CN112114034B - Surface acoustic wave device with radio frequency identification and wireless sensing integrated function and method - Google Patents
Surface acoustic wave device with radio frequency identification and wireless sensing integrated function and method Download PDFInfo
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- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/02—Analysing fluids
- G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
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- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
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- G06K17/00—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
- G06K17/0022—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device
- G06K17/0029—Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations arrangements or provisious for transferring data to distant stations, e.g. from a sensing device the arrangement being specially adapted for wireless interrogation of grouped or bundled articles tagged with wireless record carriers
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- G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
- G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
- G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
- G06K19/0716—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising a sensor or an interface to a sensor
- G06K19/0717—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising a sensor or an interface to a sensor the sensor being capable of sensing environmental conditions such as temperature history or pressure
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Abstract
The invention discloses a surface acoustic wave device with radio frequency identification and wireless sensing integrated functions and a working method thereof. In a plurality of reflecting gratings of the surface acoustic wave device, a reference reflecting grating is used for eliminating the influence of distance on a phase measurement result, and a temperature compensation reflecting grating is used for compensating the influence of temperature on the phase measurement result. The invention is characterized in that the information tracing and quality detection in the food safety field can be realized simultaneously only by one passive device, and the functions are easy to realize and the cost performance is high.
Description
The technical field is as follows:
the invention relates to a surface acoustic wave device with a radio frequency identification and wireless sensing integrated function and a working method thereof, belonging to the field of radio frequency identification and wireless sensing.
Background art:
information traceability and quality detection are two indispensable aspects of food safety. The core of tracing the food information source is to emphasize the unique code of the food, convert a series of information of the food from a production base to a dining table into specific data and store the data in a central database on the basis of the unique code, and can call, check, summarize and analyze all data of the food from a farm to the dining table in real time through the unique code to realize the tracing function. However, it is impossible to solve the food safety problem only by tracing and tracing after the occurrence of an accident, and more importantly, in combination with the sensor technology, the quality detection of food is used to avoid the accident and guarantee the food safety in advance, such as:
(1) the temperature detection can be carried out on refrigerated and frozen foods or foods with specific requirements on temperature in the processes of transportation, circulation and storage, the quality of the foods can be known in time by detecting the temperature of each link, whether the foods are kept fresh or not is determined, and corresponding measures are taken.
(2) The food such as meat products and the like which are easy to oxidize and deteriorate and grow microorganisms is often packaged by adopting a modified atmosphere packaging technology, namely, a certain proportion of mixed gas comprising carbon dioxide, oxygen and nitrogen is filled into the package according to actual requirements so as to play the roles of keeping freshness, keeping color and taste and inhibiting bacterial reproduction. The quality of the food can be ensured by detecting the corresponding gas in the modified atmosphere package.
The following problems in the field of food safety in information tracing and quality detection currently exist and need to be solved:
(1) the existing food information tracing mainly adopts a bar code technology, and has the problems of short identification distance, low identification efficiency, poor environmental adaptability and the like.
(2) The existing food quality detection mainly adopts a sampling inspection mode, can not realize all-round real-time detection on all foods, and some methods belong to destructive detection, such as a headspace gas analyzer for detecting the gas concentration in gas-conditioned packaged foods.
(3) In recent years, the information tracing and quality detection of food can be simultaneously realized through an advanced intelligent Packaging (Smart Packaging) technology, but currently, two technologies of radio frequency identification and wireless sensing are adopted in a mode of being independent and respectively performing own functions, so that the difficulty of system integration is high, and the cost is high.
The invention content is as follows:
the invention provides a surface acoustic wave device with radio frequency identification and wireless sensing integrated functions and a working method thereof, aiming at the problems of information traceability and quality detection in the field of food safety at present.
The invention adopts the following technical scheme: a surface acoustic wave device with radio frequency identification and wireless sensing integrated functions is characterized in that: the surface acoustic wave device adopts a double-frequency four-channel single-ended delay line type structure and comprises a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a first reference reflection grating, a second reference reflection grating, a third reference reflection grating, a first temperature compensation reflection grating, a second temperature compensation reflection grating, a third temperature compensation reflection grating, a fourth temperature compensation reflection grating, a first coding reflection grating, a second coding reflection grating, a third coding reflection grating, a fourth coding reflection grating, a fifth coding reflection grating, a sixth coding reflection grating, a seventh coding reflection grating, a first gas sensing reflection grating, a second gas sensing reflection grating, a first gas sensitive film, a second gas sensitive film and an antenna;
the first interdigital transducer is deposited on the upper left half part of the piezoelectric substrate, and the second interdigital transducer is deposited on the lower left half part of the piezoelectric substrate;
the first interdigital transducer and the second interdigital transducer have the same aperture and are smaller than half of the width of the piezoelectric substrate, and the first interdigital transducer and the second interdigital transducer are connected with an antenna in a parallel connection mode;
the antenna is a dual-frequency antenna and covers two frequency bands of 840-845 MHz and 920-925 MHz;
the first reference reflecting grating, the second temperature compensation reflecting grating, the second coding reflecting grating, the fourth coding reflecting grating and the sixth coding reflecting grating are deposited on the upper part of the piezoelectric substrate, the aperture is equal to and less than half of the aperture of the first interdigital transducer, and the first reference reflecting grating, the second temperature compensation reflecting grating, the second coding reflecting grating, the fourth coding reflecting grating and the sixth coding reflecting grating form a first propagation channel of the surface acoustic wave together with the upper half part of the first interdigital transducer;
the first temperature compensation reflecting grating, the first coding reflecting grating, the third coding reflecting grating, the fifth coding reflecting grating and the seventh coding reflecting grating are deposited at the upper position in the middle of the piezoelectric substrate, the aperture is equal to and less than half of the aperture of the first interdigital transducer, and the first temperature compensation reflecting grating, the first coding reflecting grating, the third coding reflecting grating, the fifth coding reflecting grating and the seventh coding reflecting grating form a second propagation channel of the surface acoustic wave together with the lower half of the first interdigital transducer;
the second reference reflection grating, the third temperature compensation reflection grating and the first gas sensing reflection grating are deposited at the middle lower position of the piezoelectric substrate, the apertures are equal and less than half of the aperture of the second interdigital transducer, and the second reference reflection grating, the third temperature compensation reflection grating and the first gas sensing reflection grating and the upper half of the second interdigital transducer form a third propagation channel of the surface acoustic wave;
the first gas sensitive film is coated between a third temperature compensation reflecting grating of a third propagation channel of the surface acoustic wave and the first gas sensing reflecting grating;
the third reference reflecting grating, the fourth temperature compensation reflecting grating and the second gas sensing reflecting grating are deposited on the lower portion of the piezoelectric substrate, the aperture is equal to and smaller than one half of the aperture of the second interdigital transducer, and the third reference reflecting grating, the fourth temperature compensation reflecting grating and the second gas sensing reflecting grating and the lower half portion of the second interdigital transducer form a fourth propagation channel of the surface acoustic wave;
the second gas sensitive film is coated between a fourth temperature compensation reflecting grating and a second gas sensing reflecting grating of a fourth propagation channel of the surface acoustic wave;
by designing the width of a finger strip of a first interdigital transducer and the widths of a first reference reflection grating, a first temperature compensation reflection grating, a second temperature compensation reflection grating, a first coding reflection grating, a second coding reflection grating, a third coding reflection grating, a fourth coding reflection grating, a fifth coding reflection grating, a sixth coding reflection grating and a seventh coding reflection grating, the central frequency f of a first propagation channel and the central frequency f of a second propagation channel of the surface acoustic wave are enabled to be equal1922.5 MHz; by designing the width of the finger strip of the second interdigital transducer and the widths of the second reference reflection grating, the third temperature compensation reflection grating, the fourth temperature compensation reflection grating, the first gas sensing reflection grating and the second gas sensing reflection grating, the central frequency f of the third propagation channel and the central frequency f of the fourth propagation channel of the surface acoustic wave are enabled to be equal2Is 842.5 MHz.
