Wan-Doo Kim

Optimal ossicular site for maximal vibration transmissions to coupled transducers

Totally implantable middle-ear prosthetic devices, such as the Esteem system (Envoy Medical Corporation), detect vibrational motion of the middle-ear ossicles rather than acoustic stimulation to the eardrum. This eliminates the need for a subcutaneous microphone, which is susceptible to interference by ambient noises. Study of the vibrational characteristics of the human ossicles provides valuable information for determining the site of maximum ossicular motion that would be optimal for attachment of the sensor portion of the prosthesis. In this study, vibrational responses at seven locations on the middle-ear ossicles (i.e., the malleus head, 4 different points on the incus body, middle of the incus long process, tip of the incus long process) in human temporal bones (n = 6) were measured using a laser Doppler vibrometer. The measurements were repeated after separating the incudostapedial joint (ISJ). Measured displacement at each location was normalized with the sound pressure level near the tympanic membrane (TM) for representation in the form of a displacement transfer function (DTF). The normalized squared sum of the DTFs (NSSDTF) was then calculated as a measure of vibration motion through a specific frequency range at the considered sites. The relatively large NSSDTF was observed at the sites on the superior part of the malleus head (MH), on the lateral part of the incus body (IBL), and on the superior part of the incus body near the incudomalleal joint (IBS1) for the frequency ranges of 1-4 kHz and 1-9 kHz, regardless of the condition of the ISJ. This indicates that maximum vibrational motion of the middle-ear is deliverable to the piezoelectric transducer of totally implantable devices through these sites. This article is part of a special issue entitled MEMRO 2012.

Development of Piezoelectric Artificial Cochlea Inspired by Human Hearing Organ

Miniaturized artificial hearing organ with excellent sensitivity and wide dynamic frequency range over human hearing range, while requiring small amount of energy, is important step to develop artificial systems interacting in human living space. This paper presents the development of piezoelectric artificial cochlea PAC capable of analyzing incoming vibratory signals over human hearing range without external power source. The design, component and function of PAC were inspired by those of human cochlea. The PAC was made of corona-poled piezoelectric thin film with vibrating membrane part of unique shape. The vibration displacement of membrane was measured using laser Doppler vibrometer and analyzed to show the frequency separation of the developed PAC. The experimental results of mechanical vibratory behavior demonstrated successful separation of incoming signals into 13 different frequency bands depending on their frequency over 300 Hz ~ 6,000 Hz.

Power generation using piezoelectric ZnO nanowires for nano-scale devices

ZnO nanowires can convert mechanical energy into electrical energy and we investigated energy conversion of ZnO nanowires grown on a silicon substrate. First, we numerically studied the output voltages of ZnO nanowires while varying diameters and lengths of ZnO nanowires. Second, we measured the currents of ZnO nanowires grown at low temperature using a solution method. The currents were measured using a Current Atomic Force Microscope (I-AFM). ZnO nanowires produced output current pulses when scanned by I-AFM in contact mode because of the piezoelectric effect of ZnO nanowires when the I-AFM tip applied a lateral force to ZnO nanowires.