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Wireless networks are increasingly expanding due to the promotion of the smart society among other factors. However, the problem faced by wireless networks is that electromagnetic noise decreases their reliability. To secure reliability, it is necessary to identify the electromagnetic noise source and to take countermeasures. In relation to this, Hitachi has developed technology to visualize the arrival directions of the electromagnetic sources.

"What we can't see is not persuasive. That's why 'visualization' is needed," says Ms. OHMAE, who is working to enhance the reliability of wireless networks through "visualization," her favorite theme since she was a student.

(Publication: April 9, 2015)

How research started

Can you explain to us the technology you have developed?

Photo: OHMAE Aya

OHMAEThe technology measures and visualizes electromagnetic waves emitted from electronic equipment in a wide space. When electromagnetic waves are detected by a device incorporating this technology, the density of the electromagnetic noise is indicated using color gradation images. But the images alone do not identify the position of the noise in the space. Thus, the images and camera images are superposed to "visualize" the direction from where the noise is coming. What characterizes this technology is that, instead of simply measuring electromagnetic noise using instruments, it "visualizes" from "where" the electromagnetic noise is actually emitted and at "what degree of strength."

We developed this technology in the hope of creating highly reliable wireless networks. There are many electronic devices used around us that conduct wireless communications, but such wireless networks are sometimes interrupted by electromagnetic noise emitted from base stations and electronic devices. We have to further enhance the reliability of such wireless networks to expand the scope of their use.

SUGATo realize high reliability, we need to identify the electromagnetic noise that is interfering with the networks. However, conventional technologies to measure electromagnetic noise had several problems including their extremely narrow scope of measurement and high computing load. To address these issues, we encouraged Ms. OHMAE to propose the development of measurement technology featuring "visualization."

OHMAEIn fact, I was engaged in research of visualizing electromagnetic waves when I was a student. After joining Hitachi, I took every opportunity to tell people around me my wish to research visualization. In time, Mr. SUGA advised me to make a research proposal at a time when the need to visualize the source of electromagnetic noise started to arise within the company. So I decided to ride this wave.

SUGAOur company has a system that allows researchers to propose "advanced research," and I picked a good time to suggest that she apply for this. Usually, research starts at the request of business divisions and the like, but we took the initiative to make a proposal on a subject that was anticipated to become a social issue, and the research started.

So your wish since your school days came true, but what made you stick to "visualization"?

OHMAEI thought that the easiest way to identify the source of noise was to make it visible and you would say, "look, it comes from there." Since it is not persuasive, it is difficult for people to believe what they can't see, right? Since electromagnetic waves, outside of visible light, are not visible to the human eye, people do not believe you when you tell them that "electromagnetic waves are being emitted" or "not emitted at all." So I thought that "being visible" was extremely important.

Hints from human eyes

Can you explain the mechanism of the developed technology in more detail?

OHMAERoughly speaking, the system is structured like a human eye. The energy of electromagnetic waves is collected and focused on a focal point through a "lens," which corresponds to the crystalline lens of an eye, and this is detected by a "sensor" that corresponds to the retina. The information detected by the sensor is sent to the controller PC via the circuit connected from behind the sensor and goes through analysis and image processing. The outputted images, when superposed with the camera images taken separately, make from "where" the electromagnetic waves are actually emitted "visible." That's how the system works.

Figure 1: Overview of the technology

OHMAEThe system uses what is called the "Luneburg lens." It is a perfect sphere and has the characteristic that the dielectric constant varies more largely in sections nearer to its center. In sections nearer to the lens surface, the dielectric constant becomes nearer to that in the air. Because of this, electromagnetic waves are sharply bent and focused onto a focal point. The lens is also characterized by the fact that focal points are formed at different locations for different incident angles of energy.

For the sensor, the EBG (Electromagnetic Band-Gap) electric field sensor is used. The sensor has patterns of various square metal patches, each of which detects energy. As the patches can be arranged at very small intervals, they achieve high resolution. In other words, they can accurately grasp the focal points formed by the lens. Another characteristic is that they hardly reflect the electromagnetic waves and fully absorb the energy, transmitting it to the circuit connected to the sensor.

What made you think of using a lens and sensor?

Photo 1: External view of the instrument

OHMAEI thought that, because human eyes can capture visible light, electromagnetic waves of different frequencies could also be captured by applying the structure of human eyes. That was the beginning. I later found that similar ideas already existed.

