A low-cost liquid pH detection system

Abstract

The present invention discloses a low-cost liquid pH detection system. The system includes a sensor tag, a reference tag and a detection system; the detection system includes a signal transceiver subsystem for sending a continuous wave signal to activate the tag, and sending a query signal to establish communication with the tag, and collecting the reflected signal of the tag; a differential sensing subsystem for separating the reflected signal, removing the signal interference in the reflected signal, and performing signal differentiation on the reflected signal after eliminating the interference to obtain the differential amplitude and phase of the sensor tag and the reference tag; a liquid pH detection subsystem for extracting the features of the amplitude and phase from the differential amplitude and phase using a machine learning method, and determining the pH value of the liquid to be detected according to the mapping relationship between the liquid pH and the features of the amplitude and phase. The solution provided by the present invention is simple in composition, low in equipment cost, and easy to deploy on a large scale. The system has low operating difficulty and high detection accuracy, and can achieve low-cost, fast and efficient liquid pH detection.

Description

Technical Field

[0001] The invention relates to the technical field of pH value detection, and in particular to a low-cost liquid pH value detection system. Background Art

[0002] Measuring the pH of liquids is of great significance in various fields such as medical diagnosis and monitoring, agriculture and aquaculture, industry and environmental protection. Measuring the pH of human body fluids (such as blood and urine) can provide information about the acid-base balance in the patient's body to help diagnose and monitor diseases such as acidosis, alkalosis, respiratory dysfunction, etc. Abnormal pH can provide doctors with important information about the patient's health status and help doctors develop treatment plans. The pH of agricultural irrigation water will directly affect the growth and development of plants, and farmers need to adjust the soil pH according to the pH of the water quality. The pH of water bodies in the aquaculture industry can help farmers assess the acidity and alkalinity of water bodies and their effects on aquatic animals, so as to take necessary measures to maintain the acid-base balance of water bodies.

[0003] The commonly used liquid pH detection methods include pH test paper detection method and pH electrode detection method. However, the pH test paper detection method requires the human eye to judge the color change of the test paper, which will be affected by subjective factors and lead to inaccurate results. The electrodes of the pH electrode detection method are easily affected by liquid contamination and the measurement results are affected, and regular calibration and cleaning and maintenance are required, which increases the complexity and cost of use. Therefore, a urine pH detection method based on software radio and RFID tags is proposed. Two RFID tags are placed in the diaper, one tag is covered with waterproof material, and the other tag is in direct contact with urine. This method uses software radio to analyze the differential amplitude and phase of the dual tag reflection signal to detect the pH of urine, which overcomes the problems and shortcomings of common detection methods. However, this method requires the use of an expensive software radio platform, which is costly and difficult to deploy. In addition, the use of the software radio platform is complex and difficult to operate. Summary of the invention

[0004] In order to solve the technical problems that the existing pH detection method based on RFID tags uses an expensive software radio platform, is high in cost and difficult to deploy, the embodiment of the present invention provides a low-cost liquid pH value detection system.

[0005] The technical solution of the embodiment of the present invention is achieved as follows:

[0006] The embodiment of the present invention provides a low-cost liquid pH value detection system, which includes a sensor tag, a reference tag and a detection system; the sensor tag is attached to the inner wall of a container and is in direct contact with the liquid to be detected; the reference tag is attached to the outer wall of the container and is isolated from the liquid to be detected; the detection system includes a signal transceiver subsystem, a differential sensing subsystem and a liquid pH detection subsystem: the signal transceiver subsystem is used to send a continuous wave signal to activate the sensor tag and the reference tag, and send a Query signal to establish communication with the sensor tag and the reference tag, and collect reflection signals of the sensor tag and the reference tag; the differential sensing subsystem is used to separate the reflection signal using a tag signal separation algorithm, remove signal interference in the reflection signal using a differential method, and perform signal differentiation on the reflection signal after eliminating interference to obtain the differential amplitude and phase of each of the sensor tag and the reference tag; the liquid pH detection subsystem is used to extract the features of the amplitude and phase from the differential amplitude and phase using a machine learning method, and determine the pH value of the liquid to be detected according to the mapping relationship between the liquid pH and the features of the amplitude and phase.

[0007] In one embodiment, the signal transceiver subsystem includes an RFID signal receiver and an RFID signal transmitter; the RFID signal transmitter includes a development board, a radio frequency module and a first antenna; the RFID signal receiver includes a host computer, a software-defined radio module and a second antenna; the development board is used to send a control signal to the radio frequency module after programming; the radio frequency module is used to send a continuous wave signal to the sensor tag and the reference tag and send a Query signal at a preset frequency when receiving the control signal; the first antenna is used to send the continuous wave signal and the Query signal; the second antenna is used to receive the reflected signal of the sensor tag and the reference tag; the software-defined radio module is used to receive and demodulate the reflected signal at a preset sampling rate, and output the complex signal obtained after demodulation to the host computer; the host computer is used to receive the complex signal, and send the complex signal to the differential sensing subsystem after processing.

[0008] In one embodiment, the radio frequency module is specifically used to alternately send Query signals in which the Q parameter is 0 or the Q parameter is 1 to the sensor tag and the reference tag; the sensor tag and the reference tag are specifically used to, after receiving the Query signal, back-reflect the RN16 signal according to the corresponding number of response slots based on the value of the Q parameter in the Query signal, when the generated number of response slots is 0; and not reflect the signal when the generated number of response slots is not 0.

