Deepak Ranjan Sahoo

Holographic acoustic elements for manipulation of levitated objects

Sound can levitate objects of different sizes and materials through air, water and tissue. This allows us to manipulate cells, liquids, compounds or living things without touching or contaminating them. However, acoustic levitation has required the targets to be enclosed with acoustic elements or had limited manoeuvrability. Here we optimize the phases used to drive an ultrasonic phased array and show that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter. Furthermore, we introduce the holographic acoustic elements framework that permits the rapid generation of traps and provides a bridge between optical and acoustical trapping. Acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation. Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically controlled micro-machines that do not interfere with magnetic resonance imaging.

Transient-signal-based sample-detection in atomic force microscopy

In typical dynamic mode operation of atomic force microscopes, steady state signals like amplitude and phase are used for detection and imaging of material. In these methods, the resolution and bandwidth are dictated by the quality factor (Q) of the cantilever. In this letter, we present a methodology that exploits the deflection signal during the transient of the cantilever motion. The principle overcomes the fundamental limitations on the trade off between resolution and bandwidth present in existing methods and makes it independent of the quality factor. Experimental results provided corroborate the theoretical development.

Metamaterial bricks and quantization of meta-surfaces

Controlling acoustic fields is crucial in diverse applications such as loudspeaker design, ultrasound imaging and therapy or acoustic particle manipulation. The current approaches use fixed lenses or expensive phased arrays. Here, using a process of analogue-to-digital conversion and wavelet decomposition, we develop the notion of quantal meta-surfaces. The quanta here are small, pre-manufactured three-dimensional units—which we call metamaterial bricks—each encoding a specific phase delay. These bricks can be assembled into meta-surfaces to generate any diffraction-limited acoustic field. We apply this methodology to show experimental examples of acoustic focusing, steering and, after stacking single meta-surfaces into layers, the more complex field of an acoustic tractor beam. We demonstrate experimentally single-sided air-borne acoustic levitation using meta-layers at various bit-rates: from a 4-bit uniform to 3-bit non-uniform quantization in phase. This powerful methodology dramatically simplifies the design of acoustic devices and provides a key-step towards realizing spatial sound modulators.

Observer based imaging methods for Atomic Force Microscopy

In atomic force microscopy, bandwidth or resolution can be affected by active quality factor (Q) control. However, in existing methods the trade off between resolution and bandwidth remains inherent. Observer based Q control method provides greater flexibility in managing the tradeoff between resolution and bandwidth during imaging. It also facilitates theoretical analysis lacking in existing methods. Steady state signals like amplitude and phase are slowly varying variables that are suited to image low bandwidth content of the actual sample profile. Observer based transient imaging scheme with Q control has the promise of detecting high bandwidth content of the sample features during scanning. Transient detection also has the advantage of high sensitivity to small features.

An observer based sample detection scheme for atomic force microscopy

In dynamic mode operation of atomic force microscopes steady state signals like amplitude and phase are typically used for the detection and imaging of sample. Due to the high quality factor of the micro-cantilever probe the corresponding methods are inherently slow. In this paper we present a novel methodology for fast interrogation of sample that exploits the transient signals. A novel method is introduced for the detection of small time scale tip-sample interactions. Simulations and experiments show that the method results in significant increase in bandwidth and resolution as compared to the steady state data based methods.

