Ultrasonic-assisted supercritical CO2 extraction method for highly active Torreya grandis oil

Abstract

This invention relates to a method for ultrasonic-assisted supercritical CO2 extraction of highly active Torreya grandis oil, comprising the following steps: S1 Raw material preparation: Take dried Torreya grandis kernels (moisture content ≤10%), pulverize them to 80-300 μm under nitrogen protection at -20 to -10℃ to obtain Torreya grandis powder; This invention uses low-temperature nitrogen-protected pulverization, the addition of soybean lecithin and rosmarinic acid compound antioxidants, and ultrasonic-assisted supercritical CO2 periodic pressure swing extraction to synergistically inhibit oil oxidation, resulting in Torreya grandis oil with a peroxide value ≤0.87 mmol / kg, effectively preserving oil activity; The three-stage cyclic pressure swing extraction mode of "low pressure-medium pressure-high pressure" is adopted, combined with the intermittent strengthening effect of bursting ultrasound, periodically changing the pressure inside the extraction vessel, causing repeated compression and expansion of the cell wall, forming "breathing" rupture, significantly reducing mass transfer resistance, and increasing the extraction rate to over 46%.

Description

Technical Field

[0001] This invention relates to the field of extraction technology, and in particular to a method for ultrasonic-assisted supercritical CO2 extraction of highly active Torreya grandis oil. Background Technology

[0002] Torreya grandis is a cultivated variety of Torreya grandis belonging to the genus Torreya in the family Taxaceae. Torreya grandis oil, as the main deep-processed product of Torreya grandis kernels, has high nutritional value and significant health benefits, and has broad application prospects in the fields of functional foods and medicine.

[0003] The main extraction methods for Torreya grandis oil include pressing, organic solvent extraction, and supercritical fluid extraction. Pressing results in low oil yield and high residual oil in the cake, and the frictional heat generated during pressing easily leads to oil oxidation and deterioration. While organic solvent extraction has higher extraction efficiency, it carries the risk of solvent residue, and the high-temperature desolventizing process accelerates the oxidation and deterioration of unsaturated fatty acids, affecting oil quality and safety. Supercritical CO2 extraction technology has advantages such as low extraction temperature, no organic solvent residue, and good selectivity, and has been widely used in vegetable oil extraction.

[0004] However, conventional supercritical CO2 extraction of Torreya grandis oil still suffers from limited mass transfer: the cell wall structure of Torreya grandis kernels is dense, resulting in high resistance to CO2 penetration and solute diffusion. This often requires a long extraction time to obtain a high extraction rate, leading to increased energy consumption and increased residence time of the oil in hot and oxygen environments, thus increasing the risk of oxidation. Therefore, there is an urgent need for an ultrasound-assisted supercritical CO2 extraction method to solve this problem. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides the following technical solution: One method provides an ultrasound-assisted supercritical CO2 extraction method for highly active Torreya grandis oil, comprising the following steps: S1 Raw material preparation: Take dried Torreya grandis kernels (moisture content ≤10%), and pulverize them to 80-300μm under nitrogen protection at -20 to -10 ℃ to obtain Torreya grandis powder; S2 Protective Component Addition: Add soybean lecithin and rosmarinic acid to torreya powder at amounts of 0.5%–1.5% and 0.05%–0.2% of the torreya powder mass, respectively. After mixing evenly, premix at low temperature for 10–30 min under nitrogen protection and at -10–0℃. S3 Pre-soaking: The mixed Torreya grandis kernel powder is loaded into a supercritical extraction vessel and CO2 is introduced for pre-soaking for 10-20 minutes; The purpose of pre-wetting is to allow CO2 to fully wet the pores of Torreya grandis powder, reducing the resistance to subsequent extraction, and at the same time to remove air from the pores of Torreya grandis powder in advance, reducing the risk of oil oxidation. S4 Extraction: Supercritical CO2 is introduced into the extraction vessel, and periodic pressure swing extraction is adopted. The extraction process is a three-stage cycle of "low pressure-medium pressure-high pressure", with each cycle lasting 12 to 20 minutes, a total of 8 to 12 cycles, and a total extraction time of 1.5 to 3.5 hours. S5 Three-stage separation: Supercritical CO2 carrying Torreya oil is sequentially fed into the first-stage separation vessel, the second-stage separation vessel and the third-stage separation vessel. The extract is fractionated and collected under corresponding pressure and temperature conditions. The separated CO2 is recovered to the CO2 storage tank and recycled after condensation / gas-liquid separation. S6 compounding: The primary, secondary, and tertiary separation components are mixed under nitrogen protection and at a temperature below 25°C to obtain highly active Torreya grandis oil.

