Research of decreasing the influence of coupling effect on High-frequency circular piston transducer

Abstract

This paper analyzes the impact of coupling effect on the high-frequency circular piston transducer. Focuses on the impact of the direction and the transmission voltage response in the case of constant thickness and mutative diameter. Raised a new method for Circular piezoelectric wafer center opening that decreases the influence of coupling influence, and experimental study was operated. According to the method, Transducer prototype is developed and the influence of coupling influence is little. The resonant peak in the thickness direction is obvious. The new method has a good adaptability, it could be widely extended to the same type of transducer designing. Introduction Echo sounder is an important type of underwater acoustic navigation device, it can provide information on the location of the depth of the ship to ensure the safety of navigation. As an important component on the echo sounder, the high-frequency circular piston transducer is mounted on the bottom of ship and is accountable to launch vertically a frequency modulated pulse sonic to underwater. In practice the high-frequency circular piston transducer is susceptible to coupling effect. Effect of the coupling can be eliminated by the cutting method. But the cutting methods exist shortcomings of more processes, resource-intensive and long-cycle. This paper will propose a method opening hole in the center of the circular ceramic wafers. This method is simple and effective, easily produced, also can effectively avoid the impact of the coupling. The transducer prototype was developed by using the new method, it has only one resonance peak. Coupling Impact Analysis Since the thickness vibration mode frequency is relatively high, so the high-frequency transducers are generally using the thickness vibration mode of the piezoelectric vibrator. Round transducer coupling influence is mainly from the higher-order modes of radial and lateral bending mode, etc. In practice, the high frequency transducer circular transducers can’t satisfy the condition that a is much greater than t, so that the transducer is often influenced by the coupling Impact. Fig. 1 Circular piezoelectric oscillator schematic Under ideal conditions, the series resonant frequency of the thickness vibration of PZT4 is 1.39 2036.3 D t t v f t t π = = (1) International Industrial Informatics and Computer Engineering Conference (IIICEC 2015) © 2015. The authors Published by Atlantis Press 1579 Frequency constant, vibration displacement distribution, transmission voltage response of piezoelectric transducers, directivity and other properties were affected by coupling impact. According to the operating frequency of the transducer ft= 218kHz to calculate, get t = 9.34mm. Keep t values unchanged, taking a diameter a = 2 t, 3 t, 5 t, 9 t to analysis coupling vibration impact. The paper analysis focused on the voltage response curves and the directivity pattern of transducer changes in dependence of a value. Figure 2 shows, when a = 2 t, two obvious resonant peaks are present on the transmit voltage response curve, respectively, 210kHz and 248kHz, there is a deep valley between the two peaks. When a = 3 t, the two resonant peak frequencies are 208kHz and 240kHz, the valley between the two peaks becomes shallowly. Fig. 2 Transmit voltage response curves at different a values With the increase of the value a , the two resonant peaks frequency gradually move closer, and the valley between two peaks becomes shallowly. When a = 9t, the two peaks have been combined to form a resonant peak frequency of 224kHz. This phenomenon shows that when a = 2 t, 3 t, 5 t, the thickness mode is coupled strongly by the radial vibration high-frequency modes and lateral bending modes. When the a is apposite value, the thickness of the vibration frequency is clear gradually. Fig. 3 218kHz directivity pattern at different value a Figure 3 shows, at 218kHz, a = 2 t, -6dB directivity pattern of an opening angle is 30 °, the maximum side lobe level is -5dB. When a = 3 t , the main beam angle becomes smaller, the maximum side lobe level is -10.5dB, when a = 5 t ,side lobe level is -18dB, a = 9 t, side lobe level is -22.5dB. This phenomenon shows that when a = 2 t, 3 t, the round oscillator is affected by coupling impact. With a increasing, the transducer’s directivity pattern gradually is normal, the side lobe level is reducing.Visibly, Coupling Effect in circular piston transducer are: the transmit voltage response curve have multi-resonance peaks, the directivity pattern is abnormal, the side lobe level is higher. Oscillator center opening effect on coupling Keep t = 9.34mm and Inner diameter is 5mm, the outer diameter a = 2 t, 3 t, 4 t, 5 t, Analysis coupled vibration influence.