ZnO Ultrasonic Transducers for Non-Destructive Testing

The use of composite materials, advanced ceramics, and high-performance alloys is widespread and increasing because of their usefulness in improving strength and performance while reducing weight. New applications that take advantage of these advanced performance capabilities are being unveiled continuously. These new applications push the boundaries of material performance and require very high quality to achieve the desired performance. However, the complexity of their makeup with very small critical feature sizes and the scarcity of techniques to measure and monitor their characteristics and performance have inhibited their introduction, acceptance, and usefulness. New technologies and techniques with higher power, higher frequencies, and higher resolutions are needed to non-destructively interrogate these difficult materials to effectively and efficiently determine their quality and to achieve a greater understanding of their potential performance.

ZnO Bulk Crystal Image

NuMat has created a new class of zinc oxide (ZnO) piezoelectric materials that can provide these needed capabilities. By growing and processing high- quality single crystals of zinc oxide, NuMat can create directionally-oriented, ultrasonic transducers capable of high powers and very high frequencies in the 1-500 MHz range, and potentially even higher. These ultra-high frequencies enable much higher image resolutions than current ultrasonic non-destructive testing systems. The precision and uniformity of NuMat crystals results in highly-peaked waveforms centered on the desired emission frequency while removing undesirable higher and lower frequency noises.

NuMat’s zinc oxide ultrasonic transducers are directionally-oriented and emit sound in only two directions as compared to the omnidirectional nature of the common state-of-the-art materials. Therefore, NuMat zinc oxide transducers can provide more ultrasound energy in the desired direction for the same input energy resulting in a higher signal to noise ratio. This also lowers the noise floor and quiets the time between pulses allowing for smaller response signals to be detected. Because of zinc oxide’s wide band gap of about 3.3eV, it is also capable of withstanding higher voltages and can therefore achieve higher power densities than other available piezoelectric materials. These characteristics result in ultrasonic transducers capable of deeper penetration depths and larger signal-to-noise ratios that can produce much higher image resolutions and significantly improved ability to detect defects at the very small sizes found in advanced, high-performance materials.

Because of proprietary advances in signal generation and reception control electronics and programming, NuMat ZnO ultrasonic transducers are also capable of operation in a spread-spectrum mode; providing the ability to modify the frequency, waveform, penetration depth, and power of the ultrasound in real-time. The combination of a spread-spectrum mode, high power densities, and ultra-high frequencies allows NuMat to create an innovative, continuously variable, non-destructive testing (NDT) process. First, the material is rapidly characterized using multiple frequencies, waveforms, and power levels. The return signals are then analyzed and used to tailor the interrogation signal to account for the in-situ characteristics of the material. Next, the interrogation signal is optimized via the tailoring of the frequency, waveform, penetration depth, and power and is then applied to conduct the non-destructive testing. This continuously variable process allows the NuMat ultrasonic NDT system to compensate for the as-found conditions of the material in order to extract the maximum amount of information. This reduces error and improves the speed and accuracy of the ultrasonic non-destructive test. These capabilities are particularly suited for use with advanced composites but also advanced ceramics and high-performance metal alloys because of their ability to detect very small layer thicknesses and critical feature/flaw sizes.

Changing the game even further, NuMat breakthrough technologies can be used to create large area multiplexed arrays for covering 10s to 100s of square centimeters at a time. The system’s precision timing control and statistical control capabilities provides real-time, high confidence interval knowledge of the detected feature location and size resulting in more accurate and efficient NDT with higher quality assurance. Able to be integrated using standard automation and control SCADA systems, NuMat zinc oxide ultrasonic transducer NDT solutions can be brought to bear as an integrated element directly in your process line. Working with NuMat technologies and know-how, difficult NDT challenges can now be overcome.

Features and Benefits

  • High-MHz to even GHz frequencies
  • High voltages enable higher power emissions
  • Directionally-oriented transducers that put more ultrasonic energy on target for the same or lower energy input than current transducers
  • Very pure emission frequencies with highly-peaked waveforms
  • Higher resolutions allow improved detection of smaller, critical feature sizes
  • Improved speed and quality of ultrasonic non-destructive testing
  • Pixelated arrays for large area scanning
  • Direct process integration
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