40 MHz piezo-composite linear array for medical imaging and integration in a high resolution system

Evolution of high resolution ultrasonic imaging is widely dependent on the development of efficient high frequency piezoelectric transducers. Nowadays, efforts are focused on the fabrication of linear arrays in the 40-50 MHz frequency range for dermatology, ophthalmology and small animals imaging. At these frequencies, technological aspects are predominant at several stages of the array fabrication due to typical dimensions of the constitutive elements (few tens of micrometers). Moreover, the development of the imaging system and associated beamforming specifically adapted is of primary interest to optimize the use of the corresponding array and consequently image quality. A new fully operational 40 MHz 128 elements 2mm elevation linear array was manufactured using micromachined 1-3 piezocomposite: fabrication rules of low frequency probes were extended and adapted to the design of this high frequency probe. Matching layers, backing and interconnect method are used to finalize the internal structure of the array. A complete set of measurements show that a center frequency at 40 MHz is delivered with a relative bandwidth over 70%. All the 128 elements of the probe are active and very good sensitivity homogeneity along the probe is measured. Crosstalk between adjacent elements is also evaluated and the corresponding value is around -37 dB. A specific high resolution real-time ultrasonic imaging platform, called ECODERM developed by the INSERM Imagerie et Cerveau laboratory, with 128 channels using impulse electrical excitation and 100 MHz bandwidth in reception is used to perform human skin images. The very good performance of the new HF40 MHz linear array coupled with the developed imaging system result in high resolution images of the skin.