JPWO2020044643A1 - Radio wave sensor - Google Patents

Abstract

We provide sensors that are compact and have low consumption with a simple structure that is not easily affected by the environment such as heat, light, rainfall, snowfall, and wind. The antenna unit emits a transmission signal in a frequency band that allows water to pass through, for example, a 300 MHz band, and receives the reflected signal reflected by the object together with the transmitted signal. The receiver detects the change point of the signal level by homodyne detection of the reflected signal with the transmission signal, extracts the signal component of about 5 to 15 Hz from this change point, and thereby determines the presence or absence of the object or the movement of the object. Detect.

Description

The present invention relates to a radio wave sensor capable of detecting the movement of an object existing at a short distance.

A short-distance moving object detection sensor that detects a moving object of several tens of centimeters to several meters is known. In recent years, short-distance motion detection sensors have been reduced in cost, power saving, and miniaturization, and it is expected that the convenience of electronic devices equipped with them will be expanded. For example, Patent Document 1 discloses a control device that detects the movement of a driver approaching a vehicle and automatically opens and closes the door of the vehicle. The control device disclosed in Patent Document 1 detects the presence / absence and operation of a driver with a short-distance motion detection sensor provided near a vehicle door. Then, it is determined whether or not the door is operating, and the opening / closing control of the door is performed based on the determination result.

Japanese Unexamined Patent Publication No. 2016-142076

Since the control device disclosed in Patent Document 1 is attached to a vehicle, water, ice, snow, mud, etc. may adhere to the case of the short-distance motion detection sensor. In addition, water stains may accumulate or water stains may form a film. Therefore, the sensitivity for detecting a moving object may decrease, and the control device may not operate correctly. Such a phenomenon also occurs in non-contact sensors such as infrared sensors, capacitance sensors, and image sensors.

A main object of the present invention is to provide a sensor that is not easily affected by environmental impacts and has a simple structure and is compact and has low power consumption.

The present invention solves the above problems by applying it to, for example, a radio wave sensor that uses radio waves in a frequency band that transmits water (including a substance containing water). This radio wave type sensor emits a transmission signal in a frequency band lower than the quasi-millimeter wave band, and receives the reflected signal reflected by the object and the transmission signal. From the detection unit that detects the change point of the signal level by homodyne detection of the reflected signal received by the antenna unit with the transmission signal and the frequency band of the transmission signal from the change point detected by the detection unit. It also has a detection unit that extracts a signal component in a predetermined frequency band, which is also low, and thereby detects the presence or absence of the object or the movement of the object.

According to the present invention, it is possible to provide a sensor that is not easily affected by environmental influences, has a simple structure, and is compact and has low power consumption.

The front view of the radio wave type sensor which concerns on this embodiment. The side view of the radio wave type sensor which concerns on this embodiment. The rear view of the radio wave type sensor which concerns on this embodiment. Functional configuration diagram of the sensor module. It is an example figure of the waveform of the detection signal after homodyne detection by a mixer. Detailed configuration diagram of the antenna section. Front view of the mounted state of the sensor module. Side sectional view of the mounted state of the sensor module. Rear view of the mounted state of the sensor module. The figure which shows the directivity characteristic example of a radio wave type sensor. Explanatory view of the horizontal plane and the vertical plane of the radio wave sensor. An explanatory diagram of the movement of the hand, which is the object. An explanatory diagram of the input / output relationship of the active filter. Explanatory drawing of waveform of detection signal and detection signal. The waveform comparison diagram of the detection signal when the active filter is not provided and when it is provided. The explanatory view of the change point of the signal level in the detection signal. Functional configuration diagram of the sensor module according to the modified example.

Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings. In this embodiment, an example in which the present invention is applied to a radio wave sensor is shown. The radio wave type sensor is a sensor that uses radio waves to detect the presence, position, movement, etc. of an object, and has an advantage that it is not easily affected by environmental influences such as heat, light, and wind that do not hinder radio wave propagation. However, since water acts as a dielectric in both the solid phase and the liquid phase, for example, rain, fog, snow, water droplets, and ice (hereinafter collectively referred to as "water") act as a dielectric. Therefore, if these exist between the object and the object, and particularly adhere to the case of the radio wave sensor, the propagation loss becomes large depending on the frequency of the signal used, and the object may not be detected correctly.

