Final answer:
The crystal in an ultrasound device is housed within the transducer. It is key to both emitting and receiving the ultrasonic waves used for medical imaging.
Step-by-step explanation:
The crystal in an ultrasound device, which exhibits the piezoelectric effect and is responsible for both transmitting and receiving ultrasonic waves, is housed within the transducer section of the device. The transducer acts as the sender of high-frequency sound waves, which travel into the body tissues, and as the receiver that captures the echoes reflected from the tissue boundaries. Thus, in an ultrasound device, the 'd. transducer' houses the crystal.
Furthermore, this process assists in medical diagnoses, such as fetal observation during pregnancy. When performing clinical ultrasound, a coupling agent like gel is applied to efficiently conduct sound between the transducer and the skin, minimizing the reflection and allowing for clearer imaging.