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Underwater piezoelectric transducer
Ultrasonics International 87 abstracts Experiments showed that acoustic parameters could be measured at a single point with a hydrophone constructed from PVDF (piezoelectric plastic sheet) using water as the transmission medium. However, the complete spatial characterization procedure was time-consuming and unsatisfactory for use under field conditions since it was necessary to repeat the measurement process at many points by altering the relative positions of transducer and hydrophone. The solution was found using a specially developed multi-element PVDF hydrophone, capable of measurement at 21 points across the beam, and an entirely novel interface control unit to gather and analyse data at the rate of 60 million bytes per second. Under normal operation the ultrasonic transducer, together with its associated equipment, typically produces repetitive tone bursts of ultrasound at the rate of up to 8 kHz. The ultrasound frequency itself usually lies between 1 and 10 MHz, but because very high pressures are developed by harmonics, the measurement system must operate up to 25 or 30 MHz. Under test each hydrophone element signal is mutiplexed to the control system where it is amplified by up to 60 dB, demultiplexed and corrected for hydrophone element variations. It is then remultiplexed before passing through a 'flash" A to D converter and high speed ECL RAM to short-term storage in buffer RAM, which duplicates part of a microcomputer's main store. The system which is now commercially available, allows the entire process of transmission, amplification, A to D conversion and data processing to be carried out between the 8 kHz tone bursts, and the acoustic parameters to be displayed in (virtually) real time on the screen of an IBM PC.
Underwater piezoelectric transducer
M. Recuero, M. Vaquero and F. Tabernero, Escuela Universitaria de Ingenieria Te'cnica de Te/ecommunicacio'n de Madrid, Spain Transducers used in underwater detection or the communications field work in the frequency range 2 - 5 0 kHz to achieve the greatest range and the best signal-to-noise ratio in the transmission. These transducers generally use PZTtype piezoelectric ceramics as electromechanical convertors. There are several equivalent circuits (KLM, Mason) which represent the behaviour of the piezoelectric ceramics at each of their modes of vibration. These are valid only in a frequency range around the fundamental resonant frequency of the piezoelectric element and its first odd harmonics. The dimensions of the standard piezoelectric elements cause their resonant frequencies to be hundreds of kHz, high above the optimum frequency band for underwater applications. However, piezoelectric ceramics can be used at low frequencies as they present "partial' resonances under the fundamental resonance. Specialized literature provides no information on the origin of these partial resonances. Neither are there equivalent circuits which represent the piezoelectric ceramic at those frequencies close to a partial resonance. This poster provides a method to design low-frequency piezoelectric transducers working around a partial resonant frequency. To achieve this, a partial resonance with a strong thickness-type vibration must first be found. Then, the behaviour of the piezoelectric ceramic, around that partial resonance, can be simulated by an equivalent circuit of concentred elements ending in a transmission line. This model allows all the elements to be measured and makes easier the design of the water-matching plates and backings as it takes into account radiation on both sides of the ceramic. A simulation of a low-frequency underwater transducer has been carried out using a computer; the transducer was
based on the mentioned model. The validity of this model has been checked in the vicinity of the partial resonant frequency.
Ultrasonic actuator using the extensional vibration of cylindrical shell
S. Ueha, A. Ukita, M. Kurosawa and E. Mori, Tokyo Institute of Technology, Japan An ultrasonic actuator is proposed and studied experimentally. If an ultrasonic wave is excited to propagate in the stator, particles on the internal surface move elliptically. As the internal surface is machined as an internal thread and an appropriate external thread (rotor) is put into the stator, the external thread is rotated through the frictional force and moved in the axial direction. The fundamental principle is almost the same as that of an ultrasonic motor. The progressive extensional wave is excited by a piezoelectric element bonded to the stator, whose electrode is divided into eight parts. As a result of the study, the acutator is proved to operate successfully at an efficiency of 3% if an appropriate material and pitch are used.
Investigations on evaluation of transducer performance at high electric drives
V.N. Bindal, T.K. Saksena, S.K. Jain and R. Gupta, National Physical Laboratory, New DelhL India High power ultrasonic transducers in the frequency range 1 MHz, find frequent applications in primary sources for parametric generation and in ultrasonic sources for therapeutic applications and hyperthermia. The transducers have to be subjected to high electric drives which presents a need for the characterization of transducers under such conditions, so that optimal performance can be obtained. Investigations have been reported in the present work on evaluation of the performance of transducers at high electric drives up to 100 W. The parameters that have been studied include the study of motional admittance, the shifting of the resonant frequency, study of frequency asymmetry, mechanical Q, study of dielectric parameters at low frequency, and study of acoustic output using appropriate receivers. Behaviour under prolonged operation has also been investigated. Studies have been made on ultrasonic transducers with frequencies of the order of a few hundred kilohertz constructed using piezoelectric ceramic elements PZT-5 and PZT-4. The feasibility of employing different approaches using the various measured parameters has been discussed. It is hoped that this study would be helpful in achieving a comparative evaluation of transducers to a practical designer.