Furthermore, the first coding reflection grating, the second coding reflection grating, the third coding reflection grating, the fourth coding reflection grating, the fifth coding reflection grating, the sixth coding reflection grating and the seventh coding reflection grating are respectively positioned in seven coding data areas; n time slots are divided in each coding data area at equal intervals, and a coding reflection grating is positioned in one time slot; the n phase gaps are further divided in each time slot at equal intervals for 360 degrees of phase, and the coding reflection grating is positioned in one of the phase gaps.
Further, the distances between the first reference reflection grating, the first temperature compensation reflection grating, the second temperature compensation reflection grating, the first encoding reflection grating, the second encoding reflection grating, the third encoding reflection grating, the fourth encoding reflection grating, the fifth encoding reflection grating, the sixth encoding reflection grating, the seventh encoding reflection grating and the first interdigital transducer are different, so that the echo signals corresponding to all the reflection gratings of the first propagation channel and the second propagation channel are ensured not to interfere with each other in time.
Further, the distances between the second reference reflection grating, the third temperature compensation reflection grating, the fourth temperature compensation reflection grating, the first gas sensing reflection grating, the second gas sensing reflection grating and the second interdigital transducer are different, so that the echo signals corresponding to all the reflection gratings of the third propagation channel and the fourth propagation channel are ensured not to interfere with each other in time.
Further, in the field of food safety, aiming at the modified atmosphere packaged food which is filled with mixed gas comprising carbon dioxide, oxygen and nitrogen conventionally, the first gas sensitive film adopts a polyetherimide film which has selectivity and reversibility on the adsorption of the carbon dioxide, and the second gas sensitive film adopts a titanium dioxide film which has selectivity and reversibility on the adsorption of the oxygen;
the positions of the first gas sensitive film and the second gas sensitive film of the surface acoustic wave device are not packaged so as to sense the gas in the modified atmosphere package; and the other positions of the surface acoustic wave device are packaged to protect the interdigital transducer and the reflecting grating.
The invention also adopts the following technical scheme: a working method of a surface acoustic wave device with radio frequency identification and wireless sensing integrated functions is used for radio frequency identification and wireless temperature sensing of cold chain food such as cold storage and freezing or food with clear requirements on temperature in the field of food safety, and comprises the following steps:
step A: aiming at a fixed reader, food is moved to a reader action area; aiming at the handheld reader, the reader moves to the position near the food to ensure that the food is positioned in the action area of the reader;
and B: reader transmitting carrier frequency f1The excitation pulse signal is radiated outwards in the form of electromagnetic waves through the reader antenna;
and C: the surface acoustic wave device receives an excitation pulse signal through an antenna, a first propagation channel and a second propagation channel, the center frequency of which is consistent with the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal, and a first interdigital transducer converts the excitation pulse signal into surface acoustic waves through an inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the first propagation channel and the second propagation channel respectively;
step D: the surface acoustic wave propagating along the first propagation channel sequentially encounters a first reference reflection grating, a second temperature compensation reflection grating, a second coding reflection grating, a fourth coding reflection grating and a sixth coding reflection grating to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the first interdigital transducer; similarly, the surface acoustic wave propagating along the second propagation channel sequentially encounters the first temperature compensation reflection grating, the first coding reflection grating, the third coding reflection grating, the fifth coding reflection grating and the seventh coding reflection grating to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the first interdigital transducer; the first interdigital transducer converts the reflection signal into a first echo pulse train comprising 10 echo pulse signals through a positive piezoelectric effect, wherein the time sequence of the 10 echo pulse signals has a one-to-one correspondence relation with the 10 reflection grating positions; the first echo pulse train is transmitted back to the reader antenna through the antenna;
step E: the reader carries out signal processing on the first echo pulse train and directly solves time slot codes through orthogonal demodulation; constructing reference time delay through the temperature compensation reflecting grating, enabling the corresponding phase change of the reference time delay within the temperature change range not to exceed one period, and further constructing and reducing the reference time delay through a method of time delay difference solving of echo pulse signals corresponding to the first temperature compensation reflecting grating and the second temperature compensation reflecting grating; the initial phases of 7 coding reflecting gratings at the reference temperature are reversely deduced according to the phase change of the reference time delay and the position relation among 10 reflecting gratings, so that the phase gap code is solved, and the radio frequency identification function is realized;
step F: under the premise of realizing the radio frequency identification function, according to the known relation of the distance between 10 reflecting gratings in the reference temperature, the phase change caused by the reference time delay along with the temperature is gradually deduced to the phase change between two reflecting gratings with the farthest distance in the 10 reflecting gratings, namely the first reference reflecting grating and the seventh coding reflecting grating, through a mode of forward progression from near to far and in proportion, and the temperature is detected according to the relation between the temperature change and the phase change, so that the integrated function of the radio frequency identification and the wireless temperature sensing is completed.
