The coupling-of-modes approach for modeling and analyzing surface-acoustic wave devices is reviewed. We discuss the established formalism and survey the modifications introduced to account for phenomena such as resistivity, dispersion and in particular, the effects related to surface transverse wave and leaky surface-acoustic wave devices. The extraction of the COM parameters from experiments and theoretical simulations are considered. The design of various SAW devices such as resonators and resonator filters as well as practical aspects are discussed. Finally, the unresolved modeling problems are addressed.

Purpose: Mild hyperthermia can be used as an adjuvant therapy to enhance radiation therapy or chemotherapy of cancer. However, administering mild hyperthermia is technically challenging due to the high accuracy required of the temperature control. MR guided high-intensity focused ultrasound (MR-HIFU) is a technology that can address this challenge. In this work, accurate and spatially uniform mild hyperthermia is demonstrated for deep-seated clinically relevant heating volumes using a HIFU system under MR guidance. Methods: Mild hyperthermia heating was evaluated for temperature accuracy and spatial uniformity in 11 in vivo porcine leg experiments. Hyperthermia was induced with a commercial Philips Sonalleve MR-HIFU system embedded in a 1.5T Ingenia MR scanner. The operating software was modified to allow extended duration mild hyperthermia. Heating time varied from 10 min up to 60 min and the assigned target temperature was 42.5• C. Electronic focal point steering, mechanical transducer movement, and dynamic transducer element switch-off were exploited to enlarge the heated volume and obtain uniform heating throughout the acoustic beam path. Multiple temperature mapping images were used to control and monitor the heating. The magnetic field drift and transducer susceptibility artifacts were compensated to enable accurate volumetric MR thermometry. Results: The obtained mean temperature for the target area (the cross sectional area of the heated volume at focal depth primarily used to control the heating) was on average 42.0 ± 0.6• C. Temperature uniformity in the target area was evaluated using T10 and T90, which were 43.1 ± 0.6 and 40.9 ± 0.6• C, respectively. For the near field, the corresponding temperatures were 39.3 ± 0.8• C (average), 40.6 ± 1.0• C (T10), and 38.0 ± 0.9• C (T90). The sonications resulted in a concise heating volume, typically in the shape of a truncated cone. The average depth reached from the skin was 86.9 mm. The results show that the heating algorithm was able to induce deep heating while keeping the near-field temperature uniform and at a safe level. Conclusions: The capability of MR-HIFU to induce accurate, spatially uniform, and robust mild hyperthermia in large deep-seated volumes was successfully demonstrated through a series of in vivo animal experiments. C

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In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO 3 , narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y-axis and parallel to the plane of the platelet. The resonance frequency of ∼4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors (Q) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q-factor ∼300, strong piezoelectric coupling ∼25%, (indicated by the large Resonance-antiResonance frequency spacing, ∼11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ∼100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3-6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

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