The Largest Open Access Portal of Nondestructive Testing (NDT)

A number of ultrasonic testing applications, such as for very thick & attenuative composites, concrete, lumber, construction, refractories, certain produce and processed foods, and similar materials have been chronically limited by the availability of suitable transducers. Typically, such materials require Very Low Frequencies (VLF), i.e., from ~50 kHz to ~200 kHz. Conventional transducers based upon monolithic piezoelectric materials or even Polymer Matrix Piezoelectric (PMP) composites in this frequency range are: excessively resonating, extremely noisy, low sensitivity, low signal-to-noise ratios, very expensive. As a result VLF ultrasound has not advanced substantially. ? At Ultran we have been actively engaged in testing complex materials for a long time with a special focus on transducers development. This effort ultimately culminated in the development of Gas Matrix Piezoelectric (GMP?) composite (US and international patents) -- characterized by very unusual, but highly desirable features and properties. For example, GMP?s thickness coupling constant is equal to its longitudinal coupling constant and its radial coupling is practically zero. These characteristics make GMP? the highest efficiency and broadband transducer material. ? Furthermore, the manufacturability of GMP? allows us to make extremely large single element devices as well as multi-element transducers. GMP?-based contact and non-contact transducers have been perfected from less than 50 kHz to 350 kHz frequencies. ? These transducers have helped to realize many difficult ultrasound applications, and have also opened other possibilities . In this presentation we provide significant characteristics of GMP? transducers as well as a number of complex applications for testing highly attenuative and thick materials.