Radio wave sensors are mainly used in quasi-millimeter wave bands such as 10.5 GHz band, 24 GHz band, 79 GHz band and millimeter wave band from the viewpoint of miniaturization and ensuring sufficient detection accuracy. In the high frequency band, the influence of water makes it difficult for radio waves to pass through. Therefore, it is necessary to take measures such as applying a water-repellent finish to the case surface of the radio wave sensor and incorporating a heater to prevent dew condensation. The lower the frequency used, the smaller the propagation loss of radio waves due to water. However, when the frequency used is lowered, the wavelength λ becomes longer, so that the size of the antenna element becomes larger and the detection accuracy becomes lower.
Therefore, in the present embodiment, an example of a radio wave sensor that is not affected by the environmental influence of water without increasing the size of the antenna element will be described.

The radio wave type sensor of this embodiment is configured by accommodating a sensor module described later in a box-shaped case 100. 1A is a front view of the radio wave sensor (case 100), FIG. 1B is a side view, and FIG. 1C is a rear view.
The case 100 is made of resin with a long side W of 40 mm, a short side D of 20 mm, and a height H1 of 5.0 mm. Connector 110 is provided. In the connector 110, an enable pin, a power supply Vcc pin, an output pin described later, and two GND (ground) pins are arranged at a pitch of approximately 2 mm. The sensor module operates when the enable pin is logically high, and becomes standby when the enable pin is logically low. The height H2 considering the tip of the connector is about 9.5 mm, which is sufficiently smaller than a general radio wave sensor using a millimeter wave band.
In addition to such terminal output, a multi-core cable may be connected instead of the connector 110 to provide cable output.

FIG. 2 is a functional configuration diagram of the sensor module housed in the case 100. The sensor module has a transmitting unit 10, an antenna unit 20, and a receiving unit 30. The transmission unit 10 is configured by vertically connecting an oscillator 11, a filter 12, and a variable attenuator 13. The oscillator 11 oscillates a transmission signal of 300 MHz (actually, there is a fluctuation of about 5 MHz with respect to 300 MHz). This transmitted signal is a continuous wave.
The 300 MHz oscillator 11 is used as a general-purpose product used in mobile communication devices, keyless entry, wireless microphones, amateur radio, etc., and there are many types of semiconductors that can be used, which facilitates design and costs. But it is advantageous.

The filter 12 removes harmonic components of the transmitted signal. The variable attenuator 13 adjusts the output level of the transmission signal that has passed through the filter 12 to a weak power that is not limited by the Radio Law, for example, −45 dBm or less, and outputs the output to the antenna unit 20.

The antenna unit 20 integrates the antenna element 21 and the distributor 22. This will be explained in detail later. The distributor 22 outputs the transmission signal from the transmission unit 10 to the antenna element 21 and also outputs the transmission signal to the reception unit 30. Further, the distributor 22 outputs the reflected signal from the object received by the antenna element 21 to the receiving unit 30.

The receiving unit 30 includes an amplifier 31, a mixer 32, and an active filter 33. The amplifier 31 receives the transmission signal and the reflection signal from the transmission unit 10, amplifies each signal, and outputs the signal to the mixer 32. The amplifier 31 is a low-noise high-frequency amplifier capable of amplifying a signal in the 300 MHz band.

The mixer 32 outputs the detection signal 321 by performing homodyne detection using the transmission signal as a local (reference signal) and the reflected signal as a control signal. The mixer 32 is generally composed of a diode, but a bipolar transistor may be used to form a circuit having an amplification degree (gain).

An example of the waveform of the detection signal 321 is shown in FIG. The detection signal 321 is a Doppler signal in which the Doppler effect caused by the movement of the object appears. The Doppler effect appears as a frequency component of the change point (displacement portion) 3211 at the time when the signal level changes. This frequency component is lower than the transmission signal (300 MHz) and is in a predetermined frequency band determined according to the application.

The detection signal 321 output from the mixer 32 is input to the active filter 33. The active filter 33 is composed of a semiconductor, extracts a signal in a predetermined frequency band at a time when the signal level of the Doppler signal changes from the detection signal 321 by passing it through, for example, a band-passing filter, amplifies it to a predetermined signal level, and then performs it. It is output to the output pin 40 as a detection signal 331.
An operational amplifier (differential amplifier) can be used for the semiconductor, but an amplifier (low frequency amplifier) and a passive filter may be combined and configured. As a result of the experiment of the present inventor, it has been confirmed that about 5 Hz to 15 Hz is most suitable for moving object detection in a predetermined frequency band.

