A Novel Microwave Sensor for Non- Destructive Evaluation of Silicon Nitride Bearing Balls

Period of Performance: 03/20/2009 - 12/20/2009


Phase 1 SBIR

Recipient Firm

Alphasense, Inc.
510 Philadelphia Pike Array
Wilmington, DE 19809
Principal Investigator


In this proposal, Alphasense, Inc. details the development of a novel microwave NDE sensor for defect inspections in silicon nitride bearing balls. The key innovations of this proposal include the following: a) the use of the spherical bearing ball as a dielectric resonator, thus enabling us to correlate the resonance characteristics of the bearing ball with various defects; b) the measurements in the microwave region lead to very large penetration depth (several inches) in the bearing balls, allowing us to inspect defects at a large depth below the surface, not just the surface/subsurface defects, and c) the applications of Principal Component Analysis (PCA) and Support Vector Machine (SVM) facilitate automatic classification of the defect types. With such innovations, the merits of the proposed sensor and its advantages over other techniques include: a) Rugged, compact and low cost, b) Sensitive for defect inspections, c) Capable of detecting below surface defects, d) Suitable for a variety of defects, e) Real- time detection capability, and f) Easy and safe to the operators. BENEFIT: The outcome of this research is coupled to a very clear commercialization path. The most straightforward application for the proposed sensor is to detect defects in silicon nitride bearing balls used in hybrid bearings for aerospace and defense industries. Our sensor can also be used to detect defects in bearing balls made of other ceramic and plastic materials, such as zirconia, alumina, and acrylic. Bearings made of such materials have been widely used in automobile, medical, chemical and petroleum industry. A simple search on the Globalspec returns with around 500 U.S. manufacturers producing ball bearings, more than 100 companies producing ceramic bearing balls, and more than 2000 companies producing plastic bearing balls. Assume each of these companies need two sensor units for the quality check, the total demand in the U.S. alone will be 5200 units. This corresponds to a market size of ~$15.6 million if we can sell our sensor at a price of $3000/unit. Additionally, spherical and cylindrical dielectrics can be used as microwave filters and ultrahigh efficiency modulators. Our sensor may also find applications in the quality assurance of such critical microwave components.