Signal correcting device and signal correcting method

Abstract

The purpose of the present invention is to appropriately correct an output signal of a resonant tunneling diode oscillator that emits terahertz waves. A measuring device (100) comprises: the resonant tunneling diode oscillator (1) that outputs an output signal by irradiating an object with the terahertz waves and receiving the terahertz waves reflected by the object; a voltage supply unit (11) that supplies a time-varying bias voltage to the resonant tunneling diode oscillator; and a correcting unit (32) that corrects a oscillation frequency of the output signal using a set of correction values in which the correction values increase and decrease as the oscillation frequency increases.

Description

Signal correction device and signal correction method

[0001] One aspect of the present invention relates to a signal correction device that corrects an output signal from an RTD (Resonant Tunneling Diode) oscillator (hereinafter simply referred to as an "RTD").

[0002] Non-Patent Document 1 below discloses an example of a signal detection device (terahertz imaging system) by the inventors of the present application (hereinafter simply referred to as "the inventors").

[0003] Li Yi, Yosuke Nishida, Tomoki Sagisaka, Ryohei Kaname, Ryoko Mizuno, Masayuki Fujita, and Tadao Nagatsuma, Towards Practical Terahertz Imaging System With Compact Continuous Wave Transceiver, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 39, NO. 24, pp.7850-7861, 2021

[0004] The RTD that emits terahertz waves has complex nonlinear characteristics, unlike the linear characteristics of general microwave oscillators, making it difficult to perform appropriate measurements using the output signal of the RTD.

[0005] An object of one aspect of the present invention is to provide a signal correction device capable of appropriately correcting an output signal from an RTD that emits terahertz waves.

[0006] A signal correction device according to one aspect of the present invention includes an RTD (Resonant Tunneling Diode) that outputs an output signal by irradiating an object with terahertz waves and receiving the terahertz waves reflected by the object, a detection unit that detects the output signal from the RTD, a voltage supply unit that supplies a time-varying bias voltage to the RTD, and a correction unit that corrects the oscillation frequency of the output signal using a correction value set in which the correction value increases or decreases as the oscillation frequency increases.

[0007] A signal correction method according to one aspect of the present invention includes a signal acquisition step of acquiring an output signal from an RTD (Resonant Tunneling Diode) that irradiates an object with terahertz waves by supplying a time-varying bias voltage and receives the terahertz waves reflected by the object, and a correction step of correcting the oscillation frequency of the output signal using a set of correction values ​​that increase and decrease as the oscillation frequency increases.

[0008] According to one aspect of the present invention, the output signal of the RTD can be appropriately corrected.

[0009] 14 is a diagram illustrating signal transmission and reception by an RTD according to an embodiment of the present invention. FIG. 15 is a diagram illustrating the current-voltage characteristics (IV characteristics) of an RTD. FIG. 16 is a diagram illustrating an example of the relationship between the bias voltage and oscillation frequency of an RTD. FIG. 17 is a diagram illustrating the concept of a method for correcting the oscillation frequency of an RTD. FIG. 18 is a diagram illustrating the characteristics of the oscillation frequency of a general microwave oscillator. FIG. 19 is a diagram illustrating an example of the configuration of a measurement device according to the present embodiment. FIG. 19 is a diagram illustrating an example of the configuration of a frequency filter circuit. FIG. 19 is a diagram for explaining each signal in the measurement device. FIG. 19 is a diagram illustrating an example of the relationship between the bias voltage and oscillation frequency. FIG. 19 is a diagram illustrating an example of the output signal of an RTD. FIG. 19 is a diagram illustrating the peak interval of the output signal. FIG. 19 is a diagram illustrating a corrected output signal. FIG. 19 is a diagram illustrating corrected output signals corresponding to objects located at multiple distances. FIG. 19 is a diagram illustrating signals obtained by Fourier transforming each of the multiple corrected output signals shown in FIG. 13. FIG. 19 is a diagram illustrating an example of the relationship between the bias voltage and oscillation frequency of an RTD. FIG. 19 is a diagram illustrating an example of the output signal of an RTD. FIG. 19 is a diagram illustrating the relationship between the oscillation frequency f0 of the RTD when there is no reflected wave and the oscillation frequency f of the RTD when there is a reflected wave. FIG. 19 is a diagram illustrating an example of the configuration of a measurement device according to an embodiment of the present invention. FIG. 19 is a diagram illustrating the output signal before correction corresponding to multiple reflection coefficients η. 20 is a diagram showing signals obtained by Fourier transforming the output signals before correction corresponding to the plurality of reflection coefficients η shown in FIG. 19. FIG. 21 is a diagram showing an example of the configuration of a measurement device according to one aspect of the present invention. FIG. 22 is a diagram showing an image of the measurement results obtained by the measurement device.

[0010] [Embodiment 1] Unless otherwise stated, the components and values ​​described in this specification are merely examples. Therefore, for example, unless otherwise stated, the positional relationships and connection relationships of the components are not limited to the examples in the figures. Furthermore, the figures are not necessarily drawn to scale. In this specification, the expression "X to Y" for two numbers X and Y means "greater than or equal to X and less than or equal to Y," unless otherwise stated.

[0011] (Overview of RTD) Fig. 1 is a diagram illustrating signal transmission and reception by an RTD (Resonant Tunneling Diode) oscillator according to one embodiment of the present invention. In one embodiment of the present invention, the RTD 1 is used as a device that integrates a transmitter and a receiver. For this reason, the RTD 1 may be referred to as an RTD transceiver.

[0012] The RTD 1 irradiates (transmits) terahertz waves to the object TG and receives the terahertz waves reflected by the object TG, thereby outputting an output signal.

[0013] The target TG may be supported by a support (not shown). In this specification, the direction from the RTD 1 toward the target TG (depth direction) is referred to as the z direction. In the example of Fig. 1, the RTD 1 and the target TG are separated by a distance L in the z direction. In the example of Fig. 1, the direction in which the terahertz waves emitted from the RTD 1 are directed toward the target TG is defined as the positive direction of the z direction.

[0014] The RTD 1 may include a horn antenna for emitting and receiving terahertz waves. In this specification, terahertz waves refer to electromagnetic waves having a frequency in the terahertz band. For example, the frequency of the terahertz waves may be 0.1 to 10 THz.

[0015] 1 represents the terahertz wave reflected by the object TG. In this specification, for example, when it is clearly indicated that Sr is a function of time t, the notation Sr(t) is used. Sr is expressed as follows: ...(1) where f is the frequency, Ar is the amplitude of the received signal, c is the speed of light, and θ is the initial phase. f in Sr is the oscillation frequency of the RTD 1. The oscillation frequency of the RTD 1 belongs to the terahertz band.

[0016] Fig. 2 is a diagram illustrating the current-voltage characteristics (IV characteristics) of the RTD 1. As shown in Fig. 2, the current-voltage characteristics of the RTD 1 have a negative resistance region (a region where dI / dV is negative). VL and VH in Fig. 2 respectively represent the lower and upper limits of the voltage in the negative resistance region.

