An acoustic structure is provided. The acoustic structure includes an acoustic resonator structure configured to resonate in a series resonance frequency (e.g., passband frequency) to pass a signal, or cause a series capacitance to block the signal in a parallel resonance frequency (e.g., stopband frequency). The parallel resonance frequency may become higher than the series resonance frequency when the tunable capacitance is lesser than or equal to two times of the series capacitance (C.sub.Tune≤2C.sub.0), or lower than the series resonance frequency when the tunable capacitance is greater than two times of the series capacitance (C.sub.Tune>2C.sub.0). In this regard, the acoustic structure can be configured to include a tunable reactive circuit to generate the tunable capacitance (C.sub.Tune) to adjust the parallel resonance frequency. As such, it may be possible to flexibly configure the acoustic resonator structure to block the signal in desired stopband frequencies.

The present subject matter relates to systems, devices, and methods for adaptively tuning antenna elements and/or associated filter elements to support multiple frequency bands. For example, a tunable filter having an input node and an output node can be selectively tunable to define one or more pass bands associated with one or more first signal bands and one or more reject bands associated with one or more second signal bands. The tunable filter can be configured to pass signals having frequencies within the first signal bands between the input node and the output node and to block signals having frequencies within the second signal bands. Furthermore, the tunable filter can be configured to selectively tune the pass bands to have a minimum pass band insertion loss at any of a variety of frequencies, including frequencies that are greater than and less than frequencies within the reject bands.

An acoustic impedance transformation circuit and related apparatus are provided. In aspects discussed herein, the acoustic impedance transformation circuit can be configured to transform an input impedance into an output impedance higher than the input impedance. In this regard, the acoustic impedance transformation circuit can be provided in an apparatus to enable impedance matching between two electrical circuits. As a result, it may be possible to reduce signal reflection resulting from impedance mismatch between the two circuits, thus helping to improve performance of the apparatus.

An acoustic structure is provided. The acoustic structure includes an acoustic resonator structure configured to resonate in a series resonance frequency (e.g., passband frequency) to pass a signal, or cause a series capacitance to block the signal in a parallel resonance frequency (e.g., stopband frequency). The parallel resonance frequency may become higher than the series resonance frequency when the tunable capacitance is lesser than or equal to two times of the series capacitance (C.sub.Tune2C.sub.0), or lower than the series resonance frequency when the tunable capacitance is greater than two times of the series capacitance (C.sub.Tune>2C.sub.0). In this regard, the acoustic structure can be configured to include a tunable reactive circuit to generate the tunable capacitance (C.sub.Tune) to adjust the parallel resonance frequency. As such, it may be possible to flexibly configure the acoustic resonator structure to block the signal in desired stopband frequencies.

An acoustic impedance transformation circuit and related apparatus are provided. In aspects discussed herein, the acoustic impedance transformation circuit can be configured to transform an input impedance into an output impedance higher than the input impedance. In this regard, the acoustic impedance transformation circuit can be provided in an apparatus to enable impedance matching between two electrical circuits. As a result, it may be possible to reduce signal reflection resulting from impedance mismatch between the two circuits, thus helping to improve performance of the apparatus.