JP2007147406A - Searching device of object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device of object capable of accurately calculating the material quality of a target in spite of a relatively simple circuit constitution. <P>SOLUTION: The searching device of the object includes a transmitter 1 for intermittently transmitting an electromagnetic wave, a receiver 2 for receiving the electromagnetic wave from the transmitter 1 reflected by the target A, a distance calculation part 26 for calculating the distance up to the target A on the basis of the time required from the transmission of the electromagnetic wave to the reception thereof and the speed of the electromagnetic in a medium B, a specific inductive capacity estimation part 28 for calculating the reflection coefficient of the boundary surface between the medium B and the target A from the intensity of the electromagnetic wave transmitted from the transmitter 1, the intensity of the electromagnetic wave received by the receiver 2 and the distance up to the target A with respect to a plurality of frequencies and statistically estimating the specific inductive capacity of the target A using the reflection coefficient, the specific inductive capacity of the medium B and the respective frequencies of the electromagnetic waves and a material quality judging part 29 for judging the material quality of the target A on the basis of the specific inductive capacity. The transmitter 1 transmits a signal of UWB as an electromagnetic wave. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an object detection device that can determine the distance to a target and the material of the target by reflecting electromagnetic waves on the target.

  Conventionally, as this kind of object detection device, the electromagnetic wave is transmitted from the transmitter, the electromagnetic wave reflected by the object is received by the receiver, and the time required for transmitting the electromagnetic wave after receiving it is received. What is used to calculate the distance to an object is provided.

  If the intensity of the electromagnetic wave transmitted by the transmitter, the intensity of the electromagnetic wave received by the receiver, and the distance to the target are known, the reflection of the boundary surface between the medium and the target existing between the target and the target A coefficient can be obtained. This reflection coefficient is determined by the electromagnetic properties such as the relative permittivity of the medium and the object and the frequency of the electromagnetic wave. Therefore, if the reflection coefficient, the electromagnetic property of the medium and the frequency of the electromagnetic wave are known, the object The relative dielectric constant of can be estimated. If the relative permittivity of the object is known, the material of the object can be determined based on the relative permittivity.

By the way, since the electromagnetic properties (conductivity and permeability) other than the relative permittivity of the object are also unknown parameters, in order to accurately determine the material of the object, the reflection coefficient obtained for electromagnetic waves of multiple frequencies. Therefore, it is necessary to estimate the relative dielectric constant of the object. As a technique for estimating the relative dielectric constant of an object using electromagnetic waves of a plurality of frequencies, for example, there is a technique described in Patent Document 1. In Patent Document 1, a transmitter (transmission) that generates electromagnetic waves of different frequencies. It is described that the reflection coefficient is obtained for two frequencies by providing two antennas and alternately driving each transmitter.
JP-A-6-230142 (page 4-5, FIG. 1)

  However, in the configuration described in Patent Document 1, two transmitters are necessary, and timing control for driving the two transmitters is necessary, so that the circuit configuration is complicated. In addition, when obtaining the reflection coefficient for electromagnetic waves with more frequencies in order to obtain the material of the object more accurately, more transmitters are required, and timing for driving more transmitters. Therefore, the circuit configuration becomes more complicated.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide an object detection device that can accurately determine the material of an object while having a relatively simple circuit configuration.

  According to the first aspect of the present invention, a transmitter that intermittently transmits an electromagnetic wave to the detection region and a received signal that is an electric signal by receiving the electromagnetic wave from the transmitter reflected by the object existing in the detection region. Based on the velocity of the electromagnetic wave in the medium determined from the time required for the electromagnetic wave to be received after being transmitted to the receiver and the relative permittivity of the medium existing between the object and the object The distance calculation unit for calculating the distance to the object, the intensity of the electromagnetic wave transmitted by the transmitter for each of a plurality of frequencies, the intensity of the electromagnetic wave received by the receiver, and the distance to the object, and the medium and the object A relative dielectric constant estimator that statistically estimates the relative dielectric constant of the object using each reflection coefficient, the relative dielectric constant of the medium, and each frequency of the electromagnetic wave. The material of the object is judged based on the relative dielectric constant estimated by the A that a material determination unit, transmitter, characterized by transmitting the UWB signal as electromagnetic wave.

