橋本 研也

This paper reports development of an integrated tunable active filter for lower UHF band based on the recursive architecture and its application. The recursive filter core gives the 2-pole bandpass response, and its center frequency can be tuned from 270 to 850 [MHz]. The auto setting mechanism was developed for the filter center frequency and passband width. Higher order filters were synthesized by combining multiple cores.

A direct-conversion receiver (DCR) can reduce the power consumption and cost. However, a DCR in Orthogonal frequency division multiplexing (OFDM) systems suffer from IQ imbalance and Carrier Frequency Offset (CFO). Until this time, many algorithms are proposed to compensate IQ imbalance and CFO in OFDM. However, it is insufficient for the joint IQ imbalance and CFO estimation. On the other hand, time-frequency interferometry-OFDM (TFI-OFDM) system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we focus on the channel identification property of TFI-OFDM and propose the novel IQ imbalance and CFO estimation schemes. In the proposed system, by using the feature of the TFI pilot symbols, we can identify an IQ imbalance in the presence of CFO, and the influence of the noise power can be mitigated by subcarrier selection. Moreover, by using autocorrelation of the TFI pilot symbols, we can estimate CFO after IQ imbalance estimation. From the simulation results, the proposed scheme can estimate IQ imbalance and CFO and compensate without a significant degradation of the BER performance.

This paper proposes a configuration of the radio frequency surface acoustic wave (SAW) filter with wide tunability for both the passband width and the center frequency. At first, it is shown how the center frequency and the passband width are adjustable with the VC setting. It is also shown that a flat passband and steep transition bands are realizable when multiple stages are cascaded with mirror inversion. Then, influence of Q factors is discussed. Finally, two types of tunable filters are designed, and applicability of this filter topology is demonstrated. (c) 2013 The Japan Society of Applied Physics

This paper discusses applicability of the Bragg reflection in a periodic grating placed on the top electrode of the film bulk acoustic resonator structure in order to forbid lateral propagation of the spurious Lamb mode. The finite element analysis is performed for two representative structures, namely, Mo/ZnO/Mo and Ru/AlN/Ru, on which the first-order symmetric Lamb mode exhibits the "Type-I" and "Type-II" dispersion, respectively. It is demonstrated theoretically that for both cases, the stop band is generated by the Bragg reflection, and a spurious free resonance is obtainable provided that the grating period and height are set so that the stop band covers the frequency range where the lateral mode resonances occur. (C) 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801401]

Because of their excellent features such as small size, wide bandwidth, and low insertion loss, ladder-type filters based on surface acoustic wave (SAW) technology have been widely used as radio-frequency (RF) filters in mobile communications. We can realize wide bandwidth and low insertion loss in ladder-type SAW filters on a Cu-grating/15 degrees LiNbO3 substrate structure. On the other hand, it is said that wide-bandwidth filters have poor temperature characteristics. Therefore, this paper discusses dynamic temperature compensation for wideband ladder-type SAW filters. First, we investigate how wide tunability is achievable using variable capacitors connected in parallel and/or series to SAW resonators in the filter configuration. Second, we measured the temperature characteristics of the resonator. Finally, we simulated temperature compensation in wideband ladder-type SAW filters. As a result, we were able to compensate the change of the characteristics with the ladder-type SAW filter connected using variable capacitors. (c) 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(4): 6166, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10420

This paper reviews current status and future prospects of radio frequency (RF) filters employing bulk acoustic wave (BAW) resonators. First, their fundamental operation is explained, and it is shown how these devices are fabricated with the skillful use of MEMS and thin film technologies in state of the art. It is also shown how high performances are achieved up to now and what are demanded and investigated for further evolution.

This paper reports development of an integrated tunable filter for lower UHF band based on the recursive architecture and its application. The recursive filter core gives the 2-pole bandpass response, and its center frequency can be tuned from 250 to 500 [MHz]. The auto setting mechanism was developed for the filter center frequency and passband width. Higher order filters were synthesized by combining multiple cores. A simple spectrum scope was constructed as a demonstration. © 2013 EuMA.

