Polymers and papers, which exhibit piezoelectricity, find a wide range of applications in the industry. Ever since the discovery of PVDF, piezo polymers and papers have been widely used for sensor and actuator design. The direct piezoelectric effect has been used for sensor design, whereas the inverse piezoelectric effect has been applied for actuator design. Piezo polymers and papers have the advantages of mechanical flexibility, lower fabrication cost and faster processing over commonly used piezoelectric materials, such as PZT, BaTiO3. In addition, many polymer and paper materials are considered biocompatible and can be used in bio applications. In the last 20 years, heterostructural materials, such as polymer composites and hybrid paper, have received a lot of attention since they combine the flexibility of polymer or paper, and excellent pyroelectric and piezoelectric properties of ceramics. This paper gives an overview of piezoelectric polymers and papers based on their operating principle. Main categories of piezoelectric polymers and papers are discussed with a focus on their materials and fabrication techniques. Applications of piezoelectric polymers and papers in different areas are also presented.
Biomedical wearable sensors enable long-term monitoring applications and provide instantaneous diagnostic capabilities. Physiological monitoring can help in both the diagnosis and the ongoing treatment of a vast number of cardiovascular and pulmonary diseases such as hypertension, dysrhythmia, and asthma. In this paper, we present a system capable of monitoring several vital signals and physiological variables that determine the cardiopulmonary activity status. We explore direct measurements of multiple vital parameters with only one sensor and without special constraints. The system employs a PZT-4 piezo transducer stimulated by a suitable analog front-end. The system both generates pulsed ultrasound waves at 1 MHz and amplifies reflected echoes to track internal organ motions, mainly that of the heart apex. According to the respiratory motion of the heart, the proposed system provides respiratory and heart cycles information. Promising results were obtained from six subjects with an average accuracy of 96.7% in heartbeats per minute (BPM) measurement, referenced to a commercial photoplethysmography sensor. It also exhibits 94.5% sensitivity and 94.0% specificity in respiration detection compared to a SPR-BTA spirometer signal as a reference.
Robustness of estimating cardiorespiratory parameters from photoplethysmography (PPG) signal is highly dependent on the quality of the signal, which heavily affected by motion artifacts. To increase the estimation accuracy of cardiorespiratory parameters, the present work describes a novel fusion method to efficiently and effectively reduce the motion artifacts from the acquired PPG signal. The proposed fusion technique requires simultaneously acquiring data from a PPG sensor and accelerometer. To filter out the frequencies associated with motion, the method uses stopband filters with a central rejection frequency and bandwidth determined by the output signal of the accelerometer. Under such, the proposed method to remove the motion artifacts does not depend on the quality of the reference signal and has almost no impact on the nature of PPG signals (i.e., amplitude, baseline, and periodicity). The effectiveness of the proposed method in the suppression of in-band and out-of-band frequencies of motion is numerically and experimentally evaluated. It is shown that the filtered PPG signal has sufficient information to estimate different cardiac parameters such as heart-rate (HR), respiration rate (RR) and blood oxygen saturation (SpO2). The motion artifacts free PPG signal obtained using our proposed method can estimate HR, RR, and SpO2 with an accuracy of above 95%. This level of accuracy confirms the usefulness of the proposed fusion method for accuracy improvement of cardiorespiratory parameters monitoring by the filtered PPG signal.
Lead zirconate titanate and polydimethylsiloxane (PZT− PDMS) thin films are an attractive choice for a flexible piezoelectric substrate. In this work, the surface modification of the PZT−PDMS composite with plasma treatment is developed to fabricate flexible conductor patterns or devices directly on the composite surface. Optimized plasma treatment conditions are achieved by varying plasma parameters such as the pressure of treatment, type of gas, gas flow, and time of treatment. Plasma polymerization is carried out using C 2 H 4 − CO 2 , and argon (Ar) is used for the surface ablation effect in lowpressure conditions. Atmospheric pressure plasma (APP) is performed in a N 2 atmosphere which has a surface etching effect. All the treatments create a hydrophilic layer, which is confirmed with water contact angle measurements, X-ray photoelectron spectroscopy, and Fourier transform infrared analysis. Silver conductive ink was printed on the plasmatreated films to fabricate flexible conductive patterns, and the bonding strength was tested by performing adhesive tests such as tape, ultrasonic, and soak tests. APP treatment under a N 2 environment with a 300 V input voltage, 21.5 kHz frequency, and 2 min deposition time proves to be the most efficient surface modification technique. This treatment produces a silica-like layer on the composite surface and results in better wettability. It reduces the contact angle from 108 to 20°immediately after the treatment and shows strong adhesion during several rigorous adhesion tests. The printed conductive patterns on the N 2 -treated film show strong mechanical stability and exhibit great electric conductivity under bending and releasing. The APP treatment under N 2 environment can overcome the adhesion issue of the printed conductive layer on the hydrophobic composite surfaces. Moreover, all the above plasma treatments have a negligible effect on the piezoelectric properties of PZT−PDMS films.
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