This work presents the development of flexible dual-mode surface acoustic wave (SAW) sensor based on single crystalline thin film lithium niobate (TF-LN). Numerical modeling is conducted to investigate the SAW propagation and the effects on strain sensitivity. The dependence of strain sensitivity on angles between the applied strain and SAW propagation direction is analyzed numerically and experimentally, showing that the maximum strain sensitivity is at 45° rather than longitudinal direction. 128° Y-cut TF-LN (~50 µm), obtained by micromachining technique, is utilized as the piezoelectric substrate to fabricate the SAW strain sensors with dual-mode, namely Rayleigh mode and thickness shear mode. The sensor has excellent flexibility and demonstrates remarkable capability for an ultra-wide range strain measurement up to ±3000 µε. Temperature effects on resonant frequency and strain sensitivity are investigated in the range of 25 °C-100 °C, and similar temperature characteristics are observed for the dual modes. A method of beat frequency between the dual modes is introduced which is able to eliminate the temperature effect on strain sensing, an on-chip temperature influence removing capability. All the results clearly show that this sensor exhibits great potential for applications in flexible electronics and microsystems.

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Vanadium dioxide (VO2) coating plays an important role in energy saving and environmental protection due to its unique reversible phase transition. To solve the daylighting issue of VO2 coating, a VO2 (M)–silicon dioxide (SiO2) composite coating is fabricated from ammonium citrato-oxovanadate(IV) by a SiO2-assisted coating method. The VO2 (M)–SiO2 composite coating possesses excellent thermochromic properties that have produced varying results, i.e. 49.2% of visible transmittance, 52.3% of transmittance reduction at 2000 nm wavelength, 12% of solar energy modulation (ΔT sol ) and a phase transition temperature of 56.0 °C. Our findings may pave the way to extending the large-scale application of smart windows based on thermochromic VO2.

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