Ultrasonic-Frequency-Based Visualization of Columnar Soft Matter Beyond Wavelength Limitations
发现柱状软物质直径与超声反射频率的反比关系，提出利用宽带超声和短时傅里叶变换的可视化方法，可突破波长限制测量100-300微米直径。
This paper first describes a relation between the frequency and the diameter of columnar soft matter by using broadband ultrasonic single-probe testing. We found an inverse relation between the diameter (100-300 μm) and frequency (1.0-6.0 MHz) of the ultrasonic reflection waveform from columnar soft matter in water. This fact shows that we can determine diameters that are not possible to determine by the standard pulse-echo method. An ultrasonic wavelength with center frequency of 15 MHz is limited to measurements of less than 100-μm thickness in water (wave speed: around 1500 m/s). However, the relation found in this paper enables us to determine these diameters by broadband ultrasonic testing with center frequency of 5.0 MHz, beyond the previous wavelength limitation. Second, this paper proposes a visualization method that uses the discovered relation. An image is produced by using particular frequency components derived via short-time Fourier transform. We employ a phantom consisting of two types of nylon lines, one with thin and the other with thick diameters. The experimental result clearly demonstrated line width and depth beyond the wavelength limitation.