The Research On Radio Frequency Thawing Mechanism And Adaptive Radio Frequency Power

As one of the national strategic reserve resources,frozen meat has always occupied a certain share in the market,and it must be thawed before used.Traditional thawing methods such as air thawing and water thawing have a slow thawing rate,serious quality loss and easy occurrence by microbial infection,and microwave thawing has a serious uneven temperature.The principle of radio frequency thawing is similar to microwave thawing,both rely on electromagnetic fields to generate heat through the interaction of polar molecules in frozen meat.But its wavelength is longer and the penetration depth is larger,so the thawing rate and the thawing uniformity can be balanced,and at the same time,it is easier to control,and can effectively avoid the thawing problems such as declining quality.In order to study the mechanism of RF thawing and the influence of external factors on thawing effect,based on the effective specific heat method,the material property change in the thawing process is fitted into piecewise functions,and then established a electrostatic field-heat conduction bidirectional coupling model by using the finite element simulation software,to study the effect of the position of frozen pork,the distance between the electrode plates and the voltage waveform.The results show that the larger the distance between the plates,the slower the thawing rate,and the more uniform of temperature distribution,the distance between the plates is nonlinear with the thawing speed.When the voltage waveform is a square,the thawing rate is faster but the temperature uniformity is poorer,the overheating area is concentrated in the middle of frozen meat.When the voltage waveform is a sine,the overheating area is concentrated on the corners and edges.The frozen meat is located in the middle of the two plates has a higher thawing rate and better thawing uniformity than it on the lower plate.According to the simulation results,the thawing effect is best when the frozen pork is located in the middle of two plate,the voltage waveform is sine,and the distance between two polar plates is 7.5 cm.Frozen meat parameters change in real time during thawing,which makes the load impedance change all the time,so it makes a higher requirements for RF power.Under this circumstance,a medium RF power with adjustable frequency,power and Impedance matching is designed.The RF signal source is based on direct digital frequency synthesis and can realize a minimum of 0.04Hz of frequency adjustment,the RF signal enters an amplification circuit after low-pass filtering.A varistor is connected in series at the input of the amplification circuit,so as to realize power adjustment by adjusting the size of the input signal.The amplified signal is applied to the load through an automatic impedance matching network,which uses a dual directional coupler to monitor the incident signal and the reflected signal on the signal transmission line.After processing,it is transmitted to the microcomputer,and the microcomputer finds the optimal impedance through the impedance matching algorithm.Then the component value in the network is changed by controlling the rotation angle of the motor,thereby achieving automatic matching of the impedance.