Oral-History:Hans Severin

About Hans Severin

Hans Karl Friedrich Severin was a senior professor and researcher specializing in microwave physics at Ruhr University-Bochum in Germany. A graduate of the University of Goettingen, Severin served on the faculty there from 1943 to 1957, with a brief interruption in 1955-1956, when he accepted a one-year research position at RCA Laboratories in Princeton New Jersey. Severin headed up the microwave department of Philips Research Labs in Hamburg between 1956 and 1965 and served as professor of physics at the University of Hamburg in 1960. Severin left Phillips and Hamburg 1965, when he was appointed to the engineering faculty at Ruhr University-Bochum. He served as director of the university's Institute of High Frequency and Microwave Technique until his retirement in 1985. Severin wrote extensively, contributing more than 80 articles to professional articles during his career. Severin died in 2008.

In this interview, Severin discusses his education, which was interrupted by his service in the German Army as a radar technician during the Second World War, and his postwar educational work research in microwave physics in both the private sector and academia. Severin notes that he supervised the doctorates of more than thirty students and almost single-handedly built the Institute of High Frequency and Microwave Techniques at Ruhr-Universität Bochum.

About the Interview

HANS SEVERIN: An Interview Conducted by Frederik Nebeker, Center for the History of Electrical Engineering, 31 August 1994

Interview #225 for the IEEE History Center, The Institute of Electrical and Electronics Engineers, Inc.

Copyright Statement

This manuscript is being made available for research purposes only. All literary rights in the manuscript, including the right to publish, are reserved to the IEEE History Center. No part of the manuscript may be quoted for publication without the written permission of the Director of IEEE History Center.

Request for permission to quote for publication should be addressed to the IEEE History Center Oral History Program, IEEE History Center, 445 Hoes Lane, Piscataway, NJ 08854 USA or ieee-history@ieee.org. It should include identification of the specific passages to be quoted, anticipated use of the passages, and identification of the user.

It is recommended that this oral history be cited as follows:

Hans Severin, an oral history conducted in 1994 by Frederick Nebeker, IEEE History Center, Piscataway, NJ, USA.

Interview

INTERVIEW: Hans Severin

INTERVIEWER: Frederik Nebeker

DATE 31 August 1994

PLACE Bochum, Germany

Background

Nebeker:

Can we start with where and when you were born?

Severin:

I was born on 6 May 1920 in Grafenwoehr, South Germany, where I finished my Grammarschool. I became very interested in Physics. So, I told this to the teacher, and he said you can come every week when I am preparing the experiments for the class for the next day. I learned much more than I would have just from the one hour in class.

Nebeker:

Had you been interested in technology earlier?

Severin:

Not really. My first goal was to become a teacher of Physics, Chemistry, and Mathematics.

In 1938, if one wanted to become a teacher, one had to go to a special type of school for teachers for one year. So when I started in '39 my real study at University, after a while I realized I liked Physics much more than teaching, and I considered changing.

Nebeker:

I see, and you were admitted to Goettingen.

Severin:

Yes. No problem.

Education and Military Service

Nebeker:

Were you subject to military service?

Severin:

Yes, of course, but in 1938 I had suffered from blood sickness, so it was delayed a little bit, and they called me in August 1941.

Nebeker:

And by that time you had completed almost two years at Goettingen?

And what happened when you received this call to military service?

Severin:

I became a soldier, and I was with the Flak –air defense — and after basic training, of eight or twelve weeks, I went to a school for the Wuerzburg geraet. It was radar measuring equipment to measure the position of the airplanes. And at this time with a wavelength of ten centimeters, a big mirror of three meters in diameter, and first I learned this thing myself during a training of eight weeks.

Nebeker:

So this was fire control radar.

Severin:

Yes. After several months I came back to school, which moved more to the east in the neighborhood of Rostock because of the many air attacks to west Germany.

Nebeker:

Why were you permitted to go back to school?

Severin:

It was a military school!

Nebeker:

It was the school where you were teaching, I see.

