Takashi Harada Doctor of Engineering Innovation Producer, Research Planning Division NEC Corporation
I have been researching noise for over twenty years. In that time I have systematically organized the strategies for EMI suppression and analyzed them in a scientific manner.One outcome of the research is now commercially available as a tool enabling users to check for EMI and simulate circuit board designs.My current focus is on sensor networks, a core wireless communications technology even in which EMI problems do occur. The human network of noise experts that I have cultivated over the years has been an invaluable asset, which I believe will prove useful in my current interest in societal solutions for cities and infrastructure.
Unintended Noise Emission — From Noise Strategy Reliant on Experience and Intuition to Research on EMC Design Technology
I joined NEC in 1983. When I was assigned to the laboratory, my first research subject was microwave-absorbing materials. More specifically, I was involved in the development of materials that were useful for improving the characteristics of parabolic antennas by suppressing unwanted radio wave reflections. I have been working with “noise” from the very beginning of my research career. As I continued my research, the concept of EMI (Electromagnetic Interference) appeared and then was followed by the movement to regulate EMI that adversely affects broadcast and wireless communication services. In 1992, NEC established the EMC Technology Center which was the start of my serious involvement with noise research.
The challenges at that time were unintended and unpredictable emission of noise. We would only realize that a product exceeded acceptable standards when its noise was measured AFTER it was assembled. It was a time when not many people understood the nature of noise, and prevention was dependent on experience and intuition. The initial approach was to enclose the noise sources with shielding, thereby preventing the noise from affecting other parts even if noise was being emitted. Then, building on studies of noise absorbing bodies and materials, research turned to EMC (Electromagnetic Compatibility) design technology whereby noise would be suppressed by design, instead of addressing emitted noise.
Classification of Antenna Structures Susceptible to Noise, Studying Solutions for Each Type of Problem
Since the source of noise in electronic devices is in the printed circuit board, the board design is important. What is a desirable circuit board trace and layout of components? What is a noise-cancelling structure? Since noise suppression had been based on experience and intuition, we examined various methods in an effort to shed light on the know-how in a scientific manner. Even if the same structural design to counter noise was implemented, sometimes it was effective against noise and other times it was ineffective. So what kind of wiring pattern is desirable? Frequency characteristics and data transmission speeds also influence noise. We meticulously and scientifically examined all sorts of such problems.
Earlier I said noise originates in the circuit board, but it is not the printed circuit board itself that generates the noise. ICs are mounted on the printed circuit board, and when electric currents flow on the traces of the board, they generate electromagnetic fields which are exactly what causes EMI. A printed circuit board can have wiring patterns and traces with a structure similar to an antenna, emitting electromagnetic waves, thereby becoming a source of noise emissions. We classified wiring patterns and traces that had an antenna effect by structure, to which we applied solutions. Categorizing these structures helped us to understand the mechanism of noise radiation. It was as if we had become able to differentiate the types of noise that exist. An experiment with the movement of a music box will help explain the issue. Imagine the musical movement is an IC and a table as the printed circuit board. The sound of the movement when placed on the center of the table is different from when placed at the edge. How noise can be suppressed – this is the strategy against noise.
Research Crystallized in DEMITASNX®, Contributing to Society Through Noise Suppression
Our philosophy in noise research has been funneled into “DEMITASNX®” , an EMI suppression design support tool released in 2001 by NEC. The application checks the layouts of printed circuit board against the rules during the design phase and helps users identify and remove sources of noise from the board. However, since the application contained engineering design expertise that normally would not be publicly released by an electronics manufacturer such as NEC, internal debate did take place on commercialization of our know-how. Eventually we did decide to release the product because noise suppression was becoming critical to the development of electrical and electronic devices and we wanted to make a contribution to society.
