Patent Publication Number: US-2010109480-A1

Title: Method for manufacturing a membrane and object provided with such a membrane

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for manufacturing a membrane or wall of a material, which is capable of vapour/vacuum deposition, over an opening of an object. The invention also relates to such an object provided with a membrane, and particularly an ultrasonic transducer provided with a front membrane. 
     BACKGROUND OF THE INVENTION 
     In medical applications, it is known to coat devices to be introduced in the human body to protect the body from e.g. metallic contact. For example pacemakers are usually coated with Parylene, which is a depositable material well tolerable to the human body. 
     Ultrasonic probes for insertion in the human body for various treatments are also known. They may require cooling of the ultrasonic transducer. Also, they may require a liquid in front of the ultrasonic probe to assist in coupling the ultrasonic radiation to tissue to be treated. For this reason it has been contemplated to provide a chamber at the front end of the ultrasonic probe to distribute cooling liquid, typically saline, in front of an ultrasonic transducer. 
     The problem is to form a wall over the opening of the probe in an easy and efficient way. 
     SUMMARY OF THE INVENTION 
     One purpose of the invention is to provide a method for manufacturing a membrane over an opening in a simple and efficient way, the membrane having the required strength and bonding to the probe body. 
     A further purpose is to provide a method for manufacturing a membrane of a material tolerable to the human body on an ultrasonic transducer. 
     A further purpose is to provide an object provided with such a membrane. 
     In a first aspect, the invention provides a method for manufacturing a membrane of a depositable material at an opening of an object. 
     The method includes:
     placing the opening with a defined rim against a backing surface coated with a layer repellent to the depositable material;   depositing of the depositable material on the object and the backing surface to form an element;   separation of the element from the backing surface leaving a membrane integral with the element.   

     Suitably, at least one hole is manufactured in the element by arranging a recess in the rim, placing the recess against the backing surface, so that the depositable material is deposited on surfaces of the recess and the backing surface, leaving a hole in the element adjacent the membrane after the separation. 
     The depositable material may be Parylene, and the repellent layer may be a wax coating. 
     In a second aspect, the invention provides an object characterised by: a membrane of a depositable material at an opening, the membrane being attached to a defined rim of the opening and being integral with an element deposited on the object. 
     In one embodiment, the object is an ultrasonic transducer. 
     The membrane may form a front wall of a chamber arranged between an ultrasonic crystal and said wall. 
     The invention is defined in claims  1  and  7 , while embodiments are set forth in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail below with reference to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of an ultrasonic transducer before manufacturing the membrane, 
         FIG. 2  is a front view of the transducer of  FIG. 1 , 
         FIG. 3  is a cross sectional view of the transducer and the backing surface in a step of the manufacturing process, and 
         FIG. 4  is a perspective view of an ultrasonic transducer provided with a membrane according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention relates generally to a method for manufacturing a membrane applicable to objects with one or more openings to be covered with a membrane using a depositable material. The invention will be described with reference to a specific example of arranging a membrane on an ultrasonic probe or transducer, but it will be appreciated that the method is equally applicable to other objects. 
     The method was developed for arranging a membrane on an ultrasonic probe. An ultrasonic probe comprises a handle, a generally tubular introducer, electric wires, fluid lines etcetera (not shown) connected to a transducer. A schematic, exemplary ultrasonic transducer  11  is shown in the drawings. The transducer  11  comprises a probe head  2  carrying an ultrasonic crystal  1  and a conduit  7  for conducting cooling fluid to a region generally in front of the crystal  1 . Cooling fluid should be distributed over the front surface, to the right in  FIG. 3 , of the crystal  1 . Thus, a front wall or membrane  3  is needed. 
     In the present specification, the term depositable material is intended to mean any material that is capable of vapour/vacuum deposition. Parylene is a suitable choice for ultrasonic probes. 
     Parylene is the generic name for the poly-para-xylylenes. Parylene is a conformal protective polymer coating material utilized to uniformly protect any component configuration on such diverse substrates as metal, glass, paper, resin, plastic, ceramic, ferrite and silicon. Because of its unique properties, Parylene conforms to virtually any shape, including sharp edges, crevices, points; or flat and exposed internal surfaces. 
     In an embodiment of the invention, the method comprises the following steps. The transducer  11  is placed on a backing surface  4  provided with a repellent layer, in case of Parylene as depositable material, preferably a wax coating. The backing surface is suitably horizontal so that the transducer  11  is held in place by gravity. Alternatively, the backing surface is placed on top of the transducer  11  or they are clamped together by means of other arrangements. Several transducers  11  may be provided with membranes simultaneously. The front opening of the probe head  2  has a rim  8  in contact with the repellent layer  5 . 
     The backing surface  4  with the transducer  11  is placed in a vacuum chamber. Evaporation of the Parylene may be performed according to known techniques. The evaporated Parylene enters between the crystal  1  and the backing surface through the conduit  7 . The Parylene will cover all surfaces of the transducer  11  and the repellent layer  5  on the backing surface  4 . The evaporation continuous until the membrane  3  formed on the backing surface reaches a sufficient thickness. The thickness should be sufficiently great to provide the necessary strength, but in case of an ultrasonic probe, a too great thickness could result in unwanted attenuation losses of the transmitted ultrasound. The penetration depth of the ultrasound depends on the ultrasound frequency. A thickness in the range of 20 to 30 micrometers, for example around 25 micrometers has been found adequate with an ultrasound frequency around 4 MHz. 
     In the figures only the membrane  3  is shown, but the Parylene forms a continuous integral element or body covering also the other surfaces of the transducer  11  including the front surface of the crystal  1 . Thus, a chamber  10  is formed by the Parylene material in front of the crystal  1 . 
     Thanks to the evaporation process, there are no seams and sharp corners in the Parylene material and all transitions between portions of the Parylene body are smooth. Thus, the membrane is bonded with high strength to the Parylene body attached to the probe head  2 , the crystal  1  and other surfaces of the transducer  11 . 
     To separate the transducer  11  from the backing surface  4 , a cut is performed around the probe head  2 . Then the transducer  11  may be pulled from the backing surface, as the membrane is only weakly adhered to the repellent layer  5 . Suitably, the edges round the rim  8  are trimmed to a desired smooth shape. 
     In case of cooling of an ultrasonic probe, the chamber  10  needs at least one opening  6  to discharge the cooling fluid. To produce openings in the Parylene material, at least one recess  9  is provided in the rim  8 . Suitably, a number of recesses  9  are distributed over the rim  8 . When the rim  8  is placed against the backing surface, the recess  9  will form an opening. In the evaporation process the depositable material will coat the surfaces of the recess and the backing surface thus forming a continuous material layer of Parylene forming the opening  6 . Thus, the hole  6  is defined by the coated surfaces of the recess  9  and by the membrane  3 . There are no seams and sharp corners in the hole  6 , resulting in a hole resistant to any tearing forces. 
     In the embodiment shown the backing surface  4  is flat. It will be appreciated that concave and convex shapes may be used as well for forming other desired shapes of the membrane in dependence of the intended application. 
     Also, the method is applicable to manufacturing a membrane on a general object comprising an opening. Generally the whole object is covered by the depositable material as well, and trimmings may be performed as required. In case of an ultrasonic probe, it is in any case desired that the whole transducer is covered by Parylene, even if the probe head usually is made of plastic. 
     The method may be used with any material capable of deposition and forming a continuous membrane, e.g. plastics and metal. The repellent surface is selected in dependence of the material to be deposited. For example, wax and Teflon™ may be used. The scope of the invention is only limited by the claims below.