Quartz crystals, due to their unique piezoelectric effect, play a vital role in numerous fields. Their applications span a wide range of high-tech sectors, including electronics, communications, and aerospace.
1.Quartz Crystal Oscillators
A quartz crystal oscillator uses a quartz crystal as the core of a resonant frequency-selective circuit. This oscillator is constructed by precisely slicing a quartz crystal into thin slices and attaching metal plates to their surfaces. Its operating principle is based on the inverse piezoelectric effect: quartz crystals vibrate mechanically under the influence of an alternating electric field. Because each quartz crystal has a specific natural vibration frequency, resonance occurs when an applied electric field matches this frequency. This characteristic makes quartz crystals an ideal choice for high-precision resonant frequency-selective circuits. Quartz crystal oscillators, due to their excellent frequency stability, play a key role in numerous devices, including standard frequency generators, pulse counters, and quartz clocks.
2. Quartz Crystal Microbalance
Quartz Crystal Microbalance (QCM) is an instrument that uses the piezoelectric effect of quartz crystal to measure changes in electrode surface mass. Since its introduction in the early 1960s, it has become a powerful tool for nanogram-level mass detection due to its extremely high sensitivity. Its working principle is that the change in the surface mass of the quartz crystal electrode will be converted into a frequency change of the output electrical signal of the oscillation circuit. This process is then analyzed by auxiliary equipment such as computers to obtain high-precision measurement results. Therefore, the quartz crystal microbalance plays a vital role in many fields such as medicine, chemical industry, food, biomedicine, environmental monitoring, industry and military.
3. Piezoelectric biosensor
(1) Piezoelectric immunosensor
The working principle of the piezoelectric immunosensor is to fix antibodies or antigens on the surface of quartz crystal and use the specific affinity reaction between antigen and antibody. When the antigen or antibody to be measured interacts with the fixed recognition substance and produces specific adsorption, the surface mass load of the crystal will increase accordingly. This change can be monitored by the frequency change of the sensor, thereby determining the amount of adsorbed antibody or antigen.
(2) Piezoelectric gene sensor
The basic principle of piezoelectric gene sensor for DNA detection is to fix the single-stranded DNA probe on the crystal surface. When the DNA sequence to be detected is complementary to it, hybridization reaction occurs on the chip to form double-stranded DNA. This process will lead to an increase in crystal mass and changes in surface viscoelasticity. These changes can be measured by frequency change of the sensor and network analysis.