Methods of solving in-band ripples and out-of-band suppression for yarn tension sensor based on surface acoustic wave

The two key problems of the in-band ripples and out-of-band suppression are proposed in the design of the SAW yarn tension sensor and the methods of decreasing them are achieved. The unbalanced split-electrode interdigital transducers (IDT) are designed so that the total phase of the regenerated reflection wave and mass load feedback is close to 180°, leading to an effective reduction of the in-band ripples effect characterised by the sensor frequency response. The engraved bi-directional slots on the back of the substrate can block the propagation path of the bulk acoustic wave (BAW) to a certain extent, reducing the influence of BAW propagation and suppressing the out-of-band suppression of the frequency response. The experimental results show that the SAW yarn tension sensor with the unbalanced split-electrode IDT can reduce the in-band ripples from 23.34 to 0.93 dB, and the engraved bi-directional slots can suppress the out-of-band suppression from 28.03 to 7.71 dB.