Thermographic micro-imaging based hot-wire MEMS sensor testing device and measurement method thereof

Abstract

The present application relates to the technical field of sensor measurement evaluation, and particularly relates to a hot-wire MEMS sensor testing device based on microscopic thermal imaging technology and a measurement method thereof, which comprises an acoustic emission unit, an acoustic receiving unit and an MTIT thermal field monitoring unit working in cooperation with each other, the acoustic emission unit is composed of a horizontal and vertical high-precision positioning support, an acoustic emitter, a power amplifier, an acoustic spectrum analyzer and a full anechoic chamber, and is used to generate uniform sound fields of different frequencies; the acoustic receiving unit is composed of a slidable clamp, a horizontal high-precision positioning long support rod, a standard vector microphone and a signal acquisition and analysis instrument, and is used to receive sound field information at a certain position in the full anechoic chamber; the MTIT thermal field monitoring unit is composed of a slidable clamp, a horizontal high-precision positioning short support rod, a refrigeration focal plane detector and an infrared microscopic objective, and is used to monitor real-time changes of the thermal field of the thermal sensing module of the hot-wire MEMS sensor, and the present application can provide comprehensive evaluation of the performance of the hot-wire MEMS sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensor measurement evaluation, and particularly relates to a hot-wire MEMS sensor testing device based on microscopic thermal imaging technology and a measurement method thereof. BACKGROUND

[0002] Vector sensors can simultaneously grasp the scalar and vector information of the sound field, and have unique advantages in capturing target direction and trajectory information, and are particularly suitable for working in a low marine background noise environment, and are of great significance to the field of detecting low-observable targets such as submarines and unmanned platforms. The hot-wire vector sensor based on micro-electro-mechanical system (MEMS) performs better than other types of vector sensors in low-frequency detection, and can realize a test frequency of at least 5 Hz. However, there is still a significant gap between the actual engineering application and the theoretical research of domestic MEMS hot-wire sensors, especially in the field of underwater acoustic sensing and detection in extremely low frequency and high water pressure environment. To fill this gap and improve performance, the key lies in the precise control of each link of the sensor and the comprehensive understanding of its thermal dynamics, fluid mechanics and acoustic characteristics. At present, the test method mainly evaluates the overall acoustic characteristics of the hot-wire vector sensor based on the acoustic standing wave tube, and can only analyze the data after the electronic warehouse processing, but cannot quantitatively measure the acoustic-induced heat convection, the key part of the sensor, to evaluate its accuracy and stability. Therefore, a new device or technical method is developed to accurately measure and evaluate the distribution of the thermal field and the flow field in the MEMS hot-wire vector sensor, which can provide guidance for developing fine testing technology for local components of new MEMS hot-wire vector sensors and help to find and solve key problems in the research and development stage. SUMMARY

[0003] In view of the deficiencies in the prior art, the present application aims to provide a hot-wire MEMS sensor testing device based on microscopic thermal imaging technology and a measurement method thereof, which is used for measuring the temperature sensing sensitivity of the hot-wire MEMS vector sensor, reflecting the strength of temperature change in the sensor within the measurement range, and analyzing the matching degree between the output thermal field of the hot-wire MEMS sensor and the real thermal field output by the MTIT, the real flow field based on the MEMS three-suspended hot-wire model in the hot-wire MEMS sensor and the real flow field, and the matching degree between the flow field calculated by the MTIT based on the MEMS three-suspended hot-wire model and the real flow field, to provide fine data guidance for the development of the hot-wire MEMS vector sensor.