[0017] By supplying a voltage belonging to the negative resistance region (a voltage in the range of VL to VH) to the RTD 1 as a bias voltage, the RTD 1 can be made to oscillate. In other words, the RTD 1 can be made to function as a local oscillator (LO). The elliptical region in FIG. 2 indicates a partial region of the negative resistance region that is suitable for the RTD 1 to oscillate.

[0018] The oscillation signal SLO in the example of FIG. 1 is generated in association with the oscillation of the RTD 1. ...(2) where ALO is the amplitude of the oscillation signal. f in SLO is also the oscillation frequency of the RTD 1.

[0019] The RTD 1 outputs a signal indicating its own detection result as an output signal Sout. Sout depends on Ar and ALO. Specifically, Sout is expressed as follows: Sout=(Sr+SLO) ２ ...(3)

[0020] Here, by expanding the right-hand side of equation (3) based on equations (1) and (2), As shown in equation (4), Sout depends on L. Therefore, for example, L can be derived based on Sout.

[0021] However, Sout shown in equation (4) is complex. High-frequency components with a frequency twice or more of Sout can be removed without propagating through the circuit. Also, high-frequency components may be intentionally removed from Sout by using a low-pass filter. In this case, the low-frequency components of Sout (for convenience, referred to as VLPF) are obtained. The VLPF is approximately: ...(5)

[0022] In a conventional continuous wave (CW) radar, the oscillation frequency f can be considered as a constant. In this case, the value of the argument of cos on the right side of equation (5) can be considered to vary only depending on L. Therefore, for example, the distance L to the target TG can be derived based on the VLPF.

[0023] On the other hand, the RTD1, which is a resonant tunneling diode oscillator, is both a transmitter and a receiver that receives reflected waves from the target TG. Therefore, the oscillation frequency of the RTD1 is affected not only by the bias voltage but also by the reflected waves it receives. The oscillation frequency f of the RTD1, taking the influence of the reflected waves into consideration, is given as follows: ...(6) where f is the oscillation frequency of the RTD1 when there is a reflected wave, f0 is the oscillation frequency of the RTD1 when there is no reflected wave, and Q is a constant (Q factor) determined by the elements of the RTD1. η is the ratio of the power of the reflected wave returning to the RTD1 to the power of the terahertz wave emitted from the RTD1. η is proportional to the reflectivity of the target TG. Because equation (6) is complex, an analytical solution for the VLPF cannot be obtained from equations (5) and (6). Therefore, numerical analysis is required to obtain an accurate VLPF from equations (5) and (6). However, when η is sufficiently small, it can be assumed from equation (6) that f ≒ f0. Therefore, when η is sufficiently small, the VLPF obtained from the RTD1 from equations (5) and (6) is approximately as follows: ...(7) However, the VLPF actually obtained from the RTD 1 changes in a complex manner according to equations (5) and (6), and does not follow equation (7). Note that the DC component (constant part) is omitted.

[0024] FIG. 3 is a diagram showing an example of the relationship between the bias voltage and oscillation frequency of the RTD 1. The horizontal axis represents the bias voltage (V), and the vertical axis represents the oscillation frequency (GHz). Here, the graph is drawn when the distance to the target TG is L = 1 m. The oscillation frequency characteristics of the RTD 1 change depending on the reflection coefficient η. η = 1 × 10 －２ The case where η=1×10 corresponds to a situation where reflection is strong, that is, the reflectivity of the object TG is high and the distance from the RTD 1 to the object TG is very short. In this case, the oscillation frequency increases stepwise with increasing bias voltage. η=1×10 －６ and η = 1 × 10 －８ In this case, the oscillation frequency increases nonlinearly with increasing bias voltage, undulating (while alternating between positive and negative curvature sections). For example, when the distance from RTD1 to the target TG (metal plate) is 0.2 m, η = 1 × 10 －５ At 0.5 m or more, η = 1 × 10 －８ This value may vary depending on the reflectance of the target TG and the element characteristics of the RTD 1. A metal plate has the highest reflectance among common reflectors. For a normal target TG, η is one to two orders of magnitude smaller.

[0025] FIG. 4 is a diagram showing the concept of a method for correcting the oscillation frequency of the RTD 1. FIG. 5 is a diagram showing the oscillation frequency characteristics of a general microwave oscillator. In FIGS. 4 and 5, the horizontal axis represents the bias voltage, and the vertical axis represents the oscillation frequency. It is not easy to determine the distance L from the output signal (VLPF) to the target TG using the above-mentioned equations (5) and (6). Therefore, as shown in FIG. 4, it is conceivable to perform a correction such that the oscillation frequency characteristics of the RTD 1 are linearly corrected in the output signal.

[0026] As shown in Figure 5, in a microwave oscillator, the slope of the oscillation frequency with respect to the bias voltage increases monotonically. In other words, in a microwave oscillator, the curvature of the oscillation frequency with respect to the bias voltage is always positive within the operating range. Therefore, it is relatively easy to linearly correct the oscillation frequency characteristics of a microwave oscillator. For example, it is conceivable to correct the characteristics using a correction value that monotonically increases as the oscillation frequency increases.

[0027] On the other hand, since the oscillation frequency characteristics of the RTD 1 are not simple, the characteristics cannot be appropriately corrected using a monotonically increasing correction value. Below, a method for appropriately correcting the output signal obtained from the RTD 1 will be described.

[0028] (Configuration of Measuring Device 100) FIG. 6 is a diagram showing an example configuration of the measuring device 100 according to this embodiment. The measuring device 100 includes an RTD 1, a voltage supply unit 11, a frequency filter circuit 12, a detection unit 20, and a control unit 30. The measuring device 100 (signal correction device) measures the distance from the RTD 1 to the target TG. The frequency filter circuit 12 includes a high-pass filter 13 and a low-pass filter 14. The detection unit 20 includes a differential amplifier 21 and an AD converter 22. The control unit 30 includes a correction value acquisition unit 31, a correction unit 32, and a distance determination unit 33. The measuring device 100 includes an auxiliary path HK that connects the voltage supply unit 11 and the differential amplifier 21 of the detection unit 20 without passing through the frequency filter circuit 12. The measuring device 100 may include an optical system (not shown) including a lens, a mirror, etc., between the RTD 1 and the target TG.

[0029] The voltage supply unit 11 supplies a time-varying bias voltage to the RTD 1. Here, the voltage supply unit 11 supplies a DC voltage and an AC voltage to the RTD 1 via a frequency filter circuit 12. The voltage supply unit 11 outputs the AC voltage to the differential amplifier 21 via an auxiliary path HK. The voltage supply unit 11 may generate a bias voltage Vbias expressed by the following equation (8).