Estimation of efficiency of a transducer using self-reciprocity technique
V.N. Bindal, T.K. Saksena, J.N. Som and S. Chandra, National Physical Laboratory, New DelhL India Reciprocity techniques have been used extensively for absolute measurement of sensitivity of the ultrasonic hydrophone in the megahertz frequency range. The method was used to compute the efficiency of ultrasonic projectors in the frequency region about 1 MHz, such as used in ultrasonic therapeutic systems. The efficiency has also been obtained using motional admittance analysis using a circle diagram
Ultrasonics 1987 Vol 25 November
375
Underwater piezoelectric transducer
M. Recuero, M. Vaquero and F. Tabernero, Escuela Universitaria de Ingenieria Te'cnica de Te/ecommunicacio'n de Madrid, Spain Transducers used in underwater detection or the communications field work in the frequency range 2 - 5 0 kHz to achieve the greatest range and the best signal-to-noise ratio in the transmission. These transducers generally use PZTtype piezoelectric ceramics as electromechanical convertors. There are several equivalent circuits (KLM, Mason) which represent the behaviour of the piezoelectric ceramics at each of their modes of vibration. These are valid only in a frequency range around the fundamental resonant frequency of the piezoelectric element and its first odd harmonics. The dimensions of the standard piezoelectric elements cause their resonant frequencies to be hundreds of kHz, high above the optimum frequency band for underwater applications. However, piezoelectric ceramics can be used at low frequencies as they present "partial' resonances under the fundamental resonance. Specialized literature provides no information on the origin of these partial resonances. Neither are there equivalent circuits which represent the piezoelectric ceramic at those frequencies close to a partial resonance. This poster provides a method to design low-frequency piezoelectric transducers working around a partial resonant frequency. To achieve this, a partial resonance with a strong thickness-type vibration must first be found. Then, the behaviour of the piezoelectric ceramic, around that partial resonance, can be simulated by an equivalent circuit of concentred elements ending in a transmission line. This model allows all the elements to be measured and makes easier the design of the water-matching plates and backings as it takes into account radiation on both sides of the ceramic. A simulation of a low-frequency underwater transducer has been carried out using a computer; the transducer was
based on the mentioned model. The validity of this model has been checked in the vicinity of the partial resonant frequency.
Ultrasonic actuator using the extensional vibration of cylindrical shell
S. Ueha, A. Ukita, M. Kurosawa and E. Mori, Tokyo Institute of Technology, Japan An ultrasonic actuator is proposed and studied experimentally. If an ultrasonic wave is excited to propagate in the stator, particles on the internal surface move elliptically. As the internal surface is machined as an internal thread and an appropriate external thread (rotor) is put into the stator, the external thread is rotated through the frictional force and moved in the axial direction. The fundamental principle is almost the same as that of an ultrasonic motor. The progressive extensional wave is excited by a piezoelectric element bonded to the stator, whose electrode is divided into eight parts. As a result of the study, the acutator is proved to operate successfully at an efficiency of 3% if an appropriate material and pitch are used.
Investigations on evaluation of transducer performance at high electric drives
V.N. Bindal, T.K. Saksena, S.K. Jain and R. Gupta, National Physical Laboratory, New DelhL India High power ultrasonic transducers in the frequency range 1 MHz, find frequent applications in primary sources for parametric generation and in ultrasonic sources for therapeutic applications and hyperthermia. The transducers have to be subjected to high electric drives which presents a need for the characterization of transducers under such conditions, so that optimal performance can be obtained. Investigations have been reported in the present work on evaluation of the performance of transducers at high electric drives up to 100 W. The parameters that have been studied include the study of motional admittance, the shifting of the resonant frequency, study of frequency asymmetry, mechanical Q, study of dielectric parameters at low frequency, and study of acoustic output using appropriate receivers. Behaviour under prolonged operation has also been investigated. Studies have been made on ultrasonic transducers with frequencies of the order of a few hundred kilohertz constructed using piezoelectric ceramic elements PZT-5 and PZT-4. The feasibility of employing different approaches using the various measured parameters has been discussed. It is hoped that this study would be helpful in achieving a comparative evaluation of transducers to a practical designer.
Estimation of efficiency of a transducer using self-reciprocity technique
V.N. Bindal, T.K. Saksena, J.N. Som and S. Chandra, National Physical Laboratory, New DelhL India Reciprocity techniques have been used extensively for absolute measurement of sensitivity of the ultrasonic hydrophone in the megahertz frequency range. The method was used to compute the efficiency of ultrasonic projectors in the frequency region about 1 MHz, such as used in ultrasonic therapeutic systems. The efficiency has also been obtained using motional admittance analysis using a circle diagram
Ultrasonics 1987 Vol 25 November
375