Severin:

Yes, I was still a soldier. I was still not at my own school, the University. Then I had the opportunity to go to an Engineering course, and there I was trained as an engineer soldier, who had to repair the equipment.

Nebeker:

So you went from place to place repairing the equipment?

Severin:

Yes. I traveled on a motorcycle.

Nebeker:

And these were ten centimeter radars of different sorts? Anti-aircraft radar?

Severin:

Ten centimeter. So I was very lucky to meet one higher ranking engineer from the Ministry of Air Defense from Berlin who came to visit us and to command us and I told him my story, that I had been interrupted from my studies just shortly before promotion. It was about three to five months before I got my doctor's degree when I had to move over to the Army. He was thinking it over for a while and told me, “You are too young for me to give you vacation for study.” “You have to go there to do your service, from seven to five, and what you will do in the evening it is not necessary that I tell you that.” So I told him all this would make no sense if I had still to be in the barracks. Because I would have to be home at ten o'clock and so on, and if you wanted to work in the Physics institute will do that to midnight or so, and well he wrote also to the commander in Goettingen that he should give me license to live at home. So I took the examination, and afterwards my chief told me that under a special order of Hitler he could keep me as a scientist at his institute. From this time I was still a soldier and worked as a soldier for two years – but then I had to go back to the barracks or to the frontier or whatever.

Nebeker:

What work did you have to do then?

Severin:

That is the point. I must say that my Doctor's degree in Physics was in Solid State Physics.

Nebeker:

That was not a large field at that time.

Severin:

No we made rare earth crystals. We did spectroscopy on rare crystals – it was the field of Institute — Second Physical Institute of the University of Goettingen.

Nebeker:

And how did you become interested in that branch of Physics?

Severin:

This is quite natural. One founder of the Institute was R. Pohl, and the other one was G. Joos, who wrote a very famous book on Physics. I applied to work with him. There was also the possibility to go to the theoretical physics, but since I didn't like that so much – I was more interested in experimental work.

Nebeker:

And what was your thesis itself?

Severin:

Okay, now to the project I was working on during the war. This was the point where I became familiar with microwaves. Because this was radar camouflage for submarines.

Nebeker:

Yes. I have encountered this project before, because the fellow who I mentioned – Herman Schwan, happened to work on that also — Project Chimney Sweeper. It was the project to make the Snorkel — to put an anti-radar coating on the snorkel.

Severin:

Yes. And where was he working?

Nebeker:

He was in Frankfurt —

Severin:

They made the application, and we made the measurement. Quite funny that they didn't do it themselves, we had in Goettingen rented a big sports hall because the wooden wouldn't reflect too much like a metal — at this point we didn't have anechoic rooms, and so we made the measurements in a big hall.

Nebeker:

What was the task of the group at Goettingen? Was it to design the coating?

Severin:

No. In the very beginning yes , the so called Dellenbachkleinstorbe Layers – but this was only for one frequency. So, very narrow banded and multi layers coatings with different absorbers had to be developed. This was a theory made by Professor Franz at this time, and the material was really formed by Hoechst in Frankfurt – this is a chemical firm and we made the measurements.

Nebeker:

And you were measuring the absorption of this material at different wavelengths. And that was because you had the equipment to generate those wavelengths?

Severin:

This was very simple – or very pure. We had ten centimeter magnetrons and six centimeter magnetrons, and this was about all. And then we picked up one for three centimeter that was made in an Institute in Vienna – a colleague Gubault — who was later on at Fort Monmouth in New Jersey. Tricky to work with these tubes developed in a university lab, not coming from a factory – very hard to get a replacement if they failed.

Nebeker:

So you found this sports hall to make the measurements in, and was it a difficult job to do those measurements?

Severin:

No.

Nebeker:

And did it turn out that this coating was working as it should? As expected?

Severin:

Yes.

Nebeker:

And was it used on the snorkels?

Severin:

Yes.

After the War

Nebeker:

Was that the work that you did the remaining two years of the war?