This paper reports development of an integrated tunable filter for lower UHF band based on the recursive architecture and its application. The recursive filter core gives the 2-pole bandpass response, and its center frequency can be tuned from 250 to 500 [MHz]. The auto setting mechanism was developed for the filter center frequency and passband width. Higher order filters were synthesized by combining multiple cores. A simple spectrum scope was constructed as a demonstration. © 2013 European Microwave Association.

This paper investigates origin of the excess acoustic propagation loss caused in silicon dioxide (SiO2) with deposition temperature T. It is shown that SiO2 prepared lower T gives higher surface acoustic wave (SAW) attenuation and larger optical attenuation in the UV region. The Raman spectroscopy shows the increase of the peak in the small wave number region. These results show that the acoustic propagation loss is caused by the distortion of Si-O network structure and the optical characterization is quite useful for the analysis of the attenuation mechanism as well as the TCE behavior in SiO2-based films. © 2013 IEEE.

The correlation between the propagation loss and SiO2 film properties has been studied for temperaturecompensated SAW devices using the SiO 2/LiNbO3 structure. The SAW devices were prepared under different deposition temperatures for SiO2 film. Although they possessed excellent temperature coefficient of elasticity characteristics, devices prepared at lower temperature showed lower Q-factors. The SiO 2 films were also deposited on a Si substrate under the same deposition conditions used for the SAW device preparation. Optical characterization was performed with Fourier transform infrared spectroscopy (FT-IR), spectrometer measurement, and Raman spectroscopy. IR absorbance spectra were almost same in the FT-IR measurement. However, optical attenuation in the UV region decreased with the deposition temperature in the spectrometer measurement. The optical attenuation is caused by the increase of the extinction coefficient in the SiO2 layer, and its optical wavelength dependence indicated that observed excess attenuation is caused by Rayleigh scattering. The Raman scattering also decreased with the deposition temperature in the Raman spectroscopy. The scattering is caused by the distortion of the SiO2 network. These results indicate that the Rayleigh scattering caused by the distortion of the SiO2 network is the main contributor to the excess SAW propagation loss in this case. © 1986-2012 IEEE.

A direct-conversion receiver (DCR) reduces the power consumption and cost. However, DCR in Orthogonal frequency division multiplex (OFDM) systems suffer from IQ imbalance. Until this time, many algorithms are proposed to compensate IQ imbalance in OFDM. However, the complexity is still considerable work. On the other hand, time-frequency interferometry-OFDM (TFI-OFDM) system has been proposed to achieve an accurate channel identification property with small number of pilot symbols. In this paper, we propose a novel IQ imbalance estimation and compensation scheme using TFI-OFDM system. In the proposed system, by using the feature of the TFI pilot symbols, we can identify IQ imbalance without high calculation complexity. Furthermore, by using subcarrier selection, the influence of the noise power can be reduced. From the simulation results, the proposed scheme can achieve the low-complexity IQ imbalance estimation and compensation without a degradation of the BER performance.

This paper proposes a filter configuration with wide tunability, which is composed of high Q RF resonators and variable capacitors (VCs). High Q resonators can be realized by surface and bulk acoustic wave (SAW/BAW) technologies. At first, the fundamental operation of the filter is presented, and it is shown how the center frequency and the passband width are adjustable with the VC setting. It is also shown that narrow transition bands are realizable when multiple stages are cascaded with mirror inversion. Then, influence of Q factors is discussed. Finally, two types of tunable filters are designed, and applicability of this filter topology is demonstrated. Furthermore, the filter configuration is realized using SAW resonators and fixed capacitors, and its operation is simulated.

This paper discusses applicability of the Bragg reflection in a periodic grating placed on the top electrode of the film bulk acoustic resonator (FBAR) structure in order to forbid lateral propagation of the spurious Lamb mode. The finite element analysis is performed for two representative structures, namely, Mo/ZnO/Mo and Ru/AIN/Ru, on which the first-order symmetric Lamb mode exhibits the "Type-I" and "Type-II" dispersion, respectively. It is demonstrated theoretically that for both cases, the stop band is generated by the Bragg reflection, and a spurious free resonance is obtainable provided that the grating period and height are set so that the stop band covers the frequency range where the lateral mode resonances occur.

