JP6168588B2 - Method for measuring the specific absorption rate of electromagnetic waves from multiple electromagnetic sources - Google Patents

Description

  The present invention measures and evaluates the specific absorption rate (hereinafter referred to as “SAR”) of electromagnetic waves from a radio device of a multi-antenna transmission system such as a mobile phone that transmits simultaneously at the same frequency using two or more antennas. The present invention relates to a method for measuring the specific absorption rate of electromagnetic waves from a plurality of electromagnetic wave sources.

  In recent years, multi-antennas operating at the same frequency have been increasingly used in wireless communication systems using various technologies such as multi-input multi-output antennas or antenna arrays.

  These systems require specific absorption rate (SAR) measurements to assess compliance of radio equipment with radio wave protection guidelines. The SAR indicates the amount of absorption per unit mass of living tissue when exposed to an electromagnetic field. In the SAR measurement, the living body is represented by a dielectric medium having an electrical constant that simulates the living body.

The SAR is proportional to the absorbed electromagnetic field power (| E | ² ) and is expressed by the following equation.

Here, σ and ρ represent conductivity (S / m) and medium density (kg / m ³ ), respectively.

  This SAR is used in particular to evaluate the power generated and absorbed from wireless devices used near the human body. In a conventional normal system, a single antenna is used on the transmission side (or a single antenna on the reception side). In this case, the SAR is measured by using, for example, an electric field probe, and calculated by Equation (1). Basically, the SAR distribution can be obtained by scanning the electric field probe inside the liquid and recording the electric field. FIG. 1 shows an example in which (b) the SAR distribution is evaluated for electromagnetic waves from a single antenna (a) on the observation surface in the phantom. The electric field probe extends from the underside of the phantom, but this is for convenience of illustration.

  However, when two or more antennas are used on the transmission side, the electromagnetic field at each observation point strongly depends on the phase difference at the antennas. Therefore, the SAR measurement of such a system needs to be performed with all combinations of the intensity and phase difference of each electromagnetic wave source and the electromagnetic wave source (see Non-Patent Document 1).

  In particular, when many antennas are used in the device, the number of combinations increases, and this measurement becomes very time consuming. In order to reduce the measurement time in such a case, several measurement methods have been introduced as follows.

  For example, during SAR measurements, the antennas are turned on and off, and individual SARs are measured for the active (ON) antenna. A comprehensive SAR value is obtained by combining individual SAR values (see Non-Patent Document 2).

  In addition, other methods have been proposed, which activate all antennas being measured. The time averaged SAR is obtained with a predetermined time average using a scalar probe in a conventional SAR measurement system (see Non-Patent Document 3).

  The SAR measurement method described above still has some significant drawbacks. For example, the technique for turning the antenna on and off during SAR measurement only provides the upper limit of the SAR and potentially tends to overestimate the SAR. Not only that, but an additional switch to turn the antenna on and off is required, which makes the measurement system more complex and more expensive.

  In addition, the technique of turning on the antenna during the SAR measurement requires time averaging. In fact, the SAR at a particular phase difference of the electromagnetic wave source can be higher or lower than the time averaged value. Furthermore, the averaging time of each evaluation point of this technique is considerably longer than that of the conventional method, so that the total measurement time becomes longer.

  In contrast, the present invention provides a simple SAR measurement method and a very accurate evaluation method, which is an arbitrary combination of phase differences (or / and intensities) based on electromagnetic field evaluation. The SAR value is evaluated. Only a short measurement time is required at the point to be measured. An arbitrary combination of phase differences of the electromagnetic wave source can be evaluated based on measurement data.

  The above measurement method and evaluation method can be applied to a SAR measurement system in which a conventional scalar probe is used, and similarly, can be applied to an advanced SAR measurement system provided with a vector probe.

  According to the technique of the present invention, in a multi-antenna transmission system having N element antennas, only N measurements are required for a vector probe, and N (N−1) +1 measurements are required for a scalar probe. That's it. When reducing the number of measurements, particularly when the number of element antennas is large, the evaluation method proposed in the present invention is very meaningful.

IEC / TR 62630, “Guidance for Evaluating Exposure from Multiple Electromagnetic Sources,” Ed. 1.0, 2010. T.Iyama and T.Onishi, "Maximum Average SAR Measurement Procedure for Multi-Antenna Transmitters", IEICE Trans. Comm., Vol. E93-B, no. 7, 1821-1825, Jul. 2007. DTLe, T. Iyama, L. Hamada, S. Watanabe, and T. Onishi “Electric Field Measurements for MIMO Wireless Communication Transmitters in Electromagnetic Exposure Evaluation” in Proc. Of Pan-Pacific EMC Joint Meeting (PPEMC'12), Tokyo , Japan, Nov. 2012

  To reduce the time taken to measure the specific absorption rate (SAR) of electromagnetic waves from a radio device of a multi-antenna transmission system such as a mobile phone that transmits two or more antennas at the same frequency at the same time compared to the conventional method. We propose a possible measurement method.

