JP6475523B2 - Control circuit and detector - Google Patents

Description

  The present invention relates to a technique for detecting terahertz waves using a superconducting tunnel junction element (hereinafter referred to as “STJ element”).

  Techniques have been proposed in the past for detecting dangerous substances such as clothes worn by humans, illegal drugs such as narcotics contained in envelopes, containers, luggage, and explosives using terahertz waves. Patent Document 1 discloses a technique for emitting a terahertz wave from a light source toward a predetermined inspection object and detecting the terahertz wave transmitted through the inspection object.

JP 2006-71412 A

The detector for detecting the terahertz wave is configured to detect a phonon generated from the terahertz wave by a superconducting tunnel junction (STJ) element and output a signal corresponding to the detected terahertz wave. There is something. In this detector, since the current value of a weak signal flowing through the STJ element is read, in order to ensure sufficient detection accuracy of the terahertz wave, the bias voltage applied to the STJ element must be set appropriately. However, since the optimum bias voltage of the STJ element varies depending on individual differences and the like, it may take a long time to set the bias voltage.
Accordingly, an object of the present invention is to provide a technique for facilitating setting of a bias voltage applied to an STJ element.

The control circuit of the present invention relates to the superconducting tunnel junction with respect to each of a terahertz wave irradiation time and a non-irradiation time with respect to the receiving portion of the detector that detects the terahertz wave from the inspection object by the superconducting tunnel junction element A calibration process is performed in which a bias voltage for detection is set based on a current value of a detection signal current flowing through the superconducting tunnel junction element when a plurality of bias voltages having a plurality of voltage values are respectively applied to the element.
According to the present invention, for each of terahertz wave irradiation and non-irradiation, detection is performed based on the current value of the detection signal current flowing through the superconducting tunnel junction element when a plurality of bias voltages are applied. Since the calibration process for setting the bias voltage is performed, the bias voltage applied to the STJ element can be easily set.

In the control circuit of the present invention, the superconducting tunnel junction is applied when the detection bias voltage is applied to the superconducting tunnel junction element with respect to each of the terahertz wave irradiation and non-irradiation to the detector. The necessity of re-execution of the calibration process may be determined based on the current value of the detection signal current flowing through the element.
According to the present invention, the calibration process is performed in order to determine the necessity of re-execution of the calibration process based on the current value of the detection signal current when the set detection bias voltage is applied to the superconducting tunnel junction element. Necessary timing can be accurately determined.

In the control circuit of the present invention, the calibration process may be performed based on a timing at which the inspection object is inspected.
According to the present invention, it is easy to increase the detection accuracy of the terahertz wave when the inspection is performed.

In the control circuit of the present invention, the calibration process may be performed at predetermined time intervals.
According to the present invention, it is possible to reduce the time variation of the terahertz wave detection accuracy.

In the control circuit of the present invention, the calibration processing may be performed based on the temperature of the superconducting tunnel junction element, electrical noise received by the superconducting tunnel junction element, noise due to electromagnetic waves, or vibration.
According to the present invention, it is possible to reduce fluctuations in detection accuracy caused by an external element that easily affects terahertz wave detection accuracy.

In the control circuit of the present invention, an error signal may be output when the detection bias voltage cannot be set.
According to the present invention, it is possible to output a signal indicating that a certain degree of terahertz wave detection accuracy cannot be ensured.

The detector of the present invention applies a bias voltage having a plurality of voltage values to the control circuit having the above-described configuration, irradiation means for irradiating the receiving unit with terahertz waves, and the superconducting tunnel junction element. Voltage applying means and measuring means for measuring a current value of a detection signal current flowing through the superconducting tunnel junction element.
According to the present invention, for each of terahertz wave irradiation and non-irradiation, detection is performed based on the current value of the detection signal current flowing through the superconducting tunnel junction element when a plurality of bias voltages are applied. Since the calibration process for setting the bias voltage is performed, the bias voltage applied to the STJ element can be easily set.