[0004] In order to achieve the above object, the present application provides the following technical scheme: a hot-wire type MEMS sensor testing device based on microscopic thermal imaging technology, comprising a sound emitting unit, a sound receiving unit and an MTIT thermal field monitoring unit which work cooperatively, the sound emitting unit is composed of horizontal and vertical high-precision positioning support, sound emitter, power amplifier, sound spectrum instrument and full anechoic chamber, and is used to generate uniform sound field of different frequencies; the sound receiving unit is composed of slidable clamp, horizontal high-precision positioning long support rod, standard vector microphone and signal acquisition and analysis instrument, and is used to receive sound field information of a position in the full anechoic chamber; the MTIT thermal field monitoring unit is composed of slidable clamp, horizontal high-precision positioning short support rod, refrigeration focal plane detector and infrared microscopic objective, and is used to monitor real-time change of thermal field of the hot-wire type MEMS sensor thermal sensing module, and the sound emitting unit, the sound receiving unit and the MTIT thermal field monitoring unit work cooperatively through computer and peripherals.

[0005] In order to achieve the above object, the present application also provides the following technical scheme: a measurement method of the hot-wire type MEMS sensor testing device based on microscopic thermal imaging technology, according to the hot-wire type MEMS sensor testing device, the steps are as follows:

[0006] Step one: determine relevant physical information of the hot-wire type MEMS sensor, including distance between the hot wires, type of internal filling liquid, and thermal conductivity, specific heat capacity and density of the liquid;

[0007] Step two: build horizontal and vertical high-precision positioning support, and move the slidable clamp to the specified position, install the infrared microscopic objective on the horizontal high-precision positioning short support rod, install the MEMS sensor to be tested and the standard vector microphone at the same height on the horizontal high-precision positioning long support rod, arrange the sound emitter under the MEMS sensor to be tested and the standard vector microphone, and connect the instruments including power amplifier, sound spectrum instrument, signal acquisition and analysis instrument, refrigeration focal plane detector, computer and peripherals, etc.

[0008] Step three: start the sound emitter, so that the test area forms a stable sound field, the sound field shows uniformity in the horizontal direction, that is, the sound pressure of each point at the same height should be equal, and the environmental temperature value is recorded;

[0009] Step four: use the standard vector microphone to obtain the sound field information in the test area, and ensure that the sound field is in a stable state, at the same time, start the hot-wire type MEMS sensor, confirm the initial power value of the hot-wire excitation, record the real-time resistance temperature change value of the hot wire and the generated sound field information, in addition, start the infrared microscopic objective, and collect the internal temperature field distribution information of the hot-wire type MEMS sensor;

[0010] Step five: data import post-processing program, the post-processing program module calculates the temperature field sensing sensitivity by formula, and analyzes the matching degree of the thermal field output by the hot-wire MEMS sensor and the real thermal field output by the MTIT, the flow field calculated based on the MEMS three-suspended hot-wire model in the hot-wire MEMS sensor and the real flow field, and the matching degree of the flow field calculated based on the MEMS three-suspended hot-wire model by the MTIT and the real flow field.

[0011] In some embodiments, the calculation formula in step five is:

[0012] M T-MTIT = T MTIT-center / p

[0013] T MTIT-matched-degree = T / T MTIT-center

[0014]

[0015] In the formula, M T-MTIT is the temperature field sensing sensitivity, T MTIT-center is the temperature at the center hot-wire position of the hot-wire MEMS sensor thermal sensing module obtained by micro-thermal imaging technology, p is the sound pressure value collected by the standard vector microphone, T MTIT-matched-degree is the matching degree of the thermal field output by the hot-wire MEMS sensor and the real thermal field output by the MTIT, T is the temperature value of the center hot-wire, c f is the specific heat capacity of the liquid filled in the hot-wire MEMS sensor, ρ f is the density of the liquid filled in the hot-wire MEMS sensor, u sim-centre is the theoretical flow velocity near the center hot-wire of the hot-wire MEMS sensor thermal sensing module, Δh is the distance between adjacent two hot-wires, Q is the heat source power of the hot-wire MEMS sensor, k is the thermal conductivity of the liquid filled in the hot-wire MEMS sensor, T1, T2, and T3 are the temperatures of the upper, middle, and lower hot-wires, respectively, u sim-MTIT-centre is the flow velocity calculated from the hot-wire temperature values of the hot-wire MEMS sensor thermal sensing module obtained by micro-thermal imaging technology, T 1-MTIT , T 2-MTIT , and T 3-MTIT are the temperatures of the upper, middle, and lower hot-wires, respectively, obtained by micro-thermal imaging technology, u MTIT-matched-degree is the matching degree of the flow field calculated based on the MEMS three-suspended hot-wire model by the MTIT and the real flow field, u sim-matched-degree is the matching degree of the flow field calculated based on the MEMS three-suspended hot-wire model in the hot-wire MEMS sensor and the real flow field, and u real is the particle velocity obtained by the standard vector microphone.

