This study introduces a novel image capture and lighting techniques using a cutting-edge hybrid MEMS scanner system designed for compact microscopic imaging. The scanner comprises a tapered optical fiber waveguide and innovative aerosol-jet printed PZT (lead zirconate titanate) bimorph push-pull actuators on a stainless-steel substrate, effectively addressing issues that are commonly associated with PZT on silicon substrates such as fracture and layer separation. By leveraging nonlinear vibration, the scanner achieves a spiral scan pattern from a single signal input, in addition to the expected two-dimensional scanning and target illumination from two phase-shifted inputs. This capability is further enhanced by a novel process to taper the optical fiber, which reduces illumination scattering and tunes the fiber to the resonant frequencies of the scanner. The precisely tapered tip enables large fields of view while maintaining independent 2-axis scanning through one-degree-of-freedom actuation. Experimental validation showcases the successful generation of a spiral scan pattern with a 60 μm diameter scan area and a 10 Hz frame rate, effectively reconstructing scanned images of 5 μm lines, cross patterns (15 μm in length with a 5 μm gap), and structures of a Psychodidae wing.

Non-reciprocal transmission of elastic waves through a solid is an exciting phenomenon that could open up new applications for elastic metamaterials. Non-reciprocal transmission of elastic waves can be achieved with spatio-temporally modulated boundary conditions. Some previous studies of non-reciprocal metamaterials have used uniformly modulated piezoelectric patches on metal host beams. Those beams have the advantage of electrically tunable boundary conditions due to the electro-mechanical coupling in piezoelectric patches, but are multi-material composites that are not easy to scale down. Instead, we show multi-electrode (patterned) piezoelectric plates, which are practical for a large range of geometric scales and frequencies, can exhibit non-reciprocal transmission with spatio-temporally modulated shunted circuits connected to the electrodes. In this work a study of sub-wavelength, ultrasonic band gaps that arise from shunted circuits on piezoelectric plates will be presented. The achievement of spatio-temporal modulation by using time-modulated capacitor-inductor circuits that vary in phase with their neighbors will be discussed. The results of frequency domain simulations of non-reciprocal transmission will be presented, and future directions for this research will be discussed. [Work funded by the Office of Naval Research.]

In this study, we explore binder jet printing and sintering piezoelectric ceramic samples consisting of barium titanate (BaTiO3) and small amounts of sintering aids. Binder jet printing of piezoelectric ceramics shows promise for being a preferred additive manufacturing method for piezoelectric ceramics. Thus far binder jet printed piezoelectric ceramics have suffered from lower piezoelectric and dielectric properties than conventionally manufactured piezoelectric ceramics. This is mainly due to the high porosity of sintered binder jet printed samples. This investigation uses sintering aids that enable printed samples to sinter at lower temperatures and compact into higher densities than printed samples consisting of pure BaTiO3. In this presentation, we will discuss our selection of sintering aids, our investigation of sintering temperature profiles, and the properties of sintered samples. We will show a comparison of properties between our printed and sintered samples with BaTiO3 samples manufactured using uniaxial pressing. We will finish by discussing future steps in printing and sintering fully dense piezoelectric ceramics given the current state of this technology. [Work funded by the Office of Naval Research.]

We discuss progress on additive manufacturing (AM) methods for the fabrication of millimeter-wave (mmW) vacuum electronic (VE) devices. Polymer 3D printing is discussed for fabrication of light-weight RF body assemblies with many integrated RF components such as waveguide power couplers and power combiners. Stainless-steel binder-jetting is discussed for fabrication of high-power VE circuits in metal, combined with infiltration of the bulk metal with a filler metal (such as Cu) to increase the electrical and thermal conductivity to the high level needed for mmW circuits.

This study details property measurements from 3-3 BaTiO3-epoxy composite discs, fabricated using binder jet printing and post-sinter epoxy infiltration. Binder jet printing is a highly scalable additive manufacturing technique that has the potential to produce transducers with non-conventional geometries and without expensive tooling. Piezoelectric ceramic-epoxy composites are useful for certain applications, such as biomedical imaging and underwater communications, but ordinarily require difficult fabrication processes. Density, dielectric, and piezoelectric property measurements from discs sintered at temperatures between 1200-1400 degrees C are presented. Measured samples had porosity as low as phi = 32.4%, while having a piezoelectric coefficient, electromechanical coupling coefficient, and permittivity as high as d33 = 110 pC/N, kp = 0.274, and epsilon T33/epsilon 0 = 411, respectively. Findings show a limitation to increasing sintering temperature to decrease porosity, and suggest a trade-off when selecting a sintering temperature between minimizing phi and maximizing kp. Measurements from the printed discs are compared to measurements from a disc fabricated using a traditional uniaxial pressing method.