The block diagram which shows the structure of the terahertz wave detector which concerns on one Embodiment of this invention. The figure which shows the structure of the board | substrate absorption type STJ element which concerns on the same embodiment. The block diagram which shows the electric constitution of the control apparatus which concerns on the same embodiment. 6 is a flowchart showing calibration processing according to the embodiment. The graph which shows an example of the voltage-current characteristic of the STJ element which concerns on the same embodiment. The flowchart which shows the necessity determination process I concerning the embodiment. The graph which shows an example of the voltage-current characteristic of the STJ element which concerns on the same embodiment. The figure which shows an example of the test | inspection system by which the necessity determination process II concerning the embodiment is employ | adopted. 6 is a flowchart showing necessity determination processing II according to the embodiment. 6 is a flowchart showing necessity determination processing III according to the embodiment. The block diagram which shows the structure of the terahertz wave detector which performs the necessity determination process IV concerning the embodiment. 6 is a flowchart showing necessity determination processing IV according to the embodiment.

[Embodiment]
FIG. 1 is a block diagram showing a configuration of a terahertz wave detector 1 according to an embodiment of the present invention. The terahertz wave detector 1 is a detector that detects the presence or absence of the substance S and the type of the substance S by detecting a terahertz wave from the inspection target T that is an inspection target. The terahertz wave is an electromagnetic wave belonging to a frequency band from 0.7 THz to 30 THz, for example. The substance S is, for example, illegal drugs such as narcotics and dangerous materials such as explosives. The inspection object T is, for example, a person who visits a predetermined place such as an airport or customs, an object (luggage) possessed by the person, or a postal item such as an envelope or a parcel.

As shown in FIG. 1, the terahertz wave detector 1 includes an irradiation device 10, a condensing device 20, a substrate absorption STJ element 30, a cooling device 40, a control device 50, and a substance determination device 60. . In FIG. 1, a solid arrow means a signal flow, and a two-dot chain arrow means a direction in which a terahertz wave propagates.
The irradiation device 10 includes, for example, a terahertz wave generation device, and selectively generates the generated terahertz wave for the inspection target T existing in the detection region of the terahertz wave detector 1 and the receiving unit of the terahertz wave detector 1. It is an apparatus that irradiates. As shown in FIG. 2, the wave receiving unit of the terahertz wave detector 1 is a light collecting device 20 in the present embodiment. The irradiation apparatus 10 further includes irradiation direction changing means for changing the irradiation direction of the terahertz wave. The irradiation direction changing means includes, for example, an optical system including a mirror and a lens that reflects the generated terahertz wave in a predetermined direction, and a driving device such as a motor that changes the direction of the mirror. The irradiation apparatus 10 irradiates the condensing device 20 with terahertz waves as shown in FIGS. 1 and 2 during the calibration process, and when inspecting the inspection target T, the irradiation apparatus 10 applies the inspection target T as shown in FIG. Terahertz waves are irradiated to the target.

  The condensing device 20 is a device that includes a super hemispherical lens made of, for example, high-resistance silicon, and condenses incident terahertz waves at the position of the substrate absorption STJ element 30. Here, the condensing device 20 condenses the terahertz wave reflected by the substance S among the terahertz waves irradiated by the irradiation device 10. The condensing device 20 corresponds to a wave receiving unit that receives a terahertz wave.

  The substrate absorption type STJ element 30 is a substrate absorption type superconducting tunnel junction element. FIG. 2 is a diagram showing a configuration of the substrate absorption type STJ element 30. The substrate absorption type STJ element 30 includes an absorber substrate 31 and an STJ element 32. The absorber substrate 31 is a substrate that receives terahertz waves and generates phonons. The absorber substrate 31 is a single crystal substrate made of, for example, LiNbO3 (lithium niobate) or LiTaO3 (lithium tantalate), which easily absorbs terahertz waves, and the light collecting device 20 is adhered by adhesion or the like.

