Which type of digitizer senses a wave that travels at the speed of sound and computes position from acoustic time-of-flight measurements?

Introduction / Context:
Digitizing tablets and pens use several physical principles to detect the cursor's position. Some rely on electric fields, others on magnetic induction, and another family uses sound waves. Identifying which technology measures a propagating wave at the speed of sound requires understanding of the underlying sensing physics.

Given Data / Assumptions:

• A wave traveling at the speed of sound is mentioned explicitly.
• Position is inferred from time-of-flight between emitters and sensors.
• We compare electrostatic, sonic, electromagnetic, and capacitive approaches.

Concept / Approach:
Sonic digitizers use ultrasonic transducers. Either the pen emits an ultrasonic pulse and multiple receivers on the tablet measure arrival times, or the tablet emits and the pen receives. Using time = distance / speed, the controller triangulates x,y. Electrostatic/capacitive systems sense electric field coupling and do not involve acoustic propagation. Electromagnetic systems use inductive coupling and magnetic fields, not sound.

Step-by-Step Solution:
Match the clue “speed of sound” to acoustic/ultrasonic sensing.Recognize that triangulation from arrival times determines coordinates.Select “Sonic” as the correct digitizer type.

Verification / Alternative check:
Vendor literature for sonic digitizers describes calibration using known transducer spacing and computing intersections from time-of-flight differences, confirming the sound-based method.

Why Other Options Are Wrong:
Electrostatic/Capacitive: measure electric field coupling, not acoustic waves.Electromagnetic: uses magnetic induction; wave speed is not the speed of sound.None of the above: incorrect because “Sonic” precisely matches the description.

Common Pitfalls:
Confusing capacitive touch (common in phones) with digitizers; ignoring environmental noise—air currents and reflections can affect sonic accuracy; neglecting temperature compensation since speed of sound varies with temperature.

Final Answer:
Sonic