[0009] In one embodiment, the sensor tag and the reference tag are specifically used to generate a response slot number of 0 when the Q parameter in the Query signal is 0; and to generate a response slot number of either 0 or 1 when the Q parameter in the Query signal is 1.

[0010] In one embodiment, the radio frequency module is specifically used to convert the PIE-encoded Query signal into an OOK-encoded QueryBytes signal for transmission based on an established conversion mechanism between OOK encoding and PIE encoding; the conversion mechanism is to convert the data 1 in the PIE encoding into 1110 in the OOK encoding, and to convert the data 0 in the PIE encoding into 10 in the OOK encoding.

[0011] In one embodiment, the differential sensing subsystem includes a carrier frequency offset elimination module, a self-interference elimination module, a dual-tag simultaneous reflection interference elimination module and a signal differential module; the carrier frequency offset elimination module is used to eliminate the frequency offset in the reflected signal; the self-interference elimination module is used to eliminate the self-interference caused by the continuous wave signal in the reflected signal; the dual-tag simultaneous reflection interference elimination module is used to separate the reflected signal and extract the RN16 cluster reflected by each tag in the reflected signal; the signal differential module is used to perform K-means clustering on the RN16 cluster reflected by each tag to obtain the central complex vector of each RN16 cluster, respectively calculate the amplitude and phase of the central complex vector, differentiate the amplitude and phase, and take the absolute value to obtain the differential amplitude and phase of each tag.

[0012] In one embodiment, the carrier frequency offset elimination module specifically eliminates the frequency offset in the reflected signal using the following calculation formula:

[0013]

[0014] in, To obtain the signal after frequency offset is eliminated, The signal collected by the signal receiving and sending subsystem, , It is the carrier signal sent, which provides energy for the tag during the communication process. is the tag reflection signal RN16, is the coded signal, when When , the tag reflects the carrier signal; when When , the tag does not reflect the carrier signal; is the carrier frequency offset, is the self-interference term, the unknown phase offset .

[0015] In one embodiment, the self-interference elimination module specifically eliminates the self-interference caused by the continuous wave signal in the reflected signal using the following calculation formula:

[0016]

[0017] in, is the tag reflection signal, To obtain the signal after frequency offset is eliminated, , is the self-interference term.

[0018] In one embodiment, the dual-tag simultaneous reflection interference elimination module is specifically used to obtain the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 0, and the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 1: from the RN16 cluster in the reflected signal when the Q parameter is 1, the RN16 cluster that overlaps with the RN16 cluster in the reflected signal when the Q parameter is 0 is removed to obtain the RN16 cluster reflected by each tag individually.

[0019] In one embodiment, the liquid pH detection subsystem includes a feature extraction module and a feature classification module; the feature extraction module is used to extract amplitude and phase features from the differential amplitude and phase of each tag; the feature classification module is used to determine the pH value corresponding to the feature based on the mapping relationship between the liquid pH and the amplitude and phase features.

[0020] The embodiment of the present invention provides a low-cost liquid pH value detection system, which includes a sensor tag, a reference tag and a detection system; the sensor tag is attached to the inner wall of a container and is in direct contact with the liquid to be detected; the reference tag is attached to the outer wall of the container and is isolated from the liquid to be detected; the detection system includes a signal transceiver subsystem, a differential sensing subsystem and a liquid pH detection subsystem; the signal transceiver subsystem is used to send a continuous wave signal to activate the sensor tag and the reference tag, and send a Query signal to establish communication with the sensor tag and the reference tag, and collect the reflection signals of the sensor tag and the reference tag; the differential sensing subsystem is used to separate the reflection signal using a tag signal separation algorithm, and use a differential method to remove signal interference in the reflection signal, and perform signal differentiation on the reflection signal after eliminating interference to obtain the differential amplitude and phase of each of the sensor tag and the reference tag; the liquid pH detection subsystem is used to extract the features of the amplitude and phase from the differential amplitude and phase using a machine learning method, and determine the pH value of the liquid to be detected according to the mapping relationship between the liquid pH and the features of the amplitude and phase. The solution provided by the present invention has simple composition, low equipment cost, and is easy to deploy on a large scale. The system has low operation difficulty and high detection accuracy, and can realize low-cost, rapid and efficient liquid pH detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a low-cost liquid pH value detection system according to an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the system framework of a detection system according to an embodiment of the present invention;

[0023] Figure 3 Schematic diagram of RN16 amplitude collected when the system of the embodiment of the present invention communicates with dual tags; wherein, Figure 3 (a) Schematic diagram of RN16 with dual tags responding to back reflection simultaneously; Figure 3 (b) Schematic diagram of RN16 where the tag responds to back reflection alone;

[0024] Figure 4 This is a schematic diagram of PIE encoding according to an embodiment of the present invention;

[0025] Figure 5 A schematic diagram of conversion between OOK encoding and PIE encoding according to an embodiment of the present invention;

[0026] Figure 6 Schematic diagram of RN16 amplitude in an embodiment of the present invention; wherein, Figure 6 (a) is the amplitude diagram of RN16 when Q=0; Figure 6 (b) is the amplitude of RN16 when Q=1 Figure 1 Schematic diagram of Figure 6 (c) is the amplitude of RN16 when Q=1 Figure 2 Schematic diagram of Figure 6 (d) is the amplitude of RN16 when Q=1 Figure 3 Schematic diagram of

