So is it possible that somebody could patent my design and sue me
laterwards for patent infringement even when my product sale started
before the other person's patent application's date and that over the
fact that my technology is completely open-source?? And is there any
open-source hardware licence available ??
In copyright law (in the United States, under the Copyright Act of 1976 which took effect January 1, 1978), the default rule is that everything that is capable of being copyrighted is immediately and automatically protected by copyright and that filing a copyright registration only increases your legal remedies. So, in copyright, there is infringement in the absence of an open source license, and you must contribute your copyright to the public domain or open source license it to protect users of the copyrighted work.
In patent law, the default rule is that nothing is protected by patent law unless a patent application is promptly filed after an event that triggers the deadline to file it (this is a somewhat complex and heavily litigated issue). Disclosure of the material aspects of a patent without applying of a patent within the required time period automatically puts it into the public domain so an open source licenses is not necessary to prevent patent liability.
This rule is primarily implemented through the doctrine of prior art. This doctrine can be invoked both in the patent application process (which concludes with a public notice during which the public can provide prior art and object to its issuance) and also as a defense to a patent infringement action. It can also be invoked in an action to have a patent that was issued cancelled administratively by the PTO (a procedure which is incidentally facing a legal challenge as to its validity on constitutional grounds).
In the application process, the burden of proof is on the patent applicant, while in the infringement defense and cancellation proceeding context, the patent is presumed valid and the burden of proof is on the challenger of its validity. But, in practice, burden of proof is rarely important, because there is evidence presented about the prior art that is not ambiguous.
About 50% of patent infringement lawsuits that go to trial result in a finding that the patent is invalid, although this is, in part, because where the patent is clearly valid the cases rarely go to trial. This high invalidity percentage is also due to the fact that the bar necessary to have a valid patent has risen rapidly in recent years. In 2001, 45% of business method patent applications were granted. In 2004, the grant percentage had dropped to 11%. Similarly, in January of 2004, only a little more than 2% of patent applications were rejected on Section 101 grounds which governs what is patentable, but by July of 2015, that percentage was about 15%.
The only reason to have an open source license for a patentable design would be to prevent someone from fearing a copyright lawsuit from using a design that is derivative of the one that you disclose.