This paper describes the design of RF SAW/BAW filters with constant group delay. The band-pass LC filter is designed based on the traditional Bessel filter design. Then, LC resonators in the filter are replaced by SAW/BAW resonators with finite capacitance ratio gamma. Finite gamma generates passband ripples in the group delay. However, it is shown the ripples can be suppressed by optimal design of the SAW/BAW resonators. Norton's first transform is also applied to the designed filter to reduce variation of resonator shunt capacitances. Finally, extremely flat group delay with deviation of 4 ns over the frequency range of +/-20 MHz at the center frequency of 1 GHz is theoretically demonstrated.

In a wireless network, the signals transmitted from one sender to different users have independent channel fluctuation characteristics. The diversity that exists between users is called multiuser diversity and can be exploited by the sender to enhance the capacity of wireless network. In multiuser diversity OFDMA system, exploiting channel fluctuation diversity is in essence done by selecting the user with the strong subcarrier channels. The individual subcarrier selection for each user can achieve the best system performance but high signaling overhead and high system complexity are required. On the other hand, the adaptive subcarrier block method achieves worse BER than that of individual subcarrier selection. This is because the selected block contains the poor channel subcarriers. To overcome this problem, in this paper, we propose an adaptive subcarrier block selection with frequency symbol spreading for an OFDMA system. (C) 2012 Elsevier Inc. All rights reserved.

This paper investigates origin of the excess acoustic propagation loss caused in fluorine doped silicon oxide (SiOF) films with large fluorine content r. The authors proposed to use SiOF films for temperature compensation of radio frequency (RF) surface acoustic wave (SAW) devices because of their large temperature coefficient of elasticity and small acoustic attenuation. It was also reported that when r is too large, the SAW attenuation became very large. The FT-IR measurement showed that the peak frequency omega(4) of the Si-O stretching vibration decreases significantly while its peak width Delta omega(4) increases dramatically in the situation. The Raman spectroscopy showed that the Raman scattering between 110 and 400 cm(-1) also becomes very strong. No obvious change was observed for the other optical frequencies. These results suggest that the excess propagation loss is mainly caused by the scattering at the damaged SiO2 network and fluorine termination.

Theoretical analysis showed that high performance surface acoustic wave (SAW) resonator with an extremely large electromechanical coupling factor K 2 could be realized on Y cut X propagating Pb(In1/2Nb1/2)O-3- Pb(Mg1/3Nb2/3)O-3-PbTiO3 (YX-PIN-PMN-PT) substrate. A one-port SAW resonator was designed, fabricated, and characterized on Cu-grating/YX-PIN-PMN-PT substrate structure. The experimental results demonstrate that very large K-2 of 57.3% is realizable. Such an extremely large K-2 makes PIN-PMN-PT single crystal great potential for realizing wideband SAW filters and tunable SAW filters. The influence of inhomogeneity and instability of the domain structure on the fabricated resonators has been discussed thoroughly for further improvement of the devices. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3675908]

Widely tunable dual-T SAW BEF (band elimination filter) and its application to VCSO (voltage controlled SAW oscillator) operating in UHF range are discussed. It is shown theoretically that owing to very low capacitance ratio (gamma similar to 4) of utilised SAW resonators, the notch frequency of the dual-T SAW BEF can be tuned for about 10% at 1 GHz. The designed voltage controlled current adder works properly for the dual-T SAW BEF, although the tuning frequency range is narrowed to about 4% by gain and phase dependence on control voltage. To check validity of the circuit design concept, a 430 MHz VCSO was fabricated by using a couple of narrow band SAW resonator of which resonant frequencies are 433.42 and 433.92 [MHz], respectively. The oscillation frequency could be continuously controlled from 433.56 to 433.65 [MHz]. Measured phase noise was -120 dBc/Hz at 10 kHz offset.

