You have (at least) the following three ways to Sendai.
(1) Fly to the Sendai Aiprot (SDJ). We have very few international flights directly coming to the Sendai Airport. We have a few connecting flights to the Sendai Airport from the Tokyo Narita Airport (NRT), the Kansai International Airport (KIX) and the Nagoya Airport (NGO). You can take a train from the Sendai Airport to the Sendai Station. It takes 25 minutes and 650 yen.
(2) Fly to the Tokyo Narita Airport (NRT), then take trains. Take Narita Express of JR to the Tokyo Station first. It takes about one hour. Then take the Tohoku Shinkansen to Sendai. It takes one hour and a half to two hours. You can buy a ticket up to Sendai at the Narita Airport Station of JR. The fare depends on the kind of an express train, but it is around 14,000 yen. Do not get confused at another railway company, Keisei Line, at the Narita Airport Station.
(3) Fly to the Tokyo Haneda Airport (HND), then take trains. Take Tokyo Monorail to Hamamatsucho first and then take JR Line to Tokyo. It takes about 30 minutes. You can buy a ticket up to the Tokyo Station for 650 yen at the Haneda Airport Station of Tokyo Monorail. Do not get confused at another railway company, Keikyu Line, at the Haneda Airport Station. Then take the Tohoku Shinkansen to Sendai. You can buy a ticket within the Tokyo Station of JR. The fare depends on the kind of an express train, but it is around 11,000 yen. It takes one hour and a half to two hours.
The conference site, Sakura Hall, Tohoku University, is within a walking distance from the Sendai Station. Here is a map for Sakura Hall.