| ABSTRACT: | HIGH EFFICIENCY NON-CONTACT TRANSDUCERS AND A VERY HIGH COUPLING
PIEZOELECTRIC COMPOSITE
M. Bhardwaj, and A.Bhardwaj
Ultran Laboratories, Inc., Boalsburg, PA, United States
Despite the usefulness of ultrasound for materials analysis, this age-old method has been stifled by direct or
indirect transducer contact to the test media, generally by liquids. Consequently, a branch of materials that
are porous, liquid-sensitive, food, pharmaceuticals, wood lumber, concrete, consolidated powders, or in
early stages of formation cannot be analyzed by ultrasound without adversely affecting them. While Non-
Contact Ultrasound (NCU) is highly desired, yet its realization calls for overcoming natural barrier of
massive Z-mismatch between NTP coupling air and solids, which can be between <3 to >7 orders of
magnitude! This is only possible if transducers are characterized by phenomenally high transduction
efficiency in air.
After a struggle of more than 20 years, in 1997 we finally succeeded in creating ultrasound devices between
<100kHz to >5MHz, capable of generating 10s to 100s of Pa/V acoustic pressure in air -- US and
internationally patented. These transducers are approximately 12dB to 30dB lower in sensitivity relative to
their contact/immersion counterparts. In practical terms, the NCU transducers are capable of driving
ultrasound through any material even with relatively low energy excitation and amplification. However, it is
understood that NCU transmission is inversely proportional to test material Z. Also, that attenuation in a
medium of transmission, including air, increases relative to four powers of frequency.
This paper presents acoustic characteristics of NCU transducers, experimental evidence of their
exceptionally high efficiency, and applications possibilities for NDT, sensing, proximity analysis, and more.
In this paper we also introduce a new piezoelectric composite that is characterized by the highest coupling,
zero cross-talk, broad bandwidth, very low dielectric constant, and several other advantages -- US and
international patents pending. NCU and other transducers based upon this material are characterized by
efficiency that is twice that of conventional piezoelectric composites.
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