The present invention relates to a method for measuring the specific absorption rate of electromagnetic waves from a plurality of electromagnetic wave sources,
A plurality of electromagnetic wave sources capable of controlling the phase of the radiated electromagnetic wave, an observation point irradiated with each electromagnetic wave from the electromagnetic wave source, a probe for detecting electromagnetic field intensity at the observation point, and measurement of the probe In an electromagnetic field strength measuring means comprising a computing means for performing a predetermined calculation from data and a control means for performing the control, a method for obtaining a phase condition in the electromagnetic wave source of the electromagnetic wave that gives the maximum electromagnetic field strength at the observation point. There,
The number of the electromagnetic wave sources is N, the angular frequency of the frequency is ω, the phase at the electromagnetic wave source is β _j (j = 1, 2,..., N), and the three-dimensional component of the electric field vector [E] at the point is [Ex, Ey, Ez] e ^iωt , the combined electric field at the above point,

age,
(1) The electric field vector at the observation point or the square of its intensity is measured for a predetermined combination of the phases,
(2) From the measurement value obtained by the measurement, determine the square of the intensity of the electric field vector as a function of the phase only,
(3) The maximum value of the determined function is obtained by adjusting the combination of the phases with a predetermined accuracy.
Including a method.
Here, the observation point is a measurement point in the measurement, and is a point of interest where attention is paid to the value of the electromagnetic field intensity in the simulation.

In (2) above, when the square of the intensity of the electromagnetic field vector is determined as a function of the phase only,
Dividing the square of the intensity of the electromagnetic field vector into a constant term independent of the phase, a cosine term including the cosine of the phase difference of the phase, and a sine term including the sine of the phase difference of the phase,
From the measurement value obtained by the above measurement, the square of the intensity of the electromagnetic field vector is determined as a function of the phase only.

In the measurement of the electromagnetic field vector, each set value of the phase is a value in which a pair of cosine and sine values is a pair of 1 and 0, 0 and 1, or −1 and 0 .

As each set value of the phase, 0 or π is used, and the coefficient of the constant term or the cosine term is determined in a state where there is no contribution from the sine term.

  The above measurement is performed using a vector probe. Since the measured value of the electric field strength can be obtained from the vector probe, it is easy to obtain the square of the strength, and it can be used instead of the scalar probe. Here, the vector probe detects the phase and amplitude of the electric field as a set of vector components.

  The above measurement is performed using a scalar probe. At this time, the square of the intensity of the electric field vector is measured and determined as a function of only the phase. Here, the scalar probe detects only the intensity.

  According to the present invention, one component of the electric field at one point of the electromagnetic wave from the multi-antenna is measured N times in the case of the vector evaluation method using the vector probe, and N (N−1) in the case of the scalar evaluation method using the scalar probe. ) The SAR can be evaluated by one measurement and the required number of measurements is reduced, so that the measurement time can be shortened.

