Abstract: This paper introduces a control system for a microwave hyperthermia instrument based on the ARM series microprocessor S3C2410 and the WinCE embedded operating system. The hardware composition, structural characteristics, and software design methods are elaborated. This system integrates signal acquisition, communication, control, and recording functions, and boasts advantages such as small size, high precision, high speed, and strong data exchange capability, achieving intelligent control of the hyperthermia instrument. Keywords : embedded system; serial communication; WINCE; thread Introduction With the development of science and technology, various medical devices have emerged and been widely used. Among them, microwave therapy [1][2] has been promoted and applied in the medical industry for many years due to its superior hemostatic effect and minimal tissue damage. Its efficacy has been affirmed by the medical community. When microwaves act on the body tissues, they cause high-frequency oscillations of ions, water molecules and dipoles in the tissue cells. When a small dose of microwave is used, it produces a low-heat effect, enhances blood circulation in the affected area, accelerates metabolism, and enhances immunity. Therefore, it can promote the absorption of edema and relieve inflammation and pain. When a large dose of microwave is used, it produces a high-heat effect, causing protein denaturation, coagulation and necrosis. At this time, microwaves have the effect of "burning" and "cutting". Microwave therapy is a medical device that uses the biological characteristics of microwaves to treat various diseases. It integrates high-tech technologies such as microwaves, sensors, automatic control, computer software and hardware. Most of the control systems of microwave therapy devices on the market are implemented using single-chip microcomputers. They generally have the disadvantages of cumbersome operation, no graphical operation interface and unintuitive display. The use of PCs as control terminals for thermotherapy devices increases the cost of the equipment. These factors restrict the rapid popularization and promotion of this application. Because ARM embedded technology can make the control system miniaturized, and the developed products are powerful, inexpensive and have a high cost performance. Therefore, according to the market demand for microwave thermotherapy instruments, we developed a new type of microwave thermotherapy instrument based on ARM embedded system [3][4] and configured with WINCE.NET operating system [5]. This application was developed using Embedded Visual C++ tool [6]. The product can monitor human body temperature in real time and has the functions of microwave knife and ablation needle. The system has the characteristics of high control integration, stable operation, convenient operation and intuitive graphical interface display. 1 Hardware System 1.1 Introduction to Hardware Functions A microwave knife is a microwave surgical knife that uses microwave energy to perform surgery. It consists of a microwave power source with a frequency of 2000～10000 MHz and a power of 70～150 W that is continuously adjustable, which is connected to the surgical knife through a transmission line. The energy generated by the microwave source enters the patient's surgical site through the transmission line and the surgical knife to achieve the purpose of surgery. It has the characteristics of good hemostasis, no carbonization of the blade, sterilization, prevention of surgical infection, etc., and is small in size and flexible in operation. Ablation technology is a technique that allows microwave therapy sources to be precisely inserted into the local lesion site of the human body through the natural cavities, and automatically and accurately controls its treatment power, time and treatment range. Using ablation needles can effectively treat diseases without abdominal surgery, with less pain. The microwave transmitter of this system can be connected to a microwave knife and an ablation needle. The working conditions are as follows: (1) Microwave knife: When the microwave knife is used during surgery, the user controls the output power of the microwave knife through the human-computer interaction interface. At the same time, the system automatically accumulates the running time of the microwave knife, which is convenient for medical record recording. (2) Ablation needle: When the ablation needle is used for thermotherapy, the user can preset the running power, time and warning temperature of the ablation needle. The system uses a countdown method to calculate the running time of the ablation needle. After the time is zero, the system automatically cuts off the power output. During the treatment process, in order to prevent the temperature of the patient's treatment site from being too high and causing tissue damage, the system can also monitor the temperature change of the affected area. When the detected temperature is higher than the warning temperature, the system automatically reduces the output power of the ablation needle; when the detected temperature returns to normal, the system restores the output power of the ablation needle to the preset value. 