  The STJ element 32 is an element that detects a phonon generated by the absorber substrate 31 and outputs an electric signal corresponding to the terahertz wave. The STJ element 32 has a structure in which a lower electrode 32a, a tunnel barrier (tunnel barrier) 32b, and an upper electrode 32c are stacked in this order from the absorber substrate 31 side. The lower electrode 32a is an electrode that is provided on the upper surface of the absorber substrate 31 and is made of a single layer of a superconducting electrode material or two layers of films having different superconducting energy gaps. The tunnel barrier 32b is made of an insulating film made of, for example, AlOx (aluminum oxide). The upper electrode 32c is an electrode composed of a single layer of a superconducting electrode material or two layers of films having different superconducting energy gaps.

  The cooling device 40 is a device that includes, for example, a small mechanical refrigerator and cools the substrate absorption type STJ element 30.

  The control device 50 is a device that controls the terahertz wave detector 1. As main control performed by the control device 50, there is control related to calibration processing for setting a bias voltage to be applied to the STJ element 32. Further, the control device 50 controls the presence / absence and irradiation direction of the terahertz wave by the irradiation device 10.

  The substance determination device 60 is an apparatus that determines the presence or absence and type of the substance S that emits the terahertz wave based on the signal output from the STJ element 32.

FIG. 3 is a block diagram showing an electrical configuration of the control device 50.
As shown in FIG. 3, one end (for example, the lower electrode 32 a) of the STJ element 32 is connected to the ground point GND, and the other end (upper electrode 32 c) is connected to one end of the ammeter 52. A bias power supply 51 is further connected in parallel to the STJ element 32. Here, the bias power supply 51 has a positive electrode connected to the ground point GND and a negative electrode connected to one end of the ammeter 52. The bias power source 51 is a DC variable voltage source and applies a bias voltage for operating the STJ element 32 to the STJ element 32.

  The ammeter 52 is a measuring unit that measures the current value of the current flowing through the STJ element 32. The ammeter 52 outputs an analog signal indicating the measured current value to the A / D converter 53. The A / D converter 53 converts an analog signal from the ammeter 52 into a digital format.

  The data buffer 54 buffers current value data based on the signal from the A / D converter 53. The data storage unit 55 is a memory that stores data buffered in the data buffer 54 and data according to the control of the control circuit 57. The comparison unit 56 compares the current value of the current flowing through the STJ element 32 during irradiation of the terahertz wave by the irradiation device 10 with the current value of the current flowing through the STJ element 32 during non-irradiation, and indicates a detection signal indicating the difference therebetween. A current value signal is output to the control circuit 57.

  The control circuit 57 includes an arithmetic processing unit such as a CPU (Central Processing Unit) and a memory, for example, and is used for detection based on the current value of the detection signal current when bias voltages having a plurality of voltage values are respectively applied to the STJ element 32. A calibration process for setting a bias voltage is performed. The detection bias voltage refers to a bias voltage used when detecting a terahertz wave from the inspection target T (substance S). The control circuit 57 outputs a digital voltage control signal for controlling the bias voltage applied to the bias power supply 51 to the D / A converter 58. The D / A converter 58 is a voltage application unit that applies a bias voltage to the STJ element 32 by converting the voltage control signal from a digital format to an analog format and controlling the bias power source 51 with the converted voltage. . In addition, the control circuit 57 outputs an irradiation control signal for controlling irradiation or non-irradiation of the terahertz wave, and further, an irradiation direction of the terahertz wave to the irradiation apparatus 10. The control circuit 57 outputs a detection signal indicating the current value of the current measured by the ammeter 52 to the substance determination device 60 when the substance S is detected.

  FIG. 4 is a flowchart showing the calibration process performed by the control circuit 57. FIG. 5 is a graph showing an example of voltage-current characteristics of the STJ element 32. In the graph of FIG. 5, the horizontal axis represents the voltage value of the bias voltage, and the vertical axis represents the measured current value. Moreover, a solid line is a graph at the time of irradiation, and a broken line is a graph at the time of non-irradiation. The first calibration process is performed, for example, at a timing before the terahertz wave detector 1 is shipped or at a timing at which the terahertz wave detector 1 is used.

First, the control circuit 57 sets a variable m for designating the voltage value Vm of the bias voltage to “1” (step S1). Here, the voltage value Vm of the bias voltage is divided into n equal parts of the voltage range from 0V to the voltage value Vg of the gap voltage of the STJ element 32 (n = 100), and is the m-th counted from the low voltage side. Voltage. Here, the voltage value V1 is Vg / 100.
Note that n may be a value other than 100, and the voltage range may be divided other than equally divided.

