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Profª. Zoya Popovic

Speech by Professor Zoya Popovic

Thank you Senor Rector Magnifico Juan Romo, and thanks to all academic authorities, colleagues and friends. I am humbled by this honor and hope to deserve it through continued collaborations with UC3M.  Receiving my first PhD from Caltech took a considerable amount of work and dedication. Earning this doctorate from Carlos III took a lot more effort; in fact, an entire career. It was also especially difficult due to my very strict and demanding advisor Prof. Luis Enrique Garcia Munoz (Quique). I will never be able to fully repay his many kindnesses, or the incredible hospitality I experienced at UC3M from colleagues, students and staff. 

I am a radio engineer and my research is in applied electromagnetics and analog high frequency electronics. We are users of an incredible resource called the electromagnetic spectrum. We design and constantly improve and innovate devices that control air traffic, allow weather predictions, cook our food, and are the main part of the cell phone in your pocket or purse. Radio engineering is an old field with its roots in Maxwell’s theory and pioneering discoveries by giants such as Faraday, Hertz and Tesla. The current modern radio is no different in principle than the first superheterodyne transceiver invented by Armstrong over 100 years ago - it is such a good idea that nobody came up with a better one. However, the technology improved and today we can make radios handle a lot more information in a device the size of a watch. These devices are very popular and a large part of the global economy - the number of wireless phones on the planet exceeded the number of people in October 2014 and in the 1st quarter of 2015 the i-phone made Apple $50 billion. (I would not be American if I did not include a $ sign.)

There are two main challenges in new radios due to the exponential increase in the amount of information people want to send through the air: (1) energy efficiency when transmitting and (2) sensitivity when receiving. Surprisingly, globally telecommunications consumes as much energy as aviation. The main power consumer in a radio system is the high-frequency (GHz) power amplifier of the transmitter, e.g. in a satellite it is responsible for 40% of the total power consumption. Consider an older base-station that used about 20% efficient 100-W amplifiers in each antenna sector (direction). This implies 500W of heat produced and the transmitters need to be cooled since electronics does not like to operate when hot. This means even more power needed by the fridge, so the energy bill increases further. If instead of 20% we can increase the efficiency to 50%, about 4 times less heat is produced and the cost dramatically drops. As a bonus, manufacturers can refer to their technology as “green”.  My research has enabled new types of very efficient transmitters using integrated circuits in advanced semiconductors like gallium nitride. For example, we designed chips for Lockheed Martin that enable large satellite transmit phased array antennas to operate in space because they get less hot while transmitting 30,000 channels. The same type of transmitters can improve high power (many kilowatt) applications such as radar and industrial heating and sterilization. 

On the other hand, when a radio receives information, the signal is incredibly weak. Radios are really astonishing – they can receive 10^15 times lower power than they transmit! (This is a 1 followed by 15 zeros!) Radio waves (EM waves) travel large distances, through and around objects, and are attenuated heavily. The received signals are not only tiny but also buried in noise, so we need to add as little noise as possible inside the receiver in order to recover the information with high fidelity. This can be done by cooling the electronics, which is expensive and takes energy. My group is working on very low noise receivers that do not require cooling, and this is a common interest with colleagues at UC3M, who have developed new ways to recover ultra-low power signals coming from distant galaxies and at very high frequencies. During my stay as Banco Santander Chair of Excellence in 2018/2019, we have together been able to analyze and understand the fundamental limitations in radio-receiver noise reduction. We are now extending this research to new types of ultra-sensitive quantum electric field detectors, and a former UC3M PhD student is spending a few years in my group working in this new exciting area.  

One of the largest challenges we are facing in my field is the lack of young people who want to learn applied electromagnetics and radio-frequency analog electronics. It is considered to be “black magic” and a very difficult subject. Yet, there are so many jobs waiting for trained people in this field, and not just for cellular communications and radar. Emerging fields of quantum sensing, time keeping, navigation and computing are in desperate need of experts in our field since most atoms/molecules have transitions at radio frequencies, and cryogenic readout circuits for quantum computers are also done at radio frequencies. One of the goals throughout my career has been to motivate students to get into our field, and to be able to learn from books and by deep thinking. 

Although I feel that I also still have a lot to learn, I am very proud of my students’ achievements and of how they have become real experts and honest people and contributors. I have had the incredible good fortune to have fantastic students with over 60 graduated PhDs and 20 current ones, and also wonderful role models and mentors, starting from my late father Prof. Branko Popovic who had many Spanish colleagues, and my PhD advisor Prof. Dave Rutledge, my second PhD advisor here at UC3M, and my husband and colleague Prof. Dana Anderson. I can only hope that I transferred some of their knowledge and wisdom to students in Colorado and Madrid, so that they can continue innovating and making a better world. I am passionate about increasing the number of excellent women engineers and scientists, with 9 women Ph.D. students currently in my group (almost 50%!), and personally contributed by giving birth to three girls, with 66.7\% retention rate in STEM. 

When I was honored with the UC3M Chair of Excellence in 2018, I had little idea of how much it would enrich not only my professional life, but also my personal life. My day would start by going to the bus stop near Retiro and waiting for the bus that had Quique’s smiling face peaking out through the window. On the 30-minute ride to Leganes, we discussed millimeter-wave receivers, quantum mechanics, superheroes and what the next thing about Spain I need to learn. By the time I came to my office, which Dani Segovia so graciously surrendered to me for many months, the day was already productive. I worked with many excellent students at UC3M, several of my students from the US visited, and we got a number of joint papers published only after a few months of collaboration. I could talk more about our joint papers on millimeter-wave receivers, microwave wireless powering tee-shirts, etc. and you can read them if you are interested. What you cannot read about are: 

Professional visits to Polytechnic of Madrid, Automata Univ. of Madrid and Barcelona, Univ. of Malaga, Univ. in Alcala de Henares, Polytechnic of Valencia, Univ. of Cantabria in Santander, attending the National URSI in Granada, etc. that were all terrific and led to new collaborations;

many outings with Quique, Maria and the superheroes Lara and Martin where I got a deep appreciation of Spanish history and culture; 

horchatas and great conversations with Dani (partly as a reward for cleaning his office);

tennis a few times per week with Masters student Monica and dinner with her family from Murcia; 

big BBQ party and hiking at Luis Emilio’s country home with the whole group;

walks with Ana in Retiro; wine tasting with Eva and Mati;

museum tours and tinto di veranos with Gabriel; 

invitation to Adri’s and Lula’s wedding in September; 

visits to Toledo and La Granja (with Quique), Segovia, Cordoba, Avila (with Dani), Barcelona, Valencia, Bilbao, San Sebastian, Burgos, and so many other fantastic and diverse places. In fact, I feel that I could write a tour guide for visitors to Spain. 

And so, 6 months went by extremely quickly and Madrid became like a third home to me (my first being Belgrade, Serbia). UC3M is a treasured part of my life, and also a part of my research group in Colorado and my family in the US. This is a great and rare gift. Today as I am dressed in this robe, I feel like I am officially becoming in part Spanish. Except that this speech is in English, so prometo intentar aprender espanol. Espero sequir colaborando y los invito a todos a visitarnos en Colorado.