1.2 Hardware Composition The entire hardware system is divided into three main parts: the embedded system module, the temperature acquisition and control module, and the microwave source. Figure 1 is the hardware structure diagram of the system. [align=center] Figure 1 Hardware System Structure Diagram[/align] [align=center] Figure 2 Embedded System Module Structure Diagram[/align] 1.2.1 Embedded System Module The structure of the embedded system module is shown in Figure 2. The module uses Samsung's ARM9 series microprocessor S3C2410, which includes 64M RAM and 64M Flash. The embedded system module is connected to a 10.4-inch LCD screen from Sharp, with a resolution of 640×480, serving as the human-machine interface platform for user operation. The embedded system module is the core control part of the entire system. It provides a user-friendly human-machine interface for users to set parameters such as power, time, and alarm temperature. Then, it communicates with the microcontroller via serial port to control the output power of the microwave source and displays the real-time temperature curve on the LCD screen. 1.2.2 Temperature Acquisition and Control Module The temperature acquisition and control module consists of a microcontroller and a temperature acquisition circuit: (1) Microcontroller. The microcontroller uses the C8051F005 chip from Silabs, which has an embedded 12-bit A/D and 12-bit D/A converter. It acquires 8 temperature signals through A/D and sends them to the embedded system module via serial port. At the same time, it converts the power value from the embedded system module into voltage through D/A to drive the microwave source. In addition, considering the convenience of practical application, a foot switch is connected to the module so that the user can directly control the microwave output power with the foot switch. (2) Temperature Acquisition Circuit. In order to detect the temperature change of the affected area of ​​the human body during the hyperthermia process, the system is equipped with a temperature acquisition circuit. It consists of 8 thermistors and a signal amplification circuit. The thermistors are first divided by a fixed resistor, and then amplified by the signal amplification circuit and connected to the A/D converter of the microcontroller. The microcontroller then transmits the temperature signal to the embedded system module via serial port and displays it on the LCD. 1.2.3 Microwave Source The microwave source uses a magnetron as the microwave oscillator. When the magnetron's operating point is set reasonably and the internal oscillation is stable, the microwave can be coupled to a specially designed circular radiator via a resonant coupler and coaxial cable. This microwave source mainly consists of a microwave drive circuit and a microwave radiator. It can be externally connected to a scalpel and ablation needle (see Figure 3) to provide microwave output for different components. [align=center] Figure 3 Microwave Source[/align] Since the output power of the microwave source has a non-linear relationship with the driving voltage, in this design we pre-measured the correspondence table between power and driving voltage. The control program converts the power set by the user into a voltage value by looking up the table and sends it to the microcontroller via a serial port. The microcontroller then outputs an analog voltage through its built-in D/A converter to control the power output of the microwave source. 2 Software System 2.1 Embedded Operating System WINCE.NET Microsoft Windows CE.NET (also known as WINCE.NET) is a compact, efficient, and customizable operating system suitable for various embedded system development. It features multi-threading, multi-tasking, and full preemptive priority, making it a real-time operating system for embedded environments. Embedded Visual C++ (EVC) is a visual development tool based on the WINCE.NET platform, launched by Microsoft. It supports a subset of the MFC class library, providing powerful support for developers. Similar to ordinary Win32 program development methods, this design uses EVC 4.0. 2.2 Software System Design Based on the characteristics of the hardware platform and actual functional requirements, the software system is divided into two parts: scalpel control and ablation needle automatic control. The ablation needle automatic control function provides three functions: human body temperature monitoring, microwave power automatic adjustment, and ablation needle running status control. The human body temperature monitoring function provides three waveforms: temperature-time (seconds), temperature-time (minutes), and power-time (minutes), as shown in Figure 4. The specific system flowchart is shown in Figure 5. [align=center] Figure 4 Software Structure Diagram Figure 5 Program Flowchart[/align] 2.2.1 Surgical Knife Control Function Block The interface of this module is shown in Figure 6(a). It provides the following functions: controlling the microwave knife start/stop status, calculating the microwave knife running time, adjusting the microwave