Structure Of Medical Ultrasonic Transducer

Piezoelectric crystal is the main functional part, which is used to transmit and receive ultrasonic waves and complete the sound-electricity and electricity-acoustic conversion. Its geometric shape and size are designed according to diagnostic requirements. Since piezoelectric crystals are brittle and require insulation, sealing, corrosion resistance, etc., piezoelectric crystals must be installed in the shell.
Electrodes are plated on both ends of the piezoelectric crystal, and a lead is welded to the upper and lower electrodes respectively, which are connected to the electrode plug-in on the shell to transmit electrical signals.
The padding sound-absorbing material (also known as the absorption block, the sound-absorbing block) is used to attenuate and absorb the ultrasonic energy radiated back by the piezoelectric crystal, so that it does not reflect back and forth in the probe and prolong the ringing time of the crystal. Therefore, the padding is required to have a large attenuation capacity and an acoustic impedance close to that of the piezoelectric material, so that the sound waves radiated back from the piezoelectric crystal all enter the padding and no longer reflect back to the crystal. The sound-absorbing material is generally made of epoxy resin plus tungsten powder, or ferrite powder plus rubber powder.
Acoustic insulation layer prevents the ultrasonic energy from being transmitted to the probe shell and causing reflection, causing interference to the signal.
The protective layer is used to protect the vibrator from wear. Since the protective layer is in contact with the vibrator and human tissue at the same time, it is a layer of material between the vibrator and the human tissue. The protective layer is required to prevent wear and protect the vibrator, and to have no attenuation as much as possible in the transmission of ultrasonic waves, and have good transmission function; therefore, the acoustic impedance of the protective layer is required to be close to the acoustic impedance of human tissue, and have an optimal thickness with both wear resistance and good transmission. The protective layer should be made of a material with a low attenuation coefficient and wear resistance, and the protective layer should also be used as an acoustic impedance gradient layer inserted between layers, and its thickness should be λ/4.
The shell serves as a support for the internal material of the probe, supporting, containing, sealing, insulating, bearing pressure, shielding and protecting the vibrator, and is used to fix the cable lead. The shell usually indicates the model and nominal frequency of the probe.
Sometimes the shell is also equipped with accessories such as impedance converter, preamplifier, damping resistor and adjustable inductor.