[0027] Figure 7 Schematic diagram of IQ of RN16 when Q=0 and Q=1 in an embodiment of the present invention; wherein, Figure 7 (a) IQ diagram of RN16 when Q=0; Figure 7 (b) IQ diagram of RN16 when Q=1; Figure 7 (c) IQ diagram of RN16 when Q=0 and Q=1;

[0028] Figure 8 Schematic diagram of differential amplitude and phase of tag reflection signal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0030] The embodiment of the present invention provides a low-cost liquid pH value detection system. Figure 1As shown, the low-cost liquid pH value detection system 100 includes a sensor tag 101, a reference tag 102 and a detection system 103; the sensor tag 101 is attached to the inner wall of the container and is in direct contact with the liquid to be detected; the reference tag 102 is attached to the outer wall of the container and is isolated from the liquid to be detected; the detection system 103 includes a signal transceiver subsystem 201, a differential sensor subsystem 202 and a liquid pH detection subsystem 203;

[0031] The signal transceiver subsystem 201 is used to send a continuous wave signal to activate the sensor tag 101 and the reference tag 102, and send a Query signal to establish communication with the sensor tag 101 and the reference tag 102, and collect reflection signals of the sensor tag 101 and the reference tag 102;

[0032] The differential sensing subsystem 202 is used to separate the reflected signal using a tag signal separation algorithm, remove signal interference in the reflected signal using a differential method, and perform signal differentiation on the reflected signal after eliminating interference to obtain the differential amplitude and phase of the sensor tag 101 and the reference tag 102 respectively;

[0033] The liquid pH detection subsystem 203 is used to extract amplitude and phase features from the differential amplitude and phase using a machine learning method, and determine the pH value of the liquid to be detected based on a mapping relationship between the liquid pH and the amplitude and phase features.

[0034] This embodiment uses low-cost equipment (i.e., detection system 103) and RFID tags (i.e., sensor tag 101, reference tag 102) to implement a liquid pH detection system. The system uses the detection system 103 to measure the reflection signals of the sensor tag 101 and the reference tag 102, and detects the liquid pH value based on the characteristics that the tag reflection signals are affected by the liquid pH. The system is less affected by temperature, can automatically complete the liquid pH detection, and output the detection results in real time.

[0035] The basic principle of the liquid pH detection in this embodiment is that the antenna impedance of the RFID tag is affected by the contact liquid material, and liquids with different pH values ​​will change the antenna impedance of the RFID tag, thereby changing the amplitude and phase of the tag reflection signal. That is, in this embodiment, one RFID tag is attached to the inner wall of the container in direct contact with the liquid (i.e., the sensing tag 101), and the other tag is attached to the outer wall of the container in isolation from the liquid (i.e., the reference tag 102). By analyzing the differential amplitude and phase of the dual-tag reflection signals, a mapping relationship between the liquid pH and the signal amplitude and phase is established to complete the pH detection.

[0036] Specifically, the present invention uses a low-cost RFID system to send radio frequency signals to activate the sensor tag and the reference tag, and collects the reflection signals of the dual tags. Then, the corresponding tag signal separation algorithm is used to separate the reflection signals of the dual tags. Then, the dual tag reflection signals are differentiated to remove signal interference and environmental noise interference, and a signal affected only by the liquid pH is obtained. Finally, a machine learning method is used to extract the characteristics of the signal amplitude and phase, and a mapping relationship between the liquid pH and the amplitude and phase of the tag reflection signal is established to achieve liquid pH detection.

[0037] Specifically, see Figure 2 , Figure 2 Schematic diagram of the system framework of the detection system 103. In this embodiment, the detection system 103 includes a signal transceiver subsystem 201, a differential sensing subsystem 202 and a liquid pH detection subsystem 203. Among them, the signal transceiver subsystem 201 includes an RFID signal receiver and an RFID signal transmitter. The differential sensing subsystem 202 includes a carrier frequency offset elimination module, a self-interference elimination module, a dual-tag simultaneous reflection interference elimination module and a signal difference module. The liquid pH detection subsystem 203 includes a feature extraction module and a feature classification module.

[0038] The RFID signal transmitter in the signal transceiver subsystem 201 in this embodiment specifically includes a development board, a radio frequency module and a first antenna. Here, the development board, specifically an Arduino Uno Rev3 development board, is used to send a control signal to the radio frequency module after programming. Here, the RadioHead library can be used to program the Arduino Uno Rev3 development board. The radio frequency module, specifically an RFM69HW radio frequency module, is used to send a continuous wave signal to the sensor tag and the reference tag and send a Query signal at a preset frequency when receiving the control signal. Here, the RFM69HW radio frequency module can specifically send a Query signal periodically at a frequency of 915MHz. The first antenna is used to specifically execute the sending of the continuous wave signal and the Query signal.

[0039] Correspondingly, the RFID signal receiver specifically includes a host computer, a software defined radio module and a second antenna. The second antenna is used to specifically receive the reflected signals of the sensor tag and the reference tag. The software defined radio module can be specifically an RTL-SDR dongle, which is used to receive and demodulate the reflected signal at a preset sampling rate, and output the complex signal obtained after demodulation to the host computer; here, the sampling frequency can be specifically 1M / s. The host computer is used to receive the complex signal, and send the complex signal to the differential sensing subsystem 202 after processing the complex signal.

