I have not posted updates here for a while, but I work on this continually.  The latest possible technology that I will be trying to adapt is related to piezoelectric films and piezoelectric fibers.  I have seen several efforts to use piezo disks, but not these films.  As I am reading the history of these materials and devices, particularly polyvinyliden fluoride polymers -  https://en.wikipedia.org/wiki/Polyvinylidene_fluoride it goes back about 50 years.

There are many related topics that make this messy, and lots of people grabbing after money. Too much marketing and high priced things.

"piezo film", "piezoelectric film", "PVDF film", "PVDF energy harvesting", "piezoelectric energy harvesters", "piezoelectric nanogenerators", "piezoelectric polymers", and many more.

("piezoelectric film" OR "piezo film") ("gravimeter" OR "accelerometer") has close to 60,000 entry points.  Many of them false leads or hype.

These films, mounted along X Y Z axes with some fairly simple electronics for interface - plus some sophisticated algorithms for noise classification, management and reporting - should be able to beat the MEMS gravimeters (hyped up MEMS accelerometers sensitive enough to track the sun and moon, and - at high time of flight sampling rates - all kinds of imagine of masses.  My target is to map the interior of the moon, but lots of things found looking for how to do it.

The main reason I am excited about these films is they can support up to Gsps (samples per second)  or GHz data streams for time of flight.  The key issue I  realized many years ago is the need to use time of flight (gravity has exactly the same speed as light) for locating, characterizing and calibrating sources.  Once a source of gravitational (or electromagnetic) "noise" has been identified, it is no longer "noise" but a "signal" that can be used as a reference source. Since the natural thing it so find the strong noises first, that means many earth and solar system gravitational reference sources.  The strongest is NOT earthquakes. But rather atmospheric density fluctuations and flows. The reason they are "good" sources, is they can be independently verified by lidar and many 3D imaging methods now. Same with ocean waves and currents.  And subsurface imaging of seismic waves.

I have been learning how to design chips and PCBs.  How to order and manufacture test devices.  I have always known the data engineering and statistical side of the problem.

I measured the speed of gravity about 20 years ago.  I hope to get a device that any kid in high school or college or on their own, can build and use with readily available tools.  I have many of Arduino type processors, Raspberry Pi, Jetson, Ryzen and Intel devices for the data handling.  95 % of the problem is collecting and processing the data streams.

"It is not hard, just tedious".  I don't know how much 7312347343*434388234377234 might be, but it is not hard to get an exact answer - just tedious to work out by hand.  This problem is now "gravitational engineering".  Nothing really much unknown, just tedious working out of tedious details.