Non-contact bolt axial force measurement based on the deformation of bolt head using quartz crystal resonator and coils

As a health monitoring tool of bolts in infrastructures, we propose a non-contact evaluation method for the axial force of a bolt. Deformation of the bolt head is measured as an electrical capacitance variation detected as a frequency shift of a simple circuit composed of a quartz crystal resonator and coils. The measurement was carried out via magnetic field coupling between the coil installed on the bolt head and another coil connected to the measurement instrument. Since the method requires no active electronic circuit or battery for the bolt, low cost and high durability can be expected. First, the circuit was analyzed and optimized using an equivalent circuit model. Then, the feasibility of the proposed method was experimentally studied using a prototype. It was demonstrated that the method enabled non-contact axial force estimation in which the dependence on the distance between the coils is sufficiently small for detecting bolt looseness.

Research on Trimming Frequency-Increasing Technology for Quartz Crystal Resonator Using Laser Etching

A quartz crystal resonator (QCR) is an indispensable electronic component in the field of the modern electronics industry. By designing and depositing electrodes of different shapes and thicknesses on a quartz wafer with a certain fundamental frequency, the desired target frequency can be obtained. Affected by factors such as the deposition equipment, mask, wafer size and placement position, it is difficult to accurately obtain the target frequency at a given time, especially for mass-produced QCRs. In this work, a laser with a wavelength of 532 nm was used to thin the electrodes of a QCR with a fundamental frequency of 10 MHz. The electrode surface was etched through a preset processing pattern to form a processing method of local thinning of the electrode surface. At the same time, the effect of laser etching on silicon dioxide and resonator performance was analyzed. Satisfactory trimming frequency-increasing results were achieved, such as a frequency modulation accuracy of 1 ppm, frequency distribution with good consistency and equivalent parameters with small changes, by the laser partial etching of the resonator electrode. However, when the surface electrode was etched into using through-holes, the attenuation amplitude of the equivalent parameter became larger, especially in terms of the quality factor (Q), which decreased from 63 K to 1 K, and some resonators which had a serious frequency drift of >40%. In this case, a certain number of QCRs were no longer excited to vibrate, which was due to the disappearance of the piezoelectric effect caused by the local thermal phase change in the quartz wafer.