  Next, the control circuit 57 controls the bias power supply 51 to apply a bias voltage having a voltage value Vm to the STJ element 32 (step S2). Next, the control circuit 57 controls the irradiation device 10 to irradiate the condensing device 20 with the terahertz wave (step S3). Next, the control circuit 57 uses the ammeter 52 to measure the current value of the current flowing through the STJ element 32 (step S4). The current value measured here is Im1. As shown in FIG. 5, the current value Im1 is a current value of a current flowing through the STJ element 32 when a bias voltage having a voltage value Vm is applied at the time of irradiation with a terahertz wave.

  Next, the control circuit 57 performs control to prevent the irradiation apparatus 10 from irradiating the terahertz wave (that is, non-irradiation) with the irradiation apparatus 10 as a control (step S5). Next, the control circuit 57 uses the ammeter 52 to measure the current value of the current flowing through the STJ element 32 (step S6). The current value measured here is Im2. As shown in FIG. 5, the current value Im2 is a current value of a current flowing through the STJ element 32 when a bias voltage having a voltage value Vm is applied when no terahertz wave is irradiated.

  Next, the control circuit 57 controls the comparison unit 56 to calculate Im1-Im2, which is the difference between the current value Im1 and the current value Im2, as the current value Im of the detection signal current (step S7). The control circuit 57 stores the data of the current value Im in its own memory or the data storage unit 55.

Next, the control circuit 57 determines whether n = 100 (step S8). That is, the control circuit 57 determines whether or not the current value Im has been calculated over the entire voltage range from the voltage value 0 V to the voltage value Vg. Here, the control circuit 57 determines “NO” in step S8, increments the variable m by “1” (step S9), and returns to the process of step S2.
The control circuit 57 calculates the current value Im by executing the processes of steps S2 to S8 even when each value from the variable m = 2 to 100 is set. When the voltage-current characteristic of the STJ element 32 is represented by the graph of FIG. 5, the current value Im corresponding to the voltage value of each bias voltage corresponds to the difference between the graph of the current value Im1 and the graph of the current value Im2. .

If the determination is “YES” in step S8, the control circuit 57 obtains the variable m having the maximum current value Im (step S10). Next, the control circuit 57 determines whether or not the maximum current value Im is greater than or equal to a threshold value (step S11). If “YES” is determined in step S10, the control circuit 57 sets the current value Im to “Ib0”, sets the voltage value Vm of the bias voltage from which the current value Im is obtained to “Vb0”, and sets the data storage unit 55. (Step S12). By this processing, the control circuit 57 sets a detection bias voltage.
The substance determination device 60 determines the presence and type of the substance S based on a detection signal indicating a current flowing through the STJ element 32 when the detection bias voltage is applied to the STJ element 32.

If it is determined “NO” in step S8, the control circuit 57 outputs an error signal (step S13). The error signal is a signal that is output when the current value Im is smaller than the threshold value and terahertz wave detection accuracy is not sufficiently ensured. In this way, the control circuit 57 outputs an error signal when the terahertz wave detector 1 cannot set a bias voltage for ensuring a certain degree of terahertz wave detection accuracy. The format of the error signal is not particularly limited. For example, the error signal is a signal for notifying an error by displaying an image or by sound.
The above is the description of the calibration process. This calibration process makes it easy to set the bias voltage because it is not necessary to optimize the bias voltage while manually changing the voltage value of the bias voltage.

  After performing the initial calibration process, the control circuit 57 performs a necessity determination process which is a process for determining whether the calibration process needs to be re-executed. That is, the necessity determination process is a process for determining whether the calibration process needs to be re-executed. Hereinafter, necessity determination processes (I) to (IV) will be described as necessity determination processes.

