This is a top-down 2D rebuild of the same physical Materials Recovery Facility (MRF) line: a mixed conveyor stream passes three physically distinct sorting stages, staged one after another along the belt (drag the canvas to pan along its length):
1. Magnetic drum — pulls FERROUS metal (steel) off the belt
2. NIR optical sort — classifies polymers by near-infrared
reflectance, then fires an air jet
3. Eddy-current separator (ECS) — launches conductive NON-
ferrous metal (aluminum) further than
everything else at the belt's end
Eddy-current separation uses a rotor with alternating magnetic poles spinning faster than the belt. Its changing flux induces eddy currents in any conductive item (Lenz's law); those currents create their own opposing magnetic field, which repels the item — a real, non-contact force that only acts on metals. The top-down view can't draw height directly, so each item's airborne hop is tracked as a hidden vertical state driven by real gravity and drawn as a growing/shrinking drop-shadow — the same projectile timing as the 3D version, just rendered as a shadow instead of a camera-visible arc:
F_eddy ∝ σ · B² · ω · r (σ = conductivity)
Launch range: R = v·t_fall + Δv_eddy·t_fall
Non-conductive items get no Δv_eddy → shorter range
→ fall into "residual", metal lands further → "metals" bin
NIR optical sorting shines near-infrared light on each item; every polymer (PET, HDPE, …) reflects a distinct absorption spectrum, and a classifier fires a compressed-air jet to eject the correct type. Moisture, food residue and grime scatter the signal, so classification success probability falls as contamination rises:
P(correct ID) = clamp(accuracy − 0.6 × contamination, 0.05, 0.99)
- Belt speed — sets throughput; faster belts also carry more inertia into the eddy-current launch.
- Contamination rate — fraction of the stream that is un-sortable residue; it also jams the NIR classifier and can trigger false-positive air jets.
- NIR accuracy — the sensor's baseline classification quality before contamination is subtracted.
- Eddy-current field strength — how much extra launch velocity aluminum gets; too weak and it falls short into the residual bin with everything else.
Purity and recovery are exactly the two numbers real MRFs are graded on: purity keeps buyers paying full price for the recovered bale, recovery (diversion rate) is what actually stays out of the landfill. The strip below the main view is a live dashboard of both, plus throughput and overall diversion.