Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you like the idea of investing in patent-rich companies with significant growth potential, the Guggenheim Ocean Tomo Growth Index ETF (NYSE: OTR) could save you a lot of trouble. Instead of trying to figure out which such companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The patent ETF's expense ratio -- its annual fee -- is 0.65%. That's a bit higher than many ETFs, but also considerably lower than most stock mutual funds. The ETF is small, too, so if you're thinking of buying, beware of occasionally large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has performed reasonably, but it's also very young, with just a few years on the books. It outperformed the S&P 500, on average, over the past three years, and is ahead of it so far this year. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a very low turnover rate of 6%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several patent-rich companies had strong performances over the past year. Elan (NYSE: ELN), for example, has doubled over the past year, despite having taken a hit recently after posting disappointing revenue, bigger-than-expected losses, and shrinking margins. Still, long-term investors are quite bullish on the prospects for its multiple sclerosis drug Tysabri, thinking it could be a big blockbuster.

Boeing (NYSE: BA) gained 10%, with investors relieved that its long-delayed 787 Dreamliner finally debuted and happy about its robust backlog of orders. But all is not rosy, as Air India recently demanded a $1 billion payment to compensate for the late Dreamliner delivery; if other customers follow suit, Boeing might have a rather big headache. Its near-term future is a little more uncertain than many would like.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. Ford (NYSE: F), for example, shrank by 15%, and for several reasons, that only makes it look like more of a bargain: It's poised to profit from our finally recovering economy, it's expanding in emerging markets, it's competing successfully against the other big carmakers, and it's even catching up to Toyota in environmentally friendly vehicles.

Vertex Pharmaceuticals (Nasdaq: VRTX) shed 11%, with some investors disillusioned with the potential for its Hepatitis C drug Incivek. (Once the virus is vanquished, patients won't need the drug any longer.) Still, Incivek is selling briskly, and bulls are quite excited about the prospects for its cystic fibrosis drug, Kalydeco.

The big picture
Patents can be powerful assets, paving the way for innovative (and potentially lucrative) new products and even sometimes simply generating licensing revenue. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about the 5 ETFs That Could Soar in 2012. And if you're looking for some great investments beyond ETFs, consider these 12 Dividend Stocks for 2012.