The development of THz electron devices by coupling time-dependent electron quantum transport and electromagnetism is studied. A novel proposal for a frequency multiplier that generates a 1 THz harmonic from a 200 GHz input signal is described in detail with numerical simulations. The proposed electron device is a nanoscale double-gate field-effect transistor with a double barrier tunneling structure. Its functionality is based on dynamically modulated tunneling: a gate voltage forces the oscillation of the double barrier at frequencies comparable to the inverse of the electron transit time. This example points out the viability of using driven tunneling phenomena to develop room-temperature electron device for THz applications that can reduce the cost, the size and the complexity of present prototypes. (C) 2007 Elsevier Ltd. All rights reserved.