High Frequency Ultrasonic Research Articles

Preparation, Micro‐Patterning and Electrical Characterization of Functionalized Carbon‐Nanotube Polydimethylsiloxane Nanocomposite Polymer

AbstractSummary: We present the preparation, improved micro‐patterning, and electrical property characterization of COOH‐ functionalized mutli‐walled carbon nanotube (MWCNT) and polydimethylsiloxane (PDMS) conductive nanocomposite polymers that can be employed for lab on a chip applications. The nanocomposites are prepared by mixing functionalized MWCNTs into an uncured PDMS matrix and employing high frequency ultrasonics (∼ 42‐50 kHz) using a horn tip probe. The prepared nanocomposites are micromolded using soft lithography techniques down to a feature size of 25 µm against a micropatterned SU‐8 polymer master. An array of peg like microstructures have been fabricated with a radii of 25 µm and height of 100 µm, that are embedded on a non‐conductive PDMS substrate using novel and improved fabrication techniques. The percolation threshold of the prepared nanocomposite is achieved at 1.5 weight percentage (wt.%) of COOH‐ functionalized MWCNT in the PDMS matrix. Resistivity levels at 2 wt.% of functionalized MWCNTs are 62 Ω‐cm or better, which is an improvement over our previously reported nanocomposite resistivity value of 100 Ω‐cm at 2 wt.% of nonfunctionalized MWCNT's in a PDMS matrix. The nanocomposites also have fairly uniform dispersion and no agglomeration of COOH‐ functionalized MWCNT as shown by SEM analysis. Furthermore, the nanocomposites show a negative temperature coefficient of resistivity (NTCR), making them ideal candidates for micropatternable temperature microsensors for lab on a chip systems.

Transcranial Evaluation of Blood Flow Velocity in the Basilar Artery in Rats by High Frequency Ultrasonic Doppler Technique

The possibility of recording the blood flow velocity in the basilar artery (a. basilaris) in rats through the occipital membrane by a two-channel ultrasonic Doppler system with single-element transducers was demonstrated. A. basilaris was located with a contact transducer working at a frequency of 33 MHz in two modes: pulsed and permanent. The mean blood flow velocity in narcotized male Wistar rats was 4.93+/-0.78 cm/sec. Functional loading tests (acute elevation of blood pressure and occlusion of the common carotid arteries) showed that this method allows recording dynamic characteristics of the blood flow reactions in a. basilaris with evaluation of its pulse wave pattern and analyzing their correlations with blood flow parameters in the carotid arteries using simultaneously the second (bandage) transducer.

High-Frequency Ultrasonic Hydrophone Based on a Cladding-Etched DBR Fiber Laser

Distributed-Bragg-reflector (DBR) fiber-laser-based ultrasonic hydrophone has been found to possess increased detectable frequency range due to the improved sensitivity in the high-frequency region when the fiber cladding thickness was reduced. A wet etching technique is utilized to reduce the fiber diameter of the DBR laser. The peak response frequency moves from 21 to 40 MHz when the fiber diameter was reduced from 125 to 68 m.

3J7a-3 Measurement of Scatterer-Size Dependent Frequency Characteristics of High Frequency Ultrasonic Echoes for Assessment of Red Blood Cell Aggregation(Medical imaging)

3J7a-3 Measurement of Scatterer-Size Dependent Frequency Characteristics of High Frequency Ultrasonic Echoes for Assessment of Red Blood Cell Aggregation(Medical imaging)

A High-Frame Rate High-Frequency Ultrasonic System for Cardiac Imaging in Mice

We report the development of a high-frequency (30-50 MHz), real-time ultrasonic imaging system for cardiac imaging in mice. This system is capable of producing images at 130 frames per second (fps) with a spatial resolution of less than 50 microm. A novel mechanical sector probe was developed that utilizes a magnetic drive mechanism and custom-built servo controller for high speed and accuracy. Additionally, a very light-weight (< 0.28 g), single-element transducer was constructed and used to reduce the mass load on the motor. The imaging electronics were triggered according to the angular position of the transducer in order to compensate for the varying speed of the sector motor. This strategy ensured the production of equally spaced scan lines with minimal jitter. Wire phantom testing showed that the system axial and lateral resolutions were 48 microm and 72 microm, respectively. In vivo experiments showed that high-frequency ultrasonic imaging at 130 fps is capable of showing a detailed depiction of a beating mouse heart.

