The ‘how & why’ a deceptively simple acoustic resonator became the basis of a multi-billion dollar industry

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Abstract
The ability to achieve ubiquitous connectivity and run powerful `Apps' on today's Smart phones requires a front-end radio able to handle tremendous data rates; and that, requires access to the full bandwidth owned by service providers. Once, the front-end radio consisted of a single power amplifier (PA), filter/duplexer, a switch and a low noise amplifier (LNA). Early on, a cell phone might be able to access 2 or 3 frequency bands. Today, the iPhone 7 accesses 23 to 24 GSM, CDMA and LTE frequency bands, while the Galaxy flag ship phones from Samsung have 16 bands (not counting the GPS, Wi-Fi, Bluetooth and NFC radios). Power amplifier, Low noise amplifier and switch functions can be combined-important for cost and size - but, proliferation of usable bands has driven up filter count. New bands are being created (opening up more frequency spectrum) and more challenging; existing bands are now being combined in what is called Carrier Aggregation. This requires better performance from the filter and also drives filters to become smaller as handset manufacturers struggle to add more filters into a limited space. This has created (in just a few years) a whole new billion dollar industry focused on building high quality ultra-miniature filters; An industry where better quality filters enable better wireless communication, which-in turn-drives the technology to build better filters.