  According to this configuration, since the transmitter transmits a UWB signal as an electromagnetic wave, an electromagnetic wave having a plurality of frequencies can be transmitted from a single transmitter. That is, it is not necessary to provide a plurality of transmitters as in the conventional configuration, and timing control for driving the plurality of transmitters is unnecessary, so that the circuit configuration is relatively simple. Therefore, the material of the object can be accurately obtained by obtaining the reflection coefficient for electromagnetic waves having a plurality of frequencies, while having a relatively simple circuit configuration. According to the definition by the FCC (Federal Communications Commission), a bandwidth measured at a point 10 dB below the peak of the spectrum has a bandwidth of 500 MHz or more or a specific bandwidth of 20% or more is UWB (Ultra Wide Band). ).

  The invention of claim 2 is the time required for the electromagnetic wave reflected on the back surface of the object to be received after the electromagnetic wave reflected on the surface of the object is received in the invention of claim 1. And a thickness calculator that calculates the thickness dimension between the front surface and the back surface of the object using the velocity of the electromagnetic wave in the object determined from the relative dielectric constant estimated by the relative dielectric constant estimator. It is characterized by.

  According to this configuration, the thickness dimension of the object can be obtained using the speed of the electromagnetic wave in the object obtained from the relative dielectric constant of the object. Here, since the relative dielectric constant of the object can be accurately obtained by the configuration of the first aspect, the thickness dimension of the object can also be accurately obtained.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the apparatus includes a relative dielectric constant setting unit that sets a relative dielectric constant of the medium used in the distance calculation unit and the relative dielectric constant estimation unit. Features.

  According to this configuration, the relative permittivity estimation unit can determine the relative permittivity of the object more accurately by setting the relative permittivity of the actual medium. In the distance calculation unit, the speed of electromagnetic waves in different media depending on the material of the medium can be obtained from the relative dielectric constant of the actual medium, so that the distance to the object can be obtained more accurately.

  In the present invention, since the transmitter transmits a UWB signal as an electromagnetic wave, electromagnetic waves having a plurality of frequencies can be transmitted from a single transmitter. That is, there is an advantage that the material of the object can be accurately obtained by obtaining the reflection coefficient for electromagnetic waves having a plurality of frequencies, while having a relatively simple circuit configuration that does not require a plurality of transmitters.

  As shown in FIG. 1, the object detection apparatus of the present embodiment includes a transmitter 1 that transmits an electromagnetic wave to a detection area, and a transmission reflected by an object A that exists in the detection area away from the object detection apparatus. The signal processing unit 3 for obtaining the distance to the object A, the material of the object A, and the like based on the output of the receiver 2 that receives the electromagnetic wave from the device 1 and the receiver 2, and the signal processing unit 3 A display unit 4 for displaying distance, material, and the like is provided.