FIG. 1 shows the related art of the SAR distribution of a single antenna transmitter. FIG. 2 shows the arrangement of a two-element antenna 1 array placed on a horizontal phantom 6. The two-element antenna 1 has the same polarization. FIG. 3 shows an example of an antenna 1 array placed on a horizontal phantom 6. The array consists of N individual electromagnetic wave sources (antenna 1). FIG. 4 shows the relationship between the 2D measured electric field distribution and the 2D estimated electric field distribution. This is mentioned in the first example showing the utility of the vector evaluation method. (A) shows the SAR distribution measured at β = π, (b) shows the SAR distribution measured at β = 0, and (c) shows the SAR distribution evaluated for an arbitrary β. FIG. 5 is a flowchart for finding the maximum value of the electric field when vector evaluation or scalar evaluation is used for a two-element antenna array. The SAR is obtained from the maximum value of the electric field. FIG. 6 shows (b) calculation and (a) by the 2D (two-dimensional) FDTD method (Finite-difference time-domain method) when the vector evaluation method is used for the antenna arrangement of FIG. Comparison with evaluation is shown. FIG. 7 shows a comparison between the SAR distribution (□) along the X axis and the FDTD calculation when the vector evaluation method is used in the antenna arrangement of FIG. The phase difference β is 45 degrees. FIG. 8 shows the arrangement of a two-element antenna 1 array placed on a horizontal phantom 6. The two antennas 1 are arranged so as to be orthogonal. FIG. 9 shows the arrangement of a two-element antenna 1 array placed on a horizontal phantom 6. The two antennas 1 are arranged at a certain distance and rotated by an angle. The distance and angle are arbitrarily selected so as to obtain a general-purpose structure. FIG. 10 shows a comparison between (a) the result of using the vector evaluation method for the antenna arrangement of FIG. 8 and (b) calculation of FDTD. FIG. 11 shows a comparison between (a) the result of using the vector evaluation method for the antenna arrangement of FIG. 9 and (b) calculation of FDTD. FIG. 12 shows a comparison of the maximum value (solid line) of the SAR when it is used in the antenna arrangement of FIG. 2 and the relative phase at the electromagnetic wave source is different. Circles (◯) are FDTD calculations. FIG. 13 shows a comparison between 2D electric field distribution measurement and 2D electric field distribution evaluation. This is the evaluation described in the second embodiment that demonstrates the effectiveness of the second scalar evaluation method. (A) is β = π, (b) is β = π / 2, (c) is the measured SAR distribution when β = 0, and (d) is the SAR distribution evaluated for an arbitrary β. . FIG. 14 shows a comparison between (a) the result of using the scalar evaluation method for the antenna arrangement of FIG. 2 and (b) calculation of FDTD. FIG. 15 shows an arrangement of a three-element antenna 1 array placed on a horizontal phantom 6. FIG. 16 is a flowchart for finding the maximum value of the electric field when the vector evaluation method or the scalar evaluation method is used for the three-element antenna array. FIG. 17 shows a comparison of (a) scalar evaluation SAR distribution, (b) vector evaluation SAR distribution, and (c) FDTD calculation in the antenna arrangement of FIG. FIG. 18 shows a comparison of the maximum SAR of a set of different relative phases in the electromagnetic wave source in the antenna arrangement of FIG. FIG. 19 shows a flowchart for obtaining the maximum electric field at one point as in the above case. FIG. 20 shows a flowchart for obtaining the maximum electric field in the plane. FIG. 21 shows a flowchart for obtaining the maximum electric field in a solid body. FIG. 22 is a diagram showing an outline of the measurement system of the present invention, and is a configuration for evaluating SAR caused by electromagnetic waves from a multi-antenna system.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  An outline of the measurement system of the present invention is shown in FIG. This is a configuration for evaluating SAR caused by electromagnetic waves from the multi-antenna system. The high frequency from the oscillator 4 is adjusted in phase shift amount by the phase shifter 3, amplified by the amplifier 2, and radiated from the antenna 1 which is an electromagnetic wave source. The electric field is detected by, for example, an electric field probe 8 using an electro-optic effect, and converted into an electric signal by a photoelectric converter. This electrical signal is analyzed by a network analyzer (circuit network analyzer) 10 or the like. As the network analyzer, there are a vector type that can read amplitude and phase, and a scalar type that can read either amplitude or phase, but any of them can be used in the present invention. The output of the network analyzer 10 is sent to the personal computer 11 and data is organized according to the method of the present invention described below. The personal computer 11 controls the phase shift controller 5 and is used for positioning the probe scanner 7. However, the personal computer used for positioning the probe scanner 7 may not be the same as the personal computer that controls the phase shift controller 5.

In general, the total electric field by the antenna array is determined by the vector sum of the electric fields radiated by the individual elements and depends on their excitation phase and amplitude.
Here, for simplicity of explanation, it is assumed that only the phase difference of the electromagnetic wave source is considered and the excitation amplitude does not change. That is, there is no problem in evaluating the maximum local SAR as long as the maximum amplitude of the electromagnetic wave source to be fed can be converted.
Further, for clarity of discussion, the basic calculation and evaluation of a two-element antenna array is first presented. The generalized case of an N-element antenna array will be expanded later.

In order to evaluate the SAR values for all types of antenna arrangements, it is necessary to measure the three components (E _x , E _y , E _z ) of the vector [E] of the high-frequency electric field [E] e ^iωt . Also, the evaluation needs to be performed on the maximum length of the vector [E]. Below, evaluation of _Ez component is shown as a representative example, without losing generality. Other components can be evaluated in the same manner.

1. Two Element Antenna Array FIG. 2 shows a simple arrangement of a two element antenna array placed on a horizontal phantom. The total electric field radiated by the two electromagnetic wave sources at the evaluation point (P) is equal to the sum of the electric fields by the respective electromagnetic waves. The E _z component at the evaluation point is given as follows.

