measurement in the measurement apparatus 200, step ST3 for performing spectrum separation in the measurement apparatus 100 is replaced with step ST4. In the measurement apparatus 200, stray light W included in the composite wave is ｒ The amplitude C ｒ is the reflected light W ｓ The amplitude C ｓ is always larger than (C ｒ >C ｓ ) and this fact can be utilized to simplify the processing in step ST4. Fig. 16 shows a flowchart of the spectrum separation processing in the measurement apparatus according to the second embodiment.

[0079] Step ST4: The signal processing unit 5 calculates the stray light W measured in advance in step ST1. ｒUsing the reference spectrum, the reflected wave W is calculated from the spectrum of the composite wave measured in step ST2. ｓ 16, steps S3 to S8 are removed from step ST3 in FIG. 9, and step S12 is inserted instead of step S3. Note that steps S1, S2, and S9 to S11 are the same as in FIG. 9.

[0080] Step S1: Set 1 as the initial value of the counter value j that specifies the frequency (j=1).

[0081] Step S2: Refer to the spectrum of the composite wave and find the jth frequency f ｊ Position x at １ ~x Ｎｘ From the Nx measured values ​​at ｓ and the minimum value minI ｓ and asks for.

[0082] Step S12: The calculated maximum value maxI ｓ and the minimum value minI ｓ By substituting into the above equation [5], the amplitude I of the measured composite wave is obtained. ｓ Reflected light W contained in ｓ The amplitude C ｓ Calculate.

[0083] Step S9: Determine whether the counter value j is the maximum value Nf (j=Nf).

[0084] Step S10: If the counter value j is not the maximum value Nf (step S9: NO), the counter value j is incremented by 1, and the process returns to step S2.

[0085] Step S11: If the counter value j is the maximum value Nf (step S9: YES), the calculated frequency f １ ~f Ｎｆ Nf amplitudes C ｓ Based on this, a spectrum of the reflected light is constructed.

[0086] By the above procedure, the measurement device 200 can separate the spectrum of the reflected wave from the spectrum of the composite wave. Furthermore, the measurement device 200 can separate the spectrum of the reflected wave more easily than the measurement device 100, and is expected to achieve faster processing.

[0087] Furthermore, compared to the first embodiment, the path of stray light is controlled by the reflector, so that it is possible to prevent or suppress stray light from entering the detector 4 via other paths when no reflector is present. This also makes it possible to reduce the burden on the design of the measurement device, which takes into account stray light from unexpected paths.

[0088] Embodiment 3 In the first and second embodiments, an example was described in which the sample was made of a single material. However, the sample to be measured may contain objects of different compositions buried therein, such as rebar buried in a concrete pillar. In this case, it is preferable to be able to acquire not only the reflected wave from the sample surface but also the spectrum of the reflected wave from the buried object. If the reflected wave spectrum from the buried object can be acquired, it can be used as a non-destructive testing method for investigating the internal structure of the object to be measured, and is considered to be useful.

[0089] Therefore, in this embodiment, a method for detecting an object buried in a sample will be described by applying the spectral separation in the measurement device 100 described in Embodiment 1. Note that, hereinafter, an object buried in a sample and made of a material different from the medium constituting the sample will be simply referred to as an embedded object.

[0090] First, the reflected wave from the buried object will be explained. A part of the electromagnetic wave W incident on the sample S is reflected by the surface of the sample S, and the reflected wave W ｓ The electromagnetic wave W incident on the sample S returns to the optical system 2 as a reflected beam. The part of the electromagnetic wave W that is not reflected by the surface of the sample S propagates through the medium of the sample S and reaches the buried object M.

[0091] The electromagnetic wave W that reaches the buried object M is reflected by the surface of the buried object M, and becomes a reflected wave W ｍ Then, the light returns to the optical system 2.

