Ten Daily Electronic Common Sense-Section 62

In the RFID positioning, what are the two main methods?

In RFID positioning, it is mainly divided into two categories: triangulation method and scene perception method.
The triangulation method adopts the method of multi-point cooperation, and locates by elements such as distance and angle. The scene perception method interprets the positioning information through pre-research or real-time response to the radio signal characteristics in the entire scene. 
The triangulation method is divided into two types: TOA/TDOA and AOA. The former is enough to estimate the distance as a reference standard for positioning measurement. The latter is based on the estimated angle as a reference standard for positioning measurement. In the TOA method, three base points are used as reference points, and the distance between the grate-like daily marker and each base point is used to draw a circle indicating the possible existence of the area. TDOA is slightly flexible, and the corresponding base points are determined in pairs among the three base points, and the distance difference between the target and one pair of base points is measured, and a curve is drawn through the distance difference. Each pair of base points depicts a curve, and the intersection of the curves is the estimated target position. The AOA method is more based on measuring the angle between the target and the base point. In this method, each base point can measure the azimuth angle information of the target and itself, and through the angle information of multiple base points, the result of the intersection is the position estimation area of ​​the target. 
The scene perception method is mainly divided into the reference node method, the scene fingerprint method, and the rule modeling method. Among the current hottest research fronts, most of these methods rely on the reflected signal energy index (RSSI). In the reference node method, by appropriately deploying reference nodes in the scene, the target is compared with the reference node set for radio characteristics, so as to locate. In the scene fingerprint method, the radio characteristic fingerprint information of each reference point in the scene is collected in advance, and then the positioning is carried out. In the regular modeling method, the propagation model in the scene is established through the laws of radio characteristic attenuation, and then the positioning is carried out by distance.

What is a three-electrode system?

For the electrolytic cell, sometimes it is necessary to know or control the potential of the working electrode, and a reference electrode needs to be inserted into the electrolytic cell. At this time, the system contains three electrodes: working electrode, auxiliary electrode and reference electrode. This configuration of the sensor is called a three-electrode system.

Please briefly explain the illuminating process of 0LED?

1. Carrier injection: Appropriate forward bias is applied to the device, and electrons and holes are injected through the cathode and anode after overcoming the interface energy barrier. Electrons are injected from the low work function metal cathode to the lowest unoccupied orbital energy level of the electron transport layer, and holes are injected into the highest occupied orbital energy level of the hole transport layer from the wide bandgap transparent ITO thin film.
2. Carrier transport: Driven by an external electric field, the injected electrons and holes migrate to the light-emitting layer in the electron transport layer and the hole transport layer.
3. Recombination: electrons and holes recombine with each other in an organic substance with luminescent properties to form excitons in an excited state.
4. Migration of excitons: excitons transfer energy to organic light-emitting molecules, and excite electrons of organic light-emitting molecules to transition from the ground state to the excited state.
5. Electroluminescence: The excited state electrons are deactivated by radiation, generating photons and releasing energy to return to the stable ground state.

What is the internal photoelectric effect?

When a semiconductor material is irradiated with light, due to the absorption of photons, electron-hole pairs, ie carriers, are excited inside the semiconductor material. The electrical conductivity of the object changes or photoelectromotive force is generated, which is called the internal photoelectric effect.

What is ECD?

