A linear piezoelectric micromachined ultrasound transducer (PMUT) array was fabricated and integrated into a device for photoacoustic imaging (PAI) of tissue phantoms. The PMUT contained 65 array elements, with each element having 60 diaphragms of 60 μm diameter and 75 μm pitch. A lead zirconate titanate (PZT) thin film was used as the piezoelectric layer. The in-air vibration response of the PMUT array elements showed a first mode resonance between 6 and 8 MHz. Hydrophone measurements showed 16.2 kPa average peak ultrasound pressure output at 7.5 mm from one element excited with 5 Vpp input. A receive sensitivity of ~0.48 mV/kPa was observed for a PMUT array element with 0 dB gain. The PMUT array was bonded to a custom-printed circuit board to enable compact integration with an optical fiber bundle for PAI. A broad photoacoustic bandwidth of ~89% was observed for the photoacoustic response captured from absorbing pencil lead targets. Linear scanning of a single element of a PMUT array was performed on different tissue phantoms embedded with light-absorbing targets to successfully demonstrate B-mode PAI using PMUTs.

Lead zirconate titanate (PZT) based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized and tested. The PMUTs had a diaphragm diameter of 60 lm, a resonant frequency of ∼ 8 MHz and an operational bandwidth of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 Vpp. The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 lm silica beads was shown to be possible with 5 Vpp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move towards diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational bandwidth. Levitation planes were generated above 30 MHz driving frequency.

The further development of 5G and 6G communication systems introduced new frequency allocations beyond 6 GHz, necessitating the development of compact bandpass filters that can operate over wide gigahertz frequency ranges. Herein, we report on the design, fabrication, and characterization of an edge-coupled magnetostatic forward volume wave bandpass filter (MSFVW). Using micromachining techniques, we fabricate both 2-pole and 4-pole filters from a yttrium iron garnet (YIG) film grown on a gadolinium gallium garnet (GGG) substrate with inductive transducers. By adjusting an out-of-plane magnetic field, we demonstrate linear center frequency tuning for a 4^th-order filter from 4.5 GHz to 10.1 GHz while retaining a fractional bandwidth of 0.3%, an insertion loss of 6.94 dB, and a − 35 dB rejection level. We characterize the filter nonlinearity in the passband and stopband with IIP3 measurements of − 4.85 dBm and 25.84 dBm, respectively. In this work, we demonstrate a compact octave tunable narrowband channel-select filter with a significant degree of design flexibility and performance comparable to the state-of-the-art.

The first successful validation of a forward-looking Piezoelectric Micromachined Ultrasound Transducer (PMUT) ring array designed for photoacoustic endoscopic imaging applications is presented. PMUT ring arrays were fabricated with a 0.5 mm inner diameter, to allow insertion of an optical fiber for light delivery, and ~2.5 mm overall outer diameter. Each ring array consisted of 6 elements, with a total of 102 PMUT cells, or 17 cells per element. Each PMUT cell has a 100 μm diameter multi-layered diaphragm having a ~700 nm thick c-axis oriented aluminium nitride (AlN) thin film as the piezoelectric layer over a Si (handle layer) / SiO₂ (1 μm) / Si (10 μm) / SiO₂ (100 nm) / TiO₂ (40 nm) / Pt (150 nm) substrate to act as an ultrasound receive element. The resonant frequency was ~ 6 MHz in water. The output end of an optical fiber, coupled to a pulsed laser diode (PLD), was fitted with a 2.5 mm ferrule. The PMUT ring array was concentrically mounted on the ferrule to obtain a miniaturized endoscopic PAI device. The observed photoacoustic bandwidth was ~75%, and a strong photoacoustic signal of ~13 mV peak-to-peak output was observed from a light absorbing target kept 5 mm away from the PMUT array. 2D and 3D photoacoustic images of the targets were obtained via raster scanning of the phantom sample. In the future, the functionality of the PMUT ring array will be enhanced through multichannel acquisition to obtain variable acoustic focus and limited view photoacoustic images in real time.

We report a non-resonant piezoelectric microelectromechanical cantilever system for the measurement of liquid viscosity. The system consists of two PiezoMEMS cantilevers in-line, with their free ends facing each other. The system is immersed in the fluid under test for viscosity measurement. One of the cantilevers is actuated using the embedded piezoelectric thin film to oscillate at a pre-selected non-resonant frequency. The second cantilever, the passive one, starts to oscillate due to the fluid-mediated energy transfer. The relative response of the passive cantilever is used as the metric for the fluid’s kinematic viscosity. The fabricated cantilevers are tested as viscosity sensors by carrying out experiments in fluids with different viscosities. The viscometer can measure viscosity at a single frequency of choice, and hence some important considerations for frequency selection are discussed. A discussion on the energy coupling between the active and the passive cantilevers is presented. The novel PiezoMEMS viscometer architecture proposed in this work will overcome several challenges faced by state-of-the-art resonance MEMS viscometers, by enabling faster and direct measurement, straightforward calibration, and the possibility of shear rate-dependent viscosity measurement.

Spin-wave (SW) filters using single-crystal yttrium iron garnet (YIG) is an attractive technology for integration in frequency-adjustable or frequency-tunable communication systems¹. However, existing SW devices do not have sufficient bandwidth for future 5G and 6G communication systems^2,3, are too large or have strong spurious passbands, creating unintentional cross-channel interference. Here we report a SW ladder filter architecture requiring only a single external magnetic bias, which is enabled by modern micromachining fabrication methods capable of wafer-scale production. The filters developed in this work demonstrate loss as low as 2.54 dB, bandwidths up to 663 MHz, centre-frequency tuning over several octaves from 7.08 to 21.6 GHz and high linearity with an input-referred third-order intercept point of more than 11 dBm in the passband. The operation of the filter is also experimentally demonstrated in a frequency-tunable radio system.