High-Frequency Ultrasonic Imaging of the Anterior Segment Using an Annular Array Transducer

Very high-frequency ultrasound (VHFU; >35 megahertz [MHz]) allows imaging of anterior segment structures of the eye with a resolution of less than 40 microm. The low focal ratio of VHFU transducers, however, results in a depth of field (DOF) of less than 1 mm. The aim was to develop a high-frequency annular array transducer for ocular imaging with improved DOF, sensitivity, and resolution compared with conventional transducers. Experimental study. Cadaver eyes, ex vivo cow eyes, in vivo rabbit eyes. A spherically curved annular array ultrasound transducer was fabricated. The array consisted of 5 concentric rings of equal area, had an overall aperture of 6 mm, and a geometric focus of 12 mm. The nominal center frequency of all array elements was 40 MHz. An experimental system was designed in which a single array element was pulsed and echo data were recorded from all elements. By sequentially pulsing each element, echo data were acquired for all 25 transmit-and-receive annuli combinations. The echo data then were focused synthetically and composite images were produced. Transducer operation was tested by scanning a test object consisting of a series of 25-microm diameter wires spaced at increasing range from the transducer. Imaging capabilities of the annular array were demonstrated in ex vivo bovine, in vivo rabbit, and human cadaver eyes. Depth of field, resolution, and sensitivity. The wire scans verified the operation of the array and demonstrated a 6.0-mm DOF, compared with the 1.0-mm DOF of a conventional single-element transducer of comparable frequency, aperture, and focal length. B-mode images of ex vivo bovine, in vivo rabbit, and cadaver eyes showed that although the single-element transducer had high sensitivity and resolution within 1 to 2 mm of its focus, the array with synthetic focusing maintained this quality over a 6-mm DOF. An annular array for high-resolution ocular imaging has been demonstrated. This technology offers improved DOF, sensitivity, and lateral resolution compared with single-element fixed focus transducers currently used for VHFU imaging of the eye.

High Frequency Ultrasonic Imaging: System Design and Performance Optimization

High Frequency Ultrasonic Imaging: System Design and Performance Optimization

Piezoelectric 1–3 Composites for High Frequency Ultrasonic Transducer Applications

A new net shape process has been developed to fabricate 1–3 piezocomposites. Solid polymer moulds and high solid loading lead zirconate titanate (PZT) paste, made by the viscous polymer processing (VPP), have been utilised in an embossing/lost mould method. 1–3 structures with PZT pillar feature sizes of 50–100 μm and aspect ratios of 5–10 have been fabricated successfully, and the composites have been characterized by electrical impedance and pulse-echo measurements. The results show that the viscous polymer processing is a very promising technique for the fabrication of 1–3 composites for high frequency ultrasonic transducer applications.

F-1 Design of High Frequency Ultrasonic Probes with Separation between a Transmitter and a Receiver(Measurement techniques, Imaging, Nondestructive testing)

F-1 Design of High Frequency Ultrasonic Probes with Separation between a Transmitter and a Receiver(Measurement techniques, Imaging, Nondestructive testing)

Dry Coupling Ultrasonic High Frequency (10–100 MHz) Sensors for Detection of Surface and Tribological Properties at a Submicrometric Scale

