In the future, defensive technology has advanced so much that weapons strong enough to kill an enemy soldier tend to cause unacceptable collateral damage. Sure, we can make a weapon that generates the force required to punch through a personal forcefield, but the blast tends to also destroy everything else within hundreds of meters making war a very messy and environmentally unfriendly business.
Then one day, a well intentioned inventor figures out how to cause oscillations in an object's effective mass causing gravitational waves to radiate from the object. These waves have the same average pull as the original object, but the oscillations cause an alternating plus and minus gravitational effect. Any effects that gravitational waves have on space-time are assumed to still apply.
The inventor quickly finds ways to manipulate these gravitational waves in pretty much all of the same ways that we can currently manipulate radio waves such as adjusting frequency, amplitude (measurable as plus or minus m/s²), directional transmission, etc.
The government funding his research quickly realizes that gravity is not affected by any known defensive technologies; so, they decide to take over the inventor's research and try to find a way to use gravitational waves to kill a person through their armor, shields, etc. without causing lots of collateral damage.
Given the nature of the human body, what is the ideal amplitude, frequency, and methodology required to kill a person with gravitational waves while minimizing collateral damage.
As per comments: While this would require a ridiculous, down-right stupid amount of power as per our current understanding of physics, assume his method relies on a handwavium mechanic that can be achieved with a power source that would not itself cause collateral damage.