[0030] Vbias=Vdc+Vac (8) Vdc is a DC voltage, and Vac is a periodically changing AC voltage. The bias voltage Vbias is the AC voltage Vac superimposed on the DC voltage Vdc.

[0031] The bias voltage Vbias includes a voltage that belongs to the negative resistance region. This allows the RTD 1 to oscillate. The bias voltage Vbias changes in the negative resistance region. This allows the output signal Sout of the RTD 1 to be modulated. The frequency of Vac is referred to as the modulation frequency. The modulation frequency may be in the kilohertz band. As an example, the modulation frequency in this embodiment is set to 1 kHz.

[0032] The bias voltage Vbias is input from the voltage supply unit 11 to the low-pass filter 14 of the frequency filter circuit 12. The low-pass filter 14 attenuates the AC component of the bias voltage Vbias but passes a portion of the AC component. The low-pass filter 14 outputs an input signal Sin, which is the partially attenuated bias voltage Vbias, to the RTD 1. The input signal Sin can be considered a time-varying bias voltage.

[0033] The RTD 1 oscillates in response to an input signal Sin and irradiates the target TG with terahertz waves. The RTD 1 receives the terahertz waves reflected by the target TG and outputs an output signal Sout. The output signal Sout is input to the frequency filter circuit 12.

[0034] Sout is input from the RTD 1 to the high-pass filter 13 of the frequency filter circuit 12. Meanwhile, Sin is input from the voltage supply unit 11 to the high-pass filter 13 of the frequency filter circuit 12. The high-pass filter 13 outputs a detection signal Sdet containing an AC component of Sout to the detection unit 20.

[0035] The detection unit 20 detects the output signal of the RTD 1. The differential amplifier 21 has an input terminal that accepts a signal input and an input terminal that accepts a reference input. The differential amplifier 21 amplifies the voltage difference between the signal input and the reference input and outputs an amplified differential signal Sdiff_amp to the AD converter 22.

[0036] The AD converter 22 converts the input amplified differential signal Sdiff_amp into a digital value, and outputs the converted digital amplified differential signal to the control unit 30.

[0037] (Detection of Output Signal of RTD 1) FIG. 7 is a diagram showing an example of the configuration of the frequency filter circuit 12. The frequency filter circuit 12 may be a three-terminal circuit. The frequency filter circuit 12 may be, for example, a bias tee. Therefore, the frequency filter circuit 12 can be realized using, for example, a commercially available bias tee.

[0038] The frequency filter circuit 12 may include a first terminal T1 connected to the voltage supply unit 11, a second terminal T2 connected to the detection unit 20, and a third terminal T3 connected to the RTD 1. The frequency filter circuit 12 may include an internal node Nin connected to the first terminal T1, the second terminal T2, and the third terminal T3.

[0039] The high-pass filter 13 in the frequency filter circuit 12 may be located between the internal node Nin and the second terminal T2. The frequency filter circuit 12 may have a capacitor C as the high-pass filter 13 between the internal node Nin and the second terminal T2.

[0040] The low-pass filter 14 in the frequency filter circuit 12 may be located between the internal node Nin and the first terminal T1. The frequency filter circuit 12 may have an inductor L as the low-pass filter 14 between the internal node Nin and the first terminal T1.

[0041] In this specification, for example, the transmittance of a DC signal (e.g., DC voltage) from the first terminal T1 to the second terminal T2 in the frequency filter circuit 12 is denoted as T12DC. Also, for example, the transmittance of an AC signal (e.g., AC voltage) from the first terminal T1 to the second terminal T2 is denoted as T12AC.

[0042] In conventional signal detection devices, it is intended that only a DC voltage be supplied from a power supply (e.g., a DC power supply) via a frequency filter circuit (e.g., a bias tee) to the RTD 1. In other words, in the prior art, there has been no idea of ​​supplying an AC voltage from a power supply to the RTD 1 via the frequency filter circuit.

[0043] For this reason, in the prior art, to simplify theoretical considerations, the ideal characteristics of a frequency filter circuit have been assumed to be T13DC = 1, T13AC = 0, T32AC = 1, T32DC = 0, T12DC = 0, and T12AC = 1. These ideal characteristics are equivalent to (i) the high-pass filter 13 not attenuating AC signals (e.g., AC voltages) at all and completely blocking DC signals (e.g., DC voltages), and (ii) the low-pass filter 14 not attenuating DC signals at all and completely blocking AC signals.

[0044] However, in reality, there are no frequency filter circuits (more specifically, the high-pass filter 13 and the low-pass filter 14) that perfectly meet the ideal characteristics. For example, the high-pass filter 13 actually attenuates AC signals slightly and passes AC signals slightly. Similarly, the low-pass filter 14 actually attenuates DC signals slightly and passes AC signals slightly.

[0045] In the actual characteristics of the frequency filter circuit 12, the following relationships hold for the transmittance of DC signals: 0<T32DC, T12DC<T13DC<1. Similarly, in the actual characteristics of the frequency filter circuit 12, the following relationships hold for the transmittance of AC signals: 0<T13AC, T12AC<T32AC<1. In the following example, it is assumed that the transmittance of each DC signal and each AC signal is given as a known value.

[0046] 8 is a diagram illustrating each signal in the measurement apparatus 100. Reference numeral 700A in FIG. 8 is a diagram illustrating Vbias. Vbias is expressed as in equation (8) above. Reference numeral 700A illustrates an example of the waveforms of Vdc and Vac.

[0047] Reference numeral 700B in Fig. 8 is a diagram for explaining Sin. Reference numeral 700B also shows an example of the waveform of Sout for comparison. According to the configuration of the frequency filter circuit 12, Vdc is input from the voltage supply unit 11 to the RTD 1 via the first terminal T1 and the third terminal T3. Similarly, Vac is input from the voltage supply unit 11 to the RTD 1 via the first terminal T1 and the third terminal T3.

[0048] From this, Sin can be expressed as follows: Sin = Vdc × T13DC + Vac × T13AC (9) The first and second terms on the right side of equation (9) are the DC and AC components of Sin, respectively. Reference numeral 700B shows an example of the waveforms of the first and second terms on the right side. Sin changes with the modulation frequency.

[0049] Here, the amplitude of Vac is represented as Vm. In this case, the maximum value Sin(max) and minimum value Sin(min) of Sin are respectively expressed as follows: Sin(max) = Vdc × T13DC + Vm × T13AC ... (10) Sin(min) = Vdc × T13DC - Vm × T13AC ... (11) Therefore, Sin can take all values ​​from Sin(min) to Sin(max).

[0050] As described above, when Sin belongs to the negative resistance region, the RTD 1 oscillates. On the other hand, when Sin does not belong to the negative resistance region, the RTD 1 does not oscillate. Therefore, in the first embodiment, Vdc and Vm may be set so that one of Sin(max) and Sin(min) belongs to the negative resistance region. In this case, in the first embodiment, Vdc and Vm may be set so that the other of Sin(max) and Sin(min) does not belong to the negative resistance region.

