narrow band transducer has large  mechanical quality factor and small band-with. You can calculate band-with of the transducer from impedance test.

Ehsan,

The difference lies in the transmission properties of both transducers. While the narrow band transducers pass narrow band signals dictated by their narrow bandwidth the wide band transducers pass the input signals in larger bandwidth. The advantage of the narrow band transducer is that it could have better signal to noise ratio as the noise generated in the transducer is proportional to their bandwidth. So, the noise added to the signal is smaller in case of narrow band transducer. While the wideband transducer is more economical since it can detect multiple narrow band signal.

Best wishes

Dear experts;

I really appreciate your answers

I was going to give a one-word answer: "Q".  

But that would be too flip.

I believe you'll find that Q is nonetheless related to the degree of damping in the structure.  The more damping, the lower the Q.  This also implies structural losses to heat.  Maybe that's also a fairly trivial statement but may be of some use in your pondering the answer to your question.

The more damping, the wider the bandwidth.

Of course, this suggests a model of a transducer to make it clearly understandable.  In the model diagrams in www.ultrasonic.co.ir/files/003.pdf Figure 1,  R1 provides the damping function.

The noise will increase with bandwidth but probably originating in the environment and not the transducer itself.

hi, see   

https://www.linkedin.com/pulse/broadband-vs-narrowband-transducers-fernando-villanueva

i think that is very helpful

Dear Ehsan,

In the narrow band signal, we can generate single mode wave in single frequency but

in the broad band signal multiple modes in different frequencies are generated.

Dear Dr. Taghipour,

I sincerely appreciate your help. Thank you.