Our society seems to have drifted away from formal Thank You’s. But this isn’t the time to ignore the tradition. You should ask each interviewer for a business card, mainly for the purpose of sending a thank you note. I personally find it hugely respectful and professional when I receive a written Thank You card but I believe it’s OK to send an email thank you. In the email, you want to 1) thank them for taking valuable time from their schedule to meet with you 2) reiterate your interest in their company and the role they are hiring 3) remind them of something you discussed about yourself that uniquely qualifies you for the job/company. In closing your email you can show your willingness to have a follow-up phone discussion or in-person visit, if needed.