Sensor Selection

What is the proper sensor, or maybe method for a robot to distinguish between cardboard (i.e. cardboard boxes) and wood. And the same with glass and transparent-plastic?

What is the proper sensor, set of sensors, or maybe a method to make a robot categorize each item?

@salman12 Not an easy question to answer, so looking forward to seeing what ideas the community has. Take a look into the sensor technology used in automated recycling sorting, such as:

Some preliminary ideas:
Ferrous materials:
Use magnetic principles

Non-ferrous materials:
Eddy Current and compare to database

Destructive testing
Apply known pressure (ex a solid metal cone) and measure the deformation and compare to a database

Non-destructive testing
Volume (displacement of known liquid) vs. weight measurement gives density
Light transmission & reflectivity
Color (some help with differentiation)
Camera (compare “grain”)
Humidity (wood)
Sound (ex: glass ball hitting the surface should produce a certain pitch within a range).

Wish there was a simple “all in one” sensor.