Piezoelectric elastic metamaterials offer the ability to overcome the fixed, narrow bandwidth characteristics of passive elastic metamaterials. Interesting ultrasonic band gaps exist in piezoelectric plate metamaterials with periodic electrodes connected to shunted circuits. These band gaps result from an avoided crossing between electrical and mechanical bands, and can arise at lower frequencies than Bloch wave band gaps. Current analytical modeling techniques for these systems are numerically cumbersome, and assume an infinitely periodic plate. We present an approximate two-dimensional analytical model that can be used to directly calculate scattering coefficients for finite length plates. This model is shown to predict a band diagram that compares well with diagrams obtained from finite element analysis (FEA). Lower than 10% difference in the estimation of the location of the band gap was found for a plate thickness of $2$ mm, electrode width of $1$ mm, and gap between electrodes greater than $1.2$ mm. We calculate effective impedances and effective wavenumbers from global scattering coefficients. The calculated effective normalized wavenumber swings from positive values ($0k_{\mathrm{eff}}\geq -1$) at the low-frequency band gap, resembling wavenumbers for negative stiffness Helmholtz resonator metamaterials. This presents a new perspective on periodic shunted circuit piezoelectric plates as electrically tunable, negative stiffness metamaterials analogous to Helmholtz resonator lined acoustic waveguides.

In this study, we measure the properties of barium titanate (BaTiO3) piezoceramic discs that have been binder jet printed and infiltrated with epoxy. Binder jet printing is a scalable and relatively inexpensive additive manufacturing technique. With binder jet printing, it is possible to produce atypical geometries, and large quantities of transducers on demand without expensive tooling. However, there are many practical challenges with binder jet printing ceramics, and sintered parts tend to have relatively low densities. We seek to address these challenges and explore the suitability of binder jet printing piezoelectric transducers and active materials. In this presentation we will discuss our techniques for printing and post-processing BaTiO3 ceramic discs. We will discuss porosity, and how epoxy infiltration can improve the functionality of discs. We will present measurements of discs fabricated using a traditional pressing method and measurements of printed discs. These measurements include density, dielectric permittivity, piezoelectric coefficient d33, impedance and dielectric loss. From our measurements, we will attempt to model relationships between printing parameters and final properties. Printing and powder processing techniques that can increase relative density of sintered parts will also be discussed. [Work sponsored by the Office of Naval Research Distribution A: Approved for public release.]

We report on efforts toward a monolithic Ka-band sheet-beam coupled-cavity TWT circuit. This new circuit serves as a drop-in replacement for a demonstrated device that was originally fabricated using the method of brazing stacked plates.

The function of electrowetting liquid lenses is expanding beyond tunable focal length lensing. Recently, single and multi-mode oscillations on the meniscus profile of two non-miscible liquids have been used for optical phase modulation and fast focal length sweeping. To achieve a user-defined phase modulation, a prediction model of oscillation patterns and amplitudes is needed. We present digital holographic interferometry (DHI) measurements of oscillation patterns and amplitudes on a 5.8mm aperture lens up to 160 Hz, including frequency responses from 26-100 Hz. We discuss using Bessel function and Legendre polynomial models for oscillations on a conical frustum shaped electrowetting lens.

A novel optical encryption technique that uses oscillations on a liquid lens surface and random phase masks to encode images is presented. Excited liquid surface patterns can encode optical wave fronts, making the optical transfer function of the system a function of time. This allows for possible protection against known and chosen plaintext attacks and potentially enables more flexible realizations of random phase mask security systems. However, the periodic nature of liquid surface oscillations and the geometry of the patterns can potentially place constraints on the efficacy of such a system. Simulation results show that the entropy of encrypted images depends on the liquid surface mode shape and the recording duration of the encrypted image. Additionally, it is shown that mistiming the liquid system during decryption gives significant error in the recovered images. The simulations presented here use a model of a commercial available liquid lens, giving the possibility for future comparison with experimental results.

Liquid surface patterns are used for the first time in random phase mask optical image encryption. Time-dependence from the liquid surface patterns can potentially remove known-plaintext attack vulnerabilities. Simulations were conducted to investigate the security of such a system. The system is shown to maintain the maximum entropy in the encrypted images without leaving a significant correlation with the liquid surface patterns. Significant error between recovered and plaintext images when a mismatched liquid surface pattern is used for decryption demonstrates the ability of the liquid system to vary the encryption and decryption of images with a tunable surface.

Piezo devices made of lead-zirconium-titanate (PZT) are known for driving mechanical device for positioning control and vibration actuation. Here we present a new rapid prototyped PZT actuator for potential 2D scanner application. The proposed 5-ae m thick film PZT actuator is made by directly deposited on a thin 100 mu m thick stainless steel substrate by using an aerosol deposition (AD) method. The actuator features a stable linear vibration and frequency response. Fabrication results, electrical impedance and mechanical response will be presented and discussed.

