Advantages for ultrasonic Pulmonary Function Testing device: 1.No drift, no preheating, no calibration, no maintenance (flow measurement only depends on time measurement and sensor geometry, so no calibration) 2.Non-contact flow detection technology, the ultrasound probe does not touch the patient, preventing cross infection 3.High measurement accuracy, especially for very weak airflow 4.Direct flow measurement, wide linear range, no nonlinear distortion 5.There are no obstacles in the middle of the breathing tube, no breathing resistance 6.Not afraid of water vapor, real-time BTPS correction 7.The sensor is not affected by humidity, air pressure and pollution 8.Can obtain gas concentration information at the same time 9.Greatly expanded the scope of application: adults-children-newborns