A Photocured Bio-based Shape Memory Thermoplastics for Reversible Wet Adhesion.

Development of reversible wet or underwater adhesives remains a grand challenge. Because weakened intermolecular interactions by water molecules or/and low effective contact area cause poor interface to the wet surfaces, which significantly decreases adhesive strength. Herein, a new photocured, bio-based shape memory polymer (SMP) that shows both chemical and structural wet adhesion to various types of surfaces is developed. The SMP is polymerized from three monomers mainly from bio-sources to form linear polymer chains dangled with hydrophobic side chains. The hydrogen acceptor and donor groups in the chains form hydrogen bonding with the surfaces, which is protected by the hydrophobic chains in the interface. The SMP shows tunable phase transition temperature (Tg) of 17-38 °C. In a rubbery state above Tg, the adhesive forms conformable contact with the targeted surfaces. Below Tg, a transition to a glassy state locks the conformed shapes to largely increase the effective contact area. As a result, the adhesive exhibits long-term underwater adhesion of > 15 days with the best adhesion strength of ~ 0.9 MPa. Its applications in leak repair, underwater on-skin sensors were demonstrated. This new, general strategy would pave avenues to designing bio-based, long-lasting, and reversible adhesives from renewable feedstocks for widespread applications.

A single source microwave photonic filter using a novel single-mode fiber to multimode fiber coupling technique.

In this paper we present a fully tunable and reconfigurable single-laser multi-tap microwave photonic FIR filter that utilizes a special SM-to-MM combiner to sum the taps. The filter requires only a single laser source for all the taps and a passive component, a SM-to-MM combiner, for incoherent summing of signal. The SM-to-MM combiner does not produce optical interference during signal merging and is phase-insensitive. We experimentally demonstrate an eight-tap filter with both positive and negative programmable coefficients with excellent correspondence between predicted and measured values. The magnitude response shows a clean and accurate function across the entire bandwidth, and proves successful operation of the FIR filter using a SM-to-MM combiner.

Photonic microwave finite impulse response filter using a spectrally sliced supercontinuum source.

A novel photonic microwave discrete-time finite-impulse response filter is created by spectrally slicing a supercontinuum source, generated from a mode-locked laser. We experimentally demonstrate a four-tap filter with a 28.16 dB extinction ratio. Comparison between measured and predicted magnitude responses shows an excellent match in the performance of the notch filter across the entire bandwidth. The small amount of individual deviation points from the predicted response shows the stability of the amplitude fluctuations between each of the individual, spectral sliced filter taps.