Here, β is the phase difference at the electromagnetic wave source between the two components E _z1 and E _z2, and these two components are the respective E _z components due to radiation from the electromagnetic wave sources 1 and 2. In order to avoid notation complexity, a ₁ = E _z1 and a ₂ = E _z2 . As a result, Equation 3 becomes as follows. Further, the _Ex component and the _Ey component can also be expressed in the same manner as Equation 3.

Here, it should be noted that at the same evaluation point (P), the components a ₁ and a ₂ do not depend on β for changes in the relative excitation phase of the antenna. Therefore, the E _z component can be considered as a function of ^eiβ .

In the electric field measurement, for example, a well-known electric field probe and a network analyzer that inputs the output signal are used, and the amplitude and phase are measured. At this time, it can be divided into a vector type and a scalar type depending on the type of the network analyzer. The probe referred to in the present invention refers to, for example, an electric field probe and a network analyzer that are viewed as a probe again. In this case, there will be two types of probes. One is a vector probe that detects the phase and amplitude of the electric field as a set of vector components, and the other is a scalar probe that detects only the intensity. Since these different types of electric field probes can provide measurement data of different types, it is useful to identify different evaluation methods for two different types.
Moreover, since the electric field obtained by the measurement with the vector probe can be easily squared, the square of the electric field strength can be easily obtained from this. For this reason, it is easy to use a vector probe as a substitute for a scalar probe.

1.1. Expression for Vector Evaluation When the vector probe is used for electric field measurement, the components a ₁ and a ₂ in Equation 4 are calculated from the two measured values under the phase differences β ₁ and β ₂ as follows: Can be calculated.

In this expression, complex numbers E _z ^{β (1)} and E _z ^{β (2)} are E _z components corresponding to phase differences β ⁽¹⁾ and β ⁽²⁾ , respectively. The E _x component and the E _y component can also be expressed in the same manner as Equation 5.

In general, the phase differences β ⁽¹⁾ and β ⁽²⁾ can be arbitrarily selected. Therefore, for example, in order to simplify the measurement of E _z ^{β (1)} and E _z ^{β (2)} , for example, the following selection may be made.

In this case, Equation 5 is simplified as follows.
E _x component, for coefficients for E _y component, by the z and x or y, can be expressed in the same manner as the number 7.

1.2. Expression for Scalar Evaluation Next, a case where a scalar probe capable of measuring the intensity is used will be described. Also in this case, similarly to the above, the phase and coefficient in Equation 4 are the phase at the electromagnetic wave source and the coefficient at the observation point.
In Equation 4, if a _1R , a _2R , a _1I , and a _2I are the real part and imaginary part of a ₁ and a ₂ , respectively, the square of E _z in Equation 4 can be expressed as follows.

Here, the following replacements are made.

To evaluate the magnitude of E _z along _Equation 8 for any β _est , measure the intensity of E _z for three phase differences, β ⁽¹⁾ , β ⁽²⁾ , and β ⁽³⁾ There is a need to. As in the case of the vector evaluation described above, the following settings can be made to facilitate measurement.

In this case, it is possible to determine the b _1, b _2, and b ₃ by the following equation.

Here, absolute values | E _z ⁰ |, | E _z ^{π / 2} |, and | E _z ^π | are respectively positions on the antenna side equal to 0, π / 2, and π using scalar probes. It can be obtained directly from the electric field measurements on the phase difference.

Eventually, the E _z component for an arbitrary β _est can be obtained by substituting the factor of Equation 11 into Equation 8.

  In either case (when using a vector probe or a scalar probe), the expression is very simple. The expression can be used to evaluate the SAR value in a short time.

  More importantly, in these evaluation methods, the number of measurements may be measured for two types of phase differences for a vector probe and for three types of phase differences for a scalar probe. The number of measurements or the total measurement time can be reduced compared to the case where it is required.

2. Next, an evaluation method generalized to an N-element antenna array will be described.
FIG. 3 shows an example of an array consisting of N individual electromagnetic wave sources (antennas). Assume that each antenna is excited with a phase difference β _i (i = 1, 2,..., N). Without loss of generality, β ₁ = 0 can be taken (ie, the first antenna is a reference, the other β _i is considered the phase difference between the first antenna and the i th antenna). The sum of the electric fields due to the electromagnetic waves radiated by the N antennas is equal to the sum of the electric field vectors of the electromagnetic waves from all the individual antennas. That is, the electric field at the evaluation point can be expressed by the following equation.

Here, each component {a ₁ , a ₂ ... A _N } that is a complex number is independent of a phase difference {β ₁ , β ₂ ... Β _N } that is a real number. Therefore, by calculating each component {a ₁ , a ₂ ... A _N } from a specific set of β _i and applying it to Equation 12, the electric field can be evaluated for an arbitrary phase difference β _i . As in the case of the above two elements, there are two evaluation methods corresponding to the vector probe and the scalar probe in the SAR measurement.