[0092] In this case, the composite wave W ｃ is expressed by the following formula: In addition, C ｍ (f) is the reflected wave W from the buried object ｍ is the amplitude of ｒｍ (f, x) is the composite wave W incident on the detector 4 ｃ is the amplitude of θ ｍ (f, x) is caused by interference and is the phase shift of the composite wave relative to the electromagnetic wave W emitted from the electromagnetic wave source 1. d is the cover thickness of the buried object, i.e., the distance between the surface of the sample S and the surface of the buried object M. ε is the relative dielectric constant of the medium of the sample S. Here, it is assumed that the dielectric constant ε is a constant value in the frequency band of the electromagnetic wave irradiated to the sample S. In the following, C ｍ (f) is simply C for simplicity. ｍ It can also be written as:

[0093] As in the case of equation [2], the amplitude component I of the detection signal when an object M is buried in the sample S is ｍ is expressed by the following equation from equation [9]. Let us consider the positional deviation φ in equation

[10] . Figure 17 shows the positional deviation φ. Here, if a sample without an embedded object M (a reference sample S to be described later) is used, ＲＥＦ） In the spectrum of the composite wave when measuring ｊ The periodic pattern formed by the curve CV showing the relationship between the amplitude Im of the composite wave at the time and the position x of the stage 3 is defined as P ｍ In addition, a sample in which the buried object M does not exist (a reference sample S described later) ＲＥＦ） In the spectrum of the composite wave when measuring ｊ Amplitude of the composite wave at I ｓ The periodic pattern formed by the curve CV showing the relationship between the position x of the stage 3 and the ｓ In this case, the periodic pattern P ｍ and the periodic pattern P ｓ means that the same frequency f ｊ , it can be seen that the patterns oscillate with the same period in the x direction. However, due to differences in the measurement objects, the periodic pattern Pｍ and the periodic pattern P ｓ When these are overlapped, a positional deviation occurs in the x direction. ｍ and the periodic pattern P ｓ 17, x is converted to Θ based on equation [3].

[0094] reflected wave W ｓ and W ｍ The amplitude D(f) of the composite wave is given by the following equation: Furthermore, cos φ and sin φ are expressed by the following equations. Note that Θ is the same as in equation [3]. ｍ For simplicity, (f, x) is simply I ｍ For simplicity, D(f) is also written simply as D.

[0095] In this state, the spectrum of the composite wave is measured and spectral separation is performed in the same manner as in the first embodiment, whereby the stray light W ｒ The spectrum of the reflected wave W ｓ and W ｍ The spectrum of the amplitude D of the composite wave of the above can be obtained.

[0096] In this embodiment, the amplitude D of the composite wave is converted into the amplitude W of the reflected wave. ｍ The amplitude C ｍ In order to extract the reflected wave W ｓ The amplitude C ｓ Here, the reflected wave W ｓ The amplitude C ｓ is a reference sample S made of the same material as sample S, but without the buried object M embedded therein. ＲＥＦ is assumed to be acquired in advance by performing the same measurement as described in the first embodiment. Here, the memory unit 51 of the signal processing unit 5 stores the measured reflected wave W ｓ The amplitude C ｓ is stored in advance.

[0097] 18 shows the relationship between the distance x to the sample S and the response when measuring the sample S in which the buried object M is buried. ｍ is the origin (0,0) and the point (C ｒ 18, the point P moves on the circle with the center at Θ (0), and the point P moves on the circle with the center at Θ (0).

[0098] As mentioned above, the displacement φ is a function of a single frequency f ｊ The curve PL when there is a buried object M measured in ｍ and the curve PL when there is no buried object ｓ This can be easily determined by comparing

[0099] The reflected wave W from the surface of the sample S ｓ The amplitude C ｓ When the positional deviation φ is given in advance, the amplitude D of the composite wave measured is used to calculate the reflected wave W by the buried object M. ｍ The amplitude C ｍ is expressed by the following equation: Here, the positional deviation φ is stored in advance in the storage unit 51 of the signal processing unit 5.

[0100] As explained above, according to this method, even if the depth d of the buried object and the relative dielectric constant ε of the sample S are unknown, the reflected wave W ｍ The amplitude C ｍ can be measured and its spectrum can be obtained.

[0101] Next, an example of measuring the spectrum of a reflected wave in embodiment 2 will be described. Here, measurements were performed using three different types of samples.

[0102] Example 4: Spectral measurements were performed on a sample in which an aluminum plate was embedded in a polyethylene plate under the same measurement conditions as in Examples 1 to 3. In this example, the aluminum plate was embedded at a depth of 21 mm from the surface of the polyethylene plate on the side where the electromagnetic waves were incident. Figure 19 shows the spectrum measured in Example 4. Figure 19 also shows the spectrum of a reference sample made of a polyethylene plate as a comparative example.