This paper investigates acoustic properties, including the temperature coefficient of elasticity (TCE), of fluorine-doped silicon oxide (SiOF) films and proposes the application of the films to the temperature compensation of RF SAW devices. From Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. We fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO3-substrate structure, and evaluated their performance. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO2-based films even when the dopant is added. In comparison with pure SiO2 with the film thickness h of 0.3 wavelengths (lambda), TCF was improved by 7.7 ppm/degrees C without deterioration of the effective electromechanical coupling factor K-2 when r = 3.8 atomic % and h = 0.28 lambda. Fluorine inclusion did not obviously influence the resonators' Q factors when r < 8.8 atomic %.

Orthogonal space-time block code (OSTBC) can achieve full diversity with a simple MLD, but the rate of OSTBC only achieves 3/4 of the maximum rate when applying more than two transmit antennas. To solve this problem, a quasi-orthogonal STBC (QOSTBC) scheme has been proposed. Even though a QOSTBC scheme can achieve the full rate, there are interference terms resulting from neighboring signals during detection. The existing QOSTBC using the pairs of transmitted symbols can be detected with two parallel MLD. Therefore, MLD based QOSTBC has higher complexity than OSTBC. To reduce the detection complexity, in this paper, we propose the heterogeneous constellation based QOSTBC for improving the detection property of QRD-MLD with maintaining a simple decoding structure.

This paper discusses modification of the scalar potential (SP) theory for the analysis of surface acoustic wave (SAW) devices to take asymmetry of the SAW slowness curve into account. First, it is shown that the SP theory is equivalent to the two-dimensional wave equation for a shear-vertical bulk wave, where variation of acoustic properties is expressed as that of the mass density while the elastic properties are uniform in the structure. Then the modified boundary conditions and the mode orthogonality relations are derived from the wave equation to take the asymmetry into account.

One-port SAW resonators were designed and fabricated on YX-PMN-PT substrate with Cu electrode, the measured results demonstrated the large electromechanical coupling factor K-2 of 60.5%. The strong spurious Rayleigh-type SAW was also observed and should be suppressed. Au electrode with large thickness of 6%lambda was applied and decreased it into very small value. With further increasing the Au electrode thickness into 10%lambda, the spurious Rayleigh-type SAW was shown to be sufficiently suppressed without seriously deteriorating the large K-2 of the main response. The temperature stability and homogeneity of the substrate were also evaluated.

We investigated the correlation between the temperature coefficient of elasticity (TCE) and Fourier transform infrared (FT-IR) absorption spectra of SiO(2) for SAW devices. The measurement indicated that the TCE is strongly correlated with peak frequencies; that is, with the fractional change of the Si-O-Si bond angle with temperature.

We investigate how the apodization applied to interdigital transducers (IDTs) affects the quality factor Q at the antiresonance frequency of surface acoustic wave (SAW) resonators. First, we fabricated SAW resonators with different apodization patterns on a SiO(2)/Cu/0 degrees YX-LiNbO(3) structure, and showed that the Q factor become worse when the apodization becomes steeper and the IDT aperture is narrower. Next, it was shown by optical measurement that the Q degradation is mainly due to the radiation of SH waves from the resonator. The radiation consists of energy leakage as bulk waves, diffraction, and scattering of incident SAWs, and their strength strongly depends on the steepness of the apodization pattern. (c) 2011 The Japan Society of Applied Physics

This paper describes the existence of piezoelectric boundary acoustic wave (PBAW) propagating in a Cu electrode/Y-cut X-propagating (YX) LiNbO3 substrate structure partially covered with a SiO2 layer. In the analysis, two types of structures are taken into consideration: one is the so-called slotted structure with SiO2 pillars placed in the grating slots; the other is the so-called topped structure with SiO2 pillars placed on the top of grating electrodes. The top surface could be fully covered with an additional layer (like epoxy) to bridge the grating slots for encapsulation. Results show that SH-type PBAW begins to propagate in the slotted structure when the SiO2 thickness exceeds 0.3 wavelength. Strong electromechanical coupling factor K-2 of 21%, and temperature coefficient of velocity (TCV) of -33 ppm/degrees C are obtained. In the topped structure, on the other hand, the boundary acoustic wave mode is not supported. Instead, the thickness resonance modes in the SiO2 pillar do exist. Comparison of the obtained results with those in the structure fully covered with the SiO2 layer indicates that, as for the PBAW mode, the slotted structure offers improved K-2 but with worse TCV compared with the fully covered SiO2 structure.

