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    What parameters are affected by the identification range?

    The recognition range is one of the most important parameters of RFID tags, which is mainly affected by two parameters.
    They are the maximum distance Rtag (tag activation distance) at which the tag can just obtain enough power from the reader and the maximum distance Rreader at which the reader can detect the backscattered signal of the tag.
    The effective recognition range takes the smaller value min(Rtagg, Rreader) of these two distances.

    What is the load capacitance?

    Load capacitance is an extremely important parameter to describe the application characteristics of a quartz crystal oscillator. the
    In the application, the crystal oscillator forms an oscillation circuit with other circuits and components. When the crystal oscillator is powered on, it will resonate and trigger the oscillator circuit to oscillate. Generate the same signal as the resonant frequency of the crystal oscillator, so that the electrical appliances can work normally and stably. the
    The load capacitance of the crystal oscillator refers to the equivalent capacitance seen from the two pins of the crystal oscillator to the direction of the oscillation circuit. It refers to the sum of the effective capacitance formed by the circuit and components associated with the two pins of the crystal oscillator. the
    In practice, the crystal oscillator and load capacitance must be matched. Otherwise, it will affect the oscillation signal to deviate from the resonant frequency of the crystal oscillator, so that the electrical appliances cannot work normally or stop working. the
    There are two types of load capacitors for common crystal oscillators. One is low load capacitance and the other is high load capacitance.

    Compared with the international advanced level, what are the main gaps in the design of RFID chips in China?

    1. Foreign countries started earlier in the design of RFID chips, and applied for many technical patents. However, China started relatively late, and the foundation of RFID chip design in UHF and microwave frequency bands is still relatively weak.
    2. In terms of memory, developed countries have begun to use standard CMOS technology to design non-volatile memory. It is possible to make all modules of the electronic tag under the standard CMOS process, so as to reduce the production cost. However, it is still in the research stage in China.
    3. Electronic tags are sensitive to cost, and chip design requires professionals with rich experience in analog circuit and digital-analog hybrid circuit design. The domestic technical force in this area is relatively weak.

    What are the characteristics of the parallel process program?

    • The parallel flow program with 3 branches has the following characteristics:
      1. If S20 has been activated, only the branch transfer condition X0 is established. The three processes (S21, S22, S31, S32, S41, S42) are executed in parallel at the same time, and there is no sequence.
      2. When the actions of each process are all finished (the process that is executed first must wait for the completion of all process actions). Once X2 is ON, the confluence state S50 will act, and all S22, S32, and S42 will be reset. If one of the processes is not finished, then S50 cannot act. In addition, a parallel process program may have two or more states in the “active” state at the same time.

    What are the disadvantages of barcodes?

    • The barcode must face the scanner to successfully read the barcode information.
    • If the barcode or label is torn, undamaged, or peeled off, these items cannot be identified.
    • Bar codes can only identify the manufacturer and product category, not a specific and unique item.

    What are the main characteristics of the magnetic triode?

    1. Volt-ampere characteristics
    2. Magnetoelectric characteristics、
    3. Temperature characteristics

    What is the reason why the vibrator is selected as a tuning fork type?

    Because the two vibrators move in opposite directions, the direction of the Coriolis force is also opposite.
    In this way, the deflection deformation caused by acceleration in the front, rear and left and right directions of the vehicle can cancel each other out.
    Therefore, only the angular velocity signal can be output from the detection PZT.

    Why pyroelectric sensors?

    The polarization (charge per unit area) of ferroelectrics is temperature dependent.
    When infrared radiation strikes the surface of an already polarized ferroelectric sheet, it causes the sheet to increase in temperature. It reduces the polarization intensity and reduces the surface charge. This is equivalent to releasing part of the charge, so it is called a pyroelectric sensor.

    What are the main features of the bundle layer structure?

