Contact-free measurement of respiratory rate using infrared and vibration sensors

• A multi-modal system for respiratory rate measurement is described.
• The multi-modal system consists of two PIR sensors and a vibration sensor.
• An error of less than 2 breathings/min is achieved for different lying positions.
• Fusion of the data of different types of sensors provides a robust respiratory monitoring.
• The multi-modal system is capable of detecting sleep apnea as well.

Respiratory rate is an essential parameter in many practical applications such as apnea detection, patient monitoring, and elderly people monitoring. In this paper, we describe a novel method and a contact-free multi-modal system which is capable of detecting human breathing activity. The multimodal system, which uses both differential pyro-electric infrared (PIR) and vibration sensors, can also estimate the respiratory rate. Vibration sensors pick up small vibrations due to the breathing activity. Similarly, PIR sensors pick up the thoracic movements. Sensor signals are sampled using a microprocessor board and analyzed on a laptop computer. Sensor signals are processed using wavelet analysis and empirical mode decomposition (EMD). Since breathing is almost periodic, a new multi-modal average magnitude difference function (AMDF) is used to detect the periodicity and the period in the processed signals. By fusing the data of two different types of sensors we achieve a more robust and reliable contact-free human breathing activity detection system compared to systems using only one specific type of sensors.