15 research outputs found
Stepper microactuators driven by ultrasonic power transfer
Advances in miniature devices for biomedical applications are creating ever-increasing
requirements for their continuous, long lasting, and reliable energy
supply, particularly for implanted devices. As an alternative to bulky
and cost inefficient batteries that require occasional recharging and replacement,
energy harvesting and wireless power delivery are receiving increased
attention. While the former is generally only suited for low-power diagnostic
microdevices, the latter has greater potential to extend the functionality to
include more energy demanding therapeutic actuation such as drug release,
implant mechanical adjustment or microsurgery.
This thesis presents a novel approach to delivering wireless power to remote
medical microdevices with the aim of satisfying higher energy budgets
required for therapeutic functions. The method is based on ultrasonic power
delivery, the novelty being that actuation is powered by ultrasound directly
rather than via piezoelectric conversion. The thesis describes a coupled mechanical
system remotely excited by ultrasound and providing conversion
of acoustic energy into motion of a MEMS mechanism using a receiving
membrane coupled to a discrete oscillator. This motion is then converted
into useful stepwise actuation through oblique mechanical impact.
The problem of acoustic and mechanical impedance mismatch is addressed.
Several analytical and numerical models of ultrasonic power delivery
into the human body are developed. Major design challenges that have
to be solved in order to obtain acceptable performance under specified operating
conditions and with minimum wave reflections are discussed. A novel
microfabrication process is described, and the resulting proof-of-concept devices
are successfully characterized.Open Acces
Thick film PZT transducer arrays for particle manipulation
This paper reports the fabrication and evaluation of a two-dimensional thick film PZT ultrasonic transducer array operating at about 7.5 MHz for particle manipulation. All layers on the array are screen-printed and sintered on an Al2O3 substrate without further processes or patterning. The measured dielectric constant of the PZT is 2250 ± 100, and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis has been used to predict the behaviour of the array and impedance spectroscopy and laser vibrometry have been used to characterise its performance. The measured deflection of a single activate element is on the order of tens of nanometres with 20 Vpp input. Particle manipulation experiments have been performed by coupling the thick film array to a capillary containing polystyrene microspheres in water
Investigating the motility of Dictyostelium discodeum using high frequency ultrasound as a method of manipulation
Cell motility is an essential process in the development of all organisms. The earliest stages of embryonic development involve massive reconfigurations of groups of cells to form the early body structures. Embryos are very complex systems, and therefore to investigate the molecular and cellular basis of development a simpler genetically tractable model system is used. The social amoeba Dictyostelium Discoideum is known to chemotax up a chemical gradient. From previous work, it is clear that cells generate forces in the nN range. This is above the limit of optical tweezers and therefore we are investigating the use of acoustic tweezers instead. In this paper, we present recent progress of the investigation in to the use of acoustic tweezers for the characterisation of cell motility and forces. We will describe the design, modelling and fabrication of several devices. All devices use high frequency (>15MHz) ultrasound to exert a force on the cells to position and/or stall them. Also, each device is designed to be suitable for the life-sciences laboratory where form-factor and sterility is concerned. A transducer (LiNo) operating at 24 MHz excites resonant acoustic modes in a rectangular glass capillary (100um by 2mm). This device is used to alter the directionality of the motile cells inside the fluid filled capillary. A quarter-ring PZT26 transducer operating at 20.5MHz is shown to be useful for manipulating cells using axial acoustic radiation forces. This device is used to exert a force on cells and shown to pull them away from a coverslip. The presented devices show promise for the manipulation of cells in suspension. Currently the forces produced are below that required for adherent cells; the reasons for this are discussed. We also report on other issues that arise when using acoustic waves for manipulating biological samples such as streaming and heating
Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress
Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018