<Necessity determination processing I>
FIG. 6 is a flowchart showing the necessity determination process I performed by the control circuit 57. FIG. 7 is a graph showing an example of voltage-current characteristics of the STJ element 32. The necessity determination process I is performed at an arbitrary timing after the initial calibration process.
First, the control circuit 57 reads the voltage value Vb0 of the bias voltage and the current value Ib0 of the detection signal current from the data storage unit 55 (step S21). Next, the control circuit 57 controls the bias power supply 51 to apply the bias voltage having the voltage value Vb0 to the STJ element 32 (step S22). Next, the control circuit 57 controls the irradiation device 10 to irradiate the condensing device 20 with the terahertz wave (step S23). Next, the control circuit 57 uses the ammeter 52 to measure the current value of the current flowing through the STJ element 32 (step S24). The current value measured here is Ib1. As shown in FIG. 7, the current value Ib1 is a current value of a current flowing through the STJ element 32 when a bias voltage having a voltage value Vb0 is applied during irradiation with terahertz waves.

  Next, the control circuit 57 performs control to prevent the irradiation apparatus 10 from irradiating the terahertz wave (that is, non-irradiation) with the irradiation apparatus 10 as a control (step S25). Next, the control circuit 57 uses the ammeter 52 to measure the current value of the current flowing through the STJ element 32 (step S26). The current value measured here is Ib2. As shown in FIG. 7, the current value Ib2 is the current value of the current flowing through the STJ element 32 when a bias voltage having the voltage value Vb0 is applied when no terahertz wave is irradiated.

  Next, the control circuit 57 controls the comparison unit 56 to calculate Ib1-Ib2, which is the difference between the current value Ib1 and the current value Ib2, as the current value Ib of the detection signal current (step S27).

  Next, the control circuit 57 determines whether or not it is necessary to re-execute calibration processing based on the current value Ib (step S28). When it is determined that the re-execution of the calibration process is not necessary (step S28; NO), the control circuit 57 ends the necessity determination process I. When it is determined that the calibration process needs to be re-executed (step S28; YES), the control circuit 57 performs the calibration process (step S29). This calibration process may be the same as the calibration process described in FIG.

  If the voltage-current characteristics of the STJ element 32 have not changed since the first calibration process, the bias voltage is optimized with the voltage value Vb0, and therefore the current value Ib of the detection signal current is a sufficiently large value. Should be. However, the voltage-current characteristics of the STJ element 32 may change due to the location where the terahertz wave detector 1 is used, the surrounding environment, or the like. As a result, the bias voltage at which the detection signal current peaks may also change.

  Therefore, in step S28, the control circuit 57 determines that re-execution of the calibration process is unnecessary when the current value Ib is equal to or greater than the threshold value, and re-executes the calibration process when the current value Ib is less than the threshold value. judge. The condition for determining whether re-execution is necessary may be other conditions. For example, when the current value Ib is less than the threshold value compared to the current value Ib0 of the detection signal current at the time of the previous calibration process, the control circuit 57 determines that re-execution of the calibration process is unnecessary, If it is greater than or equal to the threshold value, it may be determined that re-execution of the calibration process is necessary. As described above, the control circuit 57 may determine whether or not the calibration process needs to be re-executed based on the predetermined condition indicating whether or not the current value Ib sufficiently secures the terahertz wave detection accuracy. .

  In the example shown in FIG. 7, the voltage value Vb0 of the bias voltage is reset to the low potential side by re-execution of the calibration process. In the terahertz wave detector 1, the reset bias voltage of the voltage value Vb0 is used at least until the next calibration process.

<Necessity determination process II>
The necessity determination process II is a process for determining whether or not the calibration process is necessary based on whether or not the inspection target T is inspected. FIG. 8 is a diagram illustrating an example of an inspection system in which the necessity determination process II is employed. As shown in FIG. 8, this inspection system is a system for inspecting an inspection target T that is a mail. This inspection system includes a conveyance belt 81 that conveys the inspection target T to a detection region D that is a detection target of the terahertz wave detector 1, and a gate device 82 through which the inspection target T that has been conveyed passes. The terahertz wave detector 1 is disposed inside the gate device 82. Further, in this inspection system, an object detection sensor 80 for detecting the presence / absence of the inspection target T on the transport belt 81 is fixedly provided on the upstream side in the transport direction of the inspection target T as viewed from the detection region D. It has been. The object detection sensor 80 is, for example, an infrared sensor, but may be another type of sensor. When the object detection sensor 80 detects the presence of the inspection target T, the object detection sensor 80 outputs a signal notifying the detection to the control circuit 57. The control circuit 57 determines the inspection timing based on this signal.

