Conformal Transducer Research Articles

Toward transcranial ultrasound tomography: design of a 456-element low profile conformal array

We have been investigating a ‘belt-type’ conformal transducer array designed for transcranial brain imaging. In precursory simulation work it was estimated that an array consisting of approximately 500 channels would be sufficient to achieve two-dimensional brain imaging utilizing a tomographic approach valid on irregular boundaries [G T Clement 2014 Inverse Probl. 30 1–22], such as the human head. To achieve such an array in practice we describe here a transducer designed and constructed around an assembly of rigid 1–3 composite planar sub-arrays (500 kHz, 1–3 random-fiber, 20 mm × 20 mm) consisting of 19 elements. Sub-arrays are bonded to custom-printed circuit boards wired to shielded ribbon cable. The full transducer is created by ultra violet (UV) bonding the electrodes to a flexible 3D-printed head band. Element performance is assessed by underwater scanned hydrophone characterization in the far-field. Measurements are then numerically back-projected to the transducer face to assess isolation. It is determined that elements function independently with little impact on the nearby elements. The maximum measured pressure amplitude crosstalk of the neighbouring elements to the active element is less than −14 dB, which making appropriate connections to the 1–3 composite tile was a significant consideration satisfies the later tomography imaging requirements. Results also show a maximum 3 dB decrease in the pressure amplitude as referenced to the maximum pressure amplitude of elements. Due to the limited number of channels on the data and control acquisition system (N = 128), an expander was designed and fabricated using 4:1 multiplexers (MUXs) to cover all the required number of transducer elements for the imaging system. The electrical characterization of the expander was addressed in terms of noise and crosstalk. Results show crosstalk of about −58.7 ± 2.9 dB for the MUXs. Average signal to noise ratio (SNR) decreased by about 0.05 dB after adding the expander. Noise levels remained almost the same after increasing the average detected signal power. Overall, the design and measured results are found to satisfy the key transducer requirements for a conformal array designed for transcranial diffraction tomography. This ‘work in progress’ will be combined with an optical registration technique to form a complete imaging device.

Design of a low profile conformal array for transcranial ultrasound imaging

In our ongoing work toward transskull ultrasound brain imaging, we investigate an optically-registered “belt-type” conformal transducer designed to maximize energy transfer while maintaining precise phase control. Previous simulations determined that approximately 500 channels is sufficient for two-dimensional brain imaging by utilizing a tomographic approach valid on irregular boundaries [Clement, Inverse Problems 30 125010 (2014)]. The present design is based around an assembly of rigid planar sub-arrays with flexible interconnects. Each piezo-composite sub-array (500 kHz, 1-3 random-fiber, 20 mm X 20 mm) is formed by electroding both faces of the composite before partially dicing the rear surface to produce 19 signal electrode terminals (width~0.85 mm, height~20 mm, and kerf~0.18 mm) with a shared ground face. Sub-arrays are bonded to a custom printed circuit boards and wired to shielded ribbon cable. The full transducer is then created by UV bonding the electrodes to a flexible band, forming the front...

Experimental techniques for ballistic pressure measurements and recent development in means of calibration

This paper presents a study carried out with the commonly used experimental techniques of ballistic pressure measurement. The comparison criteria were the peak chamber pressure and its standard deviation inside specific weapon/ammunition system configurations. It is impossible to determine exactly how precise either crusher, direct or conformal transducer methods are, as there is no way to know exactly what the actual pressure is; Nevertheless, the combined use of these measuring techniques could improve accuracy. Furthermore, a particular attention has been devoted to the problem of calibration. Calibration of crusher gauges and piezoelectric transducers is paramount and an essential task for a correct determination of the pressure inside a weapon. This topic has not been completely addressed yet and still requires further investigation. In this work, state of the art calibration methods are presented together with their specific aspects. Many solutions have been developed to satisfy this demand; nevertheless current systems do not cover the whole range of needs, calling for further development effort. In this work, research being carried out for the development of suitable practical calibration methods will be presented. The behavior of copper crushers under different high strain rates by the use of the Split Hopkinson Pressure Bars (SHPB) technique is investigated in particular. The Johnson-Cook model was employed as suitable model for the numerical study using FEM code

Polyimide-Based Conformal Ultrasound Transducer Array for Needle Guidance

A conformal ultrasound imaging system has been developed that may potentially decrease the user variability associated with operation of rigid transducer-based medical ultrasound systems. Conformal transducer arrays were built and characterized, featuring bulk piezoelectric elements mounted on an array of silicon islands, connected with flexible polyimide joints. The joints successfully supported electrodes while bending, and were sufficiently soft to enable both conformation to body surfaces and needle insertion for ultrasound guidance procedures. A signal-to-noise ratio (SNR) of 39 dB was achieved from a needle target in a soft tissue phantom. A space-time backward propagation image reconstruction algorithm was simulated to demonstrate needle detection using a conformal transducer with an arbitrary array architecture.

A generalized differential effective medium model of piezoelectret foams.