Severin:

Yes. The problem was, you had to measure the reflection coefficient. And of course, to measure the reflection in the open air, in a big sheet, if it's not big enough compared to the wavelengths you have always diffraction. In a slotted line you get very good and very equal standing waves, but on a finer object, you get overload and then diffraction from the diffraction waves, they oscillate. And to get the correct measurement, you had to calculate this diffraction. Some were published in 1940. Yes, the first publication was “The Diffraction of Electromagnetic Centimeter Waves by Metallic Openings”.

Nebeker:

1946. I see. Did this cause problems with calculations? It looks like this was very calculational.

Severin:

Yes. There was quite a bit of mental work involved.

Nebeker:

Did you have any mechanical calculators to help you or anything?

Severin:

Not really calculator. I had one man who made these calculations all day. Very many trigonometric functions that had to be developed too, and it was quite a lot to get one point, But it was very interesting.

Nebeker:

Yes, I can imagine. So you did this work because you found it interesting?

Severin:

Yes, this was not the order of the military people who made this contract. I just did it on the side and on my own time, and I continued this after the war. In 1945 of course we lost all of our equipment – this was completely destroyed by the troops coming in.

Nebeker:

They just destroyed it?

Severin:

Completely, yes.

Nebeker:

In some places I know they just confiscated the equipment.

Severin:

At the Federal Institute they shot around and what they really meant had to be destroyed, they threw it out from the window, put it together, put rope on it, and carted it off.

Nebeker:

Was this the Allied soldiers, or German soldiers before..?

Severin:

No, this was really US troops.

Nebeker:

Is that right? I would have thought that they would want to just take the equipment?

Severin:

They had closed the institute for six weeks, and then we could go in first time and we realized that all this stuff was not available anymore. So I then decided to go on with these investigations, because I was mostly interested in the diffraction problem. In optics, all these problems were really solved, but this was a situation where the wavelengths were very small compared with the dimensions of the obstacles. But I was interested in the other case, where the wavelengths were compatible so I continued this study in acoustic waves because I didn't have any equipment.

Nebeker:

So you remained at Goettingen?

Severin:

I remained at Goettingen until 1957.

Nebeker:

What was the nature of your position? I assume you didn't stay in the Army.

Severin:

No. After the War, I became a Scientific Assistant at one of these Institutes.

Nebeker:

The Physical Institute?

Severin:

No, this came later. This contact work I made at the Second Physical Institute were all promoted. And after the war, my professor –my chief — he put me in an Assistant position in the Institute of Applied Electricity. It was a small institute at the same campus – there was only one assistant. But anyway, I had a place where I could work, where I could continue this, and where I started this echo signal work. And then in 1946 came Professor Meyer, the famous acoustical man – I didn't know him before. He was interested in my work.

Nebeker:

So you had already decided to do acoustics?

Severin:

No. After his main field, acoustics, he was also working with electromagnetic centimeter waves. And we prepared a lot of papers then on analogous problems which could be done electrically – for example the absorber. The acoustic absorber, and then we switched it over to an electrical absorber. The same principles are used in acoustics, we took it over for electromagnetic fields.

Nebeker:

I see.

Severin:

Audio File

MP3 Audio
(225 - severin - clip 1.mp3)

And so I was made an Assistant Professor by him, and stayed there for about ten years. And during this time I got an invitation to work for one year at the research institute of the Swiss Post Office in Bern, Switzerland. This was of course very interesting for me because at this time I could work for the first time with equipment of centimeter waves, of microwaves. They just started with these radio links, and Switzerland is very much suited for this – it goes from one mountain to another one – you do not need a cable through the mountain, you have on both mountains transmitter and receiver and a short distance to the valley, and this started at this time and of course there was a large competition with all the cable people who didn't like the idea. One funny thing. They made two such links – one from Bern to the Swiss border was fifty kilometers and from the Swiss border to Genf was 180km. And of course you had to have a line of sight.

Nebeker:

Can you have sight over those distances?

