Method and system for nondestructive testing of freezing degree of fruits and vegetables based on ultrasonic technology

Abstract

The invention discloses a method and system for nondestructive testing of fruit and vegetable freezing degree based on an ultrasonic technology, and relates to the technical field of agricultural product nondestructive testing, and the method comprises the following steps: S1, based on fruit and vegetable characteristics, setting parameters of a sound wave parameter tester; s2, detecting the freezing degree of the fruits and vegetables by using an acoustic parameter tester and a temperature sensor, and obtaining an ultrasonic test result and the center temperature of the fruits and vegetables in the freezing process; s3, extracting a characteristic acoustic index according to an ultrasonic test result, and establishing a fitting equation in combination with the center temperature; and S4, based on the fitted equation, verifying the accuracy of ultrasonic nondestructive testing of the fruit and vegetable freezing degree. The method has the characteristics of rapidness, accuracy, penetrability and non-destructiveness, and is suitable for online temperature monitoring in the fruit and vegetable freezing processing process, so that the product quality control is better realized.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing of agricultural products, and more particularly to a method and system for nondestructive testing of freezing degree of fruits and vegetables based on ultrasonic technology. Background Art

[0002] Traditional biochemical analysis technology can well conduct qualitative and quantitative analysis of food quality and related substances, but it has disadvantages such as long testing time and damage to food. Non-destructive testing technology is a testing technology that accurately obtains physical and chemical information such as internal and external properties and composition without destroying the physical state and chemical properties of the object being tested. It has the advantages of being fast, convenient, and non-destructive. Among them, ultrasonic testing technology is a type of non-destructive testing technology. When ultrasonic waves propagate in different objects being tested, they show different acoustic characteristics. Studying these acoustic characteristics can predict changes in the performance and structure of the object being tested. It has the advantages of being non-destructive, fast, accurate, and relatively cheap.

[0003] Freezing is an effective way to preserve fruits and vegetables. It can inhibit the reproduction of microorganisms and biochemical reactions in food through low temperature, thereby achieving long-term preservation of food. Generally speaking, freezing requires the core temperature of the food to be frozen to below -18°C. The current temperature measurement method mainly uses a handheld thermometer for destructive testing, but this measurement method will damage the food and is easily affected by the external environment, resulting in the inability to measure the temperature of large-scale samples in actual processing and production. Infrared thermal imaging can measure the temperature of objects non-destructively, but this technology can only measure the surface temperature of food and cannot detect the core temperature. Different core temperatures and degrees of freezing of food can reflect different acoustic properties, mainly because during the freezing process, the food will undergo a transition from liquid to solid phase, during which the acoustic properties will change.

[0004] In summary, the development of a method and system for non-destructive detection of the degree of freezing of fruits and vegetables based on ultrasonic technology is of certain importance and is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, the present invention provides a method and system for non-destructively detecting the freezing degree of fruits and vegetables based on ultrasonic technology, which solves the problems existing in the background technology.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology comprises the following steps:

[0008] S1: Set the parameters of the acoustic parameter tester based on the characteristics of fruits and vegetables;

[0009] S2: Use an ultrasonic parameter tester and a temperature sensor to detect the freezing degree of fruits and vegetables, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process;

[0010] S3: Extract characteristic acoustic indicators based on ultrasonic test results, combine with center temperature, and establish fitting equations;

[0011] S4: Based on the fitting equation, verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables.

[0012] Optionally, in S1, the frequency of the acoustic parameter tester is set based on the size of the fruit or vegetable;

[0013] For fruits and vegetables with a diameter of 50 mm, the frequency of the acoustic parameter tester is set to 70 kHz;

[0014] For fruits and vegetables with a diameter less than 50 mm, the frequency of the acoustic parameter tester is set to 70-100 kHz;

[0015] For fruits and vegetables with a diameter greater than 50 mm, the frequency of the ultrasonic parameter tester is set to 40-70 kHz.

[0016] Optionally, in S1, the attenuation multiple of the acoustic wave parameter tester is set based on the hardness of fruits and vegetables;

[0017] For fruits and vegetables whose hardness exceeds the preset threshold, the attenuation multiple of the acoustic wave parameter tester is set to 30 to 50;

[0018] For fruits and vegetables whose hardness does not exceed the preset threshold, the attenuation multiple of the ultrasonic parameter tester is set to 10 to 20.

