The generation of RF/microwave power is required not only in wireless communications, but also in applications such as jamming, imaging, RF heating, and miniature dc/dc converters. Each application has its own unique requirements for frequency, bandwidth, load, power, efficiency, linearity, and cost. RF power is generated by a wide variety of techniques, implementations, and active devices. Power amplifiers are incorporated into transmitters in a similarly wide variety of architectures, including linear, Kahn, envelope tracking, outphasing, and Doherty. Linearity can be improved through techniques such as feedback, feedforward, and predistortion.
A design-oriented analysis of the microwave transmission-line class-E amplifier is presented. Experiments and harmonic-balance circuit simulations verify the theoretical equations which predict class-E-amplifier output power, maximum frequency of operation, and dc-RF conversion efficiency. Experimental results at 0.5, 1, 2, and 5 GHz are presented. At 0.5 GHz, 83% drain efficiency and 80% poweradded efficiency (PAE) are measured, with an output power of 0.55 W, using the Siemens CLY5 MESFET. These results are compared to a class-A and class-F power amplifier using the same device. At 5 GHz, 81% drain efficiency and 72% PAE are measured, with an output power of 0.61 W, using the Fujitsu FLK052WG MESFET. Finally, the 5-GHz class-E power amplifier is successfully integrated into an active-antenna array, demonstrating power combining of four elements with an 85% power-combining efficiency. At 5.05 GHz, the class-E power-amplifier antenna array delivers a total of 2.4 W of output power, with a dc-RF conversion efficiency of 74% and a PAE of 64%.
The objective of this study is to develop a wireless ultrasonic structural health monitoring
(SHM) system for aircraft wing inspection. In part I of the study (Zhao et al 2007
Smart Mater. Struct. 16 1208–17), small, low cost and light weight piezoelectric (PZT) disc
transducers were bonded to various parts of an aircraft wing for detection, localization and
growth monitoring of defects. In this part, two approaches for wirelessly interrogating the
sensor/actuator network were developed and tested. The first one utilizes a pair of reactive
coupling monopoles to deliver 350 kHz RF tone-burst interrogation pulses directly to
the PZT transducers for generating ultrasonic guided waves and to receive the
response signals from the PZTs. It couples enough energy to and from the PZT
transducers for the wing panel inspection, but the signal is quite noisy and the
monopoles need to be in close proximity to each other for efficient coupling. In
the second approach, a small local diagnostic device was developed that can be
embedded into the wing and transmit the digital signals FM-modulated on a
915 MHz carrier. The device has an ultrasonic pulser that can generate 350 kHz,
70 V tone-burst signals, a multiplexed A/D board with a programmable gain
amplifier for multi-channel data acquisition, a microprocessor for circuit control
and data processing, and a wireless module for data transmission. Power to the
electronics is delivered wirelessly at X-band with an antenna–rectifier (rectenna)
array conformed to the aircraft body, eliminating the need for batteries and their
replacement. It can effectively deliver at least 100 mW of DC power continuously from
a transmitter at a range of 1 m. The wireless system was tested with the PZT
sensor array on the wing panel and compared well with the wire connection case.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.