[0103] As shown in FIG. 19, the measurement device 100 measures the reflected wave W ｍ The amplitude C ｍ is the reflected wave W from the polyethylene plate, which is the reference sample. ｓ The amplitude C ｓ It can be seen that it is possible to measure it separately.

[0104] Example 5: Spectral measurements were performed on a sample in which an aluminum plate was embedded in a plate made of ZEONEX 480 under the same measurement conditions as in Examples 1 to 3. In this example, the aluminum plate was embedded at a depth of 2 mm from the surface of the plate made of ZEONEX 480 on the side where the electromagnetic wave was incident. Figure 20 shows the spectrum measured in Example 5. As a comparative example, Figure 20 also shows the spectrum measured using a plate made of ZEONEX 480 as a reference sample.

[0105] As shown in FIG. 20, the measurement device 100 can measure the reflected wave W from the aluminum plate, which is the embedded object, even if the medium in which the aluminum plate is embedded is changed. ｍ The amplitude C ｍ is the reflected wave W from the reference sample ZEONEX 480 plate. ｓ The amplitude C ｓ It can be seen that it is possible to measure it separately.

[0106] 21 shows the comparison result between the spectrum SP4 of the buried object in FIG. 19 and the spectrum SP5 of the buried object in FIG. 20. As shown in FIG. 21, even if the medium in which the aluminum plate is buried changes, the reflected wave W ｍ The amplitude C ｍ This shows that the measurement device 100 can acquire the spectrum of the reflected wave from the buried object while suppressing the dependency on the medium in which the buried object is buried.

[0107] Example 6: Spectral measurements were performed on a sample in which an aluminum plate was embedded in concrete under the same measurement conditions as in Examples 1 to 3. In this example, the aluminum plate was embedded at a depth of 10 mm from the surface of the concrete plate on the side where the electromagnetic waves were incident. Figure 22 shows the spectrum measured in Example 6. As a comparative example, Figure 22 also shows the spectrum of a reference sample consisting only of an aluminum plate, along with the results of sample measurement using a general method. The results of the sample measurement using the general method used as the comparative example were obtained by subtracting the results of measurement of a sample consisting only of concrete using the method of Comparative Example 1 from the results of measurement of a sample in which aluminum was embedded using the method of Comparative Example 1 described above.

[0108] In Figure 22, the sample measurement results obtained using a conventional method exhibited spectra that were far removed from reality, such as negative values, making the results unreliable. In contrast, while the spectral measurement using this method did not eliminate the effects of absorption by concrete and internal interference, the measurement results obtained using this method were close to those of the reference sample. This demonstrates that this configuration can effectively separate the spectrum of the reflected waves from a sample even when the sample is buried in a medium with a different composition.

[0109] As described above, the measuring device 100 can acquire the spectrum of the reflected wave from an embedded object even when the embedded object has a composition different from that of the medium on the sample surface.

[0110] The reflected wave W from the buried object M obtained by this method ｍ The amplitude C ｍ is affected by interference due to reflection between the surface of the buried object M and the surface of the sample S. In addition, the reflected wave W ｍ The spectrum of the reflected wave W ｍ The ideal spectrum is the product of the absorption spectrum of the medium of the sample S. Therefore, the reflected wave W ｍThe spectrum of the reflected wave is different from the spectrum of the reflected wave observed when the electromagnetic wave W is incident directly on the buried object M without passing through the medium of the sample S.

[0111] However, the reflected wave W ｍ The amplitude C ｍ Whether or not the reflected wave W due to the buried object M is measured can be easily determined by measuring the spectrum of the composite wave. ｍ By monitoring whether or not the spectrum can be acquired, it is possible to investigate whether or not there is an object buried in the sample, even if the internal structure of the sample is unknown.

[0112] As a result, the measuring device 100 can also detect buried objects in the sample.

[0113] Other Embodiments The present invention is not limited to the above-described embodiments, and modifications can be made as appropriate without departing from the spirit of the present invention. For example, in the third embodiment, the buried object M is detected by applying the spectral separation in the measurement device 100 according to the first embodiment, but the present invention is not limited to this. Similarly, the buried object M may be detected by applying the spectral separation in the measurement device 200 according to the second embodiment.

