Flying cars are the perennial example of a technology from the future that we may never see come to light. Seemingly just as impossible of a pipe dream is male birth control.

How is that possible? While the technological world will need a breakthrough in miniaturization before we ever see flying cars, science has been perfecting birth control in females since the first intrauterine device in 1909.

Here is a look at some of the most promising methods of male birth control, the amazing science behind them and where they are in development.

The 'male pill'

There has been a push to get an oral contraceptive for men on the market, much like the female "pill." Many methods have been tried, but some of the most promising seem to have fallen by the wayside.

The so-called "Bright Pill" was being developed from Israel's Bar-Ilan University researchers and claimed to be five years away from hitting the market back in 2010. But with no major updates on their clinical trial process, the future looks less than, well, bright.

Other methods are still being tested, including Adjudin, an analog of the chemotherapy drug lonidamine. It works by disrupting cell adhesion during spermatogenesis, or the creation of sperm.

However, this drug could never work as an oral contraceptive, as the dosage levels required would damage muscles and the liver. The future of this drug likely lives in localized injections or implantable devices.

JQ1

JQ1 is a chemical compound that works as a selective inhibitor of BRDT, a protein required for spermatogenesis. While a delivery method hasn't been discussed for this method, it has been proven to block the creation of sperm without the usual negative side effects of hormonal contraceptives. Without a planned delivery method, there's no timeline for when this might hit the market.

Ultrasound

This method is still in early stages, but initial testing showed some promising results. A 2012 study found that ultrasound treatments can reduce sperm counts to below fertile levels in both rats and dogs.

However, no human testing has been conducted yet, and the amount of treatments required for human subjects is currently unknown, with rats and dogs requiring two and three, respectively, 15-minute ultrasound sessions over as many days.

Reversible inhibition of sperm under guidance (RISUG)

The RISUG method is by far the most promising and furthest-developed method, and it's backed up by some really cool science. Essentially, this method is performed by injecting the vas deferens (the tube that carries sperm) with a polymer gel that uses some magic-level science on that sperm.

It creates a positive electrical charge, which rips the negative ions out of the sperm, rendering them inert. Or, in even more scientific terms, “Within an hour, the drugs produce an electrical charge that nullifies the electrical charge of the spermatozoa, preventing it from penetrating the ovum,” according to Dr. Sujoy Guha, who developed the RISUG method.

The cost is less than the syringe used to administer it, and the effectiveness is 1 in 250, or 99.6 percent (though that one case is believed to have been caused by an improper injection). The duration of RISUG is 10 years or more and there is a likely 100 percent chance of reversibility (only been tested in primates so far).

Those numbers are astounding, and handily beat even the most effective methods of female birth control. So why is this not available right now?

Well, the RISUG method is still in Phase III clinical trials in India, while a similar method called VasalGel is undergoing clinical trials in the U.S. VasalGel is hopeful to be on the market by 2016, and with a recent funding boom Jan. 30, they might just get there.