  The transmitter 1 has a timing control circuit 6 to which an oscillation circuit 5 is connected. The transmitter 1 intermittently outputs a reference signal serving as a reference for the timing of transmitting an electromagnetic wave at a constant period. The output of the timing control circuit 6 is input to the pulse control circuit 7 that outputs the timing signal at a frequency of once every time the reference signal is received a predetermined number of times (here, twice). The timing signal determines the timing at which the transmitter 1 transmits an electromagnetic wave, whereby the transmitter 1 intermittently repeatedly transmits the electromagnetic wave at the same cycle as the timing signal (hereinafter referred to as “transmission cycle”). Will wave. Therefore, if the frequency of the timing signal with respect to the reference signal is reduced in the pulse control circuit 7, the number of pulses of the electromagnetic wave output from the transmitter 1 per unit time can be reduced, and the radiated power can be reduced. Power consumption can be reduced. The output of the pulse control circuit 7 is input to the pulse drive circuit 8 at the subsequent stage. The pulse drive circuit 8 generates a signal for driving the subsequent short pulse generation circuit 9 in accordance with the timing of the timing signal. The short pulse generation circuit 9 generates a short pulse of UWB (Ultra Wide Band) when the signal output from the pulse driving circuit 8 falls. The short pulse generation circuit 9 is configured using a step recovery diode (SRD) or the like, and generates a UWB short pulse with a pulse width of several tens to several hundreds ps. The output of the short pulse generation circuit 9 is output to a UWB transmission antenna 11 through a BPF (band pass filter) 10. As a result, a UWB short pulse signal is repeatedly radiated from the transmitting antenna 11 as an electromagnetic wave in the transmission period.

  On the other hand, the receiver 2 includes a UWB receiving antenna 12 for receiving a UWB short pulse signal. The receiving antenna 12 converts the received electromagnetic wave (UWB short pulse signal) into a received signal that is an electrical signal, and the received signal is input to one of the mixers 14 via a high-frequency amplifier circuit 13 that amplifies high-frequency components. Is input. The mixer 14 constitutes a down converter together with a circuit that generates a pulse equivalent to a short UWB pulse generated by the transmitter 1, and converts the received signal into a relatively low frequency band and outputs the converted signal. . That is, the other inputs of the mixer 14 are the same as those on the transmitter 1 side constituted by the oscillation circuit 15, the timing control circuit 16, the pulse control circuit 17, the pulse drive circuit 18, the short pulse generation circuit 19, and the filter 20. A pulse generated by the circuit is input.

  In order to reproduce the waveform of a UWB short pulse signal (pulse width of several tens to several hundreds ps) repeatedly received by the receiver 2 with high resolution, the signal processing unit 3 sets the sampling time resolution to several to several So-called equivalent sampling which can be set to 10 ps is employed. That is, the signal processing unit 3 has an integration circuit 22 connected to the output of the mixer 14 via the filter 21, and the integration circuit 22 calculates an average value of the amplitude of the received signal for a section of several to several tens of ps. Take out. Specifically, a sampling period that is larger (or smaller) by several to several tens of ps than the transmission period of the transmitter 1 is input from the timing control circuit 16 of the receiver 2 to the integration circuit 22. Performs a process of extracting the average value of the amplitude of the received signal in a section of several to several tens ps which is the difference between the transmission period and the sampling period for each sampling period. Here, the entire waveform of the received signal can be reproduced by the integration circuit 22 repeating the above process over a plurality of short pulses. The output of the integration circuit 22 is input to the A / D conversion circuit 23, and the analog value is converted into a digital value by the A / D conversion circuit 23. The A / D conversion circuit 23 is also connected to the timing control circuit 16 and operates in the sampling period. As a result, in the signal processing unit 3, the received signal is received with a time resolution (several to several tens of ps which is a difference between the transmission period and the sampling period) much higher than the sampling period of the A / D conversion circuit 23. Since the waveform can be reproduced, this is equivalent to performing very high-speed sampling.

  With the configuration described above, the A / D conversion circuit 23 outputs a received signal that is sampled, quantized and encoded with a time resolution of several to several tens of ps. Is output to the unnecessary wave removing unit 24 in the subsequent stage. The unnecessary wave removing unit 24 reflects an unnecessary signal component other than the component of the electromagnetic wave (hereinafter referred to as “reflected wave”) that is reflected by the object A and reaches the receiver 2 from the input received signal, that is, an external signal. Noise components and components of electromagnetic waves (hereinafter referred to as “direct waves”) that have directly reached the receiver 2 from the transmitter 1 are removed. As a result, only the component of the reflected wave is output from the unnecessary wave removing unit 24. The output of the A / D conversion circuit 23 is also input to a direct wave arrival time detection unit 25 that detects the arrival time of the direct wave.

