Ultrasound is an outpatient procedure requiring little preparation, which means a person does not have to be admitted to the hospital. Exams are usually administered in the hospital's radiology or imaging department in a small, specially equipped room, or, sometimes, a doctor's office. Sound is a mechanical wave that occurs when vibrations travel throughout a medium, such as air, blood, or body tissue. At a microscopic level, these vibrations consist of the collective oscillations of molecules or atoms about their undisturbed configurations. Ultrasound waves are generated in many commonly used consumer appliances, including ultrasonic cleaning baths, cool mist humidifiers, and antipest devices. Although humans cannot hear ultrasound, many animals can hear into the ultrasound regime. The method for producing sound always involves setting up a vibration in an object, called a transducer. Ordinary loudspeakers cannot be induced to vibrate efficiently at ultrasound frequencies. Instead, the transducers used to generate ultrasound are constructed of ceramic discs.