Future sixth-generation (6G) Ad Hoc networks must sustain ultra-reliable, low-latency, and energy-efficient connectivity in highly dynamic wireless environments, where interference management, real-time antenna reconfiguration, and computational constraints remain major challenges. Fluid Antenna Systems (FAS) provide additional spatial degrees of freedom through position- and shape-reconfigurable radiating elements, but existing optimization schemes for FAS and next-generation reconfigurable antennas either treat beamforming, phase control, and antenna positioning separately or rely on high-complexity Artificial Intelligence (AI) models that are difficult to deploy under slot-level latency and power budgets. This paper aims to design a unified, low-complexity framework for real-time control of FAS in 6G ad hoc networks. We propose AI-HFASO, a hybrid AI framework in which a Multi-Task Coordination Controller (MTCC) jointly optimizes beamforming, interference mitigation, and antenna positioning by integrating deep learning (DL) for fast beamforming initialization, reinforcement learning (RL) for adaptive element positioning, and a delay-aware genetic algorithm (GA) for phase refinement under latency constraints. The main novelty lies in the joint multi-objective optimization of spectral efficiency, interference suppression, and energy efficiency at the slot level, while reducing computational complexity through lightweight AI modules and a hybrid AI-traditional optimization loop. Simulation results under realistic multi-user, multi-cell 6G scenarios show that AI-HFASO achieves up to 31% interference reduction, 21% throughput improvement, and 18% spectral-efficiency gain, while lowering computational overhead by about 30% compared to state-of-the-art MIMO, RIS, and AI-based baselines, demonstrating its potential as a scalable and latency-aware solution for FAS-enabled 6G ad hoc networks.

This study reports significant progress in the field of high temperature wireless surface acoustic wave (SAW) sensors in the 2.45 GHz ISM band, using AlN/Sapphire based resonators. AlN thin films with a thickness of 0.6 & micro;m, synthesized on (0001) sapphire substrates by Metal Organic Chemical Vapor Deposition (MOCVD), demonstrated high crystalline quality and nanometric surface roughness, essential properties for SAW applications. Initially, SAW devices operating in the 2.45 GHz ISM band were tested up to 500 degrees C in both wired and wireless configurations using aluminium electrodes. Wireless interrogation was carried out successfully at a distance of 3 m up to 500 degrees C, with a temperature coefficient of frequency (TCF) measured at -58 ppm/degrees C. Critically, when the NiAl alloy was used for the thin film electrodes, the operating temperature was extended to 600 degrees C while maintaining a TCF of -43 ppm/degrees C and stable wireless performance at 3 m, with potential up to 10 m. These results exceed the state-of-the-art for high temperature SAW sensors in the wide 2.45 GHz ISM band. A long-duration annealing test has confirmed the self-passivation properties of the NiAl electrodes and the robustness of the NiAl/AlN/Sapphire structure, with a minimal degradation after 176 h at 500 degrees C, thus demonstrating its potential for long term use in extreme environments.

Surface acoustic waves (SAW) magnetic field sensors based on single-port resonator configurations with the advantages of temperature compensation and wireless functionality are promising candidates for magnetic field and electric current wireless sensing applications. In this work, an on-chip integrated single-port differential SAW magnetic field sensor that consists of two SAW resonators based on a Pt/Co40Fe40B20/Ta/Co40Fe40B20/Ta/SiO2/ quartz multilayered structure is investigated. By designing the SAW propagation directions of the two SAW resonators, one is parallel to the hard axis and the other is perpendicular to the hard axis of magnetization of the Co40Fe40B20 films. The magnetic sensitivity of the SAW magnetic field sensor is improved by utilizing the difference frequency between Love wave modes, while the magnetic hysteresis remains low. The temperature drift of the differential SAW magnetic field sensor is suppressed. A magnetic field sensitivity of -2350.4 kHz/mT with a low temperature drift of 1.6 kHz/degrees C is achieved. These results are promising for the development of temperature compensated SAW magnetic field sensors with high magnetic field sensitivities and temperature drift suppression.

