A medical device may be configured to transmit energy from a position outside of a subject's body to a position inside the subject's body. The device may include a flexible substrate having a thickness of between 5 and 100 micrometers and a flexible antenna comprising between 10 and 15 windings on a first surface of the flexible substrate, the antenna having a transmission frequency of between 6.4 to 8.3 MHz, and wherein the antenna is configured to transmit energy to a penetration depth of at least 1 cm into the subject's body. The device may also include an adhesive disposed on at least one surface of the flexible substrate for adhering to skin of the subject.