Generally, the Doppler effect is obtained by detecting the entire waveform of a sine wave for one cycle or more of the Doppler signal. Therefore, when trying to detect the movement of an object based on the Doppler signal, it is a condition that the object moves a distance (about 1 m at 300 MHz) or more of one wavelength or more of the transmission signal. Therefore, if the moving distance of the object is shorter than the wavelength of the transmission signal, the Doppler signal cannot be detected accurately.
On the other hand, in the sensor module of the present embodiment, only the frequency component of the signal level change point 3211, which is a part of the overall waveform of the Doppler signal, is extracted. Therefore, it is not necessary to detect the entire waveform of the Doppler signal, and even a movement in which the moving distance of the object is short with respect to one wavelength (about 1 m in this example) of the transmission signal can be detected. For example, even if the moving distance is about 15 cm, the movement can be detected.

Detection of the movement of an object can be realized, for example, by converting the detection signal 331 into a digital signal with an analog / digital converter and performing detection processing of the converted detection signal 331 with, for example, a DSP (digital signal processor). be. In this example, the analog-to-digital converter and DSP are assumed to be provided as a post-stage circuit that conducts with the output pin 40 of the connector 110, but are inserted between the active filter 33 and the output pin 40. Is also good.

Next, the antenna unit 20 will be described in detail. FIG. 4 is a detailed configuration diagram of the antenna unit 20. 5A is a front view of the mounted state of the sensor module, FIG. 5B is a side sectional view, and FIG. 5C is a rear view. The antenna element 21 of the antenna unit 20 is formed by arranging the transmitting element 211 and the receiving element 212 formed of the conductive pattern in close proximity to each other on one plane, for example, on the upper exposed portion of the printed circuit board 1.

For the printed circuit board 1, FR (Flame Retardant Type) -4 having a thickness of 0.6 mm can be used. The components of the transmission unit 10 and the reception unit 30 are mounted on a portion of the printed circuit board 1 other than the antenna element 21. The printed circuit board 1 has front and back surfaces, and the components of the transmitting unit 10 and the receiving unit 30 are mounted on one surface, for example, the front surface, and then loaded with the shield case 2 to be affected by noise from the outside. I try not to.

In the mounted state, the transmitting element 211 and the receiving element 212 preferably have a shape in which a part thereof includes a curve or a corner. There are no particular restrictions on the curvature of the curve or the angle of the corners. The angle of the corner can be, for example, 90 degrees. In this embodiment, as shown in FIGS. 5A and 5B, the transmitting element 211 and the receiving element 212 have a shape having a plurality of 90-degree corners or a meander mosaic shape. The gaps formed by these corners in one element are arranged so that the other elements do not intersect each other in the same plane. As shown, the receiving element 212 is formed on the front surface of the printed circuit board 1, and the straight line portion 2120, which is a part of the receiving element 212, is formed on the back surface side of the printed circuit board 1 so as not to intersect with the transmitting element 211. Will be done. The other portion of the receiving element 212 is formed on the surface side of the printed circuit board 1. The straight line portion 2120 formed on the back surface side of the receiving element 212 and the other portion formed on the front surface side can be electrically connected by a via hole or the like.
The tips 211, 2121 of the transmitting element 211 and the receiving element 212 are formed so as to face each other at predetermined intervals. Therefore, the transmitting element 211 and the receiving element 212 are electrically coupled to each other. The degree of coupling can be adjusted by the interval P. As a result, the distributor 22 is integrated with the antenna element 21. That is, the transmission signal S211 input from the input unit IN of the antenna unit 20 is radiated from the transmission element 211 toward the object, but a part of the transmission signal S211 is transmitted to the reception element 212 by electrical coupling, and the output unit is output. Reach OUT. The reflected signal S212 received by the receiving element 212 also reaches the output unit OUT. As described above, since it is not necessary to separately provide the distributor 22, the antenna portion 20 can be miniaturized and the configuration can be simplified.

