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We are now surrounded by objects that run on electricity-devices like mobile phones, personal computers (PCs), tablet computers, and electric vehicles.
In a society in which such electronic devices are closely packed, importance is being placed on countermeasures against "electromagnetic noise" from two aspects: First, if electromagnetic noise is generated, it must not influence surrounding electronic devices; second, if surrounding electromagnetic waves affect a device, it must not cause that device to malfunction. It is thus necessary to design electronic devices and devise countermeasures in such a manner that both these aspects are addressed.
In this interview, "electromagnetic-noise measurement technology"—as a basic technology for supporting a safe and secure society—is introduced.
FUNATOIt's become normal for us to carry around a number of electronic devices. For example, a large majority of people now carry mobile phones, and the number of people carrying tablet computers has recently been increasing. It is a result of unwiring and miniaturization of information-technology devices.
In the meantime, against the backdrop of environmental protection, there has been a trend towards electrification; examples of which are hybrid cars and electric vehicles. Moreover, in accordance with that trend, devices that consume a huge amount of electrical power, namely, "power electronics devices," have continued to permeate into our daily lives.
Under these circumstances, a growing problem affecting societies with a high density of electronic devices is "electromagnetic noise problem." Electromagnetic waves generated by various electronic devices and power-electronics equipment can interfere and cause problems with operation of those devices. Accordingly, designs and countermeasures that stop such phenomena occurring are required. Since cars can be fatal to human lives, it is necessary to ensure an especially high level of safety when electrifying them. Moreover, in the case of communication devices like mobile phones, it is necessary to ensure that electromagnetic noise does not cause interruptions in transmission or reductions of transmission rate.
FUNATOThat's right. The ability to handle the problem of electromagnetic noise is termed "electromagnetic compatibility" (or EMC for short). We have been working on fundamental technology for ensuring EMC.
EMC can be considered from two aspects. The first refers to a characteristic called "emission"—which should be reduced to ensure that a device does not emit electromagnetic noise. The second refers to "immunity"—which implies that a device will not malfunction even if it is affected by electromagnetic noise.
As a result of current trends towards miniaturization, densification, and low power consumption of electronic devices, it has become necessary to devise shrewder technologies to address the long-understood problem of electromagnetic noise. Moreover, electronic devices are operating at ever higher frequencies, so it has become necessary to deal with electromagnetic noise generated by devices operating in the high-frequency range.
Figure 1: Problems concerning the unwiring and electrification of society
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Figure 2: Trend of electrical devices towards high frequency and low power
FUNATOTo design electronic devices so that electromagnetic noise does not leak out, it is necessary to clarify the mechanism by which electromagnetic noise is generated. As a means of clarification, theoretical calculation and simulation are performed. However, the reliability of a simulation cannot be verified without comparing the simulation results with real phenomena. That means it is becoming necessary to develop measurement technology for investigating those phenomena. With that requirement in mind, we have improved the accuracy of magnetic-field sensors for measuring electromagnetic noise.
Incidentally, although electromagnetic waves are composed of an electric field and a magnetic field, we first focused on a measurement technology for magnetic fields.
FUNATOThere are three main improvements. The first point is "fineness". With the miniaturization of electronic devices, electrical components are being packed into a small space. As a result, it has become necessary to differentiate places from which electromagnetic noise is radiating at an extremely fine level. The second point is "sensitivity". Since the electromagnetic noise that causes problems is extremely low level, it has to be measured at that level. The third point is "handling high frequencies." To handle increased speeds and frequencies of electronic devices, it must be possible to measure electromagnetic noise in the high-frequency range.
First, I'll explain the improvements concerning "sensitivity" and "handling high frequency." As I mentioned before, an electromagnetic wave is composed of an electric field and a magnetic field. Increasing the sensitivity of a magnetic field entails picking out only the magnetic field without sensing the electric field. With that requirement in mind, we investigated a model for accurately differentiating the electric field and the magnetic field.
As shown on the right side of Figure 3, a magnetic-field sensor is configured with a tip in the shape of a loop. This loop is the part that detects a magnetic field. The shaded areas are shielding. And a cover is placed over the shielding to ensure that it is unaffected by anything other than the magnetic field.
Figure 3: Magnetic-field sensor for experimental tests
FUNATOIn recent times, the question "If the part for detecting the magnetic field is covered by a certain amount, to what extent will doing so reduce the effect of the electric field?" has not been clearly answered. Accordingly, to grasp the relation between the shielding extent and the effect of the electric field, we compared the accuracy of magnetic-field measurement with two types of sensors: one with the detector part completely un-shielded (type A); and one with a portion of the detector shielded (type B). The result of this comparison made it clear that adjusting the proportion of the detector part that is shielded makes it is possible to improve the sensitivity of the magnetic-field measurement. And we found that controlling the shape of the shield makes it possible to handle measurements in the high-frequency region. Applying the results of this study, we were able to determine the best sensor shape to handle each challenge.