Acoustic plane sensors adequately pressed against materials are suitable to measure elastic constants from flight-time measurement, without any coupling fluid for high temperature, with longitudinal and transverse acoustic waves in the megacycle range. Soft delay lines are generally used to match the sample roughness and to make mechanical play correction easier. At the opposite, our sensors use a hard delay line with a mirror-polished end surface. An experimental set-up is presented to perform acoustic reflection measurement in various contact conditions by increasing the applied mechanical load. The frequency dependence of this parameter is also measured in the 10- to 100-MHz range. Reproducibility tests are presented to validate this experimental set-up, but the main results concern the surprising ability of this technique to detect surface property modifications limited to thickness less than 1 μm. Indeed, surface modification induced by different solvents on glass substrates has been detected by this means. This technique has also been used to detect surface property modifications of lixiviated glasses. In this case, atomic force microscopy and inductively coupled plasma analyses have demonstrated that the earlier stage of the surface damage had been detected whereas the thickness altered by ionic diffusion was less than 100 nm with almost no roughness variation. Similarly, tests on mechanically scratched glasses have shown that samples with an average roughness, respectively, of 4 and 120 nm were easily identified from their reflection coefficient versus load curves. Moreover, the pressure dependence of the acoustic reflection is used to estimate the contact stiffness and the contact area between the sensor and the material as a function of the applied compressive stress for contact, adhesion, and friction investigations.

Double-structured ultrasonic high frequency reactor using an optimised slant bottom

The present work has been carried out in order to design a new type of ultrasonic reactor consisting of a double-structured tank. The inner working compartment is built with a slant bottom to allow a better ultrasonic transmission. This paper reports the effect of the inclination angle on acoustic efficiency for several different plates, e.g. two plates made of glass (2 mm and 3 mm thickness) and one made of PVC (3 mm thickness). The acoustic efficiency was determined as the ratio of the signal measured by a hydrophone in the presence of the plate to that signal in the absence of the plate. Having optimised the system, the ultrasonic powers in the inner and the outer compartments of the slant bottom reactor were determined by hydrogen peroxide dosimetry.

Preparation of Finely Dispersed-Palladium Metal in Zeolite by High Frequency-Ultrasonic Irradiation

Abstract New technique to prepare finely dispersed metallic species in a zeolitic framework has been developed by a high frequency-ultrasonic (HFUS) irradiation. The parent Pd ions in the zeolite were reduced with isopropyl alcohol into carbon containing Pd metal during the irradiation. These species was observed by EXAFS analysis to be highly dispersed into small clusters consisted of less than several atoms in zeolitic crystal.

Three-dimensional Highfrequency Ultrasonic Parameter Imaging of Anterior Segment Pathology

Purpose: High-frequency ultrasound allows high-resolution imaging of anterior segment anatomy and pathology. Acoustic echo data, however, contain information relating to the microanatomic structure of the interrogated tissue which is not evident in B-mode images. The aim of this study is to develop imaging techniques to demonstrate and quantify the distribution of acoustic scattering properties in ocular tissues in three dimensions.Methods: A tumor of the iris and a hyphema were scanned using a 50-MHz ultrasound probe mounted on a computer-controlled two-axis positioning system. Scan data from sequential parallel planes were used to make three-dimensional reconstructions. Digital signal processing and a mathematical model of acoustic backscatter then were used to represent the effective size and acoustic concentration of scattering elements using a false color representation superimposed on B-mode images.Results: Three-dimensional reconstructions improved appreciation of the size and extent of pathology and allowed computation of tissue volumes. Parameter images demonstrated distinctive differences between diffuse and organized blood and allowed quantification of tumor scattering properties.Conclusions: Three-dimensional imaging of the anterior segment with high-frequency ultrasound allows construction of perspective images, which adds to the already significant clinical use of individual high-resolution B-mode images. Acoustic backscatter properties determined by tissue microstructure can be computed from echo data and represented in false color in three-dimensional reconstructions.

High Frequency Ultrasonic Investigation for Ceramic Materials to Test the Manufacturing Process

High frequency ultrasonic techniques for nondestructive tests of fine grained ceramic materials are presented. Green and partially sintered are considered. To this purpose, ultrasonic velocities and attenuation were measured and correlated to the porosity degree reached in different phases of the manufacturing process. A physical understanding of the experimental results is achieved by comparing them with the theoretical predictions provided by a self consistent scattering theory introduced in the 1980s. Finally, porosity maps are proposed since they give a comprehensive view of the process quality.

