This paper reviews the latest developments in microwave acoustic wave devices. After an introduction and brief history of bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, a review is given for guided SAWs and XBARs - two new technologies, which are promising for future 5G applications. Following this, we discuss recent simulation techniques, such as 3D finite element method (3D FEM) and simulation of nonlinearities, as well as filter synthesis. Next, a review on tunable and reconfigurable acoustics is given. Finally, we present the latest developments in microwave acoustics for millimeter-wave (mm-wave) operation as well as BAW oscillators.

In a scenario where the segment of wireless communication systems are allocated in an ever more crowded frequency spectrum, the design of filtering structures, stand-alone, duplexers, or multiplexers, become a challenging task. Moreover, filters based on acoustic wave resonators are the more suitable technology in this context due to the small size and the exhibited outstanding performance. However, to accommodate the technological requirements to the mask fulfillment is not straightforward unless a systematic synthesis methodology is used. Taking advantage on the nodal approach, the general synthesis methodology for ladder-type filters based on acoustic wave resonators is presented in this paper. This is a very fast procedure, which allow a better understanding of the interaction between technological constraints and filter performance. An experimental validation is proposed for a B28Rx band filter.

In this article, we explore how acoustic wave filters starting with shunt resonator require particular reflection phase conditions to ensure that the synthesized filter is feasible. The position of transmission zeros (TZs) along with the phase of the objective filter function might lead to nonfeasible solutions where the first and last resonators require elements with positive reactance slope in the static branch, or equivalently, a nonphysical negative static capacitor. Since the reflection phase of a duplexer-oriented filter is fixed to reduce loading effects, the feasibility problem is solved by bringing the resonance frequency of the first resonator beyond the central frequency of the counter band. However, this entails surpassing the limits of the electromechanical coupling coefficient. We demonstrate how two reactive elements at the input overcome this resonance position limitation and provide a simple rule to decide the right topology. The position of the first TZ of duplexers will play an important role. Moreover, we provide rules on the reflection phase values that ensure that all resonators have a capacitive static branch.

In designing acoustic wave (AW) ladder filters, synthesis methods utilize the lowpass prototype (LP) representation to analyze bandpass responses in the normalized domain. This technique reduces the filter’s polynomial order and achieves asymmetric responses by incorporating frequency-invariant reactance (FIR) elements. While this technique is particularly effective for narrowband filter designs, it faces limitations with wideband filters due to errors that arise when transforming extracted LP elements to the bandpass domain. There are different approaches for the exact modeling of AW ladder filters in the real frequency domain. However, current direct bandpass (DB) techniques for AW ladder filters cannot be generalized, as they lack flexibility in characterizing frequency-dependent input and output (I/O) phases and suffer from numerical issues during parameter extraction due to excessively large polynomial coefficients in high-order or narrowband filter designs. This work aims to address both problems: first, to generalize the DB methodology for AW ladder filters by computing the transfer function while considering the asymptotic behavior at both the origin and infinity, as well as controlling the frequency-dependent I/O phases through complex reflection zeros (CRZs). Second, to enhance numerical accuracy during parameter extraction by relying on precise root-finding methods rather than interpolated coefficients. To validate the effectiveness of the proposed DB approach, the synthesized model has been compared with a manufactured LiNbO₃ thin-film AW ladder filter, which features a wide fractional bandwidth (FBW) of 18% and demonstrates excellent agreement between the simulated and measured responses. Finally, an 18th-order AW ladder filter has been synthesized to validate numerical stability even for narrowband filters.

Polyethylene connection pipes of wall thickness ranging from 3.0 to 4.5 mm, used for 0, 5, 9, 12, and 18 years in the French network of drinking water disinfected by bleach, have been analyzed. The stabilizer thickness profiles reveal that bleach destroys the stabilizer in a superficial layer of about 0.5 mm depth at the water–polymer interface. In the rest of the wall, stabilizer is lost by physical processes, i.e., transport by diffusion into the bulk, extraction at the water–polymer interface, and evaporation at the polymer–air interface. The whole loss kinetics is governed by extraction and evaporation. The classical scheme for evaporation–diffusion process has been used to model physical loss processes, but with boundary conditions different from the literature ones. Concerning chemical aspects, some mechanisms proposed in the literature are criticized. The identification of the bleach reactive species remains an open question. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.