The invention adopts the following technical scheme: a working method of a surface acoustic wave device with radio frequency identification and wireless sensing integrated functions is used for radio frequency identification, wireless temperature sensing and gas sensing of modified atmosphere packaged food in the field of food safety, and comprises the following steps:
step a: the same as the steps A, B, C, D, E and F in the claim 6, the radio frequency identification and wireless temperature sensing functions are realized;
step b: reader transmitting carrier frequency f2The excitation pulse signal is radiated outwards in the form of electromagnetic waves through the reader antenna;
step c: the surface acoustic wave device receives an excitation pulse signal through an antenna, a third propagation channel and a fourth propagation channel, the center frequency of which is consistent with the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal, and the second interdigital transducer converts the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the third propagation channel and the fourth propagation channel respectively;
step d: the surface acoustic wave transmitted along the third transmission channel sequentially encounters the second reference reflection grating, the third temperature compensation reflection grating and the first gas sensing reflection grating to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the second interdigital transducer; similarly, the surface acoustic wave propagating along the fourth propagation channel sequentially encounters the third reference reflection grating, the fourth temperature compensation reflection grating and the second gas sensing reflection grating to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the second interdigital transducer; the second interdigital transducer converts the reflected signal into a second echo pulse train comprising 6 echo pulse signals through a direct piezoelectric effect, wherein the 6 echo pulse signal time sequences have one-to-one correspondence with the 6 reflection grating positions; the second echo pulse train is transmitted back to the reader antenna through the antenna;
step e: the reader carries out signal processing on 3 echo pulse signals corresponding to the second reference reflection grid, the third temperature compensation reflection grid and the first gas sensing reflection grid in the second echo pulse train, when the concentration of carbon dioxide in the modified atmosphere package changes, the amount of carbon dioxide adsorbed by the first gas sensitive film, namely the polyetherimide film, changes, and further the phase difference of the echo pulse signals corresponding to the third temperature compensation reflection grid and the first gas sensing reflection grid changes; constructing a reference time delay by the time delay difference of the echo pulse signals corresponding to the second reference reflecting grating and the third temperature compensation reflecting grating, and pushing the reference time delay to the position between the third temperature compensation reflecting grating and the echo pulse signal corresponding to the first gas sensing reflecting grating along with the phase change caused by the temperature, so as to compensate the phase difference caused by the temperature change and measure the concentration of the carbon dioxide in the modified atmosphere package;
step f: e, the reader processes 3 echo pulse signals corresponding to the third reference reflection grating, the fourth temperature compensation reflection grating and the second gas sensing reflection grating in the second echo pulse train, and the concentration of oxygen in the modified atmosphere package is measured by adopting the method the same as that in the step e;
step g: because the sum of the concentrations of the carbon dioxide, the oxygen and the nitrogen in the modified atmosphere package is 100%, the concentration of the nitrogen in the modified atmosphere package can be obtained after the concentration of the carbon dioxide is measured in the step e and the concentration of the oxygen is measured in the step f, and the integrated functions of radio frequency identification, wireless temperature sensing and gas sensing are completed.
The invention has the following beneficial effects:
1. compared with the bar code technology, the surface acoustic wave radio frequency identification technology has the advantages of long identification distance, high identification efficiency, strong environmental adaptability and the like.
2. The surface acoustic wave device has small volume, pure passivity and low price, and is convenient to integrate with food packaging, thereby realizing the omnibearing real-time detection of all foods. When the method is used for detecting the concentration of gas in the modified atmosphere packaged food, the modified atmosphere packaging does not need to be damaged.
3. The surface acoustic wave device has the integrated functions of radio frequency identification, wireless temperature sensing and gas sensing, can simultaneously realize information tracing and quality detection of food only through a passive device, and has the advantages of easy realization of the functions and high cost performance.
4. The surface acoustic wave device adopts a mode of combining time slot coding and phase slot coding, so that the coding capacity of radio frequency identification can be greatly improved, and the large-scale application is facilitated; the single-frequency double-channel integrated function of radio frequency identification and temperature sensing is realized, compared with the single-channel, the reflectivity of the reflecting grating can be designed to be higher, and the distance between the radio frequency identification and the temperature sensing can be longer; the two temperature compensation reflecting gratings are adopted to realize the integrated function of radio frequency identification and temperature sensing, and compared with the single temperature compensation reflecting grating, the temperature measurement range during temperature sensing can be greatly enlarged.
Description of the drawings:
fig. 1 is a schematic view of the structure of a surface acoustic wave device of the present invention.
FIG. 2 is a schematic diagram of the RFID encoding method of the SAW device of the present invention.
Fig. 3 is a schematic diagram of echo signals (first echo pulse train) corresponding to all reflection gratings of the first propagation channel and the second propagation channel of the saw device according to the present invention.
Fig. 4 is a simplified single frequency, dual channel, single ended delay line configuration of a saw device according to the present invention.
Fig. 5 is a schematic diagram of echo signals (second echo pulse train) corresponding to all the reflection gratings of the third propagation channel and the fourth propagation channel of the surface acoustic wave device according to the present invention.
Reference designations in the above figures: 1. the piezoelectric substrate, 2, a first interdigital transducer, 3, a second interdigital transducer, 4, a first reference reflection grating, 5, a second reference reflection grating, 6, a third reference reflection grating, 7, a first temperature compensation reflection grating, 8, a second temperature compensation reflection grating, 9, a third temperature compensation reflection grating, 10, a fourth temperature compensation reflection grating, 11, a first coding reflection grating, 12, a second coding reflection grating, 13, a third coding reflection grating, 14, a fourth coding reflection grating, 15, a fifth coding reflection grating, 16, a sixth coding reflection grating, 17, a seventh coding reflection grating, 18, a first gas sensing reflection grating, 19, a second gas sensing reflection grating, 20, a first gas sensitive film, 21, a second gas sensitive film and 22, an antenna.
