Flexible hearing aids can benefit from piezoelectric actuators to generate vibrations on epidermis layer of skin behind the ear and noninvasively bypass conductive hearing loss. However, the major challenge is to generate a strong level of vibrations on the surface of skin that can reach cochlea with thin and low-power actuators. Lead zirconium titanate has a high piezoelectric constant and can generate vibrations with elevated levels of force and acceleration. In this paper, we assembled arrays of unimorph piezoelectric actuators composed of lead zirconium titanate to increase the vibration level and overcome damping in flexible substrate, skin, and bone. Finite element analysis was conducted to study the vibrations from a single actuator as well as an array of actuators. Also, the experimental data showed that an array of two actuators with adjusted phase increased the velocity of vibrations by 18 dB at 9 kHz compared to a single actuator on a flat aluminum foundation.
Implementation of microsystems on flexible substrates has enabled a new class of noninvasive medical devices. Flexible substrates are interfaced with soft tissues without causing damage or discomfort for the users. This will enable noninvasive attachment of medical microsystems to the surface of fragile tissues such as infants’ skin. In this talk, we will introduce two noninvasive medical microsystems on flexible substrates: a smart, wireless, battery-free, chipless patch for detection of cutaneous melanoma and a Band-Aid-like conductive hearing aid for pediatric patients. The patch will be placed on the epidermis layer for detection of abnormality in impedance of skin, and the flexible hearing aid will be attached to an infant’s skin behind the ear to bypass pediatric conductive hearing loss. These technologies will enable early action on melanoma and pediatric hearing loss, avoiding long-term consequences of these diseases.
Uveal melanoma is the most common intraocular cancer in adults and may cause vision loss as well as death due to distant metastases. Early detection of tumors is critical for vision preservation and may reduce mortality. Many patients with uveal melanoma do not develop symptoms in early stages of disease when tumors are small. Diagnosis requires examination of the eye using specialized equipment and may require advanced imaging techniques. Here, we studied the electrical properties of eyes to investigate a novel, easy-to-use method for detecting uveal melanoma. We used finite element analysis to study the electrical impedance and current density in bovine eyes. We also measured the impedance and current flow in the preserved bovine eyes using a high precision impedance analyzer. Our experimental data show that a 6 mm-diameter added tissue was detected inside a 30-mm diameter eyeball by impedance analyzer, paving the way toward detection of solid tumors in eyeballs.
Wearable technologies are essential for telehealth services and for reducing the load on the healthcare systems. The wearables enable individuals to personalize health monitoring out of hospitals and allow physicians to remotely assess the health status of individuals and track the recovery process. Here, we developed a multimodal wearable device to record breathing patterns and cough events with a low noise, wide dynamic range microelectromechanical accelerometer. In addition, the wearable device included a high-sensitivity pulse oximeter and heart rate to record blood oxygen saturation levels. The device recorded cough vibrations, oxygen saturation level and a respiratory profile that can be used for evaluation of the respiratory system. The device was tested on healthy volunteers and a subject with COVID-19 during quarantine.
Conductive hearing loss (CHL) is the most common type of hearing impairment among infants and young children. Most conductive hearing aids, including bone-anchored aids, are invasive and require surgical procedures to be implanted into the skull. In addition, non-invasive wearable conductive hearing aids are bulky, rigid, and unstable. Neither aid is ideal for infants and pediatric patients with conductive hearing loss. Here, we implemented a unimorph piezoelectric actuator into a flexible substrate to achieve a micro-epidermal actuator for non-invasive Band-Aid-like conductive hearing aids. The flexible aid will generate vibrations on the surface of skin and transmit to the cochlea through a skin-bone path, thus bypassing obstructions and damage in the auditory canal. We used finite element analysis to study vibrations from microepidermal actuators and obtain output force level. A Laser Doppler vibrometer was also used to measure displacement of vibrations for an actuator placed on a segment of a cadaveric skull calvarium.
We designed and fabricated microscale lens arrays on a flexible substrate. The flexibility of the substrate allows for wide field of view imaging as well as optical focus scanning. Fresnel zone plates (FZPs), which are compact and lightweight, are used as microlenses for focusing. The arrangement of FZPs on flexible substrate can be reconfigured to maximize FOV. Tunable focus can also be achieved by stretching the FZPs laterally. In addition, the lightweight microlenses can be actuated to scan the focus axially. The lenses have a wide range of applications including displays, contact lenses, microscopy, surveillance and optical communications.
The diameter of the microlenses ranges from 100 to 500 µm. The thickness of the lenses is 100 µm. Unlike refractive and reflective lenses, the focusing capability of FZPs is achieved via diffraction. FZPs consist of alternating black and white zones to modulate the phase of the incident light. The light diffracted from edge of the regions to achieve multiple focus. Most of the energy is diffracted into the first focus. The dark regions are made of silicon nanowires which are highly absorbent for visible spectrum. Standard processes, including wet and dry etching, are used to etch silicon substrate and form nanowires. The white zones are designed for both reflective and transmissive lenses. The lenses are implemented on PDMS as flexible substrate. The silicon nanowires are embedded into PDMS so that the shape of individual lens as well as the arrangement of the array can be reconfigured. In this article, we report our design, fabrication process and experiments.
MEMS deformable mirrors are versatile elements for optical focus control. Electrostatic-pneumatic
actuation of the mirrors offers relatively large membrane stroke to increase focus range. Moreover, this novel
actuation method provides high speed focus control with either positive or negative focus. The speed of focusing is
dependent on membrane tension, membrane size, air channel configuration, and the size of the backchamber. A
3 mm diameter mirror with 5 mm diameter actuator membrane achieves 30 kHz bandwidth with electrostatic
actuation and 8 kHz bandwidth with pneumatic actuation. The settling time of the step response for both
electrostatic and pneumatic actuation is approximately 100μs.
