{'fraction_non_alphanumeric': 0.02402745995423341, 'fraction_numerical': 0.011441647597254004, 'mean_word_length': 4.833333333333333, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 1, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Development of a 20 MHz annular-array - a first step to a multichannel microscope

This paper describes the development of an annular-array transducer with a center frequency of 20 MHz constructed of custom-built composite material. In contrast to linear element arrays, annular-arrays work effectively despite a small number of large transducer elements. The active aperture and the layout of the array are optimized by sound field calculation. Despite the large elements of the annular-array, contact plating and bonding of the 20 MHz annular-array transducer is a challenge due to physical as well as chemical properties of the composite material. An annular-array with four quartered rings (16 elements) and an outer diameter of 5.4 mm (aperture) was manufactured. The sound fields of the different elements are characterized by scanning with a point reflector in water.