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This study reports a piezoelectric poly(vinylidene fluoride) (PVDF) polymer-based sensor patch for respiration detections in dynamic walking condition. The working mechanism of respiration signal generation is based on the periodical deformations on a human chest wall during the respiratory movements, which in turn mechanically stretch the piezoelectric PVDF film to generate the corresponding electrical signals. In this study, the PVDF sensing film was completely encapsulated within the sensor patch forming a mass-spring-damper mechanical system to prevent the noises generated in a dynamic condition. To verify the design of sensor patch to prevent dynamic noises, experimental investigations were carried out. Results demonstrated the respiration signals generated and the respiratory rates measured by the proposed sensor patch were in line with the same measurements based on a commercial respiratory effort transducer both in a static (e.g., sitting) or dynamic (e.g., walking) condition. As a whole, this study has developed a PVDF-based sensor patch which is capable of monitoring respirations in a dynamic walking condition with high fidelity. Other distinctive features include its small size, light weight, ease of use, low cost, and portability. All these make it a promising sensing device to monitor respirations particularly in home care units.

The method of third harmonic (3f0 transmit phasing is capable of providing effective tissue background suppression for contrast-to-tissue ratio (CTR) improvement in harmonic imaging. With the additional 3f0 transmit signal to generate both the frequency-sum and the frequency-difference components of harmonic signal, the tissue suppression is achieved when the two components are opposite in phase and mutually cancel out. One major problem in 3f0 transmit phasing is the limited signal-to-noise ratio (SNR) due to the constraint on transmit amplitude. Chirp excitation can be applied in contrast harmonic imaging to enhance the SNR with minimal destruction of the microbubbles. In this paper, the effect of chirp waveform in combination with the 3f0 transmit phasing was studied using both in-vitro experiments and simulations. Our results indicate that, though the chirp transmit pulse can increase the SNR of harmonic imaging in 3f0 transmit phasing (3 dB, p < 0.001), it suffers from degraded tissue harmonic suppression and thus provides less CTR improvement as compared to a conventional pulse. The spectral mismatch between the frequency-sum and the frequency-difference components of tissue harmonic signal is particularly evident in the off-center region of second harmonic band, leading to significant residue tissue background. Consequently, with the chirp waveform, the improvement of CTR decreases from 9.5 dB to 5.9 dB (p < 0.0006) and thus a tradeoff exists between the SNR improvement and the CTR improvement in 3f0 transmit phasing.

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