[0040] This embodiment adopts a full-duplex RFID reader decoupling solution, decoupling the full-duplex RFID reader in the prior art into an RFID signal receiver and an RFID signal transmitter, that is, in terms of hardware, this embodiment only replaces the full-duplex RFID reader in the prior art with an RFID signal receiver and an RFID signal transmitter, thereby achieving the effect of reducing the system hardware cost. The full-duplex RFID reader is decoupled into an RFID signal transmitter and an RFID signal transmitter, and the decoupled system has a simple composition, reduced equipment cost, and improved versatility.

[0041] In addition to the above improvements in hardware, this embodiment also makes improvements in software programs, which are specifically reflected in the sending of Query signals and the processing of reflected signals. The above two aspects will be described in detail below.

[0042] Specifically, the Query signal in this embodiment is a complete Query frame based on the EPC Gen2 standard RFID protocol. The frame structure is shown in Table 1 below. In this embodiment, a parameter Q is set in the Query frame. The size of Q determines the number of tags that can be read at the same time, that is, When the sensor tag 101 and the reference tag 102 within the read / write range receive the Query frame, the tags will A random integer is generated within the range as the tag response slot number. The EPC Gen2 standard RFID protocol stipulates that when the tag generates a response slot number of 0, this tag will reflect a 16-bit random signal RN16, and other tags will not reflect any signal. That is, the setting of parameter Q determines the probability of a tag response within the read / write range. This embodiment can avoid the situation where the number of response slots of multiple tags is 0 at the same time by setting a reasonable Q value, and prevent multiple tags from responding at the same time and causing conflicts. In addition, the number of tag response slots can be continuously reduced until it reaches 0 through subsequent commands, so that multiple tags can be counted one by one.

[0043]

[0044] Based on the above-mentioned Query frame, the communication between commercial RFID readers and tags in the prior art consists of multiple handshake processes: ① The reader sends a continuous wave signal to activate the tag, and sends a Query frame to establish communication with the tag. ② After the tag receives the Query, it generates a response slot number. When the response slot number is 0, the tag back-reflects the RN16 signal. ③ After receiving RN16, the reader sends an ACK (Acknowledge) signal. ④ After receiving the ACK, the tag back-reflects its tag ID. Commercial RFID readers ultimately distinguish different tags by different IDs.

[0045] In order to save costs, this system simplifies the communication steps between the system and the tag in the software program, and only performs the above ①② process, and extracts the amplitude and phase of the tag reflection signal from RN16. However, this simplification will result in the system being unable to distinguish the reflection signals of different tags based on the tag ID when communicating with the tag. The RN16 signal collected when the system communicates with two tags is as follows: Figure 3 As shown in FIG. 1 , there are two situations: two tags simultaneously respond to the back-reflected RN16 and one tag responds to the back-reflected RN16. When two tags simultaneously back-reflect RN16, the signals are superimposed at the receiving end, as shown in FIG. Figure 3 (a) The RN16 signals in these two cases cannot be distinguished at this time.

[0046] To solve the above problems, the system uses a programmable low-cost RFID signal transmitter to alternately send Query signal frames of Q=0 and Q=1, and keep other fields in the frame consistent, and establish communication with the sensor tag 101 and the reference tag 102 (referred to as dual tags). When the system sends a Query signal of Q=0, the number of response slots generated by the dual tags is 0, that is, at this time, the dual tags simultaneously respond and back-reflect RN16 signals. When the system sends a Query signal of Q=1, the number of response slots generated by the tag is 0 or 1, so there will be four situations: dual tags respond and back-reflect RN16 at the same time, the reference tag responds and back-reflects RN16 alone, the sensor tag responds and back-reflects RN16 alone, and the dual tags do not respond or back-reflect RN16. Based on the above situation, the differential sensing subsystem 202 in this embodiment will successfully achieve dual tag signal separation during the processing process based on the RN16 back-reflected by the dual tags when receiving the Query signals of Q=0 and Q=1, without obtaining the tag ID. This part will be described in detail below when introducing the differential sensing subsystem 202.

[0047] The query signal is a complete query frame formulated for the EPC Gen2 standard RFID protocol. The EPC Gen2 standard RFID protocol uses the pulse interval encoding (PIE) scheme to encode the query frame. Figure 4 As shown, data 0 is represented by a high level with a short duration and a low level with a short duration, while data 1 is represented by a high level with a long duration and a low level with a short duration.

[0048] The decoupled RFID signal transmitter in this embodiment uses a low-cost RFM69HW RF module. The RFM69HW RF module only supports OOK (On-Off Keying, OOK) encoding (i.e., data 1 sends a high level, and data 0 sends a low level), and does not support the PIE encoding of the EPC Gen2 standard RFID protocol. Therefore, in order to be compatible with the EPC Gen2 standard RFID protocol, this embodiment needs to convert the OOK encoding and the PIE encoding.

[0049] Specifically, this embodiment makes the following improvements: data 1 in the Query frame is represented by three consecutive high levels and one low level 1110, and data 0 is represented by one high level plus one low level 10. Different bits of data represent the duration of different levels, so as to achieve conversion and compatibility between OOK encoding and PIE encoding. Figure 5 As shown, this embodiment converts OOK encoding and PIE encoding, converts the Query frame into QueryBits, and then converts the binary QueryBits into hexadecimal QueryBytes supported by RFM69HW. By programming the Arduino development board, the RF module is controlled to send QueryBytes to realize the sending of the Query signal.