[0016] In some embodiments, in step two, the measuring device should be arranged in an anechoic chamber environment to reduce the influence of environmental noise on the test.

[0017] In some embodiments, in step four, the hot-wire MEMS sensor, the standard vector microphone and the infrared microscope are realized to realize synchronous real-time acquisition.

[0018] In some embodiments, in step five, based on the MEMS three-suspended hot-wire model of steady-state heat transfer, the finite difference method is used to obtain the flow field data near the center hot-wire.

[0019] Compared with the prior art, the beneficial effects of the present application are: the present application is used for evaluating the effectiveness of sensor data measurement. The device comprises a sound emitting unit, a sound receiving unit and an MTIT heat field monitoring unit which work together, based on the finite difference method, the temperature field sensing sensitivity is obtained through the relationship between temperature and sound pressure, the matching degree of the output heat field of the hot-wire MEMS sensor, the real heat field output by the MTIT, the flow field calculated based on the MEMS three-suspended hot-wire model in the hot-wire MEMS sensor and the real flow field, and the flow field calculated based on the MEMS three-suspended hot-wire model by the MTIT and the real flow field are analyzed, so as to accurately measure and evaluate the distribution of the heat field and the flow field in the MEMS hot-wire vector sensor, which can provide guidance for developing fine test new type MEMS hot-wire vector sensor local components, and help to find and solve key problems in the research and development stage.

[0020] The test device and the measurement method provided by the present application innovatively integrate acoustic and thermodynamic technologies, and can provide a method for comprehensively evaluating the performance of the hot-wire MEMS sensor. The highlights of the device and the method are stable sound field, heat field information acquisition, temperature field sensing sensitivity calculation and real-time monitoring and post-processing, which provide a new method with better effect for performance evaluation of the hot-wire MEMS sensor, and are expected to promote the research and development in this field.

[0021] The details of one or more embodiments of the present application are presented in the following drawings and description to make the other features, purposes and advantages of the present application more concise and easy to understand, and to make the present application more fully described and understood through the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the test device of the present application;

[0023] Figure 2 It is a flowchart of the measurement method of the present application. DETAILED DESCRIPTION

[0024] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0025] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application. Figure 1 The present application provides a technical solution: a hot-wire type MEMS sensor testing device based on microscopic thermal imaging technology, comprising a sound emitting unit, a sound receiving unit and an MTIT thermal field monitoring unit which work cooperatively, the sound emitting unit is composed of a horizontal and vertical high-precision positioning support 1, a sound emitter 2, a power amplifier, a sound spectrum instrument and a full anechoic chamber, used to generate uniform sound field of different frequencies; the sound receiving unit is composed of a slidable clamp, a horizontal high-precision positioning long support rod 7, a standard vector microphone 3 and a signal acquisition and analysis instrument, used to receive sound field information at a certain position in the full anechoic chamber; the MTIT thermal field monitoring unit is composed of a slidable clamp 8, a horizontal high-precision positioning short support rod 6, a refrigeration focal plane detector and an infrared microscopic objective 5, used to monitor the real-time change of the thermal field of the hot-wire type MEMS sensor 4 thermal sensing module, and the sound emitting unit, the sound receiving unit and the MTIT thermal field monitoring unit work cooperatively through a computer and peripherals.

[0026] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application. Figure 1 The hot-wire type MEMS sensor 4 to be measured should be placed in the full anechoic chamber for 1 hour to balance the internal and ambient temperature. The hot-wire type MEMS sensor 4 to be measured is installed in the full anechoic chamber environment through the horizontal high-precision positioning long support rod 7, wherein the horizontal high-precision positioning long support rod 7 is selected to be a carbon fiber hollow thin rod with a diameter of 1 cm to reduce the influence of the support rod on the sound field, and the front section of the rod is arranged with the slidable clamp 8.

