Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Acoustic Wave Filter Technology–A Review

Micromachined ultrasonic transducer (MUT) arrays capable of multiple resonant modes and techniques for operating them are described, for example to achieve both high frequency and low frequency operation in a same device. In embodiments, various sizes of piezoelectric membranes are fabricated for tuning resonance frequency across the membranes. The variously sized piezoelectric membranes are gradually transitioned across a length of the substrate to mitigate destructive interference between membranes oscillating in different modes and frequencies.

Micromachined ultrasonic transducer arrays with multiple harmonic modes

The applicability of surface acoustic wave (SAW) based actuators was demonstrated for a variety of microfluidic tasks, including fluid mixing, particle separation, localized heating or fluid atomization. But as traditionally the main field of application lies in high-frequency telecommunication, SAW devices are only marginally optimized for microfluidics, especially in respect to an energy efficient operation. In lab setups incorporating SAW-based microfluidic actuators, insufficient energy efficiency resulting e.g. from interdigital transducers (IDTs) with inadequate electrical impedance, absorption of SAW power in vessel walls or maladjusted wavelengths, is often simply counteracted by an increase of the output power of the signal source. For the operation of portable or highly integrated devices, though, or for devices with high power needs, energy efficiency is crucial. Additionally, an inefficient mode of operation can result in severe device degradation. In order to extend the performance of SAW actuators, we discuss different approaches regarding the optimization of their power efficiency and provide selected experimental results, highlighting the importance of the governing power loss effects. Depending on the intended microfluidic task, several of the demonstrated optimization strategies can be combined and – as will be shown – considerable improvements in the device performance can be achieved.

Towards efficient surface acoustic wave (SAW)-based microfluidic actuators

Piezoelectric micromachined ultrasonic transducer (pMUT) arrays and techniques for frequency shaping in pMUT arrays are described, for example to achieve both high frequency and low frequency operation in a same device. The ability to operate at both high and low frequencies may be tuned during use of the device to adaptively adjust for optimal resolution at a particular penetration depth of interest. In embodiments, various sizes of piezoelectric membranes are fabricated for tuning resonance frequency across the membranes. The variously sized piezoelectric membranes are lumped together by two or more separate electrode rails, enabling independent addressing between the two or more subgroups of sized transducer elements. Signal processing of the drive and/or response signals generated and/or received from each of the two or more electrode rails may achieve a variety of operative modes for the device, such as a near field mode, a far field mode, and an ultra wide bandwidth mode.

Multi-frequency ultra wide bandwidth transducer

Piezoelectric micromachined ultrasonic transducer (pMUT) arrays and systems comprising pMUT arrays are described. Coupling strength within a population of transducer elements provides degenerate mode shapes that split for wide bandwidth total response while less coupling strength between adjacent element populations provides adequately low crosstalk between the element populations. In an embodiment, differing membrane sizes within a population of transducer elements provides differing frequency response for wide bandwidth total response while layout of the differing membrane sizes between adjacent element populations provides adequately low crosstalk between the element populations. In an embodiment, elliptical piezoelectric membranes provide multiple resonant modes for wide bandwidth total response and high efficiency.

Ultra wide bandwidth piezoelectric transducer arrays

A surface wave component contains at least two interdigital transducers having natural unidirectionality, disposed on a piezoelectric crystal substrate, which form a transducer pair consisting of transmission transducer and reception transducer. The transducers consist of an interdigital electrode structure having prongs and bus bars, and have opposite forward directions. At least two of the prongs form a transducer cell that has at least one excitation center for exciting an electrical potential wave and at least one reflection center for reflection of electrical potential waves, The transducer cells consist of two prongs having the same width, having a distance between the prong centers equal to half the length of a transducer period, whereby the electrode structures of the two transducers consist of the same material, but have different layer thicknesses.

Surface acoustic wave component

SPUDT cells including two fingers are only known thus far for so-called NSPUDT directions. In that case, usual solid-finger cells are used. The purpose of the present paper is to find SPUDT cell types consisting of two fingers only for pure mode directions. Two-finger (TF) cells for pure mode directions on substrates like 128°YX LiNbO3 and YZ LiNbO3 were found by means of an optimization procedure. The forward direction of a TF-cell SPUDT on 128°YX LiNbO3 was determined experimentally. The properties of the new cells are compared with those of conventional SPUDT cells. The reflectivity of TF cells on 128°YX LiNbO3 turns out to be two to three times larger than that of distributed acoustic reflection transducer (DART) and Hanma-Hunsinger cells at the same metal layer thickness.

Two-finger (TF) SPUDT cells [Correspondence]

SPUDT cells including two fingers only are hitherto known for so-called NSPUDT directions. In this case, usual solid-finger cells are used. The purpose of the present paper is to find SPUDT cell types consisting of two fingers only for pure mode directions. Moreover, SPUDT cells composed of two fingers suited to complete imperfect NSPUDT behavior or to compensate that are to be found. TF cells for pure mode directions on substrates like 128degYX LiNbO3, YZ LiNbO3 and STX quartz were found by means of an optimization procedure. The forward direction of a TF-cell SPUDT on 128degYX LiNbO3 was determined experimentally. The properties of the new cells are compared with those of conventional SPUDT cells. The reflectivity of TF cells on 128degYX LiNbO3 turns out to be two up to three times larger than that of DART and Hanma-Hunsinger cells at the same metal layer thickness. Furthermore, properties of TF cells on STX and SST quartz are reported. Examples for completing and compensating imperfect NSPUDT behavior are given.

Two-finger (TF) spudt cells

The present invention relates to a transducer for surface acoustic waves, in particular the present invention relates to a resonator and a filter for surface acoustic waves on basis of the transducer according to the present invention. The object of the present invention is to propose a transducer for surface acoustic waves which is composed of cells containing two electrode fingers per cell, wherein the transducer according to the present invention shows unidirectional behaviour for propagation directions of the surface acoustic waves parallel to highly symmetrical directions of the crystal substrate. Each of the two electrodes comprises a plurality of electrode fingers, the electrode fingers having centre axes extending parallel to their longitudinal axes and being spaced apart from centre axes of adjacent electrode fingers of the same electrode by a distance which equals the ratio of the velocity of the surface acoustic wave and the cut-off frequency of the transducer, wherein the electrode fingers of both electrodes define a plurality of cells each consisting of two fingers, wherein each of a plurality of said cells consists of a first finger having a first width and second finger having second width, wherein the first finger of the cell and the second finger of the cell is connected with electrode bars of different electrodes and wherein the first width is different from the second width.

Converters, resonators and filters for acoustic surface

A transducer for surface acoustic waves, and a resonator and a filter for surface acoustic waves having the transducer are provided. The transducer for surface acoustic waves has cells containing two electrode fingers per cell, wherein the transducer exhibits unidirectional behavior for propagation directions of the surface acoustic waves parallel to highly symmetrical directions of the crystal substrate. Each of two electrodes have a plurality of electrode fingers, the electrode fingers having center axes extending parallel to their longitudinal axes and being spaced apart from center axes of adjacent electrode fingers of the same electrode by a distance which equals the ratio of the velocity of the surface acoustic wave and the cut-off frequency of the transducer. The electrode fingers of both electrodes define a plurality of cells each consisting of two fingers.

Bernd Steiner

Papers

Surface acoustic wave component

Two-finger (TF) SPUDT cells [Correspondence]

Two-finger (TF) spudt cells

Converters, resonators and filters for acoustic surface

Transducer for surface acoustic waves and a resonator and a filter having said transducer