In this paper, a sensor based on polyvinylidene fluoride (PVDF) piezoelectric thin film was designed and fabricated to detect wrist motion signals. A series of dynamic experiments have been carried out, including the contrast experiments of different materials and force-charge signal characterization. The experimental results show that when the excitation signal exceeds 15 Hz, the sensitivity of the sensor is always stable at 3.10 pC/N. The signal acquisition experiment of the wrist motion has been carried out by using this sensor. The experiment results show that, with the advantages of small size, good flexibility, and high sensitivity, this wrist PVDF sensor can be used to detect the wrist motion signals with weak amplitude, low frequency, strong interference, and randomness.

An all-dielectric metamaterial absorber based on water resonator encapsulated in resin container is proposed. The absorber can afford the maximum absorption up to 98% at 190 GHz, as well as the wide absorption frequency range from 115 GHz to 300 GHz and a nearly 90% relative absorption bandwidth. The role of water resonator sealed in the resin shell in improving absorption capability is demonstrated by the comparison result that the proposed absorber is superior to pure water or pure resin absorber with the same dimension and interpreted by a further study on the fields and power loss density distributions. Moreover, the proposed absorber can remain excellent absorption performance even for the oblique incidence with large angles. Besides the outstanding absorption performance, the proposed absorber has the advantage of low cost endowed by the use of water, which makes it promising for EM compatibility in the millimetre-wave and high-power cases.