[0114] In the above-described embodiment, the present invention has been described mainly as a hardware configuration, but is not limited to this. For example, any processing in one or both of the signal processing unit 5 and the control unit 6 can be realized by having a CPU (Central Processing Unit) execute a computer program. In this case, the computer program can be stored using various types of non-transitory computer-readable medium and supplied to the computer. Non-transitory computer-readable medium includes various types of tangible storage medium. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, programmable ROMs (PROMs), erasable PROMs (EPROMs), flash ROMs, and random access memories (RAMs)). The program may also be supplied to a computer by various types of transient computer-readable media. Examples of transient computer-readable media include electric signals, optical signals, and electromagnetic waves. The transient computer-readable medium can supply the program to a computer via a wired communication path such as an electric wire or optical fiber, or via a wireless communication path.

[0115] Next, an example of a hardware configuration for realizing one or both of the signal processing unit 5 and the control unit 6 is shown. FIG. 23 shows an example of the hardware configuration. One or both of the signal processing unit 5 and the control unit 6 can be realized by a computer 1000, such as a dedicated computer or a personal computer (PC). However, the computer does not need to be physically single; multiple computers may be used when performing distributed processing. As shown in FIG. 23, the computer 1000 has a CPU (Central Processing Unit) 1001, a ROM (Read Only Memory) 1002, and a RAM (Random Access Memory) 1003, which are interconnected via a bus 1004. Note that although an explanation of the OS software for operating the computer will be omitted, it is assumed that the computer that constitutes this information processing device also has such software.

[0116] An input / output interface 1005 is also connected to the bus 1004. To the input / output interface 1005, for example, an input unit 1006 including a keyboard, mouse, sensor, etc., a display including a CRT, LCD, etc., an output unit 1007 including headphones, speakers, etc., a storage unit 1008 including a hard disk, etc., and a communication unit 1009 including a modem, terminal adapter, etc. are connected.

[0117] The CPU 1001 executes various processes in accordance with various programs stored in the ROM 1002 or various programs loaded from the storage unit 1008 to the RAM 1003. In this embodiment, for example, the processes of the various units of the information processing device described below. A graphics processing unit (GPU) may be provided to execute various processes in accordance with various programs stored in the ROM 1002 or various programs loaded from the storage unit 1008 to the RAM 1003, similar to the CPU 1001. In this embodiment, for example, the processes of the various units of the information processing device described below. The GPU is suitable for performing routine processing in parallel, and by applying it to neural network processing described below, for example, it is possible to improve processing speed compared to the CPU 1001. The RAM 1003 also stores data necessary for the CPU 1001 and the GPU to execute various processes.

[0118] The communication unit 1009 performs communication processing via the Internet (not shown), for example, transmits data provided by the CPU 1001, and outputs data received from a communication partner to the CPU 1001, RAM 1003, and storage unit 1008. The storage unit 1008 exchanges data with the CPU 1001 and stores and erases information. The communication unit 1009 also performs communication processing of analog or digital signals with other devices.

[0119] The input / output interface 1005 is also connected to a drive 1010 as needed, and, for example, a magnetic disk 1011, an optical disk 1012, a flexible disk 1013, or a semiconductor memory 1014 is appropriately attached, and computer programs read from these are installed in the memory unit 1008 as needed.

[0120] An information processing system according to embodiment 1 will be described. The information processing system according to this embodiment is configured to include a plurality of local stations that perform supervised learning of local models using images as input data, and a central station that constructs an integrated model based on the learning results at each distributed learning station.