[0050] From the above content, it can be known that the working process of the signal transceiver subsystem 201 is as follows: the RFID signal transmitter alternately sends the Query signal of Q=0 and Q=1, and sets the number of response slots of the dual tags to control the occurrence of the tag back-reflected RN16 signal. The RFID signal receiver collects the RN16 back-reflected by the dual tags when receiving the Query signal of Q=0 and Q=1, and inputs the RN16 signal into the differential sensing subsystem 202 to separate the dual tag signals.

[0051] Next, the process of how the differential sensing subsystem 202 realizes the dual-label signal separation will be described in detail.

[0052] See also Figure 2 The differential sensing subsystem 202 in this embodiment includes a carrier frequency offset elimination module, a self-interference elimination module, a dual-tag simultaneous reflection interference elimination module and a signal differentiation module.

[0053] A carrier frequency offset elimination module is used to eliminate the frequency offset in the reflected signal. A self-interference elimination module is used to eliminate the self-interference caused by the continuous wave signal in the reflected signal. A dual-tag simultaneous reflection interference elimination module is used to separate the reflected signal and extract the RN16 cluster reflected by each tag in the reflected signal. A signal difference module is used to perform K-means clustering on the RN16 cluster reflected by each tag to obtain the central complex vector of each RN16 cluster, calculate the amplitude and phase of the central complex vector respectively, differentiate the amplitude and phase, and take the absolute value to obtain the differential amplitude and phase of each tag.

[0054] Since the present application decouples the full-duplex RFID reader in the prior art into a transmitter and a receiver. The components that make up the transmitter and the receiver may be manufactured by different suppliers and equipped with different oscillators. Therefore, in practical applications, the clock frequencies of the transmitter and the receiver may not be strictly synchronized. The carrier frequency offset elimination module can eliminate the frequency offset (Carrier Frequency Offset, CFO) generated during the modulation and demodulation process because the clock frequencies of the RFID signal receiver and the RFID signal transmitter are not strictly synchronized.

[0055] Specifically, the complex signal collected by the signal transceiver subsystem 201 is the superposition of the carrier and the tag reflection signal, and the expression is as follows:

[0056]

[0057] After sorting:

[0058]

[0059] In the formula, It is the transmitted carrier signal that provides energy to the tag during the communication process. It is the tag reflection signal RN16. is the coded signal, when When , the tag reflects the carrier signal; when When , the tag does not reflect the carrier signal. is the carrier frequency offset, or CFO. Due to the existence of CFO, The phase changes over time.

[0060] The carrier frequency offset elimination module uses the continuous wave (CW) and The CFO consistent characteristics will Dividing by the CW complex signal eliminates The CFO of the signal, the specific principle is as follows:

[0061]

[0062] After processing, the signal with CFO eliminated is obtained .for The self-interference term affecting RN16 and unknown phase offset , which will be processed in the self-interference cancellation module.

[0063] That is, in one embodiment, the carrier frequency offset elimination module specifically eliminates the frequency offset in the reflected signal using the following calculation formula:

[0064]

[0065] in, To obtain the signal after frequency offset is eliminated, The signal collected by the signal receiving and sending subsystem, , It is the transmitted carrier signal that provides energy to the tag during the communication process. is the tag reflection signal RN16, is the coded signal, when When , the tag reflects the carrier signal; when When , the tag does not reflect the carrier signal. is the carrier frequency offset, is the self-interference term, the unknown phase offset .

[0066] In addition to the frequency offset caused by the RFID signal receiver and the RFID signal transmitter not being strictly synchronized in the modulation and demodulation process, the reflected signal also has self-interference. That is, the system needs to continuously send continuous waves to provide energy for the tag while receiving the tag back-reflection signal. This causes the continuous wave reflected in the environment and the tag back-reflection signal to be received by the system at the same time, forming self-interference at the receiving end, affecting the analysis of the tag back-reflection signal. Commercial RFID readers in the prior art integrate chips for self-interference elimination, which can achieve good self-interference suppression effects. However, the low-cost equipment used in the present invention is not specially designed for RFID communication and does not have corresponding hardware, so it is necessary to use software algorithms to eliminate self-interference.

[0067] Specifically, through observation, we can know that The self-interference term affecting RN16 is a constant term, which can be calculated by hour, The mean value of the signal is obtained, and the following processing can be performed:

[0068]

[0069] After processing, the self-interference term and unknown phase offset that affect RN16 can be effectively eliminated , get the tag reflection signal .

[0070] That is, in one embodiment, the self-interference elimination module specifically eliminates the self-interference caused by the continuous wave signal in the reflected signal using the following calculation formula:

[0071]

[0072] in, is the tag reflection signal, To obtain the signal after eliminating the frequency offset,

[0073] , is the self-interference term.

[0074] After eliminating the above interference, the dual-label signals in the reflected signal can be separated. The separation process is mainly performed by the dual-label simultaneous reflection interference elimination module and the signal difference module.

[0075] The dual-tag simultaneous reflection interference elimination module can successfully separate the dual-tag signals without obtaining the tag ID and extract the RN16 signal reflected by each tag separately.

