JP2013101140A - Specific absorption rate measuring system and method - Google Patents

Abstract

A specific absorption rate measurement system and method for accurately and quickly measuring a SAR (specific absorption rate) distribution.
A living body equivalent phantom unit for use in a specific absorptivity measuring system for evaluating absorption of electromagnetic wave energy includes a pseudo human body for receiving electromagnetic wave absorption and a measured electromagnetic wave generator. A plurality of electro-optic crystals 3 for measuring the electric field generated in the first and second, and a plurality of bare fibers 10 laid in the pseudo human body for coupling each of the electro-optic crystals to the outside. A specific absorptivity measuring system that evaluates the absorption of electromagnetic wave energy using a living body equivalent phantom unit includes a light source 4, a polarization adjuster 7 that adjusts the polarization state of light emitted from the light source, and light sequentially incident on each electro-optic crystal. And a specific absorptivity measuring unit 44 for measuring the specific absorptance by detecting the light reflected from the optical path switch 9 and the electro-optic crystal.
[Selection] Figure 4

Description

  The present invention relates to a bioequivalent phantom unit for use in a specific absorptivity measuring system for evaluating absorption of electromagnetic wave energy, and a specific absorptivity measuring system and method using the unit.

  In recent years, there has been an increasing need to quantitatively evaluate the thermal effect of electromagnetic waves emitted from transmitters on living bodies such as humans. Specific Absorption Rate (below) is an index of the effects of electromagnetic waves on living bodies. Development of a system that accurately and quickly measures SAR) is desired.

The SAR is a value proportional to the electric field (| E | ² ) as defined by the following formula (1), and is mainly used for evaluating the power absorbed when using, for example, a mobile phone in the vicinity of the human body. It has been.
[Equation 1]
SAR = σ | E | ² / ρ Equation (1)
Here, σ and ρ are the electrical conductivity [S / m] and density [kg / m ³ ] of the biological equivalent phantom, respectively.

  Usually, when measuring SAR, a method is adopted in which an electric field generated in a medium is detected by a small dipole and converted into SAR using equation (1) (electric field measurement method).

  FIG. 1 shows a conventional specific absorption rate measurement system 100. The specific absorptivity measuring system 100 includes a pseudo human body (hereinafter referred to as a phantom) 101 that simulates the electrical constant of a human body with a liquid, a container 102 for containing a liquid, an electric field detection probe 103, a probe scanning device 104, a signal cable 105, It comprises an electric field detector 106 and a processor device 107 for measurement operation and data analysis.

  As shown in FIG. 1, an electric field generated in a phantom is measured by placing a device under test 108 such as a mobile phone in the vicinity of the specific absorption rate measuring system 100. The probe scanning device 104 three-dimensionally scans the electric field detection probe 103 to measure SAR.

  FIG. 2 shows another conventional specific absorption rate measuring system 200. The specific absorption rate measurement system 200 includes a phantom 121 that simulates the electrical constant of a human body with a solid, an electric field detection probe 122, a signal transmission cable 123, an electric field detection device 124, a processor device 125 for measurement operation and data analysis, and a scanning device. 126.

  As shown in FIG. 2, an electric field generated in the phantom is measured by disposing a device 127 such as a mobile phone in the vicinity of the specific absorptivity measuring system 200. However, unlike the conventional example of FIG. 1, the mobile phone 127 is scanned by the scanning device 126 to measure the SAR.

  In any conventional example, the electric field detection probe 103 or 122 is used. The detection unit 110 of the electric field detection probe 103 or 122 is shown in detail on the right side in FIG. The electric field detected by the minute dipole elements 111 and 112 is detected by the Schottky diode 113 inserted in the gap, and an electric signal is transmitted to the electric field detectors 106 and 124 via the high resistance line 114. A voltage generated by a minute dipole element formed of a conductor of about 2 to 5 mm is detected by a Schottky diode.

