A method to analyze the radiation characteristics of a liquid column resonance transducer based on fluid motion.

Liquid column resonance (LCR) transducers have been widely used in deep-sea acoustic applications because of their fluid-filled structures. Until now, studies of pipe resonance have generally been based on the plane acoustic wave equation, but for a vibrating object, the velocity is the primary focus instead of the pressure. Thus, the motion equation of a pipe resonance mode can be deduced based on the Navier-Stokes (N-S) equations. In this work, the velocity of an LCR transducer is obtained using the finite element model, and the velocity distribution inside the liquid column is examined. In addition, the radiating surface of the LCR transducer is identified and a simplified model of the radiation that consists of concave pistons and ring sources is proposed and verified. The theory behind the high mechanical quality (Q) value of the LCR transducer is explained through the radiation of the LCR transducer and the low viscosity of the water. This is also verified through a finite element model and measurements. Due to the high mechanical Q value and the low frequency of the LCR transducer, such measurements should be carried out in open-field water and the pulse should be long enough to achieve a steady state.

A liquid column resonance transducer driven by Class IV flextensional transducer.

A liquid column resonance (LCR) transducer, also referred to as an organ pipe transducer, is a type of transducer that utilizes the liquid column resonance mode to produce acoustic energy underwater. Traditional transducers, such as piezoelectric rings or Janus transducers, are commonly used as the driving source in LCR transducers. A flextensional transducer (FT) is introduced into the LCR transducer as the driving source because of the relatively larger volume velocity at low frequencies. Moreover, the eigen-mode of the Class IV FT is easier to couple with the LCR mode to broaden the bandwidth of a LCR transducer. To overcome the problems associated with the low stiffness of elliptical metal pipes, an improved aluminum pipe, which has a cross-beam to increase the stiffness, was proposed and utilized in a LCR transducer driven by a Class IV FT. The fabricated LCR transducer prototype driven by the Class IV FT has two resonance peaks from 700-2000 Hz, and the transmitting voltage response values of these peaks are 132.1 and 137.8 dB (re 1 µPa/V @1 m). Comparing with an LCR transducer driven by a 33-mode ring, the results show that the LCR transducer driven by a Class IV FT provides good efficiency and broadband characteristics.

Influences of length and position of drive-stacks on the transmitting-voltage-response of the broadband Tonpilz transducer.

Most broadband Tonpilz transducers are achieved by coupling first-order longitudinal mode with other modes introduced by an elaborately designed structure (e.g., flexural mode of the head mass). To further expand the bandwidth is difficult and, even if successful, inevitably makes the structure more complex. Longitudinal modes are the inherent vibration modes of rod-shaped Tonpilz transducers. Using high-order longitudinal modes to achieve broadband performance can retain the simple structure similar to the conventional Tonpilz transducer. However, activating continuous, equal-amplitude longitudinal modes is not easy. The longitudinal length and position of the drive-stacks have significant influences on the generation of resonances and their vibration amplitude. In this paper, these influences are studied using the equivalent circuit method for a rod transducer having two drive-stacks, and finally we provide the drive-stack arrangement that can activate the first-three longitudinal modes to obtain the desired broadband response effectively. We also find that the response value of resonances can be balanced to reduce band fluctuation by adjusting drive lengths. The design procedure for the broadband Tonpilz transducer is proposed. The finite element method is used to design broadband transducers having bandwidth greater than one octave following the procedure. A transducer prototype with a simple structure is fabricated and measured to verify the validity of the proposed method.

Ultra-wide operation band of the high-frequency underwater acoustic transducer realized by two-layer 1-3 piezoelectric composite.

In this paper, the two-layer 1-3 composite transducer using an unconventional part-excitation method is presented to achieve the ultra-wide operation band for the high-frequency underwater devices, in which the part-excitation refers to the method that only the lower-layer is excited, while the upper-layer in contact with the propagation medium is not excited. This method is first proposed by analyzing the longitudinal vibration modes of one piezoelectric rod in the 1-3 composite and finally, we conclude that if the excited lower-layer can be controlled to have thickness given by 3l/2n, where l is the whole thickness of the two-layer rod and n (n > 1) denotes the number of the coupled modes, then first n order modes can be activated simultaneously to form an ultra-wide operation band containing n response peaks. Finite element method (FEM) is employed to investigate the two-layer 1-3 composite with a thickness of 10 mm. The results show that when the thickness of the excited lower-layer is 3 mm (n = 5), the transducer attains the ultra-wideband by coupling five resonances, nearly covering the frequency range from 100 kHz to 1 MHz. According to the difference of response level, the whole band can be divided into multiple local wide bands. A prototype transducer is fabricated based on the FEM results, and the measured results show that the whole band contains three wide bands, covering the frequency ranges 125-295 kHz, 300-480 kHz, and 500-915 kHz, respectively.