In this paper, we discuss a simplified boundary modeling for numerical simulation of complex real resonator devices by prior scattering analysis. Appropriate boundary conditions are a crucial factor for accurate simulation of resonator devices. We propose to analyze the scattering of propagating eigenmodes at the substrate-to-membrane anchor of the resonating structure and show that model simplification is feasible, provided that the backscattered energy at the anchor/substrate boundary is small and the contribution of energy tunneling by evanescent modes is negligible. Exemplarily, we analyze the model of a film bulk acoustic resonator (FBAR). (C) 2011 The Japan Society of Applied Physics

In our paper, we investigates acoustic properties including temperature coefficient of elasticity (TCE) of fluorine doped silicon oxide (SiOF) films and proposes their application to the temperature compensation of radio frequency (RF) surface acoustic wave (SAW) devices. From the Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. Then we fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO3-substrate structure, and their device performances were evaluated. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO2-based films even when the dopant is added. In comparison with the pure SiO2 with the film thickness h of 0.3 wavelengths (lambda), TCF was improved by 7.7 ppm/degrees C without deterioration of the effective electromechanical coupling factor K-2 when r=3.8 atomic % and h=0.28 lambda. The F inclusion did not influence the resonator Q factors obviously when r<8.8 atomic%.

Diamond has the highest known surface acoustic wave (SAW) phase velocity, sufficient for applications in the gigahertz range. However, although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all have large propagation loss in comparison to single-crystal materials such as LiNbO3. In this study, we successfully fabricated low-propagation-loss one-port SAW resonators on single-crystal diamond synthesized using a high-pressure and high-temperature method. The devices had an interdigital transducer (IDT)/AlN/diamond structure. The best performing device exhibited a resonance frequency of 5.3 GHz and a Q-value of 2440. After correcting for ohmic losses, the propagation loss was found to be 0.012dB/wavelength. Furthermore, a large fQ product value of 10(13) was also obtained. These results show that single-crystal diamond SAW resonators have great potential for use in 5-GHz-band oscillators.

携帯電話に代表される移動体通信機器には，表面弾性波やバルク波等の弾性波共振子を利用した高周波フィルタ，デュプレクサが多用されている．ほとんどの機能が半導体集積回路で，しかもディジタル技術で実現されている現在，残されたアナログ素子にもより一層の性能向上とともに新機能の付加が要請されている．本稿では，通信機器でこれらの素子がなぜ利用されるのか，特徴は何か，そして，更にはそれらの素子の限界がどこにあり，それに対してどのような解決法が提案されているのかを明らかにする．

Because of there excellent features such as small-size, wide bandwidth, and low insertion loss, the laddertype filters based on surface acoustic wave (SAW) technology have been widely used as radio-frequency (RF) filters in mobile communications. We can make wide bandwidth, and low insertion loss, the ladder-type SAW filters on a Cu-grating/15°LiNbO3 substrate structure. On the other hand, it is said that wide bandwidth filters is bad temperature characteristic. So this paper discusses dynamic temperature compensation of wideband ladder-type SAW filters. First, we investigate how wide tunability is achievable using variable capacitors parallel- and/or series-connectted to SAW resonators in the filter configuration. Second, we measured the temperature characteristic of resonator. Finally, we simulated temperature compensation of wideband ladder-type SAW filters. As a result, we were able to compensate the change of the characteristic with the ladder-type SAW filter connected variable capacitors. © 2011 The Institute of Electrical Engineers of Japan.

This paper reviews recent progress of temperature compensated surface acoustic wave (SAW) devices for wireless communications. First, temperature compensation techniques based on the SiO2 deposition and the wafer bonding are explained, and their implementation into real devices are discussed. Finally, we will show how high performances have been realized by the use of these technologies.

