Payam Razavi

Transient Response of the Eardrum Excited by Localized Mechanical Forces

The Tympanic Membrane (TM, eardrum) is the interface between the middle and outer ear and helps transform the variations in sound pressure in the ear canal into vibrations of the ossicles. However, the transient acoustic response of TM due to the complexity of wave interference, hinders the understanding of the motions. Therefore, to reduce this effect, local ( 100 μm indentation of TM surface towards the camera. The results include characterization of wave travelling speed versus input force and localized mechanical properties, such as damping ratio, modal frequencies, and time constants. We expect that the results will lead to an improved understanding of the TM’s localized material properties and modeling of the eardrum behavior.

High-Speed Shape and Transient Response Measurements of Tympanic Membrane

We are developing a High-speed Digital Holographic (HDH) system to measure acoustically induced transient displacements of live mammalian Tympanic Membranes (TM) for research and clinical applications. To date, the HDH can measure one-dimensional displacements along a single 1-D sensitivity vector. However, because of the TM’s tent-like shape and angled orientation inside the ear canal, 1-D measurements need to be combined with measurements of the shape and orientation of the TM to determine the true surface normal (out-of-plane) displacements. Furthermore, TM shape also provides invaluable information for better diagnostic and modelling of the TM. To introduce shape measurements capabilities into our HDH, a tunable laser (line width 67 kHz temporal and <15 nm displacement resolutions) in response to broadband acoustic click excitations (50 μs duration). Both shape and displacement can be measured in less than 150 ms, which avoids slow disturbances introduced by breathing and heartbeat, with the promise of future measurements in vivo. Representative shape and displacement measurements capabilities are demonstrated on cadaveric human temporal bones.

High-Speed Holography for In-Vivo Measurement of Acoustically Induced Motions of Mammalian Tympanic Membrane

Measurements of human Tympanic Membrane (TM, eardrum) motions require nanometer and microsecond spatio-temporal resolutions while maintaining a field-of-view of about one centimeter. Previously, we have developed holographic methods to successfully measuring continuous and transient responses of post-mortem TM’s. To expand our capabilities to in-vivo measurements, it is necessary to overcome such challenges as the influence of submillimeter physiological motions as well as the confined location of the TM. We are developing novel High-speed Digital Holographic Methods (HDHM) in combination with recently developed image and data processing algorithms to overcome such challenges. Our developments have unique capabilities that utilize the full spatio-temporal resolution of high-speed cameras (i.e., >147,000 points at >42,000 fps) to measure nanometer-scale TM motions in the audible range (0.02–20 kHz). We present preliminary holographic measurements made on an anesthetized chinchilla in a controlled anechoic chamber in-vivo and in-vitro. To the best of our knowledge, these data are reported for the first time and establish the potential of HDHM as a hearing research and clinical tool to further expand our understanding of the human hearing processes.

Synthetic Muscle electroactive polymer (EAP) based actuation and sensing for prosthetic and robotic applications

Ras Labs Synthetic MuscleTM – a class of electroactive polymers (EAPs) that contract and expand at low voltages – mimic the unique gentle-yet-strong nature of human tissue. These EAPs also attenuate force and sense mechanical pressure, from gentle touch to high impact. This is a potential asset to prosthetics and robotics, including manned space travel through protective gear and human assist robotics and for unmanned space exploration through deep space. Fifth generation Synthetic MuscleTM is very robust and attenuates impact force through non-Newtonian mechanisms. Various electrolyte solutions and conductive additives were also explored to optimize these EAPs. In prosthetics, the interface between the residual limb and the hard socket of the prosthetic device is a pain point. EAP pads that gently contract and expand within the prosthetic socket using 1.5 V batteries will allow for extremely comfortable, adjustable, perfect fit throughout the day for amputees. For robot grippers, EAP linkages can be actuated and EAP sensors placed at the fingertips of the grippers for tactile feedback. Onset of actuation of these EAPs at the nano-level was determined to be within 48 milliseconds, with macro-scale actuation visible to the naked eye within seconds. Smart EAP based materials and actuators promise to transform prostheses and robots, allowing for the treatment, reduction, and prevention of debilitating injury and fatalities, and to further our exploration by land, sea, air, and space.

Full-Field Digital Holographic Vibrometry for Characterization of High-Speed MEMS

Development of quantitative full-field high-speed imaging modalities are indispensable to monitor the real-time transient performance of Micro-electromechanical Systems (MEMS). Their performance is a direct result of how devices are designed and fabricated and any imperfection in either of them renders undesirable results. Furthermore, new devices are being designed to comply with tighter geometrical tolerances while operating at higher speeds. In this paper, we report progress in the development of a new High-speed Digital Holographic System (HDHS) for characterization of nanometer scale transient (i.e., >100 kHz) displacements of MEMS in full-field. Comparisons of the results obtained with our HDHS and those obtained with Laser Doppler Vibrometery (LDV) indicate a high level of correlation, which validates the measuring capabilities of our developed system. The high temporal and spatial (i.e., microseconds at >100k data points) resolutions of our HDHS enable concomitant measurements at all points to quantify spatially dependent motion parameters, including modal frequencies, time constants, Q-factors, changes in shapes, and surface strains. Representative results of the study of a high-speed MEMS deformable mirror are presented to show the capabilities of our method.

