Understanding the temperature dependence of acoustic and photoacoustic (PA) properties is important for the characterization of materials and measurements in various applications. Ultrasound methods have been developed to estimate these properties, but they require careful consideration of multiple variables and steps to obtain reliable results. This study aimed to develop an automated system for simultaneous characterization of acoustic and PA properties of materials. The system was designed to minimize operator errors, ensuring robust temperature control and reproducibility for acoustic measurements. This was made possible through the integration of a commercially available PA imaging system with a custom-built platform specifically tailored for ultrasound-based acoustic characterization. This platform consisted of both hardware and software modules. The system was evaluated with NaCl solutions at different concentrations and a gelatin/agar cubic phantom prepared with uniformly distributed magnetic nanoparticles serving as optical absorbers. Results obtained from the NaCl solution samples exhibited a high Lin s concordance coefficient (above 0.9) with previously reported studies. In the ultrasound/PA experiment, temperature dependences of the speed of sound and PA intensity revealed a strong Pearson s correlation coefficient (0.99), with both measurements exhibiting a monotonic increase as anticipated for water-based materials. These findings demonstrate the accuracy and stability of the developed system for acoustic property measurements.

In this work, we investigated the design of low loss and wideband shear horizontal surface acoustic wave (SH-SAW) acoustic delay lines (ADLs) on a sapphire-based thin-film lithium niobate on insulator (LNOI) platform. The SH-SAW propagates in a Y-cut LN/SiO2 double-layer thin film atop the sapphire substrate, where the significant acoustic impedance mismatch between the thin film and the substrate confines the acoustic energy at the surface, thus minimizing the propagation loss. The single-phase unidirectional transducers (SPUDT) used in this work is implemented with gold (Au) to maximize the electromechanical coupling as well as the directionality. The proposed ADLs based on YX-LN/SiO2/Sapphire centered at 830 MHz showed a minimum insertion loss (IL) of 3 dB, a wide fractional bandwidth (FBW) of 4.19\%, and a low propagation loss (PL) of 2.51 dB/mm, which yields an effective quality factor (QPL) exceeds 2,700. These results demonstrate the competitive performance of the proposed devices compared to state-of-the-art thin film LN ADLs, offering extremely low propagation loss for RF signal processing.

This paper presents the design of a MEMS resonator with capacitive transduction as an acoustic sensor, intended for cantilever-enhanced photoacoustic spectroscopy. The sensor employs area-variable capacitive detection by surrounding the silicon resonator with dense comb teeth. To reduce gas damping effects on the resonator motion, the anchor height is increased to 260 µm. This approach successfully resolves the capacitance detection sensitivity and motion damping trade-off commonly seen in acoustic detection. Experimental results exhibit a maximum sensitivity of 3749 mV/Pa at the resonant frequency of 1870 Hz with a 15 V bias voltage. The equivalent noise has a peak value of 7.9 µPa/Hz1/2 and the noise sources are analyzed.

This work presents a modified AlN/Sapphire layered SAW structure localized partial removal of AlN thin film and sapphire, respectively. The SAW propagation and resonance characteristics of the proposed structure with periodic grooves and voids are analyzed using finite element method (FEM). Compared with conventional AlN-based SAW, the proposed structure with optimization configuration and parameters effectively improves the K2 while maintaining a high V, meanwhile eliminates spurious modes. It is demonstrated that the Sezawa mode on the proposed SAW resonator structure offers operating frequencies above 5GHz, K2 values above 6.5\%, and an excellent impedance ratio of 98dB, which makes it a potential candidate for advanced 5G applications.

In this work, the shear horizontal surface acoustic wave (SH-SAW) resonators were demonstrated on 15° YXLiNbO3/SiO2/sapphire (LiNbO3-on-sapphire, LNOS) substrate. Compared to the reported gigahertz SAW resonators based on piezoelectric heterogeneous substrates, the fabricated resonator in this work exhibits a state-of-the-art electromechanical coupling coefficient (k2) of 42.2\%, a maximum Bode-Q (Qmax) of 1457 and an excellent figure of merit (k2×Qmax) of 615. Besides, several methods for suppressing transverse modes were implemented and compared. Tilted interdigital-transducers combined with the apodization technique can suppress the transverse modes more thoroughly while maintaining decent Q values. Overall, SAW devices based on the LNOS substrate have great potential for RF filters with low insertion loss, steep skirts, and wide bandwidth.