[0121] This application claims priority based on Japanese Patent Application No. 2024-31501, filed March 1, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0122] REFERENCE SIGNS LIST 1 Electromagnetic wave source 2 Optical system 3 Stage 4 Detector 5 Signal processing unit 6 Control unit 21, 23, 24 Lens 22 Beam splitter 25 Housing 26 Reflector 51 Storage unit 100 Measuring device 1000 Computer 1001 CPU 1002 ROM 1003 RAM 1004 Bus 1005 Input / output interface 1006 Input unit 1007 Output unit 1008 Storage unit 1009 Communication unit 1010 Drive 1011 Magnetic disk 1012 Optical disk 1013 Flexible disk 1014 Semiconductor memory S Sample M Buried object DET Detection signal W, Wa Electromagnetic wave W ｍ , W ｓ Reflected wave W ｒ stray light

Claims

1. A measuring device comprising: an electromagnetic wave source that emits electromagnetic waves; a stage that can be driven in the propagation direction of the electromagnetic waves and holds a measurement object to be irradiated with the electromagnetic waves; an optical system that emits the electromagnetic waves emitted from the electromagnetic wave source to the measurement object, and receives reflected waves of the electromagnetic waves from the measurement object, and emits a composite wave resulting from interference between the reflected waves and stray light generated by the incidence of the electromagnetic waves, from a path different from the propagation path of the electromagnetic waves; a detector that detects the composite wave emitted from the optical system and outputs a detection signal indicative of the detection result; a control unit that controls the electromagnetic wave source to switch the frequency of the electromagnetic waves among a plurality of frequencies, and controls the stage to move to a plurality of positions for each of the plurality of frequencies; and a signal processing unit that measures the spectrum of the composite wave, which has an intensity that depends on the frequency of the electromagnetic waves and the position of the stage, in accordance with the detection signal, and obtains the spectrum of the reflected wave by removing the spectrum of the stray light that has been obtained in advance from the spectrum of the composite wave.

2. The measurement device according to claim 1, wherein the spectrum of the composite wave is measured by performing a process of measuring the spectrum of the composite wave by moving the stage to a plurality of positions for one frequency among the plurality of frequencies, for each of the plurality of frequencies, wherein the process comprises the steps of: the control unit instructing the electromagnetic wave source to select the one frequency, causing the electromagnetic wave source to emit an electromagnetic wave of the one frequency to the optical system; the control unit moves the stage to the plurality of positions while the signal processing unit is monitoring the detection signal; once the stage has been moved to all of the plurality of positions, the control unit determines whether each of the plurality of frequencies has been selected as the one frequency; if each of the plurality of frequencies has been selected as the one frequency, the control unit terminates measurement of the spectrum of the composite wave; if each of the plurality of frequencies has not been selected as the one frequency, the control unit updates the one frequency to a frequency among the plurality of frequencies that has not yet been selected, and repeats the process.

3. The frequency of the electromagnetic wave is f, and the composite wave W that appears in the detection signal is ｃ is expressed by the following formula: However, c ０ is the speed of light in a vacuum, C ｒ (f) is the amplitude of the stray light, C ｓ is the amplitude of the reflected wave from the surface of the measurement object, x is the distance from the optical system to the surface of the measurement object, θ is the phase shift of the stray light relative to the electromagnetic wave emitted from the electromagnetic wave source, C ｒｓ (f, x) is the amplitude of the composite wave, θ ｓ (f, x) is the phase shift due to interference, and the amplitude I ｓ is expressed by the following formula: Θ is expressed by the following formula: The amplitude of the composite wave I ｓ The maximum value maxI ｓ and the minimum value minI ｓ The amplitude C of the reflected wave ｒ and the amplitude C of the stray light ｓ is C ｒ >C ｓ in the case of, It is expressed as C ｒ <C ｓ in the case of, and the signal processing unit calculates the amplitude C of the stray light. ｒ The spectrum of the composite wave and the amplitude C of the stray light given in advance are stored. ｒ and for each of the plurality of frequencies, either Equation [4] or Equation [5] is applied to calculate the amplitude C of the reflected wave. ｓ The measurement device according to claim 2 , wherein the spectrum of the reflected wave is obtained by extracting:

4. The measuring device according to claim 3, wherein the object to be measured is made of a single material, the reflected waves are electromagnetic waves irradiated onto the surface of the object to be measured and reflected from the surface, and the signal processing unit acquires the spectrum of the reflected waves from the surface of the object to be measured.