  However, these electric field measurement methods use a small dipole and a high resistance wire as described above, so that there is a conductor in the electric field to be measured, and the electromagnetic field distribution around the detection unit is disturbed. is there. Further, since it is difficult to make the dipole length smaller, it is expected that the disturbance becomes larger as the frequency becomes higher.

  Therefore, in order to reduce disturbance to the electromagnetic field to be measured by the electric field detection probe itself as described above, an electric field sensor using a waveguide type optical modulator and laser light as shown in FIG. 3 has been developed. .

  The electric field sensor 300 shown in FIG. 3 includes a laser light source 131, an electric field probe 132, a waveguide type optical modulator 133, a minute dipole 134 made of metal, and a light receiving unit 135.

  Since the electric field sensor 300 is composed entirely of a dielectric material except for the minute dipole 134, it is possible to measure the electric field with higher accuracy than the electric field detection method having a high resistance line.

International Publication No. 03/014717

  Since the electric field measurement method using the waveguide type optical modulator and the laser light like the electric field sensor 300 described above uses a minute dipole, the disturbance is smaller than the electric field measurement method using a high resistance wire. There is a problem that the electromagnetic field distribution around the detection unit is disturbed. Further, in the SAR measurement in the liquid phantom, the phantom solvent is agitated in order to three-dimensionally scan the electric field detection probe or electric field sensor, and noise due to probe vibration is generated. In order to remove this noise, if a time until the solvent settles to a steady state is provided, a long time is required for the measurement. If a plurality of electric field sensors are arranged two-dimensionally or three-dimensionally in the phantom in order to shorten the measurement time, a group of a plurality of minute dipoles behave as conductors for the electromagnetic field to be measured, resulting in a great disturbance. As a result, there is a possibility of measuring a SAR distribution that is completely different from the actual one, which is a problem.

  The present invention solves the above-described problems, and provides a specific absorption rate measurement system and method capable of accurately and quickly measuring a SAR distribution, and also provides a bioequivalent phantom unit suitable for that purpose. Is an issue.

In order to solve the above-described problem, a biological equivalent phantom unit for use in a specific absorptivity measuring system for evaluating the absorption of electromagnetic wave energy according to one aspect of the present invention is a biological equivalent phantom for receiving electromagnetic wave absorption. A plurality of zinc flashes disposed at a plurality of measurement points in the biological equivalent phantom to measure an electric field generated in the biological equivalent phantom by the electromagnetic wave generator to be measured, each having a cross-sectional area of 0.01 mm ² or less A plurality of optical fibers laid in a bio-equivalent phantom for coupling each of the electro-optic crystals to the outside.

  In such a biological equivalent phantom, a high dielectric constant material that makes the equivalent dielectric constant of the optical fiber equal to that of the biological equivalent phantom may be applied to the surface of the optical fiber. The electro-optic crystal may be CdTe.

  According to another aspect of the present invention, a specific absorptance measurement system for evaluating the absorption of electromagnetic wave energy using the biological equivalent phantom unit as described above includes: a light source that emits light; a polarization state of light emitted from the light source A polarization adjuster that adjusts the light; an optical path switch that sequentially causes the light emitted from the polarization adjuster to enter each electro-optic crystal; and a ratio that measures the specific absorptance by detecting the light reflected from the electro-optic crystal. An absorptivity measuring unit;

According to another aspect of the present invention, a specific absorption rate measuring method for evaluating absorption of electromagnetic wave energy using a biological equivalent phantom that is irradiated with electromagnetic waves is an electric field generated in a biological equivalent phantom by a measured electromagnetic wave generator. Measuring a plurality of zinc blende-type electro-optic crystals each having a cross-sectional area of 0.01 mm ² or less at a plurality of points to be measured in a biological equivalent phantom; After adjusting the polarization state, sequentially entering each electro-optic crystal by an optical path switch; reflecting light incident on the electro-optic crystal; guiding light reflected from the electro-optic crystal to the analyzer Converting the light that has passed through the analyzer into an electrical signal by a photodetector and deriving a specific absorption rate.

