Generation Of Ultrasonic Signals Research Articles

A Low Intensity Ultrasound Neural Modulation System for Brain Stimulation

Non-pharmacological and non-surgical transcranial stimulation of the nerve function may become a new and very effective treatment of cranial nerve diseases. In this paper, a low-intensity portable ultrasound system was designed, which includes the arc-phased array and the ultrasonic electronic system. The arc phased array is composed of 203 single transducers. The electronic system includes ultrasonic signal generator, amplifier and delay unit. The system can independently modulate the frequency of 203 output signals and its frequency resolution is less than 1Hz, the phase difference is adjustable and less than 0.1degrees. It can focus on different parts of the brain by controlling the delay parameters.

Design and fabrication of MEMS based electrostatic cantilever as ultrasonic signal generator

This paper presents the design and fabrication of a 500μm×200μm×0.070μm micro-cantilever as ultrasonic frequency generator. Actuation energy (up to 4.1V dc) after fixed intervals was necessary to produce stable oscillations. The device relies on the principle of electrostatic effect and the output in the form of low ultrasonic frequency signal is generated from the piezoelectric surface (ZnO) due to switching action. The dimensions of the proposed device are first optimized by modeling and the same design is then fabricated and characterized as high frequency signal generator. From the results, a huge difference between the simulated (22.67kHz) and experimental (30.76kHz) output signals has been found out. This may be caused due to a propagation delay and slow switching action in fabricated device. This work may be useful as an electrostatic micro-switch where low actuation dc voltage is needed to generate ultrasound signals.

Ultrasonic signal analysis according to laser ultrasound generation position for the detection of delamination in composites

Carbon-fiber-reinforced plastic should be inspected in the fabrication process to enhance quality by preventing defects, such as delamination and voids. Conventional ultrasonic evaluation methods cannot be applied during the fabrication process because they require contact measurement by a transducer. Thus, an optical method using a laser was employed in this study for non-contact ultrasonic evaluation. Ultrasonic signals were generated by a pulsed laser and received by using a laser interferometer. First, an ultrasonic signal was generated from the back side of a material sample with artificial internal defects in the composite. The ultrasonic signal directed through the interior of the specimen was then detected at the front side. After determining the locations of the internal defects, the defects were quantitatively evaluated from the front side of the composite by using ultrasonic signal generation and reception.

Study on Ultrasonic Generator for Ultrasonically Assisted Machining

Ultrasonic vibration cutting can be widely used in lathe, planer, milling machine, grinding machine, thread processing and gear processing, etc. Ultrasonic vibration cutting system is composed mainly of ultrasonic generator, ultrasonic transducer, luffing rod, cutting tool, etc. Here, ultrasonic generator is the most important. The stand or fall of signal, which is produced by ultrasonic generator, has direct influence on anticipated effect and ability of ultrasonic machining. In order to generate a signal, which can be suitable for ultrasonic machining, ultrasonic vibration cutting system is studied, and ultrasonic signal generator based on direct digital frequency synthesis (DDS) is designed and conducted a cutting test with this ultrasonic machining system. The results show that the signal generator, which is made up by DDS technology, can generate the signal with stability, reliability and greater flexibility, and can be fully applicable to the ultrasonic machining.

고성능 초음파 결함탐상기를 위한 압전변환기

In this paper, a new piezoelectric transducer for high performance ultrasonic flaw detector used in non-destructive test (NDT) is implemented. Here, the goals for some major characteristics such as piezoelectric strain constant and electro-mechanical coupling factor are fixed in advanced. Then, the parameters obtained by finite element analysis (FEA) are exploited to design and implement the piezoelectric transducer. As a result of experiments using manufactured samples, it is proved that the new PZT ceramics satisfy the goals very well. It has much improved impedance characteristic at the resonant frequency and generation of ultrasonic signals. In addition, ultrasonic flaw detector with the new transducer provides increased flaw detecting gain than the conventional one. Thus, it is considered that the new flaw detector contributes significantly to improve reliability of the NDT.

