JP2007263656A - Leaked electromagnetic field information evaluation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leaked electromagnetic field information evaluation system for leaking electromagnetic waves. <P>SOLUTION: The leaked electromagnetic field information evaluation system comprises an antenna which measures electromagnetic waves leaking from an instrument to be evaluated on which a test pattern is displayed and receives the electromagnetic waves leaking from the instrument to be evaluated, a band-pass filter circuit, and a processor which quantifies information obtained from the band-pass filter circuit by controlling the central frequency of the band-pass filter circuit. The processor comprises pattern position detection processing which changes the central frequency of the band-pass filter circuit within a predetermined range, samples the electromagnetic waves and acquires them as measured data, calculates a correlation value between the measured data and the test pattern, and detects the position of the measured data in the test pattern and a quantification processing which quantifies information obtained from the electromagnetic waves for each central frequency by performing a product-sum operation on the test pattern and the measured data on the basis of the detected position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a leakage electromagnetic field information evaluation system for measuring electromagnetic waves leaking from a cable or the like connected to a display device in an information device such as a personal computer and quantifying the amount of information obtained from the electromagnetic waves.

  When the information processing device main body and the display device (display such as a CRT) are connected by a cable, such as a personal computer, the information processing device main body is transmitted as display information even if it is shielded. Since the signal leaks to the outside as an electromagnetic wave from a cable or the like, the information displayed on the display device can be reproduced by receiving the leaked electromagnetic wave. Due to the recent development of IT technology, business-related information is also processed by such an information processing apparatus. Therefore, if the display information leaks to the outside, there is a high possibility that a business loss will occur. Therefore, by strengthening the shield of the cable so that display information does not leak as electromagnetic waves from the cable, installing a filter, or changing the frequency of the synchronization signal when transmitting display information to the display device, A method has been developed to prevent the display screen from being reproduced even when electromagnetic waves leak and are received by a third party (see, for example, Patent Document 1).

JP 2003-244104 A

  However, in introducing such an information processing device, how much electromagnetic wave is leaking from the cable etc. used for connection with the display device, and information displayed on the screen by receiving the electromagnetic wave is There is a problem that there is no method for quantitatively evaluating whether the information is reproducible, that is, the amount of information obtained from such leaked electromagnetic waves.

  The present invention has been made in view of such problems, and an object thereof is to provide a leakage electromagnetic field information evaluation system that measures electromagnetic waves leaking from an evaluation target device and quantifies the amount of information obtained from the electromagnetic waves. And

  In order to solve the above problems, a leakage electromagnetic field information evaluation system according to the present invention measures electromagnetic waves leaking from an evaluation target device on which a test pattern is displayed on a display device, and information on test patterns obtained from the electromagnetic waves. The amount is quantified, the antenna that receives electromagnetic waves leaking from the evaluation target device, and the center frequency can be set within a predetermined range, and the electromagnetic waves in a predetermined band centered on the center frequency are passed. A band-pass filter circuit; and a processing device that controls the center frequency of the band-pass filter circuit to quantify the amount of information obtained from the electromagnetic wave that has passed through the band-pass filter circuit. Then, the processing device changes the center frequency of the band-pass filter circuit within a predetermined range, samples the electromagnetic wave and acquires it as measurement data, calculates a correlation value between the measurement data and the test pattern, The first processing means for detecting the position of the measurement data (for example, the pattern position detection process S10 in the embodiment) and the product-sum operation of the test pattern and the measurement data based on the detected position, the center And a second processing means for quantifying the amount of information obtained from the electromagnetic wave for each frequency (for example, quantification processing S20 in the embodiment).

  In such a leakage electromagnetic field information evaluation system according to the present invention, the band-pass filter circuit passes only a low-frequency region of the electromagnetic wave received by the antenna, and a sine wave signal having a frequency set by control of the processing device A signal generator that outputs the signal, a multiplier that multiplies the electromagnetic wave that has passed through the low-pass filter and the sine wave signal output from the signal generator, and has a predetermined center frequency among the signals output from the multiplier It is preferable that the filter is composed of a bandpass filter that allows band signals to pass therethrough.

