Control system

Abstract

To provide a control system which has high convenience, while suppressing power consumption.SOLUTION: A control system 1 which is mounted on a vehicle and which controls communication with a communication device located in the periphery of the vehicle includes: a detection unit 20 which generates an electromagnetic field around an antenna 10 in a first mode which operates under a preset first condition, and which detects turbulence of the electromagnetic field based on the change in impedance of the antenna 10; a communication unit 30 for, when turbulence is detected, outputting information for the communication device associated with the vehicle by short-distance radio communication to the periphery of the vehicle; and a counting unit 40 for counting the number of times of information output in the case where there is no response with respect to the information even though the communication unit 30 has outputted the information. In the case where the counting result by the counting unit 40 within the preset first time has exceeded the preset number, the detection unit 20 shifts to a second mode which operates under a second condition which has further reduced power consumption than the first condition.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control system that is mounted on a vehicle and controls communication with communication devices present around the vehicle. [Background technology]

[0002] Conventionally, a technology has been used that detects whether or not a communication device is present around a vehicle based on disturbances in a magnetic field, and when the presence of the communication device is detected, transitions to a communication state in which communication with the communication device is performed. Examples of such a technology include those described in Patent Documents 1 and 2.

[0003] Patent Document 1 describes a door handle device provided on a vehicle door handle. This door handle device has an antenna and an NFC reader arranged in the handle. The antenna generates a magnetic field around it, and the NFC reader detects disturbances in the magnetic field. The NFC reader is configured to transition from a power-saving operating state to an active operating state in response to the proximity of an NFC tag.

[0004] Patent Document 2 describes a vehicle authentication system. This vehicle authentication system includes an on-board device mounted on the vehicle and an electronic key carried by the vehicle user. Authentication is performed by wireless communication between the on-board device and the electronic key, and when the user leaves the vehicle, if the user performs an intended operation, authentication is suspended for a certain period of time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2021 / 0370877 [Patent Document 2] JP 2016-79600 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the door handle device described in Patent Document 1, for example, when a metal object other than the NFC tag is brought close by tampering, the magnetic field is disturbed and the NFC reader transitions to an active operating state. The NFC reader also transitions to an active operating state when the magnetic field is disturbed in an EMI environment. If the NFC reader transitions to an active operating state in this way even when it cannot communicate, unnecessary communication will be performed, resulting in increased power consumption.

[0007] In addition, in the vehicle authentication system described in Patent Document 2, when a user wants to lock or unlock the vehicle earlier than originally intended, a different operation is required, which is inconvenient. In addition, after a certain period of time has passed, authentication can be resumed, which increases the dark current.

[0008] Therefore, there is a demand for a control system that can reduce power consumption. [Means for solving the problem]

[0009] A characteristic configuration of the control system of the present invention is a control system that is mounted on a vehicle and controls communication with a communication device present around the vehicle, and includes a detection unit that generates an electromagnetic field around an antenna in a first mode operating under preset first conditions and detects disturbances in the electromagnetic field based on changes in the impedance of the antenna, a communication unit that outputs information for a communication device associated with the vehicle to the surroundings of the vehicle via short-range wireless communication when the disturbance is detected, and a counting unit that counts the number of times the information is output when there is no response to the information despite the communication unit outputting the information, and the detection unit transitions to a second mode operating under second conditions that consume less power than the first conditions when the counting result by the counting unit within a preset first time period exceeds a preset number.

[0010] With this characteristic configuration, when the detection unit detects a disturbance in the electromagnetic field, if there is no response to the information within a first time period even though the communication unit outputs information for the communication device through short-range wireless communication, the operation of the detection unit can be shifted to an operation in a second mode with reduced power consumption. Therefore, if there is no response to the information within the first time period, it is possible to reduce power consumption. Moreover, with a simple configuration in which the counting unit counts when there is no response to the information within the first time period, it is possible to prevent erroneous detection due to a metal object other than the NFC tag being brought into proximity due to tampering, etc. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows a vehicle equipped with a control system. [Diagram 2] FIG. 2 is a block diagram showing a configuration of a control system. [Diagram 3] 4 is a timing chart showing the operation of the control system. [Figure 4] 4 is a flowchart showing the process of the control system. [Diagram 5] 10 is a flowchart showing a process of transitioning to a first mode (a return process). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The control system according to the present invention is configured to control communication with communication devices present around a vehicle. The control system 1 of the present embodiment will be described below. However, the control system 1 is not limited to the following embodiment, and various modifications are possible without departing from the gist of the invention.

