Po-Jen Shih

Design, Fabrication, and Application of Bio-Implantable Acoustic Power Transmission

Fully packaged acoustic power receivers are introduced. They can provide electronic energy to other implanted devices by receiving an external acoustic wave generated from the skin surface of the subcutaneous tissue. Piezoelectric ceramics make the internal devices of the receivers, and they are directly charged, converting pressure into an extractable electrical energy. Moreover, cohesive gel is used to package the internal devices, and the packages are biocompatible and sufficiently soft to absorb the incident wave that is generated at the skin surface. Additionally, the effects of the shape of the scattering package and ratio of the stiffness of the package to that of the tissue are considered in designing the receivers. The dominant frequencies and the energy efficiency of the receivers are measured in the very streaky pork, which is used to simulate human subcutaneous tissue. The results indicate that the spherical packaging is preferable to the cubic packaging when buried in the muscular layer. The maximum efficiency of the power transmission is found to be -48.2 dB, using the spherical package in the muscular layer of the streaky pork.

Fabrication and application of iron(iii)-oxide nanoparticle/polydimethylsiloxane composite cone in microfluidic channels

This paper presented the fabrication and applications of an iron(III)-oxide nanoparticle/polydimethylsiloxane (PDMS) cone as a component integrated in lab on a chip. The two main functions of this component were to capture magnetic microbeads in the microfluid and to mix two laminar fluids by generating disturbance. The iron(III)-oxide nanoparticle/PDMS cone was fabricated by automatic dispensing and magnetic shaping. Three consecutive cones of 300 µm in height were asymmetrically placed along a microchannel of 2 mm in width and 1.1 mm in height. Flow passing the cones was effectively redistributed for Renolds number lower than 3.45×10-3. Streptavidin-coated magnetic microbeads which were bound with biotin were successfully captured by the composite cones as inspected under fluorescence microscope. The process parameters for fabricating the composite cones were investigated. The fabricated cone in the microchannel could be applied in lab on a chip for bioassay in the future.

E-Beam Photoresist and Carbon Nanotubes as Biomimetic Dry Adhesives

This paper presents the fabrication and characterization of nano-fibrils mimicking gecko foot-hairs for enhanced dry adhesion. High contact area ratio of the polymer and carbon nanotube fibrils is achieved, respectively, using e-beam lithography and chemical vapor deposition. The adhesion forces from gecko foot-hairs and the artificial fibrils are measured with a customized AFM tip to evaluate the effects of different materials and surface density. With the water-vapor assisted deposition, the surface density of the carbon nanotubes is optimized for comparable adhesion forces to gecko foot-hairs.

Acoustic polarization for optimized implantable power transimittion

We present a fully-packaged acoustic power receiver which is implantable in the subcutaneous tissue to receive the acoustic energy generated from a compressive wave emitter on the skin. The implanted receiver is a piezoelectric acoustic transducer and is packaged by biocompatible cohesive gels. This specific package is soft enough to absorb the incident wave from the subcutaneous tissue. The receiver employs direct charging to convert the acoustic energy into the extractable electrical energy through piezoelectricity when exposed to the acoustic field. The effects of the scattering package shape and the stiffness ratio between the package and subcutaneous tissue are considered to design the receivers. The energy efficiency of the fabricated receiver is measured inside real streaky pork, which is used to simulate human subcutaneous tissue. The result indicates that the spherical package is more suitable than the cubic one when they are buried in the fatty layer. The maximum efficiency of the power transmission is found to be -40dB.

A corneal elastic dynamic model derived from Scheimpflug imaging technology.

To simultaneously extract the corneal Youngs modulus and the damping ratio from Scheimpflug imaging data.

