Distinguished KAIST Professor and Dean of College of Engineering on 3 month stay at Acoustic Group

Jeong-Guon Ih

I come from Daejeon, South Korea, the 5^th largest city in Korea, with about 1.5 million in population and located in the very middle of South Korea, 140 km away from Seoul. I was born in Seoul, lived there until earning my Ph.D., so Daejeon is now my second home town where I have lived for more than 20 years. It is said that the people of Daejeon area are very gentle among Koreans, but the city itself is a bit boring though.

I have been a professor in mechanical engineering at KAIST (Korea Advanced Institute of Science and Technology) since 1990. Within the ME department, I belong to the Center for Noise and Vibration Control (NoViC), which is quite famous in sound and vibration research fields. At the moment, I am currently serving as the Dean of College of Engineering, which encompasses about 65% of the whole KAIST resources, and has 14 departments including EE, ME, etc. Although KAIST was established only for science and engineering, we have a business school and a small-size College of Human Sciences. At the  College of Engineering, there are about 380 regular professors, 6800 students including 1650 master students and 2600 Ph.D. students.

I got a special leave permit from the President in this occasion to stay in DTU, perhaps because I looked too much fed up with daily administrative jobs.

I graduated from the ME at Seoul national University in 1979, and earned MS and Ph.D. in ME at KAIST in 1981 and 1985, respectively. I was employed by Daewoo Motor Co. (now liquidated and absorbed into Chevrolet Korea Co.) from 1979 until 1990, supporting a full scholarship to study for MS and Ph.D. degrees in KAIST. I spent 1 year at the ISVR in Southampton University in the UK, as a Post Doc research staff supported by the FCO scholarship. At Daewoo Motor Co., I was in charge of the NVH (noise, vibration, and harshness) section and, for a while, the test department including the durability, ride & handling, etc. My job at that automotive company included the development, test, and even design for low noise and vibration car. I joined the KAIST faculty in 1990, and since then, 28 Ph.D.’s and 59 MS’s have be produced from my Acoustics Lab.

The data includes 3 dual-degree master students from DTU. I had been a visiting professor at the Math Department in Loughborough University, Loughborough, UK in 1999, for a collaboration research on the in-duct source identification of time-varying and nonlinear fluid machines. In 2006, I was invited to the Electro-mechanical Eng. Department at Seikei University, Tokyo, Japan for a collaboration research on the design of product sound quality of machineries and some area in psychoacoustics. I was the visiting professor in the Mechanical Eng. Department at Canterbury University, Christchurch, New Zealand, in 2006 for teaching Fundamentals of Acoustics course for a semester.

My academic interest has been directed on the design of machines, devices, and systems that are acoustically and perceptively acceptable, or even favored, by the people and environment as well as satisfying the other performance needs.

I have  studied  the duct acoustics area for a long time since I was a master student. There are various duct and pipe: automotive intake and exhaust systems, HVAC system in a building and ship, corridors in buildings and train, pipelines in many machines, e.g., washing machines, ear canals and hearing aids, vocal tract, municipal water and sewage systems, jet engine nacelle, tunnel, etc. The study on the sound propagation in a duct including the following topics: The presence of flow counting the convection, turbulence, flow-generated noise, and dissipation; The inhomogeneity in sectional area, medium, and wall absorption; Different source characteristics in time variance, linearity, and spectral cue; Reactive and/or dissipative silencing with the change of sectional size, structural shape, wall impedance including the absorbing liner, discharge method, etc.

Vibro-acoustics research field has been explored since I was a Post Doc research staff at ISVR, Southampton Univ. This area is particularly related with structural acoustics, which deals with the wave propagation within elastic solids. Those waves are often mentioned as transient or steady vibrations on the surface of the structure, which can radiate the sound a lot. The sound can reach in various routes that can be classified as structure-borne sound or air-borne sound depending on the transmission medium and direct excitation mechanism. Almost all machines and devices radiating the sound are related to this subject field. For example, an internal combustion engine of a car can radiate the noise directly due to the vibration of its surface that can be transmitted into the cabin through the dash panel, holes, and insulations; while the engine vibration causes the noise in the passenger cabin due to the secondary radiation from the car panels surrounding the interior cavity, of which the vibrations are the result of the transferred energy through the engine mounting, structural members, welded connections, damping materials, insulations, and rubber mounts and grommets. Steady state, transient, and impulsive excitations to the structures are also of concern.