[0051] By setting Sin(max) and Sin(min) as described above, Sin falls within the negative resistance region during a certain period (oscillation period) and does not fall within the negative resistance region during the other period (non-oscillation period). Therefore, the oscillation of the RTD 1 can be stopped during the non-oscillation period. In other words, Sout can be output to the RTD 1 as an oscillation signal only during the oscillation period. As described above, Vac allows Sout to be modulated by the modulation frequency.

[0052] As another example, Vdc and Vm may be set so that both Sin(max) and Sin(min) belong to the negative resistance region. In this case, the oscillation frequency of the RTD 1 changes depending on Vac.

[0053] 8 is a diagram for explaining Sdet. According to the configuration of the frequency filter circuit 12, Sout is input from the RTD 1 to the detection unit 20 via the third terminal T3 and the second terminal T2. On the other hand, Vac is input from the voltage supply unit 11 to the detection unit 20 via the first terminal T1 and the second terminal T2.

[0054] From this, Sdet can be expressed as follows: Sdet=Sout×T32AC+Vac×T12AC (12)

[0055] In equation (12), the first term on the right-hand side is the component of Sdet that originates from Sout, and the second term on the right-hand side is the component of Sdet that originates from Vac. Reference numeral 700C shows an example of the waveforms of the first and second terms on the right-hand side. In this way, when the actual characteristics of the frequency filter circuit 12 are taken into consideration, both Sout and Vac contribute to Sdet.

[0056] In the example of the first embodiment, in order to avoid complicating the equation for Sdet, it is assumed that T12DC is sufficiently small. Therefore, it can be considered that the relationship Vdc×T12DC≈0 holds. For this reason, the right side of equation (12) does not include a term corresponding to Vdc.

[0057] In the detection unit 20, the differential amplifier 21 receives Sdet from the frequency filter circuit 12. Sdet can be expressed as an output signal obtained via the frequency filter circuit 12. The differential amplifier 21 receives a reference voltage Vref, which changes at the modulation frequency, from the voltage supply unit 11. Sdet is input to the differential amplifier 21 as a signal input, and Vref is input as a reference input. Vref may be a voltage corresponding to Vac. As described below, Vref may be used to remove components derived from Vac from Sdet.

[0058] As an example, the voltage supply unit 11 may generate Vref given by Vref=Vac×T12AC (13) In other words, the voltage supply unit 11 may generate Vref that is the same as the signal input from the voltage supply unit 11 to the detection unit 20 via the frequency filter circuit 12 when the RTD 1 is not present.

[0059] The differential amplifier 21 amplifies a differential signal Sdiff between Sdet and Vref. Sdiff in the first embodiment is expressed as follows: Sdiff=Sdet−Vref=Sout×T32AC (14).

[0060] The differential amplifier 21 generates an amplified differential signal Sdiff_amp by amplifying Sdiff. That is, based on Sdiff, the differential amplifier 21 generates the following: Sdiff_amp=K×Sdiff=K×Sout×T32AC (15) where K is the gain of the differential amplifier 21. Sdiff_amp is an amplified version of the output signal Sout of the RTD1. In this way, the detection unit 20 detects the output signal Sout from the RTD1.

[0061] The differential amplifier 21 supplies Sdiff_amp to the AD converter 22. The AD converter 22 converts Sdiff_amp from an analog value to a digital value. The AD converter 22 supplies the digitally converted Sdiff_amp to the control unit 30. This allows the control unit 30 to perform various processes on Sdiff_amp as a digital value.

[0062] (Correction of Output Signal) Fig. 9 is a diagram showing an example of the relationship between bias voltage and oscillation frequency. Fig. 8 shows an example in which the AC component Vac of the bias voltage is a sine wave, but the following will be explained using an example in which a sawtooth wave bias voltage is supplied to the RTD 1, as shown in Fig. 9. The modulation frequency is 1 kHz. Over one period, the bias voltage increases linearly, and the oscillation frequency also increases. However, as can be seen from Fig. 9, the oscillation frequency of the RTD 1 does not increase linearly, but rather increases in a wavy manner, as shown in Fig. 3.

[0063] FIG. 10 shows an example of the output signal of RTD 1. The horizontal axis indicates the sampling points of the output signal data converted to digital values, and the vertical axis indicates the amplitude. The sampling points correspond to the measurement time. FIG. 10 shows data for one cycle of the bias voltage. That is, as the horizontal axis increases in the graph shown in FIG. 10, the bias voltage and oscillation frequency increase. Therefore, the horizontal axis in FIG. 10 can be considered to correspond to the oscillation frequency. The measurement was performed under conditions where the target TG was a reflective mirror located 0.4 m from RTD 1. In FIG. 10, the dotted line indicates the actually measured output signal of RTD 1. In FIG. 10, the solid line indicates the output signal obtained by simulation using Equation (7) under the same conditions, assuming that the change in oscillation frequency with respect to bias voltage is linear. The peaks of the output signal are indicated by *.

[0064] The output signal shown by the solid line corresponds to equation (7). The horizontal axis corresponds to the oscillation frequency f, and the "waveform frequency" of the solid line corresponds to 2L / c (the round-trip time of the terahertz wave). Therefore, if the data of the solid line is Fourier transformed, a spectrum in the time (2L / c) domain can be obtained. Since equation (7) is a simple cosine wave, the spectrum is concentrated at a specific 2L / c. In other words, the distance L to the target TG can be determined.

[0065] On the other hand, the actual output signal shown by the dotted line corresponds to equations (5) and (6). Note that the DC component (constant part) is removed by the high-pass filter 13. Because equations (5) and (6) are not simple cosine waves, if the dotted line data is directly Fourier transformed, multiple peaks may appear or the peak may deviate from 2L / c. Therefore, the distance L to the target TG cannot be accurately determined.

[0066] Therefore, taking advantage of the fact that the reflection coefficient η in equation (6) is very small (i.e., √η / Q is sufficiently smaller than 1), a correction is made to the output signal so that equations (5) and (6) approximate equation (7).

[0067] Here, the peak interval of the output signal, indicated by the dotted line, is corrected. The peak interval is the distance between peaks on the horizontal axis. However, due to the nonlinear characteristics of the oscillation frequency specific to the RTD 1, it is not possible to perform appropriate correction using a monotonically changing correction value.

[0068] FIG. 11 is a diagram showing the peak intervals of the output signal. The horizontal axis shows the order of the peak points, starting from the smallest sampling point. The vertical axis shows the peak intervals. In FIG. 11, the dashed dotted line shows the peak intervals of the output signal obtained by simulation when it is assumed that the oscillation frequency characteristics are linear. The solid line shows the peak intervals of the actual output signal. In the actual output signal, the peak intervals are not constant, and both smaller and larger peak intervals may exist compared to the simulation.