  When the leakage electromagnetic field information evaluation system according to the present invention is configured as described above, the amount of information obtained from electromagnetic field information leaked from the evaluation target device can be quantified. Can be greatly promoted in the development of protective products. Further, by configuring the band-pass filter circuit as an analog circuit such as a low-pass filter or a band-pass filter, signal processing in the processing device can be simplified and the evaluation time can be shortened.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the leakage electromagnetic field information evaluation system 1 according to the present invention will be described with reference to FIG. This leakage electromagnetic field information evaluation system 1 receives, analyzes and evaluates electromagnetic waves leaking from an evaluation target device 6 such as a personal computer including a display device 60, a main body 61, and a cable 62 connecting them. The configuration is such that the display device 60, the main body 61, and the high frequency antenna 2 that receives electromagnetic waves leaking from the cable 62, the amplifier 3 that amplifies the received electromagnetic waves 3, and band processing are performed on the received electromagnetic waves. The band filter circuit unit 4 and the processing device 5 that quantifies the measurement data of the electromagnetic waves by the processing described later.

  Now, a method for evaluating the evaluation target device 6 using the leakage electromagnetic field information evaluation system 1 will be described. The leakage electromagnetic field information evaluation system 1 displays a still image of a predetermined pattern (for example, the display image 70 shown in FIG. 2) on the display device 60 by the main body 61 of the evaluation target device 6, and at that time The electromagnetic wave leaking from the evaluation target device 6 is received, and the display screen reproduced from the electromagnetic wave and the pattern of the still image are correlated and quantified.

  Here, in the present embodiment, it is necessary to suppress as much as possible the electromagnetic field that leaks from other components of the evaluation target device 6 other than the measurement target. For example, when evaluating the electromagnetic field leaking from the cable 62, the main body 61 having a small leakage electromagnetic field is selected, or the main body 61 is shielded and, at the same time, the display device 60 is turned off, or the display device is 60 is removed and a terminal resistor (for example, about 75Ω) is connected to the cable 62 instead. When evaluating the electromagnetic field leaking from the display device 60, the cable 62 having a high shielding effect is used, and the main body 61 having a small leakage electromagnetic field or the main body 61 is shielded. Further, when evaluating the electromagnetic field leaking from the main body 61, the cable 62 and the display device 60 are detached from the main body 61. In the following description, the case where the electromagnetic field leaking from the cable 62 is evaluated will be described. However, the display device 60 and the main body 61 can be evaluated by the same method.

  The band filter circuit 4 is configured to remove a high-frequency component of the received electromagnetic wave and output a sine wave signal having a predetermined frequency under the control of the low-pass filter 41 that passes the low-frequency component and the processing device 5. Signal generator 42, a multiplier 43 that multiplies a signal that has passed through low-pass filter 41 and a sine wave signal output from signal generator 42, and a band that passes only a signal in a predetermined frequency band among the outputs of multiplier 43. The filter 44 and the amplifier 45 that amplifies the output of the band filter 44 are included.

In the band-pass filter circuit 4, the frequency of the signal passed through the low-pass filter 41 and fin, when the frequency of the output sine wave signal from the signal generator 42 and f _SG, the output of the multiplier 43, these signals Signals of fin + f _SG and abs (f _SG −fin), which are frequencies of the sum and difference, are output (abs is an absolute value). When the center frequency of the band of the band filter 44 through which these signals pass is fca, the frequency of the signal that can pass through the band filter 44 is fca + fSG or abs (f _SG −fca). At this time, since the signal component having the frequency of fca + f _SG can be easily removed by the low-pass filter 41 in the previous stage, the signal output from the band-pass filter circuit 4 is expressed by the following equation (1) assuming that the center frequency is fc. The band filter circuit 4 has a function of a band filter having a center frequency fc.

fc = abs (fSG-fca) (1)

Further, the processing device 5 acquires the output of the band-pass filter circuit 4 via the A / D converter 5a, and stores a data processing unit 51 that performs processing to be described later and data that is processed by the data processing unit 51. 52, and an output unit 53 that outputs the evaluation result. Therefore, the center frequency fca of the band filter 44 constituting the band filter circuit 4 is fixed, and the frequency f _SG of the sine wave signal output from the signal generator 42 is supplied to the data processing unit 51 via the GPIB interface 5 b of the processing device 5. Thus, the band filter circuit 4 can be used as a band filter having a variable center frequency.