TableHop: An Actuated Fabric Display Using Transparent Electrodes

We present TableHop, a tabletop display that provides controlled self-actuated deformation and vibro-tactile feedback to an elastic fabric surface while retaining the ability for high-resolution visual projection. The surface is made of a highly stretchable pure spandex fabric that is electrostatically actuated using electrodes mounted on its top or underside. It uses transparent indium tin oxide electrodes and high-voltage modulation to create controlled surface deformations. Our setup actuates pixels and creates deformations in the fabric up to +/- 5 mm. Since the electrodes are transparent, the fabric surface functions as a diffuser for rear-projected visual images, and avoid occlusion by users or actuators. Users can touch and interact with the fabric to experience expressive interactions as with any fabric based shape-changing interface. By using frequency modulation in the high-voltage circuit, it can also create localized tactile sensations on the users fingertip when touching the surface. We provide simulation and experimental results for the shape of the deformation and frequency of the vibration of the surface. These results can be used to build prototypes of different sizes and form-factors. We present a working prototype of TableHop that has 30x40 cm2 surface area and uses a grid of 3x3 transparent electrodes. It uses a maximum of 9.46 mW and can create tactile vibrations of up to 20 Hz. TableHop can be scaled to make large interactive surfaces and integrated with other objects and devices. TableHop will improve user interaction experience on 2.5D deformable displays.

Real-time detection of probe loss in atomic force microscopy

In this letter, a real-time methodology is developed to determine regions of dynamic atomic force microscopy based image where the cantilever fails to be an effective probe of the sample. Conventional imaging signals such as the amplitude signal and the vertical piezoactuation signal cannot identify the areas of probe loss. It is experimentally demonstrated that probe-loss affected portion of the image can be unambiguously identified by a real-time signal called reliability index. Reliability index, apart from indicating the probe-loss affected regions, can be used to minimize probe-loss affected regions of the image, thus aiding high speed AFM applications.

Transient Force Atomic Force Microscopy: A New Nano-Interrogation Method

Atomic force microscopes (AFMs) are the primary investigation systems at the nanoscale. In existing dynamic mode AFM methods steady-state response of microcantilever is monitored for imaging tip-surface interaction forces at the nano-scale. In these methods microcantilevers with high quality factor are employed for high force sensitivity but at the cost of speed due to dependence on steady-state signals. In this paper, a novel methodology for fast interrogation of material that exploits the transient part of the cantilever response is presented. This method effectively addresses the perceived fundamental limitation on bandwidth due to high quality factors. Analysis and experiments show that the method results in significant increase in bandwidth and resolution as compared to the steady-state-based methods. This paper demonstrates the effectiveness of a systems perspective to the field of imaging at the nano-scale and for the first time reports real-time imaging at the nanoscale using the transient method with scan speed 40 times faster than conventional methods.

JOLED: A Mid-air Display based on Electrostatic Rotation of Levitated Janus Objects

We present JOLED, a mid-air display for interactive physical visualization using Janus objects as physical voxels. The Janus objects have special surfaces that have two or more asymmetric physical properties at different areas. In JOLED, they are levitated in mid-air and controllably rotated to reveal their different physical properties. We made voxels by coating the hemispheres of expanded polystyrene beads with different materials, and applied a thin patch of titanium dioxide to induce electrostatic charge on them. Transparent indium tin oxide electrodes are used around the levitation volume to create a tailored electric field to control the orientation of the voxels. We propose a novel method to control the angular position of individual voxels in a grid using electrostatic rotation and their 3D position using acoustic levitation. We present a display in which voxels can be flipped independently, and two mid-air physical games with a voxel as the playable character that moves in 3D across other physical structures and rotates to reflect its status in the games. We demonstrate a voxel update speed of 37.8 ms/flip, which is video-rate.

High-throughput intermittent-contact scanning probe microscopy

Large arrays of micro-cantilevers operating in parallel are essential for achieving high throughput in such applications as life sciences, nanofabrication and semiconductor metrology. A novel intermittent-contact mode operation is presented that is suitable for such applications. The cantilevers are electrostatically actuated. The oscillation amplitude is kept small to enable high-frequency operation and to reduce the tip-sample interaction force, and thus the tip and sample wear. Input shaping of the actuation signal is employed for high-speed reliable operation in the presence of the tip-sample adhesion forces. The deflection signal is sampled once per oscillation cycle to enable high-speed imaging. Experimental results are shown which demonstrate the efficacy of the proposed scheme. In particular, during continuous high-speed imaging, the tip diameter is maintained over a remarkable 140 m of tip travel.