DESIGN OF A SIMPLE LOW-COST QUARTZ CRYSTAL MICROBALANCE SYSTEM

This article describes a simple design of a low-cost, real-time, and computerized quartz crystal microbalance system. The system measures resonance frequencies up to 6 MHz with a resolution of 1 Hz, i.e., it can monitor mass change in the range of nano-gram and thickness change in the range of micrometer. The designed system consists of three main parts: input circuitry, control, and counting parts. In the input circuitry, three separated input signals types are allowable: the first is direct TTL compatible, the second is analog signal, while the third is the signal that may come from the quartz crystal microbalance. The last two signals are converted to TTL signals using wave-shaping circuitry. The control part is interfaced with the status and control ports of the computer LPT1 parallel port. It consists of time base circuitry and different multiplexers to control data sending to computer according to the input signal under investigation. The counter consists of six binary counters in cascade and directly interfaced to the computer through the LPT1 data port; the transfer process was carried out by two different ways according to the measuring mode of the system. All parts were controlled by specially designed software. Finally, the frequency readings of the quartz crystal microbalance were found to be in good agreement with those of a frequency counter model GFC-8055G connected in parallel during an experiment performed to test the system.     

BEVELING OF QUARTZ CRYSTAL BLANKS: MODEL DEVELOPMENT

A process model for the beveling of quartz crystal blanks is presented in this paper. Given a beveled crystal blank specification, material removal rate, initial bevel depth, and critical gap height can be calculated from the process parameters including powder type, machine rpm, barrel diameter, etc. Material removal rate and initial bevel depth are used to predict the beveling time, and critical gap height is used to predict the bevel profile. This model has been validated using various blanks and good agreement with experiments is found. Process optimization is also possible with the aid of this process model. Thus, this model provides an efficient and cost-effective way to the design of quartz crystal resonators. The model being developed has been successfully used in the design of quartz crystal blanks for the real batch production. Because this model is a combined physical and empirical one, it can be expanded to the batch processing of other materials.     

BEVELING OF QUARTZ CRYSTAL BLANKS: AN EXPERIMENTAL STUDY

An experimental study on the beveling of quartz crystal blanks is presented in this paper. Two issues in the beveling are addressed: beveling time and the shape of bevel. The time needed for beveling is determined by material removal rate. The concept of critical gap height is introduced to evaluate the bevel profile. In addition, a side effect, frequency shift is also studied. Seven potential relevant process factors: blank quantity, powder/blank ratio, powder type, machine rpm, powder changing time, barrel diameter and powder heating were identified. The influences of these process factors on material removal rate, critical gap height and frequency shift were studied using Design of Experiments (DOE). It is shown from the results that (1) machine rpm has the most significant effect on material removal rate, followed by barrel diameter. Material removal rate increases with machine rpm and barrel diameter; (2) steeper bevel profiles can be achieved by using barrels of smaller diameter and finer powders; and (3) machine rpm has the most significant effect on the frequency shift, followed by barrel diameter and powder type. The frequency shift increases with the machine rpm and barrel diameter. Using finer powders can reduce the frequency shift.