Thanks for a very instructional video. I have a question about the RFBs: you've said if the target is not perfectly absorbing and some of the waves are reflected back at the transducer, this will affect its radiation efficiency. Why is it so? Thank you!
Glad to you like it. Two reasons: Firstly, highly resonant devices (as is often found in therapeutic devices) can be very dependent upon the impedance they are radiating into. When a wave is reflected back from an imperfectly absorbing target, there will be some effective pressure that arrives back at the source transducer, thus changing the instantaneous radiation impedance experienced by the transducer, and thus how much is radiated out into the fluid. Secondly, a portion of the reflected wave arriving back at the transducer will be converted by the piezo-electric crystal into an electrical signal within the transducer. This is unlikely to be fully in-phase with the electrical signal that is driving the transducer, and therefore there will be some level of destructive intereference and cancellation, so the output signal is reduced. In either case, less acoustic power is radiated from the transducer for the same power input, so radiation efficiency is reduced. Hope that helps!
Thanks for a very instructional video. I have a question about the RFBs: you've said if the target is not perfectly absorbing and some of the waves are reflected back at the transducer, this will affect its radiation efficiency. Why is it so? Thank you!
Glad to you like it. Two reasons: Firstly, highly resonant devices (as is often found in therapeutic devices) can be very dependent upon the impedance they are radiating into. When a wave is reflected back from an imperfectly absorbing target, there will be some effective pressure that arrives back at the source transducer, thus changing the instantaneous radiation impedance experienced by the transducer, and thus how much is radiated out into the fluid. Secondly, a portion of the reflected wave arriving back at the transducer will be converted by the piezo-electric crystal into an electrical signal within the transducer. This is unlikely to be fully in-phase with the electrical signal that is driving the transducer, and therefore there will be some level of destructive intereference and cancellation, so the output signal is reduced. In either case, less acoustic power is radiated from the transducer for the same power input, so radiation efficiency is reduced. Hope that helps!