  Here, consider a case where the display still image 70 shown in FIG. 2 is displayed on the display device 60 of the evaluation target device 6 as described above. When an image is displayed on the display device 60, a one-dimensional signal corresponding to a scanning line running from the left to the right of the display device 60 (in the following description, this one-dimensional signal is referred to as “test pattern P0 (k)”). Is repeatedly transmitted from the main body 61 to the display device 60 via the cable 62. That is, assuming that the total number of pixels of the display device 60 is N, this test pattern P0 (k) can be expressed as a one-dimensional signal P0 (1) to P0 (N). The value of the signal P 0 (k) corresponding to the portion 72 is represented as 0, and the value of the signal P 0 (k) corresponding to the image portion (character information portion) 61 is represented as 1.

  At this time, the total number of pixels N is expressed by the following equation (2), where Nh is the number of horizontal pixels and Nv is the number of vertical lines.

N = Nh x Nv (2)

  For example, when the synchronization frequency is 60 Hz in the VGA format of a personal computer, Nh = 800 (display portion effective pixel number is 640) and Nv = 525 (display portion effective line number is 480), so the total pixel number N = 420,000.

  On the other hand, the leakage electromagnetic field information evaluation system 1 in the present embodiment has a comparison pattern P (k) that is stored in advance in the processing device 5 and is compared with the image on the display screen reproduced from the leaked electromagnetic wave. The comparison pattern P (k) is for two cycles of the test pattern P0 (k). That is, P (k) = P0 (k) when k = 1 to N, and P (k) = P0 (k−N) when k = N + 1 to 2N. As described above, the test pattern P0 (k), k = 1 to N is repeatedly transmitted to the cable 62. In order to reproduce an image displayed by receiving electromagnetic waves leaking from the cable 62, the test pattern P0 (k) It is necessary to acquire data for the period. When measuring such an electromagnetic wave, it is difficult to determine and acquire the start point (P0 (1)), and the acquired signal (measurement data d1 (n) described later) is a test pattern P0 (k ) To the middle of the next cycle. Therefore, the comparison pattern P (k) is set to two cycles of the test pattern P0 (k).

  Now, the processing procedure in the processing device 5 will be described with reference to FIGS. As shown in FIG. 3, the overall process flow includes a pattern position detection process S10 and a quantification process S20. The data processing unit 51 of the processing device 5 first executes a pattern position detection process S10. The pattern position detection processing S10 is configured to perform quantification corresponding to each center frequency fc by changing the center frequency fc at intervals of Δfi between the frequency ranges in which the leakage electromagnetic field is quantified as f1 to f2. Has been.

  First, the pattern position detection process S10 sets the center frequency fc to f1 (step S101). Since the center frequency fc changes between f1 and f2 at intervals of Δfi as described above, Δfi is added to the intermediate frequency fc after steps S102 to S108 described later are executed (step S108). Steps S102 to S108 are repeated until the center frequency fc exceeds f2 (step S109). In step S101, the initial value of the maximum correlation value is set to 0 in order to obtain the maximum value U of the correlation value between the frequencies f1 and f2 and the phase ph at that time.

Then, the data processing unit 51 controls the frequency f _SG of the sine wave signal of the signal generator 42 so as to become the current center frequency fc based on the above equation (1) (step S102), and the sampling frequency fs. Thus, the signal output from the band filter circuit 4 is acquired (step S103). Here, assuming that the number of samples in one line time in step S103 is Nhs, the number of samples Ns in one screen in the sampling space is expressed by the following equation (3).

Ns = Nhs x Nv (3)

  Since the value of the number of samples Nhs and the value of the total number of pixels N for one line time are different for each evaluation target device 6, they are measured in advance and set in the processing device 5 (data processing unit 51). In addition, the amplitude data (referred to as “measurement data”) at each point measured in this way is d1 (n), where n = 1 to Ns.