knife output power and initializing the power, and time parameters. [align=center] (a) Surgical knife status display (b) Ablation needle control diagram Figure 6 Software Part Function Diagram[/align] The embedded system module and the temperature acquisition and control module mainly communicate via serial port[7] (see Figure 1). The application program needs to encode/decode the serial port data to achieve the control purpose. The serial communication data format is uniform as follows: (1) The data length sent by the digital-to-analog converter to the embedded system module is 21 bytes per frame, and the transmission format (see Table 1) is as follows: ① Preamble is 0x55 (1 byte); ② Start/Stop (1 byte): 0x00 indicates stop; 0xFF indicates start ③ Power value (2 bytes): The power value is a range (0-4095); ④ Temperature value (16 bytes): Each temperature value ranges from 0 to 4095 (2 bytes), so a total of 16 bytes are required; ⑤ End code is 0xAA. Table 1 Data format of temperature acquisition and control module - embedded module (2) The data format sent by the embedded system module to the digital-to-analog converter is shown in Table 2, which is 5 bytes in total, and the definition is the same as above. Table 2 Embedded Module - Temperature Acquisition and Control Module Data Format 2.2.2 Ablation Needle Control Function Block As shown in Figure 6(b), this module provides the following functions: ① Ablation Needle Operation Control Function: Selected microwave source model, warning temperature, pre-run time, and pre-output power; controls the start/stop status of the ablation needle. ② Microwave Power Automatic Adjustment Function: When the temperature of the treated area exceeds the warning temperature, the system automatically reduces the microwave output power until the temperature returns to normal. ③ Temperature Monitoring Function Displays three waveforms: temperature-time (seconds), temperature-time (minutes), and power-time (minutes) waveforms. 3 Experiment and Conclusion After system integration, we tested the entire instrument at a room temperature of 17℃. The scalpel output power was 35W. After starting the scalpel function, the relationship between the analog voltage value representing the output power of the system and time was measured as shown in Table 3: Table 3 Analog Voltage-Time Chart for Scalpel Output In addition, the ablation needle output power was set to 35W, and the warning temperature was set to 30℃. The ablation needle thermotherapy function was activated. Initially, the temperature-sensitive probe was placed in water at 11.5℃; after 5 minutes, it was placed in water at 31.7℃, removed after 6 minutes, and then placed back in 11.5℃ water; after 10 minutes, it was placed in water at 29.1℃, removed after 11 minutes, and then placed back in 11.5℃ water. During this process, the voltage values ​​after power conversion were measured, as shown in Table 4. Table 4: Ablation Needle Output Simulated Voltage-Time Schedule. The experiment shows that the control system can accurately control the microwave output power. Simultaneously, through the temperature-sensitive probe, it can accurately monitor the temperature changes at the affected area and adjust the output power according to the warning temperature value to prevent burns caused by excessively high temperatures. The consistency between the experiment and the theory indicates that the system performance meets the design requirements. Future efforts should continue to improve the human-computer interface to enhance operability; and improve the coupling interface between the software modules and different microwave transmitters to enhance the system's compatibility and scalability. The innovation of this paper lies in its use of popular embedded technology to improve the control system of a microwave hyperthermia device. This system represents a significant step forward in miniaturization, intelligence, accuracy, and cost reduction of the hyperthermia device control system. Its multiple interfaces enable it to be compatible with popular microwave transmitters on the market, providing high scalability and realizing significant market value. References [1] Lin Yina, Bian Xueping, Wang Junhui, et al. Progress in clinical application and mechanism research of microwave [J]. Zhongyuan Medical Journal, 2007, 34 (3): 54-56. [2] ALBANESE RA, MEDINA RL, PENN JW Mathematics, Medicine and Microwaves [J]. Inverse Problems, 1994, 10: 995-1007. [3] SEGSRS S, CLARKE K, GOUDGE L. Embedded Control Problems, Thumb and the ARM7TDMI [J]. IEEE Micro, 1995, 15 (5): 22-30. [4] Deng Chengzhong, Huang Weigong, Wan Songfeng. Design of small monitoring system based on embedded ARM & WinCE [J]. Microcomputer Information, 2005, 21 (23): 47-49 [5] Microsoft Corporation. Windows Embedded CE Overview and Benefits [2007-6-20]. [6] Wang Bing, Li Cun, Chen Peng, et al. Advanced EVC Programming and Its Application Development [M]. Beijing: China Water Resources and Hydropower Press, 2005: 290-299. [7] Tang Jun, Mao Daheng, Xie Jinghua, et al. Serial Communication between Microcomputer and OMRON PLC Using Multithreading [J]. Microcomputer Information, 2006, 10: 74-76.