RESUMEN
The mechanical pre-stress applied in piezotransducers used to generate high power ultrasound is needed to avoid ceramics fracture on traction cycle. Pre-stress levels inferior to 50 MPa can yield resonance shifting due to effectiveness of acoustic coupling between transducer pieces. Symmetrical transducers with different thickness of passive parts were submitted to axial mechanical pre-stress up to 50 MPa and their resonances were measured. The experimental results show the increasing of the resonances frequencies with the level of applied pre-stress. Similar effect is verified in simulations by using a model based on Mason's equivalent electric circuit. Due to the similarity of these effects, a relation between applied pre-stress and pieces coupling was proposed for the transducer assembled. In addition, the dependence of the thickness of non-piezoelectric pieces on the coupling effectiveness between them is discussed. The results show that transducers with small thickness present more expressive shifting resonance ratio.
RESUMEN
The piezotransducers employed in high power ultrasound are composed of piezoelectric ceramics and metallic pieces. These transducers are mechanically pre-stressed in order to avoid the ceramic fractures when high voltage is applied under resonance. The resonance and anti-resonance frequencies are shifted depending on the level of applied mechanical pre-stressing. This paper discusses some causes of this shifting on a experimental study. The discussion takes into account the variations on characteristic parameters of the ceramics and the acoustic coupling between parts of the transducer.
Asunto(s)
Transductores , Ultrasonografía/instrumentación , Acústica , Cerámica , Análisis de Falla de Equipo , Humanos , Metales , Estrés MecánicoRESUMEN
Composed piezotransducers submitted to mechanical pre-stressing present shifts on resonance and anti-resonance frequencies. Changes on characteristic parameters of the ceramic and in the coupling between the parts of the transducer can be the causes for this behavior. In applications where the level of pre-stressing is low (up to 50 MPa) the parameters of the ceramic are not altered, therefore, the shifting on frequencies are attributed to coupling between parts. This paper describes a mathematical model to explain this effect based on difference of effective cross-section between transducers parts under pre-stressing. The results show a proportional relation between pre-stressing and effective coupling of the parts.
Asunto(s)
Transductores , Ultrasonografía/instrumentación , Cerámica , Conductividad Eléctrica , Análisis de Falla de Equipo , Humanos , Metales , Modelos Teóricos , Estrés MecánicoRESUMEN
O ultra-som é uma das principais ferramentas para diagnósticos na área médica. Através da interação dos campos ultra-sônicos pode-se obter várias características dos tecidos biológicos, portanto é importante conhecer sua distribuição de pressão no meio de propagação. Neste trabalho é estudado o campo ultra-sônico produzido por um transdutor piezoelétrico anular. Os resultados experimentais mostram que o campo ultra-sônico depende do material empregado na construção do transdutor.
The ultrasound is a important tool for diagnostics on medical area. Throught of ultrasonic fiel d interaction we can obtain some characteristics of the biologycal tissues, thus it is important to know the pressure distribuition in the propagation medium. ln this paper is studied the ultrasonic field generated by a ring piezoelectric transducer. The experimental results show the ultrasonic field depends of the material employed in the transducer construction.