In this blog post, we will look at how the piezoelectric effect and crystal oscillators can be used to measure extremely small masses such as gas molecules and DNA, and explore some of their applications.
Scales commonly measure mass by using the principle of levers or by measuring changes in electrical resistance. So how do ultra-high-precision scales measure the mass of microscopic substances such as gas molecules and DNA? To answer this question, we need to understand the piezoelectric effect.
There are two types of piezoelectric effects: the primary piezoelectric effect, in which mechanical deformation of a material generates voltage, and the secondary piezoelectric effect, in which applying voltage to a material causes mechanical deformation. Materials that exhibit both piezoelectric effects are called piezoelectric materials, and quartz is mainly used for this purpose.
Quartz is widely used as a piezoelectric material because of its stability and accuracy. Quartz is very suitable for precise measurements because it maintains a constant structure and is less affected by external factors. Quartz used as a piezoelectric material is cut and processed in a specific direction to form a flat disc shape. After electrodes are made on both sides of the disc, a voltage with alternating (+) and (-) poles is applied, causing the quartz to vibrate.
A quartz crystal oscillator is a device that makes it easy to measure vibrations by matching the frequency of the voltage to the natural frequency of the quartz crystal so that the quartz crystal vibrates widely. The natural frequency is the unique vibration frequency of an object, and even for piezoelectric materials of the same material, it varies depending on the shape and size of the piezoelectric material.
When a substance adheres to a quartz crystal oscillator and increases its mass, the frequency of the quartz crystal oscillator, which was vibrating at its natural frequency, decreases. The frequency of a quartz crystal oscillator is very sensitive to even small changes in mass, so it can be used to measure the mass of microscopic substances such as gas molecules and DNA. The mass sensitivity of a vibrator is the degree of change in frequency divided by the measured mass, and the mass sensitivity of a crystal vibrator is very high.
The principle of measuring mass with a crystal oscillator can be applied to detect the concentration of a specific gas. When a crystal oscillator is treated so that a specific gas adheres to it, the specific gas sticks to it, causing a change in mass and a decrease in the frequency of the crystal oscillator. At a certain point, the frequency of the crystal oscillator stops decreasing and remains constant. The reason why the frequency remains constant is that no more than a certain amount of the specific gas adheres to the crystal oscillator. In a mixture of gases, the higher the concentration of a specific gas, the lower the frequency at which the frequency remains constant. The reaction time is the measure of how quickly a specific gas adheres to the crystal oscillator and the frequency becomes constant. The shorter the reaction time, the faster the concentration of the specific gas can be measured.
However, if gases other than the target gas adhere to the crystal oscillator, it is difficult to accurately measure the concentration of the target gas. Furthermore, even if only the target gas adheres to the crystal oscillator, it is not possible to determine the concentration of that gas. For this reason, the frequency change of the crystal oscillator must be measured in advance according to the concentration of the target gas. The sensitivity to concentration can be obtained by dividing the degree of frequency change of the crystal oscillator by the concentration.
Crystal resonators are used in various fields as ultra-precise scales. For example, in the life sciences, they can be used to measure the concentration of specific proteins or DNA. In environmental science, they are useful for measuring the concentration of pollutants in the air, and in the medical field, they open up the possibility of measuring the concentration of specific viruses or bacteria in the blood in real time. As such, crystal resonators are used as innovative measurement tools in various fields thanks to their sensitivity and accuracy.
In addition, technological advances in quartz crystals, combined with nanotechnology, are enabling even more precise measurements. Nanotechnology allows for the production of smaller crystals, which are more sensitive to even smaller changes in mass. Therefore, quartz crystals are expected to play an increasingly important role in a wide range of fields in the future.