A single-port surface acoustic wave (SAW) resonator based on a CoFeB/ SiO2/(X+90°) ST-quartz multilayer structure is presented for high-sensitivity magnetic field sensing, targeting industrial and medical applications where wireless interrogation is required. The achieved performance relies on the excitation of a Love wave mode, the optimization of CoFeB/SiO2 bi-layer thicknesses through numerical simulations, and a high-frequency design operating in the 2.45 GHz ISM band. Experimental results demonstrate an absolute sensitivity of 1200 Hz/μT.

In this work, a single-port surface acoustic wave (SAW) resonator with a Co40Fe40B20/SiO2/(X+90 degrees) ST-cut quartz multilayer structure is investigated as a magnetic field sensor. The Love wave resonator design is aimed at achieving a high magnetic field sensitivity, together with a temperature compensation. Two versions of sensitive layers are studied: Co40Fe40B20 (100 nm) and Co40Fe40B20(100 nm)/ SiO2(3 nm)/Co40Fe40B20(100 nm). For the latter, the 3-nm-thick SiO2 layer is inserted between two 100-nmthick amorphous Co40Fe40B20 layers, with the objective of controlling the magnetic properties of the magnetoelastic layer. A quartz crystal is selected as the piezoelectric substrate and a 375-nm-thick SiO2 layer is used as insulating medium. This thickness is chosen to achieve insensitivity to temperature variations of the Love wave velocity at 433 MHz industrial, scientific, and medical (ISM) band, when no magnetic field is applied. Optimized structures are fabricated and characterized, demonstrating a good agreement between experimental results and the simulation. The structure exhibits high magnetic field sensitivity of -6900 ppm/mT (corresponding to 3 Hz/nT) along the hard axis with the 200 nm total thickness of Co40Fe40B20 bi-layer. A substantial 26-fold increase in magnetic field sensitivity is achieved compared to that of the 100-nm-thick Co40Fe40B20.

This study reports significant progress in the field of high temperature wireless surface acoustic wave (SAW) sensors in the 2.45 GHz ISM band, using AlN/Sapphire based resonators. AlN thin films with a thickness of 0.6 µm, synthesized on (0001) sapphire substrates by Metal Organic Chemical Vapor Deposition (MOCVD), demonstrated high crystalline quality and nanometric surface roughness, essential properties for SAW applications. Initially, SAW devices operating in the 2.45 GHz ISM band were tested up to 500°C in both wired and wireless configurations using aluminium electrodes. Wireless interrogation was carried out successfully at a distance of 3 m up to 500°C, with a temperature coefficient of frequency (TCF) measured at −58 ppm/°C. Critically, when the NiAl alloy was used for the thin film electrodes, the operating temperature was extended to 600°C while maintaining a TCF of −43 ppm/°C and stable wireless performance at 3 m, with potential up to 10 m. These results exceed the state-of-the-art for high temperature SAW sensors in the wide 2.45 GHz ISM band. A long-duration annealing test has confirmed the self-passivation properties of the NiAl electrodes and the robustness of the NiAl/AlN/Sapphire structure, with a minimal degradation after 176 h at 500°C, thus demonstrating its potential for long term use in extreme environments.

Guided elastic waves are a truly cross-disciplinary key enabling technology. For more than five decades, surface acoustic wave (SAW) and bulk acoustic wave devices find widespread applications. Nowadays, different types of guided elastic waves cover the wide spectrum of applications spanning from quantum technologies to the life sciences, from controlling single excitations to macroscopic collective states in condensed matter. Six years after the first 2019 SAW roadmap, we believe it is time to make a step back and take a fresh look at the status of the field and its future challenges. Since the first roadmap in 2019, the spectrum clearly expanded and this new edition presents a current snapshot of the status of this vibrant field and prospects for potential future developments.