A study of implantable power harvesting transducers

The power harvesting technologies for low-power electronic devices, such as wireless sensor networks and biomedical sensor applications, have received a growing attention in recent years. Of all possible energy sources such as mechanical vibrations, electromagnetic radiations and magnetic fields, the mechanical vibrations have been considered a promising choice for power harvesting in a wide variety of applications. This paper presents the development of two different piezoelectric MEMS generators to harvest energy at different vibration frequencies. For power harvesting at 1.5kHz vibration frequency, we present a generator comprising a silicon micro-cantilever with laminated PZT (lead zirconate titanate) material, and the interdigital electrode on the top of the PZT layer to transform mechanical strain energy into electrical charges by using the d33 mode of PZT. The piezoelectric cantilever generator was tested with using a shaker as the external vibration source. For power harvesting at frequency higher than 20kHz, we present a piezoelectric disk-shaped generator which is packaged by cohesive gel. The power generation efficiency of the fabricated devices was characterized. For the application of the power to the implanted medical sensors, the piezoelectric MEMS generator is claimed to be a power receiver of an additional vibration sources. An experimental model was also developed to study the power transmission efficiency and the charge ability of the MEMS generator device. A feasibility study of the piezoelectric MEMS generator as a power receiver was performed and some testing results are presented.

Impact dynamics of vibratory microprobe for microcoordinate measurement

This article presents an impact dynamics analysis of the vibratory probe in a microcoordinate measuring machine. The chaotic behavior of the vibratory probe was identified when the driving frequency was changed. A multimode analysis was carried out to investigate the microprobe in both noncontact and contact states. An orthogonal mode transformation was used to maintain continuities when impact occurred. The analytical results indicated that mode coupling and mode coexistence suppressed subbifurcation and pulled down the impact period under particular driving frequencies. To achieve accurate identification of the microprobe in contact with microstructures, the frequency spectra of vibration signals at different contact states were compared. It was shown that the optimum driving frequency should be in the pull-down region. In this region, the dominant frequencies before and after the contact can be clearly separated, resulting in negligible background vibrations.

Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Recent advances in the analysis of corneal biomechanical properties remain difficult to predict the structural stability before and after refractive surgery. In this regard, we applied the finite element method (FEM) to determine the roles of the Bowman’s membrane, stroma, and Descemet’s membrane in the hoop stresses of cornea, under tension (physiological) and bending (nonphysiological), for patients who undergo radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), or small incision lenticule extraction (SMILE). The stress concentration maps, potential creak zones, and potential errors in intraocular pressure (IOP) measurements were further determined. Our results confirmed that the Bowman’s membrane and Descemet’s membrane accounted for 20% of the bending rigidity of the cornea, and became the force pair dominating the bending behaviour of the cornea, the high stress in the distribution map, and a stretch to avoid structural failure. In addition, PRK broke the central linking of hoop stresses and concentrated stress on the edge of the Bowman’s membrane around ablation, which posed considerable risk of potential creaks. Compared with SMILE, LASIK had a higher risk of developing creaks around the ablation in the stroma layer. Our FEM models also predicted the postoperative IOPs precisely in a conditional manner.

A Method of Measuring Corneal Young’s Modulus

Eye is very important to human, where there is a problem with the eye, it is always desirable to seek medical care early on; however, delay still exists due to miscalculation and examination uncertainties. This paper thus tries to provide a more accurate non-intrusive measurement of the cornea properties for doctor’s reference. One of the properties that is very sensitive to the condition of the eye is the Young’s modulus of the cornea. The cornea material exhibits different behavior in patients with different conditions. This paper proposes a mathematical model for describing the mechanical properties of the cornea. By comparing the model behavior with the non-intrusive measurement data taken off the Oculus Corvis® ST non-contact tonometer, it is possible to deduce the corneal Young’s modulus. Sensitive to the condition of the eye is the Young’s modulus of the cornea. The cornea material exhibits different behavior in patients with different conditions. This paper proposes a mathematical model for describing the mechanical properties of the cornea. By comparing the model behavior with the non-intrusive measurement data taken off the Oculus Corvis® ST non-contact tonometer, it is possible to deduce the corneal Young’s modulus.

Self-Aligned Stylus with High Sphericity for Micro Coordinate Measurement

This paper presents a mask-free fabrication of styluses with high sphericity for micro coordinate measurement machine (muCMM), a mechanical system using micro-scale contact probes to measure the profile of high-aspect-ratio micro-structures. This new process combines micro-pellet and stylus into one mechanical device. The micro-pellets are self-configured inside aqueous environment in which the surface tension deforms the pellets into prefect spheres. Stylus arrays were patterned by self-aligned waveguides. This process enables the center of the micro-sphere to accurately coincide with the longitudinal axis of stylus and hence the Abbe error for the muCMM can be significantly reduced.