Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Guided Lamb waves for identification of damage in composite structures: A review

Applied Numerical Analysis. By C.F. Gerald. Pp. xii, 340. £3·60. 1970. (Addison-Wesley.)

Utilizing the coupled piezoelectric and semiconducting dual properties of ZnO, we demonstrate a piezoelectric field effect transistor (PE-FET) that is composed of a ZnO nanowire (NW) (or nanobelt) bridging across two Ohmic contacts, in which the source to drain current is controlled by the bending of the NW. A possible mechanism for the PE-FET is suggested to be associated with the carrier trapping effect and the creation of a charge depletion zone under elastic deformatioin. This PE-FET has been applied as a force/pressure sensor for measuring forces in the nanonewton range and even smaller with the use of smaller NWs. An almost linear relationship between the bending force and the conductance was found at small bending regions, demonstrating the principle of nanowire-based nanoforce and nanopressure sensors.

Piezoelectric field effect transistor and nanoforce sensor based on a single ZnO nanowire.

http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

Optical frequency combs consisting of evenly spaced discrete frequencies have been used for a number of applications such as frequency metrology, range finding and molecular fingerprinting. Recently, the acoustic equivalent of these frequency combs, known as phononic frequency combs (PFCs), have been demonstrated in micro and nanoscale resonators. However, such demonstrations are restricted to PFC generation in high-Q mechanical resonators under carefully controlled operating conditions with limited practical applications. In this work, we demonstrate a novel method of generating PFCs with a parametrically driven capacitive micromachined ultrasonic transducer (CMUT) operating in a fluid medium. The proposed system consists of an electrically driven CMUT array that forms part of a resonant RLC circuit of frequency w0. By applying two drive tones of frequency w0 and w0+Δ, we are able to generate broadband acoustic frequency combs via a parametric four-wave mixing process. The intensity and number of combs generated is strongly dependent on the relative strength of the two driving tones whereas the comb spacing is determined by the frequency difference Δ between the drive signals. We also briefly discuss a potential application of PFCs in extended non-ambiguous range (NAR) distance metrology with interferometric resolution.

Broadband phononic frequency comb generation in a parametrically excited capacitive micromachined ultrasonic transducer

Multiple Annular Ring Capacitive Micromachined Ultrasonic Transducer Arrays for Forward-Looking Intravascular Ultrasound Imaging Catheters

Introduction to the 2014 IUS Special Issue on Ultrasonics.

The disclosed technology relates to imaging catheters. A method is provided that includes: receiving, from a plurality of transducers disposed on a catheter probe, a corresponding plurality of analog signals; selectively sampling the plurality of analog signals; multiplexing to produce a sequence of samples; and transmitting the sequence of samples to a receiver circuit. The receiver circuit includes a clock; an analog to digital converter (ADC) in communication with the clock; and a sampling phase correction circuit in communication with the clock and the ADC. The method further includes: determining optimum sampling times based on measured signal delays associated with the system; adjusting a phase of the clock based on the measured signal delays; and communicating the phase-adjusted clock to the transmitter circuit for the selective sampling of the analog signals. Certain embodiments of the disclosed technology may further be utilized in conjunction with beamforming.

Analogue time division multiplexing for cable reduction in imaging catheters

An optical displacement detection method for micromachined microphones is described and experimental results are presented. The microphone membrane is fabricated on a transparent substrate and the back electrode is patterned in the form of diffraction fingers. This structure forms a phase sensitive diffraction grating, providing the displacement sensitivity of an optical interferometer. The diffraction fingers are also used for electrostatic actuation, providing sensitivity adjustment and self‐calibration capabilities. Optically semitransparent coatings are also employed to create Fabry–Perot resonant cavities that enhance the optical detection sensitivity by an order of 10 dB. The high electrical sensitivity provided by optical displacement detection relaxes requirements on mechanical sensitivity, and small microphone membranes on the order of 200 μm with vacuum‐sealed and air‐sealed cavities are used to fabricate microphones with a flat response from dc to over 200 kHz. The optical detection and electro...

F. Levent Degertekin

Papers

Broadband phononic frequency comb generation in a parametrically excited capacitive micromachined ultrasonic transducer

Multiple Annular Ring Capacitive Micromachined Ultrasonic Transducer Arrays for Forward-Looking Intravascular Ultrasound Imaging Catheters

Introduction to the 2014 IUS Special Issue on Ultrasonics.

Analogue time division multiplexing for cable reduction in imaging catheters

Broadband self‐calibrating micromachined microphones with integrated optical displacement detection