Unfortunately, noise suppression itself does not correlate to the competitiveness of a product. Even if we release a product with low levels of noise, that alone does not drive sales. In any case, noise issues must be properly addressed before they become a substantial social problem, and we are pleased that our research is contributing to solutions for society.
e-Design Solution
The “Design System Solution” employs DEMITASNX® and PIStream to provide assistance in the design of power supply noise suppression. The “Design Support Solution” provides assistance in EMI suppression strategies, consulting services, and digital circuit and printed circuit board design work services. The “Trial Manufacture and Evaluation Solution” provides measurements of magnetic fields or services for EMI certification and evaluation of prototype and volume-manufactured products. Our multifaceted approach covering the three categories of EMI enables us to offer the best-fit solution for our customers.
DEMITASNX®, an EMI suppression design support tool, features a function for validating a design against EMI design rules for suppressing undesired electromagnetic wave generation during circuit board operation and a function for resonance analysis. These functions assist in evaluating the components layout prior to actually assembling a prototype circuit board.
The EMI design rules include carefully selected items that were proven to be effective in EMI suppression by NEC laboratories and Japanese and overseas universities. The tool assists in reducing the product development period and minimizes EMI suppression costs early in the design phase.
(Note) EMIStream is the brand name for the overseas version of DEMITASNX®.
Product site http://www.nec.com/en/global/prod/emistream/index.html
EMI Check Tool
DEMITASNX®, a tool for checking the presence of EMI and simulating circuit board designs, is commercially available overseas under the EMIStream name. NASA (National Aeronautics and Space Administration) selected DEMITASNX® along with PIStream for use in the Johnson Space Center in May 2011 to assist them in the design of power supply noise suppression.
The EMI check tools developed by NEC were awarded the Japan Institute of Electronics Packaging (General Incorporated Association*) “Technology Award” in 2011. The award is bestowed to recognize superior new electronics technology that also has a practical application. NEC was recognized for its “development of EMI rule check tools for the design of printed circuit boards.”
*The institute used to be an Incorporated Association in 2011.
Meeting Experts on Noise, Shedding Company Affiliations in Standing Against the Problem Together
At the time I started my research on noise over twenty years ago, previous materials and data were scarcely available on the topic, making it a very nebulous subject to research. On the other hand, it was also a time when digital devices were making advancements, with higher frequencies being used in devices and systems were becoming larger and more complex. EMI was becoming a problem affecting society. In those days, many of my fellow researchers had the same aspirations as I did. In one academic society, we would go camping as part of a working or study group where we would debate various topics over drinks. In this way, university professors, senior colleagues from other companies in the industry, and NEC retirees, were comrades-in-arms who had shed their company affiliations in standing together against a single problem. We would take back any gained insights to our respective companies, experiment and debate the ideas with the product development engineers. My experience in working with such people has been invaluable.
The Growing Impact of Noise, Anticipation for Components to Optimize Systems
I am now focusing on the M2M (machine-to-machine) field. I believe sensor networks will be critical in the context of solutions for society. The primary method of communication between sensors in M2M is wireless communication where many electromagnetic field-related problems such as noise are expected. The sensor network is important, but there will be increasing focus on the technology associated with noise.
The noise problem will never go away. Basically, as long as digital circuits rely on 0 and 1 states for switching, the switching operation will generate EMI. Recently there is concern of ESD (Electrostatic Discharge) which could damage circuits or ICs. Also observed is an “intraference” phenomenon in which EMI emitted by wireless devices is misinterpreted as a communication radio wave by the same device.
We must have an integrated approach in the future for examining systems from every possible angle. In the past, Murata has developed components specifically targeting noise suppression such as the three-terminal capacitor. At that time, that capacitor was technically very challenging, requiring extensive application of Murata’s unique ceramic technology. Device components are just one factor on a circuit board, but sometimes a single component can have a significant impact on the performance of an entire system. I am really looking forward to Murata’s efforts in discovering the function of components as part of a system and your subsequent development of new EMI components based on those discoveries.