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HOME > No.11, Dec 2017 > "Resonance Q Theory" – A Breakthrough Discovered by TUT

"Resonance Q Theory" – A Breakthrough Discovered by TUT

Corroborating technology with science supporting implementation of wireless power supply By Takashi Ohira

"Societal implementation" is defined as developing practically oriented research designed to solve problems in society. As such, it is assumed that “research results” have been obtained in order for this integration to succeed. What comes to mind when you hear the phrase “research results?” Perhaps you picture hardware such as a newly developed machine or an electronic device? Or do you think of software for computers and information processing? These are all examples taken from our everyday lives which are the fruit of invention and manufacturing research. The R&D departments of corporations also produce these kinds of products. What kinds of research results does the world expect from Toyohashi University of Technology?

Corroborating technology with science. This is the basic concept behind science and technology. Instead of stopping at just manufacturing, we develop breakthrough theories that no one else has discovered. This is the true result of scientific and technological research. Needless to say, new theories are not created every day. Researchers need to review existing scientific theories and generalize basic theories found in our current textbooks in order to move on to higher-level concepts. Below, we will have a look at one example of a breakthrough theory that will force textbooks on electronic circuits to be rewritten.

If you open a textbook on electronic circuits for high school or university, you will come across the following equation:

This is a Q factor formula for a series circuit comprising a resistor and a coil shown in Fig. 1. Students generally memorize formulae and how to apply them verbatim. It is important to become familiar with equations such as the one above when you first start your studies, so this technique is somewhat useful. However, once you start to use these equations, you begin to wonder why they are written as they are. There is always some reasoning behind any physical phenomena. Finding out what that is, or “corroborating technology with science” is the true mission of technical universities.

Now, let’s look at Fig. 2. A condenser has been added to the circuit. We have learned that resonance occurs between a coil and a condenser in our last year of high school. The problem to solve here is to “calculate the Q factor in the circuit’s resonance state.” Although the problem itself is quite simple, it actually requires a lot of thought. Textbooks do not readily provide a formula that can be used to solve this problem. So, what are you supposed to do?

Fig.1:Series RL circuit
Fig.2 Series LC resonator with loss R in parallel to C

In order to solve this problem, you need to take a step back and really think about what a Q factor is. Throwing away our preconceived notions and ignoring general knowledge, we reached the concept of “natural logarithm impedance.” This is expressed as follows:

At first glance, this equation seems mysterious or enigmatic to solve, and is likely to be labeled as unorthodox. Generally speaking, Z is a complex number, and so ζ is also a complex number. By using this ζ, the Q factor in a resonance circuit of any structure can be determined by using the following equation:

Here, ωo represents resonance angular frequency of the circuit, and the two vertical lines represent the absolute value of the complex number. This theoretical expression was used in our IEEE journal and was selected for a Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology. The physical meaning of the logarithm impedance ζ is explained in “What in the world is Q?” (Ohira, 2016).

First, try and calculate the Q factor of the circuit shown in Fig. 1 using the above equation. You will need to derive the complex numbers part way through, and our second-year students learn how to do this. If your answer matches the following textbook equation, you have passed the first stage:

If you were able to calculate this, have a go at the problem in Fig. 2. The answer can be found in “Enigma on resonant quality.” (Ohira, 2017)

This theory applies not only to resonance circuits, but can also be expanded to various functional circuits such as those for filters or oscillators. The discovery of Log Z has given us engineers the ability to derive a Q factor equation under a resonance state from a given circuit diagram with just a pencil and paper.

The discovery of this resonance Q theory will contribute greatly to R&D into revolutionary systems that use the principle of resonance, such as those for telecommunications and wireless power transfer, and the implementation of those research results into society.

Resonance Q theory is extended and applied to the circuit design of the wireless power transfer system. This photo shows an electric vehicle on an electrified roadway (EVER) on a test course at our campus. The students in our laboratory are remodeling an EV to EVER by removing all the batteries and replacing them with onboard RF power electronics .

Editor's Note

On Nobember 29th, TUT and DENSO unveiled the result of their cooperative venture - a compact high-speed robot that conveys parts on DENSO's assembly line. Electrical power is supplied wirelessly from the guideway to the robot by means of a practical application of "Resonance Q Theory". DENSO is looking to use this robot in not only in its own factories, but also planning to sell it as part of a logistics systems that can operate non-stop around the clock. (Japanese version only)



技術を科学で裏付ける: 世界中の誰も見いだせなかった画期的理論を構築
By 大平 孝

「社会実装」とは得られた研究成果を社会問題解決のために応用展開することとされています。ということは、社会実装のためには、当然ながら「研究成果」が得られていることが前提となります。研究成果と聞いてどのようなものを思い浮かべますか? 新しく開発した機械装置や電子デバイスなどのハードウェアでしょうか。それとも、コンピュータ・情報処理などのためのソフトウェアでしょうか。これらはいずれもものづくりという意味でわかりやすい研究成果といえます。このようなものづくりは企業のR&D部門でも行われています。豊橋技術科学大学ならではの研究成果とはどのようなものだと期されているのでしょうか。





Fig.1:Series RL circuit
Fig.2 Series LC resonator with loss R in parallel to C






この理論は共鳴回路のみならずフィルタや発振器など様々な機能回路に発展可能です。Log Zの発見により、私たちエンジニアは、与えられた回路図から紙と鉛筆だけでその共鳴状態でのQファクタ公式を導き出す技を得たのです。


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Researcher Profile

Takashi Ohira
Name Takashi Ohira
Affiliation Department of Electrical and Electronic Information Engineering
Title Professor / Director of Research Center for Future Vehicle City
Fields of Research Wave Engineering / RF Circuits / Mobile Power Transfer