The body of a traditional acoustic upright bass is a wooden box. The material and shape properties of the body have a large influence on the tonal quality; the bass’ body is shaped, tuned in a way that it easily resonates at desired frequencies. This tuning is what gives the acoustic instrument its specific character.
The acoustic bass needs a large surface to drive air in motion, while the electric upright bass delegates this job to the amplifier and speaker cabinet. The essence of an electric upright bass is so to say that it doesn't need a soundbox to drive air in motion.
But if you eliminate the soundbox, you also remove the tonal character of the soundbox. So the idea of this body design is to remove the large surface but keep the wood resonances. To achieve this, the body consists of a bundle of 18 wooden slats in 5 layers (4x fichte, 1x maple), that is held together at top and bottom ends so the middle is free to resonate.
And then you need something to distribute the strings vibrational energy over the bundle of wooden slats. To accomplish this, the tailpiece is attached to an aramid cable (red line). This aramid cable runs all the way through the body; from the tailpiece to a free floating hinge at the bottom of the bass up through the back of body. A cascade of carbon tubes between the layers (green) distributes the strings' energy over the body. And so the body becomes a vibrant, lightweight, layered spring.
Since the 'body surface' is very small, the acoustic volume is comparable to that of a solid body electric bass guitar. The small surface also means it is much less susceptible to feedback problems than large surface basses.
I use aramid because aramid is very strong material and has extremely low stretch under tension (negligible for this purpose), which allows to work with relatively thin and plyable cables.