The specific implementation mode is as follows:
the invention will be further described with reference to the accompanying drawings.
Referring to fig. 1, the surface acoustic wave device with integrated functions of radio frequency identification and wireless sensing of the present invention adopts a dual-frequency four-channel single-ended delay line type structure, which includes a piezoelectric substrate 1, a first interdigital transducer 2, a second interdigital transducer 3, a first reference reflection grating 4, a second reference reflection grating 5, a third reference reflection grating 6, a first temperature compensation reflection grating 7, a second temperature compensation reflection grating 8, a third temperature compensation reflection grating 9, a fourth temperature compensation reflection grating 10, a first encoding reflection grating 11, a second encoding reflection grating 12, a third encoding reflection grating 13, a fourth encoding reflection grating 14, a fifth encoding reflection grating 15, a sixth encoding reflection grating 16, a seventh encoding reflection grating 17, a first gas sensing reflection grating 18, a second gas sensing reflection grating 19, a first gas sensitive film 20, a second gas sensitive film 21, and an antenna 22.
The first interdigital transducer 2 is deposited on the upper left half of the piezoelectric substrate 1, and the second interdigital transducer 3 is deposited on the lower left half of the piezoelectric substrate 1; the first interdigital transducer 2 and the second interdigital transducer 3 have the same aperture and are smaller than half of the width of the piezoelectric substrate 1, and the first interdigital transducer and the second interdigital transducer are connected with an antenna 22 in a parallel connection mode; the antenna 22 is a dual-band antenna covering two frequency bands of 840-845 MHz and 920-925 MHz.
The first reference reflection grating 4, the second temperature compensation reflection grating 8, the second coding reflection grating 12, the fourth coding reflection grating 14 and the sixth coding reflection grating 16 are deposited on the upper part of the piezoelectric substrate 1, the aperture is equal to and less than half of the aperture of the first interdigital transducer 2, and the first reference reflection grating, the second temperature compensation reflection grating, the second coding reflection grating, the fourth coding reflection grating and the sixth coding reflection grating form a first propagation channel of the surface acoustic wave together with the upper half part of the first interdigital transducer 2; the first temperature compensation reflecting grating 7, the first coding reflecting grating 11, the third coding reflecting grating 13, the fifth coding reflecting grating 15 and the seventh coding reflecting grating 17 are deposited at the upper position in the middle of the piezoelectric substrate 1, the apertures are equal and less than half of the aperture of the first interdigital transducer 2, and the first temperature compensation reflecting grating, the first coding reflecting grating, the third coding reflecting grating, the fifth coding reflecting grating and the seventh coding reflecting grating form a second propagation channel of the surface acoustic wave together with the lower half of the first interdigital transducer 2; the second reference reflecting grating 5, the third temperature compensation reflecting grating 9 and the first gas sensing reflecting grating 18 are deposited at the middle lower position of the piezoelectric substrate 1, the apertures are equal and less than half of the aperture of the second interdigital transducer 3, and form a third propagation channel of the surface acoustic wave together with the upper half part of the second interdigital transducer 3; the third reference reflecting grating 6, the fourth temperature compensation reflecting grating 10 and the second gas sensing reflecting grating 19 are deposited on the lower portion of the piezoelectric substrate 1, the aperture is equal to and smaller than half of the aperture of the second interdigital transducer 3, and the third reference reflecting grating, the fourth temperature compensation reflecting grating and the second gas sensing reflecting grating form a fourth propagation channel of the surface acoustic wave together with the lower half portion of the second interdigital transducer 3.
The first gas sensitive film 20 is coated between the third temperature compensation reflecting grating 9 and the first gas sensing reflecting grating 18 of the third propagation channel of the surface acoustic wave; the second gas sensitive film 21 is coated between the fourth temperature compensation grating 10 and the second gas sensing grating 19 of the fourth propagation channel of the surface acoustic wave.
According to the center frequency f being v/lambda, wherein v is the propagation speed of surface acoustic wave and depends on the tangent type of the piezoelectric substrate, lambda is the wavelength of the surface acoustic wave, the lambda has a corresponding relation with the width of the finger strip of the interdigital transducer and the width of the grating strip of the reflecting grating, and the 800/900MHz frequency band is divided into two independent frequency bands of 840-845 MHz and 920-925 MHz according to the national standard, through designing the width of the finger strip of the first interdigital transducer 2, the first reference reflecting grating 4, the first temperature compensation reflecting grating 7, the second temperature compensation reflecting grating 8, the first coding reflecting grating 11, the second coding reflecting grating 12, the third coding reflecting grating 13 and the fourth coding reflecting grating 11The widths of the grating strips of the grating 14, the fifth encoding reflection grating 15, the sixth encoding reflection grating 16 and the seventh encoding reflection grating 17 enable the center frequency f of the first propagation channel and the second propagation channel of the surface acoustic wave to be equal1922.5 MHz; by designing the width of the finger strip of the second interdigital transducer 3 and the widths of the second reference reflection grating 5, the third reference reflection grating 6, the third temperature compensation reflection grating 9, the fourth temperature compensation reflection grating 10, the first gas sensing reflection grating 18 and the second gas sensing reflection grating 19, the central frequency f of the third propagation channel and the fourth propagation channel of the surface acoustic wave is enabled to be2Is 842.5 MHz.
Referring to fig. 2, a first encoding reflection grating 11, a second encoding reflection grating 12, a third encoding reflection grating 13, a fourth encoding reflection grating 14, a fifth encoding reflection grating 15, a sixth encoding reflection grating 16 and a seventh encoding reflection grating 17 of the saw device are respectively located in seven encoding data areas; each coding data area is divided into N time slots at equal intervals, and the coding reflection grating is positioned in one time slot, such as the 1 st time slot of the second coding data area of the second coding reflection grating 12 shown in FIG. 2; the n slots are further divided in each slot with equal spacing for 360 ° phase, and the encoding reflection grating is located in one of the slots, such as the 2 nd slot of the second encoding reflection grating 12 shown in fig. 2, which is further located in the 1 st slot of the second encoding data area; when the time slot N is 4, the coding capacity of the surface acoustic wave device adopting time slot coding is only N716384; if the phase measurement precision of the reader is within +/-20 degrees, the phase gap N can be designed to be 9, and the coding capacity of the surface acoustic wave device adopting a mode of combining time slot coding and phase gap coding is (N multiplied by N)778364164096, the insufficiency of time resolution can be compensated by the high resolution of phase measurement, and the coding capacity of the radio frequency identification is greatly improved for scale application.