FUNATOSince sensitivity and fineness of a sensor are predetermined by the size of loop at the sensor tip, it has become a mainstream idea around the world to try to make the sensor smaller. Taking that approach, however, did not go so well, so we changed our way of thinking. That is to say, we searched for a way that can measure magnetic fields in a fine manner without changing the size of the sensor. Through that search, we conceived a different approach, namely, shifting the measurement position. During the measurement, the measurement position is shifted slightly after the first measurement, and another measurement is taken at the shifted position. Certain numerical processing is then carried out, and only measurement values of the shifted finite difference regions are elicited. In this manner, finer measurement is possible without changing the size of the sensor.
Figure 4: Approach to attain "fineness"
FUNATOWhat I have talked is a measurement technology targeting one kind of electronic device. In the case of systems such as PCs in which multiple electronic components are built in, it is necessary to determine what components will generate electromagnetic noise, what route that noise will take, and how it will leak outside the identified component. As a means of measuring that noise, we developed a magnetic-field sensor for measuring electromagnetic noise concerning screw parts.
In the case of businesses, tests on electromagnetic noise are invariably performed before products are launched. When it is attempted to fit many components into a PC, it is a common phenomenon that electromagnetic noise becomes large even though the electromagnetic noise from each component is low. When we consider this phenomenon, the place from which electromagnetic noise is leaking can be predicted. In other words, if the electromagnetic noise from screw parts connecting electronic components were measured, it would be possible to conclusively calculate the amount of electromagnetic noise leaking to the outside. By using our "magnetic-field sensor for measuring screw parts," it is now possible to measure electromagnetic noise leaking from electronic devices with complicated structures.
Photo 1: Magnetic-field sensor for measuring screw parts
FUNATOYes, in contrast to the technology I described in the previous section, it is a measurement technology that aims to ensure that a device is unaffected by electromagnetic waves. It was developed while I was temporarily assigned to Hitachi America, Ltd. as a researcher of EMC for electric vehicles. When I was performing tests in collaboration with a car manufacturer (namely, we were subjecting a car body under test production to electromagnetic waves and evaluating their effects on the car's internal electrical devices), I found discrepancies (i.e., fluctuations) in the values of certain signals. So I thought, "Why are such fluctuations occurring at this stage?" Individual components suffered no electromagnetic problems, and the car body encloses them with several layers of metal. So I thought there was no reason that electromagnetic waves could affect the electrical components.
I decided to make the mechanism behind this penetration by electromagnetic waves clear. However, it was not so easy in practice. That was because there was no method for measuring an electric field in a sealed interspace. Since electric-field sensors in existence at that time were connected by cables, to make use of them, it was necessary to handle tasks such as dismantling a complete car and drilling holes in the housings of equipment as well as move the car while it was connected to measuring devices fixed to the vehicle exterior. Naturally, it wasn't possible to do that. Given that impossibility, I thought that I should make a sensor that can measure an electric field even in a closed space. The sensor had to be small enough to fit inside the electrical equipment to be measured. On top of that, it had to be fitted with its own memory and battery so that it was freely movable without impediment from cables. With these requirements in mind, I developed a stand-alone, compact electric-field sensor.
Utilizing this sensor made it possible to reveal the extent of the distribution of electromagnetic waves penetrating into the car interior. It thus became possible to design future models in consideration of the results of these electromagnetic measurements.
Figure 5: Concept and application of compact electric-field sensor
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Photo 2: Compact electric-field sensor
FUNATOTo satisfy requirements such as ensuring compactness and sufficient battery life, we had to make prototypes time and time again. And this development was a struggle done mostly on my own. In fact, it was not the main theme of my research team at that time; that is, during the daytime, I worked on the main theme, and in the following hours, I worked on developing the sensor. All the same, since I was amongst research colleagues who were all too happy to help if I asked them, I asked them to handle parts of the development that I couldn't do myself. I'd say that's the reason the development was successful.
FUNATOIt was enjoyable, of course. That's because although it was tough at times, it was fun to make something as a world's first. Through my research results, I found things that had not been revealed up till then, and I want to link those findings with my next research theme. I think that's the point that motivates my research.
What's more, I have belief of "invariably shaping ideas." With my fellow engineers, I often have conversations containing ideas such as "Wouldn't it be good to have so-and-so..." and "We should create such-and-such a technology." However, when we tried to shape those ideas, it didn't go well, and many problems arose. "Putting ideas into shape" in this manner is tough work that involves the most time and energy. So I am placing the upmost emphasis on overcoming problems and challenges and shaping ideas. In the case of the developed compact electric-field sensor, it is, in fact, a combination of conventional technologies, so if the sensor's individual components are looked at alone, it doesn't seem so innovative. But by adopting a new viewpoint, I combined those technologies to provide new functions. Since I believed that was the most important point, I was able to complete this development successfully.
FUNATOFrom now on, I think the spread of wireless devices will continue, and the electrification of social infrastructure, such as electric vehicles, will push ahead. I see, just around the corner, a future in which all cars are running while using energy provided by a large amount of electric power and everyone walking along the sidewalk is communicating by wireless devices.
If that is the case, I think technologies related to EMC will become more and more important; in fact, the EMC-related research field is already getting wider. Improved performance of products being launched around the world is based on infrastructure technologies such as EMC. With pride in that achievement, I want to continue research and development in such a manner that continues to support the safety and security of our daily lives.
(Publication: November 13, 2012)