[0076] As described above, this embodiment realizes the separation of dual-tag signals by alternately sending Query frames with Q=0 and Q=1. The RN16 reflected back by the dual-tag when the system sends Query frames with Q=0 and Q=1 is as follows: Figure 6 When the system sends a Query signal with Q=1, the system collects three RN16s with different amplitudes, see Figure 6 (b) Figure 6 (c) Figure 6 (d). When the system sends a Query signal with Q=0, the system only collects one type of RN16, see Figure 6 (a), and one of the RN16 when Q=1, see Figure 6 The amplitude of (b) is similar. This is because no matter whether the system sends a Query signal of Q=0 or Q=1, there is a situation where the number of response slots generated by both tags is 0 at the same time, and both tags back-reflect RN16 at the same time.

[0077] The process of separating the dual-label signals adopted in this embodiment is as follows: after performing carrier frequency offset and self-interference elimination on all RN16, the RN16 signal is obtained. After that, extract the part of the tag reflected carrier signal from the RN16 signal (i.e. In ) to draw an IQ graph, such as Figure 7 When the system sends a Query signal with Q=0, only one RN16 cluster appears on the IQ graph. Figure 7 (a); When the system sends a Query signal with Q=1, three RN16 clusters appear on the IQ graph, see Figure 7 (b).

[0078] The IQ diagram of the RN16 signal when Q=0 and Q=1 is as follows: Figure 7 As shown in (c), we can find that there are two almost overlapping RN16 clusters, that is, the dual tags simultaneously back-reflect RN16. Therefore, we calculate the distance between the RN16 clusters at Q=1 and Q=0, and exclude the RN16 cluster closest to the RN16 cluster at Q=0, that is, we can successfully extract the RN16 cluster reflected by each tag from the RN16 at Q=1.

[0079] That is, in one embodiment, the dual-tag simultaneous reflection interference elimination module is specifically used to obtain the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 0, and the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 1: from the RN16 cluster in the reflected signal when the Q parameter is 1, the RN16 cluster that overlaps with the RN16 cluster in the reflected signal when the Q parameter is 0 is eliminated to obtain the RN16 cluster reflected by each tag individually.

[0080] After obtaining the RN16 cluster reflected by each tag individually, the signal differential module performs K-means clustering on the RN16 cluster reflected by each tag individually, and obtains the central complex vectors of the two RN16 clusters. However, since this embodiment simplifies the communication steps between the system and the tag, it is impossible to distinguish the complex vectors of the reference tag and the sensor tag based on the tag ID. Therefore, this embodiment calculates the amplitude and phase of the two complex vectors, differentiates the calculation results of the amplitude and phase respectively, and takes the absolute value to extract the differential amplitude and phase of the dual-tag reflection signal, thereby realizing dual-tag differential sensing.

[0081] The sensor tag 101 and the reference tag 102 are in the same position and are affected by the same environmental factors. The sensor tag 101 is located on the inner wall of the container and is in direct contact with the liquid, and its reflection signal is affected by the pH of the liquid; the reference tag 102 is located on the outer wall of the container, isolated from the liquid, and its reflection signal is not affected by the pH of the liquid. Therefore, dual-tag differential sensing can remove environmental noise interference and extract a signal that is only affected by the pH of the liquid from the tag reflection signal for detecting the pH of the liquid.

[0082] After the differential amplitude and phase of the dual-tag reflection signals are extracted, since the reflection signal of the RFID tag is affected by the contacting liquid material, liquids with different pH values ​​will affect the amplitude and phase of the tag reflection signal to different degrees. Therefore, the liquid pH detection subsystem 203 in this embodiment will use a support vector machine (SVM) to extract the features of the differential amplitude and phase of the tag reflection signal, and then use the SVM machine learning model to classify the extracted features, establish a mapping relationship between the liquid pH and the amplitude and phase of the tag reflection signal, and realize liquid pH detection.

[0083] That is, in one embodiment, the liquid pH detection subsystem 203 includes a feature extraction module and a feature classification module;

[0084] The feature extraction module is used to extract the features of amplitude and phase from the differential amplitude and phase of each tag;

[0085] The feature classification module is used to determine the pH value corresponding to the feature according to the mapping relationship between the liquid pH and the amplitude and phase features.

[0086] The low-cost liquid pH detection system based on RFID proposed in this embodiment uses a low-cost radio frequency communication module, i.e., a signal transceiver subsystem 201, to transmit a signal compatible with a standard RFID communication protocol (such as the EPC Gen2 protocol), and extracts and analyzes the amplitude and phase of the RFID tag reflection signal to achieve real-time and accurate liquid pH detection. That is, the system collects the reflection signals of the two tags, and realizes the difference of the dual-tag signals without reading the tag ID, thereby eliminating the influence of factors such as distance and environmental noise on the signal, obtaining information only affected by the liquid pH, and realizing liquid pH detection.

[0087] The present invention will be described in detail below in conjunction with experimental scenarios.

[0088] In the experimental scenario, this embodiment uses six pH standard buffer solutions and tap water for experiments. The liquid to be tested is poured into a container with two RFID tags for pH detection. The RFID signal receiving antenna and the transmitting antenna are placed vertically to each other. There are no special requirements for the position of the container and the antenna. Keep other experimental scenarios unchanged and add six pH standard buffer solutions and tap water to the container respectively. The system sends a continuous wave signal to activate the two tags attached to the container, sends a Query signal to communicate with the dual tags, and then collects the reflected signals of the dual tags for differential processing.

[0089] The experimental results are as follows Figure 8As shown in the figure, liquids with different pH values ​​will affect the amplitude and phase of the tag reflection signal to varying degrees. Specifically, the differential amplitude and phase of the tag reflection signal will form a cluster related to the liquid pH, and the relationship between the liquid pH and the differential amplitude and phase is nonlinear. The system uses the pre-collected differential amplitude and phase of the tag reflection signal through the SVM machine learning model for training to obtain a mapping relationship model between the amplitude and phase and the liquid pH. Finally, the system uses the mapping relationship model to detect the liquid pH.

