Yuan-Fang Chou

Optimal Graft Thickness for Different Sizes of Tympanic Membrane Perforation in Cartilage Myringoplasty: A Finite Element Analysis†

Objective: The purpose of this study was to determine, using finite element analysis, the optimal graft thickness for cartilage myringoplasty in patients with different sizes of tympanic membrane (TM) perforations.

A novel opto-electromagnetic actuator coupled to the tympanic membrane

A new type of electromagnetic vibration transducer designed to be placed onto the tympanic membrane was developed. The actuator consisted of two photodiodes, two permanent magnets, an aluminum ring, two opposing wound coils, a latex membrane and a Provil Novo membrane. An optic probe was designed to allow sound and light signals to enter the ear canal, thereby preventing the acoustic occlusion effect of traditional ear molds. Two light-emitting diodes were used for carrying the input signals. The corresponding photodiodes were used for receiving the light signals and generating currents in the actuator. The opto-electromagnetic vibration actuator was fabricated and tested using a Laser Doppler vibrometer. The actuator showed displacements of vibration between 30 and 1 nm from 300 to 6500Hz and reduced in amplitude at higher frequencies. The average gain of the actuator with 140microA on the umbo displacement was about 20 dB relative to 87 dBA at the distance of 6cm from the tympanic membrane and 0microA in actuator.

Computer aided modeling of human mastoid cavity biomechanics using finite element analysis

The aim of the present study was to analyze the human mastoid cavity on sound transmission using finite element method. Pressure distributions in the external ear canal and middle ear cavity at different frequencies were demonstrated. Our results showed that, first, blocking the aditus improves middle ear sound transmission in the 1500- to 2500-Hz range and decreases displacement in frequencies below 1000 Hz when compared with the normal ear. Second, at frequencies lower than 1000 Hz, the acoustic pressures were almost uniformly distributed in the external ear canal and middle ear cavity. At high frequencies, higher than 1000 Hz, the pressure distribution varied along the external ear canal and middle ear cavity. Third, opening the aditus, the pressures difference in dB between the middle ear cavity and external ear canal were larger than those of the closed mastoid cavity in low frequency (<1000 Hz). Finally, there was no significant difference in the acoustic pressure between the oval window and round window is noted and increased by 5 dB by blocking the aditus. These results suggest that our complete FE model including the mastoid cavity is potentially useful and can provide more information in the study of middle ear biomechanics.

Biomechanical Modeling and Design Optimization of Cartilage Myringoplasty Using Finite Element Analysis

The purpose of this study was to determine the acoustic transfer characteristics of cartilage for optimal cartilage myringoplasty. In order to do so, we developed a cartilage plate/tympanic membrane-coupled model using finite element analysis. Cartilage specimens of the tragus were obtained from fresh human cadavers, and the parameters of the tragus were determined by curve fitting and cross-calibration. A cartilage plate was used to repair an eardrum perforation, and the new coupled tympanic membrane-cartilage complex was loaded into our 3-dimensional biomechanical model of the middle ear for analysis. Our results show that first the β-damping value of the cartilage plate depends on frequency. The value of β damping was close to 3 × 10–4 s at lower frequencies and 5 × 10–6 s at higher frequencies. Secondly, reducing cartilage thickness leads to an improvement of its acoustic transfer qualities. From an acoustics point of view, the 0.1- to 0.2-mm cartilage plate seems to be most preferable with regard to tympanic membrane vibration. Furthermore, thicknesses of 0.2 mm at lower frequencies and 0.1 mm at higher frequencies were regarded as good compromises between sufficient mechanical stability and low acoustic transfer loss.

THE OPTIMAL MAGNETIC FORCE FOR A NOVEL ACTUATOR COUPLED TO THE TYMPANIC MEMBRANE: A FINITE ELEMENT ANALYSIS

A new type of electromagnetic vibration transducer designed to be placed onto the tympanic membrane will be developed. Such an electromagnetic transducer should have the following characteristics: small in size, high-energy efficiency and suitable frequency bandwidth. In order to find out the optimal electromagnetic force and to predict the frequency-amplitude characteristics, a finite element middle ear biomechanical model was used to derive the optimal magnetic force of the actuator in this study. First, the electromagnetic transducer coupled to the ear drum was created by using a computer-aided design (CAD). Then the new coupled tympanic membrane-transducer complex was loaded to a 3-dimensional biomechanical model in the middle. The air gap between magnet and coil, input current and vibration force were calculated by finite element analysis simulation. In addition, gain and frequency response curves of the actuator were also calculated. Predicted displacement of tip of the malleus induced by the sound pressure of 80 dB SPL with different input currents are computed from the finite element model over the auditory frequency range of 100–8000 Hz as the force input into the ANSYS software. Simulated results show displacements of vibration are about 100 nm in the range from 100–1000 Hz and reduced when the frequencies are higher than 1000 Hz. Functional gains were about 20–25 dB across the 100 to 8,000 Hz frequency range.