Design of the product sound quality is based on the psychoacoustic theory, psychometrics, signal processing technique, understanding of the operation mechanism of machineries, and general vibro-acoustic knowledge. Because the sound quality is perceived by the customer of a product, the fundamental knowledge on the physiology in hearing, psychology in perception, culture, age trend in a society, and multi-modal operation is required for a truly effective design of a desired product sound. For a machine designer or developing engineer, it is not easy to equip all required knowledge in full depth, but, with a firm background of science and engineering, one can at least try to integrate all such knowledge as far as possible, so as to design a perceptively-correct product in an interdisciplinary manner. In particular, it is quite interesting to design and optimize a product sound, which has a two-faced, or Janus-faced, perception characters. When you drive a car, you may want to hear a sporty engine noise, but, simultaneously, you want a pleasant acoustic feeling. When you use your vacuum cleaner, you want a comfortable sound, actually noise, but also you need a feeling of powerful suction of dust. In hearing the music reproduced from a loudspeaker, you want to hear a silky smooth sound harmonically enveloping your whole body, but also you need to discern the sound from each musical instrument distinctly and sharply. Such two different demands are contradictory, so it can be a target of acoustical optimization. I have been studying on this subject since I worked for an automotive company.

How you became interested in this particular field?

When I was the master student, in the first semester, a list of research topics and areas were notified, and each student was supposed to contact a professor and decide the supervisor and research topic within a week. At that time, I wanted to continue to study the automatic control area, which had been studied during the last two years in the undergraduate courses. I was lazy, slow, and optimistic, so I contacted the professor specializing the control theory in the middle of that week. He already selected the other agile students. At that time, the acoustics in mechanical engineering was very rare at KAIST, so it was not popular, and even people did not know what was for in mechanical engineering, not physics. I was so naïve that the topic noise control hit my eye because it contains a word ‘control.’ The professor told me that the control is the same for any field application, so I believed his words. At that time, for a youngster at early twenties, the professor looked like an academic god. When I took the Fundamentals of Acoustics course, I learned about the flutter echo phenomenon, then, I could solve the mystery in my life at that time. I had been very curious about the buzzing sound when I passed by a long narrow alley with two parallel concrete walls in my home town. After understanding that unsolved long-time mystery, I forgot about control (I forget things nearly in a level of art), and started to study about acoustics as my life job. Started my career in a rather funny way, but I am very sincere and enjoying for my research now (happy end?).

What has motivated you to further research in this area?

As an undergraduate, I had seriously thought about working in the business area of publishing books, similar to the company that my father had run. However, after hearing from my football mates that they planned to continue to study in the graduate school and discussed about its merit, I was motivated to study as like them in the subject of control theory, but the last problem was that I wanted to be financially independent from my parents. Luckily, an automotive company hired me and they suggested full scholarship for the 2-year master course. Furthermore, the mandatory military service for 3 years could be exempted by entering KAIST. When you are in the military service for a long time, your girlfriend would marry with rich old guy, after finishing it, your mathematics skill would be reset to your middle school level, and your favorite topic would be often on your past experience in military life, about which no attractive sane girl do not want to hear. I have studied acoustics in MS course, and my thesis supervisor and company head agreed that they would like to support me in the Ph.D. course to foster as a pioneer in the vehicle NVH engineering field. The real interest and motivation were created when I worked for the automotive company, especially in the test department within the tech center, and I could deal with many practical engineering problems to solve. For 6 years, I could not publish any technical articles due to the company restrictions, that period was not futile at all in expanding my research capability and further research motivation.

Why the collaboration with DTU Electrical Engineering in Denmark and KAIST?

In 2005, I have sent one of my bright Ph.D. students, Cheol-Ho Jeong, to DTU, Acoustic technology Group in EE, to collaborate with Prof. Jens Holger Rindel in the field of room acoustic simulation as an exchange student. He did very well, and, now, he is the associate professor in DTU. I had a good acquaintance with the late Prof. Finn Jacobsen, because some of our research interests were similar, and thought that a dual degree master program would be very beneficial to our students and teaching staffs. When I was the Chair of School of Mechanical and Aerospace Engineering at KAIST, about 4-5 years ago, I have made the dual degree agreement with DTU ME, ACT group in DTU EE, and biomechanics and robotics group in DTU EE. Until this time, there have been many in-bound and out-bound MS students at both universities. It looks quite successful compared to the DD programs with the other universities. I have already co-supervised Philip Franek (with Efrén Fernandez Grande), Gustav Jacobsen (with Finn Agerkvist), Boris Mondet (with Cheol-Ho Jeong), Mi-Seong Kim (with Jakob Søndergaard Jensen), and under supervision on a student, Ji-Su Jeon (with Jonas Brunskog).

Co-supported from Danish and Korean research foundations, we have an exchange collaboration program this year. In February, 3 professors and 3 graduate students at KAIST visited ACT EE, DTU, and had a workshop on acoustics. We also had a similar event in the last year. In July, 5 professors at ACT EE, DTU (E Fernandez, V Henriquez, CH Jeong, J Brunskog, JH Kook) visited KAIST, and we had a workshop introducing what research works are going on at each party. Profs. Efren Fernandez and Jonas Brunskog stayed for a longer time having good experiences in exchanging ideas and understanding KAIST environment and staffs. In the acoustic technology group in EE at DTU, the academic fields as like electro-acoustics, audiology, room acoustics, micro electro-mechanical systems including hearing aids, structural acoustics look strong and active. Expertise and interested fields are partly overlapping and partly different, so I think that the two institutions can have a very good synergy effect with such tight collaboration.

