Heat switches are a key enabling element of efficient refrigerators that are based on the electrocaloric effect. We
demonstrate a new concept for a heat switch that is based on micro-scale electrohydrodynamic (EHD) flows in thin
layers of dielectric fluids. In this device, convective flow of the fluid is controlled by applying an electric field across the
fluid layer. This creates a heat switch that can be cycled between a “closed” state with efficient convective heat transport and an “open” state with less efficient conductive heat transport. Substantial switching of the thermal transport coefficient was achieved in 500 μm thick layers of commercial hydrofluoroethers and bias voltages of typically 390 V. The efficacy of the heat switch varied by almost four orders of magnitude for different biasing schemes. The highest efficacy was achieved by biasing a patterned strip electrode and using a planar ground electrode. A preliminary experiment found a thermal conductivity contrast of 4.7±1.1 for the switch in the closed vs. open state. We also characterize the electrocaloric response of commercial multilayer ceramic chip capacitors and show that they can serve as serve as a useful surrogate material for first-generation electrocaloric refrigerators until higher performing multilayer structures of ferroelectric polymers are available.
In this paper we briefly present the theory of Fourier Transform Heterodyne (FTH), describe past verification experiments carried out, and discuss the experiment designed to use this new imaging technology to perform optical correction. FTH uses the scalar projection of a reference laser beam and a test laser beam onto a single element detector. The complex current in the detector yields the coefficient of the scalar projection. By projecting a complete orthonormal basis set of reference beams onto the test beam, the amplitude and phase of the test beam can be measured, allowing the reconstruction of the phasefront of the image. Experiments to determine this technique's applicability to optical correction and optical self-correction are continuing. Applications of this technique beyond optical correction include adaptive optics; interferometry; and active, high background, low signal imaging.
Spectrally tunable quantum-dot infrared photodetectors (QDIPs) can be used to approximate multiple spectral responses with the same focal-plane array. Hence, they exhibit the potential for real time adaptive detection/classification. In the present study, it is shown that we can perform the detection/classification operation at the adaptive focal-plane array (AFPA) based on QDIPs by fitting the QDIP's response to the correspondent operators. With a new understanding of spectral signature in the sensor space, the best fitting can be achieved. Our simulation results show how well QDIPs perform in different regions of the spectrum in the mid- and long wave infrared. The results indicate that the AFPA performance does not match that of the ideal filtering operators, but reliable measurement can be accomplished.