Development of Micro-Magnetron for Terahertz Imaging Applications

Informations projet

Micro-magnetron

N° de convention de subvention: 101068135

DOI

10.3030/101068135

Projet clôturé

Date de signature de la CE 17 Octobre 2022

Date de début 1 Novembre 2022

Date de fin 28 Février 2025

Financé au titre de

• Marie Skłodowska-Curie Actions (MSCA)

Coût total

Aucune donnée

Contribution de l’UE

€ 206 887,68

Coordonné par

UPPSALA UNIVERSITET
Sweden

Periodic Reporting for period 1 - Micro-magnetron (Development of Micro-Magnetron for Terahertz Imaging Applications)

Période du rapport: 2022-11-01 au 2025-02-28

Résumé du contexte et des objectifs généraux du projet

The development of tools and instruments enables scientific advancements. For example, Roentgen discovered X-rays, a significant scientific tool, using Lenard's vacuum tube, and soon, X-ray technology opened the path for medical technology and material science. Despite the colossal success of X-ray technology over a century, we are still facing the danger of generated ionizing radiation. The millimetre wave and terahertz radiations are non-ionizing solutions for imaging applications. However, the lack of technological infrastructure creates the THz gap between photonics and microwaves. In this project, we deliver the source/instrumentation to fill the gap between microwave and photonics.

Recent reports on the risk of skin cancers have highlighted a rapid increase in cases in the Nordic region, with the geographical distribution of skin cancer posing a significant concern. In this context, the non-ionizing properties of THz and millimetre waves have emerged as promising research areas for diagnosing skin cancer, breast and blood cancers and burn diagnostics. A compact, efficient, and durable electron device is required to advance research in this critical area and develop a safe imaging source.
Due to the collisionless propagation of electron beams, magnetron tubes do not create friction/heat in the channel, i.e. vacuum and produce more power per unit volume compared to solid-state electron devices and lasers. From their crucial role in the victory of World War II to their continued use in everyday kitchen appliances, magnetron tubes have proven highly effective across numerous scientific and industrial applications. Inspired by this success, we propose utilizing this reliable technology in the millimetre and THz spectrum. The micro-magnetron is intended for medical imaging, RADAR applications for homeland security, and material analysis.

The project is strategically aligned with broader European objectives aimed at enhancing technological independence and promoting innovation in key sectors. It plays a crucial role in developing specialized research and manufacturing capabilities within the EU, which will support future applications and industries. The long-term vision involves creating practical, high-performance systems for clinical, industrial, and security environments, ultimately delivering tangible benefits to public health, safety, and technological leadership.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

77 GHz micro-magnetron- Novel Frequency-Wise: We investigated the theoretical background, and the preliminary literature review was extended to determine the design goal. During the literature, we have investigated spatially harmonic magnetron at various frequencies, and since there have been no development efforts on micro magnetron at 77 GHz. We have designed a micro magnetron at 77 GHz to exploit the millimetre wave advantages. Nowadays, research efforts on 77GHz RADAR medical imaging are also a point in choosing the 77 GHz frequency in millimetre waves. Also, the License regulation for spectrum crowding and the need for higher bandwidth force the 24 GHz frequency technology on 77 GHz.
Implementing vane strapping to avoid mode competition in MMW magnetrons is not feasible. Instead, SH magnetrons are a better solution, which operates in pi/2-1 mode and has better mode separation than conventional magnetrons. The design parameters of the SH magnetron are determined using the B-H curve and Eigenmode analysis. The Eigenmode simulation exercise is performed to determine the frequency of SH magnetron with geometrical parameters.

We have determined the geometrical parameters of the 77 GHz SH magnetron. Figure 1 shows that SH magnetrons operating in pi/2 mode have DC voltage and magnetic field requirements of 14-16kV and 0.7-0.8 Tesla, respectively, considering the operating regime between the upper region of the Hull cutoff and the Hartree line.
The performance of the beam wave interaction mechanism is evaluated by PIC simulation. Modelling and simulation are done using the CST Particle Studio suite. The structure is divided into two major parts: Anode and Cathode, which are electrically isolated, and the model is shown in Figure 2. Vanes are part of the anode and couple out the developed RF power from the RF Interaction structure. Discrete ports are created between the cathode and anode to implement the DC voltage signal. On a central cathode assembly, an annular ring is defined as an emitter strip longitudinally bounded by an end hat to trap electrons in the interaction region.
A DC voltage signal of 15kV is applied between the anode and cathode near the input. A DC magnetic field of 0.765 Tesla was taken to achieve the synchronism between electron drift velocity and phase velocity of the RF wave. PIC simulation predicted the RF power of 21 kW, which can be seen in Figure 3. Figure 4 shows the Fourier transform of the developed amplitude signal, confirming the power at 77 GHz.
We designed a magnetic system/circuit based on permanent magnets to improve efficiency and sustainability. Figure 5 shows the magnetic system model (Left) and vector field plot (Right), confirming axial field uniformity in the interaction region. This ensures stable electron dynamics for efficient device operation.