Research and Fabrication of Broadband Ring Flextensional Underwater Transducer.

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells. The transducer realizes broadband transmission by means of the coupling between radial vibration of the piezoelectric rings and high-order flexural vibration of the spherical cap metal shells. The low-frequency directional transmission of the transducer is realized by using excitation signals with different amplitude and phase on two mosaic piezoelectric rings. The relationship between transmitting voltage response (TVR), resonance frequency and structural parameters of the transducer is analyzed by finite element software COMSOL. The broadband performance of the transducer is also optimized. On this basis, the low-frequency directivity of the transducer is further analyzed and the ratio of the excitation signals of the two piezoelectric rings is obtained. Finally, a prototype of the broadband ring flextensional underwater transducer is fabricated according to the results of simulation. The electroacoustic performance of the transducer is tested in an anechoic water tank. Experimental results show that the maximum TVR of the transducer is 147.2 dB and the operation bandwidth is 1.5-4 kHz, which means that the transducer has good low-frequency, broadband transmission capability. Meanwhile, cardioid directivity is obtained at 1.4 kHz and low-frequency directivity is realized.

Motion of a rigid prolate spheroid in a sound wave field.

The motions of a rigid and unconstrained prolate spheroid subjected to plane sound waves are computed using preliminary analytic derivation and numerical approach. The acoustically induced motions are found comprising torsional motion as well as translational motion in the case of acoustic oblique incidence and present great relevance to the sound wavelength, body geometry, and density. The relationship between the motions and acoustic particle velocity is obtained through finite element simulation in terms of sound wavelengths much longer than the overall size of the prolate spheroid. The results are relevant to the design of inertial acoustic particle velocity sensors based on prolate spheroids.

Blood lead and cadmium levels in children: A study conducted in Changchun, Jilin Province, China.

OBJECTIVES: Exposure to lead and cadmium in developing countries is considered to be a public health emergency. The present study was designed to investigate children's exposure to lead and cadmium in Changchun, China. METHODS: A total of 1619 blood samples were collected at random from 1426 children between one and 14 years of age, and 204 adults from Changchun, China. Blood lead and cadmium levels were determined using atomic absorption spectrophotometry. RESULTS: The average blood lead level in children was 60.29 µg/L, with boys exhibiting higher blood lead levels than girls. The average blood cadmium level in children was 1.26 µg/L, and differences were not observed between boys and girls. CONCLUSIONS: Children from Changchun exhibited relatively low blood lead and cadmium levels compared with children from other cities, and higher lead and lower cadmium levels than adults. This may be related to leaded gasoline environmental pollution and children's hand-to-mouth activities.

OBJECTIFS: L'exposition au plomb et au cadmium est considérée comme une urgence de santé publique dans les pays en développement. La présente étude était conçue pour examiner l'exposition des enfants de Changchun, en Chine, au plomb et au cadmium. MÉTHODOLOGIE: Les chercheurs ont colligé au hasard un total de 1 619 prélèvements de sang auprès de 1 426 enfants de un à 14 ans et de 204 adultes de Changchun, en Chine. Ils ont déterminé leur taux de plomb et de cadmium dans le sang au moyen de la spectrophotométrie d'absorption atomique. RÉSULTATS: La plombémie moyenne des enfants s'élevait à 60,29 µg/L et était plus élevée chez les garçons que chez les filles. Le taux moyen de cadmium dans le sang des enfants s'élevait à 1,26 µg/L et n'était pas différent entre les garçons et les filles. CONCLUSIONS: Les enfants de Changchun présentaient un taux relativement faible de plomb et de cadmium dans le sang par rapport aux enfants d'autres villes, et un taux plus élevé de plomb et plus faible de cadmium que les adultes. Ce phénomène peut être lié à la pollution environnementale par l'essence au plomb et au fait que les enfants portent beaucoup leurs mains à leur bouche.