Crown ether is a form of ethylene oxide cyclo-oligomer. Crown ether has a strong ability to form a complex with cations. The crown ether has been used as part of the electrochemical sensor and optical sensor because of its selectivity to several cations. There was no report on the use of the 18-crown-6-ether as a single coating layer on the QCM sensor. This work investigates the loading effect of the 18-crown-6-ether as a selective coating for QCM sensors as a pre-requirement for a selective coating layer. The impedance spectrum of the QCM sensor coated with 18-crown-6-ether at different concentrations solved in three different solvents was measured. The effects of solvents and 18-crown-6-ether concentrations to the calculated thickness and the effect of the QCM sensor impedance was investigated. The solvents used are Toluene, Tetrahydrofuran (THF), and Chloroform. The results show that the film behaves like a rubber material, which is shown by the impedance value of the sensor at the series resonance frequency. It can be concluded that the thickness of the 18-crown-6-ether layer must be maintained less than one μm to avoid damping on the QCM sensor.
Piezoelectric material produces electric fields due to a change of material dimension as an impact of external force/stress applied. One of the piezoelectric materials that widely used for a sensor is quartz crystals. Cutting crystal at its AT-Cut angle causes this material to have piezoelectric properties. Phenomena that occur on quartz surfaces can be observed and expressed as changes in the resonance frequency of sensors. In this experiment, a continuous uniaxial force from 0 N to 10 N was applied to the surface of the quartz crystal microbalance (QCM). The result shows that the resonance frequency of the QCM depends on the applied force. The resonance frequency increases as the applied force is increased. When the applied force is gradually decreased, the resonance frequency is also decreased and back to its original resonance frequency when there is no applied force. The frequency change of the sensor was linearly depend on the applied uniaxial force to the sensor.
The thermoelectric device has advantages for heating and cooling element. The thermoelectric can be used easily as a heater. In applications for small volumes, the temperature distribution of the heating element is necessary to ensure that different samples at different locations receive the same heat treatment. This experiment shows an aluminum fin’s temperature distribution heated using different heat amount. TEC-12706 was used to heat an aluminum fin with a dimension of 40×40×20 mm. The aluminum was placed in an chamber made using a 3D printer with a material of ABS. The surface temperature distribution of the aluminum fin was measured using a thermal camera Fluke-Ti20S. The measurement data showed that the fin’s surface temperature is not the same at all points at the surface, especially the center and the edge. During the heating process, the temperature at the aluminum fin’s center has a higher temperature than the fin’s edge. The lower the duty cycle used, the better the temperature distribution on the heatsink. For 50% duty cycle or more, the temperature variation in the middle with a square dimension of 20×20 mm has a temperature variation of less than 1°C. Therefore, if the temperature distribution between points is important, it is recommended to use an aluminum fin around the center.
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