In the present embodiment, the transmitting element and the receiving element are not shared, but by separating them, it is possible to set different antenna characteristics. For example, in order to realize short-range communication using weak radio waves, the radiation efficiency of the transmitting element 211 is lowered to reduce the effective radiated power, while the radiation efficiency of the receiving element 212 is increased in order to improve the detection performance. It can meet the demand for larger size.
In this case, assuming that the length of the transmitting element 211 is L1 and the length of the receiving element 212 is L2, it is desirable that L1 <L2 from the viewpoint of radiation efficiency. Further, the total length (L1 + L2) of the antenna element 21 is set to about 1/4 or about 3/8 of the wavelength λ of the transmission signal (the same applies to the reflected signal). In one example, the length L1 of the transmitting element 211 is set to approximately 1 / 8λ, and the length L2 of the receiving element 212 is set to approximately 1 / 4λ. In this example, L1 is 65 mm, L2 is 142 mm, the pattern width W is 0.2 mm, the element spacing P is 1 mm, and the printed circuit boards 1 are arranged on the front and back surfaces of the upper half.

The reason why the tip 2111 of the transmission element 211 and the tip 2121 of the reception element 212 are separated is that when they are connected, they operate as a loop element. When such an operation is allowed, the length of the wavelength λ is required as the total length, which requires a large area. Therefore, such an operation mode is avoided.

FIG. 6A is a graph showing an example of the directivity characteristics of the antenna element 21 when the wide surfaces (front surface and back surface) of the case 100 of the radio wave sensor are installed horizontally with respect to the ground. In this graph, as shown in FIG. 6B, 0 degree is an angle vertically above the wide surface of the case 100, 180 degrees is an angle vertically below, and a surface including both angles is a vertical surface V. Further, 90 degrees and −90 degrees are angles parallel to the wide surface of the case 100, and the surface including both angles is the horizontal plane H. In the graph of FIG. 6A, the broken line 62 is a pattern showing the directivity of the horizontal plane H, and the solid line 61 is a pattern showing the directivity of the vertical plane V.

Next, an operation example of the radio wave sensor of the present embodiment will be described. Here, as shown in FIG. 7A, it is assumed that the user's hand moves across 15 cm above the case 100. FIG. 7B shows a state in which the detection signal 321 at this time is input to the active filter 33 and the detection signal 331 is output. FIG. 7C shows an example of waveforms of the detection signal 321 and the detection signal 331 on the same scale. The vertical axis of FIG. 7C is the amplitude of the signal component, and the horizontal axis is time.

The detection signal 321 is a Doppler signal including 15 Hz, which is a frequency component of the change point of the signal level, and has a frequency of 300 MHz. On the other hand, the detection signal 331 is obtained by extracting and amplifying only the frequency component of 15 Hz from the detection signal 321 and has a waveform that faithfully captures the movement of the hand. For convenience, the signal waveform 322 when the detection signal 321 is simply amplified regardless of the active filter 33 is shown in the upper part of FIG. The lower waveform in FIG. 8 is the waveform of the detection signal 331 in the lower row of FIG. 7C. The vertical axis of FIG. 8 is the amplitude of the signal component, and the horizontal axis is time.
As described above, when the active filter 33 is not used, as shown in the upper waveform of FIG. 8, there is a lot of noise and a large number of frequency components are superimposed, so that it becomes difficult to identify the movement of the hand. However, it can be seen that the waveform-formed detection signal 331 is output by using the active filter 33.

As shown in FIG. 9, the change points of the signal level of the detection signal 321 (Doppler signal) are the first change point (rising point) 3211 in which the movement starts from normal times and the second change point (rising point) 3211 in which the movement stops and returns to normal times. There is a fall) 3212. The former is the same as the change point 3211 shown in FIG. 3, and the description so far relates to an example in which only the frequency component at the first change point 3211 is extracted. However, the frequency components of only the second change point 3212, or one or both of the first change point 3211 and the second change point 3212, which are easy to extract, may be extracted.

<Effect of embodiment>
As described above, since the Doppler effect of radio waves in the 300 MHz band is used in the present embodiment, a conventional radio wave type sensor using millimeter waves or quasi-millimeter waves, or an infrared type, capacitance type, or image type sensor is used. Compared to the above, it is less affected by the presence or absence of water and mud. Therefore, for example, it can be used not only as a sensor for automatically opening and closing the door of a cold region specification vehicle, but also can detect an object even when it is buried in water or snow. In addition, since maintenance (cleaning) of the case 100 due to dirt etc. is not required, it can be installed outdoors, around water, or in a storage room with dew or frost, which was difficult to use in the past. It can contribute to the diversification, miniaturization, and power saving of on-board equipment.