  In the above specific absorptance measurement method, the step of reflecting the light incident on the electro-optic crystal is reflected by the dielectric reflecting film provided on the surface of the electro-optic crystal opposite to the surface on which the light is incident. It may consist of stages.

  Alternatively, the optical path switch and each electro-optic crystal may be connected with an optical fiber, and light may be sequentially incident on each electro-optic crystal by selecting the optical fiber with the optical path switch.

  Furthermore, by applying a high dielectric constant material on the surface of the optical fiber that makes the equivalent dielectric constant of the optical fiber equal to that of the biological equivalent phantom, the equivalent dielectric constant of the optical fiber is substantially equal to the dielectric constant of the biological equivalent phantom. You may make it do.

  In the specific absorptance measuring method, the electro-optic crystal may be CdTe.

  In the present invention, since the electric field detector is made of a non-metal, it is possible to measure the SAR distribution by removing disturbances that have occurred in the prior art. In addition, by using an electro-optic crystal having a dielectric constant close to that of a phantom as a sensor head, reflection due to a difference in dielectric constant can be reduced and a more accurate SAR distribution can be measured. Furthermore, since the spatial resolution in measurement is proportional to the beam diameter of the light transmitted through the electro-optic crystal, in principle, the spatial resolution can be reduced to the wavelength of light (several μm). Furthermore, since the refractive index change of the electro-optic crystal at the point to be measured is caused by the bias of the dipole that follows the electromagnetic wave, broadband SAR measurement from the MHz band to the THz band is possible.

  According to the present invention, by using an electro-optic crystal having a dielectric constant close to that of a phantom, not only the reduction of the electric field in the electro-optic crystal due to interface reflection is reduced, but also the electromagnetic field around the electro-optic crystal due to interface reflection. It becomes possible to reduce the influence of. Therefore, an accurate specific absorption rate (SAR) distribution can be obtained by using the specific absorption rate (SAR) measurement system according to the embodiment of the present invention.

1 is a schematic view of a conventional specific absorption rate measurement system 100. FIG. It is the schematic of the other conventional specific absorption rate measuring system 200. FIG. It is the schematic of the electric field sensor using the conventional waveguide type optical modulator and a laser beam. 1 is a block diagram of a specific absorption rate (SAR) measurement system according to an embodiment of the present invention. It is a perspective view of the phantom vicinity according to embodiment of this invention. It is a graph which shows the error of the electric field strength in an electro-optic crystal by a relative dielectric constant difference.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, members having the same function are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 4 is a block diagram of a specific absorption rate (SAR) measurement system according to an embodiment of the present invention. The biological equivalent phantom unit 42 of the specific absorptivity measurement system 40 includes a pseudo human body (phantom) 1 that simulates the electrical constant of a human body composed of liquid, gel, solid, and the like, and an electro-optic crystal 3 having a dielectric constant close to that of the phantom 1. And the bare fiber 10.

  The specific absorptivity measuring system 40 further includes a measured electromagnetic wave generator 2 such as a mobile phone, a linearly polarized light source 4 such as DFB-LD, a polarization maintaining fiber (PMF) 5, a circulator 6, and a quarter wavelength. A polarization adjuster 7 composed of a plate or a half-wave plate, a single mode fiber (SMF) 8, an optical path switch 9 formed by MEMS technology or PLC technology, and a specific absorptance measurement unit 44. Has been.

  The specific absorptivity measuring unit 44 includes an analyzer 11, a photodetector 12, an electric signal line 13, a signal processing unit 14, and a SAR distribution image display 15.

  As shown in FIG. 4, the specific absorption rate measurement system 40 is a system for measuring an electric field generated in the phantom 1 by the measured electromagnetic wave generator 2 arranged in the vicinity of the phantom 1 using the electro-optic crystal 3. It is.

  The linearly polarized light emitted from the linearly polarized light source 4 is propagated by the polarization maintaining fiber (PMF) 5 via the circulator 6 to the polarization adjuster 7. The polarization adjuster 7 adjusts the incident linearly polarized light to a specific polarization state and emits it.