[0013] FIG. 1 is a diagram showing a vehicle 2 equipped with a control system 1. As shown in FIG. 1, the control system 1 is provided on a door handle 4 of the vehicle 2. The control system 1 of this embodiment detects a smart key (one example of a "communication device") 3 present around the vehicle 2. The smart key 3 is a key associated with the vehicle 2, and the lock mechanism of the door of the vehicle 2 can be locked or unlocked by pressing a lock / unlock switch of the smart key 3 or touching a predetermined part of the door. If the communication device is a mobile terminal such as a smartphone, the doors can also be locked or unlocked by operating an application.

[0014] Next, a description will be given of the configuration of the control system 1. Fig. 2 is a schematic diagram showing the configuration of the control system 1. As shown in Fig. 2, the control system 1 is configured to include an antenna 10, a detection unit 20, a communication unit 30, and a counting unit 40, and each functional unit is constructed of hardware or software or both with a CPU as a core member in order to perform processing related to communication with the smart key 3.

[0015] The antenna 10 is fed with power from a power feed section (not shown) and generates an electromagnetic field around the antenna 10. In this embodiment, the antenna 10 is fed with power so that an electromagnetic field is generated around the antenna 10 periodically with a period of several hundred milliseconds.

[0016] The antenna 10 is configured to be able to switch the operating state (operation that generates an electromagnetic field) between a first mode and a second mode. The first mode is a mode in which the antenna 10 operates under a first condition that is set in advance. The first condition specifies the power supplied to the antenna 10, the period of generation of the electromagnetic field from the antenna 10, and the like. On the other hand, the second mode is a mode in which the antenna 10 operates under a second condition that has lower power consumption than the first mode. "Lower power consumption than the first mode" means that the power supplied to the antenna 10 is lower than the power specified in the first condition. "Lower power than the power specified in the first condition" may mean that the power supplied itself is smaller, or the power supply period is longer. Therefore, the second condition specifies a power lower than the power specified in the first condition or a longer power supply period. Of course, the second condition may specify only one of the power and the power supply period.

[0017] The detection unit 20 detects disturbances in the electromagnetic field based on changes in the impedance of the antenna 10. As described above, an electromagnetic field is periodically generated around the antenna 10. If a metal object, including the smart key 3, is present in the area where this electromagnetic field is generated, the electromagnetic field is disturbed. When the electromagnetic field is disturbed in this way, a change appears in the impedance of the antenna 10. The detection unit 20 detects disturbances in the electromagnetic field based on such changes in impedance, and when the detection unit 20 detects the disturbance, it transmits detection information indicating that the electromagnetic field disturbance has been detected to the communication unit 30, which will be described later. This disturbance in the electromagnetic field due to the presence of a metal object occurs even when the battery of the smart key 3 is dead, which is highly convenient.

[0018] When a disturbance in the electromagnetic field is detected, the communication unit 30 outputs information for the smart key 3 associated with the vehicle 2 to the surroundings of the vehicle 2 by short-range wireless communication. When the detection unit 20 detects a disturbance in the electromagnetic field as described above, detection information indicating that a disturbance in the electromagnetic field has been detected is transmitted to the communication unit 30. The smart key 3 associated with the vehicle 2 is a smart key 3 capable of operating a locking mechanism of the door of the vehicle 2. The information is information capable of switching the locking mechanism from one of an unlocked state and a locked state to the other. Specifically, this corresponds to an electronic lock. Here, the communication unit 30 outputs information from the antenna 10 where the disturbance has occurred. Specifically, the short-range wireless communication corresponds to NFC (near field communication).

[0019] When the smart key 3 acquires the information output by the communication unit 30, the smart key 3 responds according to the information, and the communication unit 30 checks whether the smart key 3 is associated with the vehicle 2. If the check result indicates that the smart key 3 is associated with the vehicle 2, the communication unit 30 continues to communicate with the smart key 3. On the other hand, if the check result does not indicate that the smart key 3 is associated with the vehicle 2, the communication unit 30 ends communication with the smart key 3.

