Here, for the first time, we propose a simple strategy to realize an ultra-wideband metamaterial absorber by using room temperature ionic liquids (ILs) which are a new class of organic salts containing purely anions and cations. At first, the microwave loss characteristics of methylimidazolium ILs were investigated. The results reveal that these ILs have large ionic conductivities and dielectric loss factors which means high conductive loss and dielectric loss of microwaves can both be caused, and the IL with a shorter carbon chain on cation has potential to produce a higher absorption. When the IL [EMIm][N(CN)₂] is properly arranged into periodic cylinders supported by a 3D-printed dielectric bracket, impedance matching can be enhanced in a wide band, and a strong absorption of microwave above 90% can be achieved within the whole frequency range of 8.4–29.0 GHz, which was verified in simulations and experiments. In addition, the IL-based metamaterial absorber can work efficiently at arbitrary polarization angles and wide incident angles from 0° to 45°. Mechanism investigations show that the perfect absorption in ILs-based MMAs is mainly originated from the loss of dielectric polarization and induced ionic currents in ILs. Distinct from metamaterial absorbers based on water or other liquids, such IL-based metamaterial absorber can not only broaden the absorption bandwidth significantly, but also have potential application in a wider temperature range because of the exceedingly high thermal stabilities of ILs.

This work presents ionic liquid based variable focus lenses using electrowetting, which exhibit excellent performance over a conventional saline based lens such as good tolerance of sharp temperature variation, wide operating temperature range (which is up to 100 °C) and in particular high stability at high temperatures.

In this study, we develop an innovative low voltage reversible electrowetting of water droplet based on perfluorinated silane-modified slippery lubricant-infused porous surface (SLIPS) that is impregnated by silicone oil. The electrowetting properties of SLIPS modified with and without 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) are investigated initially. After modifying the lubricated PTFE membrane with PFOTS, the driving voltage of electrowetting decreases sharply; the threshold voltage is only 5 V, which exhibits an immediate 15-fold decrease compared to that of the unmodified SLIPS. Subsequently, the electrowetting reversibility based on SLIPS modified with different concentrations of PFOTS solution is studied. Our results show that the initial contact angle increases with an increase in the concentration of PFOTS solution, but the electrowetting reversibility has an obvious depravation. The optimal concentration is about 0.03 wt%, in which the electrowetting hysteresis is less than 5°, and a large modulation can be achieved in the contact angle ranging from 107° to 60° with 60 V driving voltage in ambient air. On the basis of surface topography characterization, this low voltage electrowetting is attributed to the contact interface transformation from liquid–oil interface to the combination of liquid–oil and liquid–PFOTS interface. Therefore, the surfaces maintain low surface energy property of PFOTS and retain SLIPS property. In addition, a marked asymmetric contact angle variation with respect to voltage polarity on SLIPS modified with PFOTS is observed for the first time; the low voltage electrowetting occurs at positive voltage but does not occur at negative voltage. Our study provides a new pathway to achieve low voltage electrowetting without decreasing the thickness of the dielectric layer or increasing the dielectric constant.

This paper reports an open-loop method for highly efficient and precise droplet manipulation with polarity-dependent low-voltage electrowetting on a perfluorinated silane modified slippery liquid infused porous surface (SLIPS) in which a droplet can be driven between individual square electrodes. The electrowetting phenomenon on modified SLIPS was investigated first, and it exhibited an up to 55° contact angle difference with respect to voltage polarity while the threshold voltage was reduced to only 2 V. Then, a coplanar electrode experiment was designed to study the performance of droplet manipulation on several modified SLIPS samples with different vertically placed times and silicon oil viscosities. The optimal condition for preparing a modified SLIPS membrane is that a sample is placed vertically for 2 hours after infusing 10 cSt silicon oil, on which the droplet can be driven with the fastest velocity, and the activation voltage for moving a droplet is only 8 V. Finally, multi-droplet simultaneous and continuous manipulation on modified SLIPS in bi-direction on a loop of square electrodes was achieved. Interestingly, unlike asymmetric electrowetting, actuation methods on a solid insulator and hydrophobic layers, the droplet actuation velocity was not limited by the contact angle saturation effect and always increased with the applied voltage on modified SLIPS. This method achieves a very wide range of droplet continuous manipulation velocities from 0.075 mm s⁻¹ to 123 mm s⁻¹ under 20 V to 500 V applied voltage and the continuous droplet actuation voltage exhibits at least a 15-fold decrease compared to that of an unmodified SLIPS membrane.

Here, the microwave-absorbing properties of 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium ([E and BMIm] ⁺ -based) room-temperature ionic liquids (ILs) with different anions were systematically investigated by measuring dielectric properties in the 1–14 GHz microwave-frequency range. First, the dielectric properties of the [E and BMIm] ⁺ -based ILs were studied with a typical open-ended coaxial probe system. The results showed that the real part of permittivity values decreased from 13 to 4 and the values of loss tangent decreased from 5.91 to 0.24, meaning that ILs displayed high dielectric-loss characteristics at microwave-frequency ranges. Furthermore, it was found that the conductivity loss was dominant for dielectric loss in the low-frequency band, and the polarization loss played a major role in high-frequency bands. For the same anion ILs with different cations, the permittivity became higher as the length of the alkyl chain decreased. The absorption properties of [E and BMIm] ⁺ -based ILs could be obtained based on their dielectric properties, and found the ILs absorption bands were mainly concentrated in the C band and X band. It was noted that the maximum reflection loss (RL) of [BMIm][NTf ₂ ] with a thickness of 4 mm reached −27.6 dB at 8.73 GHz, and the bandwidth of an RL less than −10 dB could be up to 4.3 GHz. The absorption peak frequency of the ILs gradually shifted to lower frequencies with increasing temperature and coating thickness, which might be caused by the change in impedance matching.