Patents CANNOT be searched by keyword alone. The U.S. and other countries have classification systems that categorize issued and pending patents into technology groups identified by a number, and these must be used in order to do a thorough search. Start with a keyword search in Google Patents to identify relevant patents, examine their classifications, and then search key classifications. Google Patents may be used on its own to identify just one or two relevant patents.
Steps to Starting a Preliminary U.S. Patent Search
Google Patents covers the entire collection of granted patents and published patent applications from the USPTO, EPO, and WIPO. US patent documents date back to 1790, EPO and WIPO to 1978. Google features the full text of pre-1976 USPTO patents, but be aware that this text was generated with an Optical Character Recognition (OCR) program and may contain errors.