[0020] As described above, the detection target detected by the detection unit 20 is a disturbance in the electromagnetic field, and this disturbance in the electromagnetic field is caused not only by the presence of the smart key 3 but also by the presence of a metal body. When the smart key 3 acquires information from the communication unit 30, it responds to the information, but the metal body does not respond even if the information from the communication unit 30 reaches it. In addition, the smart key 3 cannot respond appropriately to information from the communication unit 30 even if it is another smart key that is not associated with the vehicle 2. Therefore, the counting unit 40 counts the number of times the communication unit 30 outputs information when there is no response to the information even though the communication unit 30 outputs information. The number of times this information is output corresponds to the number of times the communication unit 30 fails to communicate. Therefore, the counting unit 40 counts the number of times the communication unit 30 fails to communicate. The counting result by the counting unit 40 is transmitted to the detection unit 20.

[0021] The number of times communication unit 30 fails to communicate may be counted only when TD (Technology Detection) in the NFC Forum fails, or may be counted when TD and CR (Collision Resolution) in the NFC Forum fail.

[0022] The detection unit 20 transitions to the second mode when the counting result by the counting unit 40 in a preset first time exceeds a preset number. The preset first time can be changed as appropriate, but as described above, if the communication unit 30 continues to output information even though there is no response to the information, power is wasted. Therefore, the first time should be set based on the power consumption by the communication unit 30 and the capacity of the battery that serves as the power source for the communication unit 30 to output the information. The first time can be set to, for example, about several tens of seconds (for example, about 30 seconds). If the number of times that the communication unit 30 fails to communicate during this first time exceeds a preset number, the detection unit 20 transitions to the second mode in which the operation is performed under a second condition with reduced power consumption compared to the first mode.

[0023] When the detection unit 20 transitions to the second mode, it suspends the generation of the electromagnetic field for a preset second time. The second time may be set to, for example, about several minutes (e.g., about 5 minutes). Even if the communication unit 30 fails to communicate as described above, if a metal object or a smart key that is not associated with the locking mechanism of the vehicle 2 is present within the range where the electromagnetic field is generated, the detection unit 20 continues to detect the disturbance in the electromagnetic field and the communication unit 30 continues to communicate. Therefore, by suspending the generation of the electromagnetic field, it is possible to eliminate communication failures and reduce the power consumption required for communication during a predetermined time.

[0024] The detection unit 20 measures the disturbance of the electromagnetic field for a preset third time after the second time has elapsed, and if a disturbance is detected during the third time, it determines whether or not there is a response to the information output from the communication unit 30 based on the detected disturbance of the electromagnetic field. If there is a response to the information output from the communication unit 30, it transitions to operation in the first mode, and if there is no response to the information, it continues operation in the second mode. The third time may be approximately the same as the above-mentioned first time. Of course, the third time may be longer or shorter than the first time. In addition, the detection unit 20 may be configured to measure the disturbance of the electromagnetic field for a third time, and if a disturbance is detected during the third time, it may be configured to determine whether or not the disturbance continues based on the detected disturbance. In such a configuration, if no disturbance of the electromagnetic field is detected, there is no risk of an increase in current consumption due to erroneous detection, so it is possible to configure it to transition to operation in the first mode in preparation for the next holding up of the user's device (card, smart key in this text).

[0025] In addition, whether or not the disturbance of the magnetic field caused by the surrounding environment continues may be determined by driving the antenna of the communication unit 30. Specifically, if the number of times that the disturbance is detected among the multiple times that the antenna of the communication unit 30 is driven does not reach a predetermined number, it may be determined that the disturbance of the electromagnetic field does not continue, and if the number of times that the disturbance is detected among the multiple times that the antenna of the communication unit 30 is driven is equal to or greater than a predetermined number, it may be determined that the disturbance of the electromagnetic field continues. Also, if the disturbance of the electromagnetic field is detected during such a determination, the operation in the second mode may be continued and it may not be necessary to shift to communication by the communication unit 30 (TD or CR in the NFC Forum). A configuration that does not shift to communication by the communication unit 30 if the disturbance of the electromagnetic field is detected during such a determination is preferable because it has a high power consumption reduction effect compared to a configuration in which the communication unit 30 outputs information for the smart key 3 by short-range wireless communication when the disturbance of the electromagnetic field is detected. In addition, in this case, if the third time is set to, for example, about several hundred milliseconds (for example, about 100 milliseconds to 500 milliseconds), the power consumption reduction effect is further increased, which is preferable.

