Fiber or nanowire composites offer many benefits for piezoelectric sensor and actuator applications. Piezoelectric composite is comprised of piezoelectric ceramics lain in polymer matrix. The composite with the piezoelectric ceramics connected in one direction and the polymer in three directions is named as 1-3 composite. 1-3 composites are most ordinary used and the anisotropic alignment of PZT in the composite may substantially lower lateral piezoelectric coupling and increases the sensitivity of the transducer mechanically. Piezoelectric fiber composites are suitable for sensor applications, medical diagnostics and nondestructive testing. udSingle crystal zinc-oxide nanowires were synthesized through a simple hydrothermal route and subsequently mixed with polyimide matrix to form ZnO nanocomposites. Superimposed a.c. and d.c. electric fields were applied to microscopically tailor the alignment of ZnO nanowires in polyimide matrix to form anisotropic nanocomposites. Piezoresistive property of ZnO nanocomposite was investigated for strain sensor application. A large gauge factor was obtained from the monotonic uniaxial stress-strain experiment for this nanocomposite and it is much higher than that of ordinary metal strain sensor. A low frequency fiber composite vibration sensor was fabricated and experimentally studied. The global parameters of the composite were substituted into lumped and distributed element constituent equations for piezoelectric unimorph to theoretically predict the sensitivity and effective frequency response range of the vibration sensor. An experiment was carried out to validate the result from the theoretical model. The output voltage per unit input displacement keeps stable in a wide frequency range with a suitable damping ratio. This PZT fiber composite sensor was also applied for soft material strain measurement and soft biomaterial surface morphology and elastic modulus characterization. From the theoretical evaluation and experiment result, this strain sensor is suitable for strain measurement with high sensitivity and high softness. A rectangular breathing sensor and an annular breathing sensor were fabricated for breathing rate and depth monitoring. Both sensors were tested under different physiological conditions and measurement results could be utilized for precaution and monitoring of breathing diseases. Both of them are excellent for monitoring breathing rate and depth and be nice choices for daily use and diagnose purpose.
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