  By the way, the signal processing unit 3 of the present embodiment has a function of calculating the distance to the object A using the outputs of the unnecessary wave removing unit 24 and the direct wave arrival time detecting unit 25 and the output of the unnecessary wave removing unit 24. And a function for determining the material of the object A and a function for calculating the thickness dimension of the object A using the output of the unnecessary wave removing unit 24. Below, the structure which implement | achieves these functions is demonstrated in order.

First, a configuration for calculating the distance to the object A will be described. The signal processing unit 3 includes a distance calculation unit 26 connected to the outputs of the unnecessary wave removal unit 24 and the direct wave arrival time detection unit 25. In the distance calculation unit 26, the electromagnetic wave in the medium B (here, air) existing between the object detection device and the object A during the time required from the time when the electromagnetic wave is transmitted to the time when the electromagnetic wave is received. The round trip distance to the object A is obtained by multiplying by the speed of, and the distance to the object A (one way distance) is calculated by dividing this round trip distance by 2. In the present embodiment, the time when the reflected wave is received from the output of the unnecessary wave removing unit 24 is detected, and the difference between this time and the arrival time of the direct wave output from the direct wave arrival time detection unit 25 is determined by the electromagnetic wave. It is used as the time required from receiving a wave to receiving it. The velocity v ₁ of the electromagnetic wave in the medium B is obtained as follows using the relative dielectric constant ε _γ1 of the medium B.

Here, v is the velocity of electromagnetic waves in air (3 × 10 ⁸ (m / s)). In the present embodiment, since the medium B is air (relative permittivity ε _γ1 = 1), v ₁ = v.

By the way, the distance resolution in the distance calculation unit 26 corresponds to the above-described possible reception signal sampling time, and the higher the sampling time resolution, the higher the resolution when calculating the distance. In the signal processing unit 3 of the present embodiment, since the sampling time resolution is increased to several to several tens ps by adopting equivalent sampling as described above, the distance resolution in the distance calculation unit 26 is relatively high. . For example, when the sampling resolution is 1 ps, the distance resolution in the air is obtained by multiplying the time resolution by the velocity of the electromagnetic wave (the speed of light) in the air, 1 (ps) × 3 × 10 ⁸ (m / s) = 300 (μm). Since this distance resolution corresponds to the reciprocating distance to the object A, the distance resolution is 150 (μm) when converted to a one-way distance to the object A. When the sampling resolution is 10 ps, the distance resolution is 1.5 (mm) by the same calculation.

  Next, a configuration for determining the material of the object A will be described. The signal processing unit 3 includes a relative permittivity estimation unit 28 that is connected to the output of the unnecessary wave removal unit 24 and estimates the relative permittivity of the object A. The output of the distance calculation unit 26 is also connected to the relative dielectric constant estimation unit 28. A method for estimating the relative permittivity in the relative permittivity estimating unit 28 will be described later. The output of the relative permittivity estimation unit 28 is input to the material determination unit 29 that determines the material of the object A based on the relative permittivity of the object A. The material determination unit 29 is connected to a relative dielectric constant data storage unit 30 in which relative dielectric constants of various materials are stored in advance in association with the materials. The material determination unit 29 receives from the relative dielectric constant estimation unit 28. A relative dielectric constant that approximates the relative dielectric constant is selected from the relative dielectric constant data storage unit 30, and a material corresponding to the relative dielectric constant is determined as the material of the object A. Table 1 below shows the relative dielectric constants of several materials. In the relative permittivity data storage unit 30, by storing a set of a material that can be the object A and a relative permittivity according to the use of the object detection device, it is possible to accurately determine the material.

  A method for estimating the relative permittivity of the object A in the relative permittivity estimating unit 28 will be described below.