[0026] When the detection unit 20 continues to operate in the second mode, it is preferable that the generation of the electromagnetic field is suspended for a period of time longer than the second period of time, which makes it possible to further reduce power consumption.

[0027] Next, the operation of the control system 1 will be described with reference to a timing chart shown in FIG. 3. FIG. 3 is a timing chart showing the case where the detection unit 20 and the communication unit 30 are driven based on the NFC standard (hereinafter referred to as "NFC driven"). First, calibration is performed (#1) (indicated with "C" in FIG. 3) in order to use the antenna 10 as an inductive sensor that detects the presence or absence of an object and the distance to the object. After the calibration is completed, the low power consumption card detection function transmits signals at intervals of, for example, 200 milliseconds (#2-#5). One transmission may take about several tens of microseconds. Note that the "card" in the "low power consumption card detection function" includes not only cards but also smart devices and the like.

[0028] For example, when the detection unit 20 detects a disturbance in the electromagnetic field in response to the transmission in #6, the communication unit 30 outputs information by NFC (#7) (indicated by "I" in FIG. 3). If there is no response to the output information, it is assumed that the NFC communication has failed, and calibration is performed again (#8). When the calibration is completed, transmission is performed again by the low power consumption card detection function (#9), and when the detection unit 20 detects a disturbance in the electromagnetic field, the communication unit 30 outputs information by NFC (#10). Such calibration, transmission by the low power consumption card detection function, and information transmission by the communication unit 30 are repeated, and when the number of communication failures within a preset first time period exceeds a preset number (four times in the example of FIG. 3), NFC operation is stopped for a second time period.

[0029] After the second time has elapsed, NFC operation is performed for a third time, that is, calibration is performed (#17) and transmission is performed (#18, #19).

[0030] Next, the processing of the control system 1 will be described with reference to the flowchart of FIG. 4. First, calibration is performed (step #100). When calibration is completed, detection by the antenna 10 is started (step #101). Specifically, transmission is performed by the low power consumption card detection function. If the detection unit 20 does not detect any disturbance in the magnetic field (step #102: No), detection by the antenna 10 continues (#101).

[0031] When the detection unit 20 detects a disturbance in the magnetic field (step #102: Yes), the communication unit 30 outputs information (step #103). If there is a response to the output information (step #104: Yes), communication is performed (step #105) and continues until the communication is terminated (step #106: Yes).

[0032] In step #104, if there is no response to the output information (step #104: No), the counting unit 40 counts the number of times the information was output (step #107). If the counting result by the counting unit 40 in the first time exceeds a preset number (predetermined value) (step #108: Yes), detection by the antenna 10 is suspended for a second time (step #109). If detection by the antenna 10 is to be resumed (step #110: Yes), the process returns to step #100 and continues. If detection by the antenna 10 is not to be resumed (step #110: No), the process returns to step #109 and continues. Also, in step #108, if the counting result by the counting unit 40 in the first time is equal to or less than the preset number (predetermined value) (step #108: No), the process returns to step #100 and continues. The process is carried out according to the above flow.

[0033] Next, the transition from the second mode to the first mode (return process) will be described with reference to the flowchart of Fig. 5. As described above, the detection unit 20 transitions to the second mode when the counting result by the counting unit 40 within a preset first time period exceeds a preset number. When the detection unit 20 is performing detection in such a second mode (step #200), if there is a return trigger (step #201: Yes) and this return trigger is from a higher-level system (step #202: Yes), the detection unit 20 transitions to the first mode (step #203).

[0034] In step #201, if there is no recovery trigger (step #201: No), detection continues in the second mode (step #200). Also, in step #202, if the recovery trigger is not from the upper system (step #202: No), calibration is performed (step #204), and detection is performed by the antenna 10 (step #205).

[0035] If the detection unit 20 detects a disturbance in the electromagnetic field (step #206: Yes) and the number of detections is greater than a predetermined value (step #207: Yes), the process returns to step #200 and continues. On the other hand, if the number of detections is equal to or less than the predetermined value (step #207: No), the process transitions to the first mode (step #203).

