The present invention relates to a flexible antenna that can harvest energy for short-range wireless communication such as near-field communication. The flexible antenna comprises a plurality of metal loops arranged in a concentric manner and disposed on a flexible base substrate. In some embodiments the flexible antenna can be stretchable. In some embodiments, the flexible antenna can be conformal. A flexible device comprising a chip or an integrated circuit electrically connected to the antenna can be used to perform one or more desirable functions (including user authentication, mobile payments, and/or location tracking). The flexible device can adhere to a surface such as the skin of a user.