C.-K. Jen

Bio: C.-K. Jen is an academic researcher from National Research Council. The author has contributed to research in topics: Ultrasonic sensor & Acoustic wave. The author has an hindex of 11, co-authored 45 publications receiving 378 citations.

Piezoelectric thick bismuth titanate/lead zirconate titanate composite film transducers for smart NDE of metals

Abstract: Thick film piezoelectric ceramic sensors have been successfully deposited on different metallic substrates with different shapes by a sol?gel spray technique. The ball-milled bismuth titanate fine powders were dispersed into PZT solution to achieve the gel. The films with desired thickness up to 200??m have been obtained through the multilayer coating approach. These thick films were also effectively coated onto thin sheet metals of thickness down to 25??m. Self-support films with flat and shell geometries were made. Piezoelectricity was achieved using the corona discharge poling method. The area of the top silver paste electrode was also optimized. The center frequencies of ultrasonic signals generated by these films ranged from 3.6 to 30?MHz and their bandwidth was broad as well. The ultrasonic signals generated and received by these ultrasonic transducers (UTs) operated in the pulse/echo mode had a signal to noise ratio more than 30?dB. The main advantages of such sensors are that they (1) do not need couplant, (2) can serve as piezoelectric and UT, (3) can be coated onto curved surfaces and (4) can operate up to 440??C. The capability of these thick film UTs for non-destructive evaluation of materials at 440??C has been demonstrated.

Stimulated Brillouin scattering in cascaded fibers of different Brillouin frequency shifts

Abstract: Experimental investigations of stimulated Brillouin scattering in two cascaded single-mode optical fibers with different Brillouin shifts are presented. A fiber Brillouin laser consisting of these two cascaded fibers is demonstrated. The output of such a laser exhibits two frequencies corresponding to the Brillouin-shifted frequencies of two individual fibers.

High performance clad metallic buffer rods

Abstract: Clad metallic buffer rods fabricated by thermal spray and electroplating techniques are presented. The core and cladding materials are steel, stainless steel, zirconium, titanium, nickel, copper and aluminum. The lengths of buffer rods can be more than tens of centimeters limited by the desired signal-to-noise ratio (SNR) and not by the fabrication. Pulsed ultrasonic signals of high SNR in these buffer rods make many practical applications feasible. Novel applications for on-line solidification monitoring of liquid aluminum and in situ temperature measurement are demonstrated.

Stimulated Brillouin scattering in optical fibers

Abstract: We present a detailed overview of stimulated Brillouin scattering (SBS) in single-mode optical fibers. The review is divided into two parts. In the first part, we discuss the fundamentals of SBS. A particular emphasis is given to analytical calculation of the backreflected power and SBS threshold (SBST) in optical fibers with various index profiles. For this, we consider acousto-optic interaction in the guiding geometry and derive the modal overlap integral, which describes the dependence of the Brillouin gain on the refractive index profile of the optical fiber. We analyze Stokes backreflected power initiated by thermal phonons, compare values of the SBST calculated from different approximations, and discuss the SBST dependence on the fiber length. We also review an analytical approach to calculate the gain of Brillouin fiber amplifiers (BFAs) in the regime of pump depletion. In the high-gain regime, fiber loss is a nonnegligible effect and needs to be accounted for along with the pump depletion. We provide an accurate analytic expression for the BFA gain and show results of experimental validation. Finally, we review methods to suppress SBS including index-controlled acoustic guiding or segmented fiber links. The second part of the review deals with recent advances in fiber-optic applications where SBS is a relevant effect. In particular, we discuss the impact of SBS on the radio-over-fiber technology, enhancement of the SBS efficiency in Raman-pumped fibers, slow light due to SBS and SBS-based optical delay lines, Brillouin fiber-optic sensors, and SBS mitigation in high-power fiber lasers, as well as SBS in multimode and microstructured fibers. A detailed derivation of evolutional equations in the guided wave geometry as well as key physical relations are given in appendices.

Mechanism of operation and design considerations for surface acoustic wave device vapor sensors

Abstract: Abstract Surface acoustic wave (SAW) devices offer many attractive features for application as vapour phase chemical microsensors. This paper describes the characteristics of SAW devices and techniques by which they can be employed as vapour sensors. The perturbation of SAW velocity by polymeric coating films is investigated both theoretically and experimentally. Highest sensitivity can be achieved when the device is used as the resonating element in a delay line oscillator circuit. A simple equation has been developed from theoretical considerations which offers reasonably accurate quantitative predictions of SAW device frequency shifts when subjected to a given mass loading. In this mode the SAW device behaves very like conventional bulk-wave quartz crystal microbalances except that the sensitivity can be several orders of magnitude higher and the device size can be several orders of magnitude smaller. Detection of mass changes of a few femtograms by a SAW device having a surface area of 10−4 cm2 is theoretically possible.

Acoustic Wave Microsensors

Abstract: Acoustic wave microsensors are being used for broader applications in chemical sensing and interfacial studies as more devices are invented and new sensor response mechanisms are elucidated. This report compares and contrasts the more commonly used acoustic wave devices and provide a current description of the physical origins of observed sensor responses in both gas- and liquid-phase studies. The types of waves and devices as well as information on operation and measurement methods, mass sensitivity, and detection are discussed. We focus primarily on thickness-shear mode (TSM), surface acoustic wave (SAW), flexural plate wave (FPW), and acoustic plate mode (APM) devices. 65 refs., 4 figs., 2 tabs.

The Rising Power of Fiber Lasers and Amplifiers

Abstract: The first rare-earth-doped fiber lasers were operated in the early 1960s, and produced a few milliwatts at a wavelength around 1 mum. Since the beginning of the decade, an enormous increase of fiber laser output power has been reported, the realm of kilowatt power has been entered, and power levels as high as 100 kW are envisaged. Apart from the power, fiber laser systems are renowned for their inherent compactness, monolithic architecture, and a power-independent beam quality. This paper reviews the challenges, achievements, and perspectives of high-power continuous-wave (CW) laser generation and amplification in fibers.