RFID-based new interactive life search and rescue instrument

Introduction There are four types of life detectors currently used at home and abroad: optical, audio, infrared, and radar. They have their own characteristics. The following gives a brief introduction.

The optical life detector is similar to the medical optical fiber endoscope. It uses a metal snake skin tube that can be bent freely to make the front lens pass through the crevices of the building's ruins, illuminate and observe the conditions under the rubble, and through the optical fibers in the snake skin. The bundle transmits the image back to find the person buried under the rubble. The life detector is small in size and easy to use, but it has a short detection distance and cannot be used without the ruins.

The main principle of the audio life detector is to use several high-sensitivity pickups with high-power signal amplification, special filtering and other technologies to listen to the sound and vibration information of the survivors' breathing sounds, squeaks or squeaks under rubble under rubble. To find people buried under the rubble. However, this kind of instrument requires a good signal-to-noise ratio when used in a relatively quiet environment, so the practical application effect is not satisfactory.

The infrared life detector uses infrared radiation to measure living body temperature, and it is not necessary to contact the measured living body. The measurement distance can be as short as several centimeters and as far as several tens of meters. The same kind of instrument is greatly affected by the environment.

Radar life detector is a research hotspot at home and abroad in recent years. It is based on Doppler biological radar principle. It emits ultra-wide spectrum microbeams that can penetrate non-metallic building materials and scan the space under the ruins. This special high-frequency electromagnetic wave can be reflected by the thorax surface of the human body for breathing or heartbeat movements. The phase difference of reflected waves caused by these activities can be used to resolve weak signals such as heartbeat or breathing, thereby discovering buried life. Radar life detectors are also good for detection, but they are based on detecting and distinguishing very weak vital signals. In the actual rescue, the unclear conditions under the rubble and various disturbances on the scene make it very difficult to determine whether there is extremely weak life information.

Since there are various problems with the existing life detectors, there is an urgent need to develop a practical life detector that can respond to harsh environments. In recent years, the rapidly developing RFID technology has provided feasible ideas for exploring new life detection technologies. This article will design a new type of interactive life detection instrument based on RFID technology.

1 Principle of RFID Interactive Search and Rescue Instrument The RFID technology uses space electromagnetic induction or electromagnetic propagation to communicate to achieve the purpose of non-contact automatic identification of the identified objects. The basic working method is to install an RFID tag on an object to be identified. When the object to be marked enters the reader/writer range of the RFID system reader, non-contact information communication is performed between the tag and the reader, and the tag is sent to the reader. The self-information such as the ID number, the reader receives the information and decodes it, and transmits it to the background terminal for processing. Then the processed data is returned to the tag by the reader to complete the entire information processing and data modification process.

The complete RFID system includes RFID data acquisition end, tag, reader/writer, antenna, middleware or interface, application system and so on. The narrow sense RFID system includes tags, readers and antennas. Since the life detector should be a handheld mobile device, the narrow sense RFID system is more suitable for applications.

2 Interactive search and rescue instrument functions 2.1 Design of RFID tags Due to the abrupt and unknown nature of disasters, it must be ensured that even in daily life, people should carry RFID tags instead of preparing them after the disaster. Therefore, designing RFID tags that can be accepted by most people is the key to the popularity of such life detectors. At present, the technology of large-scale integrated circuits can completely design the RFID tag with pulse sensor integrated into a chip with a very small volume, and then add a beautiful shell decoration, which can be completely made into a small handicraft effect. This can be used as a carry-on accessory, such as a car key like an electronic key, or embedded in a belt buckle or decorative buckle. Therefore, the RFID tag can be worn as a handicraft in a human-friendly manner, and does not feel any inconvenience, which is a prerequisite for the practical use of the RFID life detector.

According to the label's power supply form, RFID systems can be divided into active, passive and semi-active systems. The active system's tag uses the battery inside the tag to supply power, and actively transmits signals. The system identification distance is long and can reach tens of meters or even hundreds of meters. The battery life of active tags can theoretically reach 3-5 years, but depending on factors such as the quality of the battery, the environment in which it is used, life expectancy can be greatly reduced. The passive RF tag does not contain a battery. It uses the electromagnetic wave emitted by the reader to couple itself to provide energy. Its light weight, small size, long life, and low cost. Can be made into a variety of thin card or hang buckle card, identification distance up to 10 meters. The tag of the semi-active system has a battery, but the battery only serves the power supply to the internal circuit of the tag, and the tag itself does not emit a signal. In this system we use passive standby active activation strategies to reduce power consumption.