Piezoelectrets are closed‐cell foams consisting of a continuous polymer matrix containing preferentially oriented and electrically polarized ellipsoidal voids. These materials display low density, low characteristic impedance, thicknesses on the order of 100 μm, and potential to act as conformal transducers on complex geometries. They therefore provide an intriguing alternative to piezoelectric ceramics and piezopolymers for applications such as air‐coupled ultrasonics or underwater receive elements. Unfortunately, some fundamental attributes of piezoelectret behavior, such as their nonmonotonic change in receive sensitivity with increasing ambient pressure, remain unexplained by physical modeling or experiment. To explain this and other behavior, this work develops a fully coupled multiscale microelectromechanical model which captures the void‐scale physics and predicts macroscopically observed piezoelectric properties. The model employs volume averaged Green’s function solutions of the three‐dimensional...

Optimization of transmitting beam patterns of a conformal transducer array

A method is presented to calculate the driving-voltage weighting vector of a conformal array of underwater acoustic transmitting transducers to obtain a low-sidelobe beam pattern based on the measured receiving array manifold. The relationship among three quantities is given, which are, respectively, the radiated acoustic field, the measured receiving array manifold matrix and the driving-voltage weighting vector of the transducer array. Then, the driving-voltage weighting vector of the array is calculated using the optimization method to obtain a low-sidelobe transmitting beam pattern. At the frequency of 12.5 kHz, the receiving array manifold matrix of a 27-element conformal array is measured in an anechoic water tank. The driving-voltage weighting vector of the array is calculated using the proposed method. In addition, the computer simulation and experiments are carried out. The results agree well and show that the proposed method can obtain a low-sidelobe transmitting beam pattern and at the same time provide the largest amplitude of pressure in the axial direction when the maximum amplitude of the driving voltages of the array elements keeps unchanged.

Directional characteristics of conformal transducers on fluid loaded elastic shells

A general analytic approach is presented to evaluate the directional characteristics of conformal velocity sources representing transducers on fluid loaded elastic shells. The sources/transducers are assumed to be structurally decoupled from the shell but are coupled to the shell via the fluid. The pressure field is expressed via superposition as the sum of the pressure field from the sources on a rigid shell plus the pressure field from the elastic shell assuming zero normal velocity for the sources. An in vacuo eigenvector expansion is used to describe the velocity field of the shell. The modal coefficients of the expansion for the shell are related shells via a set of linear algebraic equations to the modal coefficients of a different expansion for the surface pressure due to the sources on the rigid shell. Shadowing effects of the sources on the response of the shell are included in the formulation. Numerical results for the directional characteristics of specified circular velocity sources on rigid and elastic spherical shells are presented as a special case. The results illustrate the effects of diffraction and shell resonances on the directional characteristics of the sources in the low, mid, and high frequency regions. [Work supported by ONR.]

Ultrasonic sensors for monitoring the condition of flow through a cardiac valve

A parameter indicative of the condition of a cardiac valve is determined by monitoring blood flow and/or velocity in a vessel that is coupled to the cardiac valve or in a chamber adjacent to an artificial cardiac valve. One or more ultrasonic transducers are provided either in a wall or a cuff disposed about a cardiac vessel to monitor the parameter in regard to a natural or artificial cardiac valve, or in a support sewing ring of an artificial cardiac valve. A conformal array transducer or a tilted element is used to monitor fluid flow or velocity based on the effect of the blood on ultrasonic waves produced by the transducers. The conformal array transducer comprises a plurality of elements that are excited with an input signal provided by an implantable electronics circuit, producing ultrasonic waves. Transit time or Doppler measurements are made using an appropriate number of these transducers to determine either blood volumetric flow or velocity. Various implantable electronic circuits are disclosed that enable a transducer to be driven and to receive an ultrasonic signal indicative of the status of blood flow and thus, the condition of the cardiac valve. A radio frequency (RF) coil is coupled to an external coil. The external coil is connected to a power supply and monitoring console, conveying power to the ultrasonic transducers and receiving data signals that enable the condition of the cardiac valve to be determined.

Ultrasonic sensors for monitoring the condition of a vascular graft

A parameter indicative of the status of fluid flow is remotely monitored in a vessel, a natural graft, or a synthetic graft (106). One or more conformal array transducers (44-46) comprising a plurality of elements that curve around the graft (106) or vessel, are excited with an input signal provided by one of various implantable electronic circuits. The implantable electronic circuits enable a selected transducer to be driven, and to receive an ultrasonic signal or pressure signal indicative of the status of fluid flow monitored by the transducer. The implanted electronic circuit is connected to an implanted radio frequency (RF) coil. An external coil that is connected to a power supply (32), receive data signals from the transducer that are indicative of the parameter being monitored.

The incorporation of rigid composites into a conformal hydrophone

Abstract During the past five years, numerous composite configurations have been analysed for hydrostatic transducer application. Although some of these composite configurations have been flexible, a configuration with good sensitivity and mechanical durability has not been produced. The need for a sheet or mat, large area transducer that will conform to the hull of a ship has led to the incorporation of small rigid composite elements into a macrocomposite. The goals set for the conformal transducer were sensitivity greater than -200 dB re 1 V/μPa, operation to at least 7 MPa, maximum frequency of 100 Hz, conforming to a 0·10 m radius and a hydrophone section of at least 0·01 m2. In the study three types of rigid composites are used to determine the effect of compliant hinge material and flexible electrodes on the hydrostatic sensitivity. Typical response of a 1–3 rod composite in flexible form is a sensitivity of -193 dB re 1 V/μPa, with a capacitance of 14 μf per m2 and only 2 dB degradation when operat...