This paper describes extension of the scalar potential (SP) theory for the analysis of surface acoustic wave (SAW) devices. First, it is shown that the SP theory is equivalent to the two-dimensional wave equation for a shear-vertical bulk wave, where variation of acoustic properties is expressed as that of the mass density while the elastic properties are uniform in the structure. When periodic variation of the mass density and stress sources is taken into account, the theory is compatible to the coupling-of-mode (COM) model. The compatibility allows us to derive primary parameters necessary for the analysis from those determined for the COM model. The theory is applied to the analysis of a SAW resonator on the 15 degrees YX-LiNbO3 substrate, and effectiveness of the present method is demonstrated.

This paper describes the development of a phase-sensitive laser probe with fast mechanical scan for RF surface and bulk acoustic wave (SAW/BAW) devices. The Sagnac interferometer composed of micro-optic elements was introduced for the selective detection of RF vertical motion associated with RF SAW/BAW propagation and vibration. A high-pass characteristic of the interferometer makes the measurement very insensitive to low-frequency vibration. This feature allows us to apply the fast mechanical scan to the interferometric measurement without badly sacrificing its SNR and spatial resolution. The system was applied to the visualization of a field pattern on the vibrating surface of an RF BAW resonator operating in the 2 GHz range. The field pattern was obtained in 17 min as a 2-D image (500 x 750 pixel with 0.4 mu m resolution and SNR of 40 dB). The system was also applied to the characterization of an RF SAW resonator operating in the 1 GHz range, and the applicability of the system was demonstrated.

TFI-OFDM system can achieve an accurate channel identification property with small pilot symbols. However, when the guard interval is longer than the maximum delay spread, the fixed guard interval is inefficient. To mitigate this problem, in this paper, we propose the path-selection based adaptive guard interval for TFI-OFDM system. In the proposed system, the paths that exceeded the threshold which was set to a noise variance, were selected. Moreover, due to the selected large delay path, the proposed system can control the guard interval adaptively. From the simulation results, the proposed adaptive guard interval TFI-OFDM can achieve 7.2% and 3.2% throughput enhancement to compare with the conventional fixed guard interval TFI-OFDM under the 15path and vehicular A channels, respectively.

This paper proposes a method for analysing the behaviour of transverse modes propagating under an SAW waveguide composed of IDT and weighted dummy electrodes. The proposed method can be used as one of the powerful tools to understand the behaviour of transverse mode propagation and to design wideband SAW resonators with suppressed spurious transverse mode resonances.

In a recent year, a high data rate and a high quality multimedia services are demanded. To meet this demand, orthogonal frequency division multiplexing (OFDM) is attractive and widely studied. In an OFDM system, the channel estimation (CE) is very important. However, since the channel is rapidly varied, many errors occur in the last part of the packet in the fast fading environment. To mitigate this problem, the joint direct and linear prediction method has been proposed. However, this method shows the large number of errors in the last part of the packet by using the linear prediction. To overcome this problem, in this paper, we propose the non-linear prediction method to compensate the channel variance in the last part of the packet.

This paper investigates the acoustic losses of propagating eigenmodes through the acoustic mirror of a solidly mounted resonator (SMR) to clarify how resonator properties are influenced by reflection coefficients for the thickness shear (TS) wave as well as that for the thickness extensional (TE) wave. To this end, we analyze the effective acoustic admittance for several test structures with different mirror properties. Leaky modes are distinguished from plate-like modes and the propagation losses are quantified by calculating mode quality factors. The dependence of the propagation properties of leaky eigenmodes is compared with the mirror properties in terms of bulk wave transmission coefficients obtained by the one-dimensional Mason's model. It is shown that the TE-like main mode couples with TS-like spurious modes, which then influence the leaky loss of the main mode as well. The coupling strength is strongly frequency-dependent and drastically changes with the mirror design. This result explains previous experimental results reported on SMR design.

