In the United States there is generally no requirement for a working
prototype in order to receive a patent on an invention. The law
(35USC112 paragraph 1) does require that the invention be enabled:

"The specification shall contain a written description of the
invention, and of the manner and process of making and using it, in
such full, clear, concise, and exact terms as to enable any person
skilled in the art to which it pertains, or with which it is most
nearly connected, to make and use the same, and shall set forth the
best mode contemplated by the inventor of carrying out his invention."

In other words, a naked idea is not patentable. It must be a fully
dressed invention.

Richard Tanzer
patent agent