Referring to fig. 1 and fig. 3, a first propagation channel and a second propagation channel of a surface acoustic wave realize an integrated function of radio frequency identification and wireless temperature sensing; the distances between the first reference reflection grating 4, the first temperature compensation reflection grating 7, the second temperature compensation reflection grating 8, the first coding reflection grating 11, the second coding reflection grating 12, the third coding reflection grating 13, the fourth coding reflection grating 14, the fifth coding reflection grating 15, the sixth coding reflection grating 16 and the seventh coding reflection grating 17 and the first interdigital transducer 2 are different, so that echo signals corresponding to all reflection gratings of the first propagation channel and the second propagation channel are ensured not to interfere with each other in time; the influence of the distance on radio frequency identification and temperature sensing is eliminated through the first reference reflecting grating 4; the influence of temperature change on phase measurement during radio frequency identification is compensated through the first temperature compensation reflecting grating 7 and the second temperature compensation reflecting grating 8, and compared with the single temperature compensation reflecting grating, the temperature measurement range during temperature sensing can be greatly enlarged; the two channels are adopted to realize the integrated function of radio frequency identification and temperature sensing, compared with the single channel, the reflectivity of the reflecting grating can be designed to be higher, and the distance between the radio frequency identification and the temperature sensing can be farther.
Referring to fig. 4, in the field of food safety, aiming at cold chain foods such as refrigeration, freezing and the like or foods with specific requirements on temperature but no requirements on gas sensing, the structure of a surface acoustic wave device can be simplified, only a first propagation channel and a second propagation channel of the surface acoustic wave are reserved to form a single-frequency dual-channel single-ended delay line type structure, and the surface acoustic wave device is attached to a food package and has the characteristic of integrating radio frequency identification and wireless temperature sensing functions; the interdigital transducer and the reflecting grating are protected in a mode of integrally packaging a single-frequency double-channel single-end delay line type surface acoustic wave device, and the packaging material has high heat conduction characteristic so as to transfer food temperature.
Referring to fig. 1 and 5, a third propagation channel and a fourth propagation channel of the surface acoustic wave realize an integrated function of parallel wireless sensing of two gases; the distances between the second reference reflection grating 5, the third reference reflection grating 6, the third temperature compensation reflection grating 9, the fourth temperature compensation reflection grating 10, the first gas sensing reflection grating 18, the second gas sensing reflection grating 19 and the second interdigital transducer 3 are different, so that the echo signals corresponding to all the reflection gratings of the third propagation channel and the fourth propagation channel are ensured not to interfere with each other in time; the influence of the distance on the sensing of the two gases is respectively eliminated through the second reference reflecting grating 5 and the third reference reflecting grating 6; the influence of temperature change on phase measurement during sensing of the two gases is compensated through the third temperature compensation reflecting grating 9 and the fourth temperature compensation reflecting grating 10 respectively.
Referring to fig. 1, in the field of food safety, for a conventional modified atmosphere packaged food filled with a mixed gas containing carbon dioxide, oxygen and nitrogen in a certain proportion, a first gas sensitive film 20 adopts a polyetherimide film having selectivity and reversibility for adsorption of carbon dioxide, a second gas sensitive film 21 adopts a titanium dioxide film having selectivity and reversibility for adsorption of oxygen, and a surface acoustic wave device is integrated in the modified atmosphere package and has the characteristic of integrating radio frequency identification, wireless temperature sensing and gas sensing functions; the positions of a first gas sensitive film 20 and a second gas sensitive film 21 of the surface acoustic wave device are not sealed, so that the gas in the modified atmosphere package is sensitive; the interdigital transducer and the reflecting grating are protected by packaging the surface acoustic wave device at other positions, and the packaging material has high heat conduction property to transfer food temperature.
Referring to fig. 4 and 3, the surface acoustic wave device with the integrated function of radio frequency identification and wireless sensing is used for radio frequency identification and wireless temperature sensing of cold chain food such as cold storage and freezing or food with clear requirement on temperature in the field of food safety, and the working method thereof comprises the following steps:
step A: aiming at a fixed reader, food is moved to a reader action area; aiming at the handheld reader, the reader moves to the position near the food to ensure that the food is positioned in the action area of the reader;
and B: reader transmitting carrier frequency f1The excitation pulse signal is radiated outwards in the form of electromagnetic waves through the reader antenna;
and C: the surface acoustic wave device receives an excitation pulse signal through an antenna 22, a first propagation channel and a second propagation channel with the center frequency consistent with the carrier frequency of the excitation pulse signal respond to the excitation pulse signal, and a first interdigital transducer 2 converts the excitation pulse signal into surface acoustic waves through an inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the first propagation channel and the second propagation channel respectively;
step D: the surface acoustic wave propagating along the first propagation channel sequentially encounters the first reference reflection grating 4, the second temperature compensation reflection grating 8, the second coding reflection grating 12, the fourth coding reflection grating 14 and the sixth coding reflection grating 16 to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the first interdigital transducer 2; similarly, the surface acoustic wave propagating along the second propagation channel sequentially encounters the first temperature compensation reflection grating 7, the first coding reflection grating 11, the third coding reflection grating 13, the fifth coding reflection grating 15 and the seventh coding reflection grating 17 to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the first interdigital transducer 2; the first interdigital transducer 2 converts the reflection signal into a first echo pulse train comprising 10 echo pulse signals through a positive piezoelectric effect, wherein the time sequence of the 10 echo pulse signals has a one-to-one correspondence relation with the 10 reflection grating positions; the first echo burst is transmitted back to the reader antenna through antenna 22;
step E: the reader carries out signal processing on the first echo pulse train, time slot codes are directly solved through orthogonal demodulation, but the directly solved phase is influenced by temperature and temperature compensation needs to be carried out on the phase; constructing reference time delay through the temperature compensation reflecting grating to enable the corresponding phase change of the reference time delay within a temperature change range not to exceed one period, and further constructing and reducing the reference time delay through a time delay difference calculating method of echo pulse signals corresponding to the first temperature compensation reflecting grating 7 and the second temperature compensation reflecting grating 8, so that the temperature measurement range during temperature sensing is expanded; reversely deducing the initial phase of each coding reflecting grating at the reference temperature according to the phase change of the reference time delay and the position relation among the 10 reflecting gratings, thereby solving the phase gap code and realizing the radio frequency identification function;
step F: the initial phase when the phase obtained by direct orthogonal demodulation minus the reference temperature is the phase change caused by temperature, but in view of the ambiguity problem of phase measurement, only the fractional part less than 2 pi in the phase can be measured directly, and the integer part of 2 pi cannot be measured; on the premise of realizing the radio frequency identification function, according to the known relation of the distance between 10 reflecting gratings in the reference temperature, the phase change caused by the reference time delay along with the temperature is gradually pushed to the phase change between two reflecting gratings with the farthest distance among 10 reflecting gratings, namely the first reference reflecting grating 4 and the seventh coding reflecting grating 17, in a mode of ascending from near to far and in a proportional mode, so that the ambiguity problem of phase measurement is solved, the high-precision detection of the temperature is realized, and the integrated function of the radio frequency identification and the wireless temperature sensing is completed.