This paper demonstrates a novel frequency domain analysis (FDA) to evaluate the scattering behavior of a waveguide mode at arbitrary scattering geometries by a time harmonic simulation based on the finite element method (FEM). To this end, we add an injection-damping mechanism (IDM) to avoid interference at the acoustic input port. The IDM can be easily constructed by a numerical operation. Our approach offers improved time consumption and calculation power necessary over the established method in the time domain. After checking the validity of the proposed method, we discuss the importance of considering wave scattering phenomena in film bulk acoustic wave resonator (FBAR) devices by applying the proposed method to two simplified models of an FBAR device.

This paper describes an attempt to develop extremely wideband multi- mode surface acoustic wave (MMS) filters in the gigahertz range. The Cu-grating/15 degrees YX-LiNbO3 (15-LN)-substrate structure is employed. First, a design tool developed for the present purpose is detailed. Precise simulation is performed using a modified coupling-of-modes model, in which the coupling between propagating surface and bulk acoustic waves is taken into account. Parameters necessary for the simulation are determined experimentally. Next, this simulation tool is used to design a wideband MMS filter employing pitch-modulated IDTs proposed by the authors. It is shown that a fractional bandwidth of more than 12% is achievable by successfully using six SAW resonances supported in the MMS structure. The designed MMS filter was fabricated on a Cu-grating/15-LN-substrate structure. The passband width of 12.6% and the minimum insertion loss of 1.2 dB were experimentally obtained around 850 MHz. The measured result was in good agreement with the simulation.

This paper proposes a method to estimate power carried by a propagating Lamb mode in an arbitrary multilayer waveguide from calculated or measured surface displacements. To this end, we calculate the so-called mode power coefficient relating the surface amplitude of the mode to the total power flow toward the lateral direction. The coefficient is given by the gradient of the effective acoustic admittance with respect to the lateral wavenumber, and can be readily calculated by slightly modifying software codes developed for calculating the dispersion relation of Lamb waves. This calculation procedure is simpler and more efficient than the conventional technique based on the estimation of total power flow passing through the waveguide cross section. We apply this technique to the quantitative evaluation of acoustic losses in a thin-film bulk acoustic wave resonator (FBAR), and the effectiveness of this technique is demonstrated.

This paper describes a phase-sensitive and fast-scanning laser probe developed by the authors' group for the diagnosis of acoustic wave devices used as a platform of highly sensitive sensors. Surface vibration is detected by the Sagnac interferometer, which is insensitive to low frequency vibration. From this feature, we can maximize the scanning speed without influence of low frequency vibration and sacrificing the signal-to-noise ratio of the measurement. It is demonstrated that high quality two-dimensional (2D) image of acoustic wave field patterns can be captured in minutes order. Currently the maximum applicable frequency is 2.5 GHz. Because of the phase sensitivity, the measured field in the space domain is readily converted into the wavenumber domain by the 2D Fourier Transform. It is also demonstrated how effective the wavenumber domain analysis is for the purpose. (C) 2010 Published by Elsevier Ltd.

This paper describes how the characteristics of shear-horizontal type piezoelectric boundary acoustic waves (PBAWs) change with combination of different overlay and metal grating materials. It is shown that PBAWs are supported in various structures provided that highly piezoelectric material(s) are employed as structural member(s). For verification, numerical simulation of different material combinations is done. The results are in good agreement with the qualitative prediction. That is, large electromechanical coupling factor K(2) is obtainable when materials having small mass densities shear modulus c(44) and shear velocity V(BS); and materials having extremely large shear modulus c(44) are chosen, respectively, for overlay and metallic grating. When YX-LiNbO(3) is assumed as a substrate, for example, the best choice seems to be SiO(2) and Au for overlay and metallic grating, respectively. Although metals with extremely large p and c(44) such as W and Ta offer large K(2), they may not be acceptable for practical PBAW applications because of their large electric resistivity.