FIG. 9 is a flowchart showing the necessity determination process II performed by the control circuit 57.
First, the control circuit 57 determines whether or not the presence of the inspection target T is detected by the object detection sensor 80 (step S31). If “NO” is determined in the step S31, the control circuit 57 determines that the re-execution of the calibration process is unnecessary.

If “YES” is determined in the step S31, the control circuit 57 performs a calibration process (step S32). This calibration process may be the same as the process described in FIG. The distance between the detection area D and the object detection sensor 80 is determined so that the calibration process is completed after the presence of the inspection target T is detected by the object detection sensor 80 until the detection area D is reached. ing. In the inspection system, the conveyor belt 81 may be stopped when an error signal is output, and then the conveyor belt 81 may be operated again when a bias voltage is set.
According to the necessity determination process II, for example, the control circuit 57 performs the calibration process before each of the inspection objects T is inspected. Therefore, the terahertz wave detection accuracy when the inspection is performed is increased. It's easy to do.

  The system for inspecting the inspection object T, which is a postal item, has been described as an example, but the necessity determination process II is also adopted in the system for inspecting luggage at airports and customs and the inspection system for inspecting people. can do. The determination of the inspection timing is not limited to the method using the object detection sensor 80. For example, the control circuit 57 may determine the inspection timing in accordance with a manual operation.

<Necessity determination process III>
The necessity determination process III is a process for determining whether or not the calibration process is necessary at predetermined time intervals. FIG. 10 is a flowchart showing the necessity determination process III performed by the control circuit 57.
The control circuit 57 measures the elapsed time from the time when the previous calibration process was executed using a timer (step S41). Next, the control circuit 57 determines whether or not the measured elapsed time has reached a predetermined time (step S42). If “NO” is determined in the step S42, the control circuit 57 determines that the re-execution of the calibration process is unnecessary, and continues the time measurement by the timer.

If “YES” is determined in the step S42, the control circuit 57 performs a calibration process (step S43). This calibration process may be the same as the process described in FIG.
The time interval for executing the calibration process may be set, for example, before product shipment of the terahertz wave detector 1 or by user settings. If the time during which the terahertz wave detection accuracy in the terahertz wave detector 1 can vary is known from an empirical rule or experiment, the time interval may be set based on that time.
According to the necessity determination process III, the time variation of the terahertz wave detection accuracy of the terahertz wave detector 1 can be reduced.

<Necessity determination process IV>
The necessity determination process IV is a process for determining whether or not the calibration process is necessary based on an external element that easily affects the terahertz wave detection accuracy. FIG. 11 is a block diagram illustrating a configuration of the terahertz wave detector 1 that performs the necessity determination process IV. The terahertz wave detector 1 includes a measuring device 90 in addition to the devices described in FIG. The measuring device 90 is a device that measures an external element that easily affects the terahertz wave detection accuracy. Specifically, the measurement device 90 includes a temperature measurement unit 91, an electrical noise measurement unit 92, an electromagnetic wave noise measurement unit 93, and a vibration measurement unit 94.

The temperature measurement unit 91 includes a temperature sensor, for example, and measures the temperature of the STJ element 32. The electrical noise measurement unit 92 includes a noise voltage measurement circuit using, for example, a voltage probe, and measures the intensity of electrical noise received by the STJ element 32. The electrical noise is, for example, noise caused by the power source of the terahertz wave detector 1. This noise comes through the power line. The electromagnetic wave noise measurement unit 93 includes, for example, an EMI noise sensor, and measures the intensity of electromagnetic wave noise received by the STJ element 32. This noise is, for example, electric field / magnetic field noise propagating in a space generated from an electronic device existing around the terahertz wave detector 1. The vibration measuring unit 94 includes, for example, a vibration sensor, and measures the strength of vibration received by the STJ element 32.
Note that some or all of the measurement units included in the measurement device 90 may have an external configuration of the terahertz wave detector 1.

