Non-traditional information storage has become increasingly ubiquitous as a means of providing interactive, environment-specific information. Two popular examples of this are Optical Quick Response (QR) codes and Radio-Frequency Identification (RFID) tags, which are used in product tags, anti-theft systems, tamper-evident seals, logistics, etc. From a security point-of-view though, these two examples have unique drawbacks. Optical QR codes can be easily viewed and replicated because they are limited to the surface of objects, and RFID tags are prone to remote RFID skimming. With this in mind, we are investigating a PZT-based information storage method which has visibly indistinguishable features, is incompatible with skimming, and can be used with a QR-type encoding scheme. This information storage method involves a frequency-dependent array of transducers with engineered resonance profiles. In this proceedings, we investigate methods of engineering these resonance profiles for the case of a square PZT wafer. Specifically, we investigate the use of non-uniform poling to enhance specific resonances. Simulation results and a discussion of changes to the resonance characteristics resulting from non-uniform poling are included.
Low-frequency ultrasonic collimated beam generation from radial modes of piezoelectric disc transducers is studied using a coupled electromechanical finite element approach. First, resonance and vibration characteristics of the radial modes of the disc transducers are obtained using an eigenfrequency analysis. The vibration patterns obtained from numerical simulation are compared with those obtained from experiments and are in good agreement. Next, ultrasonic beam profiles in water generated from the radial modes of a piezo-disc are studied. It was found that a free piezo-disc generates a Bessel-beam with multiple side-lobes. In contrast, clamping the lateral edges of the piezo-disc results in a well-collimated central beam with reduced side-lobes. This provides a novel transducer design for low-frequency collimated beam generation for imaging through highly attenuating materials
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