Sensor system and method to detect overlapping objects

An apparatus, comprising:

• a first emitter positioned to emit a first signal toward a plane from a first side of the plane;
• a second emitter positioned to emit a second signal toward the plane from a second side of the plane, the second side of the plane opposed across a thickness of the plane from the first side of the plane, and the second signal different from the first signal;
• a first receiver positioned to receive the second signal that passes through the plane when the plane is unoccupied, and further positioned to receive the first signal which reflects from a first surface of an object when the object occupies at least a portion of the plane;
• a second receiver positioned to receive the second signal which reflects from a second surface of the object when the object occupies at least a portion of the plane, and further positioned to receive the first signal that passes through the plane when the plane is unoccupied, the second surface of the object opposed to the first surface of the object across a thickness of the object;
• and
• a circuitry coupled to the first receiver and at least the second receiver, the circuitry operable to determine the thickness of the object based on reflections of the first signal and the second signal detected respectively by the first receiver and second receiver when the object occupies at least a portion of the plane.