Influence of transparent coating thickness on thermoelastic force source and laser-generated ultrasound waves

A numerical model is established to investigate the influence of transparent coating thickness on the laser-generated thermoelastic force source and ultrasound waves in the coating–substrate system by using the finite element method (FEM). Taking into account the effects of thermal diffusion, the finite width and duration of the laser source, as well as the temperature dependence of material properties, the transient temperature distributions are obtained firstly. Applying this temperature field to structure analyses as thermal loading, the thermoelastic stress field and laser-generated ultrasound wave in the specimen are obtained. The generation and propagation of the laser thermoelastically induced stress field and ultrasonic waves in coating–substrate system are presented in detail. The influence of transparent coating thickness on the transient temperature distribution, thermoelastic force source and the laser-generated ultrasound waveforms is investigated. The numerical results indicate that the thermoelastic force source and laser-generated ultrasound waveform are strongly affected by the coating thickness due to the constraint of coating. This method can provide insight into the generation and propagation of the laser-generated stress field in coating–substrate system consisting of a transparent coating and an opaque metallic substrate. It provides theoretical basics to optimize ultrasonic signal generation in particular applications and invert the physical and geometrical parameter of the coating–substrate system more accurately in the experiment.

Thermoacoustic Method for Detection of Powerful Microwave Pulses

We propose a method for detection of the envelope of a microwave nanosecond pulse, which is based on the effect of generation of sound pulses resulting from absorption of electromagnetic waves. We show that to reproduce exactly the envelope shape of a short microwave pulse, it is necessary that the wave be absorbed in a layer of thickness much less than the product of the sound speed and the pulse duration. In searching for conditions ensuring this, we study the process of thermoacoustic generation in thin metal films deposited on quartz substrates. Measurements performed at a wavelength of 8 mm show that the absorption coefficient is maximum if the aluminum-film thickness is 22–25 A. The maximum absorption coefficient amounts to 49% if the wave is incident from the quartz-substrate side. It is important that in this case, the wave reflection coefficient does not exceed 44%, whereas an aluminum plate reflects almost completely (99.8%) the incident-wave power. The phenomena observed in thin metal films are explained theoretically in terms of the anomalous skin effect. An experimental setup for a study of generation of ultrasonic signals by powerful microwave pulses is described.

Evaluation of the coating–substrate adhesion by laser-ultrasonics: Modeling and experiments

The aim of the present study is to investigate a laser-ultrasonic method to determine the oxide-coating’s adhesion strength on a metallic substrate. In order to demonstrate this method a completely contactless system is used, combining laser generation and detection of ultrasonic waves. A nanosecond pulsed Nd:YAG laser is used to irradiate the transparent oxide coatings, while the normal displacement of the rear surface of the metallic substrate is detected at the epicenter by a laser heterodyne interferometer. Increasing the laser beam energy, the generated acoustic wave forms are correlated with the thermoelastic regime, the fracture of the coating–substrate interface, and finally the expulsion of the coating. The generation of ultrasonic signals in the thermoelastic regime is described by a two-dimensional model suitable to calculate the in- and out-of-plane components of the mechanical displacement versus time. The values of the so-called practical adhesion found are in agreement with those obtained by classic contact techniques (tensile adhesion test, indentation, bending test). This work demonstrates the suitability of this quantitative and contactless test to evaluate the coating–substrate adhesion.

Specimen analysis instrument assembly

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Contrast of Electron-Acoustic Microscopic Image–For Si Tr-Chip under Bias Application–

The study investigated the relation between an electron-acoustic microscopy (EAM) image and images of several SEM modes. A pnp Darlington Si Tr-chip was used as a specimen. The site of ultrasonic signal generation by irradiated electron-beam was compared between the two kinds of images alternately photographed in “one frame scan” with the beam in a fixed condition. The results showed that (1) the contrast of electron acoustic image (EAI) changes with the bias voltage applied to the Tr-chip, (2) EAI resembles the EBIC image but is not exactly the same, and (3) an ultrasonic signal is not always generated at areas of different thermal properties.

The generation of ultrasonic signals by a New World arctiid moth

The sounds generated by the metathoracic tymbal organs of the arctiid mothMeles laodamiaDruce are described and related to their structure. Each tymbal is a swollen air-filled katepisternal sclerite with a vertical band of 15 to 20 striae on its anterior outer face. When compressed vertically by the basalar musculature it buckles inwards along the line of the striated band, which may be regarded as a linear array of 'microtymbals ’. Each stria produces a click which excites the whole structure into damped resonance and yields a briefpulseof sound with a half-decay time of about 80 μs. Muscle contraction and relaxation produce acycleofmodulationboth of pulse repetition rate, up to 1200/s, and of frequency over about an octave as a result of stress changes in the band. The audible fundamental component is relatively weak, and most energy is generated between 30 and 90 kc/s.Burstsof tymbal activity comprise from one to 20 modulation cycles. The acoustic performance of the tymbal organ is compared to that of a simple mechanical model. Previous accounts of the structures are summarized and the possible significance of the sounds discussed.