  FIG. 2 schematically shows a state where an electromagnetic wave having an electric field intensity Ei is incident on the object A from the medium B. Er is the electric field strength of the electromagnetic wave reflected by the object A. At this time, the reflection coefficient R at the boundary surface X between the medium B and the object A is expressed by the following equation.

Thus, since the reflection coefficient R is represented by the ratio of the electric field intensity Er and the electric field intensity Ei, the intensity of the direct wave that directly reaches the receiver 2 from the transmitter 1 and the wave reflected by the object A and received by the receiver. The reflection coefficient can be calculated on the basis of the intensity of the reflected wave that has reached 1 and the distance calculated by the distance calculation unit 26. That is, the relative permittivity estimation unit 28 calculates the attenuation amount of the electromagnetic wave intensity while the electromagnetic wave reciprocates in the medium B by the distance calculated by the distance calculation unit 26, and adds the attenuation amount to the intensity of the reflected wave. The reflection coefficient is obtained by calculating the ratio between the value and the intensity of the direct wave. Further, in the above formula 2, Z ₁ and Z ₂ are wave impedances of the medium B and the object A, respectively. Each of the wave impedances Z ₁ and Z ₂ has a dielectric constant of the medium B as ε ₁ , a dielectric constant of the object A as ε ₂ , a conductivity of the medium B as σ ₁ , and a conductivity of the object A as σ ₂ , When the magnetic permeability of the medium B is μ ₁ and the magnetic permeability of the object A is μ ₂ , the following expressions are used.

  Here, ω is the angular frequency of the electromagnetic wave. j is an imaginary unit. Summarizing Equations 2 to 4, the reflection coefficient R can be expressed by the following equation.

Here, the dielectric constants ε ₁ and ε ₂ of the medium B and the object A are set such that the relative dielectric constant of the medium B is ε _γ1 , the relative dielectric constant of the object A is ε _γ2, and the dielectric constant of vacuum is ε _0. , Ε ₁ = ε ₀ ε _γ1 , ε ₂ = ε ₀ ε _γ2 . Therefore, the reflection coefficient R includes the relative dielectric constants ε _γ1 and ε _γ2 of the medium B and the object A, the electrical conductivity σ ₁ and σ ₂ of the medium B and the object A, and the magnetic permeability μ of the medium B and the object A. ₁ and μ ₂ and the angular frequency ω of the electromagnetic wave. In the present embodiment, for the electromagnetic properties (conductivity and permeability) other than the relative permittivity of the medium B, the conductivity σ ₁ = 0 and the relative permeability μ _γ1 = 1 (the permeability μ ₁ is a vacuum permeability). If the magnetic permeability is μ ₀ , it is assumed that the relative permeability μ _γ1 is used and expressed as μ ₁ = μ ₀ μ _γ1 ). That is, if the reflection coefficient R is obtained based on the intensity of the direct wave, the intensity of the reflected wave, and the distance calculated by the distance calculation unit 26 as described above, this reflection coefficient R and the relative permittivity of the medium B (here, The relative dielectric constant of the object A can be estimated by using ε _γ1 = 1) and the frequency of the electromagnetic wave.

  By the way, since electromagnetic properties (conductivity and permeability) other than the relative permittivity of the object A are also unknown parameters, in order to accurately determine the material of the object A, electromagnetic waves having a plurality of frequencies were determined. Although it is necessary to obtain the relative dielectric constant of the object A from the reflection coefficient, in this embodiment, since the transmitter 1 transmits a UWB signal as an electromagnetic wave as described above, the transmitter 1 has a wide frequency range. An electromagnetic wave over a band, that is, an electromagnetic wave having a plurality of frequencies is transmitted. Then, the relative permittivity estimation unit 28 obtains the reflection coefficient for each of the frequencies based on the direct wave intensity, the reflected wave intensity, and the distance calculated by the distance calculation unit 26 for each frequency. The relative dielectric constant of the object A is statistically estimated by using each of the plurality of reflection coefficients, the relative dielectric constant of the medium B, and each frequency of the electromagnetic wave. That is, if each of the plurality of reflection coefficients, the relative dielectric constant of the medium B, and each frequency of the electromagnetic wave are used, a plurality of relative dielectric constants can be obtained. For example, by taking an average value of the plurality of relative dielectric constants, The relative dielectric constant of the object A is statistically estimated from the relative dielectric constant.