[0090] After experimental verification, the low-cost RFID-based liquid pH detection system proposed in this embodiment has been proven to be feasible. Experiments show that liquids of different pH will affect the amplitude and phase of the tag reflection signal to varying degrees. By establishing a mapping relationship between liquid pH and the amplitude and phase of the tag reflection signal, the function of detecting liquid pH can be realized. The entire system has low equipment cost and high detection sensitivity, and can realize real-time detection of liquid pH, which can meet the requirements of the expected design.

[0091] That is, based on the principle that the amplitude and phase of the RFID tag reflection signal are affected by the liquid pH, this embodiment designs a low-cost liquid pH detection system based on RFID. The system has the following advantages: (1) The system platform can realize liquid pH detection including colored solutions. (2) The system decouples the full-duplex RFID reader into a receiver and a transmitter, which is low-cost and easy to deploy, has high practical value and market prospects, and has a wide range of applications. (3) The system solves the problem that low-cost RFID systems can only read a single RFID tag, and realizes dual-tag differential sensing without obtaining the tag ID. The system has strong environmental robustness and has no strict requirements on the detection environment. (4) The system is simple to operate, can automatically complete processes such as liquid pH detection, has high detection efficiency, and is highly versatile.

[0092] The low-cost liquid pH value detection system provided by the embodiment of the present invention comprises a sensor tag 101, a reference tag 102 and a detection system 103; the sensor tag 101 is attached to the inner wall of the container and is in direct contact with the liquid to be detected; the reference tag 102 is attached to the outer wall of the container and is isolated from the liquid to be detected; the detection system 103 comprises a signal transceiver subsystem 201, a differential sensing subsystem 202 and a liquid pH detection subsystem 203; the signal transceiver subsystem 201 is used to send a continuous wave signal to activate the sensor tag 101 and the reference tag 102, and send a Query signal to the sensor tag 101 and the reference tag 102. 02 establishes communication and collects the reflection signals of the sensor tag 101 and the reference tag 102; the differential sensing subsystem 202 is used to separate the reflection signal using a tag signal separation algorithm, and remove the signal interference in the reflection signal using a differential method, and perform signal differentiation on the reflection signal after eliminating the interference to obtain the differential amplitude and phase of each of the sensor tag 101 and the reference tag 102; the liquid pH detection subsystem 203 is used to extract the characteristics of the amplitude and phase from the differential amplitude and phase using a machine learning method, and determine the pH value of the liquid to be detected based on the mapping relationship between the liquid pH and the characteristics of the amplitude and phase. The solution provided by the present invention is simple in composition, low in equipment cost, and easy to deploy on a large scale. In addition, the system has low operating difficulty and high detection accuracy, and can achieve low-cost, fast and efficient liquid pH detection.

[0093] In summary, this embodiment uses low-cost equipment to measure the RFID tag reflection signal, and based on the characteristics of the tag reflection signal being affected by the liquid pH, a system for detecting the liquid pH is provided. The system uses a full-duplex RFID reader decoupling solution to decouple the full-duplex RFID reader into a receiver and a transmitter, thereby reducing hardware costs.

[0094] The system in this embodiment has the following advantages:

[0095] (1) The system platform equipment is small in size, low in cost and universal; the hardware deployment and control are flexible, the equipment is highly sensitive and can be sensitive to changes in liquid pH.

[0096] (2) The entire system can separate the dual-tag reflection signals through algorithms without obtaining the tag ID, thus realizing dual-tag differential sensing. This solves the problem that low-cost RFID systems can only read a single RFID tag, saves calculation steps, and improves efficiency.

[0097] (3) The system adopts a differential sensing method without a tag ID and integrates the principle of coupling the detection liquid with a passive RFID tag to achieve real-time detection of liquid pH. The detection results are accurate, environmentally robust, and have no special requirements for physical conditions such as the radio frequency environment.

[0098] (4) The system describes the liquid pH using the amplitude and phase of the tag reflection signal, and uses machine learning methods to analyze the amplitude and phase of the RFID tag reflection signal. The constructed system can establish a mapping relationship between the liquid pH and the amplitude and phase of the tag reflection signal.

[0099] (5) This system has efficient detection capabilities and can perform real-time pH detection on liquids. The system automatically completes the processes of sending, collecting and processing radio frequency signals and is easy to operate.

[0100] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0101] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A low-cost liquid pH detection system, characterized in that: The low-cost liquid pH value detection system includes a sensor tag, a reference tag and a detection system; the sensor tag is attached to the inner wall of the container and is in direct contact with the liquid to be detected; the reference tag is attached to the outer wall of the container and is isolated from the liquid to be detected; the detection system includes a signal transceiver subsystem, a differential sensor subsystem and a liquid pH detection subsystem; The signal transceiver subsystem is used to send a continuous wave signal to activate the sensor tag and the reference tag, and send a Query signal to establish communication with the sensor tag and the reference tag, and collect reflection signals of the sensor tag and the reference tag; The differential sensing subsystem is used to separate the reflected signal using a tag signal separation algorithm, remove signal interference in the reflected signal using a differential method, and perform signal differentiation on the reflected signal after eliminating interference to obtain the differential amplitude and phase of each of the sensor tag and the reference tag; The liquid pH detection subsystem is used to extract amplitude and phase features from the differential amplitude and phase using a machine learning method, and determine the pH value of the liquid to be detected based on a mapping relationship between the liquid pH and the amplitude and phase features.

