ABSTRACT
Frequency-offset immunosensors based on acoustic wave devices are known to provide extremely high sensitivity and selectivity where the target is detected and identified based on the amount of frequency shift. We propose a new method to further classify chemically similar molecules extrapolating on the concept of in-phase (I) and quadrature (Q) domain used for the detection of orthogonal M-ary signals in digital telecommunication systems. We performed a series of detection experiments using samples of explosives such as cyclotrimethylene trinitramine [or royal demolition explosive (RDX)] and trinitrotoluene (TNT), containing nitrous oxide (NO2) groups and chemically analogous substances (e.g., musk oil). This detection scheme involves the use of semi-orthogonal monoclonal anti-TNT and anti-RDX antibodies immobilized onto two separate sensor surfaces. The term semi-orthogonal represents the co-option of a term used heavily in digital radio for the purpose of describing chemical orthogonality. The antibody to TNT which we use has some reactivity with RDX, and other nitrous oxide compounds. This feature of an antibody is referred to in the literature as antibody promiscuity. The antibody for RDX which we use shows very little cross reactivity with other molecules and, hence, the chemical responsiveness of the two antibodies is not quite orthogonal. Their responses are then chemically semi-orthogonal. The two semi-orthogonal immunosensor responses were then monitored and the baseline frequency shifts were recorded. After remapping the measured frequency data of the analytes onto a new 2-D domain by setting the TNT-specific sensor as the (I) or real component and the RDX-specific sensor as the (Q) or imaginary component, we could observe that all the substances were detected and mapped out to distinct regions on the I-Q plot. We assert that there is a strong resemblance between digital radio system quadrature detection techniques and our I-Q mapping scheme of the semi-orthogonal immunosensor signatures.
ABSTRACT
Recently, it has been experimentally reported that enhanced upper-sideband suppression of a longitudinally coupled (first/third) dual-mode leaky SAW (LSAW) resonator filter may be obtained by incorporation of a selectively valued capacitor between input and output terminals. In this paper, coupling-of-modes (COM) and bandstop-filter modeling is applied to realize this enhanced suppression. Tradeoffs are examined between upper and lower side-band suppression levels caused by the ensuing capacitive coupling between input and output terminals. Good agreement is obtained between this theory and reported experimental results for an 800-MHz band cellular filter.
ABSTRACT
Conductance measurements are reported on a leaky SAW (LSAW) harmonic one-port resonator on a 64 degrees Y-X LiNbO(3) substrate. This employed a short three-finger IDT for fundamental and second harmonic operation together with long reflection gratings. Conductances were measured with and without the end gratings. From an analysis of the measurements, it was deduced that, for optimum second harmonic performance, the grating stop-band frequency should be higher than the IDT unperturbed center frequency. This result is in contrast to fundamental frequency resonator designs in which the end grating stop-band frequency is placed below the IDT center frequency for optimum performance.
ABSTRACT
The use of surface-transverse-wave (STW) resonator-based oscillators as amplifiers and as carrier recovery elements is discussed. It is demonstrated that these oscillators can amplify phase-shift-keyed signals with very little added noise, while providing a constant output power. Their performance in carrier recovery amplifications is analyzed. Experimental results showing the amplification with more than 80 dB of dynamic range of a 2 Mb/s BPSK signal and the carrier recovery of an 8 Mb/s signal with a 1-GHz STW oscillator are shown.
ABSTRACT
Coupling-of-modes-in-time and coupling-of-modes-in-space analyses are applied to the modeling of a two-port two-pole waveguide-coupled SAW resonator filter. Modeling is applied to a lumped equivalent circuit and a distributed circuit. While the accuracy of the coupling estimation dictates the exact mode-splitting and bandwidth, the ensuing computations can give a good representation of the amplitude and phase response, including the effect of degenerate transverse modes.
ABSTRACT
The S(11) and equivalent S(21) frequency responses of a one-port surface acoustic wave (SAW) resonator with transverse modes derived from one-dimensional coupling-of-modes and transmission-matrix analysis. The two-dimensional nature of the problem is approximated by a summation of one-dimensional mode responses for each transverse mode. Comparison between theory and experimental data for a commercial 280-MHz one-port SAW resonator shows good agreement for the placement of transverse modes.
ABSTRACT
A minimum-shift-keyed (MSK) system using one 1-GHz surface-transverse-wave (STW) resonator in the transmitter and two identical STW resonators in the receiver is described. It is shown to operate with data rates of over 100 kb/s and consume 150 mW. The system has a very high sensitivity and is tolerant to additive noise. Since the signal is never up- or down-converted. this system eliminates high power consumption. The system should find applications in cellular radios and in industrial communications.
ABSTRACT
Mode-selection control of a multimode surface-acoustic-wave (SAW) oscillator has been obtained using SAW linear FM chirp signal injection. The prototype 60-100-MHz SAW oscillator design employed a single-phase unidirectional transducer (SPUDT) low-loss comb filter in the feedback loop, with minimum insertion loss of approximately 3.7 dB. Mode selection was achieved using an injection signal derived from the mixed output of two 27.5-52.5-MHz up- and down-chirp SAW filters. Mode switching times of less, similar2 mus were obtained. The device could be useful as a local oscillator on frequency-agile radars, where hopping is required over a moderate number of frequencies.