  Next, data compression processing is performed on the measurement data d1 (n) with respect to the center frequency fc, and the compressed data is converted into compressed data d3 (k), k = 1 to N (step S104). As described above, the test pattern P0 (k) is N data of k = 1 to N, but the measurement data d1 (k) sampled at the sampling frequency fs is Ns data. This measurement data d1 (k) needs to be compressed into N pieces of data in order to perform the processing. The compression ratio 1 / Ng at this time is expressed by the following equation (4). Ng is a real number.

Ng = Nhs / Nh (4)

  Specific processing of the data compression processing S104 is as follows. First, absolute value data d2 (n) obtained from the absolute value of the measurement data d1 (n) is obtained as in the following equation (5).

d2 (n) = abs (d1 (n)) (5)
However, n = 1 to Ns
abs () is a function for obtaining an absolute value

  Then, using the absolute value data d2 (n) obtained in this way, the compressed data d3 (k) is obtained by the following equation (6). The compressed data d3 (k) obtained in this way is stored in the storage unit 52.

d3 (k)
= Max (d2 (rnd (Ng * k-Ng + 1)),
d2 (rnd (Ng * k-Ng + 2)),
..., d2 (rnd (Ng * k))) (6)
However, k = 1 to N
max () is a function for obtaining the maximum value from Ng data.
rnd () is a function that rounds off to obtain an integer.

  Then, correlation processing is performed to obtain a correlation value M (j) at the phase j between the compressed data d3 (k) and the test pattern P (k) obtained as described above (step S105). This correlation processing S105 is performed by the following procedure. First, the average value Ap of the test pattern P (k) is obtained by the following equation (7).

  Then, a test pattern Pa (k) around the average value Ap is obtained by the following equation (8).

Pa (k) = P (k) -Ap (8)

  Further, the average value Ad of the compressed data d3 (k) is obtained by the following equation (9).

Then, the compressed data da (k) around the average value Ad is obtained by the following equation (10).

da (k) = d3 (k) -Ad (10)

  Further, the standard deviation Bp of the test pattern Pa (k) around the average value is obtained using the following equation (11), and the standard of the compressed data da (k) around the average value is obtained using the following equation (12). The deviation Bd is obtained.

  Finally, from the above result, the correlation value M (j) at the position of j is obtained using the following equation (13).

但し、ｊ＝１〜Ｎ

However, j = 1 to N

  Among the correlation values M (j), j = 1 to N in the compressed data d3 (k) of the center frequency fc thus obtained, the maximum value of M (j) and j at that time are obtained. The maximum value of (j) is set as the maximum correlation value Uc at the center frequency fc, and j at that time is stored in the storage unit 52 as the phase phc (step S106). Further, the overall correlation maximum value U and the correlation maximum value Uc at the center frequency fc are compared. If Uc> U, the overall correlation maximum value U is updated to the value of Uc (step S107).

  As described above, it is determined whether or not the total correlation maximum value U obtained by changing the center frequency fc in increments of Δfi in the range of f1 to f2 exceeds a predetermined threshold Th (step S110). Determines that the character pattern cannot be detected from the measurement data d1 (n) and ends all the processes. If it exceeds, the next quantification process S20 is executed.

  Also in the quantification process S20, the center frequency fc is changed by Δfi in the range of f1 to f2, and the quantified value S (fc) at each center frequency fc is obtained. Therefore, first, fc is set to f1 (step S201), quantification processing (steps S202 to S203) described later is executed, Δfi is added to the center frequency fc (step S204), and the center frequency fc is f2. The quantification process (S202 to S203) is repeated until the value exceeds (step S205).

  Now, the quantification process (steps S202 to S203) at the center frequency fc will be described. First, the compressed data d3 (k) and the phase phc corresponding to each center frequency fc are read from the storage unit 52 (step S203). Then, a product-sum operation is performed on the comparison pattern P (k) and the compressed data d3 (k) from the compressed data d3 (k) and the phase phc to obtain a quantified value S (fc) at the center frequency fc. It calculates | requires by the following formula | equation (14) (step S203). The quantified value S (fc) is output to the output unit 53 (display or printer).

