Fiber optic sensors for biomedical applications are mainly light-transmitting. It is highly valued for its small size, insulation, immunity from radio frequency and microwave interference, high measurement accuracy and good affinity with living organisms. This article will mainly introduce the application of optical fiber in pressure measurement, blood flow velocity measurement, and pH value measurement. In addition, it can also be used to measure temperature and transmit medical images.
Optical fiber sensors in medical applications are mainly used to measure intravascular blood pressure, intracranial pressure, intracardiac pressure, bladder and urethral pressure, etc. The pressure-sensitive part is a waterproof film on the side wall of the end of the probe catheter. A micro-reflector with a cantilever on one side is connected to the film. The opposite side of the reflector is a bundle of optical fibers, which is used to transmit the incident light to the reflector. It also transmits reflected light. When there is pressure on the membrane. The film is deformed and can drive the cantilever to change the angle of the mirror. The light beam from the optical fiber is irradiated on the mirror, and then reflected to the end of the optical fiber. Since the direction of the reflected light changes with the angle of the mirror, the intensity of the reflected light received by the fiber also changes. This change is transmitted through the optical fiber to the photodetector at the other end and becomes an electrical signal, so that the pressure at the probe can be known through the change of the voltage.
The Doppler fiber optic velocity sensor measures the blood flow velocity of subcutaneous tissue by utilizing the end face reflection phenomenon of the optical fiber, and the measuring system has a simple structure. The laser with the emitting frequency f is sent to the epidermis through the lens, and the fiber is sent to the epidermis. For immobile tissues, such as blood vessel walls, the reflected light does not have a frequency shift; for red blood cells with a flow velocity of the intensity is proportional to the concentration of red blood cells, and the change in frequency can be proportional to the speed of movement of the red blood cells. After the emitted light is collected by the optical fiber, it is first mixed on the optical fiber sensor in medical applications, and then enters the signal processing instrument, so as to obtain the moving speed and concentration of red blood cells.
Optical fiber spectroscopic sensor used to measure the pH value of living tissue and blood. Its working principle is to use the distribution spectrum of the intensity of the emitted light and transmitted light with the wavelength to measure. This fiber-optic sensor for medical applications inserts two optical fibers into an ion-permeable cellulose capsule. The bellows contains reagents, and when a needle is inserted into a tissue or blood vessel, bodily fluids seep into the reagents, causing the reagents to absorb certain wavelengths of light. The pH value of blood or tissue can be obtained by measuring this change with a spectrum analyzer.