What are requirements for a patent?

Here are for obtaining a patent under U.S. law.

Requirements for Obtaining a Patent

Patent Attorney in Vietnam

1. To obtain a patent in the U.S., you must demonstrate that the idea is:

 -Eligible for patent protection

-Novel and does not infringe on the patents of another

-Non-obvious

-Useful

2. Once you have determined that your patent meets the above through development of your idea and a thorough patent search, you would then prepare and file your patent application along with the requisite filing fee.

Is It Necessary to Have a Prototype or Are the Designs Enough? and How Specific Do the Designs Need to Be?

While a prototype can be helpful in supporting your patent application, a working prototype is not required to apply for patent protection. However, you are required to describe your invention with a level of detail such that a skilled individual could recreate your invention from the specifications. Essentially, you will need to provide as much detail as possible.

Is It Possible to Get a Patent for Free?

You will need to pay the filing fees to the USPTO associated with your patent application. You can find a schedule of the USPTO fees here. Additionally, given the complexities of the patent process, you may also want to retain a patent attorney to assist you to improve the likelihood that your application will be approved.

Source: Quora