  As a result, the object detection device of the present embodiment has an advantage that the material of the object A can be accurately obtained by statistically obtaining the relative permittivity of the object A using electromagnetic waves having a plurality of frequencies. There is. Note that Et in FIG. 2 is the electric field intensity of the electromagnetic wave that has entered the object A through the boundary surface X between the medium B and the object A. Thus, the electromagnetic wave transmitted through the object A has an amplitude obtained by multiplying the amplitude of the electromagnetic wave incident on the object A from the medium B by the following transmission coefficient T.

Next, a configuration for calculating the thickness dimension of the object A will be described. The signal processing unit 3 includes a thickness discriminating unit (thickness calculating unit) 31 connected to the output of the unnecessary wave removing unit 24, and in the thickness discriminating unit 31, the received signal reproduced by the unnecessary wave removing unit 24 is received. Of the waveform, the reflected wave pattern corresponding to the reflected wave reflected by the object A is analyzed, and the reflected wave (hereinafter referred to as “surface reflected wave”) on the surface of the object A (the boundary surface with the medium B) By multiplying the time difference generated between the reflected wave transmitted through the surface of the object A and reflected by the back surface of the object A (hereinafter referred to as “back surface reflected wave”) by the speed of the electromagnetic wave in the object A The reciprocating distance between the front surface and the back surface of the object A is obtained, and the reciprocating distance is divided by 2, thereby calculating the thickness dimension between the front surface and the back surface of the object A. Since the velocity V ₂ of the electromagnetic wave in the object A is expressed by the following equation using the relative dielectric constant ε _γ2 of the object A as in the case of the above-described formula 1, the thickness determining unit 31 has a relative dielectric constant. receiving a relative dielectric constant epsilon _.gamma.2 the object a from the estimator 28 calculates the velocity V ₂ of the electromagnetic wave in the object a by using the dielectric constant epsilon _.gamma.2.

However, since the electromagnetic wave needs to pass through the surface of the object A in order to calculate the thickness dimension of the object A, the function of calculating the thickness dimension of the object A has a relative dielectric constant ε _γ2 of 1 <ε _γ2 This is effective when a material (for example, wood) in the range of about <20 is used as the object A. Further, the thickness discriminating unit 31 of the present embodiment discriminates the front surface reflected wave and the back surface reflected wave based on the phase information (amplitude positive / negative) of the electromagnetic wave. That is, the reflection coefficient of the electromagnetic wave reflected when entering the object A from the medium B (surface reflected wave) and the electromagnetic wave reflected when entering the medium B from the object A (back surface reflected wave) are The reversal of the positive and negative is obvious from the relationship of Equation 2 described above, and as a result, the phase is shifted by 180 degrees between the front surface reflected wave and the back surface reflected wave (the amplitude is reversed). By utilizing this, it is possible to distinguish between the front surface reflected wave and the back surface reflected wave.

  Furthermore, if the reflection coefficient for each of the front surface and the back surface is obtained even for a single object A, a larger number of reflection coefficients can be obtained than when the reflection coefficient is obtained only for the front surface. The respective strengths of the surface reflected wave and the back surface reflected wave are output from the thickness discriminating unit 31 to the dielectric constant estimating unit 28, and the relative dielectric constant estimating unit 28 reflects each of the front surface and the back surface of the object A. By adopting a configuration for obtaining a coefficient, a larger number of reflection coefficients can be employed in the relative permittivity estimation unit 28. Thereby, the precision of estimation of a relative dielectric constant can be improved, and the precision of judgment of a material can be improved.

