The SparkFun Ultrasonic Distance Sensor - TCT40 (sen-24805) a user-friendly upgrade to the popular HC-SR04 sensor, offers non-contact distance measurement from 2cm to 400cm with an accuracy of 3mm.

I purchased one of each of these cheap sensors recently from aliexpress for testing purposes. Compared with the ubiquitous HC-SR04 (*), I liked the idea of having a combined emitter/receiver, i.e.

Abstract: Acoustic emission (AE) and ultrasonic sensors are integral for interpreting elastic wave data in laboratory and field experiments. This study introduces a broadband calibration toolbox for ...

Abstract: Proximity sensing is of great importance for robot control during human–robot collaboration (HRC). Commonly used machine vision sensors or photodetectors are subjected to the light block ...