Referring to fig. 1, 3 and 5, a surface acoustic wave device with integrated functions of radio frequency identification and wireless sensing is used for radio frequency identification, wireless temperature sensing and gas sensing of modified atmosphere packaged food in the field of food safety, and the working method thereof comprises the following steps:
step a: the functions of radio frequency identification and wireless temperature sensing are realized as the steps A, B, C, D, E and F in the method;
step b: reader transmitting carrier frequency f2The excitation pulse signal is radiated outwards in the form of electromagnetic waves through the reader antenna;
step c: the surface acoustic wave device receives an excitation pulse signal through the antenna 22, a third propagation channel and a fourth propagation channel with the center frequency consistent with the carrier frequency of the excitation pulse signal respond to the excitation pulse signal, and the second interdigital transducer 3 converts the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the third propagation channel and the fourth propagation channel respectively;
step d: the surface acoustic wave transmitted along the third transmission channel sequentially encounters the second reference reflection grating 5, the third temperature compensation reflection grating 9 and the first gas sensing reflection grating 18 to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the second interdigital transducer 3; similarly, the surface acoustic wave propagating along the fourth propagation channel sequentially encounters the third reference reflection grating 6, the fourth temperature compensation reflection grating 10 and the second gas sensing reflection grating 19 to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the second interdigital transducer 3; the second interdigital transducer 3 converts the reflected signal into a second echo pulse train comprising 6 echo pulse signals through a positive piezoelectric effect, wherein the 6 echo pulse signal time sequences have a one-to-one correspondence relation with the 6 reflection grating positions; the second echo burst is transmitted back to the reader antenna via antenna 22;
step e: the reader carries out signal processing on 3 echo pulse signals corresponding to the second reference reflection grating 5, the third temperature compensation reflection grating 9 and the first gas sensing reflection grating 18 in the second echo pulse string, when the concentration of carbon dioxide in the modified atmosphere package changes, the amount of carbon dioxide adsorbed by the first gas sensitive film 20, namely the polyetherimide film, changes along with the change of the concentration of carbon dioxide, so that the propagation speed of the surface acoustic wave changes, and further the phase difference of the echo pulse signals corresponding to the third temperature compensation reflection grating 9 and the first gas sensing reflection grating 18 changes, but the phase difference is not only related to the concentration of carbon dioxide, but also related to the temperature; constructing reference time delay by the time delay difference of the echo pulse signals corresponding to the second reference reflecting grating 5 and the third temperature compensation reflecting grating 9, and pushing the phase change of the reference time delay caused by temperature to the position between the echo pulse signals corresponding to the third temperature compensation reflecting grating 9 and the first gas sensing reflecting grating 18, thereby compensating the phase difference caused by temperature change and measuring the concentration of carbon dioxide in the modified atmosphere package;
step f: the reader processes 3 echo pulse signals corresponding to the third reference reflection grating 6, the fourth temperature compensation reflection grating 10 and the second gas sensing reflection grating 19 in the second echo pulse train, and the concentration of oxygen in the modified atmosphere package is measured by adopting the method the same as that in the step e;
step g: because the sum of the concentrations of the carbon dioxide, the oxygen and the nitrogen in the modified atmosphere package is 100%, the concentration of the nitrogen in the modified atmosphere package can be obtained after the concentration of the carbon dioxide is measured in the step e and the concentration of the oxygen is measured in the step f, and the integrated functions of radio frequency identification, wireless temperature sensing and gas sensing are completed.
The foregoing is only a preferred embodiment of this invention and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the invention.