Digital holographic interferometry for characterizing deformable mirrors in aero-optics

Measuring and understanding the transient behavior of a surface with high spatial and temporal resolution are required in many areas of science. This paper describes the development and application of a high-speed, high-dynamic range, digital holographic interferometer for high-speed surface contouring with fractional wavelength precision and high-spatial resolution. The specific application under investigation here is to characterize deformable mirrors (DM) employed in aero-optics. The developed instrument was shown capable of contouring a deformable mirror with extremely high-resolution at frequencies exceeding 40 kHz. We demonstrated two different procedures for characterizing the mechanical response of a surface to a wide variety of input forces, one that employs a high-speed digital camera and a second that employs a low-speed, low-cost digital camera. The latter is achieved by cycling the DM actuators with a step input, producing a transient that typically lasts up to a millisecond before reaching equilibrium. Recordings are made at increasing times after the DM initiation from zero to equilibrium to analyze the transient. Because the wave functions are stored and reconstructable, they can be compared with each other to produce contours including absolute, difference, and velocity. High-speed digital cameras recorded the wave functions during a single transient at rates exceeding 40 kHz. We concluded that either method is fully capable of characterizing a typical DM to the extent required by aero-optical engineers.

Ras Labs.-CASIS-ISS NL experiment for synthetic muscle: resistance to ionizing radiation

In anticipation of deep space travel, new materials are being explored to assist and relieve humans in dangerous environments, such as high radiation, extreme temperature, and extreme pressure. Ras Labs Synthetic Muscle – electroactive polymers (EAPs) that contract and expand at low voltages – which mimic the unique gentle-yet-strong nature of human tissue, is a potential asset to manned space travel through protective gear and human assist robotics and for unmanned space exploration through deep space. Generation 3 Synthetic Muscle was proven to be resistant to extreme temperatures, and there were indications that these materials may also be radiation resistant. The purpose of the Ras Labs-CASIS-ISS Experiment is to test the radiation resistivity of the third and fourth generation of these EAPs, as well as to make them even more radiation resistant or radiation hardened. On Earth, exposure of the Generation 3 and Generation 4 EAPs to a Cs-137 radiation source for 47.8 hours with a total dose of 305.931 kRad of gamma radiation was performed at the US Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) at Princeton University, followed by pH, peroxide, Shore Hardness Durometry, and electroactivity testing to determine the inherent radiation resistivity of these contractile EAPs and to determine whether the EAPs could be made even more radiation resistant through the application of appropriate additives and coatings. The on Earth preliminary tests determined that selected Ras Labs EAPs were not only inherently radiation resistant, but with the appropriate coatings and additives, could be made even more radiation resistant. Gforce testing to over 10 G’s was performed at US Army’s ARDEC Labs, with excellent results, in preparation for space flight to the International Space Station National Laboratory (ISS-NL). Selected samples of Generation 3 and Generation 4 Synthetic Muscle™, with various additives and coatings, were launched to the ISS-NL on April, 14 2015 on the SpaceX-6 payload, and will return to Earth in 2016. The most significant change from the on Earth radiation exposure was color change in the irradiated EAP samples, which in polymers can be indicative of accelerated aging. There was visible yellowing in the irradiated samples compared to the control samples, which were not irradiated and were clear and colorless. While the Synthetic Muscle Experiment is in orbit on the ISS-NL, photo events occur every 4 to 6 weeks to observe any changes, such as color, in the samples. The bulk of the testing will occur when these EAP samples return back to Earth, and will be compared to the duplicate experiment that remains on Earth (the control experiment). Smart electroactive polymer based materials and actuators promise to transform prostheses and robots, allowing for the treatment, reduction, and prevention of debilitating injury and fatalities, and to further our exploration by land, sea, air, and space.

Design, Fabrication, Experimental Analysis, and Test Flight of an Origami-Based Fixed-Wing Aerial Vehicle: µPlane

This article covers details the design, fabrication, experimental analysis, and first flight tests of μPlane, an origamiinspired aerial vehicle. μPlane is a monoplane with a straight wing planform that has a wingspan of 580 millimeters and can reach a maximum linear velocity of 6.12 meters-per-second. The body of the μPlane is fabricated by folding a single, unified crease pattern which includes all the sections required to construct the wing, tail, fuselage, and connection ports for external components, such as actuators and batteries. The wing of the plane utilizes a cambered profile to generate the required lift force. An optimization problem is formulated to find a solution to the set of constraints that provides the desired camber form. To validate the proposed design, a 3D scan of the top surface of the wing is accrued using a high-resolution fringe projection sys∗Vahideh Eshaghian is currently with the Space Engineering Program at the Technical University of Berlin †Address all correspondence to this author. tem. Finally, the flight performance and stability of μPlane are tested in both indoor and outdoor environments.