2.1. Expression for Vector Evaluation The first step in vector evaluation is to calculate each component {a ₁ , a ₂ ... A _N } from a specific set of measurement results. Considering them as variables in the equation, N equations must be constructed in order to be able to calculate each component {a ₁ , a ₂ ... A _N }.

  Each equation is a specific set of phase differences at the time of feeding on the electromagnetic wave source side (that is, the antenna) along the measurement time. Therefore, N equations can be expressed as follows by N measurements.

This equation can be rewritten as follows using a matrix.

Here, E _zi (i = 1, 2,..., N) is an electric field at the i-th measurement time, and β ⁽ⁱ⁾ _j (i = 1, 2,..., N); (j = 1, 2,... , N) is the phase difference between the j-th antenna and the first antenna (β _j ) at the i-th measurement time. For the variables {a ₁ , a ₂ ... A _N }, the above equation is solved using an inverse matrix as follows: For this reason, it is necessary to set the phase difference so that the solution of Equation 14 does not become trivial.

By calculating {a ₁ , a ₂ ... A _N }, this is applied to Equation 12, and an electric field having a set of arbitrary phase differences β _i is obtained by substituting them into Equation 12. It is done.

For the _EZ component, the required number of measurements for vector evaluation is exactly equal to the number of elements in the antenna array. The same number of E _x and E _y components are required, but since these three components can be measured simultaneously, the use of a vector probe and this evaluation method makes it possible to make a total comparison with the case of relying solely on measurement. The SAR measurement time can be considerably shortened.

2.2. Expression for Scalar Evaluation Since the output of the scalar probe in electric field measurement is the square of the electric field, it can be expressed as follows from Equation 12.

Here, when the real part and the imaginary part of a _p (p = 1, 2,..., N) are a _pR and a _pI , respectively, _Expression 16 is as follows.

This expression consists of N (N-1) +1 factors, which are a phase-independent term, a cosine term, and a sine term. Therefore, the key technique for evaluating the electric field due to any set of relative excitation phases is to calculate these factors based on the electric field measurement data for a particular set of excitation phase differences. It is. That is, for the E _Z component, there is a factor of the number of factors = N (N−1) +1, and since the scalar probe obtains only electric field data, the required number of measurements = N (N−1) ) +1. As a matter of course, the same number of E _x and E _y components is necessary.

As described above, the evaluation method using the scalar and the vector probe can be applied to the coefficients a ₁ , a ₂ ... A _N of several 12 with a small number of measurements even when the electromagnetic wave source is an antenna array. Thus, any set of excitation phases of the electromagnetic wave source can be evaluated. In other words, a complete evaluation can be performed for SAR with a multi-antenna transmitter that is not possible with current measurement techniques. Since the number of necessary measurements is particularly small in the case of vector evaluation, the total evaluation time is significantly shortened compared to the case of relying only on measurement.

4). Example The measurement method and evaluation method will be described more specifically. As the measurement data, not the actual measurement data but the numerical calculation result by the FDTD method was used as an ideal situation. The example given below is not the only possibility, but a simple example of measurement and evaluation method. The measurement example and the evaluation method can also be applied when the number of antennas or the antenna arrangement is different.

4.1 Example 1, SAR Evaluation Using Vector Evaluation Method for Element Antenna Array FIG. 2 is in accordance with the first embodiment of the present invention and is a two element antenna array placed on a horizontal phantom. The arrangement of In this figure, the two antennas are dipole antennas. FIG. 4 shows the relationship between the measured 2D electric field distribution and the evaluated 2D electric field distribution. On the observation surface, as shown in this figure, the SAR is simply measured with two different phase differences. Distributions at other arbitrary phase differences can be evaluated using the evaluation method proposed in the present invention.

FIG. 5 shows a flowchart for finding the maximum value of the electric field that is the basis of the SAR evaluation on the 2D observation plane in the case of the two-element antenna array. FIG. 5 includes a flow for scalar evaluation in addition to vector evaluation.
F1: First, a vector probe for vector evaluation is selected.
F2: The probe type is determined. In this case, it is a vector probe.
F3: The electric field is measured using a vector probe when the phase difference is 0 and π.
F4: Next, the electric fields at all observation points are evaluated using the vector evaluation method calculated in the case of a two-element antenna.
F5: Evaluation is performed by changing the phase difference in an arbitrary step from 0 to 2π, for example, 1 ° or 5 °. Since the calculation of the evaluation is very simple, even if the steps are made fine, each step is short, and the total time can be considerably shortened compared with the measurement for the same number of phase differences.
F6: Find the maximum value of the electric field. This step only compares the maximum value of the evaluated and measured electric field.