Severin:

Yes. You must have – otherwise you would have too many disturbances. We have chosen these two distances, but an English company did not sell the measuring equipment, for instance slotted lines, they wanted to make the measurements themselves. So my duty there was to develop the measuring equipment. We only had the American waveguides – it was a sight ratio of two to one – two inches to one inch – and the English was three to one. So what I had to do was make this total equipment slotted line wave meter observations, damping parts in these other cross sections, working together with a very good Swiss mechanical company who made these parts for me. It was really just one year, a very good learning experience for me, because I never had seen this before and this is really the grounding for my first work in microwaves.

Nebeker:

Now, you were working in Acoustics before this, is that right?

Severin:

No, only as long as I didn't have any tubes.

Microwave Diffraction

Nebeker:

I see, until you got the equipment.

Severin:

Yes. At this time, because of my diffraction papers as I showed you before, I got first invitation to an international meeting in Milan. My stay in Bern was just finished, and at the end of this I could go to Milan and gave a paper there.

Nebeker:

This was 1953?

Severin:

Yes, and it is published in Cimento “Methods of Light Optics for the Calculation of the Diffraction Phenomena within the Range of Centimeter Waves.” And very luckily, there were also a few American people from the Air Force Research Center in Cambridge. I don't know whether you know Mr. Sucker. He was working there in a high position. This was 1952, and because of this paper that I presented there I got an invitation to Montreal in 1953.

Nebeker:

What was the topic of the conference?

Severin:

Well, it was more on theoretical work on electromagnetic waves.

Nebeker:

McGraw Symposium on Microwave Optics.

Severin:

Yes. So this was an earlier one. After this meeting in Montreal I some consulting jobs at the New York University and the National Bureau of Standards.

Nebeker:

What was it that you were talking about at these places?

Severin:

On diffraction.

Nebeker:

Diffraction of microwaves. And how to calculate that?

Severin:

Yes. A Kirchhoff formula which was matched to these special problems coming from optics, and this was a much too special problem, again [according] to the case that the wavelength is compatible to the object itself.

Nebeker:

Taking a step back from this particular work – you've said that there was a similarity in the mathematics between the acoustics and the microwaves, and you're also drawing on optics work. So you have really three areas and all are dealing with the refraction phenomena.

Severin:

Yes, the big problem is that in optics, as I said, the wavelengths are small compared to objects, and you're always in the far field. Nobody is interested in the near field. So in the far field, almost all rays starting from the object are in parallel, whereas in micro optics one is mostly interested in near field. So the rays are not going parallel – they are going in different directions, and this makes the calculation – I wouldn't say more difficult, but more complicated.

Nebeker:

The situation is that optics was fairly well developed mathematical discipline early on. And then at about this time certain questions in both microwaves and acoustics arose and they were fairly similar, because you're dealing with near field calculations in both fields.

Severin:

In the basics. But acoustics is a scalar problem, and electromagnetics is a vector problem. But in the basics that's right. The basic idea is fine.

Nebeker:

Was there much transfer of results from acoustics to microwave, or vice versa?

Severin:

Basic ideas, this is correct, but not for the calculations and results. They are more complicated in the electromagnetic field.

Nebeker:

But there was at least some inspiration drawn from the results of the other realm.

Severin:

This was in 1953. I then came home and made the recitation this is one thing which is not so familiar in the United States. Here you make your Doctor's degree and you are then not allowed to give any lectures, because you have to have a second degree that you get with a Habilitation paper, which should be different from the Doctorate. This was no problem for me, because I had never done any work on spectroscopy, so at the Habilitation was really a quite different paper on the squeeze section, where you can change the phase velocity of the wave, and you can use the squeeze section as a standing wave indicator. I calculated the dependence of the wavelength on the squeezing of the guide – on the diminishing of the guide width. Yes. Habilitation was the end of '53, the examination was shortly before Christmas in 1953. You have to give a lecture of forty five minutes, to the whole faculty to show your teaching ability, and this was the end of February, the end of semester. After the Habilitation you're Privatdozent.

Nebeker:

And did you continue this sort of work?