[0036] Furthermore, in step #206, if the detection unit 20 does not detect any disturbance in the electromagnetic field (step #206: No) and the number of detections by the antenna 10 is greater than a predetermined value (step #208: Yes), the process transitions to the first mode (step #203). On the other hand, if the number of detections by the antenna 10 is equal to or less than the predetermined value (step #208: No), the process returns to step #205 and continues.

[0037] Here, the return trigger in step #201 is, for example, information indicating the approach / contact of a person from an electrostatic sensor provided on the door handle 4. In this case, the information may be directly transmitted from the electrostatic sensor to the control unit (not shown) of the control system 1, or the information may be transmitted from the electrostatic sensor to the control unit of the lock mechanism, and the information may be transmitted from the control unit of the lock mechanism or another control unit to the control unit of the control system 1. Furthermore, polling may be performed on the control unit of the lock mechanism or another control unit. The return trigger may also be the operation of a lock switch or unlock switch provided on the smart key 3. When the lock mechanism is operated using a digital key, a lock command or unlock command from the digital key may also be used.

[0038] When the electrostatic sensor installed on the door handle 4 detects the proximity / contact of a person (for example, when a user grasps the unlock sensor), the function can be naturally resumed as the user gets into the vehicle (i.e., the low power consumption card detection function can be automatically resumed), thereby improving convenience.

[0039] In addition, the communication unit 30 performs TD in NFC communication, but if there is no response to this TD, it may process it as a false detection. Also, if there is a response to this TD, it may perform CR, and if the card type is a specific type (e.g., "T4AT"), it may continue processing, and if it is not a specific type (e.g., "T2T"), it may process it as a false detection.

[0040] Other embodiments Next, other embodiments of the control system 1 will be described.

[0041] In the above embodiment, the detection unit 20 has been described as pausing the generation of the electromagnetic field for a preset second time period when the mode is switched to the second mode, but the detection unit 20 may lengthen the generation period of the electromagnetic field for a preset second time period when the mode is switched to the second mode. Alternatively, the threshold value for detecting disturbance of the electromagnetic field may be changed. In this case, it is also possible to reduce power consumption.

[0042] In the above embodiment, the detection unit 20 was described as detecting a disturbance in the electromagnetic field for a third time after the second time has elapsed, and transitioning to operation in the first mode if there is a response to the information output from the communication unit 30 based on the disturbance in the electromagnetic field detected at the third time, and continuing to operate in the second mode if there is no response to the information. The detection unit 20 may be configured to detect a disturbance in the electromagnetic field for a third time after the second time has elapsed, and transitioning to operation in the first mode regardless of whether there is a response to the information output from the communication unit 30 based on the disturbance in the electromagnetic field detected at the third time.

[0043] In the above embodiment, the detection unit 20 has been described as suspending the generation of the electromagnetic field for a period longer than the second time when continuing to operate in the second mode. However, the detection unit 20 may be configured to lengthen the generation period of the electromagnetic field for a period longer than the second time when continuing to operate in the second mode.

[0044] In the above embodiment, an example was given in which the communication device was the smart key 3, but the communication device may be a card key or a mobile terminal such as a smartphone.

[0045] [Summary of the above embodiment] The control system 1 described above will now be outlined.

[0046] (1) The control system 1 is mounted on a vehicle 2 and controls communication with a smart key 3 (communication device) present around the vehicle 2. The control system 1 includes a detection unit 20 that generates an electromagnetic field around an antenna 10 and detects disturbances in the electromagnetic field based on changes in the impedance of the antenna 10 in a first mode operating under preset first conditions, a communication unit 30 that outputs information for the smart key 3 associated with the vehicle 2 to the surroundings of the vehicle 2 via short-range wireless communication when a disturbance is detected, and a counting unit 40 that counts the number of times information is output when there is no response to the information despite the communication unit 30 outputting the information. The detection unit 20 is configured to transition to a second mode operating under second conditions that consume less power than the first conditions when the counting result by the counting unit 40 within a preset first time period exceeds a preset number.

