Abstract
We present the first group of gigahertz S0 mode low loss and wideband acoustic delay lines (ADLs). The ADLs use a single-phase unidirectional transducers (SPUDT) design to launch and propagate the S0 mode in an X-cut lithium niobate thin film with large electromechanical coupling and low damping. In this work, the theoretical performance bounds of S0 mode ADLs are first investigated, significantly surpassing those in state-of-the-art. The design tradeoffs of S0 mode ADLs, when scaled to the gigahertz frequency range, are also discussed. The fabricated miniature ADLs show a fractional bandwidth (FBW) of 4% and a minimum insertion loss (IL) of 3.2 dB, outperforming the incumbent surface acoustic wave (SAW) counterparts, and covering a wide range of delays from 20 to 900 ns for digitally addressable delay synthesis. Multiple ADLs with center frequencies from 0.9 to 2 GHz have been demonstrated, underscoring their great frequency scalability. The propagation properties of S0 waves in lithium niobate at the gigahertz range are experimentally extracted. The demonstrated ADLs can potentially enable wide-range and high-resolution delay synthesis that is highly sought after for the self-interference cancellation in full-duplex radios.
Highlights
F ULL-DUPLEX radios, where the transmitters and receivers operate simultaneously in the same frequency band, have sparked great research interest due to their great potential to enhance spectrum utilization efficiency and reduce networking complexity [1]–[3]
It can be used for various sensing applications [17], [18] and the construction of nonreciprocal networks [19], [20]. It was difficult for these surface acoustic wave (SAW) demonstrations to provide sufficiently low insertion loss (IL) and wide BW simultaneously for the SI cancellation (SIC) applications even when custom designed unidirectional transducers were adopted [21], [22]. Such a performance limit arises from the intrinsic tradeoff between the IL and fractional BW (FBW), which are fundamentally imposed by the attainable reflectivity of the distributed reflectors and the maximum electromechanical coupling (k2) of the SAW modes [23]
The propagation loss (PL) of the S0 mode at the gigahertz frequency range is experimentally measured for the first time, showing a PL of 6.08 dB/μs at 0.96 GHz or 0.0055 dB/λ
Summary
F ULL-DUPLEX radios, where the transmitters and receivers operate simultaneously in the same frequency band, have sparked great research interest due to their great potential to enhance spectrum utilization efficiency and reduce networking complexity [1]–[3]. Acoustic delay lines (ADLs) with remarkably smaller sizes and lower PL [11] are an excellent alternative platform for a compact, wideband, and low-loss delay synthesis that is capable of being scaled toward the gigahertz frequency range and overcoming the shortcomings of the EM structures. It was difficult for these SAW demonstrations to provide sufficiently low IL and wide BW simultaneously for the SIC applications even when custom designed unidirectional transducers were adopted [21], [22] Such a performance limit arises from the intrinsic tradeoff between the IL and fractional BW (FBW), which are fundamentally imposed by the attainable reflectivity of the distributed reflectors and the maximum electromechanical coupling (k2) of the SAW modes [23].
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