Narrow Results

The soft sensors for monitoring respiratory and heart sound were composed of polyurethane and microphones. In this study, silica was blended with polyurethane to change the hardness of the chambers. The hardness would influence the frequency response of the sensors. The material composed of 60 phr silica was chosen to make the chamber of the sensor. It had higher hardness and resulted in the flatten frequency response across the range of 100–1200 Hz. By the filter band designed for heart sound and respiratory sound signal, the heart sound and respiratory sound can be collected. The measured sound was verified by the physician and showed no distortion.

Many studies have identified tungsten trioxide (WO₃) as a promising candidate for optical gas sensing applications. WO₃, coated with thin catalytic metals such as Pd, was reported to show a color change from transparent to dark blue upon exposure to oxidizing gas such as hydrogen (H₂). Reliable hydrogen sensor is widely used in medical and energy application area. In this work, WO₃ nanostructured thin films were deposited onto sapphire substrates via pulsed laser deposition (PLD) technique by using ArF Excimer laser operating at very short wavelength of 193 nm, the shortest wavelength used in the fabrication of semiconductor oxide thin films. By ablating the target oxides by high energy photons, we could fabricate good crystalline nanostructure thin films. Electron microscopy studies revealed that the uniform and homogeneous WO₃ nanostructured films consist of nanorods of about 50 nm sizes. XRD and Raman studies verified good crystalline formation. Absorbance response toward H₂ gas was investigated for a WO₃ film coated with 25 Å thick palladium (Pd). The Pd/WO₃ nanostructured thin films exhibited excellent gasochromic response toward H₂ when measured in the visible-NIR range at 100°C. As low as 0.06% H₂ concentration was clearly sensed. The larger dynamic response was measured at NIR wavelength of 900 nm as compared to the response at visible wavelength of 500 nm. The dynamic response of the films observed in the range of 500–800 nm showed more significant response toward H₂ with low concentrations (0.06%–1%) than the one at single wavelength. As a result, H₂ with very low concentration was able to be sensed reliably in real time. The response and recovery times were found to be < 2 min. The results indicated that the Pd/WO₃ nanorod films on sapphire substrates responded to very low H₂ concentration (0.06%) which is well below its lower explosive level threshold (4%).