Can you give a deeper explanation of your research? 

In recent days, actually starting from the end of the last century, I have been much interested in the vibro-acoustic inverse problems. What I and my students had worked on was mostly about the source characterization of fluid machines, thus providing an essential data for the low-noise design, auralization and visualization of the vibro-acoustic source field. Most of work was closely related to the industrial problems in the design and development stage, so this has been the lucky case that the academic theoretical and experimental works are directly applied to solve the actual problems.

The developed method for characterizing the acoustic source in the intake and exhaust system of an engine is now used in the design of quiet intake and exhaust systems for Japanese and Korean automotive companies. We have developed the acoustic holography technique combined with the boundary element modeling method, so as to deal with general irregular source shape, and the method was applied in many products of automotive manufacturers, part makers, and electronic companies. A similar inverse technique is used for the rendering of the vibro-acoustic fields. Examples include the generation of regional difference in receiving sound, generation of natural plane or spherical wave in an enclosure, generation of tactile feeling on a prescribed local zone on a glass display panel of mobile phone, etc. We are now conducting an internal project on the creation of a loudspeaker and baffle on a general panel including the car roof panel, refrigerator door panel, TV glass panel, etc.

Apart from the academic work, invention of new systems for the future is an important task for me and my students. The creation of a virtual loudspeaker on a general panel mentioned above is one of such campaign outputs. Recently, we developed a virtual electronic pen which can provide a virtual resistance when you write a letter or draw a figure on a glass panel in the tablet PC or mobile phone. We developed an error compensation method for the 3D sound intensity probe, so it can track the source direction in the virtually exact manner, which can be used in the humanoid robot, industrial problem solver, and military purpose. There are many other examples. I think society demands our effort, as scientists and engineers, to create an innovative system and method as results of study, thus increasing the intellectual properties and contributing the human welfare. It is very enjoyable job…

And lastly, what are your first impressions of Denmark so far?

Before stating about the impressions of Denmark, I would rather talk about my exercise. When I was in Korea, I came to my office by car at around 7:30 am, and then the participation to a number of meetings usually continued until 5 pm. In many cases, there were dinner events with visitors or colleagues. In some schedule vacancies, I tried to meet my students in the Acoustics Lab., in a form of lab seminar or personal interviews, and I have even lectured the acoustics course in the last spring semester. So, in such a hectic and dry life, I could not properly perform the exercise to keep my health. However, here in Denmark, I walk every day for about 80 minutes, in total, so I feel my body becoming healthier everyday although I feel a little bit of pain in my knee joint occasionally. This is veeery good.

Passing in the street, I can see many people ride bicycles, perhaps almost all Danes as a national sports, perhaps for the purpose of commuting or child care or shopping. Possibly from this fact, most people looks very healthy, and it seems to me that the hospitals for obstetrics and geriatrics are only needed in Denmark. Ah, I should add surgery in the list having seen many people bikes without proper protection gears, and respiratory clinic for cigarette lovers. But, anyway, I respect peoples biking on the cobbled road, under the rainy and windy conditions, and wearing thin summer clothes.

 I am not sure that such culture is due to the word similarity in ‘Viking’ and ‘biking’. My wife really likes to see the cargo bike, having a brand name of Nihola, in which two children, a big dog with a big tongue in my hand size, and even a smiling lady are accommodated. Imagining and worrying that my wife will sit in the cargo while I am driving the bike, I persuaded her not to even think about buying the Nihola cargo bike, saying that it is very expensive and the transportation fee to Korea will be enormous.

The weather since I arrived here is fantastic. By the way, who told me that Denmark is a windy, rainy, and chilly country? It is a bright and comfortably warm country, at least now in early September.

Pigeons need some diet therapy. Otherwise, …., I know a very nice and posh pigeon restaurant in Hong Kong.

It seems to me that Danes do not eat fishes and sea weeds in a delicate way as like in Korea and Japan, except herrings. I assume that there are many fishermen in Denmark, and Danes do not waste such wonderful food material. Also, I should tell the Danes that making sushi is not so difficult at all. You should not pay 150-200 Kr for several pieces of sushi in the restaurant.

Many things are far slower than Korea except the bike speed. I am enjoying slow food, slow talking, slow speed train, etc. I also became slow in reading and responding to e-mails. Good.

I am now seriously looking for the reasons of ‘the happiest country in the world.’ Perhaps, not owing to the nice politicians…