The objective of this study is to develop an RGB-D (video + depth) camera that provides three-dimensional image data for use in the haptic feedback of a robotic underwater ordnance recovery system. Two camera systems were developed and studied. The first depth camera relies on structured light (as used by the Microsoft Kinect), where the displacement of an object is determined by variations of the geometry of a projected pattern. The other camera system is based on a Time of Flight (ToF) depth camera. The results of the structural light camera system shows that the camera system requires a stronger light source with a similar operating wavelength and bandwidth to achieve a desirable working distance in water. This approach might not be robust enough for our proposed underwater RGB-D camera system, as it will require a complete re-design of the light source component. The ToF camera system instead, allows an arbitrary placement of light source and camera. The intensity output of the broadband LED light source in the ToF camera system can be increased by putting them into an array configuration and the LEDs can be modulated comfortably with any waveform and frequencies required by the ToF camera. In this paper, both camera were evaluated and experiments were conducted to demonstrate the versatility of the ToF camera.

A new analog optical encryption scheme is presented that uses a parametrically driven shallow fluid as an oscillating phase mask in the Fourier domain. A simulation of the proposed encryption scheme is presented.

A new lead-zirconium-titanate (PZT) actuator design for a micro scanning illuminating device is being developed. The thin PZT film is deposited directly on stainless steel by using an aerosol deposition machine. The aerosol deposition method enables inexpensive, quick, room temperature fabrication while producing high quality PZT films. The presented scanners would be attractive for endoscopic device applications, where inexpensive systems with high resolution would be a move toward disposal endoscopes. The design of this scanning illuminator and fabrication method are presented. Measurements of the PZT layer surface roughness and the aerosol deposited PZT powder particle diameter are presented. Ongoing work and fabrication challenges are discussed.

A new lead-zirconium-titan ate (PZT) actuated scanning light source design is proposed. An Aerosol deposition process will be used to construct a high quality 5 μm thick film of PZT. The PZT actuator will induce non-linear vibrations to scan an area with a cantilever waveguide. The fabrication procedure for the design is presented. Fabrication results are discussed. A finite element analysis of the actuator pad is also presented. Fabrication steps needed for a comparison of the amplitude of actuation, resolution, and frequency of scan with previously developed Si based devices are also discussed.

Underwater depth measurements and point cloud images can be used for robotic navigation and haptic feedback. Structured Light and Time of Flight (ToF) depth camera systems were tested to demonstrate depth measurements and point cloud imaging underwater. A commercial ToF depth camera was modified to include a movable external light source. Images from depth measurements and constructed point cloud images from underwater tests are shown. A comparison of depth images captured while objects were positioned ~0.10-1.80 m from the camera is presented. Calibration of ToF cameras augmented with movable external light sources for underwater use is discussed.

To develop an inverse model of the magnetic signature of a surface vessel, autonomous underwater vehicles (AUVs) equipped with tri-axial, flux-gate magnetometers were used to acquire magnetic field measurements underneath the moving surface vessel. Measurements were taken by AUVs operating in a formation at 3-7 m depth below the water surface. Multiple magnetic dipoles were used to model and estimate the magnetic signature of the surface vessel from the measurements. AUV orientation was estimated from onboard inertial measurement unit (IMU) and magnetic compass measurements in an attempt to transform the measured magnetic field vector components into the Earth's inertial frame. An uncertainty propagation study predicted ~18 nT root-mean-squared (RMS) noise in the magnetic field vector components resulting from uncertainty in AUV orientation estimation and uncertainty in the magnetometer measurements. The impact of network latency in the AUV distributed control system on the magnetic field vector components was discussed. A measured deviation in the transformed, inertial frame magnetic field vertical component of ~220 nT was compared with predicted values.

In this paper we present experimental and simulated results for an improvement upon the moving short baseline (MSBL) method of navigation for a fleet of autonomous underwater vehicles (AUVs). With the goal of maintaining system simplicity and portability, the hybrid baseline (HBL) approach utilizes one or both of the objective ship-mounted MSBL transponders in conjunction with a single off-path drifting buoy-mounted transponder intended to resolve problems observed in previous MSBL navigational work. The states of the ship and buoy are estimated using extended Kalman filters (EKFs) that are updated with state broadcasts from each source. Because the system uses a synchronous communication cycle, the AUVs are also able to calculate ranges with each broadcast; with the addition of onboard sensor data, the AUVs are able to use these ranges to estimate their own state using a third EKF. Simulation and field test results indicate that with respect to previous MSBL results, the perpendicular-to-path range data from the buoy allows the EKF to more quickly reduce the initialization error in the AUV position and maintain a lower overall position error.