Low-Power Ultrasonic Front End for Cargo Container Monitoring

A low-power ultrasonic communication front end conceived for cargo container monitoring is presented. Two piezoelectric transducers (PTs) operating at 40 kHz are fixed to the metallic wall by means of a customized magnetic case, allowing a noninvasive inside-outside communication preserving the container integrity. Once the resulting ultrasonic channel is characterized, an experimental measurement setup based on field-programmable gate array (FPGA) is implemented for testing some basic modulation and detection schemes in terms of bit error rate (BER), also considering their robustness against undesired mechanical and electromagnetic perturbations. On this basis, a compact digital differential binary phase-shift keying (DBPSK) modulator using a square carrier signal is proposed. Frequency and amplitude tracking algorithms are designed for optimizing the quality and robustness of the data transmission. Finally, a low-power low-rate (up to few kb/s) architectures based on the previous elements are presented. All the proposed contributions are experimentally validated.