This work reports a simple, miniaturized optical sensing module for liquid refractometry. It is based on a stable Fabry–Pérot resonator consisting of two silicon cylindrical mirrors with a cylindrical lens in between. The lens is formed by a capillary tube through which the analyte passes. This setup enables volume refractometry, where light propagates through the sample realizing high-interaction depth. The cylindrical surfaces achieve light confinement, reducing the light escaping loss encountered in classical cavities with straight mirrors; hence, a high-quality factor (Q) over 1000 is attained. Exploiting this high Q, we adopt the refractive index (RI) measurement criterion: operating at a fixed wavelength and detecting the power drop as a consequence to the spectral shift with RI change. This technique showed that measuring RI change Δn above the RI of the reference solution can be determined for 0.0023<Δn<0.0045. Sensitivity up to 4094 dBm/RIU is achieved. A wider range is still achievable by the conventional method of tracing the shift in peak wavelengths: a range of Δn=0.0163 RIU can be scanned, with a sensitivity of 221 nm/RIU. Error analysis has been accomplished, and the device’s design parameters are discussed to evaluate the performance.
This work reports a simple, miniaturized optical sensing module for liquid refractometry. It is based on a stable Fabry-
Perot resonator consisting of two silicon cylindrical mirrors with a cylindrical lens in the core. The lens is formed by a
capillary tube through which the analyte to be analyzed passes. This setup enables volume refractometry, where light
propagates through the sample realizing high interaction depth. The cylindrical surfaces achieve light confinement,
reducing the light escaping loss encountered in classical cavities with straight mirrors; and hence high quality factor (Q)
over 1,000 is attained. Exploiting this high Q, we adopt uncommon refraction index (RI) measurement criterion: we
operate at a fixed wavelength and detect the power drop caused as a consequence to the spectral shift with RI change.
Performing experimental testing using a tunable laser and a power-meter, the normalized spectra for different mixture
ratios of acetone and deionized water are obtained. The wavelength corresponding to the maximal power transmission
from pure acetone is taken as a reference. A vertical line at this wavelength cuts the successive transmission curves and
enables measuring the power drop in the linear region, and from it the refractive index change Δn above the refractive
index of the reference solution can be determined for 0.0023<Δn<0.0045. Sensitivity up to 4,094 dBm/RIU is achieved.
A wider range is still accessible by the conventional method of tracing the shift in peak wavelengths: a range of
Δn=0.0163 RIU can be scanned, with a sensitivity of 221 nm/RIU. Error analysis has been accomplished, and the design
parameters of the device are discussed to evaluate the performance.
We have developed fabrication techniques for creating suspended electrically addressable MEMS structures in
microfluidic channels, as well as monolithic integration of sensors within microfluidic devices. As we will
demonstrate, creative use of state-of-the-art MEMS fabrication techniques allows the integrated manufacturing of a
number of sensors, for simultaneous measurement of, for example, flow velocity, thermal conductivity and normal
stress. We will demonstrate the versatility of these techniques with an example of capillary viscosity sensor
integrating independent flowrate, temperature, and pressure drop sensors.
We describe a thermal time of flight liquid flow rate measurement based on injection of a pseudo-random sequence of
thermal tracers in a microfluidic flow stream, followed by downstream detection of the temperature variation. The cross
correlation function between the injected sequence and the detected signal displays a peak corresponding to the time of
flight, which in turn provides a sensitive measure of flow rate. We demonstrate the technique by using integrated MEMS
silicon structures suspended across a microfluidic channel for both heating and detection. The encapsulation technique
we use involves 3-layer glass-silicon-glass bonding. We are capable of measuring flow rate over more than three
decades with an accuracy of a few percent (the exact measurement range scales with geometry, in our case
corresponding to 5 - 10,000 µl/min). Our technique shows excellent agreement between measurement, theory and
numerical simulation results; by comparison with other existing methods for microfluidic flow metering (anemometric,
coriolis), ours has the advantage of being largely independent of physical fluid properties. In addition, the suspended
MEMS heaters we fabricate can also be used as regular anemometer probes, extending the measurement possibilities to
gas flow metering and phase detection.
Manganese activated zinc silicate is a classical phosphor with large applications in optoelectronic device manufacture. Some aspects concerning the influence of precursor quality on Zn2SiO4:Mn phosphor formation and properties are presented. Phosphor samples were prepared by classical ceramic technique from homogeneous mixtures consisting from MnCO3 and various sorts of SiO2 and ZnO sources. The precursors and phosphor characterization was achieved by thermal analysis, surface area measurements, IR spectroscopy, x-ray diffraction and fluorescence spectroscopy. The quality and reactivity of precursors influence Zn2SiO4:Mn phosphor formation rate thus conducting to materials with different structural and luminescence characteristics.
Attempts were made to synthesize copper activated zinc sulphide phosphors sensitive to (beta) -radiation. In this purpose, homogeneous synthesis mixtures were prepared from luminescent grade zinc sulphide - thiosulfate route -, copper nitrate and alkaline and/or alkaline-earth chloride and were fired at 800-900 degrees C, in nitrogen atmosphere. ZnS:Cu,Cl phosphors prepared in various synthesis conditions were characterized by crystalline structure, particle size distribution and luminescent properties under UV excitation. Some ZnS:Cu,Cl sample phosphors were used to manufacture radioluminescent sources and their sensitivity of (beta) radiation was estimated. The optimum synthesis conditions were established.