Study Of Temperature Field Reconstruction Algorithm And Experiment Based On Ultrasonic Thermometry

As a new heating method,microwave heating is widely used in metallurgy,chemical industry and other fields.Comapared with common heating techniques,microwave heating applies miacrowave chracteristics of strong penetrability and high energy,so that microwave could penetrate heated medium in a short time,and directly generate volume heat after interacting reciprocally,which reduces heating time,saves energy and barely cause second pollution.However,during the process of microwave heating,the dielectric properties of the heated medium change with time under the influence of high power microwave.Then,the external electromagnetic field of the medium is unevenly distributed,which results in hot spots in the medium.At the same time,the temperature of the heated medium and its microwave absorption capacity are positive feedback,which leads to a sudden increase in the temperature of the medium and the phenomenon of heat out of control.Therefore,the research of temperature distribution detection technology applied in industrial microwave electromagnetic has become an important research topic in the field of microwave heating.But,traditional temperature detection methods are difficult to be used in microwave heating environment.This paper is supported by National Basic Research Pragram of China(973 Program)“The real-time intelligent control theory and key technologies of microwave sources based on load characteristics”.The key issue of this paper is temperature detection within the heated medium during the period of microwave heating.Temperature field reconstruction algorithms based on ultrasonic thermometry are proposed to reconstruct the temperature distribution inside the heated medium.The research route is that: firstly,single path temperature detection method is investigated,secondly,two-dimensional temperature field reconstruction algorithm is introduced,finally,three-dimensional temperature field reconstruction algorithm is discussed.The algorithms are verified in simulation and experiment environment and potentially applied to provide real-time and accurate temperature information for temperature control strategy of the heated medium.Thus,the hot spots and thermal runaway could be avoided and the safety control for microwave source is achieved.For the reconstruction of temperature field in two-dimensional plane and three-dimensional space,this paper proposes two kinds of two-dimensional temperature field reconstruction algorithms and one kind of three-dimensional temperature field reconstruction algorithm.In the experiment of temperature field reconstruction,a method for measuring ultrasonic time-of-flight is presented.The main research content in this paper includes the following five parts:(1)The paper introduces research background and significance,reviews temperature detection methods,temperature field reconstruction algorithms and the research status of ultrasonic thermometry at home and abroad and proposes the principle of acoustic temperature detection in detail.(2)The temperature field reconstruction algorithm based on least square method(LSM)is considered.This algorithm first obtains temperature values of finite points in testing temperature zone.Then,temperature field in the testing temperature zone could be reconstructed by interpolating.However,the temperature information of border area in the reconstruction results with LSM is missing,because the interpolation scope is limited and ultrasonic transducer location information of the border area is hardly gained.Thus,LSM cannot reflect the characteristics of the temperature distribution in the testing temperature zone.This paper presents a two-dimensional temperature field reconstruction algorithm based on radial basis function and expresses the method in detail.Compared with LSM,the simulation experiment results show that the proposed algorithm solves the problem about temperature information missing of the border area,reduces reconstruction error,improves reconstruction precision and temperature field reconstruction algorithm performance.(3)The characters of least square method and basis radial function are analyzed.Combing the characters,a modified algorithm for temperature field reconstruction based on least square method and basis radial function(LSM-RBF)is suggested.First,the temperature value in each divided block's center is acquired by least square method.Then,these temperature values are used as unknown sampled points of temperature field function and approximated by radial basis function.Finally,temperature field in testing temperature zone is reconstructed indirectly.Compare with LSM and RBF,the simulation experiment results with modified reconstruction algorithm indicate that LSM-RBF,which fully adopts the advantages of least square method in precision and radial basis function in terms of function approximation,relatively and accurately reveals the temperature distribution in the testing temperature zone and owns the smallest reconstruction error and the highest reconstruction precision.The temperature field reconstruction algorithm performance is improved further.(4)Based on the research work of temperature field reconstruction algorithm in two-dimensional plane,temperature filed reconstruction of three-dimensional space is investigated.This paper presents an algorithm for three-dimensional temperature field reconstruction based on radial basis function.In simulation environment,four three-dimensional space temperature field models with varying degrees of complexity are designed and the models are reconstructed in a rectangular cavity with proposed reconstruction algorithm.The reconstruction results show that the proposed algorithm with excellent reconstruction performance can reconstruct the temperature distribution of the testing three-dimensional space entirety and accurately,which is expected to provide theoretical support for future related research.(5)Based on research work of temperature field reconstruction algorithms,actual experiment is conducted.Temperature detection system with ultrasonic thermometry is built,which consists of signal generator,ultrasonic transmitting/receiving transducers,signal conditioning circuit,storage module,controller,multichannel gating module and PC.A method based on double excitations and double echoes for estimating ultrasonic flying time is proposed.Nine separate ultrasonic transducers are installed around a square testing area(1m?1m).When the area is heated by a heat source(simulating one-heat symmetrical heating and one-heat asymmetrical heating),temperature field in the area is reconstructed by combing RBF and the proposed method for estimating ultrasonic flying time.Reconstruction results show that the constructed system makes full use of practicability of the split ultrasonic transmitting/receiving transducer,accurately reconstructs the two-dimensional temperature distribution of the testing area and indirectly reflects the feasibility of reconstruction algorithm and the effectivity of the proposed method for estimating ultrasonic flying time.