The ultrasonic probe is a key component of the ultrasound diagnostic instrument, which can transform electrical signals into ultrasonic signals and vice versa, thus having a dual function of ultrasonic emission and reception.
Piezoelectric effect
The core of the wireless ultrasonic probe is piezoelectric crystal or composite piezoelectric material. Early transducers used crystals with piezoelectric effect, and high-polymer piezoelectric materials were used as transducers, which have the characteristics of frequency bandwidth, low impedance, and easy processing. Currently, the probe has begun to use composite materials synthesized with ceramics and high-polymer polymers. There are some special crystals in nature. When they are subjected to external forces and deformed, the charge accumulates on the surface of the crystal to form a voltage. This effect is called the piezoelectric effect, and such crystals are called piezoelectric crystals.
The piezoelectric crystal (oscillator) is the core part of the ultrasound transducer. The piezoelectric crystal can be divided into natural and artificial types. Quartz crystal is a natural piezoelectric material, but it is expensive and its performance indicators are not good. Currently, piezoelectric materials are used almost entirely in artificial piezoelectric crystals.
The structure, form, and external excitation pulse parameters, working and focusing methods of wireless ultrasonic probes have a great influence on the shape of the ultrasonic beam emitted, and have a great influence on the performance, function, and quality of the ultrasound diagnostic instrument. The transducer array material has little effect on the shape of the ultrasonic beam, but has a greater effect on the piezoelectric efficiency, sound pressure, sound intensity, and imaging quality of its emission and reception.
Single probe
It usually uses ground and polished flat circular piezoelectric ceramics as transducers. Ultrasonic focusing usually adopts two methods: active focusing of thin-shell spherical or bowl-shaped transducers and flat thin circular lens focusing. It is commonly used in ultrasound diagnostic instruments of A-type, M-type, mechanical fan scan, and pulsed Doppler work modes.
Mechanical probe
It can be divided into two types: single-element transducer reciprocating swing scanning and multi-element transducer rotating switching scanning probe according to the number of piezoelectric chips and motion methods. According to the characteristics of the scan plane, it can be divided into sector scan, panoramic radial scan, and rectangular planar line scan probes.
Electronic probe
It adopts a multi-element structure and uses electronic principles for beam scanning. According to its structure and working principle, it can be divided into linear array, convex array, and phased array wireless ultrasonic probe.
Intraoperative probe
It is used to display the internal structure and position of surgical instruments during the surgical procedure, and belongs to a high-frequency probe with a frequency of about 7MHz, which has the characteristics of small size and high resolution. It has three types: mechanical scanning, convex array, and line control.
Puncture probe
By avoiding lung gas, gastrointestinal gas, and bone tissue through the corresponding body cavity, it can approach the deep tissue to be examined and improve the detectability and resolution. Currently, there are rectal probes, urethral probes, vaginal probes, esophageal probes, gastroscope probes, and laparoscopy probes. These probes can be mechanical, line-controlled, or convex array; they have different sector angles; and have single-plane and multi-plane forms. Their frequencies are relatively high, generally around 6 MHz. In recent years, a vascular probe with a diameter of less than 2mm and a frequency of above 30MHz has been developed.
Transcavitary probe
By avoiding lung gas, gastrointestinal gas, and bone tissue through the corresponding body cavity, it can approach the deep tissue to be examined and improve the detectability and resolution. Currently, there are rectal probes, urethral probes, vaginal probes, esophageal probes, gastroscope probes, and laparoscopy probes. These probes can be mechanical, line-controlled, or convex array; they have different sector angles; and have single-plane and multi-plane forms. Their frequencies are relatively high, generally around 6 MHz. In recent years, a vascular probe with a diameter of less than 2mm and a frequency of above 30MHz has been developed.
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