Implementation of a PMN-PT piezocrystal-based focused array with geodesic faceted structure

The higher performance of relaxor-based piezocrystals compared with piezoceramics is now well established, notably including improved gain-bandwidth product, and these materials have been adopted widely for biomedical ultrasound imaging. However, their use in other applications, for example as a source of focused ultrasound for targeted drug delivery, is hindered in several ways. One of the issues, which we consider here, is in shaping the material into the spherical geometries used widely in focused ultrasound. Unlike isotropic unpoled piezoceramics that can be shaped into a monolithic bowl then poled through the thickness, the anisotropic structure of piezocrystals make it impossible to machine the bulk crystalline material into a bowl without sacrificing performance. Instead, we report a novel faceted array, inspired by the geodesic dome structure in architecture, which utilizes flat piezocrystal material and maximizes fill factor. Aided by 3D printing, a prototype with f# ≈ 1.2, containing 96 individually addressable elements was manufactured using 1–3 connectivity PMN-PT piezocrystal–epoxy composite. The fabrication process is presented and the array was connected to a 32-channel controller to shape and steer the beam for preliminary performance demonstration. At an operating frequency of 1 MHz, a focusing gain around 30 was achieved and the side lobe intensities were all at levels below −12 dB compared to main beam. We conclude that, by taking advantage of contemporary fabrication techniques and driving instrumentation, the geodesic array configuration is suitable for focused ultrasound devices made with piezocrystal

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation

This paper reports the development of a two-dimensional thick film lead zirconate titanate (PZT) ultrasonic transducer array, operating at frequency approximately 7.5 MHz, to demonstrate the potential of this fabrication technique for microparticle manipulation. All layers of the array are screen-printed then sintered on an alumina substrate without any subsequent patterning processes. The thickness of the thick film PZT is 139 ± 2 μm, the element pitch of the array is 2.3 mm, and the dimension of each individual PZT element is 2 × 2 mm2 with top electrode 1.7 × 1.7 mm2. The measured relative dielectric constant of the PZT is 2250 ± 100 and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis was used to predict the behaviour of the array and to optimise its configuration. Electrical impedance spectroscopy and laser vibrometry were used to characterise the array experimentally. The measured surface motion of a single element is on the order of tens of nanometres with a 10 Vpeak continuous sinusoidal excitation. Particle manipulation experiments have been demonstrated with the array by manipulating Ø10 μm polystyrene microspheres in degassed water. The simplified array fabrication process and the bulk production capability of screen-printing suggest potential for the commercialisation of multilayer planar resonant devices for ultrasonic particle manipulation

Micromachined Diaphragm Transducers for Miniaturised Ultrasound Arrays

Miniaturised ultrasound transducer arrays with integrated electronics will in future enable significant advances in high resolution medical imaging and in acoustic tweezing for bioscience research. However, their development has been limited by challenges in scaling down conventional piezoelectric ultrasound transducer fabrication and interconnection techniques. Piezoelectric thin film transducers on silicon substrates can overcome these challenges by reducing dimensional constraints in fabrication and facilitating integration with electronics, including allowing low drive voltages in transmission. We present the design, fabrication and testing of diaphragm transducers to evaluate the feasibility of integrated piezoelectric micromachined ultrasonic transducers (PMUTs). Transducers have been designed, then fabricated with 80 μm and 130 μm diameter diaphragms, the latter in arrays with ~500 diaphragms. Receive measurements demonstrate functionality of both devices, with pulse-echo bandwidths of approximately 90% for the 80 μm diaphragms, demonstrating initial feasibility for ultrasound imaging

Advanced electrical array interconnections for ultrasound probes integrated in surgical needles

Real-time ultrasound guidance during neurosurgery is a novel and sought-after technique that enables imaging data to be acquired with improved precision during surgical intervention. Surgical needles that are inserted in the tissue of interest can be guided using the real-time graphical information collected by an embedded ultrasound transducer. The miniaturisation capabilities of modern manufacturing technologies allow the fabrication of ultrasound probes that are small enough to be fitted in needles conventionally used in surgical practices (down to ∼2 mm inner diameter). High lateral resolution may in fact be achieved by producing miniaturised ultrasound transducer arrays with a series of emitting/receiving elements, each electrically isolated from the others. To guarantee the functionality of such devices, a series of independent electrical interconnections must be implemented that enables the external driving electronics of the imaging system to be connected to the miniaturised ultrasound probe array. This paper presents a novel interconnection scheme designed to interface ultrasound probes integrated in surgical needles with the driving electronics. The presented solution utilises a flexible printed circuit board carrying the electrical tracks and a bonding technique with an anisotropic conductive paste.</p

Ex-Vivo Navigation of Neurosurgical Biopsy Needles Using Microultrasound Transducers with M-Mode Imaging

A clinical need is evident in neurosurgery to facilitate portable, real-time image guidance of interventional tools such as biopsy needles. This work presents imaging studies with microultrasound transducers incorporated into neurosurgical biopsy needles. Two design orientations are shown with the intention to provide both a forward and side field of view to a neurosurgeon. To examine the performance of these needle devices, preliminary B-scans were obtained of resected lamb brain with an embedded target whereby the forward facing and side facing needles were mechanically scanned linearly and radially respectively. The results presented images indicating the feasibility of the transducers to identify a target within brain tissue. To further investigate the transducers potential application as a viable neurosurgical tool, real-time M-mode images were generated within ex vivo porcine brain tissue with an embedded target. Assessing the M-mode images produced by the forward and side facing transducers, the devices are seen to have the potential to offer simple but effective guidance for navigating and positioning the needle within brain tissue close to a target such as a cancerous lesion or in the ventricles