METHODS OF DETECTING LEAKAGE OF RADIO WAVES FROM OUTSIDE AN ELECTROMAGNETICALLY SHIELDED BUILDING

Abstract: In a building (1) constructed so that its structure and apertures form an electromagnetic screening to prevent leakage of radio communications from within the building, any defect in the screening is detected by a system consisting of a mobile radio wave detector (4) with an antenna (5) positioned on the ground outside the building and another detector (2) with an antenna (3) mounted, e.g. on a gondola, so as to be movable along the outside of the building (1) past each floor thereof. A transmitter (11, Fig. 3) on each floor transmits a specific frequency for that floor, or the same frequency at a different time for each floor, and any signal of relatively high intensity is detected outside by the detectors (2,4), and the signals may be amplified, processed and recorded by the equipment of Fig. 3. The deterioration of the shielding is detected by comparison with past results.

Description: The present invention relates to methods for detecting and processing an abnormality in electromagnetic shielding of building in which radio communication is carried out and which is constructed using an electromagnetic shielding material for its structure and apertures such as windows and doorways, so that the whole of the building is formed into an electromagnetic shielding structure. It is general practice in such buildings (which may be referred to as "intelligent" buildings) to utilize joint information communicating equipment such as a composite electronic switching system and a computer, for information communication with an other party inside or outside the building. As a result of an increase in value placed on information and the more diverse as well as individual nature of information, there has been a rapid increase in the amount of information handled. Under these circumstances, it is a problem to provide required information within such buildings quickly at low cost. To solve this problem, use may be made of an information network based on a data highway system that utilizes optical fiber cables, coaxial cables or the like. However, such a data highway system requires that optical fiber cables or coaxial cables are laid throughout the building so that the cables extend to every equipment terminal, and therefore it necessitates a floor duct and a double-floored structure for laying such cables, resulting in a considerable increase in both the cost and duration of construction. If radio waves are used for information communication, no cables are needed. In such a case, however, since the radio waves may have effects outside the building, the use of radio waves is subject to regulation by radio communications law; on the other hand, external radio waves may cause a malfunction of the system. Accordingly, the present applicant has already made various proposals (e.g. EP-A-0 297 597, published 23.11.88 and EP-A-0 298 161, published 11.1.89) concerning a building which is constructed using an electromagnetic shielding material for its structure and apertures such as windows and doorways so that the whole of the building is formed into an electromagnetic shielding structure, thereby enabling free radio communication inside the building without suffering from legal regulation. However, even if the whole of the building is constructed as an electromagnetically shielded structure to enable radio communication inside the building, once the electromagnetic shielding is broken at any part of the building, the radio wave which is used inside the building is released to the outside; in such a case, the released radio wave may be undesirably detected, resulting in leakage of classified information, or the released radio wave may interfere with other radios. Further, external radio waves such as broadcast and telecast waves may intrude into the building to cause noises. Therefore, if the electromagnetic shielding is broken, it becomes impossible to effect the radio communication inside the building, resulting in a paralysis of the information transmitting function. Accordingly, it is considerably important in order to avoid such problems to find any defect or deterioration of the electromagnetic shielding in its early stage. However, it is not easy to predict a position where the electromagnetic shielding of an intelligence building will probably be broken. In particular, when the size of the building itself is large, the area of inspection is correspondingly large. For this reason, it is considered difficult to make a diagnosis as to whether or not electromagnetic shielding performance is satisfactory, and there has heretofore been no system which is capable of finding a defect or deterioration (abnormality) of electromagnetic shielding of such buildings. It is an object of the present invention to provide radio wave leakage diagnosing methods which are capable of readily finding deterioration of the electromagnetic shielding performance of an intelligent building and a defect in an electromagnetic shielding structure. EP 0248501 discloses a system and method for detecting leakage of radio waves from a room which is constructed