C.K. Jen

Sensitivity analysis for Love mode acoustic gravimetric sensors

An approximate mass sensitivity formula for Love mode sensors is presented. The optimal thickness of the guiding layer, at which the sensitivity, Sfm is maximum for a given frequency or wavelength is obtained. The (Sfm)max can be expressed as −k0/ρ1λ1, where ρ1 is the density, λ1 is the wavelength of the surface transverse wave of the substrate, and k0 is a coefficient determined by the ratio of shear wave velocity and the ratio of density of the substrate to those of the overlayer. The (Sfm)max of the Love mode device can be 20 times higher than that of the shear horizontal SH–surface acoustic wave device fabricated on the same substrate and operating at the same frequency.

Piezoelectric thick bismuth titanate/lead zirconate titanate composite film transducers for smart NDE of metals

Thick film piezoelectric ceramic sensors have been successfully deposited on different metallic substrates with different shapes by a sol?gel spray technique. The ball-milled bismuth titanate fine powders were dispersed into PZT solution to achieve the gel. The films with desired thickness up to 200??m have been obtained through the multilayer coating approach. These thick films were also effectively coated onto thin sheet metals of thickness down to 25??m. Self-support films with flat and shell geometries were made. Piezoelectricity was achieved using the corona discharge poling method. The area of the top silver paste electrode was also optimized. The center frequencies of ultrasonic signals generated by these films ranged from 3.6 to 30?MHz and their bandwidth was broad as well. The ultrasonic signals generated and received by these ultrasonic transducers (UTs) operated in the pulse/echo mode had a signal to noise ratio more than 30?dB. The main advantages of such sensors are that they (1) do not need couplant, (2) can serve as piezoelectric and UT, (3) can be coated onto curved surfaces and (4) can operate up to 440??C. The capability of these thick film UTs for non-destructive evaluation of materials at 440??C has been demonstrated.

Piezoelectric thick film ultrasonic transducers fabricated by a sol-gel spray technique.

Thick film broadband ultrasonic transducers (UTs) produced by a sol-gel spray technique and operated below 10 MHz are presented. These UTs are formed by dispersing PZT and LiTaO3 particles, respectively in Al2O3 and PZT sol-gel solution. The 50-100 microm thick films have been deposited on curved steel, flat steel and aluminum substrates and steel rods. Ultrasonic pulse-echo signals with a signal to noise ratio of more than 25 dB are experimentally obtained for the operating temperatures up to 250 degrees C.

On-line ultrasonic monitoring of a die-casting process using buffer rods

On-line ultrasonic monitoring of die casting of an aluminum plate with steps of different thicknesses is studied using pulse-echo techniques. Clad buffer rods are inserted into the die wall for the monitoring. The flow front of molten aluminum inside the die has been probed by a two-channel acquisition system with a time resolution up to 1 ms. This information may be used to control the plunger movements. The gap development, due to the shrinkage of the part in the die, and the part solidification are also monitored for the understanding of the cooling process. As expected, it is observed that thicker sections take longer to solidify. The die wall temperature variation derived from the changes in ultrasonic travel time in the buffer rod is also observed.

High performance clad metallic buffer rods

Clad metallic buffer rods fabricated by thermal spray and electroplating techniques are presented. The core and cladding materials are steel, stainless steel, zirconium, titanium, nickel, copper and aluminum. The lengths of buffer rods can be more than tens of centimeters limited by the desired signal-to-noise ratio (SNR) and not by the fabrication. Pulsed ultrasonic signals of high SNR in these buffer rods make many practical applications feasible. Novel applications for on-line solidification monitoring of liquid aluminum and in situ temperature measurement are demonstrated.

Analysis of thin rod flexural acoustic wave gravimetric sensors

An analysis of thin rod flexural acoustic wave gravimetric sensors is presented. The diameter of the thin rod is much less than a wavelength. The lowest order flexural acoustics mode, F11, is of interest. For small added masses, the calculated mass sensitivity is −1/(2ρa), where ρ is the density and a is the radius of the thin rod. Measurements of velocity dispersion of the F11 mode in 21‐μm‐diam gold wires are shown to agree well with the theoretical calculation. Devices based on thin rods are shown to potentially have the same advantages as plate‐mode gravimetric sensors.

Ultrasonic evaluation and application of oriented polymer rods

Ultrasonic evaluation and application of oriented high density polyethylene (HDPE) rods are presented. Solid state ram extrusion method is used to fabricate such rods. Ultrasonic measurement results indicate that the ultrasonic signal strength and signal to noise ratio of the oriented HDPE rods are better than those of the non-oriented ones for both longitudinal and shear waves. Viscosity measurements and monitoring of epoxy cure at ambient temperature using clad rods consisting of an oriented polymer core and an epoxy cladding are also demonstrated.

SURFACE-ACOUSTIC-WAVE PROPERTIES OF MGO-DOPED LINBO3 SINGLE CRYSTALS MEASURED BY LINE-FOCUS-BEAM ACOUSTIC MICROSCOPY

Basic acoustic properties of five MgO-doped LiNbO3 rectangular parallelpiped specimens, having X-, Y-, and Z-cut planes, with different MgO dopant concentrations ranging from 0 to 13 mol % are investigated by line-focus-beam acoustic microscopy. The investigation is conducted to characterize the optical-use MgO:LiNbO3 crystals and wafers and to establish large-diameter crystal growth conditions. Leaky-surface-acoustic-wave (LSAW) velocities are measured on each crystalline plane of each specimen as a function of the wave propagation direction and are compared with the measured chemical composition ratios of Mg/Li/Nb, densities, and lattice constants. It is shown that, as the dopant concentrations increase in the experimental composition region, the LSAW velocities increase almost linearly for all the surfaces and all the propagation directions. The LSAW velocities are linearly proportional to the lattice constants, but inversely proportional to the densities.

High temperature integrated ultrasonic shear wave probes

Integrated ultrasonic shear wave probes have been fabricated using steel substrates through a paint-on method with the use of mode conversion from longitudinal to shear waves. The probe can be operated up to 150°C. A probe simultaneously generating and receiving both longitudinal and shear waves is also demonstrated.

Real-time process monitoring of micromoulding using integrated ultrasonic sensors

Real-time, non-intrusive and non-destructive process monitoring of micromoulding has been performed using novel ultrasonic sensors integrated onto the barrel and mould insert with an ultrasonic pulse-echo technique. The relative variation of the polymer melt temperature inside the extrusion barrel can be obtained using the ultrasonic velocities of the melt measured at the barrel during extrusion. Melt flow arrival in the mould, and solidification, shrinkage and detachment of the polymer inside the mould cavity are also successfully monitored. The presented ultrasonic sensors and technique enable optimizing the micromoulding process, and improving quality of the moulded parts and process efficiency.