Dear Hemant,



There are several methods of wave classification. One of them classify the waves in categories Mechanical waves and Electromagnetic waves.

Infra Sonic, Sound waves & Ultrasonic vibrations are called mechanical waves they propogate with mechanical movement of medium particles. All these mechanical waves can pass through material or mediums but they cant travel in vaccum. These waves get partially reflected whrever there's medium change. Among these three only ultrasonic waves are used for non destructive testing of materials for example detecting crack in a copper bar etc. With ultrasonic waves one can detect defect as well as precise position of defect.

Electromagnetic waves donot need any material medium for propogation but they pass through materials. These waves are classified as Radio Waves futher classified as [ LF, HF, UHF etc ], Infra Red, Visible Spectrum, Ultra Violet, X rays etc. Notice that not all these waves pass through all mediums. For example infra red and visible spectrum wont pass through copper but X ray does pass. These electromagnetic waves are used for detecting objects for example infra red proximity switches and RADAR, but they hardly find any use for crack detection etc.



No uC cannot generate sound waves on itw own. It can generate audio spectrum electrical signals which can be coverted to audible waves using speaker etc. More approapriate method for your application is Ultrasonic waves and not sound waves. You can generate ultrasound frequency electrical oscillations using micro [ say 500kHz ] and then amplify these signals with suitable Amplifier and feed these amplified signals to an ultrasound transducer which will emit ultrosound.



Reflection coeficient doesnt depend on frequency it is purely a function of the two mediums from whose boundry the reflection occurs.

- Higher frequency gives smaller beam angle.
- The amount of energy absorbtion by material depends on frequency and it increase with increasing frequency and this absorbtion weakens the beam.
- High frequency doesnt suffer from ambient noise and give better sound to noise ratio.

Regards,
Prahlad Purohit