[0047] According to this configuration, when the detection unit 20 detects a disturbance in the electromagnetic field, if there is no response to the information within a first time period even though the communication unit 30 outputs information for the smart key (communicator) 3 by short-range wireless communication, the operation of the detection unit 20 can be shifted to an operation in a second mode with reduced power consumption. Therefore, if there is no response to the information within the first time period, it is possible to suppress power consumption. Moreover, with a simple configuration in which the counting unit 40 counts when there is no response to the information within the first time period, it is possible to prevent erroneous detection due to a metal object other than the NFC tag approaching due to tampering or the like.

[0048] (2) In the control system 1 described in (1), when the detection unit 20 transitions to the second mode, it is preferable that the detection unit 20 suspends generation of the electromagnetic field or lengthens the period during which the electromagnetic field is generated for a preset second time period.

[0049] According to this configuration, in the second mode, by the detection unit 20 pausing the generation of the electromagnetic field or lengthening the period of generation of the electromagnetic field, it is possible to reduce power consumption compared to when the detection unit 20 continues generating the electromagnetic field or when the period of generation of the electromagnetic field is not changed.

[0050] (3) In the control system 1 described in (2), the detection unit 20 measures disturbances in the electromagnetic field for a preset third time after the second time has elapsed, and if a disturbance is detected during the third time, determines whether the disturbance is continuing based on the detected disturbance, and the communication unit 30 is preferably configured to continue operation in the second mode without communication if it is determined that the disturbance is continuing, and to transition to operation in the first mode if it is determined that the disturbance is not continuing.

[0051] According to this configuration, if no disturbance in the electromagnetic field is detected, there is no risk of an increase in current consumption due to false detection, so it becomes possible to prepare for the next user's device (card, smart key in this case). On the other hand, if disturbance in the electromagnetic field continues to be detected, operation in the second mode continues, making it possible to continue reducing power consumption.

[0052] If disturbance of the electromagnetic field is detected during the determination, it is not necessary to transition to communication (TD or CR in the NFC Forum) by the communication unit 30. In this case, it is possible to further reduce the power consumption required for communication.

[0053] (4) If the control system 1 described in (3) determines that the disturbance is continuing, it continues operating in the second mode, and if operating in the second mode, it is preferable to suspend generation of the electromagnetic field or lengthen the generation period of the electromagnetic field for a time longer than the second time.

[0054] According to this configuration, it is possible to further reduce power consumption, thereby enhancing the power saving effect. [Industrial Applicability]

[0055] The technology disclosed herein can be used in a control system that is mounted on a vehicle and controls communication with communication devices present around the vehicle. [Explanation of symbols]

[0056] 1: control system, 2: vehicle, 3: smart key (communication device), 10: antenna, 20: detection unit, 30: communication unit, 40: counting unit

Claims

1. A control system that is mounted on a vehicle and controls communication with communication devices present around the vehicle, a detection unit that generates an electromagnetic field around the antenna in a first mode that operates under a preset first condition and detects a disturbance in the electromagnetic field based on a change in impedance of the antenna; a communication unit that outputs information for a communication device associated with the vehicle to a periphery of the vehicle through short-range wireless communication when the disturbance is detected; a counting unit that counts the number of times the information is output when there is no response to the information even though the communication unit has output the information, The control system includes a detection unit that transitions to a second mode in which it operates under second conditions that consume less power than the first conditions when the counting result by the counting unit within a predetermined first time period exceeds a predetermined number.

2. The control system according to claim 1 , wherein when the detection unit transitions to the second mode, the detection unit suspends generation of the electromagnetic field or lengthens a generation period of the electromagnetic field for a second time period that is set in advance.

3. the detection unit measures a disturbance in the electromagnetic field for a preset third time after the second time has elapsed, and if the disturbance is detected during the third time, determines whether the disturbance is continuing based on the detected disturbance; The control system of claim 2, wherein the communication unit is configured to continue operation in the second mode without communication when the judgment determines that the disturbance is continuing, and to transition to operation in the first mode when the judgment determines that the disturbance is not continuing.

4. The control system of claim 3, wherein the detection unit continues to operate in the second mode when it determines that the disturbance is continuing, and when continuing to operate in the second mode, suspends generation of the electromagnetic field or lengthens the generation period of the electromagnetic field for a period longer than the second time.

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