Severin:

I had a big surprise after Habilitation. I gave my first lecture on microwave measuring techniques, of course, this was the first lecture. And the second one, my boss said, “ You are giving your next lecture on transistors.” So I said, well, how can I do that, not having done anything with semiconductors, there are people here at possibly one of the neighbor institutes that could do it better than I can. Anyway, he asked me, “Why do I have a Privatdozent? You now have to do what my institute is missing!” Okay! So I had to give a lecture on transistors. I learned from two books from Shockley and Bardeen, first the basic things, and then afterwards the applications, and wrote a lecture on transistors. Not one on microwaves. But then the next one, because I am still a physicist, it was at the third Physical Institute, the next one was on microwave spectroscopy.

Nebeker:

I see.

Severin:

Then it was 1955, and following this second meeting on Microwave Optics in Ann Arbor – I again got an invitation..

America and RCA Laboratories

Nebeker:

Your time RCA was '55 to'56

Severin:

Then this meeting was in 1955. Because in 1955, shortly before this meeting, one of these RCA fellows came and invited me to go for one year to RCA. And so he said, “It is not necessary that we make any agreements here, so if you come to the United States any way in summer than you can visit us in Princeton, and then we will handle the visa problem.” And this was then in 1955 in summer. First I had this invitation to come Ann Arbor, and this time I gave a talk there on microwave absorbers. On different types of microwave absorbers. Narrow band, broad band, five or six different types. And this has all been published.

Nebeker:

I see. And then that was published in IRE Transactions.

Severin:

In 1956 probably.

Nebeker:

Yes, it came out in '56. Tell me about your stay at the David Sarnoff Research Center.

Severin:

Yes. Let me say one word more. After this stay in Ann Arbor, I had the invitation from Hewlett-Packard to visit Palo Alto, because at this time I had a patent agreement with them. And I was three or four days in Palo Alto and in San Francisco for the first time. This was a very nice stay, these few days, I got to see the plant, and I got to see a little bit of San Francisco, of course. And being back, to Germany, it took me three months or so to get the permission, because you had to have as certain Visa then, a Visa H or something. I visited RCA of course in the summer, but it took about three months to get the permission, and then I went together with my wife for the first time to the States and for the first time on ship, not by plane. In order to take heavy luggage with you – all the things you need for one year – you had to take a ship. When I went there for the first day, the department head of RCA then said to me, well, we of course are not interested in your diffraction work. This is nothing for our company. We offer you two things: You can work in a group with two others on a special maser development project.

And this is one thing you can do. And second, there is a Norwegian fellow here for one year, who leaves us in the next four weeks to go home. He is working on ferrites in the microwave region. This is his magnetic material, which is of very low conductivity.

Nebeker:

This is to understand how it absorbs and reflects microwaves?

Severin:

Or transmits them! You can make phase shifts with them, or switches and so on. So I decided on the latter one, I worked on ferrites. I had not much knowledge of magnetic materials, but the first weeks I worked together with this fellow.

Nebeker:

What was his name? Do you remember?

Severin:

Ehrlander. He's now in Sweden at Sweden University. I met him several times during my career at the National Meetings. And then I continued this, and this was very informative, to do work in a new field. This was also very fortunate for me, in so far as I was just two months with RCA before I got an offer from Philips in Eindhoven, and they wrote to me that they are going to build up a new laboratory, a research laboratory for the German factories, and asked me whether I would be interested to work together with them, to come to this new laboratory, which was really in a developing status. I said yes, but now I am here in America, and I had to fulfill my contract. They have given me allowance to go for one year to Princeton and after my return to Goettingen I should stay there at least for one semester, so the earliest time it would be on April 1957. Then I got a very positive answer that said yes, this was okay for them. When I was back in Germany in October, I got a call from Philips – “ you should be here! Come to Hamburg and visit us.” So I went to Hamburg, and saw that it was a very good offer. The Director said, “Well, we have just one Director from Holland here; he is flying back to Eindhoven this afternoon, and you can go with him and go to our research director in Holland” It was quite surprising! I did so, and I accepted the offered job. It was really a good decision to go to Hamburg.