When I was considering which combinations of lens and sensor would be appropriate, by chance, I listened to a research presentation on the EBG electric field sensor. As I listened to the presentation and started to understand the characteristics of the sensor, I arrived at the idea that it could be useful. As such, we decided to use the EBG electric field sensor. Then we looked for the lens, and eventually settled on the Luneburg lens.

SUGAFor your reference, the lens is very large in size. The one we use is 80 cm in diameter and weighs as much as 50 kg.

That is fairly large, isn't it?

OHMAEYes, it is. We needed a large lens to detect electromagnetic waves with a minimum receiving sensitivity lower than that of the wireless LAN.

Moreover, the larger the lens, the more sensitively it can detect electromagnetic waves. So we made the lens as large as possible. Thanks to this, we succeeded in seeing the targeted electromagnetic waves far more sensitively than initially planned.

Success possible through the support of helping hands

Were there any difficulties encountered in creating the system?

SUGAThe essential part of this technology is the combination of the Luneburg lens and the EBG electric field sensor. However, just combining them does not make the system function. An example is the circuit connected to the back of the sensor. The metal patches that constitute the sensor detect the energy, and the energy is brought into the circuit through hundreds of leads from each of the metal patches. Each piece of information is analyzed and compiled into a single image by the circuit. So it is an extremely large-scale circuit. The staff engaged in the circuit research worked together to create it all at once. They did the tough work in the background to realize Ms. OHMAE's concept in a short period of time.

OHMAEThey gave me a very strong backing. I hardly had any experience in building a system by myself, and had absolutely no experience with circuits. So their support was very instructive for me.

The largest efforts were made by Mr. HODA. He is not in Japan now as he has been seconded to the research facility in the U.S., but I want his name mentioned in this article. He not only worked on creating the circuit but also devised the scheme of the program for superposing the electromagnetic noise images on the camera images. In fact, the preparation of the program was left to the last and no one seemed to be willing or able to prepare it. To our relief, it was then that he gave us a helping hand. We rushed to create the program, trying this way and that for proper operation. To tell you the truth, I did not gain much confidence until the test operation, feeling uneasy about whether it would really work.

SUGAYou were not confident?

OHMAENo. That is why I was a bit astonished with the test operation as the system produced images, unexpectedly smoothly, and we exclaimed, "Wow, we can see them!" I remember that I felt great satisfaction and joy at that time. But it went smoothly mainly due to the efforts of Mr. HODA, who solidly created the circuit by assuming the final output.

Figure 2: Test environment and output samples

Your research was blessed with talented members, wasn't it?

SUGAThat's right. There were several engineers from various fields who supported her. We also asked people on other teams for their cooperation under the initiatives of Ms. OHMAE. I think it was a good project in which our comprehensive capabilities were applied.

"Visualization" expands the dreams

What are some of the remaining issues to be tackled with this technology?

OHMAEAs you can assume from the size of the lens, the present system is too large to carry. It is still big because it's a prototype to verify the principles. So making the system more compact is one of the issues to address to make it possible to carry to where wireless communications are being made and to actually conduct measurements. In addition, as it takes tens of seconds to output a single image with the current system, we want to achieve real-time operation.

Moreover, the system has is suited to the frequency of wireless LAN, or 2.4 GHz, but we will have to cover a variety of frequencies to meet various requests going forward.

Your pursuit of your dream will then continue for yet some time?

OHMAEIt will. To be frank, I want to make the system very small—as small as eye-glasses and such. If it is big, its areas of application will be limited. It would become easy to use from about the size of a tablet device, if not eye-glasses. So I want to pursue such size reduction.

Photo: SUGA Takashi

SUGAI'm considering whether the principles of this technology can be applied to other research subjects we have been working on. This technology is epoch-making, as it can tell us not only the strength of electromagnetic waves but also the sources from which they are emitted.

One of our research subjects is on methods for testing electro-magnetic compatibility (EMC), or testing if the electromagnetic noise emitted from electronic equipment is within a specified scope. I wonder if the developed system can be used as the antenna for testing. If this system becomes usable in daily measurement of electromagnetic waves, it may be used in rapidly increasing areas of applications, including use by other manufacturers. That's what I envision with regard to this technology.

Moreover, when we announced this technology internally, we received a variety of feedback about possible areas of application that we had never imagined. For example, it might be applied to security, such as detecting misuse of electronic equipment in such high-security spaces as concert halls. There were also ideas proposing applications to rescue work in times of disasters. Such comments and ideas helped us realize that this principle could be applied in many ways. We are determined to work on its applications going forward.


  • Publication: April 9, 2015
  • Professional affiliation and official position are at the time of publication.

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