[0069] As a reference for the peak intervals for determining the correction value, an output signal obtained by simulation, assuming that the change in oscillation frequency with respect to the bias voltage is linear, is used. An external information processing device obtains, by simulation, an output signal of the RTD1 due to a reflected wave from an object TG located a predetermined distance away, assuming that the change in oscillation frequency with respect to the bias voltage is linear. The information processing device identifies multiple peak intervals of the output signal obtained by simulation. A correction value acquisition unit 31 of the measuring device 100 acquires information on the multiple peak intervals of the output signal obtained by simulation from the external information processing device. The correction value acquisition unit 31 stores information on the multiple peak intervals of the output signal obtained by simulation.

[0070] The measuring device 100 detects an output signal of the RTD 1 due to a wave reflected from an object TG at a predetermined distance. The correction value acquisition unit 31 acquires the detected output signal and identifies multiple peak intervals of the detected output signal. The correction value acquisition unit 31 determines the differences between the multiple peak intervals of the output signal obtained by simulation and the multiple peak intervals of the detected output signal as multiple correction values. For example, the correction value acquisition unit 31 determines the nth correction value by subtracting the nth peak interval of the detected output signal from the nth peak interval of the output signal obtained by simulation. In this case, each correction value corresponds to the difference in height between the dashed and solid lines at each peak point shown in FIG. 11 . The correction value acquisition unit 31 stores a correction value set including the multiple determined correction values.

[0071] As can be seen from Figure 11, in the correction value set, the correction value increases or decreases as the number of sampling points increases, i.e., as the oscillation frequency increases. For example, in Figure 11, as the horizontal axis increases, there are sections where the difference between peak intervals (correction values) increases and sections where they decrease. Thus, the correction values ​​in the correction value set suitable for RTD 1 do not monotonically decrease or increase as the oscillation frequency increases. The correction value set can include both positive and negative correction values.

[0072] The correction values ​​may be calculated and determined in an external information processing device. The correction value acquisition unit 31 may acquire the correction value set from the external information processing device. The correction unit 32 acquires the correction value set from the correction value acquisition unit 31.

[0073] The correction unit 32 corrects the output signal using a set of correction values ​​so as to reduce the difference between the maximum and minimum peak intervals in the detected output signal. For example, to correct the nth peak interval in the output signal, the correction unit 32 shifts the sampling point of the (n+1)th peak along the horizontal axis by the nth correction value. For example, the correction unit 32 equally distributes the nth correction value to the sampling points (relative coordinates on the horizontal axis) of each data in the section between the nth peak and the (n+1)th peak. In other words, the correction unit 32 equally expands / contracts the intervals on the horizontal axis of each data in that section. Here, the correction is performed on the peak interval (horizontal axis in FIG. 10 ), not the amplitude (vertical axis in FIG. 10 ). The correction unit 32 stretches or contracts the waveform of each section of the output signal along the horizontal axis according to the correction value for each section (between peaks). The correction unit 32 outputs the corrected output signal to the distance determination unit 33.

[0074] FIG. 12 is a diagram showing the corrected output signal. The horizontal axis represents the oscillation frequency. The vertical axis represents the amplitude. In FIG. 12, the dotted line represents the output signal before correction, which corresponds to the detected output signal in FIG. 10. In FIG. 12, the solid line represents the corrected output signal. Note that the oscillation frequency on the horizontal axis is obtained by converting the sampling point into an oscillation frequency. For example, the oscillation frequency on the horizontal axis is determined from the bias voltage applied at the time of sampling (see FIG. 9). Note that the conversion is approximated by assuming a linearly changing oscillation frequency when no target TG is present.

[0075] In the corrected output signal, the peak intervals are approximately constant. In this way, the correction unit 32 corrects the output signal so as to equalize the peak intervals in the detected output signal. In this way, correcting the sampling points of the output signal data means correcting the oscillation frequency of the output signal. This correction means correcting the wavy oscillation frequency characteristics of the RTD 1 to linear characteristics. In other words, the corrected output signal is corrected to a function close to Equation (7). Therefore, by Fourier transforming the corrected output signal, the spectrum of the output signal in the 2L / c region can be obtained.

[0076] The distance determination unit 33 uses the corrected output signal to determine the distance L to the target TG. The distance determination unit 33 performs a Fourier transform (e.g., a fast Fourier transform) on the corrected output signal to obtain a spectrum in the 2L / c region of the output signal. The distance determination unit 33 determines the position of a peak in the spectrum. The peak position can be converted to the distance L by multiplying it by c / 2. In this way, the distance determination unit 33 determines the distance L to the target TG.

[0077] 13 is a diagram showing corrected output signals corresponding to an object TG located at a plurality of distances. The horizontal axis represents the oscillation frequency, and the vertical axis represents the amplitude. FIG. 13 shows corrected output signals when the distance L to the object TG is 36 cm, 40 cm, and 62 cm.

[0078] FIG. 14 is a diagram showing signals obtained by Fourier transforming each of the corrected output signals shown in FIG. 13 . The horizontal axis represents distance L. The vertical axis represents amplitude. The horizontal axis represents 2L / c converted to L. The peaks in the three Fourier-transformed signals are located at approximately 36 cm, approximately 40 cm, and approximately 62 cm, respectively. Note that by correcting the output signals, side lobes that would appear without correction are eliminated, and the peak positions are adjusted to appropriate positions (positions corresponding to the actual distance of the target TG).

[0079] In this way, the measuring device 100 can correct the oscillation frequency of the output signal using a correction value set in which the correction value increases or decreases as the oscillation frequency increases, thereby correcting the output signal to suit the RTD 1. Therefore, the corrected output signal can be used to appropriately measure physical quantities, such as the distance to the target TG. The measuring device 100 can achieve appropriate output signal correction and physical quantity measurement using terahertz waves. Therefore, the measuring device 100 can achieve significantly improved resolution compared to conventional measuring devices using millimeter waves. This enables the inspection of objects the size of a person to carry or the measurement of minute movements of the human body, which were not possible with millimeter waves. The measuring device 100 does not require a complex optical system including a spatial light modulator or the like, and can have a simple configuration including the RTD 1. Therefore, the measuring device 100 also has the advantage of being compact.

[0080] (Variation) The correction value acquisition unit 31 may store multiple correction value sets that differ depending on the reflection coefficient η of the terahertz waves reflected by the target TG. The reflection coefficient η varies depending on, for example, the distance to the target TG. For example, the correction value acquisition unit 31 may generate correction value sets corresponding to each distance from output signals obtained by simulation corresponding to multiple distances and detected output signals corresponding to multiple distances. The distance determination unit 33 may determine an approximate distance from the detected output signal. For example, the distance determination unit 33 may tentatively determine an approximate distance from a spectrum obtained by Fourier transforming the uncorrected detected output signal. Alternatively, the distance determination unit 33 may tentatively determine an approximate distance from the peak interval in the uncorrected detected output signal. The correction unit 32 may correct the output signal using the correction value set corresponding to the tentatively determined distance. This allows the distance determination unit 33 to more accurately determine the distance from the corrected output signal. The correction unit 32 may use a first set of correction values ​​if the specified distance is within a first range, and may use a second set of correction values ​​if the specified distance is within a second range. In this way, the measurement device 100 can more appropriately correct the output signal by selectively using multiple sets of correction values ​​depending on the reflection coefficient η. In other words, it can more accurately specify physical quantities such as distance.

