![]() Among the models, the KLM model is one of the popular one–dimensional models. The behavior of the ultrasonic transducer can be modeled using the existing one– dimensional circuit models. A complicated electrical matching network may be implemented at the price of more energy loss. However, the drawback may be the deformation of the pulse shape and reduction of bandwidth. In a simple way, a series or parallel inductor is used to tune out the reactive part of the impedance at the center frequency of the transducer. Since the imaginary part of impedance would cause severe energy loss and reduction in bandwidth, the transducer input impedance should be real and the input resistance should match that of the source and receiver for the maximal power transmission. The function of the electrical part is to maximize the energy transmission by matching the electrical characteristics of the transducer to the electrical source and the receiving circuits. *The volume fraction of the loading material is ranged from 5 – 30 %. tungsten), the acoustic impedance of the composite can range from 8 to 20 MRayl. By varying the content of metal powder (e.g. Since there is a compromise between sensitivity and bandwidth, sometimes for specific applications, the acoustic impedance of the backing layer may be varied. Besides, with its high attenuation (120 dB/mm at 30 MHz) and relatively low acoustic impedance (5.92 MRayl), low insertion loss can be achieved for the transducer with an optimal front matching layer (see table 1). ![]() Besides minimizing the acoustic impedance mismatch, the backing layer can also act as a supporting layer of the fragile transducer element because of its relative rigid nature of the piezoelectric layer.Į–solder 3022 (Von Roll Isola Inc., New Haven, CT) is usually used as a backing layer material because of its electrical conductive nature, making it possible to be one of the electrodes of the transducer element. Backing layer can be used to damp out the ringing by absorbing part of the energy from the vibration of the back face. For imaging applications, it is highly undesirable to have a pulse with long duration. This would cause long ring– down of the ultrasonic pulse, which is the so–called ringing effect. ![]() Due to the acoustic mismatch between the air and the piezoelectric material, the reflected wave reverberates inside the transducer element. In fact, 100 % transmission is impossible for only considering the front matching layer. Parylene is a common polymer which minimizes the acoustic impedance mismatch and acts as a protecting layer as well. Coating a polymer onto the piezoelectric layer is also an alternative method to fabricate the matching layer. The scattering effect can be minimized efficiently by choosing proper size of the powder especially for high–frequency transducers. The acoustic impedance of the matching layer can be adjusted by the content of the powder. Mixing micro or nano scale powder into a polymer is one of the common approaches to fabricate matching layers. The transducer is usually treated as a three–port network including two mechanical ports and one electrical port as shown in Fig. Since the piezoelectric material itself exhibits much higher acoustic impedance (~30 MRayl) than that of biological tissue or water (~1.5 MRayl), a substantial part of the acoustic energy would be lost at the rear interface and not directed into the forward direction, resulting in poor resolution and sensitivity, if not properly matched acoustically. The selection criteria of these mechanical layers are presented in next section.Ī transducer rings at its natural frequency once it is excited by an electrical source. For specific applications, proper piezoelectric materials are chosen according to a number of factors such as their piezoelectric performance, dielectric properties, elastic properties and stability. Consequently, piezoelectric elements play a very important role in transducer technology. Ultrasonic transducers operate based on both converse and direct effects of piezoelectric materials in which the vibration would be produced upon the application of a potential difference across the electrodes and then the signal would be generated when receiving an echo. 1.1 Basic principles of the ultrasonic transducer
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |