Biomedical subjects

Donald C Malocha

Publications and source records attributed to Donald C Malocha.

5 recordsLinked to original sources

PubMed2006

Orthogonal frequency coding for SAW tagging and sensors.

Surface acoustic wave (SAW)-based sensors can offer wireless, passive operation in numerous environments, and various device embodiments are used for retrieval of the sensed data information. Single sensor systems typically can use a single carrier frequency and a simple device embodiment because tagging is not required. In a multisensor environment, it is necessary to both identify the sensor and retrieve the sensed information. This paper presents the concept of orthogonal frequency coding (OFC) for applications to SAW sensor technology. The OFC offers all advantages inherent to spread spectrum communications, including enhanced processing gain and lower interrogation power spectral density (PSD). It is shown that the time ambiguity in the OFC compressed pulse is significantly reduced as compared with a single frequency tag having the same code length, and additional coding can be added using a pseudo-noise (PN) sequence. The OFC approach is general and should be applicable to many differing SAW sensors for temperature, pressure, liquid, gases, etc. Device embodiments are shown, and a potential transceiver is described. Measured device results are presented and compared with coupling of modes (COM) model predictions to demonstrate performance. Devices then are used in computer simulations of the proposed transceiver design, and the results of an OFC sensor system are discussed.

Computer-Aided Design↗

PubMed2002

Simulation of short LSAW transducers including electrode mass loading and finite finger resistance.

The theory for the 2-D numerical analysis of acoustic wave generation from finite length leaky surface acoustic wave (LSAW) transducer structures is presented. The mass loading of the electrodes is incorporated through the use of the finite element method (FEM). The substrate is modeled using both analytical and numerical means. The advantages of this simulation are twofold. First, it is capable of extracting the individual bulk wave conductances from the overall conductance of a given device. At large distances from the transducer, the angular distribution of power radiated relative to the substrate surface can then be calculated for each of the three possible bulk wave polarizations. The second advantage of the simulation is that the effect of finite electrode resistance is included through the use of a series equivalent resistance for each electrode in the structure. Once the resistance for each electrode in the structure has been determined, the overall effect on the device admittance is modeled by applying a constrained minimization process to the electrical boundary conditions of the transducer. To conclude the paper, the simulation will be compared against the experimental admittance of a 37-finger uniform transducer with a metalization ratio of 0.5 on 42 degrees LiTaO3. The agreement between theory and experiment is excellent.

Journal Article↗

PubMed2002

Measurements of LGS, LGN, and LGT thermal coefficients of expansion and density.

This paper will report on the measurements of the thermal coefficients of expansion and density of langasite (LGS), langanite (LGN), and langatate (LGT). The data were obtained by fabricating cubes with X, Y, and Z faces with nominal dimensions of 1 cm on a side for each material under test. The techniques used for measurement of density and thermal coefficients of expansion (TCE) of the materials are discussed. The data sets obtained and the extracted coefficients are presented.

Chemistry, Physical↗

PubMed2002

BAW temperature sensitivity and coupling in langanite.

One of the new materials belonging to the trigonal class 32, to which quartz belongs, is langanite (LGN, La3Ga5.5Nb0.5O14). High-quality LGN single crystals are now available, and, although similar in composition and structure to langasite (LGS, La3Ga5SiO14), LGN has smaller thermal expansion coefficients and comparable piezoelectric constants to LGS. These are desirable material properties for both SAW and BAW applications that require low frequency dependence on temperature. This paper examines in detail the LGN characteristics: phase velocity, temperature coefficient of frequency (TCF), electromechanical coupling coefficient, and power flow angle for both singly and doubly rotated plate cuts. Contour plots of these characteristics are constructed, revealing orientation regions where zero TCF and high coupling exist and suggesting potentially interesting cuts for practical BAW device design. Temperature compensated cut regions with coupling coefficients as high as 0.16 are predicted, which is twice the value for AT-cut quartz, along with a temperature compensated cut with cubic behavior around room temperature for one of the sets of material constants used. With such desirable properties, LGN is a promising candidate material for BAW applications requiring low temperature sensitivity with superior bandwidth characteristics due to its values of coupling coefficient larger than quartz. Several other orientations with low TCF and high coupling are also identified.

Acoustics↗

PubMed2002

Surface and pseudo surface acoustic waves in langatate: predictions and measurements.

Langatate (LGT, La3Ga(5.5)Ta(0.5)O14) is a recent addition to materials of the trigonal crystal class 32, which is the same crystal class as quartz, langasite, langanite, and gallium phosphate. Langatate has several attractive acoustical properties, in particular: a measured bulk acoustic wave (BAW) resonator quality factor frequency product (Qf) of 16 million, comparable to that of AT cut quartz; high-piezoelectric coupling orientations, up to 0.5% for surface acoustic waves (SAWs), about five times larger than that of ST-X quartz; low power flow angle orientations in the vicinity of high coupling orientations; phase velocities about 20% smaller than those of ST-X quartz, facilitating the production of smaller, lower frequency devices; the existence of pseudo SAW modes for higher frequency applications. In this paper SAW contour plots of the phase velocity (vp), the electromechanical coupling coefficient (K2), the temperature coefficient of delay (TCD), and the power flow angle (PFA), are given showing the orientations in space in which high coupling is obtained, with the corresponding TCD, PFA, and vp characteristics for these orientations. This work reports experimental results on the SAW temperature fractional frequency variation (delta f/fo) and the TCD for several LGT orientations on the plane with Euler angles: (0 degrees, 132 degrees, psi). The temperature behavior has been measured directly on SAW wafers from 10 to 200 degrees C, and the results are compared with numerical predictions using our recently measured temperature coefficients for LGT material constants. This research also has uncovered temperature compensated orientations, which we have experimentally verified with parabolic behavior, turnover temperatures in the 130 to 160 degrees C range, and delta f/fo within 1000 ppm variation from 10 to 260 degrees C, appropriate for higher temperature device applications. Regarding the pseudo surface acoustic waves (PSAWs), results of calculations are presented for both the PSAW and the high velocity PSAW (HVPSAW) for some selected, rotated cuts. This study shows that propagation losses for the PSAWs of about 0.01 dB/wavelength, and phase velocities approximately 20% higher than that of the SAW, exist along specific orientations for the PSAW, thus showing the potential for somewhat higher frequency SAW device applications on this material, if required.

Journal Article↗