Floating Electrode Unidirectional Transducer Research Articles

Analysis and Optimization of Surface Acoustic Wave Floating Electrode Unidirectional Transducers Using Coupling-of-Mode Theory and Finite-Element Method

The performance of a floating-electrode unidirectional transducer (FEUDT) with acoustic wavelength of 30 μm is analyzed by coupling-of-mode (COM) theory. In order to extract the COM parameters, a finite element model is developed. The obtained dispersion curve shows frequencies of four stopband edges different from one another which meets the necessary condition for FEUDT. The phase shift of reflection and transduction centers is derived from the standing wave distributions of electric potential in the whole substrate. When a/p= 0.92 (electrode width/period) and h/p = 0.015 (electrode height/period), the value of ϕ–ψ = 44.8° (ϕ and ψ are phase angle of reflection and transduction centers, respectively) can be obtained fairly close to the 45°. By analyzing SAW energy transportation characteristics, FEUDT is found that the more periods it has, the better directivity it exhibits.

Low-loss Floating Electrode Unidirectional Transducer for SAW Sensor

Two types of interdigital transducer (IDT) structures of SAW devices have been investigated; one type consists in a classical single electrode transducer where the unit cell has two electrodes, and the other type has a design of floating electrode unidirectional transducer (FEUDT) where the unit cell has six electrodes per period. By taking the Fourier transform of the corresponding time response, the insertion loss (IL) of the SAW device with FEUDT is calculated as –2.6 (forward) and –20.5 dB (backward). At the same time, the device with conventional IDT exhibits an IL value of –8.4 (forward) and –7.8 dB (backward). It turns out that the design of a novel FEUDT type SAW device can efficiently reduce the insertion loss of the SAW device.

Temperature dependence of immunoreactions using shear horizontal surface acoustic wave immunosensors

In this paper, the temperature dependence of immunoreactions, which are antibody–antigen reactions, on a shear horizontal surface acoustic wave (SH-SAW) immunosensor is described. The immunosensor is based on a reflection-type delay line on a 36° Y-cut 90° X-propagation quartz substrate, where the delay line is composed of a floating electrode unidirectional transducer (FEUDT), a grating reflector, and a sensing area between them. In order to evaluate the temperature dependence of immunoreactions, human serum albumin (HSA) antigen–antibody reactions are investigated. The SH-SAW immunosensor chip is placed in a thermostatic chamber and the changes in the SH-SAW velocity resulting from the immunoreactions are measured at different temperatures. As a result, it is observed that the HSA immunoreactions are influenced by the ambient temperature and that higher temperatures provide more active reactions. In order to analyze the immunoreactions, an analytical approach using an exponential fitting method for changes in SH-SAW velocity is employed.

Surface acoustic wave unidirectional transducers for quantum applications

The conversion efficiency of electric microwave signals into surface acoustic waves in different types of superconducting transducers is studied with the aim of quantum applications. We compare delay lines containing either conventional symmetric transducers (IDTs) or unidirectional transducers (UDTs) at 2.3 GHz and 10 mK. The UDT delay lines improve the insertion loss with 4.7 dB and a directivity of 22 dB is found for each UDT, indicating that 99.4% of the acoustic power goes in the desired direction. The power lost in the undesired direction accounts for more than 90% of the total loss in IDT delay lines, but only ∼3% of the total loss in the floating electrode unidirectional transducer delay lines.

Liquid-Phase Shear Horizontal Surface Acoustic Wave Immunosensor

In this paper, we describe liquid-phase immunosensors based on shear horizontal surface acoustic waves (SH-SAWs), which can be directly dipped into a liquid. The sensor devices are fabricated using an SH-SAW delay line on quartz and LiTaO3 substrates, which is composed of a transmitting floating electrode unidirectional transducer (FEUDT), receiving FEUDT, and a biochemical reaction area between them. These FEUDTs are protected from liquids by a glass lid and epoxy walls, which are constructed using a photolithography technique. Therefore, the sensor devices can be directly dipped into a liquid and a liquid can be directly applied onto the surface of the sensor devices. In order to evaluate basic characteristics of the sensor devices, glycerol–water mixture liquids of different viscosities were used. For evaluations of their applicability to immunoassay, human serum albumin antigen–antibody reactions were investigated.

Development of a Shear Horizontal Surface Acoustic Wave Sensor System with a Floating Electrode Unidirectional Transducer

not Available.

Development of a Shear Horizontal Surface Acoustic Wave Sensor System for Liquids with a Floating Electrode Unidirectional Transducer

The development of sensors using surface acoustic wave (SAW) devices has been attracting attention. A shear horizontal SAW (SH-SAW) sensor can detect the properties and chemical reactions in liquids. To realize practical applications of the SAW sensor, it is necessary to discuss its properties. In this paper, SH-SAW sensors with a floating electrode unidirectional transducer (FEUDT) or an interdigital transducer (IDT) are compared and the insertion loss and phase characteristics are measured. Also, the phase shift between sample and reference liquids is evaluated. The results indicate that the SH-SAW sensor with the FEUDT is suitable for liquid measurements. The SH-SAW sensor with the FEUDT is then mounted in a newly developed SH-SAW sensing system. The system configuration is the same as that of a vector voltmeter measurement system. However, circuits have been developed that reduce its size. Using this system, several liquids are measured. The obtained results agree well with the theoretical values.

Coupled model analysis of SAW floating electrode type unidirectional transducers

The performance of a single-phase unidirectional transducers utilizing the internal reflections of floating electrodes of electrically open and shorted metal strips within an interdigital electrode structure (FEUDT: floating electrode unidirectional transducer) is analyzed using a coupled-mode theory. All four independent parameters (the self and mutual coupling coefficient, the transduction coefficient, and the static capacitance) governing the coupling-mode equation with an electrical transduction term are analytically derived using extended Legendre polynomial expansions of electrical fields and perturbation analysis. Frequency response of radiation admittance and insertion loss, and SAW field distributions in a transducer are calculated from simple closed-form solutions of the coupled-mode equation. The shift effect of reflection and transduction centers due to the asymmetric electrode structure is clarified. Experimental results are given for test devices fabricated on a 128 degrees C YX LiNbO(3) substrate and compared with theoretical results.

Wide Bandwidth Low Loss Filters Using Piezoelectric Leaky SAW Unidirectional Transducers with Floating Electrodes

A new configuration of SAW floating electrode unidirectional transducer (FEUDT) previously proposed is theoretically investigated using Green's function method and is also experimentally studied. The improved FEUDTs provide easier fabrication, higher operating frequency, and better characteristics for a piezoelectric leaky SAW with a low propagation attenuation and a high electromechanical coupling coefficient. Experimental filters consisting of FEUDTs and narrow gap FEUDTs (NGFEUDT) with minimum electrode width 2.5 µm on a 41° YX LiNbO3 substrate show the low insertion loss of 2.6 dB at 360 MHz and 2.8 dB at 700 MHz, respectively.

SAW Device Simulation Using Boundary Element Method

The paper has attempted to employ the expansion functions of the charge distribution on an electrode proposed by Skeie and Rønnekleiv for the boundary element method (BEM) analysis of interdigital transducers (IDTs). The accuracy and extremely rapid convergence of the analysis were confirmed by the calculation of static capacitances for several types of IDTs. The analysis was also applied to the characterisation of a floating electrode unidirectional transducer with a large number of electrodes. This confirmed that BEM mentioned in the present paper could be used as an effective tool for SAW device simulation.