The main components of RFID tags are shown in Figure 2. The passive module is only responsible for receiving the activation signal, and the active module is responsible for communicating with the reader. The system uses broadcast to activate the tag. When the passive activation module detects the activation signal, it obtains energy and verifies the demodulated data. After confirming that it is an agreed activation signal, the logic control circuit generates a digital power supply for the active standby module. Switch control signal. The digital power switch is responsible for the opening and closing of the power supply of the entire active module. When the activation signal is not received, the digital power supply is turned off, the entire active module is in the standby state, and the energy consumption is extremely small; after being activated by the passive module, the digital power is turned In the open state, the active module is powered on, and the pulse information of the human body is collected, and transmitted along with the identification information to the reader through the RF transmit front end. In this way, it can be ensured that the passive activation module activates the active module to send a distress message after it detects that the search and rescue personnel have reached the RFID radio coverage area. On the one hand, RFID tags do no useless work (near search and rescue personnel nearby). Most of the time, they are in standby mode, saving battery power and extending standby time. On the other hand, when it is determined that there are search and rescue personnel in the vicinity, active modules can actively send out strong signals. The distress signal increases the probability of being discovered.

2.2 The reader/writer interacts with the RFID tag. The reader/writer is a handheld mobile search terminal. The interaction with the RFID tag is shown in Figure 3. It first broadcasts the activation signal of the passive module. If there is a buried person in the RFID effective RF coverage area, the RFID tag on the burial personnel activates the active module and sends the distress message: the reader receives the information for help and judges The survival status of the burying personnel was decided, and a decision was made whether to rescue them or not. Because the reader and the tag share the same wireless channel, multiple tags may also enter the same radio coverage area. Inevitably, there is a channel contention problem, that is, collision occurs. Using queuing theory and anti-noise technology to achieve anti-collision technology, this paper uses a code division multiple access time slot ALOHA method, of course, there are many researchers have proposed a new effective algorithm to solve multi-label collision problem. If it is necessary to rescue, the position of the burial personnel can be further located. As for the RFID positioning, a relatively mature algorithm is available. This paper does not discuss the collision prevention technology and the RFID positioning technology in detail.

The antenna of the reader writer is divided into an active signal transmitting antenna A and a receiving signal antenna B, which may also be the same antenna; the reader writer has a control function for the activation signal, and can continue to send an activation signal after receiving a signal returned by a tag. Other tags may also stop sending activation signals; readers should be able to provide common interface modules, such as USB, RS232, SPI, wireless network interfaces, etc., to communicate with PCs or other readers; taking into account ease of operation, The reader should have a convenient human-computer interaction interface, use the LCD color screen to provide an intuitive display function and a visual function menu interface, the main module of the reader is shown in Figure 4.

2.3 Anti-collision algorithm Sends information from the reader/writer node to each searched rescue user node, uses broadcast, uses 413.475 MHz frequency in the UHF band, occupies 100 kHz channel, and any information sent by the reader is normally searched for. The user terminal controller can receive it. From each searched-saved user node to the central node, a random competition method is adopted, and at a frequency of 407.350 MHz, 100 kHz channels are also occupied. If each rescued user does not send information at the same time, the reader can receive it correctly; if each searched user sends information at the same time, a conflict will occur, making the information unrecognizable and must be reissued. Obviously, conflict of information will reduce transmission efficiency. However, considering that each searched user's data packet is short (ie, the occupied channel time is short) and the sending information is bursty and intermittent, the random access to the network is still feasible.

By dividing the equal time slice, each time slice specifies the searched user to send information at the beginning of each time for one frame. The length of each time slice should be designed rationally. Because the transmission delay from the message packets of the rescued users to the reader/writer system is different, the maximum message packet length is related to the time difference between the arrival time of the first packet packet header and the arrival time of the last packet packet. , By the time difference of this successive arrival, select the width of each time slice. For a system with a moderate number of users, the transmission efficiency of the time slice method is about 36.8%. If the number of searched rescue users is small, the transmission efficiency can be improved.

3 Conclusions The RFID-based interactive life detector proposed in this paper is mainly composed of a passively activated standby RFID tag carried on the person and a rescue worker holding a mobile embedded reader. Proposed the application of the current popular RFID technology in the field of life detection, and analyzed its feasibility. Several ideas for the production of RFID tags are given, enabling people to carry RFID tags as accessories to better respond to sudden disasters. People buried in the rubble can actively send strong distress signals through the active RFID module, increasing the probability of ground rescuers finding trapped persons. Aiming at the disadvantages of the traditional active RFID tags such as high power consumption and short battery life, a passive activation module was introduced. When no active signal is detected nearby, the power supply of the active module is cut off, leaving the active module in a standby state with almost no energy consumption. When a nearby activation signal is detected, that is, the rescue personnel are in the RF coverage area, The source module supplies power and sends a high-powered distress signal to the reader, rationally utilizing the limited energy of the battery. The pulse sensor is integrated into the RFID tag to monitor the living status of the trapped person in real time, which avoids the blind rescue of rescue workers and puts more energy into the rescue work for survivors. Embedded readers are designed, which are portable, portable and simple human-computer interaction. Without affecting people's daily life, the popularity of RFID tags will greatly increase the efficiency of post-disaster search and rescue.