  6 shows the 2D-SAR distribution calculated by the FDTD method when y = 10 mm in the xz-plane, and FIG. 7 shows the SAR distribution along the x-axis. The distribution volume shown is only 60 mm × 30 mm around the center of the phantom surface. As can be seen from these figures, the plot (□) evaluated by the vector method and the SAR value calculated by FDTD (solid line) show a very good agreement. This means that the proposed evaluation method gives an accurate SAR value for the entire observed volume.

  Figures 8 and 9 show two other antenna arrangements to demonstrate the capability of the evaluation method. In this example, the antenna has different polarizations and mutual coupling. In FIG. 8, the two antennas are arranged at right angles, but in FIG. 9, they are separated by a distance and rotated by an angle. This distance and angle are arbitrarily selected for a general arrangement.

  FIGS. 10 and 11 show a comparison of the evaluated value of the 2D-SAR distribution with the value calculated by the FDTD method in connection with FIGS. 8 and 9, respectively. Again, as is clear, the vector evaluation of the SAR distribution and the FDTD calculation agree very well.

  In order to find the maximum SAR due to the phase difference combination, the phase difference combination is evaluated in increments of 5 degrees from 0 to 2π (360 degrees). FIG. 12 shows a comparison of the maximum value of the SAR when the phase difference of the electromagnetic wave source is different. In this figure, the usefulness of the evaluation method is remarkable. If a similar comparison is made by only obtaining the SAR, it will be very time consuming or practically impossible in some cases.

  In this example, a vector evaluation method for a measurement procedure and a two-element antenna array is shown. Vector evaluation based on vector measurement data works well in evaluating different phase difference electric fields, and hence SAR. Speaking of measurement alone, the number of measurements is only twice, and this evaluation method can significantly reduce the total measurement time and burden in the SAR measurement.

4.2 Example 2, Evaluation of SAR of Two-Element Antenna Array Using Scalar Evaluation Method In the above example, it was assumed to use a vector probe that can detect the phase and intensity of the electric field. However, in SAR measurement, a scalar electric field probe that can detect only the electric field amplitude is often used. Therefore, it makes sense to use a scalar evaluation method. This can evaluate the SAR of an arbitrary phase difference combination of the electromagnetic wave source from the amplitude electric field measurement of a small number of phase difference combinations given by the electromagnetic wave source. This example demonstrates the ability of the scalar evaluation method on a two-element antenna array.

For the sake of brevity, only the arrangement shown in FIG. 2 is used to demonstrate this example. FIG. 13 shows the relationship between the SAR distribution due to the measured 2D electric field and the SAR distribution due to the evaluated 2D electric field. In measurement, it is necessary to perform electric field measurement at three different phase differences as reference data. As the phase difference, 0, π / 2, and π are selected in order to simplify the measurement preparation as described in “1.2. Expression for Scalar Evaluation” above. FIG. 5 shows a flowchart for finding the maximum value of the electric field that is the basis of the SAR in this case. The procedure in this case is similar to that for vector evaluation, but uses a scalar probe and a scalar evaluation method, respectively, instead of a vector probe and a vector evaluation method.
F1: First, a scalar probe for vector evaluation is selected.
F2: The probe type is determined. In this case, it is a scalar probe.
F13: The electric field is measured using a vector probe when the phase differences are 0, π / 2, and π.
F14: Evaluate the electric fields at all observation points using the scalar evaluation method calculated for a two-element antenna.
F5: Evaluation is performed by changing the phase difference in an arbitrary step from 0 to 2π, for example, 1 ° or 5 °. Since the calculation of the evaluation is very simple, the total time can be considerably shortened compared with the case where the same number of phase differences are measured.
F6: Find the maximum value of the electric field. For example, the maximum value of the evaluated electric field is compared.

FIG. 14 shows the 2D-SAR distribution of FDTD calculation and scalar evaluation for the antenna arrangement of FIG.
As can be seen from the figure, the evaluation by the scalar evaluation method and the calculated SAR value agree very well. The procedure after the evaluation, that is, the procedure such as finding the maximum SAR is the same in the scalar evaluation and the vector evaluation.

  The first and second examples have shown that both vector evaluation and scalar evaluation work very well in the evaluation of the electric field or SAR value for a multi-antenna transmission system. Although the vector evaluation method requires a small number of measurements, a vector probe is required. On the other hand, in the scalar evaluation method, it is necessary to perform measurement many times as compared with it. However, instead, a scalar probe can be used for the measurement, so that the evaluation method can be applied to the current SAR measurement system without upgrade of the measuring device.