[0006] As an improvement to the above technical solution, in step S4, Low-pressure section: pressure 12-16 MPa, temperature 30-35℃, time 1-2 min, applied ultrasonic power 300-700W; Medium pressure section: pressure 24-30 MPa, temperature 38-42℃, time 6-10 min, applied ultrasonic power 80-150W; High-pressure section: pressure 34-40 MPa, temperature 40-45℃, time 3-5 min, turn off ultrasound.

[0007] By setting ultrasonic power gradients at different pressure levels, extraction efficiency can be enhanced while avoiding ultrasonic-induced oil oxidation, thus balancing extraction efficiency and oil quality. As an improvement to the above technical solution, in step S5, First-stage separation: pressure 10-18 MPa, temperature 30-35℃; Two-stage separation: pressure 5-10 MPa, temperature 28-32℃; Three-stage separation: pressure 1-4 MPa, temperature 25-30℃.

[0008] As an improvement to the above technical solution, the pre-impregnation pressure in step S3 is 8-20 MPa and the temperature is 30-50℃.

[0009] As an improvement to the above technical solution, in the periodic pressure swing extraction process described in step S4, the circulating mass flow rate of CO2 is: 5-15 kg / h in the low-pressure section, 20-35 kg / h in the medium-pressure section, and 30-45 kg / h in the high-pressure section. The gradient flow rate setting can match the CO2 dissolution capacity under different pressures. The low flow rate in the low-pressure section ensures that CO2 fully wets the pores, the medium flow rate in the medium-pressure section increases the oil dissolution rate, and the high flow rate in the high-pressure section is conducive to improving the bed renewal and carrying capacity, promoting the migration of residual oil to the fluid phase and output with CO2, thereby increasing the extraction yield per unit time and further improving the extraction efficiency.

[0010] As an improvement to the above technical solution, in step S4, the low-pressure ultrasound operates in burst mode, wherein the burst duty cycle is the ratio of the power-on duration of each burst pulse to the burst repetition period. The low-pressure ultrasound operates in burst mode with a peak power to average power ratio of 5:1 to 15:1, each burst pulse contains 5 to 20 carrier cycles, the burst repetition frequency is 50 to 200 Hz, and the burst duty cycle is 1% to 20%. Compared with conventional continuous ultrasound, burst mode ultrasound can reduce the average input power and local temperature rise while maintaining peak intensity and enhancing extraction, thus avoiding the oxidation of oils and achieving the dual goals of enhanced extraction and oxidation inhibition.

