What is the physics of a stethoscope?

The stethoscope is the most commonly used diagnostic tool for gynecologists inside and outside, which include variant types like the acoustic stethoscope, electronic stethoscope, and fetal stethoscope. It becomes the symbol of doctors. The invention of the stethoscope began the development of modern medicine. Since its clinical application on March 8, 1817, the stethoscope has been continuously improved in appearance and sound transmission mode, but its basic structure has not changed much. It is mainly composed of picking up part (chest part), conducting part (rubber tube), and listening part (earpiece). So what is the physics of a stethoscope? Let's take a look. The construction for his article as follows ：

The principle for the stethoscope

Types of stethoscope

1. The principle for the stethoscope

Usually, by auscultation head, conduction tube, ear hang composition. Nonlinear amplification of the collected sound.

The principle of the stethoscope is that the vibration conduction between materials is involved in the aluminum film in the stethoscope, and the single non-air, changing the frequency and wavelength of sound, to reach the "comfortable" range of human ears, while blocking other sounds, "hear" more clearly. The reason why people hear sounds is that the so-called "sound" is the vibration conduction between substances, such as air vibration of the eardrum in the human ear, etc., which is converted into brain electricity, so that people "hear" the sound. The vibration frequency that the human ear can perceive is 20-20khz.

There is another standard for people to feel the sound, which is related to the wavelength. Normal people's hearing intensity ranges from 0dB to 140dB. In other words: the sound in the audio range is too loud and weak to hear, and the audio in the volume range is too small (insertion wave) or too large (generated wave) to hear.

Human hearing is also related to the environment, the human ear has a shielding effect, that is, strong sound can mask weak sound. Internal sounds such as heartbeats, bowel sounds, rales, and even blood flow can be hard to "hear" because the audio is too low or too low, or is obscured by noise.

In cardiac auscultation, the membrane head is good for hearing high frequencies, while the cup head is good for hearing low frequencies or murmurs. Both modern stethoscopes are double-sided stethoscopes. The head of the stethoscope has both membrane type and cup type, and the conversion between the two can be done only by rotating 180°. Experts suggest clinicians should use double-sided stethoscopes. Another patented technology, called the floating film technology, allows the membrane-shaped auscultation head to be turned into a cup-shaped head in a special way to hear low-frequency murmurs. Normal and abnormal lung sounds are high-frequency sounds, lung auscultation can only use the membrane head.

2. Types of stethoscope

Acoustic stethoscope

The acoustic stethoscope is the earliest stethoscope in history. It has become the symbol of the doctor, who wears it around his neck every day. The acoustic stethoscope is the most commonly used.

Electronic stethoscope

The electronic stethoscope is the use of electronic technology to amplify the sound of the body, overcome the acoustic stethoscope noise bug. The electronic stethoscope needs to convert the sound waves of the electrical signal, which is then amplified and processed to get the best listening. They are based on the same physical principles as the acoustic stethoscope. Electronic stethoscopes can also be analyzed with computer-assisted auscultation programs to record heart sound pathology or innocent heart murmurs.

Fetal stethoscope

In fact, a fetal stethoscope or fetal mirror is also a kind of acoustic stethoscope, but it is out of the ordinary acoustic stethoscope. The fetal stethoscope can hear the voice of the fetus in the pregnant woman. It is very beneficial to care during pregnancy.

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