FIG. 12 is a flowchart showing the necessity determination process IV performed by the control circuit 57.
The control circuit 57 uses each of the temperature measurement unit 91, the electrical noise measurement unit 92, the electromagnetic wave noise measurement unit 93, and the vibration measurement unit 94 to control the temperature of the STJ element 32 and the electrical noise received by the STJ element 32. The intensity, the intensity of noise due to electromagnetic waves, and the intensity of vibration are measured (steps S51 to S54). Each of the temperature measurement unit 91, the electrical noise measurement unit 92, the electromagnetic wave noise measurement unit 93, and the vibration measurement unit 94 repeatedly performs measurement at a predetermined interval, for example. As for electrical noise and noise due to electromagnetic waves, for example, noise in the same frequency band as the terahertz wave is measured.

  Next, the control circuit 57 determines whether it is necessary to re-execute the calibration process based on the measurement values of the temperature measurement unit 91, the electrical noise measurement unit 92, the electromagnetic wave noise measurement unit 93, and the vibration measurement unit 94. (Step S55). When the control circuit 57 determines that the re-execution of the calibration process is not necessary (step S55; NO), the control circuit 57 returns to the process of steps S51 to S54. On the other hand, when it is determined that the calibration process needs to be re-executed (step S55; YES), the control circuit 57 performs the calibration process (step S56). This calibration process may be the same as the calibration process described in FIG.

In step S55, the control circuit 57 calibrates one measured value or two or more measured values of the temperature of the STJ element 32, electrical noise received by the STJ element 32, noise due to electromagnetic waves, and vibration. When the condition indicating that the process is necessary is satisfied, it is determined that the calibration process needs to be re-executed. At this time, the control circuit 57 may use a condition that the measurement value becomes a predetermined value, or may use a condition that the magnitude of the fluctuation within the predetermined period is equal to or greater than a threshold value.
According to the necessity determination process IV, it is possible to reduce the fluctuation of the detection accuracy caused by an external element that easily affects the detection accuracy of the terahertz wave.

In the necessity determination process IV, determination based on one or more measurement values of the temperature of the STJ element 32, electrical noise received by the STJ element 32, noise due to electromagnetic waves, and vibration may be omitted. The terahertz wave detector 1 may determine the necessity of re-execution of the calibration process by combining two or more of <necessity determination process I> to <necessity determination process IV>.

[Modification]
The present invention may be implemented in a form different from the above-described embodiment. Moreover, you may combine each of the modification shown below.
The control circuit 57 may make the initial calibration process different from the calibration process to be re-executed. In the calibration process to be re-executed, the control circuit 57 selects a voltage range corresponding to the voltage value Vb0 in the voltage range from 0 V to the voltage value Vg (for example, a voltage having a predetermined width centered on the voltage value Vb0). Calibration processing may be performed based on (range). Further, the control circuit 57 may make the interval between the voltage values Vm and Vm + 1 in the calibration process to be re-executed wider than the interval between the voltage values Vm and Vm + 1 in the initial calibration process. Further, the control circuit 57 calculates the current value of the detection signal current at this wide interval, and then selects a voltage range corresponding to the voltage value of the bias voltage for which the current value is relatively large (for example, the voltage value is The current value of the detection signal current may be calculated with a width narrower than this with respect to the voltage range having a predetermined width at the center.

A part of the configuration or operation of the terahertz wave detector 1 of the above-described embodiment may be omitted.
For example, the terahertz wave detector 1 may not include a configuration for outputting an error signal. Further, the terahertz wave detector 1 may be configured not to perform necessity determination processing for determining whether re-execution of calibration processing is necessary. Further, the terahertz wave detector 1 may be configured not to include the light collecting device 20. In this case, the absorber substrate 31 corresponds to the wave receiving portion of the terahertz wave detector 1. In addition, the terahertz wave detector 1 may not include the cooling device 40 when the STJ element 32 is in a coolable state.