[0027] The standard vector microphone 3 is installed at the same height as the hot-wire type MEMS sensor 4 to be measured, and the height should be at least 2-3 times greater than the maximum dimension of the hot-wire type MEMS sensor 4 to ensure the stability of the sound field. The standard vector microphone is used to measure the real particle velocity at the installation height of the sensor.

[0028] The infrared microscopic objective 5 is installed on the left side of the hot-wire type MEMS sensor 4 to be measured using the horizontal high-precision positioning short support rod 6, the infrared microscopic objective 5 is connected with the refrigeration focal plane detector, and is connected with the computer and peripherals through the IEEE488 bus to realize synchronous temperature field data acquisition.

[0029] The sound emitter 2 is arranged on the upper part of the horizontal and vertical high-precision positioning support 1, and the sound emitter 2 is connected with the power amplifier and the sound spectrum instrument to generate sound waves of different frequencies.

[0030] The collection analyzer, the refrigeration focal plane detector and the sound spectrum meter are connected with the computer and the peripherals through the IEEE 488 connection line, so that the standard vector microphone 3, the hot-wire MEMS sensor 4 to be tested and the infrared microscopic objective 5 realize synchronous data collection.

[0031] The measurement method of the hot-wire MEMS sensor testing device based on the microscopic thermal imaging technology, according to the hot-wire MEMS sensor testing device, the steps are:

[0032] Step one: determine the relevant physical information of the hot-wire MEMS sensor 4, including the distance between the hot wires Δh, the type of the internal filling liquid, and the thermal conductivity k, the specific heat capacity c and the density ρ of the liquid; f f ;

[0033] Step two: build a horizontal and vertical high-precision positioning support 1, move the slidable clamp 8 to the specified position, install the infrared microscopic objective 5 on the horizontal high-precision positioning short support rod 6, install the MEMS sensor 4 to be tested and the standard vector microphone 3 at the same height d0 of the horizontal high-precision positioning long support rod, arrange the sound emitter 2 under the MEMS sensor 4 to be tested and the standard vector microphone 3, and connect the instruments including the power amplifier, the sound spectrum meter, the signal collection and analysis instrument, the refrigeration focal plane detector, the computer and the peripherals;

[0034] Step three: start the sound emitter 2 to form a stable sound field in the test area, the sound field shows uniformity in the horizontal direction, that is, the sound pressures of each point at the same height should be equal, and the environmental temperature value is recorded;

[0035] Step four: use the standard vector microphone 3 to obtain the sound field information in the test area, and ensure that the sound field in the action area of the sound emitter 2 is in a stable state. At the same time, start the hot-wire MEMS sensor 4, confirm the initial power value Q of the hot-wire excitation, and record the real-time resistance (temperature) change values T1, T2 and T3 of the hot wire and the generated sound field information. In addition, start the infrared microscopic objective 5 to collect the real-time distribution information of the internal temperature field of the hot-wire MEMS sensor, determine the temperature field distribution after the temperature field distribution is stable, and extract the temperature values T 1-MTIT , T 2-MTIT , T 3-MTIT ;

[0036] Step five: data import post-processing program, the post-processing program module calculates the temperature field sensing sensitivity through the following formula, and analyzes the matching degree of the output hot field of the hot-wire MEMS sensor and the real hot field output by the MTIT, the flow field calculated based on the MEMS three-suspended hot-wire model in the hot-wire MEMS sensor and the real flow field, and the flow field calculated based on the MEMS three-suspended hot-wire model in the MTIT and the real flow field: ​

[0037] M T-MTIT = T MTIT-center / p

[0038] T MTIT-matched-degree = T / T MTIT-center

[0039]