Further, by integrating the distributor 22 with the antenna element 21 by utilizing the electrical coupling between the elements, it is possible to contribute to the miniaturization and simplification of the configuration of the radio wave sensor.

In the present embodiment, the reflected signal acquired by the antenna unit 20 is homodyne-detected by the transmission signal, the detection signal 321 which is a Doppler signal is output, and the first change point 3211 of the signal level of the detection signal 321 is detected. .. Further, since the signal component of a predetermined frequency band, for example, about 5 Hz to 15 Hz is extracted from the detected first change point 3211 to detect the presence or absence of the object or its movement, it is possible to detect even a small movement of the object. It becomes.
For example, the power consumption is significantly reduced as compared with a magnetic sensor or the like. The radio wave sensor of the present embodiment operates with, for example, a 3V power supply and consumes about 10 mA, so that it can be operated with, for example, a general-purpose dry battery. As for the detection range, the detection distance can be made larger than that of the capacitance type sensor or the magnetic type sensor. In addition, since the voltage and power consumption are small, it is not necessary to obtain a license to use the radio wave sensor of this embodiment in many countries. Can be done.

In the present embodiment, the antenna element 21 of the antenna unit 20 is a separate body of the transmitting element 211 and the receiving element 212, and the antenna characteristics of each can be set independently. Therefore, the overall antenna characteristics can be flexibly changed according to the application, such as facilitating sensing suitable for short-range communication using weak electric power.

<Modification example>
In the present embodiment, among the sensor modules, the antenna element 21 is composed of the transmitting element 211 and the receiving element 212, and the two elements 211 and 212 are arranged close to each other to be electrically coupled to each other, whereby the distributor 22 is formed. An example of the case where the antenna element 21 is integrated with the antenna element 21 has been described. However, the embodiment of the present invention is not limited to such an embodiment. For example, the antenna element of the sensor module can be physically separated from the transmitting system and the receiving system.
FIG. 10 is a functional configuration diagram of the sensor module in this case. For convenience, the components having the same function as the sensor module shown in FIG. 2 are designated by the same reference numerals.

In the sensor module shown in FIG. 10, the distributor 22 is provided between the transmission element 211 and the variable attenuator 13. Further, the transmission signal for homodyne detection is distributed by the distributor 22, amplified by the amplifier 41, and then supplied to the mixer 32. Even with such a configuration, the active filter 33 operates in the same manner as in the present embodiment, so that it is less susceptible to environmental influences due to water and can detect small movements of an object.

In the present embodiment, an example in which a general-purpose 300 MHz band oscillator is used as the oscillator 11 has been described, but an oscillator having a frequency band lower than that may be used as long as it is a radio wave having a frequency that allows water to pass through. , The use of oscillators in frequencies below the quasi-millimeter wave band is not excluded.

Claims (5)

An antenna unit that emits a transmission signal in a frequency band less than the quasi-millimeter wave band and receives the reflected signal reflected by the object and the transmitted signal.
A detection unit that detects the change point of the signal level by homodyne detection of the reflected signal received by the antenna unit with the transmission signal.
A detection unit that extracts a signal component in a predetermined frequency band lower than the frequency band of the transmission signal from the change point detected by the detection unit, thereby detecting the presence or absence of the object or the movement of the object. Have,
Radio wave sensor. The antenna portion has a transmitting element and a receiving element that are close to each other so as to be electrically coupled to each other.
The receiving element receives the reflected signal and also receives the transmitting signal from the transmitting element.
The radio wave type sensor according to claim 1. The antenna characteristics of the transmitting element and the receiving element are different from each other.
The radio wave sensor according to claim 2. The transmitting element and the receiving element are arranged apart from each other so that their tips face each other.
The length of the receiving element is longer than the length of the transmitting element, and
The combined antenna length of the transmitting element and the receiving element by electrical coupling is approximately 1/4 or approximately 3/8 of the wavelength of the transmitting signal.
The radio wave type sensor according to claim 2 or 3. The predetermined frequency band is a frequency band of about 5 Hz to 15 Hz.
The radio wave sensor according to any one of claims 1 to 4.

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