of electromagnetically shielding material using a system including a rotating field and respective detectors; we now provide a method for detecting the specific floor and position in the building of a defect causing leakage. According to the present invention in a method of detecting leakage of radio waves from a buildings which is constructed of electromagnetically shielding material for its external structure and the openings therein, so as to detect defects in said shielding, a system is used which comprises: radio wave detecting means disposed outside said building for detecting a predetermined radio wave transmitted from each floor of said building, whereby both the floor and the specific position of a radio wave leakage is detectable on the basis of the intensity of the detected radio wave; in a first embodiment of the method radio waves having different frequencies are transmitted from transmitters upon the respective floors which are electromagnetically shielded from each other, so as to allow the detection of leakage and of the shielding defect causing the leakage; and in a second embodiment of the method radio waves having the same frequency are transmitted at different times from transmitters upon the respective floors which are electromagnetically shielded from each other, so as to allow the detection of leakage and of the shielding defect causing the leakage. In the radio wave leakage diagnosing methods according to the present invention, a predetermined radio wave is transmitted from each floor of the building and the transmitted radio wave is detected by the radio wave detecting means. Accordingly, the degree to which the radio wave leaks from each floor can be checked on the basis of the intensity of the received radio wave, and when the electromagnetic shielding is broken, the floor and specific position where the shielding abnormality occurs can be found on the basis of the intensity of the received radio wave. When the electromagnetic shielding performance has deteriorated, it is possible to know the degree of deterioration by making a comparison with diagnostic results obtained in the past. In the accompanying drawings: Fig. 1 shows a plan of one embodiment of a radio wave leakage diagnosing system for an intelligent building for use according to the present invention; Fig. 2 is a graph showing the radio wave leakage detecting signal; Fig. 3 shows one example of the arrangement of the radio wave leakage detector disposed on the ground; and Fig. 4 shows one example of the frequencies assigned to each floor in communication inside an intelligent building. One embodiment of the present invention will be described hereinunder with reference to the accompanying drawings. Referring to Fig. 1, the reference numeral 1 denotes a building, 2, 4 radio wave leakage detectors, and 3, 5 antennas; in Fig. 3, 11 is a transmitter, 12 a receiving section, 13 an amplifying section, 14 a processing section, 15 a memory section, 16 a print output section and 17 a display output section. The radio wave leakage detector 2 is mounted on, for example, a gondola which moves along the outer walls of the floors of the building 1. The detector 2 has an antenna 3 to detect a radio wave leaking out from the building 1. The radio wave leakage detector 4 is disposed at an appropriate position on the ground where it is able to detect a radio wave leaking out from any of the floors. The detector 4 on the ground also has an antenna 5 to detect a leaked radio wave. The radio wave leakage diagnosing system according to the present invention comprises the above-described two radio wave leakage detectors 2 and 4. First, a radio wave which is transmitted from each floor of the building 1 is detected with the radio wave leakage detector 4 to obtain data concerning the intensity of the received wave, for example, intensity data such as that shown in Fig. 2, thus identifying a floor having an abnormal radio wave leakage on the basis of the received wave intensity data. Then, a radio wave leakage position on the identified floor is detected using the radio wave leakage detector 2. Fig. 3 shows one example of the arrangement of the radio wave leakage detector 4 which is disposed on the ground. As shown in Fig. 3, in the radio wave leakage detector 4 disposed on the ground, a radio wave which is transmitted from each of the transmitters 11 installed inside the building is detected by a receiving section 12 having an antenna 12a. The detected signal is amplified in an amplifying section 13 and then processed in a processing section 14. The processing section 14 identifies received signal data from each floor of the building and stores the identified data in a memory section 15. The processing section 14 further outputs the obtained data from a print output section 16 and a display output section 17 in the form of a graph such as that shown in Fig. 2. The arrangement may be such that data for diagnosis, for example, a reference value used to judge the level of a received wave and a threshold value for judgement of a radio wave leakage, are stored in the memory section 15 in advance and these data items are output in such a manner as to