Increasing the magnetic field sensitivity is one of the major challenges in the study of magnetic surface acoustic wave (MSAW) sensors. In this paper, Love wave MSAW sensors are investigated in a Transmissive Single Port Delay Line (TSP-DL) configuration, on ZnO (700 nm)/Y-X LiNbO3. CoFeB (100 nm) or CoFeB(100 nm)/SiO2(3 nm)/CoFeB(100 nm) sensitive magnetoelastic layers are placed in the acoustic path between two electrically connected interdigital transducers. The fundamental Love wave on ZnO(700 nm)/ Y-X LiNbO3 presents a high electromechanical coupling coefficient (K2), resulting in a high signal amplitude, which is favorable for delay lines performances. Additionally, shear waves are highly sensitive to the magnetic field due to the large Delta G effect in the magnetoelastic layers. A maximum frequency shift of 0.36% was achieved using a CoFeB(100 nm)/SiO2(3 nm)/CoFeB(100 nm) stack as the sensitive layer, with a high maximum magnetic sensitivity of 3630 ppm mT-1 (1482 kHz mT-1 at 410 MHz). This sensitivity is among the highest reported in the literature on magnetic SAW sensors.

This paper presents wet chemical etching processes of piezoelectric ZnO (wurtzite atomic structure) films. ZnO films can be etched by most of acid and basic solutions. However, in MEMS processes, many etchants also attack sublayers (electrodes or insulating layers) and are therefore not compatible with MEMS processes. HCl, HF and H3PO4 were selected among the possibilities and carried out etching on Ti/Pt/ZnO sputtered silicon wafers at room temperature. Vertical etching rates are found to be in the 0.2 to 5 mu m/min and lateral etching rates are in between 0.5 to 17 mu m/min. The ratio between lateral to vertical etching speed was found to reach a minimum value for low etchant concentrations of approximately 2%. The morphology of the semi-etched borders of the samples were observed by SEM and practical conclusions are extracted on the adequation of the wet etching process on the top electrode subsequent fabrication step.

In this paper we study and fabricate surface acoustic wave devices that combine magnetic field and temperature measurements and that integrate a radio-frequency identification functionality (RFID). The use of a Transmissive-Reflective Delay Line (TR-DL) design enables to control the amplitude of the RFID signal peaks while maximizing the sensitivity of the sensor. The latter is based on a double layer of magnetoelastic CoFeB film used as sensitive layer to the magnetic field and deposited on top of a ZnO-covered LiNbO 3 Y-X substrate. This structure is used to generate a Love wave which enhances the sensitivity to the magnetic field. The achieved device demonstrates a high sensitivity to the magnetic field, a temperature compensation and reflected signal levels of -20 dB in a wired connection. The obtained sensitivity of 3630 ppm/mT (or 1.482 Hz/nT), is among the highest reported in the literature on magnetic SAW sensors.

Highly specific detection of tumor-associated biomarkers remains a challenge in the diagnosis of prostate cancer. In this research, Maackia amurensis (MAA) was used as a recognition element in the functionalization of an electrochemical impedance-spectroscopy biosensor without a label to identify cancer-associated aberrant glycosylation prostate-specific antigen (PSA). The lectin was immobilized on gold-interdigitated microelectrodes. Furthermore, the biosensor’s impedance response was used to assess the establishment of a complex binding between MAA and PSA-containing glycans. With a small sample volume, the functionalized interdigitated impedimetric-based (IIB) biosensor exhibited high sensitivity, rapid response, and repeatability. PSA glycoprotein detection was performed by measuring electron transfer resistance values within a concentration range 0.01–100 ng/mL, with a detection limit of 3.574 pg/mL. In this study, the ability of MAA to preferentially recognize α2,3-linked sialic acid in serum PSA was proven, suggesting a potential platform for the development of lectin-based, miniaturized, and cost effective IIB biosensors for future disease detection.

This letter deals with the potential of the Al/AlN/Sapphire surface acoustic wave (SAW) structure as a wireless sensor operating in the 2.45 GHz ISM band for high-temperature applications up to 500 degrees C. A first design was used to make SAW resonators by e-beam lithography and characterize them between room temperature and 500 degrees C in a wired configuration. Frequency variation with temperature showed good stability, repeatability, linearity, and sensitivity with a measured temperature coefficient (TCF) of frequency of -47 ppm/degrees C. The figure of merit value, defined by the product of the electromechanical coupling coefficient and the quality factor, varies between 0.8 and 2 throughout the whole temperature range, proving the potential of the structure for wireless interrogation at high temperatures. Consequently, the SAW resonator was successfully wirelessly interrogated up to 500 degrees C at a distance of 1 m. Moreover, wireless interrogation of the sensor was possible up to 3 m at room temperature, with additional path losses of 19 dB, which could prove troublesome for operating temperatures above 400 degrees C. An optimization of the SAW resonator design was then subsequently carried out by simulation means in order to improve the figure of merit and allow wireless interrogation at higher temperatures and greater distances.

Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths with and without magnetic field sensitive layer. The delay in path with sensitive layer leads to magnetic field detection and the one without enables temperature measurement and thus compensation for the first path. The developed sensor is based on a ZnO/LiNbO3 Y-cut (X-direction) layered structure as Love wave platform. Love wave as a shear wave being more favorable for magnetic detection. Co-Fe-B is considered as sensitive layer to detect magnetic field changes and is deposited on the top of ZnO, but only on one of the two paths. We combined an original configuration of connected IDTs with a high electromechanical coupling coefficient (K2) mode to improve the signal amplitude. The achieved sensor exhibits a high temperature and magnetic field sensitivity of −63 ppm/°C and −781 ppm/mT, respectively. The temperature compensation method for magnetic field measurement is demonstrated using a differential measurement by subtracting the delay times obtained for the two paths with and without the sensitive layer. Finally, the sensor exhibited good repeatability at various temperatures. Moreover, the device developed allows in addition to the multisensor functionality, the radio frequency identification (RFID) which is necessary for the deployment of sensor networks.

This paper shows the feasibility and the performance of a multifunctional device based on a surface acoustic wave delay line. It combines a magnetic field detection with a temperature sensing and has also a radio frequency identification (RFID) capability. This promising device consists of a Co-Fe-B thin film as a magnetic field sensitive material over a ZnO/LiNbO 3 Y-cut (X-direction) structure, used as a platform for guided Love waves. The experimental results show high sensitivities of -774 ppm/mT and -67.7 ppm/°C for magnetic field and temperature detection, respectively. The device thus allows magnetic field measurements with the possibility of temperature compensation which make it particularly attractive for industrial applications.

Wireless surface acoustic wave (SAW) reflective delay line (R-DL) technology is very powerful to carry out remote measurements of various parameters under harsh environments, while enabling the identification of a given sensor among several of them. However, R-DL technology is currently limited to 350 °C for long-term applications, likely because of aluminum electrodes oxidation and/or congruent lithium niobate (LiNbO 3 ) segregation process. In this study, an innovative alloy, namely, NiAl, is investigated as an alternative to Al to make R-DLs able to withstand high temperatures up to 500 °C on the long term. Indeed, NiAl gathers, in the bulk state, all the necessary properties (fairly low electrical resistivity and density, high melting temperature, and resistance to oxidation). The study also examines the extent of the congruent LiNbO 3 segregation process to determine its impact on the NiAl/LiNbO 3 R-DLs performances. The obtained results are very promising. NiAl electrodes self-passivate during the first 50 h of annealing at 500 °C: 20-nm-thick Al 2 O 3 layers form at the surface and in between the electrodes and the substrate, protecting the remaining NiAl layer from further oxidation. Besides, the segregation process occurs mainly in the same time. It is located in the first 150–200 nm of the substrate. Both phenomena have no significant impact on the performance of NiAl/LiNbO 3 R-DLs working at 433 MHz. Continuous in situ electrical monitoring of such devices shows a standard deviation of the operating frequency of only 1.04 ppm during an annealing process of 250 h at 500 °C. Moreover, the time-resolved ${S}_{{11}}$ response of the device at the end of this treatment is not degraded at all. Thus, 433-MHz NiAl/LiNbO 3 R-DL sensors can operate with high fidelity for at least 10 days at 500 °C under air atmosphere, and there are strong signs that their lifetime is actually much longer.

Monitoring the health of civil engineering structures using implanted deformation, temperature, and corrosion sensors would further improve maintenance and extend the service life of those structures. However, sensor integration poses a number of problems due to the presence of cables and on-board electronics. Passive, wireless surface acoustic wave (SAW) sensors offer a very promising solution here. We used commercial SAW devices mounted on steel rebars to carry out an initial feasibility study. Without cables or embedded electronics, we were able to measure the deformation of a concrete beam subjected to bending load. We were also able to measure the temperature continuously over a three-week period.