[0040] In the formula, M T-MTIT is the temperature field sensing sensitivity, T MTIT-center is the temperature at the center hot wire position of the hot-wire MEMS sensor thermal sensing module obtained by using the micro-thermal imaging technology, p is the sound pressure value collected by the standard vector microphone, T MTIT-matched-degree is the matching degree of the output thermal field of the hot-wire MEMS sensor and the real thermal field output by the MTIT, T is the temperature value of the center hot wire, c f is the specific heat capacity of the liquid filled in the hot-wire MEMS sensor, p f is the density of the liquid filled in the hot-wire MEMS sensor, u sim-centre is the theoretical flow velocity near the center hot wire of the hot-wire MEMS sensor thermal sensing module, Dh is the distance between two adjacent hot wires, Q is the heat source power of the hot-wire MEMS sensor, k is the thermal conductivity of the liquid filled in the hot-wire MEMS sensor, T1, T2 and T3 are the temperatures of the upper, middle and lower hot wires respectively, u sim-MTIT-centre is the flow velocity calculated by the hot wire temperature values of the hot-wire MEMS sensor thermal sensing module obtained by using the micro-thermal imaging technology, T 1-MTIT , T 2-MTIT , and T 3-MTIT are the temperatures of the upper, middle and lower hot wires respectively obtained by using the micro-thermal imaging technology, u MTIT-matched-degree is the matching degree of the flow field calculated by the MEMS three-suspended hot wire model and the real flow field based on the MEMS three-suspended hot wire model, u sim-matched-degree is the matching degree of the flow field calculated by the hot-wire MEMS sensor based on the MEMS three-suspended hot wire model and the real flow field, u real is the particle vibration velocity obtained by the standard vector microphone.

[0041] In step two, the measuring device should be arranged in a full anechoic chamber environment to reduce the influence of environmental noise on the test.

[0042] In step four, the hot-wire MEMS sensor, the standard vector microphone and the infrared microscope objective lens realize synchronous real-time collection.

[0043] In step five, based on the MEMS three-suspended hot wire model of steady-state heat transfer, the flow field data near the center hot wire is obtained by using the finite difference method.

[0044] By the technical scheme, accurate data can be provided for research and development of the hot-wire MEMS sensor and performance of the hot-wire MEMS sensor is evaluated, and the technical scheme is especially suitable for fields such as extremely low ocean noise environment investigation, high stealth submarine and unmanned platform positioning. The technical scheme fills the technical blank in the field, and provides important tools and data support for scientific research and engineering application.

[0045] The above embodiments only express several implementation manners of the application, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the patent scope of the application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the application, and these all belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

[0046] Although the embodiments of the application have been shown and described, it should be understood that, for ordinary skilled persons in the art, various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A hot-wire MEMS sensor testing device based on microthermography technology, characterized by: It includes an acoustic emission unit, an acoustic receiving unit and an MTIT thermal field monitoring unit that work in conjunction with each other. The acoustic emission unit consists of a horizontal and vertical high-precision positioning bracket, an acoustic emitter, a power amplifier, a sound spectrometer and a full anechoic chamber to generate a uniform sound field of different frequencies; the acoustic receiving unit consists of a slidable fixture, a horizontal high-precision positioning long support rod, a standard vector microphone and a signal acquisition analyzer to receive sound field information at a certain position in the full anechoic chamber; The MTIT thermal field monitoring unit consists of a slidable fixture, a short horizontal high-precision positioning support rod, a cooled focal plane detector, and an infrared microscope objective lens. It is used to monitor real-time changes in the thermal field of the hot-wire MEMS sensor thermal sensing module. The acoustic emission unit, acoustic receiving unit, and MTIT thermal field monitoring unit work together through a computer and peripherals.

