There are three primary measurement geometries of an ultrasound experiment: transmission, pulse-echo, and pitch-catch (Figure ). In a transmission measurement, one ultrasonic transducer is used to produce the sound wave, which goes through the sample and is measured on the other side by a receiving transducer. In pulse-echo mode, the same transducer is used to send in the ultrasound and measure the signals that are reflected off the sample. In pitch-catch mode, the sending transducer is placed at an angle to the sample and the reflected waves are measured by a similarly angled transducer.