204 GHz Micro-Magnetron – Advancing Toward the Terahertz Gap
The frequency of 205 GHz falls within the atmospheric EHF transmission window, resulting in lower attenuation of 5–10 dB/km in clear air. It effectively avoids the strong absorption lines at 183 and 325 GHz, allowing for improved signal propagation. This makes it an ideal choice for compact, high-resolution terahertz (THz) systems used in imaging and sensing applications. The frequency strikes a practical balance between performance and manufacturability, positioning it as an optimal range for efficient and reliable THz operation.
Figures 6 through 8 present key simulation results that validate the performance of the 204 GHz micro-magnetron. Figure 6 displays a 3D model of the device, featuring a compact arrangement of cathode and anode structures optimized for terahertz interaction. Figure 7 illustrates the frequency spectrum of the output signal, highlighting a sharp, dominant peak at 204 GHz with minimal spectral distortion. Figure 8 shows the temporal profile of the RF power, which stabilizes at a peak output of 4 kW. This demonstrates robust beam-wave interaction and consistent high-frequency performance, making it suitable for THz diagnostic applications.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Most spatial magnetron development has been done at 35 GHz, 94 GHz, 140 GHz and 210 GHz. Despite many RADAR development activities at 77 GHz, no vacuum electron devices are available at 77 GHz.  We have designed the 77 GHz micro magnetron, which can be an excellent source for medical imaging and RADARs. The compact and efficient millimetre wave magnetron enables imaging experiments for the detection of superficial cancers, concealed weapons and drugs, space debris/airborne objects, etc.
We are working on field emitters to achieve a very high current density from a smaller cathode for beam wave interaction in micro magnetrons. We have secured a grant to develop field emitter for magnetron and cross field amplifiers from the swedish innovation agency i.e. Vinnova with PercyRoc AB Uppsala Sweden. During the MSCA project, we secured new grants for future research on amplifier variants of magnetron from the Horizon 2020 I Fast CERN Research and Innovation program under Grant Agreement No. 101004730 and field emitters from the Vinnova Sweden Innovation agency.

Related with micro-magnetron Funding secured Funding Agency

Amplifier Variant of micro-magnetron 200.000 Euro European Union

Cathode of magnetron 150.000 SEK Vinnova Swedish Innovation agency

The slow wave structure of Cross field amplifier and field emitter with setup is shown in Figure 9 and Figure 10 respectively.

We are also working on a novel megawatt-class 750 MHz Cross-Field Amplifier that has improved performance metrics such as gain, efficiency, phase stability, and longevity. The development of the megawatt-class 750 MHz Cross-Field Amplifier involved comprehensive eigenmode simulations, particle-in-cell simulations, fabrication and experimental validation. Figure 9 (Left) shows the fabricated slow-wave structure, designed after optimising geometric parameters to support operation at 750 MHz. The performance of the structure was verified through S-parameter measurements, with S11 data shown in Figure 9 (Right). The result reveals a minimum reflection at 750 MHz with -15.51 dB, confirming proper impedance matching and successful frequency tuning. This low reflection signifies minimal power loss and validates the accuracy of the simulation-guided design.
In parallel, work on advanced field emitters focused on developing compact, high-current-density electron sources for integration into high-power vacuum devices. Figure 10(a) illustrates the electric field distribution of the emitter under a 30 kV potential difference, highlighting uniform field enhancement across the emitter tips, which is essential for stable electron emission. Figure 10(b) presents a 3D-printed field emitter prototype developed at Uppsala University, demonstrating the viability of additive manufacturing for precise, scalable cathode designs. Finally, Figure 10(c) shows the anode-cathode assembly chamber, where experimental testing of the field emitter setup is performed.

Together, these developments strengthen the technological foundation for next-generation high-power microwave amplifiers and compact electron sources, supporting various applications in communication, diagnostics, and defence systems.

Magnetic System

Model of 77 GHz micro magnetron

Frequency response of 205 GHz micromagnetron

Field Emitter (a) Simulation (b) 3D printed (c) Test setup

Fabricated 750 MHz Slow wave Structure and VSWR measurement

The temporal variation of RF power of 77 GHz micro magnetron

The Fourier transform of the developed output signal

Particle preview with CST model of 205 GHz micromagnetron

B-H curve of SH magnetron

The temporal variation of RF power of 205 GHz micromagnetron