5. The object to be measured is made of a first material, and an object made of a second material different from the first material is buried therein. When the frequency of the electromagnetic wave is f, the composite wave W that appears in the detection signal is ｃ is expressed by the following formula: However, c ０ is the speed of light in a vacuum, C ｒ (f) is the amplitude of the stray light, C ｓ is the amplitude of the reflected wave from the surface of the measurement object, C ｍ is the amplitude of the reflected wave from the surface of the buried object, x is the distance from the optical system to the surface of the object to be measured, θ is the phase shift of the stray light relative to the electromagnetic wave emitted from the electromagnetic wave source, C ｒｍ (f, x) is the amplitude of the composite wave, θ ｍ (f, x) is the phase shift due to interference, and the amplitude I ｍ is expressed by the following formula: D(f) is expressed by the following formula: Θ is expressed by the following formula: cosφ is expressed by the following formula: sinφ is expressed by the following formula: Amplitude C of the reflected wave from the surface of the buried object ｍ (f) is calculated by the following formula: The signal processing unit detects a phase shift θ due to the interference. ｍ (f, x) and the amplitude C of the reflected wave from the surface of the measurement object obtained based on the formulas [1] to [6]. ｓ and the signal processing unit stores in advance the phase shift θ due to the interference stored in advance. ｍ (f, x) and the amplitude C of the reflected wave from the surface of the measurement object ｓ and extracting the amplitude of the reflected wave from the buried object for each of the plurality of frequencies using equation [13] based on the above formula, thereby obtaining a spectrum of the amplitude of the reflected wave from the buried object.

6. Amplitude C of the reflected wave from the surface of the object to be measured ｓ is determined in advance by measuring the amplitude of a wave reflected from the surface of the object to be measured, the wave being made of the first material, based on the formulas [1] to [6].

7. The measuring device according to claim 1 or 2, wherein the optical system comprises a branching means inserted into the propagation path of the electromagnetic wave, which branches the reflected wave incident on the object to be measured through an outlet that emits the electromagnetic wave into a path different from the propagation path of the electromagnetic wave, and the branching means branches the electromagnetic wave into a path toward the outlet and another path different from the path toward the outlet, and the electromagnetic wave branched into the other path generates stray light in the optical system, and the branched reflected wave interferes with the stray light to output the composite wave.

8. The measuring device according to claim 7, wherein the optical system further comprises a reflecting means for reflecting the electromagnetic wave reflected to the other path.

9. A measurement method comprising: emitting an electromagnetic wave; using an optical system, emitting the electromagnetic wave to a measurement object held by a stage that can be driven in the propagation direction of the electromagnetic wave; receiving a reflected wave of the electromagnetic wave from the measurement object; emitting a composite wave resulting from interference between the reflected wave and stray light generated by the incidence of the electromagnetic wave from a path different from the propagation path of the electromagnetic wave; detecting the composite wave emitted from the optical system and outputting a detection signal indicating the detection result; switching the frequency of the electromagnetic wave among a plurality of frequencies; moving the stage to a plurality of positions for each of the plurality of frequencies; measuring the spectrum of the composite wave, which has an intensity that depends on the frequency of the electromagnetic wave and the position of the stage according to the detection signal; and obtaining the spectrum of the reflected wave by removing the spectrum of the stray light that was measured in advance from the spectrum of the composite wave.

10. A program that causes a computer to control a measuring device that includes an electromagnetic wave source that emits electromagnetic waves, a stage that can be driven in the propagation direction of the electromagnetic waves and holds a measurement object onto which the electromagnetic waves are irradiated, an optical system that emits the electromagnetic waves emitted from the electromagnetic wave source to the measurement object and receives reflected waves of the electromagnetic waves from the measurement object, and emits a composite wave resulting from interference between the reflected waves and stray light generated by the incidence of the electromagnetic waves, from a path different from the propagation path of the electromagnetic waves, and a detector that detects the intensity of the composite wave emitted from the optical system and outputs a detection signal indicative of the detection result, the program causing a computer to control the electromagnetic wave source to switch the frequency of the electromagnetic waves among a plurality of frequencies, a process of controlling the stage to move to a plurality of positions for each of the plurality of frequencies, a process of measuring the spectrum of the composite wave, which has an intensity that depends on the frequency of the electromagnetic waves and the position of the stage in accordance with the detection signal, and a process of obtaining the spectrum of the reflected wave by removing the spectrum of the stray light that was previously obtained from the spectrum of the composite wave.

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