[0019] Optionally, in S2, the acoustic wave parameter tester includes: a pulse signal generator, an ultrasonic transducer, a data collector, and an oscilloscope; the ultrasonic transducer includes a transmitting transducer and a receiving transducer, and the fruits and vegetables to be tested are placed between the transmitting transducer and the receiving transducer and are closely fitted;

[0020] The process of obtaining ultrasonic test results is as follows: the pulse signal generator emits ultrasonic waves, which are received by the receiving transducer after passing through the fruits and vegetables to be tested through the transmitting transducer, and finally the data acquisition device and oscilloscope collect and display the signals.

[0021] Optionally, in S3, the specific steps of establishing the fitting equation are:

[0022] Based on the ultrasonic test results, the wave speed of fruits and vegetables with different freezing degrees is obtained by c=d / t; where c is the wave speed, m / s; d is the ultrasonic propagation distance, m; t is the ultrasonic propagation time, s;

[0023] Matlab mathematical analysis software was used to fit the wave velocity and center temperature using a polynomial function. 2 The root mean square error determines the fitting equation function.

[0024] Optionally, in S4, the specific steps of verifying the accuracy of ultrasonic nondestructive testing of the degree of freezing of fruits and vegetables are:

[0025] Conduct ultrasonic analysis on frozen fruiting vegetables to obtain the measured wave velocity;

[0026] Substitute the measured wave velocity into the established fitting equation to obtain the predicted central temperature;

[0027] Use a handheld thermometer to obtain the measured center temperature of frozen fruiting vegetables at the corresponding measured wave speed;

[0028] By comparing the predicted center temperature with the measured center temperature, the accuracy of ultrasonic nondestructive testing of the degree of freezing of fruits and vegetables is verified.

[0029] A system for non-destructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology, using the method for non-destructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology as described in any of the above items, comprising:

[0030] Parameter design module, used to set the parameters of the acoustic wave parameter tester according to the characteristics of fruits and vegetables;

[0031] A freezing detection module is used to detect the freezing degree of fruits and vegetables using an ultrasonic parameter tester and a temperature sensor, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process;

[0032] The fitting module is used to extract characteristic acoustic indicators based on the ultrasonic test results and establish a fitting equation in combination with the center temperature;

[0033] The verification module is used to verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables based on the fitting equation.

[0034] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method and system for non-destructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology, which has the characteristics of being fast, accurate, penetrable and non-destructive, and is suitable for online temperature monitoring during the freezing process of fruits and vegetables, thereby better realizing product quality control. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0036] Figure 1 A flow chart of a method for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology provided by the present invention;

[0037] Figure 2 The longitudinal wave time domain diagram of the ultrasonic detection of litchi provided by the present invention;

[0038] Figure 3 The longitudinal wave velocity diagram of litchi at different central temperatures provided by the present invention;

[0039] Figure 4 This is a comparison chart of the predicted temperature and the measured temperature provided by the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] In view of the shortcomings of the existing technology for detecting the freezing degree of food, the embodiment of the present invention discloses a method for non-destructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology, such as Figure 1 As shown, the following steps are included:

[0042] S1: Set the parameters of the acoustic parameter tester based on the characteristics of fruits and vegetables;

[0043] S2: Use an ultrasonic parameter tester and a temperature sensor to detect the freezing degree of fruits and vegetables, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process;

[0044] S3: Extract characteristic acoustic indicators based on ultrasonic test results, combine with center temperature, and establish fitting equations;

[0045] S4: Based on the fitting equation, verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables.

[0046] based on Figure 1 As shown in the process, this embodiment uses an ultrasonic parameter tester to perform nondestructive testing on the freezing process of agricultural products. During the testing process, the ultrasonic wave has a high frequency, large attenuation, poor penetration, and a short wavelength; the ultrasonic wave has a low frequency, small attenuation, strong penetration, and a long wavelength.

[0047] Further, in S1, the frequency of the acoustic wave parameter tester is set based on the size of the fruit and vegetable;

[0048] For fruits and vegetables with a diameter of 50 mm, the frequency of the acoustic parameter tester is set to 70 kHz;

[0049] For fruits and vegetables with a diameter less than 50 mm, the frequency of the acoustic parameter tester is set to 70-100 kHz;

[0050] For fruits and vegetables with a diameter greater than 50 mm, the frequency of the ultrasonic parameter tester is set to 40-70 kHz.

[0051] Furthermore, in S1, the texture of fruits and vegetables will affect their absorption of ultrasonic energy. Generally, the harder the fruits and vegetables are, the smaller the attenuation of ultrasound in them is. Therefore, the attenuation multiple of the ultrasonic parameter tester is set based on the hardness of fruits and vegetables.

[0052] For fruits and vegetables whose hardness exceeds the preset threshold, the attenuation multiple of the acoustic wave parameter tester is set to 30 to 50;

[0053] For fruits and vegetables whose hardness does not exceed the preset threshold, the attenuation multiple of the ultrasonic parameter tester is set to 10 to 20.