This paper proposes a focusing method based on multiple scanning of a device surface to be observed, which is particularly-suitable for a fast-mechanical-scanning and phase-sensitive laser probe for radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. When high spatial resolution is required for the observation, one needs an objective lens of large magnifying power with extremely shallow focal depth. Accordingly, an uneven surface and tiny inclination of a BAW device cause acquired images a considerable defocus, by which it is difficult to obtain precise and reliable field quantities related to acoustic waves in the device. The proposed method is shown to be most effective in avoiding this sort of defocus and able to focus the entire surface. By this method, for example, we could clearly observe power leakage in an FBAR structure. (C) 2010 The Japan Society of Applied Physics

Because of their low insertion loss, high out-of-band rejection, and high power durability, miniature surface acoustic wave (SAW) duplexers are widely used in mobile phones. Substrate materials substantially limit and determine the performance of SAW duplexers; for their applications to Band I and Band IV systems with large pass-band widths and wide frequency separations between the transmitting and receiving frequency bands, a larger coupling coefficient (K-2) is of primary importance. We have developed a shape-controlled SiO2 film/Al electrode/LiNbO3 substrate structure for their applications. It could lead to a large K-2 and suppression of Rayleigh-mode spurious response. In this paper, we report the analysis using finite element method/spectrum domain analysis (FEM/SDA) for the SAW resonator on a nonflat SiO2 film/Al electrode/LiNbO3 structure. It was clarified that the shape-controlled SiO2 was effective in terms of achieving a large K-2 for the SAW resonator with suppressed Rayleigh-mode spurious responses and bulk wave radiation. Furthermore, the experiment results showed a good agreement with the analysis results. (C) 2010 The Japan Society of Applied Physics

In a wireless network, the signals transmitted from one sender to different users have independent channel fluctuation characteristics. The diversity that exists between users is called multiuser diversity and can be exploited by the sender to enhance the capacity of wireless network. In multiuser diversity OFDMA system, exploiting channel fluctuation diversity is in essence done by selecting the user with the strong subcarrier channels. The individual subcarrier selection for each user can achieve the best system performance but high signaling overhead and high system complexity are required. On the other hand, the adaptive subcarrier block method achieves worse BER than that of individual subcarrier selection. This is because the selected block contains the poor channel subcarriers. To overcome this problem, in this paper, we propose an adaptive subcarrier block selection with frequency symbol spreading for an OFDMA system.

This paper investigates the acoustic losses of propagating eigenmodes through the acoustic mirror of a solidly mounted resonator (SMR), aiming to clarify how resonator properties are influenced by reflection coefficients for the thickness shear (TS) wave as well as that for the thickness extensional (TE) wave. To this end, we analyze the effective acoustic admittance for several test structures with different mirror properties. Leaky modes are distinguished from plate-like modes and the propagation losses are quantified by calculating mode quality factors. The dependence of the propagation properties of leaky eigenmodes is compared to the mirror properties in terms of bulk wave transmission coefficients obtained by the one-dimensional Mason's model. It is shown that the TE-like main mode couples with TS-like spurious modes, which then influences the leaky loss of the main mode as well. The coupling strength is strongly frequency dependent and drastically changes with the mirror design. This result explains previous experimental results reported on SMR design.

In this paper, we describe possible configurations for tunable filters based on RF surface or bulk acoustic wave (SAW/BAW) technologies. The frequency tuning is made possible by variable capacitors (VCs) connected to SAW/BAW resonators in the ladder-type filter configuration. First, it is shown that the passband edges can be controlled by one VC connected to each resonator. Second, it is discussed that the width and location of a passband can be controlled flexibly by two VCs connected to each resonator both in parallel and in series. Finally, the SAW filters with the proposed configuration are fabricated on a Cu-grating/15 degrees YX-LiNbO3 substrate structure, and the tuning capability is demonstrated. (C) 2010 The Japan Society of Applied Physics

This paper reviews a phase-sensitive and fast-scanning laser probing system developed by the authors' group for the diagnosis of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. The system is based on the Sagnac interferometer, which is insensitive to low frequency vibration. From this feature, we can maximize the scanning speed without sacrificing the signal-to-noise ratio of the measurement. It is demonstrated that high quality two-dimensional (2D) image of SAW/BAW field patterns can be captured in minutes order. Currently the maximum applicable frequency is about 2.5 GHz. Because of the phase sensitivity, the measured field in the space domain is readily converted into the wavenumber domain by the 2D Fourier Transform. It is also demonstrated how effective the wavenumber domain analysis is for the purpose.