  The specific polarization state is determined by the crystal axis of the electro-optic crystal 3 disposed in the phantom 1 and the vibration direction of the electric field emitted from the measured electromagnetic wave generator 2. For example, when an electric field oscillating parallel to the y-axis is detected using CdTe, which is a zinc blende type crystal, the (001), (100), and (010) planes, which are CdTe crystal planes, are respectively shown. The polarization adjuster 7 is arranged perpendicular to the y, x, z axis or perpendicular to the y, z, x axis so that the polarization axis of linearly polarized light or elliptically polarized light is parallel to the x axis or z axis. Adjust.

  The polarization-adjusted light is propagated through a single mode fiber (SMF) 8 and sequentially incident on each electro-optic crystal 3 by an optical path switch 9.

  The incident light is reflected by a dielectric reflecting film provided on a surface opposite to the incident surface of the electro-optic crystal 3 and travels backward through the incident path. When light travels back through the incident path in an electro-optic crystal, a phase difference occurs between specific polarization components due to a refractive index change (Pockels effect) proportional to the first power of the applied electric field strength, and the polarization state changes. (Polarization modulation).

When CdTe is arranged as in the above example, a phase difference Γ represented by the following equation is generated between polarized components parallel to the x-axis and the z-axis.
[Equation 2]
Γ = (2π / λ) n ₀ ³ r ₄₁ Ed Formula (2)
Here, λ, n ₀ , r ₄₁ , E, and d are the wavelength of incident light [m], the refractive index of the electro-optic crystal 3, the Pockels constant [m / V], the electric field strength [V / m], and the electric field, respectively. The length [m] of the electro-optic crystal 3 in the vibration direction.

  The reflected and polarization-modulated light is branched to the analyzer 11 by the circulator 6 via the optical path switch 9 and the polarization adjuster 7. The modulated component of the branched light is extracted by the analyzer 11 and converted into an electrical signal by the photodetector 12. The amplitude of the electric signal is proportional to the electric field strength of the electromagnetic wave to be measured. The amplitude of the electric signal can be converted into SAR by the signal processor 14, and the SAR distribution can be displayed by the SAR distribution image display 15 with accompanying position information.

The specific absorption rate (SAR) is defined by the equation (1) by the electric field measurement method. By using the specific absorption rate measurement system 40 according to the present embodiment, the SAR is calculated from the equations (1) and (2). It can be defined by an expression.
[Equation 3]
SAR = σK | Γ | ² / ρ Formula (3)
Here, K is a constant determined by the crystal axis of the electro-optic crystal 3 and the vibration direction of the electric field emitted from the measured electromagnetic wave generator 2. When CdTe is arranged as in the above example, K can be expressed by the following equation.
[Equation 4]
K = λ / (2πn ₀ ³ r ₄₁ d) Formula (4)
Similarly, when an electric field oscillating parallel to the x (or z) axis is detected using CdTe, which is a zinc blende type crystal, the crystal planes of CdTe are (110), (1 (1 bar ) 0), (001) planes are arranged perpendicular to the x (z), y, z (x) axes, respectively, so that the polarization axis of linearly polarized light or elliptically polarized light is parallel to the x (z) axis. The polarization adjuster 7 is adjusted. In this case, a phase difference (Γ) expressed by the following equation is generated between polarized components inclined by 45 ° with respect to the x-axis and the z-axis.
[Equation 5]
Γ = (2π / λ) ln ₀ ³ r ₄₁ E Formula (5)
Here, l is the length [m] of the electro-optic crystal 3 in the direction in which light passes. Further, when the SAR is defined by the equation (3), the coefficient K can be expressed as the following equation.
[Equation 6]
K = λ / (2πln ₀ ³ r ₄₁ ) Formula (6)
In the specific absorptance measurement system 40 according to the present embodiment, since the electric field detector is made of a dielectric material, the measurement target is caused by an assembly of small dipoles that has been a problem in the conventional electric field measurement method. The disturbance to the electromagnetic field can be removed. The relative permittivity of phantom 1 is specified by ARIB. Depending on the type of the electro-optic crystal 3, reflection of electromagnetic waves (Fresnel reflection) occurs at the interface due to the difference in dielectric constant, but this reflection is very small compared to the disturbance caused by the aggregate of minute dipoles.

