The application of laser reflective tomography in near-field measurements of ultrasonic transducers

With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.

Method for Measuring Self-noise of Vector Hydrophones

The Vector Hydrophone(VH) is widely used to remotely detect underwater targets. Accurately measuring the self-noise of the VH provides an important basis for evaluating the performance of the detection system in which it is utilized, since the ability to acquire weak signals is determined by the VH self-noise level. To accurately measure the VH self-noise level in actual working conditions, the Dual-channel Transfer Function Method(DTFM) is proposed to reduce ambient background noise interference. In this paper, the underlying principles of DTFM in reducing ambient background noise is analyzed. The numerical simulations to determine the influence of ambient background noise, and the sensitivity difference of the two VHs on the measurement results are studied. The results of measuring the VH self-noise level in a small laboratory water tank by using DTMF indicate that ambient background noise interference can be reduced effectively by employing DTMF, more accurate self-noise level can be obtained as well. The DTMF provides an effective method for accurately measuring the self-noise level of VHs and also provides technical support for the practical application of the VH in underwater acoustics.

Application of piezoelectric transient response in transducer acoustic power measurement

To explore a more convenient method for measuring the focused ultrasound power, a piezoelectric ceramic plate was used to receive ultrasonic signal directly. Due to an acoustic force acts on the surface of piezoelectric ceramic plate, the piezoelectric response was obtained by means of electromechanical analogy, which was composed of voltage response caused by forced vibration and high frequency attenuation response caused by natural vibration. The conversion relationship between output signal of piezoelectric ceramic plate and acoustic power of transducer was analyzed. The envelope of output piezoelectric signal was extracted in twice, and a voltage amplitude curve with sinusoidal distribution that could describe the changes of acoustic power was obtained. Under different drive voltage of transducer, the maximum peak voltage of envelope curve was found respectively. Their squared values were made a linear fitting with acoustic power measured by acoustic power meter, and then the proportional coefficient of theoretical relational expression was calibrated. The experimental results are in good agreement with the theory. The relative error between calibrated theoretical acoustic power and that measured by acoustic power meter was less than 8.7%. The paper can provide a guideline for measuring acoustic power of transducer by using piezoelectric signal.

Using the system function to analyze the performance of transducer's impedance measurement method

Prom investigation of the advantages and disadvantages of conventional tri-voltage method,a method for the measurement of the transmitting transducer＇s impedance was presented to solve the difficult problem of examining the consistency of the transmitting phased array on the single-mode excitation sea spot.In the method based on the system function, the circuit structure of tri-voltage method was used but new parameters were measured.The principle of the method was given first.Then when resistors with different nominal values were used in the circuit,the measured results for the impedance of transducers were reported.The results were compared with the higher precision impedance analyzer.Finally,the error analysis was performed according to the impedance formula and the equivalent circuit parameters were fitted.Under the condition of guaranteeing the sampling precision,by performance analyzing, the resistor value in series was chosen relatively smaller than the impedance of transducer,the measurement of impedance could achieve the same precision as the higher precision impedance analyzer.Finally,the least squares curve-fitting of measured curves indicated that the transducer equivalent electrical parameters could be extracted accurately and used to design the matching network.