2. The low-cost liquid pH detection system according to claim 1, characterized in that: The signal transceiver subsystem includes an RFID signal receiver and an RFID signal transmitter; the RFID signal transmitter includes a development board, a radio frequency module and a first antenna; the RFID signal receiver includes a host computer, a software defined radio module and a second antenna; The development board is used to send a control signal to the radio frequency module after programming; The radio frequency module is used to send a continuous wave signal and a query signal at a preset frequency to the sensor tag and the reference tag when receiving the control signal; The first antenna is used to send the continuous wave signal and the Query signal; The second antenna is used to receive reflected signals from the sensor tag and the reference tag; The software defined radio module is used to receive and demodulate the reflected signal at a preset sampling rate, and output the complex signal obtained after demodulation to the host computer; The host computer is used to receive the complex signal, process the complex signal and send it to the differential sensing subsystem.

3. The low-cost liquid pH detection system according to claim 2, characterized in that: The radio frequency module is specifically used to alternately send a Query signal with a Q parameter of 0 or a Q parameter of 1 in the Query signal to the sensor tag and the reference tag; The sensor tag and the reference tag are specifically used to, after receiving the Query signal, back-reflect the RN16 signal according to the corresponding number of response slots according to the value of the Q parameter in the Query signal, when the generated number of response slots is 0; and not reflect the signal when the generated number of response slots is not 0.

4. The low-cost liquid pH detection system according to claim 3, characterized in that: The sensor tag and the reference tag are specifically used to generate a response slot number of 0 when the Q parameter in the Query signal is 0; and to generate a response slot number of either 0 or 1 when the Q parameter in the Query signal is 1.

5. The low-cost liquid pH detection system according to claim 3, characterized in that: The radio frequency module is specifically used to convert the PIE-encoded Query signal into an OOK-encoded QueryBytes signal for transmission based on the established conversion mechanism between OOK encoding and PIE encoding; the conversion mechanism is to convert the data 1 in the PIE encoding into 1110 in the OOK encoding, and to convert the data 0 in the PIE encoding into 10 in the OOK encoding.

6. The low-cost liquid pH detection system according to claim 1, characterized in that: The differential sensing subsystem includes a carrier frequency offset elimination module, a self-interference elimination module, a dual-tag simultaneous reflection interference elimination module and a signal difference module; The carrier frequency offset elimination module is used to eliminate the frequency offset in the reflected signal; The self-interference elimination module is used to eliminate the self-interference caused by the continuous wave signal in the reflected signal; The dual-tag simultaneous reflection interference elimination module is used to separate the reflection signal and extract the RN16 cluster reflected by each tag in the reflection signal; The signal differential module is used to perform K-means clustering on the RN16 clusters reflected by each tag individually, obtain the central complex vectors of each RN16 cluster, calculate the amplitude and phase of the central complex vector respectively, differentiate the amplitude and phase, and take the absolute value to obtain the differential amplitude and phase of each tag.

7. The low-cost liquid pH detection system according to claim 6, characterized in that: The carrier frequency offset elimination module specifically eliminates the frequency offset in the reflected signal using the following calculation formula: in, To obtain the signal after eliminating the frequency offset, The signal collected by the signal receiving and sending subsystem, is a continuous wave signal, , It is the carrier signal sent, which provides energy for the tag during the communication process. is the tag reflection signal RN16, is the coded signal, when When , the tag reflects the carrier signal; when When , the tag does not reflect the carrier signal; is the carrier frequency offset, is the self-interference term, is the phase of the continuous wave signal, is the unknown phase deviation, is an imaginary unit, For time, To eliminate the tag reflected signal after frequency offset and self-interference, is the phase of the carrier signal reflected by the tag.

8. The low-cost liquid pH detection system according to claim 7, characterized in that: The self-interference elimination module specifically eliminates the self-interference caused by the continuous wave signal in the reflected signal by using the following calculation formula: in, is the tag reflection signal, To obtain the signal after eliminating the frequency offset, , is the self-interference term, is the phase of the continuous wave signal, is the unknown phase offset, j is the imaginary unit, and t is the time; To eliminate the tag reflected signal after frequency offset and self-interference, is the coded signal, when When , the tag reflects the carrier signal; when When the tag does not reflect the carrier signal, is the phase of the carrier signal reflected by the tag.

9. The low-cost liquid pH detection system according to claim 6, characterized in that: The dual-tag simultaneous reflection interference elimination module is specifically used to obtain the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 0, and the RN16 cluster in the reflected signal when the Q parameter in the Query signal is 1: from the RN16 cluster in the reflected signal when the Q parameter is 1, the RN16 cluster that overlaps with the RN16 cluster in the reflected signal when the Q parameter is 0 is removed to obtain the RN16 cluster reflected by each tag individually.

10. The low-cost liquid pH detection system according to claim 1, characterized in that: The liquid pH detection subsystem includes a feature extraction module and a feature classification module; The feature extraction module is used to extract the features of amplitude and phase from the differential amplitude and phase of each tag; The feature classification module is used to determine the pH value corresponding to the feature according to the mapping relationship between the liquid pH and the amplitude and phase features.

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