High contrast ultrasound images of defects in food package seals

Previous work to detect defects in food packaging seals using pulse-echo ul trasound inspired the backscattered amplitude integral (BAI) imaging techni que, which could reliably identify channels with diameters 38 mu m or large r at a center frequency of 17.3 MHz (lambda = 86 mu m). The current study p resents two new processing techniques that more reliably reveal smaller cha nnels (approximate to 6 mu m in diameter). The RF sampling technique (RFS) displays a single, time-gated, pressure value from the received (not envelo pe-detected) RF waveform at each transducer position. The RF correlation te chnique (RFC) calculates the correlation coefficients of the RF signals wit h a reference signal that does not pass through a channel. The correlation coefficient can be calculated for the entire RF signal (RFCE) or over a sho rt segment of the RF signal (RFCS). The performance of these imaging method s for detecting channel defects is investigated for plastic and aluminum fo il trilaminate films with 6, 10, 15, 38, and 50 mu m channels filled with w ater or air. Data are collected with a focused ultrasound transducer (17.3 MHz, 6.35 mm in diameter, f/2, 173 mu m -6 dB pulse-echo lateral beamwidth at the focus) scanned over a rectangular grid, keeping the package in the f ocus. Performance is measured using detection rates, image contrast, and co ntrast-to-noise ratio (CNR). Both RFS and RFCS have improved detection rate s relative to BAI for channels 15 mu m or smaller, The RFCS technique is th e most effective at smoothing the background, leading to the greatest CNR i mprovements.