Nebeker:

Could I ask about the significance of the work you did at RCA? I see you have at least one publication about circular wave guides containing ferrites. Was that important work in your estimation, the work you did RCA?

Severin:

For instance in cores you had very small, iron particles in paraffin – the problem with the technique is that you need low conductivity materials. Because the losses in conducting materials are too high, because of eddy currents. They heat the transformer. The laminations are made with paper in between, the transformers for 50 Hertz it's no problem. But at 5000 Hertz, you have a thousand time higher losses, so what you need are very low conductivity materials, and this was achieved by using ferrites. And then this was starting about just after the war, by the Philips people in Eindhoven. Then it is quite funny that the first microwave application, the first so called uniline, which transmits only one direction and absorbs in the other one, was made by Hogan, at the Bell Telephone Laboratories, in 1952, with a Dutch ferrite material.

Phillips Research Laboratories

Nebeker:

I see. So you came back to the University, but then shortly after that started work at the new Philips laboratory in Hamburg.

Severin:

Yes it was quite new, which means there was nothing there when I came! We had only the plans of the architect, and it was sitting on this field where they were going to construct the building, so I was advising them on how this building should be equipped, with DC current, or AC current, and all these things, which are necessary with gas, air lines, water, etc. And it was completed after ¾ of a year or one year, we had the opening, and I started in Hamburg

Nebeker:

It says in your Vita that you were department head at this laboratory. What was the name of the department?

Severin:

Microwaves.

Nebeker:

And what work did you start?

Severin:

This was why I said before that my decision was to work on ferrites – this was the beginning. Also, Philips was of course not interested in diffraction problems. So what we started here was work in ferrite materials as well as their microwave behavior. It was at this time not quite developed, so this lasted for about the next eight or ten years. We had a very good connection to Eindhoven and the first materials we got from there. Later on the center expanded, we had our own materials. We had two groups. One handled chemistry. This group made special materials so that we could use them for particular applications. This went from attenuators to steering for antennas and such things. In the second group we were working on surface wave guides for millimeter waves.

Nebeker:

What was the essential application of that? The surface of wave guides?

Severin:

At this time, we were working on the millimeter field, but the surface waves were used for instance on the feeds for flexible antennas. You could draw them up on a sports field, for instance, forty meters high, and then instead of a cable, which has much higher losses, you use these surface wave guides. The basic idea came from Gobault, as I told you before, from Monmouth. They were invented much earlier, already in 1908, a man named Harms had made experiments with this guide. But it was very difficult to excite them, and the work of Gobault was to show how to excite such a surface wave without too many problems. It's always a problem, if you come from a wave guide and you come to an electric guide, you have almost 90% reflection. To avoid this you have a certain form of matching, and this was Gobault's contribution. We went to smaller wavelengths of two millimeters. Up to two millimeters it was very fortunate, because we could get the tubes from Eindhoven, and we developed components for measuring techniques on the basis of those surface lines. This was our main goal at this time. We had no idea to use it as a transmission line.

Nebeker:

So this was more basic research. Has it since turned out to be very useful, these surface wave devices?

Severin:

Well, in these days, one didn't have anything else. Normal waveguides have losses that are much too high, so it depends what you want to do. For measuring techniques, it's still applied

Nebeker:

How long did you continue to do that work at Philips Laboratories?

Severin:

From 1957 till 1965

Ruhr University-Bochum

Nebeker:

In 1965 you became a Professor, and Director of the Institute of High Frequency and Microwave Techniques at Ruhr-Universität Bochum. Is that soon after this soon after this University was established?

Severin:

Yes. This is again the same story! Started here, there was nothing but a model, a model of the University! So I had quite some experience from building up the laboratory in Hamburg, which I really could use here again.

Nebeker:

So you helped design the facility here?

Severin:

Yes. I got the offer in 1963, and then it was until 1965 I decided to go here.

Nebeker:

And how long did it take for the university to get going?

