Which of these sensors generates its own voltages and may be plugged directly into the head box?

The correct answer consists of thermocouples and piezoelectric crystal bands because both of these sensors are designed to generate their own electrical voltages, making them suitable for direct connection to the head box in a sleep study setting.

Thermocouples function on the principle of measuring temperature through the voltage generated when two different metals are joined at one end and exposed to temperature variations. This generated voltage provides a direct measure of temperature and is well-suited for monitoring temperature changes during sleep.

Piezoelectric crystal bands operate based on the piezoelectric effect, where mechanical stress applied to the crystal generates an electrical charge. These bands are often used for measuring respiratory effort, as they can detect changes in chest or abdominal movement during breathing. The inherent ability of these sensors to produce voltage means they can be plugged directly into the head box without needing additional conversion or amplification.

In contrast, options that include sensors like thermistors or inductive plethysmographs either do not generate their own voltage or require additional components for signal processing. Thermistors, while highly sensitive temperature sensors, do not produce voltage independently and generally need to be part of a circuit that converts resistance changes into a voltage signal. Inductive plethysmographs measure changes in inductance related to