[0011] The beneficial effects of this invention are: By using low-temperature nitrogen-protected pulverization, adding a compound antioxidant of soybean lecithin and rosmarinic acid, and combining ultrasound-assisted supercritical CO2 periodic pressure swing extraction, the peroxide value of the prepared Torreya grandis oil is ≤0.87 mmol / kg, effectively preserving the activity of the oil. The three-stage cyclic pressure swing extraction mode of "low pressure-medium pressure-high pressure" is adopted, combined with the intermittent enhancement effect of burst ultrasound, which periodically changes the pressure inside the extraction vessel, causing the cell wall to be repeatedly compressed and expanded, forming a "breathing" rupture, significantly reducing mass transfer resistance and increasing the extraction rate to over 46%. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0014] To address the difficulty of supercritical CO2 permeation, this application describes a method for pulverizing Torreya grandis kernels at a low temperature of -20°C to -10°C under nitrogen protection. This method effectively inhibits lipoxygenase activity, prevents auto-oxidation caused by frictional heat generation, and prevents unsaturated fatty acids from contacting air. Nitrogen, as an inert gas, replaces oxygen in the pulverization system, thereby blocking free radical chain reactions at the source and protecting the endogenous antioxidant components in Torreya grandis powder. Low-pressure section: The CO2 density in the low-pressure section is slightly lower than that in the high-pressure section, with lower viscosity and better permeability, which is more conducive to entering the pores of the powder and rapidly wetting it. At this time, high-power burst mode ultrasound is applied to form microscale impact and shear in the local area, which promotes the formation of microcracks or channels in the cell wall and oil film structure, reducing the internal diffusion resistance. The intermittent pulse of burst ultrasound makes it easier to drive out the residual gas in the pores of the material, and CO2 enters the intercellular space and micropores more fully, significantly increasing the effective area for subsequent solute migration. The burst mode reduces the average input power while maintaining the peak effect intensity, reducing local temperature rise, thus taking into account both the strengthening and oxidation inhibition objectives. Medium-pressure section: In the medium-pressure section, the CO2 density increases, the oil dissolving capacity is enhanced, and the "main extraction output" stage is entered. Applying ultrasound can enhance the renewal rate of the extractant in the outer boundary layer of the particles, reduce external diffusion resistance, shorten the time for solute to migrate from the inside of the particles to the fluid phase, increase the extraction yield per unit time, reduce bed channeling, and improve the uniformity of CO2 contact with materials. High-pressure section: CO2 density is highest under high pressure, and its ability to dissolve oil is strongest. Turning off the ultrasound at this time can prevent the generation of free radicals caused by the high-intensity sound field. Pure supercritical fluid is used to efficiently extract residual oil. The three-stage cycle is repeated, and each time the pressure is reduced and then increased, it promotes the "breathing" rupture of the cell wall, which greatly improves the extraction rate. Soybean lecithin acts as a surfactant / interface stabilizer, improving the distribution and accessibility of rosmarinic acid at the oil-solid interface, enabling rosmarinic acid to act more effectively on the "easily oxidized interface." On the other hand, as a phospholipid byproduct, it can complex / encapsulate and passivate trace oxidizing impurities (such as trace metal ions and peroxides) in oils, indirectly reducing the oxidation rate. Rosmarinic acid contains multiple phenolic hydroxyl groups, which can efficiently capture free radicals and interrupt chain oxidation reactions; at the same time, it can regenerate the antioxidant groups consumed in phospholipid oxidation; when the two are combined, lecithin provides a physical barrier and chelates with metals, while rosmarinic acid plays a free radical scavenging role, resulting in a synergistic antioxidant effect of 1+1>2.

[0015] Example 1

[0016] Take dried Torreya grandis kernels with a moisture content of 8%, and pulverize them to 80μm at -20℃ under nitrogen protection to obtain Torreya grandis powder; Soybean lecithin and rosmarinic acid were added to Torreya grandis powder at amounts of 0.5% and 0.2% of the powder's mass, respectively. After mixing thoroughly, the mixture was premixed at -10°C for 10 minutes under nitrogen protection. The mixed Torreya grandis kernel powder was loaded into a supercritical extraction vessel, CO2 was introduced, and the mixture was pre-soaked for 10 min at a pressure of 8 MPa and a temperature of 30℃. Supercritical CO2 was introduced into the extraction vessel, and periodic pressure swing extraction was employed, using a three-stage cycle of "low pressure-medium pressure-high pressure," with each cycle lasting 12 minutes, for a total of 8 cycles and a total extraction time of 1.5 hours. Specifically, the low-pressure stage consisted of: 12 MPa, 30°C, 1 minute, with an applied ultrasonic power of 300 W, operating in burst mode with a peak power to average power ratio of 5:1. Each burst pulse contained 5 carrier cycles, with a burst repetition frequency of 50 Hz and a burst duty cycle of 1%, where the burst duty cycle was the ratio of the duration of each burst pulse to the burst repetition period. The medium-pressure stage consisted of: 24 MPa, 38°C, 6 minutes, with an applied ultrasonic power of 80 W. The high-pressure stage consisted of: 34 MPa, 40°C, 3 minutes, with the ultrasonic power turned off. The CO2 circulation mass flow rates were: 5 kg / h for the low-pressure stage, 20 kg / h for the medium-pressure stage, and 30 kg / h for the high-pressure stage. First-stage separation: pressure 10 MPa, temperature 30℃; Second-stage separation: pressure 5 MPa, temperature 28℃; Third-stage separation: pressure 1 MPa, temperature 25℃; The primary, secondary, and tertiary separation components were mixed uniformly at a mass ratio of 60:5:1 under nitrogen protection and at 20 degrees Celsius to obtain highly active Torreya grandis oil. Example 2