FIG. 6 is a graph showing the electric field strength in the electro-optic crystal 3 in consideration of reflection at the interface when there is no electromagnetic wave absorption in the electro-optic crystal 3. In the calculation, a model in which electromagnetic waves are incident perpendicularly to the semi-infinite electro-optic crystal 3 is assumed, and the value (40.5) at 1450 MHz defined by ARIB is used as the relative permittivity of the phantom. As a result of calculation, in the case of CdTe used in the above example, it was found that a true value can be obtained by correcting the electric field measured in consideration of reflection of about 10%. Further, it is considered that the influence of the reflection on the measured electromagnetic field is proportional to the area ratio occupied by the electro-optic crystal 3. The minimum spatial resolution in SAR measurement is 1 mm. Since the minimum processing dimension of the electro-optic crystal 3 is 100 μm (= 0.1 mm) or less, the minimum area of the electro-optic crystal 3 is 0.01 mm ² . From these facts, when the reflectance per 1 mm ² area corresponding to the minimum spatial resolution in SAR measurement is converted into an area ratio, it becomes 0.01 / 1 = 1/100, that is, about 1%, which is almost negligible. Become. By using an electro-optic crystal such as LN, LT, or KD * P having a value close to the dielectric constant of the phantom, it is possible to measure SAR without correction. Table 1 shows the electrical characteristics of LN, LT, and KD * P and errors in the measured electric field due to reflection.
[Table 1]
Error of measured electric field due to electrical properties and interface reflection of electro-optic crystal Electro-optic crystal Pockels coefficient (X10 ^-12 m / V) Relative permittivity Error of measured electric field
LiNbO ₃ (LN) 19 28 0.8%
LiTaO ₃ (LT) 22 43 0.01% or less
KD ₂ PO ₄ (KD * P) 24.1 48 0.2% or less

For the same reason, about 28% of the reflection occurs in the bare fiber 11 connecting the electro-optic crystal 3 and the optical path switch 9, and there is a possibility that the measurement target electromagnetic field is disturbed. The diameter of a normal bare fiber including the coating layer is 250 μm, and the reflectance per 1 mm ² measurement cross section is 1/16 (about 1.8%). The coating layer is formed in consideration of the microbend resistance at a low temperature. However, since the bare fiber 10 in the system of the present embodiment is covered with the phantom 1, a cladding fiber having an 80 μm diameter without the coating layer is used. It is possible. By using such a clad fiber, the reflectance per 1 mm ² can be 0.2% or less.

When N electro-optic crystals 3 are arranged in the y-axis direction as shown in FIG. 5, the number of bare fibers 10 per 1 mm ² on the optical path switch 9 side is N, and the reflectance per 1 mm ² is 0. 2 × N% or less. When the allowable reflectance is set to 10% or less, the number of electro-optic crystals 3 that can be arranged in the y-axis direction is 50, and when arranged at 1 mm intervals, the length that the electro-optic crystals 3 can be arranged in the y-axis direction is 50 mm. is there. Since the size of the phantom simulating the head is about 300 mm square, the reflection on the optical path switch 9 side may become very large.

On the other hand, reflection of electromagnetic waves can be prevented by applying a material having a large dielectric constant to the surface of the bare fiber 10 and making the equivalent dielectric constant of the fiber 10 equal to that of the phantom. Since the relative dielectric constant can be adjusted to 40-120 depending on the main axis direction and the sintering temperature, TiO ₂ and BaTiO ₃ having a sintering temperature lower than the softening temperature of glass (about 1500 ° C.) are suitable as coating materials.