[0081] The correction value acquiring unit 31 may determine, as the multiple correction values, the ratios between the intervals between multiple peaks of the output signal obtained by simulation and the intervals between multiple peaks of the detected output signal. For example, the correction value acquiring unit 31 may determine, as the nth correction value, the value obtained by dividing the nth peak interval of the output signal obtained by simulation by the nth peak interval of the detected output signal. For example, the correction unit 32 may shift the sampling point of each data item in the section between the nth peak and the (n+1)th peak by multiplying the sampling point by the nth correction value. In this case, the correction value set may include correction values ​​greater than 1 and correction values ​​less than 1.

[0082] The correction unit 32 may correct the amplitude of the detected output signal. For example, the correction value acquisition unit 31 may identify multiple correction values ​​(peak ratios) that adjust the amplitude of multiple peaks of the detected output signal to the amplitude of multiple peaks of the output signal obtained by simulation. The correction unit 32 can correct the output signal by multiplying the detected output signal in each peak section by the amplitude correction value. As can be seen from FIG. 10 , the amplitude correction value also increases or decreases as the oscillation frequency (sampling point) increases. Of course, the correction unit 32 may perform both amplitude correction and oscillation frequency (sampling point, peak interval). This allows the waveform of the corrected output signal to more closely match Equation (7). Therefore, more accurate information about the target TG may be obtained.

[0083] The measuring apparatus 100 may be configured without the frequency filter circuit 12. In this case, the voltage supply unit 11, the RTD 1, and the first input terminal of the differential amplifier 21 may be connected to each other via a T-path. For example, the voltage supply unit 11 outputs a bias voltage Vbias=Vdc+Vac to the RTD 1 and the first input terminal of the differential amplifier 21. The sum of the bias voltage Vbias and the output signal Sout of the RTD 1 is input to the first input terminal of the differential amplifier 21. The voltage supply unit 11 outputs the bias voltage Vbias to the second input terminal of the differential amplifier 21 via the auxiliary path HK. The differential amplifier 21 outputs the difference between the two inputs to the AD converter 22.

[0084] The detection unit 20 may be configured to include a lock-in amplifier instead of the differential amplifier 21. Sdet is input to the input terminal of the lock-in amplifier. The lock-in amplifier is configured to extract and amplify the modulation component (component of modulation frequency f) contained in Sout.

[0085] [Embodiment 2] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0086] FIG. 15 is a diagram showing an example of the relationship between the bias voltage and oscillation frequency of the RTD 1. The horizontal axis represents the bias voltage (V). The vertical axis represents the oscillation frequency (GHz). In this case, the graph is drawn when the distance to the target TG is L=1 m. As the reflection coefficient η increases, the change in the oscillation frequency approaches a step-like change. When the reflection coefficient η becomes too large (for example, η=1×10 －３ As a result, a region appears where the oscillation frequency hardly changes, and the periodicity is lost.

[0087] FIG. 16 is a diagram showing an example of the output signal of the RTD 1. The vertical axis represents the bias voltage, and the vertical axis represents the amplitude. In the graph shown in FIG. 16, the oscillation frequency increases as the horizontal axis increases. Therefore, the horizontal axis in FIG. 16 can be considered to correspond to the oscillation frequency. The correction unit 32 corrects the output signal so that the peak intervals in the output signal are equalized. The distance determination unit 33 determines the distance to the target TG by performing a Fourier transform on the corrected output signal. Therefore, if the periodicity of the output signal is lost, the correction unit 32 cannot perform appropriate correction, and the distance determination unit 33 cannot properly determine the distance. For example, if the output signal changes in a sine wave pattern, the correction unit 32 can perform appropriate correction. If the output signal changes in a sawtooth or non-periodic pattern, appropriate correction becomes difficult. If the oscillation frequency changes in a step-like manner, such as jumping, in response to the change in bias voltage shown in FIG. 15, appropriate correction becomes difficult.

[0088] FIG. 17 is a diagram showing the relationship between the oscillation frequency f0 of the RTD 1 when there is no reflected wave and the oscillation frequency f of the RTD 1 when there is a reflected wave. FIG. 17 is a graph of equation (6). The distance L to the object is set to 30 mm. As the bias voltage increases, f0 increases. As the bias voltage increases, f0 increases, and so does f. However, for example, when η=1×10 －２In the graph, f increases continuously with increasing f0 up to just before 302 GHz, but f corresponding to the increasing f0 around 302 GHz is not continuous. Therefore, f increases in a jump as f0 increases (bias voltage increases). If the slope becomes negative at the inflection point surrounded by the dotted circle in Figure 17, such a jump in the oscillation frequency f occurs, resulting in a step-like frequency change. The inflection point where the slope can become negative is at an f that satisfies the following: 2πf 2L / c + θ = π + 2πm ... (16) where θ is the phase shift (phase difference between the incident wave and the reflected wave) due to reflection from the target TG. m is an integer. The condition for the slope at the inflection point to be positive can also be expressed as df0 / df > 0. Differentiating f0 with respect to f from Equation (6), df0 / df at the inflection point is obtained as follows: ...(17) Here, the relationship of equation (16), which is the condition for the inflection point, is used. When the following is satisfied, the slope at the inflection point becomes positive. ...(18) By setting L and η to satisfy equation (18), the oscillation frequency f can be made to change continuously without being stepped. Therefore, by reducing L or η so as to satisfy equation (18), it is possible to obtain an output signal that can be appropriately corrected by the correction unit 32.

[0089] 18 is a diagram showing an example of the configuration of a measurement device 100a according to this embodiment. The measurement device 100a includes an RTD 1, a light attenuator 2, a voltage supply 11, a frequency filter circuit 12, a detector 20, and a controller 30a. The controller 30a includes a correction value acquirer 31, a corrector 32, a distance specifier 33, and a determiner 34.

[0090] The optical attenuation unit 2 is disposed in the optical path between the RTD 1 and the target TG. The optical attenuation unit 2 is a device that attenuates terahertz waves. For example, the optical attenuation unit 2 is a variable optical attenuator that can change the attenuation rate. The optical attenuation unit 2 may be a mechanical (MEMS) variable optical attenuator, or a variable optical attenuator that utilizes the magneto-optical effect, the thermo-optical effect, or the like.

