Electric-power free impulse point sound source generation system with bubble wrap bursting phenomena for simplified non-destructive testing

• The omnidirectional impulse sound is generated by bubble wrap bursting. • The electric-power free sound system for non-destructive testing is established. • The usability of this method is verified to detect a foreign object inside a pipe. Point sound sources help understand the sound characteristics of a concert hall or the cabin of a car, aircraft, or construction machinery. In some cases, sound sources do not require the same level of accuracy and repeatability as the above, for instance, in echolocation. Humans can use echolocation to define objects’ distance, direction, and size by emitting sound or ultrasound. In such cases, inspectors need many heavy and bulky batteries, since conventional speakers require high power, resulting in undesirable situations. Electric-power free impulse point sound source generation system with bubble wrap bursting phenomena for an economical and simplified non-destructive testing method is proposed. The sound characteristics generated by bursting bubble wrap, including uncertainty, reproducibility, and frequency response, are initially evaluated via excitation tests. A bubble wrap can generate an impulse sound with high-frequency components of up to 40 kHz and semi-directional characteristics. Then a monitoring system to detect foreign objects in pipes is constructed. The monitoring system consists of bubble wrap to yield an impulse excitation and a microphone to measure the sounds. Applying a wavelet transform to the obtained time-series data with and without a foreign object can determine the location of the foreign object with an error of approximately 2 %. This method is readily available, portable, and affordable.