Claims (7)
1. A surface acoustic wave device with radio frequency identification and wireless sensing integrated functions is characterized in that: the surface acoustic wave device adopts a double-frequency four-channel single-ended delay line type structure and comprises a piezoelectric substrate (1), a first interdigital transducer (2), a second interdigital transducer (3), a first reference reflection grating (4), a second reference reflection grating (5), a third reference reflection grating (6), a first temperature compensation reflection grating (7), a second temperature compensation reflection grating (8), a third temperature compensation reflection grating (9), a fourth temperature compensation reflection grating (10) and a first coding reflection grating (11), the gas sensor comprises a second coding reflection grating (12), a third coding reflection grating (13), a fourth coding reflection grating (14), a fifth coding reflection grating (15), a sixth coding reflection grating (16), a seventh coding reflection grating (17), a first gas sensing reflection grating (18), a second gas sensing reflection grating (19), a first gas sensitive film (20), a second gas sensitive film (21) and an antenna (22);
the first interdigital transducer (2) is deposited on the upper left half part of the piezoelectric substrate (1), and the second interdigital transducer (3) is deposited on the lower left half part of the piezoelectric substrate (1);
the first interdigital transducer (2) and the second interdigital transducer (3) have the same aperture and are smaller than half of the width of the piezoelectric substrate (1), and the first interdigital transducer and the second interdigital transducer are connected with an antenna (22) in a parallel mode;
the antenna (22) is a dual-frequency antenna and covers two frequency bands of 840-845 MHz and 920-925 MHz;
the first reference reflection grating (4), the second temperature compensation reflection grating (8), the second coding reflection grating (12), the fourth coding reflection grating (14) and the sixth coding reflection grating (16) are deposited on the upper part of the piezoelectric substrate (1), the apertures are equal and smaller than one half of the aperture of the first interdigital transducer (2), and the first reference reflection grating, the second temperature compensation reflection grating, the fourth coding reflection grating and the sixth coding reflection grating form a first propagation channel of the surface acoustic wave together with the upper half part of the first interdigital transducer (2);
the first temperature compensation reflecting grating (7), the first coding reflecting grating (11), the third coding reflecting grating (13), the fifth coding reflecting grating (15) and the seventh coding reflecting grating (17) are deposited at the upper middle position of the piezoelectric substrate (1), the apertures are equal and smaller than one half of the aperture of the first interdigital transducer (2), and the first temperature compensation reflecting grating, the first coding reflecting grating, the third coding reflecting grating and the seventh coding reflecting grating form a second propagation channel of the surface acoustic wave together with the lower half part of the first interdigital transducer (2);
the second reference reflection grating (5), the third temperature compensation reflection grating (9) and the first gas sensing reflection grating (18) are deposited at the middle lower position of the piezoelectric substrate (1), the apertures are equal and smaller than half of the aperture of the second interdigital transducer (3), and the second reference reflection grating, the third temperature compensation reflection grating and the first gas sensing reflection grating form a third propagation channel of the surface acoustic wave together with the upper half part of the second interdigital transducer (3);
the first gas sensitive film (20) is coated between a third temperature compensation reflecting grating (9) of a third propagation channel of the surface acoustic wave and the first gas sensing reflecting grating (18);
the third reference reflection grating (6), the fourth temperature compensation reflection grating (10) and the second gas sensing reflection grating (19) are deposited on the lower portion of the piezoelectric substrate (1), the aperture is equal to each other and smaller than half of the aperture of the second interdigital transducer (3), and the third reference reflection grating, the fourth temperature compensation reflection grating and the second gas sensing reflection grating form a fourth propagation channel of the surface acoustic wave together with the lower half portion of the second interdigital transducer (3);
the second gas sensitive film (21) is coated between a fourth temperature compensation reflecting grating (10) of a fourth propagation channel of the surface acoustic wave and the second gas sensing reflecting grating (19);
by designing the width of a finger strip of a first interdigital transducer (2), the width of a first reference reflection grating (4), a first temperature compensation reflection grating (7), a second temperature compensation reflection grating (8), a first coding reflection grating (11), a second coding reflection grating (12), a third coding reflection grating (13), a fourth coding reflection grating (14), a fifth coding reflection grating (15), a sixth coding reflection grating (16) and the width of a grating strip of a seventh coding reflection grating (17), the central frequency f of a first propagation channel and the central frequency f of a second propagation channel of the surface acoustic wave are enabled to be equal to the width of the first reference reflection grating, the second coding reflection grating (7), the second coding reflection grating (81922.5 MHz; by designing the width of the finger strip of the second interdigital transducer (3) and the widths of the second reference reflecting grating (5), the third reference reflecting grating (6), the third temperature compensation reflecting grating (9), the fourth temperature compensation reflecting grating (10), the first gas sensing reflecting grating (18) and the second gas sensing reflecting grating (19), the central frequency f of the third propagation channel and the fourth propagation channel of the surface acoustic wave is enabled to be2Is 842.5 MHz.
2. The SAW device with RFID-based and wireless sensing integrated functions as claimed in claim 1, wherein: the first coding reflection grating (11), the second coding reflection grating (12), the third coding reflection grating (13), the fourth coding reflection grating (14), the fifth coding reflection grating (15), the sixth coding reflection grating (16) and the seventh coding reflection grating (17) are respectively positioned in seven coding data areas; n time slots are divided in each coding data area at equal intervals, and a coding reflection grating is positioned in one time slot; the n phase gaps are further divided in each time slot at equal intervals for 360 degrees of phase, and the coding reflection grating is positioned in one of the phase gaps.
3. The SAW device with RFID-based and wireless sensing integrated functions as claimed in claim 1, wherein: the distances between the first reference reflection grating (4), the first temperature compensation reflection grating (7), the second temperature compensation reflection grating (8), the first coding reflection grating (11), the second coding reflection grating (12), the third coding reflection grating (13), the fourth coding reflection grating (14), the fifth coding reflection grating (15), the sixth coding reflection grating (16), the seventh coding reflection grating (17) and the first interdigital transducer (2) are different, so that the echo signals corresponding to all the reflection gratings of the first propagation channel and the second propagation channel are ensured not to interfere with each other in time.
4. The SAW device with RFID-based and wireless sensing integrated functions as claimed in claim 1, wherein: the distances between the second reference reflection grating (5), the third reference reflection grating (6), the third temperature compensation reflection grating (9), the fourth temperature compensation reflection grating (10), the first gas sensing reflection grating (18), the second gas sensing reflection grating (19) and the second interdigital transducer (3) are different, so that echo signals corresponding to all the reflection gratings of the third propagation channel and the fourth propagation channel are ensured not to interfere with each other in time.
5. The SAW device with RFID-based and wireless sensing integrated functions as claimed in claim 1, wherein: in the field of food safety, aiming at modified atmosphere packaged food which is filled with mixed gas comprising carbon dioxide, oxygen and nitrogen conventionally, a first gas sensitive film (20) adopts a polyetherimide film which has selectivity and reversibility to the adsorption of the carbon dioxide, and a second gas sensitive film (21) adopts a titanium dioxide film which has selectivity and reversibility to the adsorption of the oxygen;
the positions of a first gas sensitive film (20) and a second gas sensitive film (21) of the surface acoustic wave device are not sealed, so that the gas in the modified atmosphere package is sensitive; and the other positions of the surface acoustic wave device are packaged to protect the interdigital transducer and the reflecting grating.
