A novel sound sensor and its package used in lung sound diagnosis

Auscultation method has been used since the early 19th century in diagnostics of heart and lung diseases. Traditional stethoscope coupled with ears of physicians detects the heart and lung sound, and it is formed by microphone, air chamber and other infrastructures. However, some disadvantages exist in this kind of detecting tools, such as bulky size, friction noise due to hand-held, and inconvenience in long-term continuing monitoring, making it impossible to be integrated with clothing and hard to be interfaced with chest or inner cloth. A novel sound sensor used in lung sound detection with small size and high sensitivity will be presented in this paper. The sound sensor and its packaging are based on asymmetrically-gapped cantilever, consisting of a movable proof mass and three connection beams with two parallel beams that integrate one piezoelectric element at the top side and one mechanical beam at the bottom of sensor. As an example of lung sound diagnosis, a sound sensor with 5g weight, 86V/g sensitivity and 40ng/√Hz minimum detection acceleration is used in this paper. Due to the advantage of small size, high sensitivity and low cost, this sensor can be used in subtle sound and acceleration detection by a long term continuous monitoring mode. The application of this sound sensor will be presented in details in the lung sound detection, with particular focus on the deep breath induced sound. The monitoring experimental results show that this new sensor makes the detection of breathing clearer and easier, and heart sound can be sensed during breath holding period. The test data for regular breathing, deep breathing, and breathing & holding cases will be reported. It has been observed that lung sound can be measured and consistent results have been achieved. In addition, heart sound was tried to be extracted from lung sound, and the heart rate for the measured person is found to be 62 pulses per minute for an individual tested.