A MEMS deformable mirror is described that uses a novel actuation scheme to increase the optical focus range. In
this method electrostatic-pneumatic actuation is used to achieve a convex surface curvature of the mirror, while
direct electrostatic actuation creates a concave surface. The fabricated device consists of two membranes made of
the photoset epoxy SU-8. One membrane serves as the deformable mirror and the other one as the pneumatic
actuator. The pneumatic membrane also provides a built-in valve for pressure equalization. The principle of
operation, fabrication process and results are presented.
Micro-optoelectromechanical systems (MOEMS) deformable mirrors are being developed for focus control in miniature optical systems including endoscopic microscopes and small form-factor camera lenses. A new process is described to create membrane mirrors made from the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low cost fabrication process. The process details and the optical properties of the resulting focus control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration, are described. Multiple actuation electrodes allow active control of more than 1.4 μm peak-to-peak of wavefront spherical aberration. The MOEMS mirror is demonstrated in a confocal microscope in which it provides focus control during capture of in vivo images.
Air flow is the dominant damping mechanism for deformable membrane mirrors that are actuated with electrostatic
pressure from a counter electrode in close proximity to the flexible membrane. We use cryogenic deep silicon etching to
create through-wafer perforations in the backplate in order to control air damping and achieve high-speed focus control.
This paper describes both our design approach and device fabrication details. We show that damping can be controlled
by selecting the proper hole pattern, and we present experimental and simulated frequency response measurements for
small membrane displacements. Also we measured the 95% settling time of a 4 mm diameter mirror subjected to a 10
μm step deflection to be less than 200 μs.
We present a miniature non-mechanical zoom camera using deformable MOEMS mirrors. Bridger Photonics, Inc.
(Bridger) in collaboration with Montana State University (MSU), has developed electrostatically actuated deformable
MEMS mirrors for use in compact focus control and zoom imaging systems. Applications including microscopy,
endomicroscopy, robotic surgery and cell-phone cameras. In comparison to conventional systems, our MEMS-based
designs require no mechanically moving parts. Both circular and elliptical membranes are now being manufactured at
the wafer level and possess excellent optical surface quality (membrane flatness < λ/4). The mirror diameters range from
1 - 4 mm. For membranes with a 25 μm air gap, the membrane stroke is 10 μm. In terms of the optical design, the
mirrors are considered variable power optical elements. A device with 2 mm diameter and 10 μm stroke can vary its
optical power over 40 diopters or 0.04mm∧(-1). Equivalently, this corresponds to a focal length ranging from infinity to
25 mm. We have designed and demonstrated a zoom system using two MOEMS elements and exclusively commercial
off-the-shelf optical components to achieve an optical zoom of 1.9x with a 15° full field of view. The total optical track
length of the system is 36 mm. The design is approximately 30 mm x 30 mm x 20 mm including the optomechanical
housing and image sensor. With custom optics, we anticipate achieving form factors that are compatible with
incorporation into cell phones.
In this paper we describe a process for creating thin SU-8 2002 films between 1.5 μm and 3.0 μm thick that are hardbaked
and can withstand a release etch in either aqueous or plasma silicon etchants. Resulting films are characterized
using both wafer bow and membrane bulge tests to monitor in-plane stress and Young's modulus. We explore the
influence on final film stress of several process variables including hard bake temperature, exposure dose, film thickness,
and various temperature profiles. We observe resultant film stress in the range of 13.8 to 32 MPa, and Young's modulus
in the range of 2.1 to 5.2 GPa for free-standing membranes. Illustrative process recipes are described for both patterned
and un-patterned SU-8 2002 membrane devices.
Deformable membrane mirrors are promising MOEMS devices for focus control and aberration correction in vital microscopy, offering high speed focus adjustment in an optical system that can be miniaturized for in vivo use. This paper describes mirrors comprising metalized polymer membranes suspended over three concentric circular electrodes for electrostatic actuation. The membranes are 2-μm thick and 3 mm in diameter, made from the fully cross-linked photoset epoxy SU-8 2002. A layer of SU-8 2025 is used to establish a 30-μm thick air gap between the electrodes and the membrane mirror. The membranes are actuated by applying voltage to each electrode individually to achieve displacement as large as 12 μm while minimizing spherical aberration. Surface deflection is studied using phase-shift interferometry under both static and dynamic excitation. Using the deformable MOEMS mirror for focus control in an optical microscope we demonstrate the ability to adjust the location of the focal plane by 85 μm using an N.A. = 0.75 optical system.
We are developing MEMS deformable mirrors for focus control in miniature optical systems, including endoscopic
microscopes and small form-factor camera lenses. This paper describes a new process to create mirrors made from
the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low
cost fabrication process. The paper describes the process details and the optical properties of the resulting focus
control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration.
Multiple actuation electrodes allow control of more than 0.4 μm peak-peak of spherical aberration.
This paper describes deformable membrane mirrors designed for focus control and aberration compensation in vital
microscopy and shows microscope images obtained using these mirrors. The mirrors are metalized polymer membranes
ranging from 1-3 mm in diameter using the photo-cured epoxy SU-8 2002, constructed using a die-bonding process.
They are electrostatically actuated using three concentric electrodes to provide large displacement while minimizing
spherical aberration.
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