High Frequency Ultrasonic Investigation for Ceramic Materials to Test the Manufacturing Process

High Frequency Ultrasonic Investigation for Ceramic Materials to Test the Manufacturing Process

Investigation of Adiabatic Compressibility and Ultrasonic Relaxation in Aqueous Solutions of N, N-Diisopropylacetamide and Zinc Acetate

Measurements of velocity at frequency of 1 MHz and absorption coefficient of ultrasonic waves within the range 3-50 MHz in aqueous solutions of N,N-diisopropylacetamide (D-i-PA) and zinc acetate ((CH3COO)2Zn) were made. Additionally, the density of the solutions was measured. The adopted method for making the solutions helped to change the ratio of the number of non-electrolyte molecules to that of electrolyte molecules, with a constant number of water molecules. Measurements of the velocity of ultrasonic waves in the solutions under study were conducted by means of an impulse-phase interferometer. Measurements of the absorption coefficient of ultrasonic waves were conducted by means of an ultrasonic high frequency system, type Matec Instruments (USA) Model 7700. All the measurements were conducted at a constant temperature of 20°C. On the basis of the analysis of excess functions of the molar volume and the adiabatic compressibility, the formation of solvatomers composed of [(D-i-PA)2Zn(H 2 O) 2 ] 2+ and [(D-i-PA)Zn(H2O)3] 2 + was found. Also the complex [Zn(CH3COO)4] 2— can be recognised. The results of measurements of sound absorption indicate the occurrence of the relaxation process in the solutions under study and the frequency range used. On the basis of the relaxation theory, relaxation parameters of the process under study were calculated. The relaxation processes discovered in the system (D-i-PA)-H2O(CH3COO)2Zn were assigned to the formation and disintegration of solvatomers composed of [(D-i-PA)Zn(H2O)3] 2+ and probably complexes mentioned before.

Evaluation of Airway Smooth Muscle Contractions in Vitro by High-Frequency Ultrasonic Imaging

To visualize ASM contraction in vitro, we measured changes in cross-sectional area and inner circumference of isolated porcine and human bronchi in response to acetylcholine or carbamylcholine chloride (Carbachol) using high-frequency ultrasound. A mechanical ultrasonic catheter (20 MHz; diameter, 1.7 mm; echo element, 1 mm2) demonstrated three histologic layers (mucosa, cartilage and adventitia) and allowed measurement of dose-dependent contraction of porcine bronchi over time. Acetylcholine (10(-4)M) significantly decreased the cross-sectional area by 17 +/- 2.85 percent but did not change the circumference. The mean initial value for area was 0.6 +/- 0.08 cm2 and for circumference was 3.0 +/- 0.24 cm (n = 5). The EC50 of acetylcholine was 1.5 x 10(-8) M. Carbachol (10(-4)M)-induced contractions of human bronchi were also observed under the same conditions. In conclusion, high-frequency ultrasonic imaging can be used to study the morphology of ASM contractions in vitro, providing valuable information on the natural dynamics of ASM.

Acoustic lenses employing PZT thin film transducers

Acoustic lenses made of thin piezoelectric lead zirconate titanate (PZT) films fabricated by a chemical sol-gel process are presented. A frequency range between 50 and 250 MHz has been achieved. PZT films have been successfully coated on substrates such as fused quartz and metals, flat and cylindrical surfaces, and substrates with a large coating area or length. The piezoelectricity of the film is achieved by electric poling. The comparison between PZT and ZnO films for ultrasonic high frequency transducers is outlined.

High Frequency Ultrasonic Measurements

The use of high frequency ultrasonic Lamb waves to measure the thickness of thin plates and foils, is discussed and the feasibility of their application to the determination of the degree of cure of polymer coating on coated tin plated steel sheet (as used by the food can industry) is evaluated. The paper also discusses briefly the design features of the purpose built precision double probe ultrasonic goniometer used to carry out these measurements.

Computer-aided ultrasonic testing of non-oxide ceramics

Defects as small as 50 μm can cause failure in brittle non-oxide ceramics. High frequency ultrasonics and radiography are two methods for detecting defects of this size. In this note the authors introduce a computer-aided system for high-frequency ultrasonic tests up to 50 MHz. Results obtained from different specimens are compared with low energy radiographic tests and show the method to have potential for flaw-type characterization.