The terahertz wave detector 1 may be a detector that detects a terahertz wave transmitted through the inspection target T or a terahertz wave naturally emitted from the substance S.
The terahertz wave detector 1 may individually include an irradiation device for detecting the terahertz wave from the substance S and an irradiation device for calibration. In this case, it is possible to adopt a configuration in which each irradiation apparatus does not include an irradiation direction changing unit for changing the irradiation direction of the terahertz wave.

The control circuit of the present invention is not limited to a control circuit built in a detector that detects terahertz waves. The control circuit of the present invention may be incorporated in, for example, a bias voltage setting device that sets bias voltages of a plurality of terahertz wave detectors before product shipment.
In addition, the control circuit of the present invention may be configured not to set a bias voltage based on the difference in the current value of the current flowing through the STJ element 32 when the terahertz wave is irradiated and when the terahertz wave is not irradiated. The bias voltage may be set based on the ratio of the current values of the currents flowing through the STJ element 32 at the time of non-irradiation.

  Each function realized by the control circuit 57 of each embodiment described above may be realized by one or more hardware circuits, or executes one or more programs for causing a computer to realize the same function. It may be realized by this, or may be realized by a combination thereof. When the function of the control circuit 57 is realized by using a program, this program includes a magnetic recording medium (magnetic tape, magnetic disk (HDD (Hard Disk Drive), FD (Flexible Disk)), etc.), optical recording medium (optical disk). Etc.), may be provided in a state stored in a computer-readable recording medium such as a magneto-optical recording medium or a semiconductor memory, or may be distributed via a communication line such as the Internet.

  The configurations, shapes, sizes, arrangement relationships, quantities, and the like described in the above-described embodiments and modifications are merely schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical idea shown in the claims.

DESCRIPTION OF SYMBOLS 1 ... Terahertz wave detector, 10 ... Irradiation device, 20 ... Condensing device, 30 ... Substrate absorption type STJ element, 31 ... Absorber substrate, 32 ... STJ element, 40 ... Cooling device, 50 ... Control device, 51 ... Bias Power source, 52 ... ammeter, 53 ... A / D converter, 54 ... data buffer, 55 ... data storage unit, 56 ... comparison unit, 57 ... control circuit, 58 ... D / A converter, 60 ... substance determination device, DESCRIPTION OF SYMBOLS 80 ... Object detection sensor, 81 ... Conveyance belt, 82 ... Gate apparatus, 90 ... Measurement apparatus, 91 ... Temperature measurement part, 92 ... Electrical noise measurement part, 93 ... Electromagnetic noise measurement part, 94 ... Vibration measurement part

Claims (7)

  A plurality of voltages are applied to the superconducting tunnel junction element with respect to the receiving part of the detector for detecting the terahertz wave from the inspection object by the superconducting tunnel junction element, when the terahertz wave is irradiated or not. A control circuit for performing a calibration process for setting a bias voltage for detection based on a current value of a detection signal current flowing through the superconducting tunnel junction element when a bias voltage of a value is applied. The detection signal current flowing through the superconducting tunnel junction element when the detection bias voltage is applied to the superconducting tunnel junction element with respect to each of the irradiation with the terahertz wave and the non-irradiation to the detector. The control circuit according to claim 1, wherein the necessity of re-execution of the calibration process is determined based on a current value. The control circuit according to claim 1, wherein the calibration process is performed based on a timing at which the inspection object is inspected. The control circuit according to any one of claims 1 to 3, wherein the calibration process is performed at a predetermined time interval. The calibration process is performed based on the temperature of the superconducting tunnel junction element, electrical noise received by the superconducting tunnel junction element, noise due to electromagnetic waves, or vibration. The control circuit described. The control circuit according to any one of claims 1 to 5, wherein an error signal is output when the bias voltage for detection cannot be set. A control circuit according to any one of claims 1 to 6,
Irradiating means for irradiating the wave receiving portion with terahertz waves;
Voltage applying means for applying a bias voltage of the plurality of voltage values to the superconducting tunnel junction element;
And a measuring means for measuring a current value of a detection signal current flowing through the superconducting tunnel junction element.

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