Impedance matching network for high frequency ultrasonic transducer for cellular applications

Abstract

An approach for the design of an impedance matching network (IMN) for high frequency ultrasonic transducers with large apertures based on impedance analysis for cellular applications is presented in this paper. The main objectives were to maximize energy transmission from the excitation source to the ultrasonic transducers for cell manipulation and to achieve low input parameters for the safe operation of an ultrasonic transducer because the piezoelectric material in high frequency ultrasonic transducers is prone to breakage due to its being extremely thin. Two ultrasonic transducers, which were made of lithium niobate single crystal with the thickness of 15 μm, having apertures of 4.3 mm (fnumber = 1.23) and 2.6 mm (fnumber = 0.75) were tested. L-type IMN was selected for high sensitivity and compact design of the ultrasonic transducers. The target center frequency was chosen as the frequency where the electrical admittance (∣Y∣) and phase angle (θz) from impedance analysis was maximal and zero, respectively. The reference center frequency and reference echo magnitude were selected as the center frequency and echo magnitude, measured by pulse-echo testing, of the ultrasonic transducer without IMN. Initial component values and topology of IMN were determined using the Smith chart, and pulse-echo testing was analyzed to verify the performance of the ultrasonic transducers with and without IMN. After several iterations between changing component values and topology of IMN, and pulse-echo measurement of the ultrasonic transducer with IMN, optimized component values and topology of IMN were chosen when the measured center frequency from pulse-echo testing was comparable to the target frequency, and the measured echo magnitude was at least 30% larger than the reference echo magnitude. Performance of an ultrasonic transducer with and without IMN was tested by observing a tangible dent on the surface of a plastic petridish and single cell response after an acoustic pulse was applied on a target cell.

A Review of Electric Impedance Matching Techniques for Piezoelectric Sensors, Actuators and Transducers

“…The source is the ultrasonic transducer operating as a receiver. A Smith chart synthesizes such a network by moving the source impedance to the center point (50 Ω) by adding capacitors and inductors in parallel or in a series [41], as shown in Figure 2. Addition of a parallel inductor moves the impedance point along the constant resistance curves.…”

“…The EIMN design procedure using Smith chart (shown at the left) where the input electrical impedance of the ultrasonic transducer is moved toward the center of the Smith chart by appropriately adjusting the inductor and capacitor component values and topology, at the center frequency. Reproduced with permission from Reference [41], Copyright Elsevier, 2016.…”

“…Kim et al [41] suggested the use of Smith chart instead of PiezoCAD from Sonic Concepts, Bothell, WA since it is not applicable for high-frequency design. They sacrificed the bandwidth and used L-type impedance matching network with tuning ability described in Section 3.4, to achieve a sharp peak at the resonance frequency.…”

“…Picture of EIMN with an ultrasonic transducer showing the printed circuit board (PCB) implemented with shunt capacitor of 100 pF and series inductor of 8 nH. Reproduced with permission from Reference[41], Copyright Elsevier, 2016. Pulse-echo waveform and echo spectrum of the ultrasonic transducer with showing the pulse-echo measurement (a) without and (b) with impedance matching network respectively.…”

“…Pulse-echo waveform and echo spectrum of the ultrasonic transducer with showing the pulse-echo measurement (a) without and (b) with impedance matching network respectively. Reproduced with permission from Reference[41], Copyright Elsevier, 2016.…”