    • Region and gateway. An area is a specific network with specific protocols and communication requirements, such as the four areas A, B, C, and D in Figure 1.1. Area B includes a bus carrying a DTN gateway, which travels between DTN gateway 3 and DTN gateway 5 . Region D includes a regularly connected satellite link. A gateway is essentially an access point used to connect two areas with different network architectures and protocol stacks. It consists of two logical parts that sit on top of the corresponding transport layer protocols of two adjacent areas. Two nodes are said to be in the same area if they can communicate without going through a DTN gateway. Area boundaries are used to represent interconnection points between different network protocol stacks, as shown in Fig. l. 2 is the logical view of the DTN gateway. When it is necessary to ensure reliable delivery of messages, DTN gateways are responsible for storing messages in persistent storage. In addition, the DTN gateway also needs to assume the responsibility of mapping between different transmission protocols.
    • Name tuple. For message routing, DTN takes the form of a name tuple to identify a destination node or group of destination nodes. A name tuple consists of two variable-length parts of the form {region-name, entity-name) . The region name is globally unique and has strict topological meaning through hierarchical construction. The entity name is the name of the node in a specific area, which is unique within the area but not unique outside the area, and can be of any structure.
    • Postal-style delivery service. All kinds of network resources in DTN are strictly limited, so it is necessary to adopt priority-based resource allocation and message transmission mechanism. Similar to postal services, the DTN architecture adopts three priorities: Bulk, Normal, and Expedited, which conceptually correspond to low, medium, and high priorities respectively.
    • Routing. In the routing and forwarding framework provided by the DTN architecture, DTN is defined as a multigraph, that is, there may be multiple connection edges between nodes. Based on network characteristics, the contact between nodes is classified as Persistent, On. There are five types of demand, Scheduled, Predicted, and Opportunistic, of which the latter three are the most common in DTN. To provide maximum flexibility in area design, the DTN architecture itself does not specify any particular type of routing mechanism.
    • Reliability and custody transfer. Custodial transport is a concept proposed to maintain end-to-end connection state and deal with high packet loss rate and lack of resources. Its core means that the message jumps from one DTN node to the next DTN node and realizes reliable delivery. According to the storage capacity of the nodes, the DTN architecture divides the nodes into two categories: persistent and non-persistent. The former has sufficient storage resources, while the latter has relatively insufficient storage resources. DTN is faced with a high message packet loss rate, and it is necessary to ensure that those nodes that do not have sufficient resources do not have to undertake and maintain the task of end-to-end reliable transmission. Therefore, once a custodial bundle is delivered to a Persistent node, the source node does not have to keep maintaining a copy of the bundle.
    • Convergence layer. There may be significant changes in the functions provided by the bottom layer of the DTN architecture, such as reliable transmission, flow control, and congestion control. Assuming that the underlying layer can achieve reliable transmission, it is necessary to add a protocol stack containing a specific aggregation layer to ensure the realization of these underlying functions. For example, when reliable delivery is provided by the underlying transport, the corresponding aggregation layer only needs to provide corresponding link state management. Figure l. 3 describes a typical DTN protocol stack.
    • Time synchronization. The DTN architecture requires time synchronization between communicating nodes. This requirement originates from the fact that many distributed applications in challenging environments need time synchronization, such as message bundle identification, routing scheduling, message lifetime calculation, etc., which are usually completed through an external non-DTN protocol.
    • Flow contr01 and Congestion contr01. Flow control in DTN architecture refers to limiting the sending rate of DTN nodes to match the receiving rate of next-hop nodes. Flow control decisions must be made within the binding layer, although it may require support from the underlying transport layer. Congestion control refers to dealing with competition for persistent storage resources in the DTN gateway. The RFC standard does not specify a specific congestion control mechanism, so the congestion control mechanism is an open research problem.
    • Security. The security of the DTN architecture requires restricting access to available scarce resources, and its main goal is to prevent unauthorized applications from exploiting network resources and to prevent authorized applications from accessing services of a higher rank than their own. Therefore, it becomes necessary to identify and discard damaged message bundles and detect damaged nodes. A popular security mechanism is the hop-by-hop and end-to-end authentication and integrity mechanisms, whose purpose is to use the data integrity of the application layer to implement access control for data forwarding and storage respectively.

    What is linearity?

    Linearity refers to the degree of linearity between the irradiation light intensity and the generated signal charge.


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