[0091] The determining unit 34 determines whether the output signal can be appropriately corrected based on the output signal of the RTD 1. The determining unit 34 controls the attenuation rate of the light attenuating unit 2 based on the determination result.

[0092] If it is determined that the output signal can be appropriately corrected, the determination unit 34 instructs the correction unit 32 to correct the output signal. The correction unit 32 corrects the output signal based on the instruction and outputs the corrected output signal to the distance determination unit 33. Based on the corrected output signal, the distance determination unit 33 determines the distance L to the target object TG.

[0093] If it is determined that the output signal cannot be properly corrected, the determination unit 34 increases the attenuation rate of the optical attenuation unit 2. This reduces the intensity of the terahertz waves received by the RTD 1. Therefore, the reflection coefficient η decreases. This makes it possible to adjust η so as to satisfy equation (18). The measuring device 100a performs measurement again. If it is still determined that the output signal cannot be properly corrected, the determination unit 34 may further increase the attenuation rate of the optical attenuation unit 2.

[0094] 19 is a diagram showing output signals before correction corresponding to multiple reflection coefficients η. The horizontal axis represents the oscillation frequency, and the vertical axis represents the amplitude. Note that the oscillation frequency on the horizontal axis is obtained by converting the sampling points into oscillation frequencies. Here, the output signal is shown when the distance to the target TG is L=1 (m).

[0095] 20 is a diagram showing the Fourier transform signals of the output signals before correction corresponding to the multiple reflection coefficients η shown in FIG. 19. The horizontal axis represents the distance L, and the vertical axis represents the amplitude. The horizontal axis represents 2L / c converted into L. For example, η=1×10 －７ In the case of η=1×10, one high peak that can be distinguished from the other peaks is obtained at the position of L≈1 (m). －４ In the case of η=1×10, a high peak appears at a position other than L=1 (m), and multiple peaks of similar height are obtained. －２ In this case, a broad peak appears at a point far away from L = 1 (m). That is, in this case, η = 1 × 10 －４ or η = 1 × 10－２ In the spectrum of FIG. 1, even if the correction unit 32 performs correction, it may not be possible to determine the accurate distance L.

[0096] The determination unit 34 obtains a spectrum in the 2L / c region of the output signal by performing a Fourier transform on the output signal before correction. The peak position corresponds to the distance L to the target TG. The determination unit 34 determines whether the spectrum contains multiple peaks of a predetermined height or higher. For example, the determination unit 34 may determine a threshold value according to the maximum peak and count the peaks that exceed the threshold value. If the spectrum contains multiple peaks (side lobes), the determination unit 34 may determine that appropriate correction is not possible. For example, the determination unit 34 may determine whether the spectrum contains multiple peaks (side lobes) of a predetermined height or higher. －２ It may be determined that appropriate correction is not possible when the half-width of the maximum peak is equal to or greater than a predetermined value, as in the spectrum of Fig. 1. It can also be said that the determining unit 34 determines whether the reflection coefficient η is too large.

[0097] In this way, the correction unit 32 can perform appropriate correction by adjusting η using the determination unit 34 and the light attenuation unit 2. By correcting the output signal after adjusting η, the distance determination unit 33 can determine the accurate distance L.

[0098] The determination unit 34 may determine whether appropriate correction is possible based on the spectrum obtained by Fourier transforming the output signal corrected by the correction unit 32. That is, the determination unit 34 may determine that appropriate correction has not been performed by the correction unit 32 if multiple peaks or a wide peak appear in the spectrum of the corrected output signal.

[0099] In the measuring device 100a of this embodiment, η can be adjusted so that η satisfies equation (18), which indicates the condition for appropriate correction, even if the distance L to the target TG is large.

[0100] The determination unit 34 may notify the user of the determination result and allow the user to change the attenuation rate of the light attenuation unit 2. For example, the user can adjust the attenuation rate by increasing or removing the light attenuation unit 2.

[0101] Instead of determining the peak by performing a Fourier transform, the determination unit 34 may determine whether the output signal contains a sine wave-like change (rather than a sawtooth wave). The determination unit 34 may determine that correction is possible if a sine wave-like change is contained. For example, the determination unit 34 may determine whether correction is possible using a learning model that has learned correctable / uncorrectable output signals.

[0102] [Embodiment 3] Another embodiment of the present invention will be described below. For the sake of convenience, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0103] 21 is a diagram showing an example of the configuration of a measuring apparatus 100b according to this embodiment. The measuring apparatus 100b includes an RTD 1, multiple mirrors 3, and a stage 4. Note that the measuring apparatus 100b also includes a voltage supply unit 11, a frequency filter circuit 12, a detection unit 20, and a control unit 30, similar to those in the first embodiment, but these are not shown here.

[0104] The multiple mirrors 3 are a pair of hyperbolic mirrors. The multiple mirrors 3 focus the terahertz waves emitted from the RTD 1 at a predetermined position. An object TG exists at the predetermined position. However, the focal position of the multiple mirrors 3 does not need to be on the surface of the object TG. If the RTD 1 has high directivity, the multiple mirrors 3 can be omitted.

[0105] The stage 4 is a movable stage to which the object TG is fixed. Here, the stage 4 is movable in two dimensions along the X and Y axes. The Z axis is parallel to the depth direction along the optical axis of the terahertz wave. The X and Y axes are perpendicular to the Z axis. By moving the stage 4 in two dimensions, the object TG can be scanned two-dimensionally. The measuring device 100b can obtain three-dimensional position information (shape information) of the object TG by measuring the distance to each two-dimensional position of the object TG.

[0106] The distance to the target object TG was actually measured in a situation where an obstacle 5 was placed in the optical path of the terahertz waves. Here, an acrylic plate and a piece of paper were stacked together as the obstacle 5. The obstacle 5 transmits the terahertz waves.

[0107] 22 is a diagram showing an image of the measurement results obtained by the measuring device 100b. Reference numeral 201 denotes an image showing the measurement results of the object TG at Z coordinate = 262 mm. Reference numeral 202 denotes an image showing the measurement results of the object TG at Z coordinate = 274 mm. Reference numeral 203 denotes a three-dimensional image of the object TG viewed obliquely based on the measurement results. Here, the object TG has the shape of the letters "THZ," with the "T" positioned at an angle relative to the "HZ."

[0108] The image indicated by the reference numeral 201 shows the spectral intensity at the Z coordinate = 262 mm position in the spectrum of the 2L / c region of the output signal (the spectrum corresponding to FIG. 14 ) using light and dark. Areas with high spectral intensity are depicted brightly. In other words, the area where an object that reflects terahertz waves exists at the Z coordinate = 262 mm position is depicted brightly. In the image indicated by the reference numeral 201, "HZ" in the foreground of the object TG is depicted brightly.

[0109] The image denoted by reference numeral 202, like the image denoted by reference numeral 201, shows the spectral intensity at the position of Z coordinate = 274 mm in the spectrum of the 2L / c region of the output signal by light and shade. In the image denoted by reference numeral 202, the "T" at the back of the object TG is depicted brightly.