  Thus, by performing smoothing equivalently and obtaining the quantified value S (fc), the influence of noise other than the image portion (character information portion) 71 can be suppressed. By measuring and quantifying the electromagnetic waves leaking from the cable 62 in this way, it becomes possible to quantitatively evaluate information leakage protection measures by comparing various cables 62 as shown in FIG. Can be greatly promoted.

  In addition, the signal generator 42, the low-pass filter 41, the multiplier 43, and analog elements such as the band filter 44 are provided for filtering the received electromagnetic wave in a predetermined band necessary for sampling and obtaining. By performing the band-pass filter circuit 4 configured as described above, the processing time can be significantly shortened compared with the case where the filtering process is performed by digital calculation after the electromagnetic wave is directly sampled by the processing device 5. Quantification processing can be speeded up. At this time, the sampling frequency fs for sampling the signal output from the band filter circuit 4 in the processing device 5 may be a little higher than the dot clock of the display device 60 of the evaluation target device 6, so A / D conversion As the device 5a, a general-purpose A / D conversion board used for a personal computer or the like can be used.

  For example, when the quantified leakage characteristic of 20 to 300 MHz (f1 = 20 MHz, f2 = 300 MHz) is obtained in 5 MHz (Δfi) steps, the number of times that the sine wave frequency of the signal generator 42 is set to the band filter circuit 4 is 57. Although the processing for the processing device 5 to set the frequency of the sine wave is about 1 second, the processing for capturing the leaked electromagnetic wave by the processing device 4 is completed in about 1 minute.

  Further, as described above, the same evaluation can be performed not only on the cable 62 of the evaluation target device 6 but also on the display device 60 and the main body 61.

It is a block diagram which shows the structure of the leakage electromagnetic field information evaluation system which concerns on this invention. It is explanatory drawing which shows the relationship between a display screen and a test pattern. It is a flowchart which shows the whole process of the said system. It is a flowchart which shows a pattern position adherence t process. It is a flowchart which shows a quantification process. It is a graph which shows the relationship between a center frequency and a quantification value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Leakage electromagnetic field information evaluation system 2 Antenna 4 Band-pass filter circuit 5 Processing apparatus 6 Target apparatus 41 Low-pass filter 42 Signal generator 43 Multiplier 44 Band-pass filter 60 Display apparatus 70 Still image (test pattern)
S10 Pattern position detection processing (first processing means)
S20 Quantification processing (second processing means)

Claims (2)

A leakage electromagnetic field information evaluation system for measuring an electromagnetic wave leaking from an evaluation target device on which a test pattern is displayed on a display device, and quantifying an information amount of the test pattern obtained from the electromagnetic wave,
An antenna for receiving electromagnetic waves leaking from the device to be evaluated;
A bandpass filter circuit capable of setting a center frequency within a predetermined range and passing the electromagnetic wave in a predetermined band centered on the center frequency;
A processing device that controls the center frequency of the bandpass filter circuit and quantifies the amount of information obtained from the electromagnetic wave that has passed through the bandpass filter,
The processing device is
The center frequency of the bandpass filter circuit is changed within the predetermined range, the electromagnetic wave is sampled to obtain measurement data, a correlation value between the measurement data and the test pattern is calculated, and the test pattern First processing means for detecting the position of the measurement data;
Second processing means for quantifying the amount of information obtained from the electromagnetic wave for each center frequency by performing a product-sum operation on the test pattern and the measurement data based on the detected position; Leakage electromagnetic field information evaluation system comprising The bandpass filter circuit is
A low-pass filter that passes only a low-frequency region of the electromagnetic wave received by the antenna; and
A signal generator for outputting a sine wave signal having a frequency set by the control of the processing device;
A multiplier that multiplies the electromagnetic wave that has passed through the low-pass filter by a sine wave signal output from the signal generator;
The leakage electromagnetic field information evaluation system according to claim 1, further comprising: a bandpass filter that allows passage of a signal having a predetermined center frequency among signals output from the multiplier.

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