[0017] Take dried Torreya grandis kernels with a moisture content of 8%, and pulverize them to 190μm at -15℃ under nitrogen protection to obtain Torreya grandis powder; Soybean lecithin and rosmarinic acid were added to Torreya grandis powder at amounts of 0.5% and 0.2% of the powder's mass, respectively. After mixing thoroughly, the mixture was premixed at -5°C for 20 minutes under nitrogen protection. The mixed Torreya kernel powder was loaded into a supercritical extraction vessel, CO2 was introduced, and the mixture was pre-soaked for 15 min at a pressure of 14 MPa and a temperature of 40℃. Supercritical CO2 was introduced into the extraction vessel, and periodic pressure swing extraction was employed, using a three-stage cycle of "low pressure-medium pressure-high pressure," with each cycle lasting 16 minutes, for a total of 10 cycles and a total extraction time of 2.5 hours. Specifically, the low-pressure stage consisted of: 14 MPa pressure, 32.5℃ temperature, 1.5 minutes, with an applied ultrasonic power of 500 W, operating in burst mode with a peak power to average power ratio of 10:1. Each burst pulse contained 12 carrier cycles, a burst repetition frequency of 125 Hz, and a burst duty cycle of 10.5%. The medium-pressure stage consisted of: 27 MPa pressure, 40℃ temperature, 8 minutes, with an applied ultrasonic power of 115 W. The high-pressure stage consisted of: 37 MPa pressure, 42.5℃ temperature, 4 minutes, with the ultrasonic power turned off. The CO2 circulation mass flow rates were: 10 kg / h for the low-pressure stage, 27.5 kg / h for the medium-pressure stage, and 37.5 kg / h for the high-pressure stage. First-stage separation: pressure 14 MPa, temperature 32.5℃; Second-stage separation: pressure 7.5 MPa, temperature 30℃; Third-stage separation: pressure 2.5 MPa, temperature 27.5℃. The primary, secondary, and tertiary separation components were mixed uniformly at a mass ratio of 75:15:5 under nitrogen protection and at 22°C to obtain highly active Torreya grandis oil. Example 3

[0018] Take dried Torreya grandis kernels with a moisture content of 8%, and pulverize them to 250μm at -12℃ under nitrogen protection to obtain Torreya grandis powder; Soybean lecithin and rosmarinic acid were added to Torreya grandis powder at amounts of 0.5% and 0.2% of the powder's mass, respectively. After mixing thoroughly, the mixture was premixed at -3°C for 25 minutes under nitrogen protection. The mixed Torreya grandis kernel powder was loaded into a supercritical extraction vessel, CO2 was introduced, and the mixture was pre-soaked for 18 min at a pressure of 17 MPa and a temperature of 45℃. Supercritical CO2 was introduced into the extraction vessel, and periodic pressure swing extraction was performed using a three-stage cycle of "low pressure-medium pressure-high pressure," with each cycle lasting 18 minutes, for a total of 11 cycles and a total extraction time of 3.0 h. Specifically, the low-pressure stage consisted of: 15 MPa pressure, 34℃ temperature, 1.8 min time, with an applied ultrasonic power of 600 W, operating in burst mode with a peak power to average power ratio of 12:1. Each burst pulse contained 16 carrier cycles, with a burst repetition frequency of 160 Hz and a burst duty cycle of 15%, where the burst duty cycle was the ratio of the duration of each burst pulse to the burst repetition cycle. The medium-pressure stage consisted of: 28 MPa pressure, 41℃ temperature, 9 min time, with an applied ultrasonic power of 130 W. The high-pressure stage consisted of: 38 MPa pressure, 44℃ temperature, 4.5 min time, with the ultrasonic power turned off. The CO2 circulation mass flow rate was: 12 kg / h for the low-pressure stage, 30 kg / h for the medium-pressure stage, and 40 kg / h for the high-pressure stage. First-stage separation: pressure 16 MPa, temperature 34℃; Second-stage separation: pressure 8 MPa, temperature 31℃; Third-stage separation: pressure 3 MPa, temperature 29℃; The primary separation component, the secondary separation component and the tertiary separation component were mixed evenly at a mass ratio of 80:25:10 under nitrogen protection and at 23°C to obtain highly active Torreya grandis oil. Example 4

