Electromagnetic interference propagation methods are generally divided into two types: conductive coupling and radiation coupling. Any electromagnetic interference must occur in the transmission and transmission path (or transmission channel) of the interference energy. It is generally believed that there are two ways to transmit electromagnetic interference: one is a conductive transmission method; the other is a radiation transmission method. Therefore, from the perspective of the interfered sensors, the interference coupling can be divided into two types: conduction coupling and radiation coupling. Conducted transmission must have a complete circuit connection between the interference source and the sensor, and the interference signal is transmitted to the sensor along this connection circuit, causing interference. This transmission circuit can include wires, conductive components of the device, power supply, common impedance, ground plane, resistors, inductors, capacitors, and mutual inductance components.
Radiation transmission is transmitted through the medium in the form of electromagnetic waves, and the interference energy is emitted to the surrounding space according to the law of the electromagnetic field. There are three kinds of common radiation coupling: 1. The electromagnetic wave emitted by the antenna is accidentally accepted by the antenna, called antenna-to-antenna coupling; 2. The space electromagnetic field is coupled by wire induction, called field-to-line coupling; 3. two High frequency signal sensing between parallel wires is called inductive coupling of wire-to-wire. In actual engineering, interference between two devices usually involves coupling of many ways. Because of the simultaneous existence of multiple ways of coupling, repeated cross-coupling, and interference together, electromagnetic interference becomes difficult to control.
The important role played by medical equipment in diagnosis and treatment is that the impact of electromagnetic interference on it is directly related to the patient's personal safety. At present, the small, high-sensitivity and intelligent realization of medical equipment makes them more susceptible to electromagnetic interference. In particular, those with poor resistance to dryness (ie, poorly compatible diagnostic instruments provide doctors with information such as distorted data, waveforms, and images, so that doctors can't make a correct diagnosis, of course, affecting effective treatment, even endangering people. Life, the international has many reports in this regard.
The FDA-recognized suspected accident caused by electromagnetic interference caused by medical devices; patients who implanted cardiac pacemakers failed to use the two-way wireless communication device during the emergency treatment of the ambulance. The patient monitor is affected by electromagnetic interference, causing the patient to die due to the detection of arrhythmia. Excessive interference on the CAT display of the device makes it difficult for medical staff to determine the heart rate, rendering the patient unable to recover.
Mobile phones interfere with baby incubators, infusion pumps, artificial dialyzers, cardiac pacemakers, and cardiac defibrillators, so hospitals in the United States expressly ban the use of mobile neonatal respiratory monitors in wards with such devices (newborns) The specially designed alarm device for breathing stops is affected by the interference modulation wave emitted by the FM radio FM, which disturbs the respiratory rhythm and causes the alarm to malfunction.
The above example only talks about the influence of external electromagnetic interference on medical equipment. It is not known that modern medical uses various high-frequency, high-frequency transmitters with high-sensitivity electrical, electronic components and components, and devices that use RF energy for diagnosis or treatment. Or the system (MAI), which may operate as a source of EMI interference to spread useful or unwanted electromagnetic waves of different frequency ranges and electromagnetic field strengths through different combinations, radio broadcast communication services and other surrounding equipment, and They may also be subject to interference between surrounding power, electronic equipment, and medical equipment in a common electromagnetic environment. Therefore, many medical devices are both sources of interference and sensitive devices, that is to say, they have both interference and interference. Therefore, a question worthy of our consideration is how to achieve a medical device that is neither immune nor minimized in this complex electromagnetic environment. Affected by various other electromagnetic interferences, and can minimize electromagnetic interference to other equipment or the human body, thereby achieving a balance, electromagnetic temperament is such a concept.
Electromagnetic compatibility (EMC) refers to the ability of a device or system to operate in its electromagnetic environment and to produce unacceptable electromagnetic interference to any device in its environment. Therefore, EMC includes two requirements: on the one hand, the electromagnetic interference generated by the equipment in the normal operation process cannot exceed a certain limit; on the other hand, the appliance has certain electromagnetic interference in the environment. The degree of immunity, ie electromagnetic sensitivity.
In order to realize that the medical equipment or system in the same electromagnetic environment can work normally without disturbing the normal radio communication without disturbing the normal work of the surrounding equipment, it is necessary to establish a rule. The anti-interference ability of the equipment or system is specified, that is, the anti-interference level of the equipment should not be too low, and the emission level and the anti-interference level are limited to the specified emission limit and the specified immunity limit, and the equipment reaches The purpose of electromagnetic compatibility. Any active medical electronic device will radiate an electromagnetic field outward, except that the radiation field is strong in magnitude and frequency, and the stronger the field strength, the stronger the external interference.
The greater the interval between the emission value and the immunity limit, the greater the electromagnetic compatibility and the higher the electromagnetic compatibility of the device. Therefore, limiting the external emission level of the medical device and improving its immunity to the electromagnetic environment can be achieved in order to achieve mutual coordination between the device and the environment.
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