Severin:

Well, I told you I got the offer the end of 1963, and then I was here in 1965, and I didn't see anything but construction. So the Ministry offered me a consulting job during the construction time.

Nebeker:

Oh yes, yes!

Severin:

So I decided to start my institute in Hamburg. The Chancellor in Bochum allowed me to rent the first floor of a factory to create a 300 square meter laboratory. There I got my first assistants and coworkers, my first technicians. So I was still with Philips. Philips was very polite in helping us to build up the institute. So I was always fourteen days here and fourteen days in Hamburg. One and a half years we were in Hamburg.

Nebeker:

Can you tell me how large the institute was, and has since become? When you started was it yourself and the people you had at Hamburg?

Severin:

Yes, just three scientific assistants, when we started here we had about seven or so, and when we ended it was twelve. Twelve scientific people.

Nebeker:

Were you the only professor in the institute?

Severin:

In the beginning, yes. But then I had one coworker – it was a man who wrote his master thesis under my direction in Goettingen, and he made his Habilitation in Goettingen when I was already in Hamburg or here, and I could win him for Bochum. He came as a Privatdozent, and after a period of three years he got the APL Professor. That means that he really has a title, but he is still paid as assistant. A short while afterwards, I got a second young man of this type from Braunschweig. And then we had three of us here in this area, and this is almost still so. One left, then another one is coming.

Nebeker:

And what had been the main areas of research here at the Institute when you were directing it?

Severin:

We started again of course with some ferrite projects, where we of course didn't make any materials ourselves because this would be too large and almost impossible for an Institute of high frequency techniques. We got the materials from Philips, and we had a tight connection to Philips in this area. But we audited some theoretical work, because the computers always got more extended, so we had to do some theoretical works. This came back to the diffraction problem, but now in another sense – more complicated structures. Of course we did also some work on antennas, which was one group. My first Privatdozent, he got a Chair at the University of Wuppertal later on, he was working on microwave optics in another sense as we did before and made fiber lines. He was also working on transmission problems along fiber lines.

Nebeker:

I see this work on symmetrical horn antennas?

Severin:

Yes. This was Dr. Hansen one of my assistants, and he has now also the Chair in Wuppertal. He was mostly interested in theoretical problems. He only has his doctor's thesis as in theory and measurement, and afterwards more and more he made only theoretical work. This is what I said with antennas.

Educational Legacy

Nebeker:

Have you had many research students who have gotten the Ph.D. here?

Severin:

About thirty.

Nebeker:

Thirty!

Severin:

Thirty in this time. You cannot count the first years because we had very much to do with building up the practica and lessons and so on. So the first Ph.D. really was a man from Philips, a coworker from former times, and this was already in 1969. But then the real Ph.D.s here from the Institute made their work here, not in Hamburg, and this started in 1972 or so.

Nebeker:

I see. So from 1972 until when did you retire?

Severin:

1985

Nebeker:

So that is quite a lot of students in that period! I see you've had quite a bit of professional activity – with different societies, chairman of the Northwest German Physical Society, and Member of the International Union of Radio Science, and so on – Can you tell me about your work with URSI?

Severin:

This is divided in groups in different countries, so my membership here concerns the German committee. We have every year a meeting in Kleinheubach. This is a small place in South Germany, and so we are preparing papers for this meeting. I was for two or three periods, the second chairman in the German group. During this time I visited International URSI meetings, the last one in Prague 1959 or so. In 1972 it was in Breslau , and it was always changing. There is an agreement on the international basis, it's always one in the States, another one in Europe. Every three years, that means every six years over here.

Nebeker:

And you've been a member a long time – since 1963 it says here. Do you feel that that work has been important?

Severin:

I think so yes. A good possibility to meet people, colleagues from all over the world.

Nebeker:

I wanted to ask you about if there are any books that have been very important to you in your own work. Sometimes engineers will tell me something like “Terman's Radio Engineer's Handbook was my bible.” or some other book was very important to them. Are there any books that you felt were extremely important to your work?

Severin:

Yes. I would say first of all that the Physics of G. Joos was a real teacher for me.