The development process of ECD Since the advent of ECD, people have continuously improved and perfected it to make its structure and performance more ideal. In the past few decades, the two most practical advances have been the replacement of 3H radioactive sources with 63Ni radioactive sources and the replacement of other power supply methods with fixed base current pulsed voltage supply.
The main advantage of using 63Ni source is that the detector temperature can be operated at 350~400℃, thus reducing the pollution problem during operation and improving the detection limit.
Using fixed base current pulse modulation voltage power supply, the linear range is extended to 104, the dynamic range is extended to 105, and the stability of the detector is increased. 
Definition of ECD: Electron Capture Detector (ECD) is the most sensitive gas chromatographic detector and the earliest selective detector. It only responds to those compounds that can capture electrons, such as halogenated hydrocarbons, and compounds containing heteroatoms such as N, O, and S. Due to its high sensitivity and good selectivity, it has been widely used in the analysis of trace pesticides, PCBs, etc. in environmental samples for many years. Its application area is second only to TCD and FID, and has always ranked third.
ECD is one of the gas-phase ionization detectors, but its signal is different from other ionization detectors such as FID, which is an increase in base current, and ECD signal is a decrease in high background base current. The downside of ECD is the small linear range, usually only 102-104. The ECD system consists of an ECD cell and a detection circuit. It differs from the FID system in only two parts: the ionization chamber and the power source E.
Principle of ECD: The carrier gas and purge gas flowing out of the column enter the ECD cell, and are ionized under the bombardment of β-rays emitted by the radioactive source, producing a large number of electrons. Under the action of the power supply, cathode and anode electric fields, the electrons flow to the anode, resulting in a base flow of 10-9-10-8A. When the electronegative component enters the detector from the back of the column, it captures the electrons in the cell, which reduces the base flow and produces a negative peak. Amplified by the amplifier and recorded in the recorder, that is, the response signal. Its size is proportional to the amount of components entering the pool. Negative peaks are inconvenient to observe and handle, and are converted to positive peak ECD by polarity conversion.
There are many classification methods for ECD. Familiar with these classification methods can better understand their operational characteristics, so that they can be reasonably selected for different analysis needs. 1. According to the use of ion source classification: ionization sources used for ECD, there are two categories of radioactive isotope sources and non-radioactive. Although non-radioactive ECDs are commercially available, they have the advantage of being non-radioactive. However, in the operation, high-purity He and some rare gases are added as carrier gas. The ECD structure and electronic equipment are also complicated, and there are still some shortcomings in the operation characteristics, so it is currently in the stage of perfect promotion and use. 2. According to the type of radioactive source: it can be divided into 63Ni and 3H. ECD requirements for radioactive sources: ① Safe to use, radioisotopes may produce α, β, and γ rays during the decay process. α is a high-speed helium nucleus with positive charge; β-ray is a kind of high-speed electron with negative charge; γ-ray is an electromagnetic wave with extremely short wavelength. All three rays have a certain amount of energy that can ionize gases and other substances. Among them, the alpha ray has the strongest ionization ability, and the alpha ray can generate 105 ion pairs per centimeter of travel. Beta rays can produce 102~103 ion pairs per centimeter, while gamma rays are weaker and only produce one pair of ions per centimeter. Although the alpha ray ionization efficiency is high, the noise is too large. However, gamma rays require sufficient ion current, and large doses of radioactive substances need to be used. The ionization and penetration strength of the beta source are moderate, so it is most suitable as an ionizing radiation source; ②The radiation energy of the source should be large enough to provide the necessary ion current; ③The range of the ray should be short enough, which is conducive to structural design and safety. Although this is contradictory to the requirements for radiation energy, it is necessary to take into account each other in use; ④ The half-life should be long enough; ⑤ The use temperature should be high.

What kinds of commonly used absolute pressure sensors?

Commonly used absolute pressure sensors include semiconductor varistor type, capacitive type, variable inductance type and surface elastic wave type driven by bellows.

What are the design elements of the state machine?

1. The clock end of the state machine: The state machine is required to be a synchronous sequential logic design.
2. The reset terminal of the state machine: restore the state machine to the default state.
3. The encoding of the state machine: use the parameter definition, there are encoding forms such as one-hot gray-code binary.
4. Definition of current state and secondary state: two regs (Verilog HDL) or two signals (VHDL).
5. Default state: generally set to idle state.

What are the input devices?

Portable keyboard interface and A/D conversion and touch screen interface.

At present, what kinds of fibers are commonly produced in China?

At present, the optical fibers produced in my country are common step-type and gradient-type multi-mode fibers and single-mode fibers.

What are the characteristics of self-oscillation?

• These four characteristics are enough to show that the self-excited oscillator is an uncompromising signal generator：
  1. The circuit has no signal input, but has a signal output.
  2. The output signal changes periodically and has a certain frequency.
  3. The output signal has a certain waveform, such as sine wave, square wave, etc.
  4. The output signal has a certain amplitude, and the amplitude is relatively stable.