[0054] Further, in S2, the acoustic wave parameter tester includes: a pulse signal generator, an ultrasonic transducer, a data collector, and an oscilloscope; the ultrasonic transducer includes a transmitting transducer and a receiving transducer, and the fruits and vegetables to be tested are placed between the transmitting transducer and the receiving transducer and are closely fitted;

[0055] The process of obtaining ultrasonic test results is as follows: the pulse signal generator emits ultrasonic waves, which are received by the receiving transducer after passing through the fruits and vegetables to be tested through the transmitting transducer, and finally the data acquisition device and oscilloscope collect and display the signals.

[0056] The acoustic wave parameter tester provided in this embodiment is a multifunctional detection device that can quickly and accurately obtain acoustic parameters such as longitudinal wave velocity, frequency, amplitude, etc.

[0057] Furthermore, in S3, the specific steps of establishing the fitting equation are:

[0058] Based on the ultrasonic test results, the wave speed of fruits and vegetables with different freezing degrees is obtained by c=d / t; where c is the wave speed, m / s; d is the ultrasonic propagation distance, m; t is the ultrasonic propagation time, s;

[0059] Using mathematical analysis software such as Matlab, the wave velocity and center temperature were fitted using a polynomial function form, and the R 2 The root mean square error determines the fitting equation function.

[0060] Furthermore, in S4, the specific steps for verifying the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables are as follows:

[0061] Conduct ultrasonic analysis on frozen fruiting vegetables to obtain the measured wave velocity;

[0062] Substitute the measured wave velocity into the established fitting equation to obtain the predicted central temperature;

[0063] Use a handheld thermometer to obtain the measured center temperature of frozen fruiting vegetables at the corresponding measured wave speed;

[0064] By comparing the predicted center temperature with the measured center temperature, the accuracy of ultrasonic nondestructive testing of the degree of freezing of fruits and vegetables is verified.

[0065] and Figure 1 Corresponding to the method described above, the embodiment of the present invention also provides a system for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology, which is used for Figure 1 The specific implementation of the method in the embodiment of the present invention is a system for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology, which can be applied to computer terminals or various mobile devices, and specifically includes:

[0066] Parameter design module, used to set the parameters of the acoustic wave parameter tester according to the characteristics of fruits and vegetables;

[0067] A freezing detection module is used to detect the freezing degree of fruits and vegetables using an ultrasonic parameter tester and a temperature sensor, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process;

[0068] The fitting module is used to extract characteristic acoustic indicators based on the ultrasonic test results and establish a fitting equation in combination with the center temperature;

[0069] The verification module is used to verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables based on the fitting equation.

[0070] Next, taking fresh lychees as an example, the technical solution of non-destructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology proposed in the present invention is implemented.

[0071] (1) Set the parameters of the acoustic wave parameter tester: the frequency is set to 100 kHz, the sampling rate is set to 20 MHz, the sampling interval is set to 0.1-0.5 μs, the transmitting pulse voltage is set to 500-1000 V, and the attenuation multiple is set to 10.

[0072] (2) The lychees were frozen in a freezer to different core temperatures (4°C, -1°C, -3°C, -5°C, -10°C, -15°C and -20°C), and ultrasonic testing was performed using an ultrasonic parameter tester. Figure 2 The ultrasonic longitudinal wave time domain diagram of litchi is shown.

[0073] (3) Extract the longitudinal wave velocity as the characteristic acoustic index of the detection center temperature for analysis, and calculate the longitudinal wave velocity at different center temperatures (freezing degree), such as Figure 3 shown.

[0074] (4) Using the longitudinal wave velocity as the abscissa and the center temperature as the ordinate, the empirical equation is fitted, as shown in Table 1.

[0075] Table 1 Polynomial fitting equation

[0076]

[0077] Based on experimental data and related analysis software, the fifth-order polynomial form with the highest accuracy was found in the polynomial fitting equation. F(x) = (1.2596e-14)*x^5+(-1.0862e-10)*x^4+(3.5227e-07)*x^3+(-5.3509e-04)*x^2+0.3713*x-89.6861, as shown in Table 1. 2 =0.9991, which is very close to 1, and RMSE = 0.6059. The above two indicators show that the quintic polynomial form has high accuracy and can be used to predict the center temperature.

[0078] (5) Ultrasonic testing was performed on the freezing process of fresh lychees. Based on the actual measured longitudinal wave velocity and the fitting equation, the central temperature of the lychees was predicted and compared with the measured value.

