Helicity Dependent Directional Surface Plasmon Polariton Excitation Using A Metasurface with Interfacial Phase Discontinuity

Surface plasmon polaritons (SPPs) have been widely exploited in various scientific communities, ranging from physics, chemistry to biology, due to the strong confinement of light to the metal surface. For many applications it is important that the free space photon can be coupled to SPPs in a controllable manner. In this Letter, we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization dependent SPP unidirectional excitation at normal incidence. Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light. This approach, in conjunction with dynamic polarization modulation techniques, opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities.Comment: 17 pages, 5 figures. Published on <Light:Science & Applications

Digital Microfluidic (DMF) devices based on electrowetting on dielectric (EWOD) for biological applications

Microfluidic devices have been used in various applications including automated analysis systems, biological applications like DNA sequencing, antigen-antibody reactions, protein studies, chemical applications, single cell studies, etc. Microfluidic devices are primarily categorised into two types. First are continuous microfluidic devices. These devices consist of predefined microchannels, micro-valves, and syringe pumps. Fluid is continuously flowing in these channels. The second type is digital microfluidic platforms. In this type, MXN array of electrodes is patterned on non-conducting substrate. Fluid is discretized to form tiny droplets. These droplets are transported, mixed and split using external electric field. Digital microfluidic devices are configurable as there are no permanently etched channels. Also, they have high throughput. Multiple reactions can be performed on the same platform at the same time. The time taken to complete one reaction is less compared to the continuous devices. Thus they help in faster analysis. These devices are controlled by electrical field and thus unlike continuous devices, digital microfluidic devices are free from mechanically moving parts. Digital microfluidic devices may suffer from charge accumulation due to electrostatic forces. Also, voltage levels applied play an important role. The applied voltage has to be enough to move droplets but should not cause electrolysis of the liquid used. Also voltage switching time between electrodes and frequency applied are important. These parameters can change the mixing quality. In this work, 2D simulations of droplet manipulation due to voltage application, transport and mixing are carried out. Also digital microfluidic device is designed and fabricated to carry out biological mixing experiments

A CMOS Analog Front-End for Tunnelling Magnetoresistive Spintronic Sensing Systems

This paper presents a CMOS readout circuit for an integrated and highly-sensitive tunnel-magnetoresistive (TMR) sensor. Based on the characterization of the TMR sensor in the finite-element simulation, using COMSOL Multiphysics, the circuit including a Wheatstone bridge and an analogue front-end (AFE) circuit, were designed to achieve low-noise and low-power sensing. We present a transimpedance amplifier (TIA) that biases and amplifies a TMR sensor array using switched-capacitors external noise filtering and allows the integration of TMR sensors on CMOS without decreasing the measurement resolution. Designed using TSMC 0.18 μm 1V technology, the amplifier consumes 160 nA at 1.8 V supply to achieve a dc gain of 118 dB and a bandwidth of 3.8 MHz. The results confirm that the full system is able to detect the magnetic field in the pico-Tesla range with low circuit noise (2.297 pA/√Hz) and low power consumption (86 μW). A concurrent reduction in the power consumption and attenuation of noise in TMR sensors makes them suitable for long-term deployment in spintronic sensing systems

Nonreciprocal Wavefront Engineering with Time-Modulated Gradient Metasurfaces

We propose a paradigm to realize nonreciprocal wavefront engineering using time-modulated gradient metasurfaces. The essential building block of these surfaces is a subwavelength unit cell whose reflection coefficient oscillates at low frequency. We demonstrate theoretically and experimentally that such modulation permits tailoring the phase and amplitude of any desired nonlinear harmonic and determines the behavior of all other emerging fields. By appropriately adjusting the phase delay applied to the modulation of each unit cell, we realize time-modulated gradient metasurfaces that provide efficient conversion between two desired frequencies and enable nonreciprocity by (i) imposing drastically different phase gradients during the up/down conversion processes and (ii) exploiting the interplay between the generation of certain nonlinear surface and propagative waves. To demonstrate the performance and broad reach of the proposed platform, we design and analyze metasurfaces able to implement various functionalities, including beam steering and focusing, while exhibiting strong and angle-insensitive nonreciprocal responses. Our findings open an alternative direction in the field of gradient metasurfaces, in which wavefront control and magnetic-free nonreciprocity are locally merged to manipulate the scattered fields