Transducer fabrication and testing

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Category: Transducers

Published on Tuesday, 02 March 2010 14:59

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Transducer fabrication and testing

• Fabrication of custom design high frequency transducers (Doppler, imaging, others).

  

• Linear and nonlinear acoustic field analysis.
  • to test the scientific ideas for possible practical applications.
  • to evaluate the materials.
  • to choose working conditions to optimize the beam shape.
  • determination of the influence of technological defects on the distribution of the acoustic field.
  • identification of properties of transmitting probes by comparison of measured and computed fields.
  • calibration of hydrophones.
The developed numerical code- nonlinear solver - provides information, which makes it possible to obtain all stationary and dynamic characteristics of the field generated by arbitrary shape transducers (including arrays of transducers). The solver allows time-spatial (3D+t) visualization of the pressure field. Our solver, besides of pure scientific applications of solving equations of nonlinear acoustics, can be used as a basic tool to support the process of design of the ultrasonic probes generating acoustic fields with finite amplitudes. It allows:

• Transducer modeling. The method of modeling and designing piezo-transducers (e.g. wide-band transducer with thickness changing gradually along its radius). Modeling is based on Mason’s equivalent circuits. Quarter-wave length matching layers, coaxial cable as well as transmitter and receiver impedance and electrical compensating circuit are taken into account.

• Inspection of the ceramic using home made scanning acoustic microscope.
• The microscope operates at the frequencies of 35MHz, 100MHz and 200MHz with corresponding lateral resolution of 40μm, 15μm and 7μm (for the surface imaging). The grey scale images represent amplitude or phase of the reflected signals. The system enables surface, subsurface and surface layer imaging. Below, some features of the microscopic imaging, in our opinion particularly useful for MINUET:
  • Phase imaging is very powerful and sensitive method for topography imaging. At 100MHz the distance changes of the order of 0.1μm can be detected. Our experience with phase imaging of the thin gold layers deposited on quartz samples show that this imaging is sensitive to any cracks, voids and other defects of the layer. At lower frequencies the topography of a big object like a focusing transducer cavity can be examined.
  • Operating in amplitude mode the microscope can be used for non-destructive micro-defectoscopy of materials. We have a good experience with subsurface imaging in metals up to several millimeters beneath the surface; however the piezo-ceramic materials would be examined for the first time in our lab.
  • The amplitude surface inspection is very sensitive to impedance changes and it can provide the information about the quality of adhesion and diffusion bonds, welds and laminates because any lack of coupling between materials changes dramatically the reflection coefficient.
  • The microscope can generate different surface waves that may be next used for imaging and measurements. The contrast in the image obtained using surface waves depends on their velocities. Thus the local velocity distribution in samples can be used for determination of the quality and homogeneity of material. Also, some stress introduced in samples and resulting elasto-acoustic effect can modify the local velocity. So, in some very homogeneous sample the stress distribution can be determined.
  • The surface waves imaging may be also applied for grains’ imaging.
  • Microscopic transmission can also generate the Lamb waves in layered structures. The measurements with Lamb waves would require constructing a new cylindrical Lamb Waves lens. The traditional lenses can of course generate Lamb waves but other modes of waves are produced as well distorting the measurements.
  • The microscope enables surface acoustic waves velocity and attenuation measurements by V(z) technique, which can be also used for material characterization. This method can be applied for determination of thickness of thin layers.

• There is the ultrasound scan system constructed in The Departament of Ultrasonics. The system can scan ultrasonic field in line, plane or 3D cube with minimal raster 0.1mm. Measurements usually are taken by stationary hydrophone where ultrasonic head is moved by a mechanical scanner controlled by PC computer. Data of the presented field distribution were taken using 2MHz frequency, 50% bandwidth and 1.5cm diameter, flat transducer on 43cm distance from hydrophone.