6. An operating method of the surface acoustic wave device with the integrated radio frequency identification and wireless sensing function according to claim 1, which is used for radio frequency identification and wireless temperature sensing of cold chain food such as cold storage and freezing or food with specific requirement on temperature in the food safety field, and is characterized in that: the method comprises the following steps:
step A: aiming at a fixed reader, food is moved to a reader action area; aiming at the handheld reader, the reader moves to the position near the food to ensure that the food is positioned in the action area of the reader;
and B: reader transmitting carrier frequency f1The excitation pulse signal is radiated outwards in the form of electromagnetic waves through the reader antenna;
and C: the surface acoustic wave device receives an excitation pulse signal through an antenna (22), a first propagation channel and a second propagation channel with the center frequency consistent with the carrier frequency of the excitation pulse signal respond to the excitation pulse signal, and a first interdigital transducer (2) converts the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the first propagation channel and the second propagation channel respectively;
step D: the surface acoustic wave propagating along the first propagation channel sequentially encounters a first reference reflection grating (4), a second temperature compensation reflection grating (8), a second coding reflection grating (12), a fourth coding reflection grating (14) and a sixth coding reflection grating (16) to generate partial reflection and partial transmission, and a reflection signal of the surface acoustic wave is transmitted back to the first interdigital transducer (2); similarly, the surface acoustic wave propagating along the second propagation channel sequentially encounters the first temperature compensation reflection grating (7), the first coding reflection grating (11), the third coding reflection grating (13), the fifth coding reflection grating (15) and the seventh coding reflection grating (17) to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the first interdigital transducer (2); the first interdigital transducer (2) converts the reflection signal into a first echo pulse train comprising 10 echo pulse signals through a positive piezoelectric effect, wherein the time sequence of the 10 echo pulse signals has a one-to-one correspondence relation with the 10 reflection grating positions; the first echo burst is transmitted back to the reader antenna via the antenna (22);
step E: the reader carries out signal processing on the first echo pulse train and directly solves time slot codes through orthogonal demodulation; constructing reference time delay through the temperature compensation reflecting grating to enable the corresponding phase change of the reference time delay within the temperature change range not to exceed one period, namely constructing and reducing the reference time delay through a time delay difference solving method of echo pulse signals corresponding to the first temperature compensation reflecting grating (7) and the second temperature compensation reflecting grating (8); the initial phases of 7 coding reflecting gratings at the reference temperature are reversely deduced according to the phase change of the reference time delay and the position relation among 10 reflecting gratings, so that the phase gap code is solved, and the radio frequency identification function is realized;
step F: on the premise of realizing the radio frequency identification function, according to the known relation of the distance between 10 reflecting gratings in the reference temperature, the phase change caused by the reference time delay along with the temperature is gradually deduced to the phase change between two reflecting gratings with the farthest distance in the 10 reflecting gratings, namely a first reference reflecting grating (4) and a seventh coding reflecting grating (17), through a mode of gradually recurring from near to far and in proportion, and the temperature is detected according to the relation between the temperature change and the phase change, so that the integrated function of the radio frequency identification and the wireless temperature sensing is completed.
7. The working method of the surface acoustic wave device with integrated radio frequency identification and wireless sensing functions as claimed in claim 5, which is used for radio frequency identification, wireless temperature sensing and gas sensing of modified atmosphere packaged food in the field of food safety, and is characterized in that: the method comprises the following steps:
step a: the same as the steps A, B, C, D, E and F in the claim 6, the radio frequency identification and wireless temperature sensing functions are realized;
step b: reader transmitting carrier frequency f2By electromagnetic waves through the reader antennaIs radiated outward;
step c: the surface acoustic wave device receives an excitation pulse signal through an antenna (22), a third propagation channel and a fourth propagation channel with the center frequency consistent with the carrier frequency of the excitation pulse signal respond to the excitation pulse signal, and a second interdigital transducer (3) converts the excitation pulse signal into surface acoustic waves through an inverse piezoelectric effect and transmits the surface acoustic waves along the piezoelectric substrate surfaces of the third propagation channel and the fourth propagation channel respectively;
step d: the surface acoustic wave propagating along the third propagation channel sequentially encounters a second reference reflection grating (5), a third temperature compensation reflection grating (9) and a first gas sensing reflection grating (18) to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the second interdigital transducer (3); similarly, the surface acoustic wave propagating along the fourth propagation channel sequentially encounters a third reference reflection grating (6), a fourth temperature compensation reflection grating (10) and a second gas sensing reflection grating (19) to generate partial reflection and partial transmission, and a reflection signal is transmitted back to the second interdigital transducer (3); the second interdigital transducer (3) converts the reflected signal into a second echo pulse train comprising 6 echo pulse signals through a direct piezoelectric effect, wherein the 6 echo pulse signal time sequences have one-to-one correspondence with the 6 reflection grating positions; the second echo burst is transmitted back to the reader antenna via the antenna (22);
step e: the reader carries out signal processing on 3 echo pulse signals corresponding to the second reference reflection grating (5), the third temperature compensation reflection grating (9) and the first gas sensing reflection grating (18) in the second echo pulse train, when the concentration of carbon dioxide in the modified atmosphere package changes, the amount of carbon dioxide adsorbed by the first gas sensitive film (20), namely the polyetherimide film, changes along with the change of the concentration of the carbon dioxide, and the phase difference of the echo pulse signals corresponding to the third temperature compensation reflection grating (9) and the first gas sensing reflection grating (18) changes; constructing reference time delay by time delay difference of echo pulse signals corresponding to the second reference reflecting grating (5) and the third temperature compensation reflecting grating (9), and pushing phase change of the reference time delay caused by temperature to a position between the third temperature compensation reflecting grating (9) and the echo pulse signal corresponding to the first gas sensing reflecting grating (18), so as to compensate phase difference caused by temperature change and measure the concentration of carbon dioxide in the modified atmosphere package;
step f: the reader processes 3 echo pulse signals corresponding to the third reference reflection grating (6), the fourth temperature compensation reflection grating (10) and the second gas sensing reflection grating (19) in the second echo pulse train, and the concentration of oxygen in the modified atmosphere package is measured by adopting the method the same as that in the step e;
step g: because the sum of the concentrations of the carbon dioxide, the oxygen and the nitrogen in the modified atmosphere package is 100%, the concentration of the nitrogen in the modified atmosphere package can be obtained after the concentration of the carbon dioxide is measured in the step e and the concentration of the oxygen is measured in the step f, and the integrated functions of radio frequency identification, wireless temperature sensing and gas sensing are completed.
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| CN112114034A (en) | 2020-12-22 |
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