be superposed on the graph, or the degree of leakage of a radio wave at each floor is automatically diagnosed and the result of the diagnosis is stored and output. The diagnostic procedure carried out by the radio wave leakage diagnosing system for an intelligent building according to the present invention will be briefly explained hereinunder. First, a radio wave having a frequency which is in the vicinity of the frequency of a radio wave used indoors is transmitted from the transmitter 11 disposed on each floor. The radio wave leakage detector 4 checks the intensity of each radio wave received to detect a floor having a radio wave leakage on the basis of the received wave intensity. For example, as shown in Fig. 2, a radio wave transmitted from a floor having no radio wave leakage has an intensity which is lower than a predetermined value, whereas radio waves from floors having a radio wave leakage have relatively high intensities as shown by the reference symbols A and B. Accordingly, it is possible to identify a floor having a radio wave leakage by a frequency having a relatively high intensity. Next, the radio wave leakage detector 2 is moved around the identified floor to check the intensity of a received radio wave having a frequency used in the floor concerned, and a radio wave leakage position is detected on the basis of the intensity level of the received wave. There may be various ways of assigning frequencies to the respective floors of an intelligent building depending upon the structure of the building. The applicant of this invention has already proposed a system in which an electromagnetic shielding space in an intelligent building having its outer wall surface covered with an electromagnetic shielding layer is divided into electromagnetic shielding regions corresponding to the respective floors of the building and a desired service frequency band is assigned to each floor to enable radio communication inside the building [see Japanese Patent Application No. 61-73051 (1986)]. The proposed arrangement enables the same service frequency band to be assigned to all the floors. In this case, assuming that the number of channels for each floor is n and the frequency band width for 1 channel is 25 kHz, it suffices to install, on each floor, communication equipment designed for a frequency band of 25 kHz x n In other words, it is only necessary for an m-story building to prepare m sets of communication equipment of the same kind. Therefore, it is possible to reduce the installation cost. However, in the case where there is a radio wave leakage because of unsatisfactory electromagnetic shielding between a pair of adjacent floors, the communication equipment installed on each of the floors may be caused to malfunction by the radio wave leaking out from the adjacent floor. In order to solve such a problem, service frequency bands for a pair of adjacent floors are made different from each other. One example of the arrangement is shown in Fig. 4. In this example, three different kinds of frequency bands 1 ○, 2 ○ and 3 ○ are set, each frequency band having a width of 25 kHz x n, and these frequency bands are assigned to the respective floors of the building in such a manner that the set of frequency bands 1 ○, 2 ○ and 3 ○ is repeatedly assigned to the floors from the top to the bottom, or vice versa. With this arrangement, since the service frequency bands which are respectively assigned to each pair of adjacent floors are different from each other, even if there is a little radio wave leakage between a pair of adjacent floors, no radio interference occurs and therefore no malfunction of the communication equipment occurs. In this case, it suffices to prepare three different kinds of communication equipment each designed for a frequency band of 25 kHz x n and to dispose them in such a manner that the frequency bands for each pair of adjacent floors are different from each other. It should be noted that, since different frequency bands are used at each pair of adjacent floors, it is basically sufficient to assign two different frequency bands alternately to the floors. In the case where the same frequency is used at every floor and the same frequency is used for radio waves transmitted for diagnosis of a radio wave leakage as in the foregoing embodiment, a radio wave having a predetermined frequency is transmitted successively from the floors with a time lag. On the other hand, the radio wave leakage detector 4 checks the intensity of a received signal having the predetermined frequency on the time base. More specifically, as will be clear from the graph of Fig. 2 in which the abscissa represents time (T) and the ordinate intensity (I), it is possible to identify a floor having a radio wave leakage on the basis of the time when the intensity of the received wave increases, as shown by the reference symbols A and B. As the electromagnetic shielding performance becomes deteriorated, the average intensity of the received wave on the graph of Fig. 2 rises gradually. Therefore, it is possible to readily know the degree of deterioration of the electromagnetic shielding performance at each floor by comparison with the