4.3 Evaluation of SAR for Example 3, three-element antenna array The above two examples were for two-element antenna arrays, but now we demonstrate the electric field evaluation of the present invention in a three-element antenna array . For comparison, both the vector evaluation method and the scalar evaluation method are used in the demonstration.

  Since the capability of the vector evaluation method and the scalar evaluation method does not depend on the antenna arrangement as pointed out in the first embodiment, the arrangement of the three-element antenna array is simply placed on a horizontal phantom as shown in FIG. The model used in this embodiment is assumed.

FIG. 16 shows a flowchart for finding the maximum value of SAR in the case of a three-element antenna array. Here, β ₂ and β ₃ are excitation phase differences between the antennas 2 and 3 and the antenna 1.
G1: First, a scalar probe for vector evaluation is selected.
G2: The probe type is determined. The number of times required for measurement varies depending on the probe type used in the SAR measurement.
G3: When using a vector probe, three measurements are performed for one set of phase differences β ₂ β ₃ = {0, 0; 0, π / 2; π / 2, π / 2}.
G13: On the other hand, when a scalar probe is used, one set of phase differences β ₂ β ₃ = {0,0; 0, π; π, 0; π, π; π, π / 2; π / 2, π / 2; 0, π / 2} will be measured.
G4: Evaluation is performed using a vector evaluation method calculated in the case of a three-element antenna. This result is used to calculate the SAR value at G6.
G14: Evaluation is performed using a scalar evaluation method calculated in the case of a three-element antenna. This result is used to calculate the SAR value at G5.
G5: Evaluation is performed by changing the phase difference in an arbitrary step from 0 to 2π, for example, 1 ° or 5 °. Since the evaluation calculation is very simple, the total time can be considerably reduced.
G6: Find the maximum value of SAR. For example, the maximum value of the evaluated and measured SAR is compared.

  FIG. 17 shows a comparison of (a) scalar evaluation, (b) vector evaluation, and (c) FDTD calculation of the 2D-SAR distribution in the case of FIG. 15 antenna arrangement. You can see a very good agreement. The above evaluation method has been shown to work well for different antenna arrays regardless of the number of element antennas or the arrangement of antenna arrays. The vector evaluation method is more important because the number of measurements does not increase much when the number of antennas is large.

  FIG. 18 shows the distribution of the maximum value of the SAR at different values of the phase difference. This figure is calculated using the scalar evaluation method. This figure clearly shows the significance of the evaluation method. That is, the evaluation can be performed with any combination of phase differences, and the SAR distribution and the maximum value when the phase differences are different can be completely evaluated. This significance is particularly important when the number of antennas is large, since it is probably impossible to measure the SAR distribution and its maximum value.

  In the above embodiment, the method for obtaining the maximum value of the electric field at one point (measurement point) and evaluating the SAR using the value has been described. Hereinafter, the evaluation of SAR in a plane and a solid will be described in addition to one point.

FIG. 19 shows a flowchart for obtaining the maximum electric field at one point as in the above case.
H1: If the number of element antennas is N, and the setting of the phase difference is changed and the number of times of electric field measurement with the electric field probe is K, K = N for vector evaluation, K = N (N−1) +1 for scalar evaluation, That is the same as above. At this time, measurement with the phase changed for each element antenna is performed K times, and the coefficient on the left side of Equation 15 is determined.
H2: The beta _1, since as a reference, and β ₁ = 0. For others, the electric field is evaluated in steps with an arbitrary predetermined accuracy in the range from 0 to 2π.
H3: The maximum value of the electric field is obtained.

FIG. 20 shows a flowchart for obtaining the maximum electric field in the plane.
J1: If the number of element antennas is N, and the setting of the phase difference is changed and the number of times of electric field measurement with the electric field probe is K, K = N in vector evaluation, K = N (N−1) +1 in scalar evaluation, That is the same as above. At this time, a two-dimensional electric field is measured on a predetermined plane.
J2: Evaluate the electric field at all measurement points in a predetermined plane. That is, in the above measurement, the measurement with the phase changed for each element antenna is performed K times, and the coefficient on the left side of Equation 15 is determined.
J3: The maximum value of the electric field is obtained at all measurement points.
J4: A two-dimensional distribution is obtained by a set from β ₁ to β _N that gives the maximum value of the electric field.
J5: The SAR peak (peak value) on the plane is obtained.