  As described above, according to the signal processing unit 3 of the present embodiment, the distance to the object A, the material of the object A, and the thickness dimension of the object A can be obtained. And the display part 4 is comprised so that all these results (distance, material, thickness dimension) can be displayed.

Further, in the present embodiment, an example is shown in which an object detection device is used to detect an object A existing in the air. Since the medium B is air, the relative permittivity ε _γ1 of the medium is set to 1. For example, detection of an object A existing on the back side (wall back) of a wall material such as a concrete wall or a plaster board (so-called wall back detection), or detection of an object A embedded in a concrete wall or other medium B In this case, the relative permittivity ε _γ1 of the medium B varies depending on the material of the medium B such as a wall material existing between the object detection device and the object A. . Therefore, in the present embodiment, the signal processing unit 3 is provided with a relative permittivity setting unit 27 connected to the distance calculating unit 26 and the relative permittivity estimating unit 28, and the medium B used when calculating the distance and estimating the relative permittivity. The relative dielectric constant can be set by the relative dielectric constant setting unit 27. The relative permittivity setting unit 27 employs a configuration in which the user manually inputs the value of the relative permittivity. The relative permittivity setting unit 27 measures the relative permittivity of the medium B every time the object detection device is used. The result may be set as a relative dielectric constant.

Hereinafter, an example of obtaining the distance to the object A and the material of the object A using the above-described object detection device will be described with reference to FIGS. However, the case where the medium B is air (relative permittivity ε _γ1 = 1) and the object A is metal (relative permittivity ε _γ2 = ∞) is illustrated here.

In this example, the electromagnetic wave (corresponding to the direct wave I1) transmitted from the transmitter 1 is totally reflected on the surface of the object A as shown in FIG. 3, resulting in the direct wave I1 and the reflected wave R1. Is received by the receiver 2. FIG. 4 shows the received signal output from the receiver 2 at this time with the vertical axis representing amplitude and the horizontal axis representing time. The signal processing unit 3 that has received such a received signal uses the time difference T1 between the direct wave I1 and the reflected wave R1 in FIG. 4 and the velocity of the electromagnetic wave in the medium B (air) in the distance calculation unit 26. To calculate the distance to the object A. Further, in the relative permittivity estimation unit 28, the reflection coefficient R is obtained using the intensity of the direct wave I1, the intensity of the reflected wave R1, and the distance to the object A previously obtained. Then, the relative dielectric constant ε _γ2 of the object A is estimated by substituting the reflection coefficient R, the relative dielectric constant ε _γ1 = 1 of the medium, and the angular frequency ω of the electromagnetic wave with respect to the above formula 5. When the electromagnetic wave is reflected on the surface of the object A, the phase is shifted by 180 degrees as shown in FIG. 4 (that is, the amplitude is reversed), and the reflection coefficient R is R = −1. The relative permittivity estimation unit 28 estimates the relative permittivity of the object A as ε _γ2 = ∞, and the material determination unit 29 determines the material of the object A as a metal based on the relative permittivity.

Next, an example of obtaining the distance to the object A and the thickness dimension of the object A using the above-described object detection device will be described with reference to FIGS. However, the case where the medium B is air (relative permittivity ε _γ1 = 1) and the object A is wood (relative permittivity ε _γ2 = 4) is illustrated here. In the following description, it is assumed that there is no attenuation of electromagnetic waves in the object A.