diagnostic results obtained in the past. It should be noted that the present invention is not necessarily limited to the above-described embodiment and various changes and modifications may be imparted thereto. For example, the radio wave leakage detector for detecting a radio wave leakage at each floor in the foregoing embodiment may be mounted on a cleaning robot which is generally used to clean the outer walls of buildings. In such a case, the arrangement may be such that leakage of a radio wave at each floor is automatically inspected during cleaning and the movement of the robot is controlled on the basis of time such that, when the level of a received wave is high, the movement of the robot is slowed down to make a closer inspection. Thus, it is unnecessary to use the radio wave leakage detector disposed on the ground and it is therefore possible to effect detection of a radio wave leakage even more efficiently with a reduced number of measuring operations. The arrangement may also be such that the radio wave leakage detector mounted on the gondola is provided with a wire or wireless transmitting means to transmit results of measurement to the radio wave leakage detector on the ground so as to display the measurement results on the display screen on the ground. In the case where the whole of a building is constructed as an electromagnetic shielding structure by using an electromagnetic shielding material for its skeleton and openings such as windows and doorways but the floors are not electromagnetically shielded from each other, the arrangement may be such that radio waves of the same frequency are transmitted from the respective floors at different times and a floor, together with a specific position, where a radio wave leaks is identified on the basis of the intensity difference between the received radio waves. As will be clear from the foregoing description, according to the present invention, the radio wave leakage detector which is moved along the outer wall of each floor can also be mounted on a cleaning robot. Therefore, it is possible to make a diagnosis of a radio wave leakage in an intelligent building at relatively low cost and with a high degree of accuracy. Combination of a radio wave leakage detector disposed on the ground and a radio wave leakage detector mounted on a gondola enables diagnosis to be carried out in two stages, i.e., coarse and fine diagnoses, and therefore permits an increase in both the efficiency and accuracy in diagnosis.

Claims: A method of detecting leakage of radio waves from a building (1) which is constructed of electromagnetically shielding material for its external structure and the openings therein, so as to detect defects in said shielding, wherein a system is used which comprises: radio wave detecting means (2,4) disposed outside said building (1) for detecting a predetermined radio wave transmitted from each floor of said building (1), whereby both the floor and the specific position of a radio wave leakage is detectable on the basis of the intensity of the detected radio wave; in which method radio waves having different frequencies are transmitted from transmitters (11) upon the respective floors which are electromagnetically shielded from each other, so as to allow the detection of leakage and of the shielding defect causing the leakage. A method of detecting leakage of radio waves from a building (1) which is constructed of electromagnetically shielding material for its external structure and the openings therein, so as to detect defects in said shielding, wherein a system is used which comprises: radio wave detecting means (2,4) disposed outside said building (1) for detecting a predetermined radio wave transmitted from each floor of said building (1); whereby both the floor and the specific position of a radio wave leakage is detectable on the basis of the intensity of the detected radio wave; in which method radio waves having the same frequency are transmitted at different times from transmitters (11) upon the respective floors which are electromagnetically shielded from each other, so as to allow the detection of leakage and of the shielding defect causing the leakage. A method according to Claim 1 or 2, wherein in said system the radio wave detecting means used comprises a first radio wave detecting means (4,5) disposed at a predetermined position outside said building (1) to detect radio waves transmitted from within the building (1) and a second radio wave detecting means (2,3) movable along the wall surface outside each floor of said building (1) to detect radio waves transmitted from that floor. A method according to Claim 1 or 2, wherein the system used also includes means (14,15) for identifying and storing signal data received by the detecting means (2,4). A method as claimed in any preceding claim, wherein the building (1) has installed therein radio communication equipment having a separate frequency, assigned to each floor.

Inventors: ISHIKAWA, TOSHIYUKI, NAGATA, KOJI, NAKAMURA, MASATAKE, TAKAHASHI, TAKESHI, YABANA, YOSHIJI
Applicants: SHIMIZU CONSTRUCTION CO. LTD.
Application year: 1988
Main classification: G01R29
IPC codes: H04B15, G01R29