FIG. 21 shows a flowchart for obtaining the maximum electric field in a solid body.
K1: A three-dimensional electric field is measured in a predetermined solid. Measurement is performed K times with different phases for each element antenna.
K2: The electric field is evaluated at all measurement points in a predetermined solid. That is, in the above measurement, the measurement with the phase changed for each element antenna is performed K times, and the coefficient on the left side of Equation 15 is determined.
K3: The maximum value of the electric field is obtained at all measurement points.
K4: A spatial average SAR is obtained by a set from β ₁ to β _N giving the maximum value of the electric field.
K5: The peak of the spatial average SAR is obtained.

  The above examples are provided to demonstrate the extensive capabilities of the evaluation methods of the present invention. This example is not the only possibility to which the evaluation method of the present invention can be applied. Even in the more general case where the antenna type, the antenna arrangement, the number of antennas, etc. are different, the above evaluation method can be applied in the SAR measurement of the multi-antenna transmission system.

  As a probe for detecting an electromagnetic field due to electromagnetic waves, in addition to a dipole antenna for detecting an electric field, a probe for converting a magnetic field detected using a loop antenna for detecting a magnetic field into an electric field, an electro-optic effect, or a magneto-optic effect is used. What was there is known. Particularly, there has been proposed a device capable of three-dimensional measurement at almost the same point by using three particularly small electro-optic effect elements. By using such a three-dimensional probe, three components of the electric field x, y, and z can be measured by one measurement, and the number of measurements can be reduced.

Further, as each phase difference (β _j (j = 1, 2,..., N)) in Expression 17, for example, by using a combination of values selected from 0 and π, the sine term can be deleted. First, the coefficients of the constant term and the cosine term are determined, and then the coefficient of the sine term is determined by using a combination of values selected from 0, π / 2, and π. Can be determined.

DESCRIPTION OF SYMBOLS 1 Antenna 2 Amplifier 3 Phase shifter 4 Oscillator 5 Phase shift controller 6 Phantom 7 Probe scanner 8 Electric field probe 9 Photoelectric converter 10 Circuit analyzer 11 Personal computer

Claims (6)

A plurality of electromagnetic wave sources capable of controlling the phase of the radiated electromagnetic wave, an observation point irradiated with each electromagnetic wave from the electromagnetic wave source, a probe for detecting electromagnetic field intensity at the observation point, and measurement of the probe In an electromagnetic field strength measuring means comprising a computing means for performing a predetermined calculation from data and a control means for performing the control, a method for determining a phase condition in the electromagnetic wave source of the electromagnetic wave giving a maximum electric field strength at the observation point. And
The number of the electromagnetic wave sources is N, the angular frequency of the frequency is ω, the phase at the electromagnetic wave source is β _j (j = 1, 2,..., N), and the three-dimensional component of the electric field vector [E] at the point is [Ex, Ey, Ez] e ^iωt , the combined electric field at the point is

age,
(1) The electric field vector at the observation point or the square of its intensity is measured for a predetermined combination of the phases,
(2) From the measurement value obtained by the measurement, determine the square of the intensity of the electric field vector as a function of the phase only,
(3) The maximum value of the determined function is obtained by adjusting the combination of the phases with a predetermined accuracy.
A method for measuring the specific absorptance of electromagnetic waves from a plurality of electromagnetic wave sources, comprising a method. In (2) above, when the square of the intensity of the electromagnetic field vector is determined as a function of the phase only,
Dividing the square of the intensity of the electromagnetic field vector into a constant term independent of the phase, a cosine term including the cosine of the phase difference of the phase, and a sine term including the sine of the phase difference of the phase,
2. The electromagnetic wave from a plurality of electromagnetic wave sources according to claim 1, wherein the square of the intensity of the electromagnetic field vector is determined as a function of only the phase from the measurement value obtained by the measurement. Specific absorption rate measurement method. In the measurement of the electromagnetic field vector, each set value of the phase is characterized in that a pair of cosine and sine values is a pair of 1 and 0, 0 and 1, or -1 and 0. The method for measuring the specific absorption rate of electromagnetic waves from a plurality of electromagnetic wave sources according to claim 2. 4. The coefficient of a constant term or a cosine term is determined using 0 or π as each set value of the phase and without contribution from a sine term. The measuring method of the specific absorption rate of the electromagnetic waves from several electromagnetic wave sources as described in one.   The method for measuring the specific absorption rate of electromagnetic waves from a plurality of electromagnetic wave sources according to any one of claims 1 to 4, wherein the measurement is performed using a vector probe.   5. The method for measuring the specific absorption rate of electromagnetic waves from a plurality of electromagnetic wave sources according to claim 2, wherein the measurement is performed using a scalar probe.