  In this example, the electromagnetic wave (corresponding to the direct wave I1) transmitted from the transmitter 1 is partially reflected on the surface of the object A (reflection coefficient R = −1 / 3) as shown in FIG. The remainder passes through the surface of the object A and enters the object A. Here, if the amplitude of the direct wave I1 is 1, the amplitude of the reflected wave R1 reflected from the surface of the object A is −1/3, and the amplitude of the electromagnetic wave incident in the object A is the above-described equation (6). 2/3. Part of the electromagnetic wave incident on the object A is reflected on the back surface (reflection coefficient 1/3) of the object A (the amplitude is 2/3 × 1/3 = 2/9), and the rest is the object. The light passes through the back surface of A and is emitted out of the object A. Further, the electromagnetic wave reflected on the back surface of the object A is partially reflected on the surface of the object A (reflection coefficient R = 1/3), and the remaining reflected wave R2 (amplitude is 2/9 × 4/3 = 8/27) passes through the surface of the object A and enters the medium B. The direct wave I1, the reflected wave R1, and the reflected wave R2 are received by the receiver 2. FIG. 6 shows the received signal output from the receiver 2 at this time with the vertical axis representing amplitude and the horizontal axis representing time.

  Upon receiving the received signal shown in FIG. 6, the signal processing unit 3 receives the time difference T1 between the direct wave I1 and the reflected wave R1 in FIG. 6 and the speed of the electromagnetic wave in the medium B (air) in the distance calculation unit 26. Use to calculate the distance to the object A. Further, only the components of the reflected waves R 1 and R 2 reflected by the object A are output from the unnecessary wave removing unit 24 to the thickness determining unit 31. The thickness determining unit 31 obtains the thickness dimension t of the object using the time difference T2 between the reflected wave R1 and the reflected wave R2 and the speed of the electromagnetic wave in the object A.

It is a block diagram which shows the structure of embodiment of this invention. It is explanatory drawing which shows reflection of the electromagnetic waves in the target object illustrated same as the above. It is explanatory drawing which shows reflection of the electromagnetic waves in the target object (metal) illustrated above. It is explanatory drawing which shows the waveform of a received signal same as the above. It is explanatory drawing which shows reflection of the electromagnetic waves in the target object (wood) illustrated above. It is explanatory drawing which shows the waveform of a received signal same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 26 Distance calculation part 27 Relative permittivity setting part 28 Relative permittivity estimation part 29 Material judgment part 31 Thickness discrimination part (thickness calculation part)
A Object B Medium

Claims (3)

  A transmitter that intermittently transmits an electromagnetic wave to the detection region, a receiver that receives the electromagnetic wave from the transmitter reflected by an object existing in the detection region, and converts the electromagnetic wave into a received signal that is an electrical signal; The distance to the object is determined based on the time required for the electromagnetic wave to be transmitted and received and the velocity of the electromagnetic wave in the medium determined from the relative permittivity of the medium existing between the electromagnetic wave and the object. The reflection coefficient of the interface between the medium and the object is calculated from the distance calculation unit to be calculated, the intensity of the electromagnetic wave transmitted by the transmitter, the intensity of the electromagnetic wave received by the receiver, and the distance to the object for each of a plurality of frequencies. The relative dielectric constant estimator that statistically estimates the relative dielectric constant of the object using each reflection coefficient, the relative dielectric constant of the medium, and each frequency of the electromagnetic wave, and the relative dielectric constant estimated by the relative dielectric constant estimator A material judgment unit that judges the material of the object based on the rate , Transmitter, an object detection device, characterized by transmitting the UWB signal as electromagnetic wave.   The time required from receiving the electromagnetic wave reflected on the surface of the object to receiving the electromagnetic wave reflected on the back surface of the object, and the relative dielectric constant estimated by the relative dielectric constant estimating unit The object detection apparatus according to claim 1, further comprising: a thickness calculation unit that calculates a thickness dimension between the front surface and the back surface of the target object using the speed of the electromagnetic wave in the target object obtained from the above.   The object detection apparatus according to claim 1, further comprising a relative dielectric constant setting unit configured to set a relative dielectric constant of the medium used in the distance calculation unit and the relative dielectric constant estimation unit.

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