A Novel Aerosol-Mediated Drug Delivery System for Inner Ear Therapy: Intratympanic Aerosol Methylprednisolone Can Attenuate Acoustic Trauma

We developed a novel aerosol-mediated drug delivery system for inner ear therapy by using a silicon-based multiple-Fourier horn nozzle. Intratympanic aerosol (ITA) methylprednisolone (MP) delivery can protect hearing after acoustic trauma. The highest concentration of MP (38.9 ± 5.47 ppm) appeared at 2 h and declined rapidly within 10 h. The concentrations of MP remained at a relatively low level for more than 10 h. Compared to the baseline, the auditory brainstem response (ABR) thresholds shifted markedly at 1 h after noise exposure in all groups (p <; 0.05). From the cochleograms, it can be noted that the main lesions encompassed the 2-20 kHz frequency range. Significant differences ( ) were observed for the range between 5 and 8 kHz in the cell loss of outer hair cells (OHCs). The losses for IHCs were lower than for OHCs. The MP movement in the middle ear was simulated by a convection diffusion equation with a relaxation time. The relaxation time was 0.5 h, and the concentration threshold of MP on the round window membrane (RWM) in the middle ear (C T) was 8900 ppm. Using the unit hydrograph (UH) method, we obtained a proper boundary concentration on the RWM at the cochlea, which resulted in a well-fit concentration. Finally, a linking mechanism between the middle ear and the cochlea was established by the RWM. The adjustable permeability and concentration threshold provide the flexibility to match the peak times and peak values of the concentration on the RWM in the middle ear and the cochlea.

Angular alignment for wafer bonding

Wafer bonding is an important fabrication step for some MEMS devices. ALignment of device patterns is vital for a successful bonding. When anisotropic wet etching is employed to fabricate microstructures on single crystal silicon wafers, the same mask may result in different etched patterns on different wafers. If the wafer pair for bonding are not matched well, the position and orientation of device patterns cannot be aligned simultaneously. This article presents a method for position and orientation alignment of the device patterns on wafer pairs. An offset angle indicating mark and a self-aligning bonding fixture are developed to satisfy the alignment requirement. The photomask for wet anisotropic etching contains patterns of indicating marks and wafer cutting targets. The indicating marks provide information of offset angles between device patterns and crystal planes after wet etching. Wafer pairs for bonding are matched with offset angles, depending on the device configuration. Simultaneously align the position and orientation is possible for the matched wafer pairs. Wafers are cut with the guide of cutting targets to ensure they have the same size. The bonding fixture consists of a steel frame and a pair of flat glass plates. The steel frame has a rectangular opening where the wafer pair are sandwiched between the glass plates. The wafer cutting process is the major source of misalignment in this bonding method.

Modeling sound transmission of human middle ear and its clinical applications using finite element analysis

We have developed a new finite element (FE) model of human right ear, including the accurate geometry of middle ear ossicles, external ear canal, tympanic cavity, and mastoid cavity. The FE model would be suitable to study the dynamic behaviors of pathological middle ear conditions, including changes of stapedial ligament stiffness, tensor tympani ligament (TTL), and tympanic membrane (TM) stiffness and thickness. Increasing stiffness of stapedial ligament has substantial effect on stapes footplate movement, especially at low frequencies, but less effect on umbo movement. Softer TTL will result in increasing umbo and stapes footplate displacement, especially at low frequencies (f < 1000 Hz). When the TTL was detached, the vibration amplitude of umbo increased by 6 dB at 600 Hz and two peaks (300 and 600 Hz) were found in the vibration amplitude of stapes footplate. Increasing the stiffness of tensor tympani resulted in a slightly decreased umbo amplitude at very low frequencies (f < 500 Hz) and significantly decreased displacement up to 12 dB at middle frequencies (1000 Hz < f < 4000 Hz). However, the amplitude change of stapes footplate is very sensitive to the TTL stiffness, especially at low frequency (f < 1000 Hz). The increased stiffness of TM resulted in reduced umbo and stapes footplate displacement at frequencies <1500 Hz and increased displacement at frequencies >1500 Hz. As (TM) thickness was increased, the umbo displacement was reduced, especially at very low frequencies (f < 600 Hz). Otherwise, the stapes displacement was reduced at all frequencies.

Novel device to measure critical point "Onset" of capillary wave and interpretation of Faraday instability wave by numerical analysis.

A capillary wave was created on a surface by vibrating from the bottom of a container. When the amplitude of the container vibration approached the critical point, called the onset state, the surface broke up and bursted into very small drops on the air. The numerical analysis was used to determine the amplitude of the onset. The onset point was found to be 0.349μm at f=500kHz. The critical amplitude h(cr) was determined by using a multi-Fourier horn nozzle (MFHN) device. The onset point was measured to be 0.37μm using a laser Doppler vibrometer (LDV) with the MFHN at f=486kHz. These drops indicate that particle size distributions of 10.8μm and 7.0μm were produced by the MFHN at f=289kHz and f=486kHz, respectively. These results agreed with those obtained using Kelvins equation, which predicted D=0.34λ.

An ultrasonic horn atomizer with closed loop driving circuit

A novel ultrasonic horn atomizer is developed for the purpose of obtaining small size droplets at a large flow rate. The ultrasonic horn has a non-monotonically decreasing cross sectional area to provide a large atomizing surface. Consisting of two horns and one actuator section, the 301 kHz atomizer nozzle is made of {100} silicon wafer with its axis aligned in the <100> direction to minimize the length. Two PZT plates are adhered to each side of the actuator section to provide driving power. This device atomizes the liquid film on its nozzle tip to generate droplets. It is capable of atomizing more than 350 μl/min water into droplet. The mean diameter of droplet is 9.61 μm and the size distribution is quite narrow. The atomizing mechanism is based on the capillary wave on liquid surface. Once the wave amplitude exceeds the critical value, the motion of surface liquid becomes unstable and releases droplets. Therefore, driving at resonant frequency is the most effective way for atomizing. Dimension deviation combined with different kind of liquid to be atomized causes resonant frequencies of nozzles changed from time to time. Due to the high Q nature of nozzles, atomizing performance will drop drastically once the driving frequency is different from its resonant frequency by very little amount. Therefore, a feedback circuit is designed to tracking resonant frequency automatically instead of adjusting driving frequency manually. Comparing the atomizing performance between the open loop system and the closed loop system, significant improvement is obtained.