This paper investigates acoustic cross-coupling and remote excitation in an array of PMUTs (piezoelectric micromachined ultrasound transducers). Though undesired cross-talk can impact on PMUT array performance, the same can be also employed for remote excitation. The device array under study comprises of 7 PMUTs with constant pitch which is designed and characterized at the fundamental and higher order modes. The insights are employed to demonstrate a remote frequency filter and dual-channel excitation employing acoustic coupling.

The availability of Piezoelectric-On-Insulator (POI) substrates, made of a thin single crystal LiTaO3 film atop a silicon substrate, has promoted the development of innovative Surface and Bulk Acoustic Wave (SAW and BAW) devices. However, these substrates are so far only commercially available in 100 and 150 mm diameter. In this work, we successfully demonstrate acoustic devices based on 200 mm POI substrates. First, we fabricate SAW resonators displaying an electromechanical coupling coefficient of 8.8\% at a resonance frequency of 1.6 GHz. Then, we implement Film Bulk Acoustic Resonators (FBAR), integrating buried electrodes and an acoustic isolation structure, which exhibits a single resonance at 2.8 GHz, with an electromechanical coupling coefficient of 8.8\% and a quality factor close to 190. Eventually, we show a Solidly Mounted Resonator (SMR) based on a dielectric (AlN/SiO2) Bragg mirror, which exhibits performances close to AlN-based resonators, i.e. a coupling coefficient of 6.1\% and a quality factor of 405 at 4 GHz. For the later, a Temperature Coefficient of Frequency (TCF) of -14 and -22 ppm/°C at resonance and antiresonance are obtained respectively. Such TCF values are among the lowest ever reported for LiNbO3 and LiTaO3 BAW resonators. These results offer promising perspectives towards the development of 200 mm SAW and BAW filters based on POI substrates.

In this paper, a 30° YX-Lithium Niobate (LN) 0-th shear horizontal (SH0) plate acoustic wave (PAW) resonator is proposed. The SH0 mode characteristics the superiority of interdigital transducer (IDT) in the frequency definition over most other plate modes. Using finite element analysis method, the rotation angle of LN and the thickness of each layer were optimized for large effective coupling coefficient (k2eff) and high acoustic velocity. The rotation angle and the thickness of LN membrane are optimized as 30° and 0.2, respectively. To improve the temperature stability of proposed PAW resonators, a SiO2 film are added and the thickness is designed as 0.2. The measurement results derived a k2eff of 25.1\%, a Bode-Qmax of 604, and a Figure of merit (FoM) of 151, which is higher than the reported similar-type PAW resonators. The measured first-order temperature coefficients of frequency at resonant frequency (TCFfs) and anti-resonant frequency (TCFfp) are -38ppm/°C and -26ppm/°C, suggesting the temperature stability improvement in comparison with only LN membrane-based resonators.

This paper presents a new method to suppress spurious modes in lithium niobate thin-film acoustic devices by twisting the piezoelectric coupling properties of the spurious modes. The excellent piezoelectric properties of lithium niobate (LiNbO3) advance performance but lead to significant spurious modes accompanied by the targeted main mode. To harvest the benefits and avoid the spurious modes, this work investigates solidly mounted LiNbO3 thin films with different substrates to twist the zero-coupling orientations of spurious modes to be close to the maximum-coupling orientation of the targeted main mode. The fabricated devices, based on the solidly mounted LiNbO3sapphire structure and surface guided acoustic wave, show an operating frequency of 2.4 GHz with a large electromechanical coupling of 22\% and a spurious-free response in the wide frequency range. This work could overcome a significant bottleneck in commercializing LiNbO3 thin-film acoustic devices.

This work proposes a novel one-port 3D acoustic resonator based on the lithium niobate thin film on conductive silicon carbide substrate (LiNbO3-on-SiC, LNCSiC). The fabricated resonator shows coupled frequency responses of the shear-horizontal surface acoustic wave (SH-SAW), the longitudinal leaky SAW (LL-SAW), and the high-overtone bulk acoustic waves (HBAWs). The HBAWs propagating in the thickness direction of LNCSiC show a wide frequency response span exceeding 4 GHz and an excellent maximum quality factor ( ) of 7980. The GHz SH-SAW propagating in the surface of LNCSiC show a large electromechanical coupling coefficient ( ) of 25.95\%, while the LL-SAW shows an extremely high velocity of \textasciitilde6900 m/s. Such hybrid resonators could potentially open up new applications in radio frequency communications, 3D imaging, and sensing.