1 Pseudo human body (phantom)
2 Electromagnetic wave generator to be measured 3 Electro-optic crystal 4 Linearly polarized light source 5 Polarization maintaining fiber (PMF)
6 Circulator 7 Polarization adjuster 8 Single mode fiber (SMF)
DESCRIPTION OF SYMBOLS 9 Optical path switch 10 Bare fiber 11 Analyzer 12 Photo detector 13 Electric signal line 14 Signal processing part 15 SAR distribution image display device 40 Specific absorption rate measurement system 42 Living body equivalent phantom unit 44 Specific absorption rate measurement unit

Claims (9)

A bioequivalent phantom unit for use in a specific absorptivity measurement system to evaluate the absorption of electromagnetic energy,
A biologically equivalent phantom for receiving electromagnetic waves;
In order to measure the electric field generated in the biological equivalent phantom by the electromagnetic wave generator to be measured, a plurality of flashes arranged at a plurality of measurement points in the biological equivalent phantom, each having a cross-sectional area of 0.01 mm ² or less. Zinc ore type electro-optic crystal;
A plurality of optical fibers laid in the bioequivalent phantom to couple each of the electro-optic crystals to the outside;
A living body equivalent phantom unit. The bio-equivalent phantom unit according to claim 1, wherein:
A bioequivalent phantom unit, wherein a high dielectric constant material that makes an equivalent dielectric constant of the optical fiber equal to the bioequivalent phantom is applied to the surface of the optical fiber. The biological equivalent phantom unit according to claim 1 or 2, wherein:
The bio-equivalent phantom unit, wherein the electro-optic crystal is CdTe. A specific absorptivity measurement system for evaluating absorption of electromagnetic wave energy using the biological equivalent phantom unit according to any one of claims 1 to 3.
A light source that emits light;
A polarization adjuster for adjusting the polarization state of the light emitted from the light source;
An optical path switch for sequentially making the light emitted from the polarization adjuster enter each electro-optic crystal; and a specific absorptance measuring unit for measuring the specific absorptance by detecting the light reflected from the electro-optic crystal;
A specific absorption rate measuring system. A specific absorptivity measurement method that evaluates the absorption of electromagnetic wave energy using a biologically equivalent phantom that is irradiated with electromagnetic waves:
In order to measure the electric field generated in the biological equivalent phantom by the electromagnetic wave generator to be measured, a plurality of zinc blende-type electro-optic crystals each having a cross-sectional area of 0.01 mm ² or less are connected to the plurality of zinc equivalents in the biological equivalent phantom. Placing at the point to be measured;
Adjusting the polarization state of the light emitted from the light source and then sequentially making the light incident on each of the electro-optic crystals by an optical path switch;
Reflecting incident light into the electro-optic crystal;
Directing light reflected from the electro-optic crystal to an analyzer;
Converting light that has passed through the analyzer into an electrical signal by a photodetector and deriving a specific absorption rate;
A specific absorptivity measuring method. The specific absorption rate measuring method according to claim 5, wherein:
Reflecting light incident on the electro-optic crystal comprises reflecting light by a dielectric reflecting film provided on a surface of the electro-optic crystal opposite to the surface on which the light is incident;
The specific absorption rate measuring method characterized by the above-mentioned. The specific absorption rate measuring method according to claim 6, wherein:
A specific absorptance characterized in that the optical path switch and each electro-optic crystal are connected by an optical fiber, and light is sequentially incident on each electro-optic crystal by selecting the optical fiber with the optical path switch. Measuring method. The specific absorption rate measuring method according to claim 7, wherein:
By applying a high dielectric constant material on the surface of the optical fiber that makes the equivalent dielectric constant of the optical fiber equal to that of the biological equivalent phantom, the equivalent dielectric constant of the optical fiber is substantially equal to the dielectric constant of the biological equivalent phantom. Specific absorptivity measuring method, characterized in that they are equal. A method for measuring a specific absorption rate according to any one of claims 5 to 8, wherein:
The method for measuring a specific absorptance, wherein the electro-optic crystal is CdTe.

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