Sanat Wagle

Ultrasonic properties of all-printed piezoelectric polymer transducers

The ability of producing ultrasonic transducers from screen-printing has been explored experimentally, through printing and characterization of a large number of transducers. In an all-printed test design, 124 transducers with four different electrode sizes ranging from 1 to 4.9 mm2, were printed layer-by-layer on a high performance polyethyleneimine polymer. Inks from ferroelectric and conductive polymers were applied to the active part of a transducer, to provide a good acoustical match between the individual layers. Ultrasonic characterizations of the transducers done by two independent methods provided a broad-banded frequency response with a maximum response around 100 MHz.

Effect of polymer electrode thickness on the acoustical properties of all-screen printed piezoelectric PVDF copolymer transducers

High frequency poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] copolymer ultrasonic transducers were prepared by screen printing as an all-printed device with conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) used the electrode material. A large number of prototypes with different electrode areas and electrode thickness were obtained by printing single or dual layers of the conductive polymer. The printed transducers were characterized using impedance and acoustic backscattering measurements. Effects imposed by the PEDOT:PSS conductivity were also evaluated both through experiments and finite element method (FEM) modeling, pointing out important limitations of conductive polymers when applied in high frequency ultrasonic transducers.

Ultrasonic measurements of surface defects on flexible circuits using high-frequency focused polymer transducers

High-frequency transducers made from a layer-by-layer deposition method are investigated as transducers for ultrasonic imaging. Prototypes of adhesive-free transducers with four active elements were made on a high-performance poly(ether imide) substrate with precision milled spherical cavities used to produce focused ultrasonic beams. The transducer prototypes were characterized using a pulse–echo experimental setup in a water tank using a glass plate as a reflector. Then, transducer was used in a three-dimensional ultrasonic scanning tank, to produce high-resolution ultrasonic images of flexible electronic circuits with the aim to detect defects in the outermost cover layer.

High-frequency poly(vinylidene fluoride) copolymer transducers used for spectral characterization of settled microparticles

High-frequency ultrasonic polymer transducers are used to investigate backscattering from spherical microparticles. These microspheres are immersed in water and allowed to settle on a polymer substrate acting as an ultrasonic contact material between the immersion fluid and the transducer. The experimental study is complemented with a three-dimensional (3D) numerical investigation; both yield rather long scattered waveforms in the time domain for the largest microparticles. The corresponding frequency spectra typically contain a number of minima values arising from wave resonances in the microparticles. The locations of these resonances, or eigenvalues, correlate strongly to the particle size. Good agreement is obtained between the experiment and the numerical model, which will help to identify the wave mode responsible for the extended scattering.

Evaluation of the acoustical properties of adhesive-free dual layer piezoelectric PVDF copolymer transducer

Dual layer piezoelectric transducer has been developed using an adhesive free process and characterized both experimentally and by FEM models. Our findings show an enhanced amplitude when both layers are used as a transceiver system for sufficiently large pulse width. The peak frequency obtained from Comsol modeling shows a good agreement with the experimental results.

Dual layer ultrasonic transducer used for touch sensing

The use of a dual layer transducer as a touch sensor has been explored both through experiments on simple prototypes, and FEM modeling. An adhesive free method was developed to deposit piezoelectric P(VDF-TrFE) polymer directly onto a standard Kapton (polyimide) film yielding touch sensors with good acoustic response in the ultrasonic band between 40 MHz to 60 MHz.

Evaluation of adhesive-free crossed-electrode poly(vinylidene fluoride) copolymer array transducers for high frequency imaging

High frequency crossed-electrode transducers have been investigated, both as single and dual layer transducers. Prototypes of these transducers were developed for 4 crossed lines (yielding 16 square elements) on a polymer substrate, using a layer-by-layer deposition method for poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] with intermediate sputtered electrodes. The transducer was characterized using various methods [LCR analyzer, a pulse–echo experimental setup, and a numerical Finite element method (FEM) model] and evaluated in terms of uniformity of bandwidth and acoustical energy output. All 16 transducer elements produced broad-banded ultrasonic spectra with small variation in central frequency and −6 dB bandwidth. The frequency responses obtained experimentally were verified using a numerical model.

Using silver nano-particle ink in electrode fabrication of high frequency copolymer ultrasonic transducers: modeling and experimental investigation.

High frequency polymer-based ultrasonic transducers are produced with electrodes thicknesses typical for printed electrodes obtained from silver (Ag) nano-particle inks. An analytical three-port network is used to study the acoustic effects imposed by a thick electrode in a typical layered transducer configuration. Results from the network model are compared to experimental findings for the implemented transducer configuration, to obtain a better understanding of acoustical effects caused by the additional printed mass loading. The proposed investigation might be supportive of identification of suitable electrode-depositing methods. It is also believed to be useful as a feasibility study for printed Ag-based electrodes in high frequency transducers, which may reduce both the cost and production complexity of these devices.

PVDF copolymer transducers used to evaluate microparticle suspensions

The ability of using high frequency ultrasonic transducers made from piezoelectric polymers, to characterize microparticle suspensions, has been investigated both in an experimental setup and in a numerical model. Both investigations, which consider microparticles settled on a glass substrate, show that the backscattered frequency spectra contain a number of minima values arising from wave resonances in the microparticles. The locations of these resonances are in the experiments, found to be independent of the particle concentration, but strongly dependent on the particle size. A comparison to previous results for floating microspheres, show that the material properties of the glass substrate, also has to be included for obtaining the correct resonance frequencies for settled particles.

Adhesive-free dual layer piezoelectric PVDF copolymer transducers in sender and receiver sequences

Adhesive free dual-layer ultrasonic transducers have been produced using a layer-by-layer deposition method. The proposed method deposits P(VDF-TrFE) copolymer from the fluid phase with intermediate electrodes on top of a PEI substrate. The processed transducers were characterized using a LCR analyzer, a pulse-echo experimental setup, and a numerical FEM model. The ultrasonic signals and frequency spectra from the different characterization methods were compared. By using one of transducer layers as a sender and the other as a receiver with an intermediate grounded electrode, the capacitive coupling between the layers was reduced significantly.