The title might sound like we are connecting two different poles but piezoelectricity played a major role in world war-I. Submarines are efficient only when they can detect and destroy a target remaining underwater. The detection of targets is not so straightforward as it is in the case of air warfare or ground war. This required a device called as hydrophone that can be used to hear the sounds of a ship staying meters down in water, which is similar to the example of Echolocation learnt during our Physics tuition class for the chapter of Sound. Hydrophones rely on the concept of piezoelectricity. Let’s discuss what piezoelectricity is and its role in the world war in the present essay.
Piezoelectricity is a phenomenon in which current is generated in a solid due to the application of mechanical stress. The converse of this is also observed i.e, when current is passed through certain objects, they undergo mechanical stress, given the conditions that make it feasible. The materials that show piezoelectric behavior have their dipoles randomized causing the effective electric field in the system to be maintained at negligible levels. But when mechanical stress is applied the dipoles are oriented in such a way that there is a surge in the effective electric field and this results in the generation of current. One can also think of a case where the nicely aligned dipoles are disrupted resulting in current.
A hydrophone has a receiver of sound waves that moves when hit by a sound wave. This movement is associated with compression and decompression of the piezoelectric material. When a sound wave hits the receiver, it moves compressing the piezoelectric material and this compression is associated with the generation of current. The minute current generated can be amplified to undergo further decryption. The patterns of the current generated can give us an insight into the frequency of the sound waves detected.
Generally ships moving on the surface generate sounds from various sources like engine, turbine movement, rudder movement, etc. These sound waves travel all the way down to the submarine and a submarine equipped with a hydrophone can effectively detect this sound. In fact a submarine can send sound waves in different directions and when these sound waves are reflected off an obstacle or an object they can detected on the hydrophone mounted and depending the amount of time taken for the echo heard one can estimate the distance between the object and the submarine. The same mechanism can be used for mapping the sea floor and finding the ships sunk at sea.