[0110] The image denoted by reference numeral 203 depicts points where the spectral intensity exceeds a predetermined threshold value as dark spots corresponding to the spectral intensity. The three-dimensional shape of the object TG located behind the obstacle 5 is depicted.

[0111] The measuring device 100b can obtain information about the three-dimensional shape of the target object TG located behind an obstacle 5 that blocks visible light, for example. The measuring device 100b can perform appropriate measurements using terahertz waves by correcting the output signal using the corrector 32.

[0112] [Example of implementation using software] The functions of the measuring device 100 (hereinafter referred to as the "device") can be realized by a program that causes a computer to function as the device, and a program that causes a computer to function as each control block of the device (particularly each part included in the control unit 30).

[0113] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The functions described in each of the above embodiments are realized by executing the program using the control device and storage device.

[0114] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0115] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0116] [Summary] A signal correction device according to aspect 1 of the present invention includes an RTD (Resonant Tunneling Diode) that outputs an output signal by irradiating an object with terahertz waves and receiving the terahertz waves reflected by the object, a detection unit that detects the output signal from the RTD, a voltage supply unit that supplies a time-varying bias voltage to the RTD, and a correction unit that corrects the oscillation frequency of the output signal using a correction value set in which the correction value increases or decreases as the oscillation frequency increases.

[0117] A signal correction device according to aspect 2 of the present invention may be configured in the above-described aspect 1 such that the correction unit corrects the oscillation frequency of the output signal using a different set of correction values ​​depending on the reflection coefficient of the terahertz wave reflected by the object.

[0118] A signal correction device according to a third aspect of the present invention may be configured in the first or second aspect above, wherein the correction section corrects the output signal so that the difference between the maximum and minimum values ​​of the peak intervals in the output signal decreases.

[0119] A signal correction device according to a fourth aspect of the present invention is the signal correction device of any one of the first to third aspects, wherein the correction section performs correction so as to equalize peak intervals in the output signal.

[0120] A signal correction device according to aspect 5 of the present invention may be configured in any one of aspects 1 to 4 above such that the correction values ​​in the correction value set do not monotonically decrease or monotonically increase as the oscillation frequency increases.

[0121] A signal correction device according to aspect 6 of the present invention may be configured in any one of aspects 1 to 5 above, wherein the set of correction values ​​includes a correction value that increases the oscillation frequency and a correction value that decreases the oscillation frequency.

[0122] A signal correction device according to aspect 7 of the present invention may be configured in any one of aspects 1 to 6 above, further comprising a judgment unit that judges whether or not appropriate correction of the output signal is possible based on the output signal.

[0123] A signal correction device according to aspect 8 of the present invention may be configured in the above-mentioned aspect 7 such that the judgment unit judges whether or not appropriate correction of the output signal is possible based on a spectrum obtained by Fourier transforming the output signal.

[0124] A signal correction device according to a ninth aspect of the present invention may be configured in accordance with the seventh or eighth aspect above, further comprising an optical attenuation unit arranged in the optical path of the terahertz wave and capable of changing the attenuation rate of the terahertz wave.

[0125] A signal correction device according to aspect 10 of the present invention may be configured such that, in aspect 9 above, if it is determined that appropriate correction of the output signal is not possible, the determination unit increases the attenuation rate of the optical attenuation unit.

[0126] A signal correction device according to an eleventh aspect of the present invention may be configured in any one of the first to tenth aspects above, further comprising a distance determination unit that determines the distance to the object using the corrected output signal.

[0127] A signal correction method according to aspect 12 of the present invention is a method including: a signal acquisition step of acquiring an output signal of an RTD (Resonant Tunneling Diode) that irradiates an object with terahertz waves by supplying a time-varying bias voltage and receives the terahertz waves reflected by the object; and a correction step of correcting the oscillation frequency of the output signal using a correction value set that increases or decreases as the oscillation frequency increases.

[0128] [Additional Notes] One aspect of the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of one aspect of the present invention.

[0129] REFERENCE SIGNS LIST 1 RTD 2 Light attenuation unit 4 Stage 5 Obstacle 11 Voltage supply unit 12 Frequency filter circuit 13 High-pass filter 14 Low-pass filter 20 Detection unit 21 Differential amplifier 22 AD converter 30, 30a Control unit (signal correction device) 31 Correction value acquisition unit 32 Correction unit 33 Distance determination unit 34 Determination unit 100, 100a, 100b Measurement device (signal correction device) T1 First terminal T2 Second terminal T3 Third terminal

Claims

1. A signal correction device comprising: an RTD (Resonant Tunneling Diode) that outputs an output signal by irradiating an object with terahertz waves and receiving the terahertz waves reflected by the object; a detection unit that detects the output signal from the RTD; a voltage supply unit that supplies a time-varying bias voltage to the RTD; and a correction unit that corrects the oscillation frequency of the output signal using a set of correction values ​​that increase and decrease as the oscillation frequency increases.

2. The signal correction device according to claim 1, wherein the correction section corrects the oscillation frequency of the output signal using a different set of correction values ​​depending on the reflection coefficient of the terahertz wave reflected by the object.

3. The signal correction device according to claim 1, wherein the correction section performs correction so that the difference between the maximum and minimum values ​​of the peak interval in the output signal is reduced.

4. The signal correction device according to claim 1, wherein the correction section performs correction so as to equalize peak intervals in the output signal.

5. The signal correction device according to claim 1, wherein the correction values ​​in the correction value set do not monotonically decrease or increase as the oscillation frequency increases.

6. The signal correction device according to claim 1, wherein the set of correction values ​​includes a correction value that increases the oscillation frequency and a correction value that decreases the oscillation frequency.

7. The signal correction device according to claim 1, further comprising a determination unit that determines whether or not the output signal can be appropriately corrected based on the output signal.

8. The signal correction device according to claim 7, wherein the determination section determines whether or not the output signal can be appropriately corrected based on a spectrum obtained by performing a Fourier transform on the output signal.

9. The signal correction device according to claim 7, further comprising an optical attenuation section arranged in an optical path of the terahertz wave and capable of changing the attenuation rate of the terahertz wave.

10. The signal correction device according to claim 9, wherein, if it is determined that appropriate correction of the output signal is not possible, the determination section increases the attenuation rate of the optical attenuation section.

11. A signal correction device according to any one of claims 1 to 10, further comprising a distance determination unit that determines a distance to the object using the corrected output signal.

12. A signal correction method comprising: a signal acquisition step of acquiring an output signal from an RTD (Resonant Tunneling Diode) that irradiates an object with terahertz waves by supplying a time-varying bias voltage and receives the terahertz waves reflected by the object; and a correction step of correcting the oscillation frequency of the output signal using a set of correction values ​​that increase and decrease as the oscillation frequency increases.

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