what is the status of an intern compared to a full-time employee with regard to intellectual property rights.

Section 101 fof the copyright act defines a "work made for hire" as, among other things, "a work prepared by an employer within the scope of his or her employement." You'll note that there is no mention of whether that employee is "permanent" or "full-time" as opposed to being an "intern" or part-time. The analysis you are asking about can get very complicated, but just to give you some pointers, some considerations might be whether the employer has control over your schedule, whether the work is done at the employer's location, whether equipment is provided by the employer, and whether the employer is in the business of producing the type of work in question. The U.S Copyright Office has a very detailed circular, No. 9, that explains the analysis quite well. You'll find a link below. You might also consider hiring any intellectual property or entertainment attorney to further analyze your particular fact pattern.

The following is not legal advice and should not be relied upon to take or refrain from taking any action.

The short answer is no. The real question, however, is whether you own any intellectual property rights in your "system" and, if so, what are those rights and what should you do with them?

Barry provides sage advice for you to consider when thinking through the copyright implications of disclosing your "system" -- whatever that means -- to your employer. I note in passing that the vast majority of interns ARE employees; "intern" being simple shorthand for someone who's a temporary employee. If you've written down a description of your "system" then you own the copyright that attaches to that description (the description being a"work of authorship" under copyright law). You should affix on the bottom of each page of that work the legend: "Copyright, [insert year first written down], [insert your name]. All rights reserved."

Your copyright provides you with the exclusive right to reproduce and distribute that particular work. It does NOT, however, provide you with the exclusive right to use your "system" or to sell or license to anyone else the right to use that "system." The exclusive right to use the "system" must come from patent law -- not copyright law.

If you think that the "system" you have developed is (1) novel (i.e., new -- as in never been done before) and (2) not obvious in light of all the other "systems" that already exist in the marketplace or in the literature then you need to speak with a patent attorney to consider whether your "system" is patentable. Methods of doing things are, nowadays, often NOT patentable unless the described process is tied to a particular machine or apparatus or if it transforms a particular article into a different state or thing. Your patent attorney will be able to discuss that patent requirement with you and, if so, whether it is cost effective to seek patent protection.

At the end of the day, you need to seriously consider the benefits of disclosing your "system" to your employer (those benefits being the possibility of a permanent job, being seen as a team player with company loyalty, someone with savvy insight into your particular business, and someone with initiative) with whatever benefits you may gain by keeping the "system" to yourself (with its attendant high cost of acquiring those benefits -- i.e., the cost and fees to file a patent application, to file one or more copyright registrations, to draft various non-disclosure agreements, and to negotiate and draft various license agreements, etc.). You should discuss that fact-intensive calculus with a patent attorney.

NOTE: if you chose to disclose your "system" publicly before filing a patent application some of the consequences of that decision are that you will very likely lose all foreign patent rights, you will have only 12 months to file a US patent application, and all the information about the "system" will no longer qualify as a trade secret. Only your patent attorney can tell you if disclosing to your employer would constitute a "public" disclosure to trigger these consequences. If you chose to disclose, you should consider publishing your "system" in a trade journal to establish credibility within your industry and to beef up your resume.

Again, speak with a patent attorney before you make any decisions.

Since you design the system before the internship, it is not relevant whether you are now an intern or an employee.
It is not automatic that all IP created while employed belongs to the employer. It usually depends on the contract between employer and employee, and on the subject matter created. There are no right for a Plastic manufacturer for a non-related invention in turbine engines. You need to discuss the matter with an attorney that know intellectual property and labor law (check attorney credentials).