Application Cases

Experiment Name: Study on the Uniformity of Excitation Magnetic Fields in Magnetic Nanoparticle Temperature Measurement Systems

Research Direction: The acousto-magnetic nanoparticle temperature measurement method holds promise for solving the problem of real-time accurate temperature measurement in tumor hyperthermia. This study analyzes issues such as low uniformity of alternating magnetic fields, low signal-to-noise ratio (SNR), and high load impedance in the practical application of magnetic nanoparticle temperature measurement methods. First, by analyzing the signal chain of the alternating magnetic field excitation system, a Helmholtz coil is proposed as the alternating magnetic field generation device. Its magnetic field uniformity is analyzed and verified through theoretical analysis, simulation, and practical measurements. Second, to address the low SNR, a ninth-order elliptic passive filter is proposed, and its SNR is validated to reach 100 dB through theoretical analysis, digital simulation, and practical measurements. Finally, based on impedance matching theory, a series resonant circuit is proposed to resolve the issue of high load impedance. Practical measurements show that the excitation magnetic field strength reaches 20 Gs. Additionally, to ensure the stability of the alternating magnetic field excitation system, a method using series-connected high-power resistors is proposed to monitor the excitation current in real time, thereby ensuring the stability of the excitation magnetic field.

Compared to existing tumor cancer treatment methods such as surgical resection and radiotherapy/chemotherapy, tumor hyperthermia not only reduces patient suffering during treatment but also achieves a higher cure rate. Therefore, tumor hyperthermia is regarded as a "green" therapy. However, the temperature measurement issue remains the biggest bottleneck hindering the widespread application of this therapy, as existing temperature measurement methods cannot accurately and safely measure the temperature of human tissues and cells. Magnetic nanoparticle temperature measurement is a novel, non-invasive method that can measure internal cell temperatures in real time with high accuracy while addressing the safety concerns associated with traditional invasive methods. Thus, hyperthermia based on magnetic nanoparticle temperature measurement has the potential to tackle one of humanity's most significant health challenges—tumor cancer—offering a new therapeutic approach for curing tumors today. Nevertheless, the alternating excitation magnetic field plays a decisive role in magnetic nanoparticle temperature measurement, and several practical issues remain, such as low magnetic field uniformity, low SNR, and high load impedance. The feasibility of this method still requires continuous experimental validation.

Experiment Objective: To verify whether selecting a Helmholtz coil as the alternating magnetic field generation device can address the issue of low magnetic field uniformity in magnetic nanoparticle temperature measurement systems.

Testing Equipment: Power amplifier, signal generator, oscilloscope, Helmholtz coil, filter, data acquisition card, computer, etc.

Experimental Procedure: The working principle of the alternating magnetic field excitation system involves generating a single-frequency, stable-amplitude sinusoidal signal controlled by a computer via an AC signal source. This signal is then amplified by an ATA-4014C high-voltage power amplifier, conditioned by a power filter, and finally used to drive the Helmholtz coil to produce the excitation magnetic field. To enable real-time monitoring of the alternating magnetic field excitation system, an oscilloscope is used to observe the voltage across the coil, while the current in the monitoring circuit is measured. Feedback control methods are employed to ensure system stability. The system workflow, based on its working principle, is illustrated in Figure 1-1.

Figure 1-1: Schematic Diagram of the Magnetic Field Excitation System

Experimental Results: The Helmholtz coil is an inductive element, and its inductive reactance is highly dependent on the signal frequency, which presents challenges in driving the load. Practical measurements show that at a frequency of 375 Hz, the impedance of the Helmholtz coil is 680 Ω, making it extremely difficult to generate an alternating magnetic field with a strength of 20 Gs. The "series resonance" method addresses the difficulty of driving the Helmholtz coil. The schematic of the series resonance circuit is shown in Figure 1-2. The principle is that at the resonant frequency, the capacitive reactance equals the inductive reactance, making the two-port network appear purely resistive. Considering that the excitation signal frequency of this alternating magnetic field excitation system is 375 Hz, this frequency is set as the resonant frequency of the series circuit. Practical matching measurements reveal that when the matching capacitance is 616.52 nF, the circuit enters resonance, and the impedance at this point is 20.719 Ω. The schematic for matching capacitance is shown in Figure 1-3.

Figure 1-2: Series Resonance Circuit Diagram
Figure 1-3: Schematic Diagram of Matching Capacitance Connection

Recommended Power Amplifier: ATA-4014C

Figure: ATA-4014C High-Voltage Power Amplifier Specifications

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