[0019] Take dried Torreya grandis kernels with a moisture content of 8%, and pulverize them to 300μm at -10℃ under nitrogen protection to obtain Torreya grandis powder; Soybean lecithin and rosmarinic acid were added to Torreya grandis powder at amounts of 0.5% and 0.2% of the powder's mass, respectively. After mixing thoroughly, the mixture was premixed at 0°C for 30 minutes under nitrogen protection. The mixed Torreya grandis kernel powder was loaded into a supercritical extraction vessel, CO2 was introduced, and the mixture was pre-soaked for 20 min at a pressure of 20 MPa and a temperature of 50℃. Supercritical CO2 was introduced into the extraction vessel, and periodic pressure swing extraction was performed using a three-stage cycle of "low pressure-medium pressure-high pressure," with each cycle lasting 20 minutes, for a total of 12 cycles and a total extraction time of 3.5 hours. Specifically, the low-pressure stage consisted of: 16 MPa pressure, 35°C temperature, 2 minutes, with an applied ultrasonic power of 700 W, operating in burst mode with a peak power to average power ratio of 15:1. Each burst pulse contained 20 carrier cycles, with a burst repetition frequency of 200 Hz and a burst duty cycle of 20%, where the burst duty cycle was the ratio of the duration of each burst pulse to the burst repetition cycle. The medium-pressure stage consisted of: 30 MPa pressure, 42°C temperature, 10 minutes, with an applied ultrasonic power of 150 W. The high-pressure stage consisted of: 40 MPa pressure, 45°C temperature, 5 minutes, with the ultrasonic power turned off. The CO2 circulation mass flow rate was: 15 kg / h for the low-pressure stage, 35 kg / h for the medium-pressure stage, and 45 kg / h for the high-pressure stage. First-stage separation: pressure 18 MPa, temperature 35℃; Second-stage separation: pressure 10 MPa, temperature 32℃; Third-stage separation: pressure 4 MPa, temperature 30℃; The primary, secondary, and tertiary separation components were mixed uniformly at a mass ratio of 90:30:15 under nitrogen protection and at 20–24 °C to obtain highly active Torreya grandis oil. Comparative Example 1 The difference from Example 2 is that: during the extraction process, a single pressure (27 MPa, temperature 40°C) extraction was used, without the three-stage "low pressure-medium pressure-high pressure" cycle, and the total extraction time was 2.5 h. Other conditions were the same as in Example 2. Comparative Example 2 The difference from Example 2 is that: in the extraction process, 500 W of ultrasound is applied throughout, the pressure is kept constant at 27 MPa, and other conditions are the same as in Example 2; Comparative Example 3 The difference from Example 2 is that the ultrasound was turned off during the extraction process, while other conditions remained the same as in Example 2; performance testing... The method for testing peroxide value is based on GB19111-2003; The performance of the Torreya grandis oil prepared in Example 14 and Comparative Example 13 was tested, and the results are shown in Table 1. Table 1 As shown in Table 1, the peroxide value of the Torreya grandis oil prepared in Examples 1-4 was all below 0.64 mmol / kg, which was far superior to that of the comparative example. This indicates that the method effectively protected the activity of the oil, significantly reduced the degree of oxidation, and obtained higher quality Torreya grandis oil. The extraction rate of Examples 1-4 was all higher than 46.12%, which was significantly higher than that of the comparative example. This proves that the three-stage cyclic pressure swing extraction process of "low pressure-medium pressure-high pressure" combined with ultrasound-assisted extraction can more effectively extract the oil from Torreya grandis kernels. To further optimize the additive ratio, the extraction process conditions of Example 1 were fixed, and the amount of soybean lecithin and rosmarinic acid added were adjusted as shown in Table 2. Table 2 The performance of the Torreya grandis oil prepared in Example 511, Example 2 and Comparative Example 46 was tested, and the results are shown in Table 3. Table 3 As shown in Table 3, the synergistic addition of soybean lecithin and rosmarinic acid can significantly improve the quality of Torreya grandis oil and increase the extraction efficiency. When the amount of soybean lecithin added is fixed at 0.5%~1.3% and the amount of rosmarinic acid added is in the range of 0.05%~0.20%, the peroxide value of the prepared Torreya grandis oil is low (≤0.87 mmol / kg). Among them, the combination of soybean lecithin at 0.9%~1.3% and rosmarinic acid at 0.12%~0.20% (Examples 8-11) performed particularly well, with the peroxide value being lower than 0.52 mmol / kg, which is significantly better than Example 2.