[0079] Figure 4 The figure shows the comparison between the predicted temperature and the measured temperature. After calculation, the relative error between the two is 16.92%, and the root mean square error is 1.92℃, which shows that the equation can predict the actual center temperature of litchi to a certain extent.

[0080] In summary, the present invention proposes a method for nondestructive detection of the freezing degree of fruits and vegetables based on ultrasonic technology, which overcomes the disadvantages of traditional temperature measurement (temperature sensor measurement method will damage food, measurement results are easily affected by the external environment, and infrared temperature measurement method cannot measure the internal temperature of food), has the characteristics of fast, accurate, penetrable and non-destructive, and is suitable for online temperature monitoring in the process of fruit and vegetable freezing processing, so as to better realize product quality control.

[0081] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0082] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology, characterized in that: The following steps are involved: S1: Set the parameters of the acoustic parameter tester based on the characteristics of fruits and vegetables; S2: Use an ultrasonic parameter tester and a temperature sensor to detect the freezing degree of fruits and vegetables, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process; S3: Extract characteristic acoustic indicators based on ultrasonic test results, combine with center temperature, and establish fitting equations; S4: Based on the fitting equation, verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables.

2. The method for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology according to claim 1, characterized in that: In S1, the frequency of the acoustic parameter tester is set based on the size of fruits and vegetables; For fruits and vegetables with a diameter of 50 mm, the frequency of the acoustic parameter tester is set to 70 kHz; For fruits and vegetables with a diameter less than 50 mm, the frequency of the acoustic parameter tester is set to 70-100 kHz; For fruits and vegetables with a diameter greater than 50 mm, the frequency of the ultrasonic parameter tester is set to 40-70 kHz.

3. The method for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology according to claim 1 is characterized in that: In S1, the attenuation factor of the acoustic parameter tester is set based on the hardness of fruits and vegetables; For fruits and vegetables whose hardness exceeds the preset threshold, the attenuation multiple of the acoustic wave parameter tester is set to 30 to 50; For fruits and vegetables whose hardness does not exceed the preset threshold, the attenuation multiple of the ultrasonic parameter tester is set to 10 to 20.

4. The method for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology according to claim 1, characterized in that: In S2, the acoustic wave parameter tester includes: a pulse signal generator, an ultrasonic transducer, a data collector, and an oscilloscope; the ultrasonic transducer includes a transmitting transducer and a receiving transducer, and the fruits and vegetables to be tested are placed between the transmitting transducer and the receiving transducer and are closely fitted; The process of obtaining ultrasonic test results is as follows: the pulse signal generator emits ultrasonic waves, which are received by the receiving transducer after passing through the fruits and vegetables to be tested through the transmitting transducer, and finally the data acquisition device and oscilloscope collect and display the signals.

5. The method for non-destructive detection of freezing degree of fruits and vegetables based on ultrasonic technology according to claim 1, characterized in that: In S3, the specific steps of establishing the fitting equation are: Based on the ultrasonic test results, the wave speed of fruits and vegetables with different freezing degrees is obtained by c=d / t; where c is the wave speed, m / s; d is the ultrasonic propagation distance, m; t is the ultrasonic propagation time, s; Matlab mathematical analysis software was used to fit the wave velocity and center temperature using a polynomial function. 2 The root mean square error determines the fitting equation function.

6. The method for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology according to claim 1, characterized in that: In S4, the specific steps for verifying the accuracy of ultrasonic nondestructive testing of the degree of freezing of fruits and vegetables are as follows: Conduct ultrasonic analysis on frozen fruiting vegetables to obtain the measured wave velocity; Substitute the measured wave velocity into the established fitting equation to obtain the predicted central temperature; Use a handheld thermometer to obtain the measured center temperature of frozen fruiting vegetables at the corresponding measured wave speed; By comparing the predicted center temperature with the measured center temperature, the accuracy of ultrasonic nondestructive testing of the degree of freezing of fruits and vegetables is verified.

7. A system for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology, using the method for nondestructive detection of freezing degree of fruits and vegetables based on ultrasonic technology as described in any one of claims 1 to 6, characterized in that: include: Parameter design module, used to set the parameters of the acoustic wave parameter tester according to the characteristics of fruits and vegetables; A freezing detection module is used to detect the freezing degree of fruits and vegetables using an ultrasonic parameter tester and a temperature sensor, and obtain ultrasonic test results and the core temperature of fruits and vegetables during the freezing process; The fitting module is used to extract characteristic acoustic indicators based on the ultrasonic test results and establish a fitting equation in combination with the center temperature; The verification module is used to verify the accuracy of ultrasonic nondestructive testing of the freezing degree of fruits and vegetables based on the fitting equation.

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