2. A measurement method for a hot-wire MEMS sensor test device based on microthermography technology, characterized in that: The hot-wire MEMS sensor testing device according to claim 1, wherein the steps are as follows: Step 1: Determine the relevant physical information of the hot wire MEMS sensor, including the spacing between the hot wires, the type of liquid filled inside, and the thermal conductivity, specific heat capacity, and density of the liquid; Step 2: Build a horizontal and vertical high-precision positionable bracket and move the sliding fixture to the designated position. Install the infrared microscope objective lens on the horizontal high-precision positioning short support rod. Install the MEMS sensor to be tested and the standard vector microphone at the same height on the horizontal high-precision positioning long support rod. Arrange the sound transmitter below the MEMS sensor to be tested and the standard vector microphone, and connect instruments including power amplifier, sound spectrometer, signal acquisition and analyzer, cooled focal plane detector, computer and peripherals. Step 3: Start the sound transmitter to form a stable sound field in the test area. The sound field shows horizontal uniformity, that is, the sound pressure at each point at the same height should be equal, and record the ambient temperature value; Step 4: Use a standard vector microphone to obtain sound field information within the test area and ensure that the sound field is stable. Simultaneously, activate the hot-wire MEMS sensor, confirm the initial power value of the hot-wire excitation, and record the real-time resistance temperature change of the hot-wire and the generated sound field information. In addition, activate the infrared microscope objective lens to collect the temperature field distribution information inside the hot-wire MEMS sensor. Step 5: Import the data into the post-processing program. The post-processing program module calculates the temperature field perception sensitivity through the formula, and analyzes the matching degree between the thermal field output by the hot-wire MEMS sensor and the actual thermal field output by the MTIT, the flow field in the hot-wire MEMS sensor calculated based on the MEMS three-suspended hot-wire model and the actual flow field, and the flow field calculated by the MTIT based on the MEMS three-suspended hot-wire model and the actual flow field.

3. The measurement method of the hot-wire MEMS sensor testing device based on microthermography technology according to claim 2, characterized in that: The calculation formula in step 5 is: M T-MTIT =T MTIT-center / p T MTIT-matched-degree =T / T MTIT-center Where M T-MTIT is the temperature field perception sensitivity, T MTIT-center is the temperature at the center of the hot wire position of the hot wire MEMS sensor thermal sensing module obtained by microthermal imaging technology, p is the sound pressure value collected by the standard vector microphone, T MTIT-matched-degree is the matching degree between the thermal field output by the hot-wire MEMS sensor and the actual thermal field output by the MTIT, T is the temperature value of the central hot wire, c f is the specific heat capacity of the liquid filled in the hot wire MEMS sensor, ρ f is the density of the liquid filled in the hot wire MEMS sensor, u sim-centre is the theoretical flow velocity near the center hot wire of the hot wire MEMS sensor thermal sensing module, Δh is the distance between two adjacent hot wires, Q is the heat source power of the hot wire MEMS sensor, k is the thermal conductivity of the liquid filled in the hot wire MEMS sensor, T1, T2, T3 are the temperatures of the upper, middle and lower hot wires respectively, and u sim-MTIT-centre The flow rate is calculated from the temperature of the hot wire of the thermal sensing module of the hot wire MEMS sensor obtained by micro thermal imaging technology, T 1-MTIT ,T 2-MTIT ,T 3-MTIT are the temperatures of the upper, middle and lower hot wires obtained using microthermal imaging technology, u MTIT-matched-degree The matching degree between the flow field estimated by MTIT based on the MEMS three-suspended hot wire model and the real flow field, u sim-matched-degree The matching degree between the flow field calculated based on the MEMS three-suspended hot wire model and the real flow field in the hot wire MEMS sensor, u real The particle velocity is acquired by a standard vector microphone.

4. The measurement method of the hot-wire MEMS sensor testing device based on microthermography technology according to claim 2, characterized in that: In step 2, the measurement device should be placed in a fully anechoic chamber environment to reduce the impact of environmental noise on the test.

5. The measurement method of the hot-wire MEMS sensor testing device based on microthermography technology according to claim 2, characterized in that: In step 4, the hot-wire MEMS sensor, standard vector microphone and infrared microscope objective lens achieve synchronous real-time acquisition.

6. The measurement method of the hot-wire MEMS sensor testing device based on microthermography technology according to claim 3, characterized in that: In step five, based on the MEMS three-suspended hot wire model of steady-state heat transfer, the finite difference method is used to obtain the flow field data near the central hot wire.

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