[0020] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil, characterized in that, Includes the following steps: S1 Raw material preparation: Take dried Torreya grandis kernels (moisture content ≤10%), and pulverize them to 80-300μm under nitrogen protection at -20 to -10 ℃ to obtain Torreya grandis powder; S2 Protective Component Addition: Add soybean lecithin and rosmarinic acid to torreya powder at amounts of 0.5%–1.5% and 0.05%–0.2% of the torreya powder mass, respectively. After mixing evenly, premix at low temperature for 10–30 min under nitrogen protection and at -10–0℃. S3 Pre-soaking: The mixed Torreya grandis kernel powder is loaded into a supercritical extraction vessel and CO2 is introduced for pre-soaking for 10-20 minutes; S4 Extraction: Supercritical CO2 is introduced into the extraction vessel, and periodic pressure swing extraction is adopted. The extraction process is a three-stage cycle of "low pressure-medium pressure-high pressure", with each cycle lasting 12 to 20 minutes, a total of 8 to 12 cycles, and a total extraction time of 1.5 to 3.5 hours. S5 Three-stage separation: Supercritical CO2 carrying Torreya oil is sequentially fed into the first-stage separation vessel, the second-stage separation vessel and the third-stage separation vessel. The extract is fractionated and collected under corresponding pressure and temperature conditions. The separated CO2 is recovered to the CO2 storage tank and recycled after condensation / gas-liquid separation. S6 compounding: The primary, secondary, and tertiary separation components are mixed under nitrogen protection and at a temperature below 25°C to obtain highly active Torreya grandis oil.

2. The method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil according to claim 1, characterized in that: In step S4, Low-pressure section: pressure 12-16 MPa, temperature 30-35℃, time 1-2 min, applied ultrasonic power 300-700 W; Medium pressure section: pressure 24-30 MPa, temperature 38-42℃, time 6-10 min, applied ultrasonic power 80-150 W; High-pressure section: pressure 34-40 MPa, temperature 40-45℃, time 3-5 min, turn off ultrasound.

3. The method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil according to claim 1, characterized in that: In step S5, First-stage separation: pressure 10-18 MPa, temperature 30-35℃; Two-stage separation: pressure 5-10 MPa, temperature 28-32℃; Three-stage separation: pressure 1-4 MPa, temperature 25-30℃.

4. The method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil according to claim 1, characterized in that: The pre-impregnation pressure in step S3 is 8–20 MPa, and the temperature is 30–50°C.

5. The method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil according to claim 2, characterized in that: In the periodic pressure swing extraction process described in step S4, the circulating mass flow rate of CO2 is: 5-15 kg / h in the low-pressure section, 20-35 kg / h in the medium-pressure section, and 30-45 kg / h in the high-pressure section.

6. The method for ultrasound-assisted supercritical CO2 extraction of highly active Torreya grandis oil according to claim 2, characterized in that: In step S4, the low-pressure ultrasound operates in burst mode, wherein the burst duty cycle is the ratio of the duration of each burst pulse to the burst repetition period. The low-pressure ultrasound operates in burst mode with a peak power to average power ratio of 5:1 to 15:

1. Each burst pulse contains 5 to 20 carrier cycles, the burst repetition frequency is 50 to 200 Hz, and the burst duty cycle is 1% to 20%.

Images