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Details the authors’ pursuit of non‐contact ultrasound.

In November 2001, Scott Carlson, in the Chronicle of Higher Education wrote an article on library use titled “The deserted library: As students work online, reading rooms empty out—leading some campuses to add Starbucks” (Carlson, 2001). The essence of this chapter is that many librarians, facing dramatic declines in library gate counts resulting from the wealth of electronic resources accessible remotely, were beginning to move away from traditional conceptions of the library as primarily a repository for print collections. Carlson describes the “tough sell” that the Georgia College and State University in Milledgeville had experienced when planning a $19.5 million library addition in the mid-1990s. In response librarians had begun “fighting back” with “plush chairs, double-mocha lattes, book groups, author readings.” Still, no one knew whether these stratagems would enhance learning or bring its readers back.

This paper aims to present the details of isotactic polypropylene (it-PP) films with a cellular structure (air-cavities) dedicated to pressure sensors. The polymer composites (thin films enriched with 5 and 10 wt% of mineral fillers as Sillikolloid P 87 and glass beads) should exhibit suitable structural elasticity within specific stress ranges. After the deformation force is removed, the sensor material must completely restore its original shape and size.

Estimating the stiffness tensor element (C₃₃) for polymer films (nonpolar space-charge electrets) by broadband resonance ultrasound spectroscopy is a relatively simple method of determining the safe stress range generated in thin pressure sensors. Therefore, ultrasonic and piezoelectric studies were carried out on four composite it-PP films. First, the longitudinal velocity (v_L) of ultrasonic waves passing through the it-PP film in the z-direction (thickness) was evaluated from the ω-position of mechanical resonance of the so-called insertion loss function. In turn, the d₃₃ coefficient was calculated from accumulated piezoelectric charge density response to mechanical stress.

Research is at an early stage; however, it can be seen that the mechanical orientation of the it-PP film improves its piezoelectric properties. Moreover, the three-year electric charge stability of the it-PP film seems promising.

Ultrasonic spectroscopy can be successfully handled as a validation method in the small-lot production of polymer films with the air-cavities structure intended for pressure sensors. The structural repeatability of polymer films is strongly related to a homogeneous distribution of the electric charge on the electret surface.